Recycled Water-Version 2.0

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ADSSC/DGDesignGuidelines

Section 5 Recycled Water Rev: 02 Mar. 2011 Page 1 of 14

ABU DHABI SEWERAGE SERVICES COMPANY(ADSSC)

DESIGN GUIDELINES

SECTION 5

RECYCLED WATER


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Design GuidelinesAbu Dhabi Sewerage Serv ices Company

(ADSSC)


Section 5 Recycled Water Rev: 02 Jan. 2011 Page 2 of 14

DOCUMENT CONTROL SHEET

Revision No. Date Revision Description / Purpose of Issue

01 April 2008 First Issue

02 March 2011

- ADSSC new logo- TSE name has been changed to read Recycled

Water as per RSB commentary.- Sludge name has been changed to read Bio-solid

as per RSB commentary.

- Sub-Section 5.1.4 revised in implementation ofRSB guidelines for the recycled Water.- Sub-Section 5.1.5 revised in implementation of

RSB guidelines for use of Recycled water forirrigation

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TABLE OF CONTENTS

5.1

GENERAL ..........................................................................................................4

5.1.1

DEFINITION OF RECYCLED WATER ...................................................4

5.1.2

APPLICATIONS OF RECYCLED WATER .............................................4

5.1.3

RESPONSIBILITIES OF ADSSC ...........................................................4

5.1.4

RECYCLED WATER STANDARDS ....................................................... 4

5.1.5

RECYCLED WATER USE IN IRRIGATION ........................................... 7

Table 5.1.5.1 Irrigation criteria for trace elements ..................................8Table 5.1.5.2 Salinity parameters ...........................................................8

5.1.6

INFRASTRUCTURE ...............................................................................9

5.2

DESIGN REQUIREMENTS ................................................................................9

5.2.1 DISINFECTION ......................................................................................9

5.2.1.1

CHEMICAL DISINFECTION ...................................................................9

5.2.1.2 ULTRAVIOLET DISINFECTION .............................................................95.2.2 STORAGE TANKS (UP TO 2,000 m3CAPACITY) ...............................105.2.2.1

CONFIGURATION ................................................................................10

5.2.2.2

INLET ARRANGEMENT .......................................................................10

5.2.2.3

OVERFLOW AND WASHOUT .............................................................10

5.2.2.4

ACCESS ...............................................................................................10

5.2.2.5

VENTILATION ......................................................................................11

5.2.3

STORAGE TANKS (UP TO 5,000 m3CAPACITY AND ABOVE) .........11

5.2.3.1CONFIGURATION ................................................................................115.2.3.2 INLET ARRANGEMENT .......................................................................115.2.3.3OVERFLOW AND WASHOUT .............................................................115.2.3.4ACCESS ...............................................................................................11

5.2.3.5

VENTILATION ......................................................................................12

5.2.3.6

WATER LEVEL INDICATION ...............................................................12

5.2.4 PIPEWORK ..........................................................................................125.2.4.1

HYDRAULIC DESIGN ..........................................................................12

5.2.4.2

SURGE PROTECTION ........................................................................12

5.2.4.3SYSTEM LOSSES ................................................................................125.2.4.4VALVE CHAMBERS .............................................................................135.2.4.5

FLOWMETERS ....................................................................................13

5.2.4.6

OTHER FEATURES .............................................................................13

5.2.5

PUMPING STATIONS ..........................................................................14

5.2.5.1

INLET ARRANGEMENT .......................................................................14

5.2.5.2

INLET CONTROL .................................................................................14

5.2.5.3

PUMP SELECTION ..............................................................................14

5.2.5.4

OUTLET CONTROL .............................................................................14


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5.1 GENERAL

5.1.1 DEFINITION OF RECYCLED WATER

a) Domestic and industrial wastewater poses a threat to both human healthand to the environment and is therefore collected and subjected toappropriate treatment to address this risk. The products of wastewatertreatment are bio-solids and Recycled Water.

b) It is the intent of ADSSC to maximize the re-use of all Recycled Water .ADSSC has identified Recycled Water as a potential source of valuableirrigation water, however strict quality standards should be applied toRecycled Water to ensure that it is safe for various and oftenunrestricted irrigation applications.

c) The processes used to treat sewage are successful in reducing theharmful chemical constituents of sewage but, unless some reliable formof disinfection is incorporated into the treatment process, there remainsa risk of biological contamination from the Recycled Water. ADSSCcurrently disinfects all Recycled Water with a tertiary chlorinationprocess and the Recycled Water meets current unrestricted irrigationstandards (see Section 4 of the Design Guides).

5.1.2 APPLICATIONS OF RECYCLED WATER

a) Recycled Water can be used for a variety of irrigation applications, suchas the irrigation of food crops, non-food crops, watering of golf coursesand watering of public parks. Consideration must also be given to thepossibility that Recycled Water may, under certain circumstances, bedischarged to the marine environment. Standards for such uses anddisposal should therefore be taken into account when considering thequality standards to be applied to Recycled Water.

5.1.3 RESPONSIBILITIES OF ADSSC

a) ADSSC has responsibilities with respect to the chemical and biologicalquality of the Recycled Water and its availability at the point of dischargeor storage for subsequent use. ADSSC does not have responsibility forthe transfer and distribution of Recycled Water from the storage tanks tothe place of irrigation, nor does it have responsibility for the application

of the Recycled Water: these are the responsibilities of the end user,which is currently the Public Gardens Directorate of the Abu DhabiMunicipality.

5.1.4 RECYCLED WATER STANDARDS

a) The standards identified in the Tables 5.4.1 define the minimum qualityrequirements for Recycled Water at the Point-of-transfer or discharