CONSTRUCTED WETLAND MANUAL

FOR DESigN, CONSTRUCTiON, OpERATiON AND MAiNTENANCE

pREpARED by ThE iNTER-iSLAMiC NETWORk ON RESOURCES DEvELOpMENT AND MANAgEMENT

(iNWRDAM, AMMAN, JORDAN)

bASED ON TRAiNiNg WORkShOp CONDUCTED iN COOpERATiON WiTh MARMARA RESEARCh CENTER, ENviRONMENT AND CLEANER pRODUCTiON iNSTiTUTE

(MAM) iN iSTANbUL, TURkEy

AMMAN, JORDANJANUARy 2016

Foreword

The primary renewable source of freshwater is continental rainfall, which generates a global supply of 40 000–45 000 km3 per year. This more or less constant water supply must support the entire world population, which is steadily increasing by roughly 85 million per year. Thus, the availability of freshwater per capita is decreasing rapidly. About 80 countries and regions, representing 40% of the world’s population, are experiencing water stress, and about 30 countries of these are in OIC regions.

Constructed wetlands (CW) are among the recently proven efficient tech-nologies for wastewater treatment. Compared to conventional treatment sys-tems, CW are low cost, are easily operated and maintained, and have a strong potential for application in developing countries. CW are especially well suited for wastewater treatment in small communities and at household in many Or-ganization of Islamic Cooperation (OIC) developing countries. However, these systems have not found widespread use, due to lack of awareness, and local of expertise in developing the technology on a local basis.

This manual discusses the capabilities of CW, a functional design ap-proach, and the management requirements to achieve the designed pur-pose. The manual also attempts to put the proper perspective on the appro-priate use, design and performance of CW. For some applications, they are an excellent option because they are low in cost and in maintenance re-quirements, offer good performance, and provide a natural appearance. In other applications, such as large urban areas with large wastewater flows, they may not be at all appropriate choice owing to their land requirements.

Primary users of this manual will be engineers who service small commu-nities and planning professionals. Secondary users will be environmental groups and the academics. This manual discusses the capabilities of CW, a functional design approach, and the management requirements to achieve the designed purpose. The manual also attempts to put the proper perspective on the appro-priate use, design and performance of CW. For some applications, they are an excellent option because they are low in cost and in maintenance requirements, offer good performance, and provide a natural appearance, if not more beneficial ecological benefits. In other applications, such as large urban areas with large wastewater flows, they may not be at all appropriate owing to their land require-ments.

The Inter-Islamic Network on Water Resources Development and Man-agement, Amman, Jordan (INWRDAM) and in cooperation with TUBITAK Mar-mara Research Center, Environment and Cleaner Production Institute (MAM) in Istanbul, Turkey and with financial support from the Islamic development Bank, Jeddah, Saudi Arabia (IDB), implemented a training workshop in Istanbul for participants from a number of OIC member countries on the subject of sewage treatment by natural processes; namely CW.

i

Many OIC developing countries are implementing improved sanita-tion services as their national commitment to achieving Target 10 of the Millennium Development Goals (MDGs). The approach of centralized, wa-ter-based sewer systems was applied to attain considerable public health improvement in urban areas of industrialized countries. However, the cost of such a sewer-based system is enormous and is unaffordable to many of the OIC developing countries. Centralized systems require convention-al (intensive) treatment systems, which are technologically complex and financially expensive, so many communities of the developing countries including those from the OIC cannot afford the construction and operation of conventional treatment systems in rural areas. For these communities, alternative natural treatment systems, which are simple in the construction and operation, yet inexpensive and environmentally friendly, seem to be appropriate.

CW are a natural, low-cost, eco-technological biological wastewater treatment technology designed to mimic processes found in natural wet-land ecosystems, which is now standing as the potential alternative or sup-plementary systems for the treatment of wastewater.

This manual aims at providing a comprehensive description of the issues related to wastewater treatment through CW. This manual has been prepared as a general guide to the design, construction, operation and maintenance of CW for the treatment of domestic wastewater.

This manual includes many citations taken from the UN HABITAT publication entitled Constructed Wetlands Manual (UN-HABITAT, 2008. Constructed Wetlands Manual) and appreciates their approval its repro-duction in whole or in part form for education or non-profit uses without special permission from the copyright holder, provided acknowledgment of the source is made.

ii

Table of Contents

Chapter One 1

Chapter Two 4

2.1 Advantages of CW 5

2.2 Limitations of CW 5

2.3 Configuration of CWs 5

2.3.1 How does a constructed wetland function  5

2.3.2 Horizontal flow (HF)  7

2.3.3 Vertical flow (VF)  8

2.3.4 Hybrid  9

Chapter Three 11

3. Design of Constructed Wetland 11

3.1 Preliminary treatment 11

3.1.1 Septic Tank  11

3.1.2 Anaerobic Baffle Reactor (Improved septic tank)  13

3.2 Sizing of the wetland 14

3.2.1 Sizing based on equation  14

3.3.2 Sizing based on specific area requirement per population

equivalent (pe)   16

3.3.3 Depth  17

3.3.4 HF wetland  17

3.3.5 VF wetland  17

3.3.6 Bed cross section area (only for HF wetland)  18

3.3.7 Media selection  19

3.3 HF wetland 19

3.4 VF wetland 19

3.5 Sealing of the bed 21

5. Operation and maintenance 26

5.1 Start-up 26

5.2 Routine operation 26

5.2.1 Adjustment of water levels  26

5.2.2 Maintenance of flow uniformity  27

5.2.3 Vegetation management  27

5.2.4 Odor control  27

5.2.5 Maintenance of berms (Walls)  27

5.3 Long-term operations 27References 29Treatment of household sewage by constructed wetland methods 1

1. Introduction 12. Methods 2

2.1 Design of septic tank 3

2.2 DESIGN OF HFCW 53. Discussion and results 7

3.1 Septic Tank Performance 7

3.2 HFCW Performance 94. Conclusions 10

References 11

Chapter Four 22

4. Construction of constructed wetland 22

4.1 Basin construction 22

4.2 Small-scale in-situ method for the determination of permeability 22

4.2.1 Extraction method  22

4.2.2 Infiltration method  23

4.2.3 Substrate filling  23

4.2.4 Sand suitability test  24

4.2.5 Planting vegetation  24

4.2.6 Water level management for the growth of vegetation  25

Chapter Five 26

1

Chapter One

1. Introduction Water is essential element for life. Water resources are needed for

human and natural activities. Increase of water demand results in steady decrease of the per capita supply of clean fresh water. Although the nature and severity of water problems varies among countries, one aspect is com-mon to most of them, which is that the water scarcity, whether qualitative, quantitative, or both; originates more from inefficient utilization and poor management. Almost all of the world’s major cities have gone in to the 21st Century facing an environmental crisis. The world’s cities not only face the challenge of supplying adequate sanitation facilities to its residents, but must also ensure that the available water resources are not contaminated. The discharge of untreated wastewater is a major contributor to deteriorat-ing health conditions and pollution of nearby water bodies. The problem is expected to increase due to rapid pace of urban growth, unless measures are taken to control and treat effluents.

The Organization of Islamic Cooperation (OIC) was established upon a decision of the Islamic Summit, which took place in Rabat, Kingdom of Morocco on 25 September 1969 in response to a criminal arson of Al-Aqsa Mosque in occupied Jerusalem. Majority of the OIC countries face major challenges due to limited fresh water resources and the arid and semi arid weather of may of its regions. Most of the world’s population growth will oc-cur in OIC and other developing countries where water is already critically short. Even today, more than one billion people do not have access to safe and affordable drinking water and perhaps twice that many lack adequate sanitation services.

A country or region has a water scarcity when the total amount of re-newable water resources is less than 1,700 m3 per capita per year. Scarcity is physical in case of unavailability of water resources, economical when available water resources are utilized inefficiently, or both. Water scarcity is emerging as a major development challenge for many countries. Demand for water in OIC member countries is steadily increasing and is being in-tensified by population growth, increasing urbanization, raising incomes, growing economies, and new patterns in consumerism. More than 53 per cent of the total population in OIC countries is living in rural areas, com-pared to 48.7 per cent at global level. This new and greater demand for water in many of the OIC member countries is unfolding when we consider the already limited water resources available in these countries. At the indi-vidual country level, the issue of water scarcity in OIC member countries is unfavorable with almost half of them face different levels of water scarcity, namely absolute water scarcity, chronic water shortage and regular water stress. While in some countries water availability is a key concern, other countries with expanding urban settlements, industrial sectors, and com-mercialized agriculture, water quality is a major concern.

2

It is also worth mentioning that the pressure on water resources in OIC member countries is estimated growing at 12.2%, rate, which far ex-ceeds the 5.3% observed in non-OIC developing countries and the 9.0%, observed in developed countries. This situation indicates the need for man-aging and utilizing the available water resources in a more productive man-ner.

Agriculture is by far the biggest user of water, accounting for almost 70 percent of all global withdrawals, and up to 95 percent in developing OIC countries. Food production may soon be limited by water availability. Agricultural water use is not sustainable in many locales around the world for reasons that include soil salinization, groundwater overdraft, and the over allocation of available surface water supplies. This situation raises questions about whether there are sufficient water resources to support the existing population on a long-term basis, to say nothing of the significantly larger population that will have to be fed in the remaining decades of this century. OIC member countries as a whole have a big challenge in tackling the causes and consequences of water scarcity.

Climate change has rising effects on water resources depletion and other related-water disasters. Many OIC member countries have already witnessed frequent droughts and floods attributable to climate change and global warming. Irregular and extreme weather conditions such as flash floods and snowfall have become recently frequent in many parts of the Gulf Arab countries.

CWs are among the recently proven efficient technologies for waste-water treatment. Compared to conventional treatment systems, CWs are low cost, are easily operated and maintained, and have a strong potential for application in developing countries, particularly by small rural communi-ties. However, these systems have not found widespread use, due to lack of awareness, and local expertise in developing the technology on a local basis.

The approach of centralized, water-based sewer systems was applied to attain considerable public health improvement in urban areas of industri-alized countries. However, the cost of such a sewer-based system is enor-mous and is unaffordable to many of the developing countries of the OIC. Centralized systems require conventional (intensive) treatment systems, which are technologically complex and financially expensive, so many com-munities of the OIC countries cannot afford the construction and operation of conventional treatment systems. For these communities, alternative nat-ural treatment systems, which are simple in the construction and operation, yet inexpensive and environmentally friendly, seem to be appropriate.

3

The literature and practitioners have classified CW into two types. Free water surface (FWS) wetlands (also known as surface flow wetlands) closely resemble natural wetlands in appearance because they contain aquatic plants that are rooted in a soil layer on the bottom of the wetland and water flows through the leaves and stems of plants. Vegetated sub-merged bed (VSB) systems (also known as subsurface flow wetlands) do not resemble natural wetlands because they have no standing water. They contain a bed of media such as crushed rock, small stones, gravel, sand or soil, which has been planted with aquatic plants. When properly designed and operated, wastewater stays beneath the surface of the media, flows in contact with the roots and rhizomes of the plants, and is not visible or available to wildlife.

CWs are a natural, low-cost, eco-technological biological wastewater treatment technology designed to mimic processes found in natural wet-land ecosystems, which is now standing as the potential alternative or sup-plementary systems for the treatment of wastewater.

This manual aim to providing practicing engineers or policy makers a comprehensive description of the issues related to wastewater treatment through CWs. This manual has been prepared as a general guide to the design, construction, operation and maintenance of CW for the treatment of domestic wastewater.

Chapter 1 presents an introduction of the CW and its development. It describes the configurations of CW and gives insight of the horizontal and vertical flow CWs. It aims also at providing an overview of working princi-ple of CWs and describes the removal mechanisms of specific pollutants. Chapter 2 illustrates the various aspects to be considered during the design of a subsurface flow CW. The constructional aspects of the wetland are illustrated with some pictures in Chapter 3. Chapter 4 states the operation and maintenance of wetlands for smooth functioning and Chapter 5 pres-ents case studies of CW conducted in Turkey and another one in conduct-ed Jordan. The case study describes the technical details, performance of the wetland.

4

Chapter Two

2. Constructed wetlandA CW is a shallow basin filled with some sort of filter material (sub-

strate), usually sand or gravel, and planted with vegetation tolerant of satu-rated conditions. Wastewater is introduced into the basin and flows over the surface or through the substrate, and is discharged out of the basin through a structure, which controls the depth of the wastewater in the wetland.

A CW comprises of the following five major components:· Basin,· Substrate,· Vegetation,· Liner,· Inlet/outlet arrangement system.

The excavated basin is filled with a permeable substrate (rock, gravel, sand and soil have all been used), and the water level is maintained below the top of the substrate so that all flow is supposed to be subsurface. This substrate supports the roots system of the same types of emergent veg-etation, which are planted in the top surface of the substrate. The equal distribution and collection of wastewater is achieved by inlet and outlet ar-rangement systems. A liner or concrete structure is used, if the protection of the groundwater is important.

Since the 1950s, CWs have been used effectively to treat different wastewaters with different configurations, scales and designs through-out the world. Existing systems of this type range from those serving sin-gle-family dwellings to large-scale municipal systems. Nowadays, CWs are common alternative treatment systems in Europe in rural areas and over 95% of these wetlands are subsurface flow wetlands. In the following years, the number of these systems is expected to be over 10,000 only in Europe.

Even though the potential for application of wetland technology in the developing world including OIC countries is enormous, the rate of adoption of wetlands technology for wastewater treatment in those countries has been slow. It has been identified that the current limitations to widespread adoption of CW technology for wastewater treatment in developing coun-tries is due to the fact that they have limited knowledge and experience with CW design and management. This is why this manual is prepared to improve understanding of the CWs construction and operation and mainte-nance by technicians and planners.

5

2.1 Advantages of CW· Wetlands can be less expensive to build than other treatment op-

tions,· Utilization of natural processes,· Simple construction (can be constructed with local materials),· Simple operation and maintenance,· Cost effectiveness (low construction and operation costs),· Process stability.

2.2 Limitations of CW· Large area requirement· Wetland treatment may be economical relative to other op-

tions only where land is available and affordable.· Design criteria have yet to be developed for different types

of wastewater and climates.

2.3 Configuration of CWsThere are various design configurations of CWs and they can be classified

according to the following items:

· Life form of the dominating macrophytes (free-floating, emergent, submerged),

· Flow pattern in the wetland systems (free water surface flow; sub-surface flow: horizontal and vertical),· Type of configurations of the wetland cells (hybrid systems, one-stage, multi-stage systems),

· Type of wastewater to be treated,· Treatment level of wastewater (primary, secondary or tertiary),· Type of pretreatment,· Influent and effluent structures,· Type of substrate (gravel, soil, sand, etc.), and· Type of loading (continuous or intermittent loading).

Among the various classifications listed above, only subsurface flow CWs has been considered in this manual. There are mainly two types of flow directions used in these wetlands. These are horizontal flow (HF) and vertical flow (VF).

2.3.1 How does a constructed wetland functionA CW is a complex assemblage of wastewater, substrate, vegetation and

an array of microorganisms (most importantly bacteria). Vegetation plays a vital role in the wetlands as they provide surfaces and a suitable environment for microbial growth and filtration. Pollutants are removed within the wetlands by several complex physical, chemical and biological processes as depicted in Fig-ure 1.

6

Settle-able and suspended solids that are not removed in the primary treat-ment are effectively removed in the wetland by filtration and sedimentation. Par-ticles settle into stagnant micro pockets or are strained by flow constrictions. The removal mechanisms for nitrogen in CWs are manifold and include volatilization, ammonification, nitrification/ de-nitrification, and plant uptake and matrix adsorp-tion. The major removal mechanism in most of the CWs is microbial nitrification/de-nitrification. Ammonia is oxidized to nitrate by

Figure 1. Pollutant removal mechanism

nitrifying bacteria in aerobic zones. Nitrates are converted to di nitrogen gas by denitrifying bacteria in anoxic and anaerobic zones. The process of metal removal in wetlands include sedimentation, filtration, adsorption, complexation, precipitation, cation exchange, plant uptake and microbial mediated reactions especially oxidation (Watson et al., 1989). Adsorption involves the binding of metal ions to the plant or matrix surface, whereas the presence of bacteria caus-es the precipitation of metal oxides and sulphides within the wetland. Some wet-land species have a well-established ability for direct uptake of metals.

Attached and suspended microbial growth is responsible for the removal of soluble organic compounds, which are degraded biologically both aerobically (in presence of dissolved oxygen) as well as anaerobically (in absence of dissolved oxygen). The oxygen required for aerobic degradation is supplied directly from the atmosphere by diffusion or oxygen leakage from the vegetation roots into the rhizosphere; however, the oxygen transfer from the roots is negligible.

The removal mechanisms for nitrogen in CW are manifold and include

volatilization, ammonification, nitrification/denitrification, and plant uptake and matrix adsorption. The major removal mechanism in most of the CW is microbial

7

nitrification/denitrification. Figure 2 shows the nitrogen transformations in CW. Ammonia is oxidized to nitrate by nitrifying bacteria in aerobic zones. Nitrates are converted to di nitrogen gas by denitrifying bacteria in anoxic and anaerobic zones.

Figure 2 shows the nitrogen transformations in CW

The process of metal removal in wetlands include sedimentation, filtration, adsorption, complexation, precipitation, cation exchange, plant uptake and mi-crobially-mediated reactions especially oxidation (Watson et al., 1989). Adsorp-tion involves the binding of metal ions to the plant or matrix surface, whereas the presence of bacteria causes the precipitation of metal oxides and sulphides within the wetland. Some wetland species have a well-established ability for di-rect uptake of metals.

Pathogens are removed in wetland during the passage of wastewater through the system mainly by sedimentation, filtration and adsorption by bio-mass. Once these organisms are entrapped within the system, their numbers decrease rapidly, mainly by the processes of natural die-off and predation (Coo-per et. al, 1996).

2.3.2 Horizontal flow (HF)Figure 3 shows schematic cross section of a horizontal flow construct-

ed wetland. It is called HF wetland because the wastewater is fed in at the inlet and flow slowly through the porous substrate under the surface of the bed in a more or less horizontal path until it reaches the outlet zone. During this passage the wastewater will come into contact with a network of aerobic, anoxic and anaerobic zones. The aerobic zones will be around the roots and rhizomes of the wetland vegetation that leak oxygen into the substrate. During the passage of wastewater through the rhizosphere, the wastewater is cleaned by microbiological degradation and by physical and

8

chemical processes (Cooper et al. 1996). HF wetland can effectively re-move the organic pollutants (TSS, BOD5 and COD) from the wastewater. Due to the limited oxygen transfer inside the wetland, the removal of nu-trients (especially nitrogen) is limited, however, HF wetlands remove the nitrates in the wastewater.

Figure 3. Schematic cross-section of a horizontal flow constructed wetland (Morel & Diener, 2006)

3

2.3.3 Vertical flow (VF)A VF CW comprises a flat bed of sand/gravel topped with sand/gravel

and vegetation (Figure 4). Wastewater is fed from the top and then gradual-ly percolates down through the bed and is collected by a drainage network at the base.

Figure 4. Schematic cross- section of a vertical flow constructed wet-land (Morel & Diener, 2006)

9

VF wetlands are fed intermittently in a large batch for flooding the sur-face. The liquid gradually drains down through the bed and is collected by a drainage network at the base. The bed drains completely free and it allows air to refill the bed. The next dose of liquid traps this air and this together with aeration caused by the rapid dosing onto the bed leads to good oxy-gen transfer and hence the ability to nitrify. The oxygen diffusion from the air created by the intermittent dosing system contributes much more to the filtration bed oxygenation as compared to oxygen transfer through plant. Platzer (1998) showed that the intermittent dosing system has a potential oxygen transfer of 23 to 64 g O2.m-2.d-1 whereas Brix (1997) showed that the oxygen transfer through plant (common reed species) has a potential oxygen transfer of 2 g O2.m-2. d-1 to the root zone, which mainly is utilized by the roots and rhizomes themselves. The latest generation of CWs has been developed as vertical flow system with intermittent loading. The reason for growing interest in using vertical flow system is:

· They have much greater oxygen transfer capacity resulting in good nitrification;

· They are considerably smaller than HF system,· They can efficiently remove BOD5, COD and pathogens.

2.3.4 HybridHF wetland is approved well to remove BOD5 and TSS for secondary waste-

water treatment level but not for nitrification due to the limited oxygen transfer capacity. As a result there has been a growing interest in VF wetland because they have a much greater oxygen transfer capacity and considerably less area requirement than HF. But VF wetlands also have some limitation like less ef-ficient in solids removal and can become clogged if the media selection is not correct. Due to these reasons, there has been a growing interest in combined (hybrid) wetlands. In these systems, the advantages and disadvantages of the HF and VF can be combined to complement each other.

Plate 1 shows image of an operating wastewater treatment of a hybrid CW in Gebce, Asia Istanbul, Turkey hybrid CW for sewage treatment from type serv-ing a housing estate composed of 200 apartments with wastewater discharge equivalent population of 1000.

10

Plate 1. Image of a hybrid CW sewage treatment plant in Gebce, Asia Istanbul, Turkey

11

Chapter Three

3. Design of Constructed WetlandBefore designing a constructed wetland, it should be borne in mind that the

substrate of the wetland can be rapidly filled up with debris, grit, and solids from raw wastewater if these materials are not removed prior to the wetland. There-fore, a minimum preliminary/ primary treatment should be provided to remove the settleable solids. However, some systems have avoided the primary treat-ment units and used staged vertical flow constructed wetlands that are operated in parallel, instead (Molle et al., 2004).

3.1 Preliminary treatmentPreliminary treatment mainly separates the coarsely dispersed solids out

of the liquid phase. The preliminary treatment prepares wastewater influent for further treatment in wetland by reducing or removing problem wastewater char-acteristic that could otherwise impede operation or unduly increase maintenance of the wetland and pumps (if any). The typical problem characteristics include large solids and rags; grit; odors etc. The preliminary treatment of wastewater comprises of mainly screen and grit chamber. A screen is a device with open-ings, generally of uniform size, that is used to retain solids found in the influent wastewater to the treatment plant, which removes coarse materials from the wastewater. Grit chamber remove grit, consisting of sand, gravel, or other heavy sold materials that have specific gravities much greater than those of the organic solids in the wastewater.

(The Reader is recommended to follow standard textbooks for preliminary treatment of wastewater.)

Primary treatment separates the suspended matter by physical operations mainly sedimentation. Raw wastewater contains suspended particulate heavier than water; these particles tend to settle by gravity under quiescent conditions. Primary treatment reduces suspended solids, organic load to the wetland and also equalizes raw wastewater quality and flow to a limited degree.

3.1.1 Septic TankThe septic tank is the most common primary treatment used in small-scale

constructed wetland worldwide. A two-compartment septic tank will remove more solids than a single compartment tank (Mara 1976). Figure 5 depicts a schemat-ic cross-section of a typical double-compartment septic tank.

Septic tanks will generally need to be de-sludged; otherwise they produce very poor effl3.1ents with high-suspended solids content, which can be detrimen-tal to the constructed wetland (clogging of beds). To ensure continuous effective operation, the accumulated material must therefore be emptied periodically. This should take place when sludge and scum accumulation exceeds 30 percent of the tank’s liquid volume. The basic design criteria for a two-chambered septic tank are shown in Table 2.

12

Figure 5. A schematic cross-section of a typical double-compartment septic tank

Table 2 on basic design criteria for two compartment septic tankFurther information on septic tank design is available from Mara D. (1996),

Crites and Tchobanoglous (1998), Sasse L. (1998) or any other standard refer-ences

Example The example presented here below is a general case. Let us calculate

the sizing of a two-chambered septic tank for a population of 400 with specific wastewater flow of 80 liters per person per day.

· Average volume of wastewater (Q) = 400 x 80 / 1000 = 32 m3/d· Hydraulic Retention time (HRT) = 1.5 day = 36 hours (assumed)· Required volume of septic tank = Q x HRT = 32 x 1.5 = 48 m3

· Volume of 1st compartment = 2/3 of required volume = 2/3 x 48 = 32 m3

· Volume of 2nd compartment = 1/3 of required volume = 1/3 x 48 = 16 v· Depth of septic tank = 2 m (assumed)· Width of septic tank = 4 m (assumed)

Then,· Length of 1st compartment = Volume/(Depth x Width) = 32/(1.7* x 4) =

4.7 m· Length of 2nd compartment = Volume/(Depth x Width) = 16/(1.7* x 4) =

2.35 m* Please note that the depth of septic tank is taken as 1.7 m after deducting

a free board of 0.3 m)

Check the HRT after sludge accumulation:· Sludge accumulation rate = 70 liters/person/year· Desludging interval = 1 year· Sludge volume = sludge accumulation rate x number of users x desludg-

ing interval = (70 x 400 x 1)/1000 = 28 m3

· Available volume for wastewater in septic tank = Total volume – sludge volume = 48 – 28 = 20 m3

13

· HRT after sludge accumulation = Available volume for wastewater in sep-tic tank/Average volume of wastewater = 20/32 =

· 0.625 days = 15 hours (Since HRT > 12 hours, the design is OK

3.1.2 Anaerobic Baffle Reactor (Improved septic tank)In recent years, anaerobic baffle reactor (improved septic tank) designs

have been developed to enhance removal efficiencies of solids and organic pol-lutants. The basic principle of such systems is to increase contact between the entering wastewater and the active biomass in the accumulated sludge. Figure 6 shows a schematic cross-section of an up flow anaerobic baffle reactor.

This is achieved by inserting baffles into the tank and forcing the waste-water to flow under and over the baffles as the wastewater passes from inlet to outlet. Wastewater flowing from bottom to top passes through the settled sludge and enables contact between wastewater and biomass.

Figure 6. A schematic cross-section of an up flow anaerobic baffle reactor

The basic design criteria for an anaerobic baffle reactor are shown in Table 3.

Table 3

Hydraulic retention > 24 hours at maximum sludge depth and scum accumulation

Sludge accumulation rate Depending on TSS removal rate and wastewater flow (70–100 liters/per-son/year)

Sludge and scum accumulation volume Sludge accumulation rate multiplied by sludge accumulation rate

Desludging interval > 1 yearNumber of upflow chambers > 2Maximum upflow velocity 1.4 – 2 m/h

Table 3. Basic design criteria for an anaerobic baffle reactor

14

Further information on anaerobic baffle reactor design is available from Sasse (1998), Wanasen (2003), Foxon et al., (2004) etc.

3.2 Sizing of the wetland

3.2.1 Sizing based on equationThe wetland might be sized based on the equation proposed by Kickuth:

Ah = Qd (ln Ci – ln Ce)/ KBOD

• Ah = Surface area of bed (m2)• Qd = average daily flow rate of sewage (m3/d)• Ci = influent KBOD5 concentration (mg/l)• Ce = effluent BOD5 concentration (mg/l)• KBOD = rate constant (m/d)KBOD is determined from the expression KTdn, where,KT = K20 (1.06)(T-20)

K20 = rate constant at 20 ºC (d-1)T = operational temperature of system (ºC)d = depth of water column (m)n = porosity of the substrate medium (percentage expressed as frac-

tion)

KBOD is temperature dependent and the BOD degradation rate generally increases about 10 % per ºC. Thus, the reaction rate constant for BOD deg-radation is expected to be higher during summer than winter. It has also been reported that the KBOD increases with the age of the system.

a) KBOD for HF wetlandFigure 7 shows KBOD for a HF wetland. The graph has been plotted based

on the above equation for temperatures ranging from 10 ºC to 25 ºC. The depth of HF wetland has been taken as 40 cm and the porosity of the substrate as 40%. The value of K20 has been taken as 1.1 d-1.

15

Figure 7. KBOD for a HF wetland

KBOD for HF plotted against Temperature for substrate depth 40 cm and porosity 40%

b) KBOD for VF wetland

Figure 8 shows KBOD for a VF wetland. The graph has been plotted based on the same equation as for HF wetland for temperatures ranging from 10 ºC to 25 ºC. The depth of VF wetland has been taken as 70 cm and the porosity of the substrate as 30%. The value of K20 has been taken as 1.1 d-1.

Figure 8 shows KBOD for a VF wetland. KBOD for VF plotted against Temperature for substrate depth 70 cm and

porosity 30%

16

3.3.2 Sizing based on specific area requirement per population equiv-alent (pe)

The specific area requirement per pe holds true where there is uniformity in the specific wastewater quantity and quality. In general, the rules of thumb sug-gested by several works can be served as a safe bed (depending on the climatic conditions). However the investment costs tend to be higher due to conservative aspects of this approach.

Specific area requirement for HF and VF constructed wetland has been calculated for various specific wastewater discharges for a certain population. The BOD contribution has been taken as 40 g BOD/pe.d, 30% BOD load is re-duced in the primary treatment and the effluent concentration of BOD is taken as 30 mg/l. The KBOD for HF and VF wetlands are taken as 0.15 and 0.20 respective-ly. It is seen that a specific area requirement of 1 – 2 m2/pe would be required of HF constructed wetlands where as a specific area of 0.8 – 1.5 m2/pe for the VF wetland.

Specific area requirement per pe for HF and VF wetland for different spe-cific wastewater discharges

Taking into considerations of the cases in Nepal, it is to be noted that the specific area requirement presented in the graph is less than the specific area requirement given in various literatures because the KBOD used in the litera-tures are lower and the specific wastewater discharges are high.

The example presented here is a general case. The local circumstances and standards need to be taken into account by the designer. Let us calculate the sizing of a constructed wetland for a population of 400 with specific waste-water flow of 80 liters per person per day.

17

· Average volume of wastewater (Q) = 400 x 80 / 1000 = 32 m3/d· To determine the influent BOD5 concentration, the wastewater sample

should be analyzed in an accredited laboratory. In the absence of a labo-ratory, the concentration can be calculated as below;

· BOD5 contribution = 40 g BOD5/pe.d· BOD5 concentration = 40 x 1000/80 = 500 mg/l· Let us assume that 30% BOD5 is removed by the primary treatment unit,

then the influent BOD5 concentration to the wetland· (Ci) = 350 mg/l· Effluent BOD5 concentration (Ce) = 30 mg/l· KBOD = 0.15 m/d for HF wetland and 0.2 m/d for VF wetland

Substituting the values in the equation below:· A = Qd (ln Ci – ln Ce)

KBOD· Area for HF wetland = 524.10 m2· Specific area per pe for HF wetland = 1.31 m2· Area for VF wetland = 393.08 m2· Specific area per pe for VF wetland = 0.98 m2

3.3.3 DepthIn general, the depth of substrate in a subsurface flow constructed wetland

is restricted to approximately the rooting depth of plants so that the plants are in contact with the flowing water and have an effect on treatment. However, Hy-draulic Retention Time – HRT (time the wastewater is retained in the wetland) is to be considered in the selection of the depth of the wetland.

3.3.4 HF wetlandMost HF wetlands in moderate OIC climates provide a bed depth of 60

cm (Cooper et al., 1996). In the United States, HF wetlands have commonly been designed with beds 30 cm to 45 cm deep (Steiner and Watson, 1993). An experimental study carried out in Spain showed that shallow HF wetlands with an average depth of 27 cm were more effective than deep HF wetlands with an average water depth of 50 cm. (Garcia et al., 2004). It is recommended to use an average depth of 60 cm taking into considerations of the precipitation, which could cause surface flow.

3.3.5 VF wetlandGenerally, VF systems are built with larger depths compared to HF sys-

tems. Most VF systems in UK are built 50 – 80 cm deep (Cooper et al., 1996). In contrast to that, depth greater than 80 cm is recommended in Germany (ATV, 1998). Similarly, in Austria a depth of 95 cm is recommended (ÖNORM 1997). A minimum of 100 cm depth is recommended in Denmark (Brix, 2004). The VF systems in Turkey were also built about 100 cm deep but nowadays shallower depths are being practiced.

In subtropical OIC climates it is possible to increase the applied loading rates above guidelines issued in moderate climates and achieves nitrification in

18

VF system. The average results by vertical beds of 75 cm depth showed better performance in comparison with vertical beds of 45 cm depth (Philippi et al., 2004).

It is recommended to use substrate depth of 70 cm, which can provide ad-equate nitrification in addition to the organic pollutants removal.

3.3.6 Bed cross section area (only for HF wetland)Dimensioning of the bed is derived from Darcy’s law and should provide

subsurface flow through the gravel under average flow conditions. Two import-ant assumptions have been made in applying the formula:

a. hydraulic gradient can be used in place of slope, andb. the hydraulic conductivity will stabilize at 10-3 m/s in the established wet-

land.

The equation is:

· Ac = Qs / Kf (dH/ds)· Ac = Cross sectional area of the bed (m2)· Qs = average flow (m3/s)· Kf = hydraulic conductivity of the fully developed bed (m/s)· dH/ds = slope of bottom of the bed (m/m)

For graded gravels a value of Kf of 1 x 10-3 to 3 x 10-3 m/s is normally cho-sen. In most cases, dH/ds of 1% is used.

There is no hard and fast rule on the optimum width of the wetland; howev-er, it is recommended that if the width of the wetland is more than 15 m, the wet-land cell should be partitioned to avoid short-circuiting of wastewater inside the wetland. It should also be kept in mind that it is better to use at least two parallel cells instead of a single wetland cell for the ease in operation and maintenance of the wetland.

EXAMPLE

Let us find the bed cross sectional area required for the HF wetland that was calculated in section 5.3

· Qs = 32 m3/d = 0.00037 m3/s· Kf = 2 x 10-3 m/s· dH/ds = 0.01

Substituting the values in the above equationAc = 18.52 m2

Considering the depth of the wetland as 0.4 m, the width of the wetland would be 46.30 m. Length of the wetland = Plan area/width= 524.1/46.3 = 11.3 m

It is recommended that if the width of the wetland is greater than 15 m, the wetland cell should be partitioned. Now let us take 3 wetlands in parallel, then

19

· Qs = 0.00012 m3/s· Kf = 2 x 10-3 m/s· dH/ds = 0.01, Substituting the values in the above equation,· Ac = 6.17 m2

Considering the depth of the wetland as 0.4 m, the width of the wetland would be 15.43m. Let us provide a width of 15 m. Length of the wetland= Plan area/width/number of wetlands = 524.1/15/3 = 11.6 m.

In VF wetlands, since the flow is vertical, the width and cross-sectional area of VF beds are not set by a requirement to keep the flow below surface and prevent surface flow.

3.3.7 Media selectionThe media perform several functions. They:

· are rooting material for vegetation,· help to evenly distribute/collect flow at inlet/outlet,· provide surface area for microbial growth, and· filter and trap particles.

Very small particles have very low hydraulic conductivity and create sur-face flow. Very large particles have high conductivity, but have little wetted sur-face area per unit volume of microbial habitat. Large and angular medium is damaging to root propagation. The compromise is for intermediate-sized mate-rials generally characterized as gravels. It is recommended that the gravels are washed because this removes fines that could block the void spaces.

3.3 HF wetlandIt is reported that the diameter size of media used in HF wetlands varies

from 0.2 mm to 30 mm (ÖNORM B 2505, 1996, Vymazal, 1997, GFA, 1998, EC/EWPCA, 1990, U.S. EPA, 1988, Steiner and Watson, 1993, U.S. EPA, 1993, Reed et al., 1995, U.S. EPA, 2000).

It is recommended that the media in the inlet and outlet zones should be

between 40 and 80 mm in diameter to minimize clogging and should extend from the top to the bottom of the system. For the treatment zone, there does not appear to be a clear advantage in pollutant removal with different sized media in the 10 to 60 mm range (U.S. EPA, 2000). Figure 10 shows the recommended substrate sizes, which uses 40 – 80 mm media at the inlet/outlet zones and 5 – 20 mm at the treatment zone.

3.4 VF wetlandThe substrate properties, d10 (effective grain size), d60 and the uniformity

coefficient (the quotient between d60 and d10) are the important characteristics in the selection of the substrate. There is not one uniform standard substrate design for the construction of VF wetland. Various literatures reports effective grain size should be 0.2 < d10 < 1.2 mm, uniformity coefficient 3 < d60/d10 < 6 and hydraulic conductivity Kf 10-3 to 10-4 m/s.

20

The rate of decrease in permeability for similar SS influent characteristics is highest for porous media with smaller pore sizes. Compared to the gravel, the sands show a relatively more rapid reduction in their permeability due to effects

FIGURE 10 Substrate arrangements in a HF wetland

of sediment accumulation at the surface of the sands. However, the depth of clogging is higher for larger particle sizes (Walker, 2006).

It is recommended to use sand (0 – 4 mm) as main substrate with d10 > 0.3 mm, d60 / d10 <4 and having permeability of 10-3 to 10-4 m/s. The substrate shall be arranged as shown in Figure 11.

The top surface of the media should be level or nearly level for easier plant-ing and routine maintenance. Theoretically, the bottom slope should match the slope of the water level to maintain a uniform water depth throughout the bed. A practical approach is to uniformly slope the bottom along the direction of flow from inlet to outlet to allow for easy draining when maintenance in required. No research has been done to determine an optimum slope, but a slope of 0.5 to 1% is recommended for ease of construction and proper draining.

21

3.5 Sealing of the bedSubsurface flow wetlands providing secondary treatment should be lined

to prevent direct contact between the wastewater and groundwater. Liners used for wetlands are the same as those typically used for ponds.

Native soils may be used to seal the wetlands if they have sufficiently high clay content to achieve the necessary permeability. The thickness of the lin-ings depends on the permeability of the soil. The advice given in the European Guidelines (Cooper, 1990) was that if the local soil had a hydraulic conductivity of 10-8 m/s or less then it is likely that it contained high clay content and could be “puddled” to provide adequate sealing for the bed. As a general guide, the following interpretations may be placed on values obtained for the in situ coeffi-cient of permeability:

· k>10-6 m/s: the soil is too permeable and the wetlands must be lined;· k>10-7 m/s: some seepage may occur but not sufficiently to prevent the

wetlands from having submerged condition;· k<10-8 m/s: the wetlands will seal naturally; · k<10-9 m/s: there is no risk of groundwater contamination (if k>10-9 m/s

and the groundwater is used for potable supplies, further detailed hydro-geological studies may be required).

22

Chapter Four

4. Construction of constructed wetlandConstruction of constructed wetland primarily involves basin construction

(common earth moving, excavating, leveling, compacting and construction of berms/walls), lining of the basin, filling the basin with substrates, constructing inlet and outlet structures and planting vegetation. The establishment of vege-tation is unique to other construction activities. It is the intent of this section to provide guidance on these special and unique aspects of wetland construction.

4.1 Basin constructionStandard procedures and techniques used in civil engineering are applied

for the basin construction, which include earthwork in excavation, leveling and compaction. It is desirable to balance the cut and fill on the site to avoid the need for remote borrow pits or soil disposal. If agronomic-quality topsoil exists on the site, it should be stripped and stockpiled. Uniform compaction of the subgrade is important to protect the liner integrity from subsequent construction activity (i.e., liner placement, gravel placement etc.) and from stress when the wetland is filled. Most wetlands are graded level from side to side and either level or with a slight slope (about 1%) in the direction of flow. Berms (walls) should be constructed in conformance with standard geotechnical considerations. An ade-quate amount of freeboard should be provided to contain a given storm rainfall amount.

Lining of the basin is required if the permeability of the soil is greater than 10-6 m/s. Liner should be selected based on its availability and cost. Proper care should be taken to prevent liner punctures during placement and subse-quent construction activity. If the subgrade contains sharp stones, a layer of sand should be placed beneath the liner and leveled.

4.2 Small-scale in-situ method for the determination of permeabilityThe method fall into two groups: those that are used to determine the per-

meability above the water table and those that are below the water table. Above the water table, the soil is not saturated. To measure the saturated hydraulic conductivity, one must therefore apply sufficient water to obtain near saturated conditions. These methods are called ‘infiltration methods’. Below the water ta-ble, the soil is saturated by definition. It then suffices to remove water from the soil, creating a sink, and to observe the flow rate of water into the sink together with the hydraulic head induced. These methods are called ‘extraction methods’.

4.2.1 Extraction methodA hole is bored into the soil to a certain depth below the water table. When the

water in the hole reaches equilibrium with the ground water, part of it is removed. The ground water thus begins to seep into the hole and the rate at which it rises is mea-sured. The hydraulic conductivity of the soil is computed with the following formula:

23

K = Cx (H0 – Ht)/tWhere,· K = hydraulic conductivity of the saturated soil (m/d)· C = a factor depending on the depth of an impermeable layer below

the bottom of the hole and average depth of the water level in the hole below the water table

· t = time elapsed since the first measurement of the level of the rising water in the hole

· Ht = depth of water level in the hole below reference level at time t (cm)· H0 = Ht when t = 0

When D > ½ D2, then• C = (4000 x r/h’)/((20 + D2/r) x (2 – h’/D2)When D = 0, then• C = (3600 x r/h’)/((10 + D2/r) x (2 – h’/D2)

4.2.2 Infiltration methodA hole is bored into the soil to the required depth, the hole is filled with

water, which is left to drain away freely. The hole is refilled with water sev-eral times until the soil around is saturated over a considerable distance and infiltration (rate) has attained a more or less constant value. After the last refilling of the hole, the rate of drop of the water level in the hole is mea-sured. The data (h + ½r and t) are then plotted on semi-log paper. The graph should yield a straight line. If the line is curved, continue to wet the soil un-til the graph shows the straight line. Now, with any two pairs of values of h + ½r and t, the K value can be calculated according to the following equation:

K = 1.15r ((log (h0 + ½r) – log (ht + ½r)/(t – t0)Where,

· t = time since the start of measuring (s)· ht = the height of water column in the hole at time t (cm)· h0 = ht at time t = 0

4.2.3 Substrate fillingOnce liner has been placed in the basin, filling with substrates shall

be commenced in conjunction with inlet/outlet arrangements. The sub-strate should be washed to eliminate soil and other fines that could block the void spaces, which contribute to substrate clogging. Round-ed river substrate is recommended over sharp-edged crushed sub-strate because of the looser packing that the rounded substrate provides.

Before filling substrates, the partitioning of inlet/outlet zones must be done. Outlet arrangements should be addressed properly while fill-ing the substrates. The substrate should be sieved and washed before fill-ing the designed substrate sizes in the inlet/outlet zones and treatment zone.

Before filling substrates in a VF wetland, the layers of different size of substrate to be filled should be properly marked inside the basin. The sub-

24

strates should be properly washed to eliminate the undesired particles. Col-lection network at the base of the basin should be laid in accordance with the design prior to the filling of the substrates. Filling shall commence once the above-mentioned activities have been completed. Since sand is the sub-strate for the main treatment zone, the properties of sand should be ana-lyzed in an accredited laboratory. Grain size analysis and determination of hydraulic conductivity should be performed. In the absence of an accredit-ed laboratory, the suitability of sand can be determined sand suitability test.

4.2.4 Sand suitability testA 300 mm long length of 110 mm diameter PVC pipe is placed on a bed of pea

gravel and filled with 200 mm of the sand to be tested. The sand should be damp but not saturated. A small square of pan scourer or similar is placed on the sand surface to reduce disturbance by the water. Next 500 ml of tap water is poured into the tube quickly, but without disturbing the sand surface too much, and the time for it to drain completely is measured. As soon as it has passed through another 500 ml of water is added and again timed. This is repeated until the time taken levels off.

Inlet and outlet structures as mentioned in chapter 5.9 should be placed in accordance with the design. Inlet and outlet pipes of HF wet-land should be laid perpendicular to the flow in the wetland. The distribution holes (orifices) in the network of inlet arrangement for VF wetlands should be so placed to assure equal distribution of wastewater throughout the en-tire area of the wetland. Similarly, the network of outlet arrangement should be so placed to assure that no short-circuiting takes place inside the wetland.

4.2.5 Planting vegetationEstablishing vegetation is probably the least familiar aspect of wetland con-

struction. Vegetation can be introduced to a wetland by transplanting roots, rhizomes, tubers, seedlings, or mature plants; by broadcasting seeds obtained commercially or from other sites; by importing substrate and its seed bank from nearby wetlands; or by relying completely on the seed bank of the original site. Many of the wetlands are planted with clumps or sections of rhizomes dug from natural wetlands. Prop-agation from seed and planting of the established plantlets is gaining popularity.

Two main techniques for planting rhizomes are:• Planting clumps• Planting cuttings

Clumps of rhizome mat can be excavated from an existing stand of reeds whilst minimizing damage to the existing wetland and the rhizomes clump ob-tained. For the small-scale wetland, it can be dug out with a spade but for large-scale projects the use of an excavator is required. When transporting or storing, clumps should not be stacked. In this way the aerial stems are not damaged. The spacing of planting depends on the size of the clumps obtained. Planting 1 m2 sclumps, at 10 m spacing or smaller clumps 1 or 2 m2 should achieve full cover within one year depending upon mortality (Cooper et. al., 1996).

25

Rhizome cuttings can be collected from the existing wetlands or from com-mercial nurseries. Sections of undamaged rhizome approximately 100 mm long with at least one internode, bearing either a lateral or terminal bud, should be used for planting. Rhizomes should be planted with one end about a half below the surface of the medium and other end exposed to the atmosphere at spacing of about 4 rhizomes per m2. Figure 11 shows techniques for planting rhizomes.

Figure 12. Planting rhizome cuttigs

4.2.6 Water level management for the growth of vegetationIt is recommended to allow plantings to develop well before waste-

water is introduced into the system; the plants need an opportunity to overcome planting stress before other stresses are introduced. Gradu-al increase in the concentration of waste applied may also be necessary. To have deep rooting water level should not be too high from the beginning.

Too much water creates more problems for wetland plants during the first growing season than too little water because the plants do not receive adequate oxygen at their roots. Wetland emergent species should be planted in a wet sub-strate (but not flooded) and allowed to grow enough to generate a stem with leaves.

The construction of sludge drying beds is similar to the construction of vertical flow constructed wetlands except in the distribution arrangement of the sludge. Usually the sludge is fed into the sludge drying beds in one edge of the bed, which will slowly spread over the entire area of the sludge drying bed by gravity.

26

Chapter Five

5. Operation and maintenanceOperation and maintenance can be classified in terms of start-up, routine

and long-term. There are important distinctions between these; start-up require-ments will show more site-to-site variability, routine operations may be more affected by design details and long- term operations reflect loading. In addition, thorough check-ups should be done at least twice a year for the effective oper-ation of the wetland. Operation and maintenance of primary treatment is of high importance for the effective functioning of the wetland.

5.1 Start-upStart-up periods for wetlands are necessary to establish the vegetation

associated with the treatment processes. The start-up period will vary in length depending on the type of design, the characteristics of the influent wastewa-ter, and the season of year. Although the start-up period for subsurface flow constructed wetlands is less critical since its performance is less dependent on vegetation, the vegetation adds up to the aesthetic values to the wetland.

During the start-up period, the operator is primarily responsible for adjust-ing the water level in the wetland. Typically, the wetlands will have to be filled with water to the surface of the substrate at the end of planting. As the plants begin to root, the water level can be gradually lowered to the design operating level.

5.2 Routine operationSince constructed wetlands are “natural” systems, routine opera-

tion is mostly passive and requires little operator intervention. The op-erator must be observant, take appropriate actions when problems de-velop, and conduct required operational monitoring as necessary.

The most critical items in which operator intervention is necessary are:• Adjustment of water levels• Maintenance of flow uniformity (inlet and outlet structures)• Management of vegetation• Odor control• Maintenance of berms (walls)

5.2.1 Adjustment of water levelsWater level and flow control are usually the only operational variables

that have a significant impact on a well-designed constructed wetland’s perfor-mance. Changes in water levels affect the hydraulic residence time, atmospher-ic oxygen diffusion into the water phase, and plant cover. Significant chang-es in water levels should be investigated immediately, as they may be due to

27

leaks, clogged outlets, breached berms, storm water drainage, or other causes.

5.2.2 Maintenance of flow uniformityMaintaining uniform flow across the wetland through inlet and outlet adjust-

ments is extremely important to achieve the expected treatment performance. The inlet and outlet manifolds should be inspected routinely and regularly ad-justed and cleaned of debris that may clog the inlets and outlets. Debris re-moval and removal of bacterial slimes from weir and screen surfaces will be necessary. Submerged inlet and outlet manifolds should be flushed periodi-cally. Additional cleaning with a high-pressure water spray or by mechanical means also may become necessary. Influent suspended solids will accumulate near the inlets to the wetland. These accumulations can decrease hydraulic detention times. Over time, accumulation of these solids will require removal.

5.2.3 Vegetation managementWetland plant communities are self-maintaining and will grow, die, and re-

grow each year. The primary objective in vegetation management is to main-tain the desired plant communities within the wetland. This is achieved through changes in the water levels and harvesting undesired plants (like weeds) when and where necessary. Where plant cover is deficient, management ac-tivities to improve cover may include water level adjustment, reduced load-ings, pesticide application, and replanting. Harvesting and litter removal may be necessary depending on the design of the wetland. A well-designed and well-operated subsurface flow wetland should not require routine harvesting.

5.2.4 Odor controlOdors are seldom a nuisance problem in properly loaded wetlands.

Odorous compounds are typically associated with anaerobic conditions, which can be created by excessive BOD and ammonia loadings. Odor oc-curs if water is flooded in the surface of the bed therefore uniform distribu-tion of water into the bed will prevent from odor. If primary treatment size is too big then wastewater may undergo anaerobic condition, which may create odor when such wastewater feed into CW. However, such odor is insignifi-cant since wastewater percolates into the bed quickly if there is no clogging.

5.2.5 Maintenance of berms (Walls)Berms (walls) should be properly maintained. Any earthen berm erosion or

crack in the walls should be repaired as soon as it is noted. Leaks around berms (walls) should also be repaired by plugging, sealing, etc. as soon as noted.

5.3 Long-term operationsRoutine operations are essential in managing a wetland. In addition to reg-

ulatory requirements, inflow and outflow rates, wastewater quality, water levels should be regularly monitored and evaluated. Over time, these data help the operator to predict potential problems and select appropriate corrective actions.

Solids from preceding treatment units and litter from decaying vegetation will gradually reduce the pore space in the wetlands. Most of the solids will accumulate at the inlet end of the HF beds where the pore space may be reduced substantially

28

in a couple of years. This may cause surface flow. The solids accumulation should be removed time to time. The rate of solids accumulation depends on loading.

The performance of the wetland should be assessed time to time. Samples should be collected and analyzed to ascertain the treatment effi-ciencies. Not the least but the following parameters need to be analyzed:

• Total Suspended Solids (TSS)• Biochemical Oxygen Demand (BOD5)• Chemical Oxygen Demand (COD)• Ammonia• Nitrate• Phosphorus• Fecal ColiformsThe operation and maintenance requirements can be summarized as listed

in Tables x to xxx:TABLE x Fortnightly O & M action list

Berm/Wall • Visual inspection for weeds, erosion and damageInlet • Visual inspection for adequate and uniform inflow and

identifition of blockages and damage • Maintain and adjust as required

Outlet • Visual inspection for blockages and damage, and visual check of water level and outflow quality and quantity

Vegetation • Visual inspection for any weed, plant health or pest problems. Take remedial action as necessary

TABLE xx Two-monthly O & M action list

Berm/Wall • Visual inspection for weeds, erosion and damage. Take remedial action as necessary

Outlet • Check functioning of discharge system and apparent health of receiving water• Where appropriate, mow or graze (sheep only) grass on outer embankments and wetland surrounds

Vegetation • Control weeds in wetland by handweeding, herbicide application, and/or temporary water level increase

Primar treatment

• Visual inspection of upstream primary treatment for structural integrity, quantity and quality of effluent

TABLE xxx Yearly O&M action list

Substrate • Check clogging of the substrate, remove the substrate, clean it and replace if necessary

Inlet • Remove end caps from inlet pipe and distribution network and flush out and clean thoroughly to remove slimes and blockages

Outlet • Clean and remove plants around outlet pipe to provide access and guard against blockages.

Vegetation • Harvest vegetation and replant if necessaryPrimartreatment

• Check sludge levels in primary treatment and desludge as necessary to maintain treatment performance and avoid sludge drift into wetland

29

References Brix, H. (1997). Do Macrophytes play a Role in Constructed Wetlands Wa-

ter Science andTechnology, Vol: 35(5), pg. 11-17.

Brix, H. (2004). Danish guidelines for small-scale constructed wetland sys-tems for onsite treatment of domestic sewage. In Proc. 9th International confer-ence on wetland systems for water pollution control, Avignon, France.

Cooper P.F., Job G.D., Green M.B. and Shutes R.B.E. (1996). Reed Beds and Constructed Wetland for Wastewater Treatment. WRc Swindon, UK.

Cooper, P.F. (1990). European Design and Operation Guidelines for Reed Bed Treatment Systems, Report No UI 17, Water Research Center, Swindon , UK.

Crites, R. and Tchobanoglous, G. (1998). Small and decentralized waste-water management systems. Water Resources and Environmental Engineering, 1. WCB/McGraw-Hill, Boston.

Foxon, K.M., Pillay, S., Lalbahadur, T., Rodda, N., Holder, F. and Buckley, C.A. (2004). The anaerobic baffed reactor (ABR): An appropriate technology for on-site sanitation. In Proceedings: 2004 Water Institute of South Africa (WISA) Biennial Conference, Cape Town, South Africa.

Garcia J., Morator J., Bayona J.M. and Aguirre P. (2004). Performance of horizontal surface flow constructed wetlands with different depths. Proceedings – 9th International Conference on Wetland Systems for Water Pollution Control, 26 – 30 September 2004, Avignon, France, pp. 269 – 276.

Gearheart, R.A. (1992). Use of constructed wetlands to treat domestic wastewater, City of Arcata, California. Water Science Technology 26, 1625-1637.

Haberl R. (1999). Constructed Wetlands: A Chance to Solve Wastewater Problems in Developing Countries. Water Science and Technology, Vol: 40(3

IWA Specialist Group on Use of Macrophytes in Water Pollution Control (2000). Constructed Wetlands for Pollution Control - Processes, Performance, Design and Operation, Scientific and Technical Report No:8. Kadlec R.H., Knight R.L., Vzmayal J,. Brix H., Cooper P. and Haberl R. (eds), International Water As-sociation, London.

Kickuth, R. (1984). The Root Zone Method. Gesamthochschule Kassel-Uni des Landes, Hessen.

Mara, D. (1996). Low-Cost Urban Sanitation, John Wiley & Sons, Chich-ester, West Sussex, England.

30

Metcalf & Eddy, Inc. (2003). Wastewater Engineering – Treatment and Re-use, Tata McGraw-Hill Publishing Company Limited, New Delhi, India.

Morel A. and Diener S. (2006). Greywater Management in Low and Mid-dle-Income Countries, Review of different treatment systems for households or neighbourhoods. Swiss Federal Institute of Aquatic Science and Technology (Eawag). Dübendorf, Switzerland.

Philippi L.S., Sezerino P.H., Bento A.P. and Magri M.E. (2004). Vertical flow constructed wetlands for nitrification of anaerobic pond effluent in southern Brazil under different loading rates. Proceedings – 9th International Conference on Wetland Systems for Water Pollution Control, 631 – 639.

Platzer C. (1998). Design recommendation for subsurface flow constructed wetlands for nitrification and de nitrification. In: Proceedings of the 6th Interna-tional Conference on Wetland Systems for Water Pollution Control, Sao Paulo State, Brazil.

Platzer C. (2000). Development of Reed Bed systems-A European Per-spective”. In: Proceedings of the IWA 7th International Conference on Wetland Systems for Water Pollution Control, Lake Buena Vista, Florida.

Reed S.C. et al. (1990). Natural systems for wastewater treatment – Man-ual of practice FD16. Water Pollution Control Federation, 601 Wyhe Street Al-exandria, Virginia. Cited by Grant, N. and Griggs J. (2001). Reed beds for the treatment of domestic wastewater, BRE.

Reed S.C., Crites R. and Middlebrooks E.J. (1995). Natural Systems for Waste Management and Treatment. 2nd Edition, McGraw-Hill, New York, Unit-ed States.

Reed, S.C.; Middlebrooks, E.J. and Crites, R.W. (1988). Natural Systems for Waste Management. McGraw-Hill Book Company, New York.

Ritzema, H.P. (Editor-in-Chief) (1994). Drainage principles and applica-tions. International Institute for Land Reclamation and Improvement, Wagenin-gen, The Netherlands.

Sasse, L. (1998). Decentralized wastewater treatment in developing coun-tries. BORDA, Bremen.

Shrestha, R. R. (1999). Application of Constructed Wetlands for Wastewa-ter Treatment in Nepal. Ph. D. Dissertation, Department of Sanitary Engineering and Water Pollution Control. University of Agricultural Sciences Vienna, Austria.

31

Steiner G.R. and Watson J.T. (1993). General design, construction and operation guidelines: Constructed wetlands wastewater treatment systems for small users including individual residences; 2nd Edition, TVA/WM-93/10, Ten-nessee Valley Authority Resource Group Water Management: Chattanooga, TN, United States.

United States Department of Agriculture (U.S.D.A.), (2002). Part 637 Envi-ronmental Engineering National Engineering Handbook – Chapter 3 Construct-ed Wetlands. 210-VINEH, U.S.D.A., Natural Resources Conservation Service, Washington DC, United States.

United States Environmental Protection Agency (U.S. EPA) (1988). Design manual: Constructed wetlands and aquatic plant systems for municipal waste-water treatment, EPA 625/1-88/022, U.S. EPA Off ce of Water: Cincinnati, OH, United States.

United States Environmental Protection Agency (U.S. EPA) (1993). Guid-ance for design and construction of subsurface flow constructed wetland, U.S. EPA Region 6 Water Management Division Municipal Facilities Branch Techni-cal Section.

United States Environmental Protection Agency (U.S. EPA) (2000). Con-structed wetlands treatment of municipal wastewater treatment. EPA 625/R-99/010, U.S. EPA Office of Research and Development: Washington, D.C., Unit-ed States.

Vymazal J. (1997). The use of subsurface flow constructed wetlands for wastewater treatment in the Czech Republic. Ecological Engineering 7 1-14.

Vymazal, J., Brix, H., Cooper, P.F., Green, M.B. and Haberl, R. (Eds.) (1998). Constructed Wetlands for Wastewater Treatment in Europe. Backhuys Publishers, Leiden.

Walker, A. (2006). Predicting the clogging of saturated substrates used in the construction of vertical flow systems by suspended solids. M.Sc. Thesis, Cranfield University, Silsoe, UK.

Wallace, S.D. and Knight, R.L. (2006). Small scale constructed wetland treatment systems – feasibility, design criteria and O&M requirements. Report 01-CTS-5, Water Environment Research Foundation (WERF), Alexandria.

Wanasen, S.A. (2003). Upgrading conventional septic tanks by integrating in-tank baffes. M.Sc. Thesis, School of Environment, Resources and Develop-ment, Asian Institute of Technology, Bangkok, Thailand.

Watson, J.T., Reed, S.C., Kadlec, R.H., Knight, R.L. and Whitehouse, A.E. (1989).

1

Treatment of household sewage by constructed wetland methods

Murad J. Bino. The Inter-Islamic Network on Water Resources Devel-opment and Management Amman, Jordan, 70 Ahmad Tarouneh Street, RSS Campus, Jubeiha 11941, Jordan. http://www.inwrdam.org.jo,

Email address of corresponding author: muradinw@nic.net.jo

ABSTRACT: More and more rural households in Jordan, Palestine, Leba-non and Yemen are interested in reuse of treated sewage to maintain productive home gardens and to conserve fresh water. The aim of this study was to assess the quality and quantity of sewage discharged by a typical rural household con-sisting of ten members in northern part of Jordan and based on that to develop a low cost and economically feasible method for sewage treatment for reuse for home garden irrigation. The domestic water consumption in most rural ar-eas of Jordan is on the average equal to 100 liters per capita per day (l/pcd). The developed sewage treatment system consists of a multi compartment septic stage designed for once per year desludging followed by sub-surface horizon-tal flow constructed wetland (HFCW) stage planted with Phragmites australis (common reed). BOD content removal efficiency of the system was (91.64%) evaluated over a period of one year starting from May 2014 to June 2015. The septic tank was found to be an essential and efficient pretreatment step.

The type of a combination of septic treatment stage followed by HFCW treatment offers a low-cost and low technology alternative to help rural house-holds conserve fresh water. Treated effluents were of better quality than stipulated by the Jordanian Standard JS 893:2002 for restricted reuse in ir-rigation. Proper training of owners of on-site, low technology constructed wet-land treatment plants will ensure sustainability of the treated effluents reuse.

Keywords: constructed wetland, wastewater, sewage treatment, rural household, reuse, low technology, septic tank design and restricted irrigation.

1. Introduction

Over the last two decades constructed wetlands (CW) treatment attracted increasing worldwide interest due to the various economic and environmental benefits they provide. They have been effectively applied for the treatment of domestic and municipal wastewater. However, there are many wastewaters of industrial sources with a substantially different composition and physicochemical characteristics that can be effectively treated with constructed wetlands methods.

In response to the need for practical alternatives for on-site treatment of wastewater, various types of CW based processes are gaining growing inter-est. Over the past three decades, organizations, scientists and engineers have developed a wealth of practical information related to CW technology (USE-

2

PA, 1988, Vyzamal, 1998). Several different types of CW systems are being used through out the world for decentralized wastewater treatment. These in-clude CW based on surface-flow, subsurface-flow, vertical-flow and hybrid systems. Use of CW process for wastewater treatment has several inherent advantages including low capital costs, less infrastructure, lower operating costs, simplicity of design and ease of operation (Platzer, 1999, Li F, 2009).

More and more rural households in Jordan, Palestine, Lebanon and Ye-men are now using treated sewage to maintain productive home gardens and to conserve fresh water. Reuse of treated sewage for irrigation at household level is one of the methods, which are currently widely promoted by interna-tional agencies and governments of the Middle East. This is particularly im-portant in arid zones, where water is scarce and reuse of treated wastewater for irrigation could reduce potable water by up to 60% (DHWA, 2002). The re-use of treated sewage for irrigation of home gardens is becoming increasingly common. It is therefore important to develop sewage treatment methods that are reliable, have low energy footprint and of affordable construction costs to majority of rural populations. These requirements are all possible when con-sidering CW methods as a household level sanitation and water conservation.

2. MethodsSewage is usually treated, depending on the final reuse of treated wastewater,

by physical, biological and chemical processes or a combination of these process-es. A primary treatment ahead of a CW stage is necessary to prevent clogging of media and reduces suspended solids by sedimentation. A septic settling and anaer-obic decomposition stage is included as a pretreatment to overcome fluctuations in quality of household sewage. CW of different water application configurations are used including flooded flow, subservice, vertical and horizontal flow regimes.

This study was based on treating a typical household sewage by a sep-tic tank stage followed by horizontal subsurface flow constructed wetland method (HFCW). This type of treatment is considered as a most environ-mentally friendly and cost effective method for sewage treatment (Li F, 2009).

The aim of this study was to:· Construct sewage treatment pilot unit consisting of a septic stage

followed by a horizontal flow HFCW to treat up to 1 M3/day of sewage effluents collected from a typical rural household comprising of ten occupants located in the village of Juhfeyeh (Juhfeyeh), in northern Jordan.

· Assess suitability of treated effluents for reuse in irrigation of home garden crops.

The household members were informed about HFCW method so they understood requirements for this type of sewage treatment method that could generate effluents suitable for irrigation of specific certain crops only and that effluents from treatment unit would be in compliance with Jordan Standard No.

3

JS 893-2002 issued by the Jordan Institution for Standards and Metrology clas-sifying quality of treated sewage effluents according to final reuse or discharged to the environment. Location of a sewage treatment plant can take advantage of gravity flow as much as possible to avoid need for pumping of influents.

Sewage flow was diverted using 0.125 M diameter PVC pipes to a manhole located outside the building. Quality and quantity of effluents were monitored on monthly basis from beginning of May to end of September 2014 by collect-ing six composite samples over 24 hours each time and were transferred for analysis in cold box at temperature of 4°C to the laboratories of the Center for Water and Environmental Studies of the University of Jordan, Amman, Jordan. Wastewater parameters analyzed are shown in Table 1. Average concentrations of chemical and biological parameters found in treated sewage included pH, EC, total suspended solids (TSS), fat, oil and grease (FOG), chemical oxygen demand (COD), five-day biological oxygen demand (BOD5). These parameters are of concern to permit restricted irrigation of treated sewage reuse (Jordan Standards and Metrology Department, 2002). All analysis was conducted ac-cording to the Standard Methods for Examination of Water and Wastewater (APHA, 2005). Table 1 shows the results of average concentrations and the standard deviations of chemical and biological parameters of interest found in the six raw wastewater samples evaluated during May to September 2009.

Table 1 Average concentration of chemical and biological parameters found in raw sewage

Parameter(mg/L)

Range Results a SD

pH (units) 5.50-7.30 6.14 0.62EC (μS/cm) 1389- 1550 1463 62

TSS 233-550 354 110.81COD 2320-3350 2729 359.48BOD5 1120-1643 1315 182.32

a Average results of six samples tested in duplicates

Estimation of the quantity of domestic water consumption was calculated from quarterly domestic water bills. Based on this estimation flow of influent to treatment plant was assumed to be 80% of fresh water used by the household Invalid source specified.. This estimation was later confirmed from the water meter readings in-stalled at discharge of treated wastewater and was found to be about 0.8 M3/day.

2.1 Design of septic tankA double compartment septic tank is used as a pre-treatment stage for

on-site household applications of CW (US EPA 1993, Otterpohl, 2003). The typical design features for the septic tank Invalid source specified. were:

A septic tank was designed based on influent quality characteris-tics and estimated daily flow of 0.8 M3/day. Figure 2 shows dimensions and construction details the septic tank. The following assumptions were made:

4

Septic tank dimensions were based on at least a 24 hours re-tention time and a once a year desludging interval and per head (hd) wastewater flow of 80% domestic water consumption.

Figure 1 Septic tank dimensions

Assuming sludge to be 0.04 M3/hd/yr (Mara, 1983) and desludging of sep-tic tank to be performed once a year when sludge occupied 1/3 of tank liquid volume, scum to occupied 1/3 tank liquid volume and clear liquid occupied 1/3 tank volume.

Assuming the tank should be emptied when it is one-third full of sludge, then desludging was estimated = waste flow {(M3/hd/yr)}/sludge accumulation rate (M3/hd yr).

Ten occupants would consume about 0.1 M3/d hd Invalid source speci-fied., and assuming 80% used water becomes wastewater flow, then 0.1 M3/hd/d x10 hd x0.8 M3/d x (3 days retention initially) = 2.4 M3 approximated to 2.5M3.

Internal dimensions of a concrete septic tank of 0.2 M concrete thick walls and international partitions were equal to 1.3 M high (H) x 1.0 M wide (W) x 2.7 M length (L).

External dimensions were = 1.3+(.2+0.15) H x 1.0 +(0.2+0.2) W + 2.7+0.2+0.2+0.2) L

Assume internal dimensions of tank with liquid height 1 M and 1 M wide and 1.7 M long first compartment + 0.8 M long second compartment. First suldge compartment internal dimensions were = 2.5x2/3=1.7 M and partitions of 0.2 M thickness and cover slab 0.15 M thickness

Second compartment internal dimensions were 2.5-1.7=0.8 M long.Tank external height and internal dimensions were 1m + 0.3 M free water

board = 1.3 M +(0.2+0.15)

5

2.2 DESIGN OF HFCWTypical design parameters for subsurface flow constructed wetland includ-

ing the HFCW (US EPA, 1988, US EPA, 1995) were required area, depth of the medium and the retention time. Removal of BOD5 in subsurface flow systems can be approximated to and described with first-order plug flow kinetics (US EPA, 1993 page 3-7; Metcalf & Eddy 2004), as described in equation No 1:

(1)

where,Ce = effluent BOD5, mg/LCo = influent BOD5, mg/LKT = temperature-dependent first-order reaction rate constant, d-1

t = hydraulic residence time, d

(2)

where,K20= 0.84 d-1 (EPA, 1993-page 3-7)T = ambient temperature.

Hydraulic residence time for unrestricted flow can be represented as:(3)

where,L = lengthW = widthD = depthQ = average flow rate = (flowin+flowout)/2

Equation 3 can be rearranged and used to estimate the required surface area for a subsurface flow system to yield,

(4)

where,Ce = effluent BOD5, mg/LCo = influent BOD5, mg/LKT = temperature-dependant first-order reaction rate constant, d-1

t = hydraulic residence time, d

6

Q = average flow rate through the system, M3/dd = depth of subsurface submergence, Mn = porosity of the bed, as fractionAs = surface area of the system, M2

US EPA Guidelines (1988) recognize the hydraulic constrains of soil media and recommended the use of sands or gravelly sands in subsurface CW flow sys-tems. In this study a HFCW was constructed next to the septic tank by digging a square trench of internal dimensions of 4 M wide by 5.3 meter long and 1.3 M deep.

The rooted plant type chosen for the wetland vegetation was a local vari-ety of common reed (Phragmites australis). Clumps were washed well to take away soil and detritus and transplanted in early October 2014. Planting density was six clumps per M2. The transplants were covered initially with a transparent plastic mulch to simulate green house effects and to speed up establishment of roots and the mulch was removed after green stems sprouted out to 0.30 M height. Plants help even distribution of the water in HFCW. The movement of the plants as consequence of wind keeps the gravel media surface open and the growth of roots within the filter media helps to decompose organic matter and prevent clogging. Vigorous growth rate of the reeds was observed but was not measured in terms of green matter production or uptake of nutrients or other constituents of the wastewater. The gravel media was dosed with 0.8 M3 /d of pretreated wastewater (Davis, 2007). Treated effluents percolated through the gravel media and were collected in a concrete tank of 1 M3 capacity installed at exit end of the CW. A one-horse electric centrifugal pump was installed near-by close to the HFCW to pump treated wastewater into drip irrigation network to irrigate garden crops of olive trees, forage and other plants for animal feed.

7

Figure 2 Schematics of the HFCW treatment plant

Samples of raw and treated effluents from the septic tank and the HFCW respectively were collected on monthly basis starting from October 3rd 2014 to April 4th 2015 and were transferred for analysis in cold box at temperature of 4°C to the laboratories of the Jordan Water Authority in Amman, Jordan. These samples were analyzed for pH, EC, TSS, COD, BOD5, Kj-N, NH4-N, NO3-N and anionic surfactants (MBAS). All chemical analysis was conducted according to the standard methods for examination of water and wastewater (APHA, 2005).

3. Discussion and results

3.1 Septic Tank PerformanceThe septic tank functioned very well in stabilizing fluctuations of raw waste-

water quality. Table 2 shows the quality of influent raw wastewater and septic tank and HFCW effluents. It was noticed in earlier work that raw wastewater content of TSS and BOD could vary from a low value of 10 mg/L for TSS and 350 mg/L for BOD5 to as high as 500 mg/L and 3000 mg/L respectively. This type of quality variation was well regulated by the septic tank treatment step, which is one of the main operation problems due to variability of feed in any subsequent treatment processes. The septic tank performed well with respect to removal of TSS (94%), Kj-N (67%) and ABS (40%) but less with respect to removal of COD (35%) and BOD5 (25%). This may be an indication that most TSS was in the form of settable inorganic solids. Although the pH of the efflu-ent was more acidic and was reduced from 7.08 to 5.82 but low percentage

8

removal of both COD and BOD5 could be due to incomplete maturation of the septic conditions in the tank at ambient temperature of 20 °C. This may improve when ambient temperature increases in summer. Odor of effluents was not of-fensive and household members or household neighbors did not complain about any odor, although the septic tank was located next to a living room window.

Table 2 Results of quality of influent of raw wastewater, and septic tank and HFCW effluents

Parameters Raw wastewa-

ter Septic effluents HFCW effluents JS 893-2002 Range Averages SD Range Averages SD Range Averages SDpH 5.75-9.1 7.08 1.41 5.42-6.25 5.82 0.35 6.70-7.25 7.07 0.20 6-9EC 1450-1656 1536.50 93.15 1389-1684 1545.00 112.47 1233-2021 1545.00 268.64 NRTSS 180-624 331.33 191.66 13-26 19.47 5.40 1233-2021 12.62 3.24 200COD 2155-3120 2504.17 342.76 1401-2028 1627.11 222.79 490-710 569.70 71.18 500BOD 1224-1633 1424.00 173.63 918-1225 1068.00 130.22 103-149 119.64 14.95 300Kj-N 47-86 67.17 14.27 14-30 22.40 5.39 103-149 11.32 2.37 45NH4-N 7.5-16.0 11.07 2.86 9.8-20.8 14.39 3.72 7.8-16.6 11.51 2.72 12NO3-N 0.5-10.5 5.05 4.92 0.8-18.0 7.58 7.39 3.9-22.0 13.27 5.89 NRMBAS 25.5-42.5 32.97 6.66 15.30-25.50 19.78 3.99 6.89-10.13 8.90 1.64 25FOG 63-166 104.83 45.79 NT NT NR a Average results of analysis of seven samples of feed raw wastewater

and effluents of septic tank and HFCW, tested in duplicates.SD= Standard deviation of results.NR= not required, NT= not tested.

Build up of dark grey colored scum was accumulated on top of septic tank water level was not much and accounted for a few millimeters over a period of seven months of continued operation and the sludge layer at bottom of the tank was not measured. This was one of the main benefits of incorporating a septic tank and resulted in much less need for regular cleaning of the wastewa-ter treatment system. Removal of nutrients was not an objective of this study. This was because wastewater was finally used for irrigation and presence of N and P within limits accepted by JS 893:2002 was considered as benefits.

The high concentrations of BOD and COD in the raw wastewater are nor-mal from rural household sources in Jordan and similar water scarce arid coun-tries (Alrajoula, 2009, Halalsheh, 2009). Also one can observe that the concen-tration of MBAS was 32 mg/L in the raw wastewater, which adds to the BOD loading. In addition, rural people in the Middle East are known to use plenty of olive oil in cooking and their daily diet where some of it ends up in kitchen sinks. The kitchen is a source of much food remains that end up in the waste-water too. The intermittent flow and the great variability of quantity of waste-water during the day adds to the difficulty of programming the auto sampler that was used to collect samples of wastewater over 24 hours per sampling attempt. All these factors aggravated by low water consumption, lead together to these very highly concentrated of COD and BOD in the Juhfeyeh wastewater.

9

3.2 HFCW PerformancePretreated effluents from the septic tank were directed into the grav-

el media of the HFCW. L:W aspect ratio of CW was for the system was 3.84:1 and that was in line with the recommended value in literature.

Equation No 5 was used to back calculate the val-ue of the surface area of Juhfeyeh HFCW as follows:

(5)

where,Ce = effluent BOD5, 1068 mg/LCo = influent BOD5, 119.64 mg/LKT = first-order reaction rate constant at 20 °C, 0.84 d-1

Q = average flow rate through the system, 0.500 M3/dd = Average depth of subsurface submergence, 0.25 mn = porosity of the bed, 0.4

And the surface area of the system was equal to 20 m2. This re-sults in less than the value of 2.2 M2 of bed surface per population equiv-alent (p.e.) as recommended by US EPA (US EPA 1993). This might be ex-plained by the fact that the value used for KT of 0.84 d-1 was a conservative value at low BOD5 reduction rate and gives more room for higher organ-ic loading on the CW in the future without increasing effluent BOD concen-tration. The average ambient temperature was taken to be equal to 20°C.

Figure 3 shows the % removal of TSS, Kj-N, ABS, COD and BOD5 (main pa-rameters) and Figure 4 shows % removal of the same main parameters by the action of the HFCW. The removal efficiency of the septic tank was higher than that of the HFCW.

0102030405060708090

100

TSS Kj-N ABS COD BOD5

Main Parameters

% R

emov

al

Figure 3. Septic tank % removal of main parameters

10

0102030405060708090

100

TSS Kj-N ABS COD BOD5

Main Parameters%

Rem

oval

Figure 4. HFCW % removal of main parameters

There was limited amount of oxygen in CW stage but it added up to other sources of oxygen coming from the plant rhizomes and helped improve bio-degradation of organic matter. The pump functioned well without problems.

The conclusion is that the quality of treated effluents from the plant was better than that required by the Jordanian standards for this type of ef-fluents. The CW vegetation grew rapidly and garden crops were also grow-ing well due to regular irrigation. The household members were also pleased with the use of drip irrigation systems that relieved them of manual irrigation.

Plates:Plate 1. Shows under construction concrete septic tank followed with CW basinPlate 2. Shows operating septic tank followed with CW basin plated with

common reeds.

4. ConclusionsWater scarcity in the region and in Jordan in particular is forcing govern-

ments and the public to look for alternative sources of water such as treat-ed wastewater including wastewater reuse. Treated wastewater is a secure source of water and it is available to all households in areas not served by central sewer networks. A combination of septic tank followed by HFCW treat-ment offers a low-cost and low technology alternative to rural households to conserve fresh water and gain additional income. The benefit to cost ra-tio of household level wastewater reuse can be as high as 2.78 was report-ed in earlier studies (Bino, M 2007) and encouraged more and more house-holds in rural areas to invest in this type of wastewater treatment plants.

The gravel used in filter bed have to be washed to remove fines and mechanical and sanitary components such of pumps and pipe work must be of high quality to resist corrosion and leaks so as to ensure reliable oper-ation by ordinary household members. This will probably result in low O&M costs. The effluents were of better quality than stipulated by the Jordani-an Standard JS 893:2002 for restricted reuse of irrigation. Proper training of owners of on this type of low technology wastewater treatment plants and in particular training on up stream pollution prevention of wastewater and on O&M will ensure sustainability of the treated wastewater reuse practice.

11

REFERENCESAlrajoula M, Halahasha M and Fayyad M (2009). Anaerobic filter for polishing effluent of UASB

reactor treating strong sewage at 23 C. Water Science and Technology- WST, 59.10, 2009

APHA, (2005). Standard Methods for the Examination of Water and Wastewa-ter 31 ed. Published jointly by American Public Health Association (APHA), American Water Works Association (AWWA) & Water Environment Federation

Bino M, et al., (2007). “Studies of IDRC supported research on grey-water in Jordan conducted by INWRDAM. Published by IN-WRDAM and a PDF file format of the report is available HERE

Davis L. C, et al., (2007). Vertical flow constructed wetland for tex-tile effluents treatment. Wat. Sci. Tech., Vol 55 No 7 pp 127-134

Department of Health Western Australia, DHWA, (2002). Draft Guidelines for the Reuse of Greywater in Western Australia. Department of Health, Perth, Australia, p. 37

Li F, Wichmann K, Otterpohl R., (2009). Review of the technological approaches for grey water treatment and uses, Science for the total environment 407, pp 3439-3449

Mara, David Duncan, Sewage treatment in hot climates, 1983, Jone Wely & Sons, Ltd.

Metcalf &Eddy (2004). Wastewater engineering- treatment and reuse. 4th Edition Pub-lished by McGraw-Hill, 1221 Avenue of the Americas, New York, NY 10020, USA

Otterpohl, R., Braun, U. and Oldenburg, M. (2003). Innovative technol-ogies for decentralized water, wastewater and biomass manage-ment in urban and peri-urban areas. Wat. Sci.Tech., 48(11/12), 23-32.

Platzer C. (1999). Enhanced nitrogen elimination is subsurface flow artifi-cial wetland- a multistage concept. In Proceedings of the 5th Internation-al Conference on Wetland Systems for Water Pollution Control. Internation-al Water Resources association, Colchester, UK. Res. 26 (1990) 939–948.

US Environmental protection Agency, (1988). Constructed Wetlands and Aquatic Plant systems for Municipal Wastewater Treatment. EPA /625/1-88/022. Cincinnati, OH.

US Environmental protection Agency, (1993). Subsurface Flow Constructed Wet-lands for Wastewater Treatment, A Technology Assessment. EPA /832/R-93/008.

Vymazal, J., Brix, H., Cooper, P.F., Harbrel R., Perfler, R., Laber, J., (1998). Removal mechanisms and types of constructed wetlands. In: Vymazal, J., Brix, H., Cooper, P.F., green, M.B., Harbrel R. (Eds.), Constructed Wetland for Wastewater Treat-ment in Europe. Blackhuys Publisher, Leiden, The Netherlands, p. 306.

12

Plate 1. View of constrcuted septic tand and far end a constrcuted wetland basin for a rural house sewage treatment

Plate 2. View of completed and operational constrcuted for a rural house sew-age treatment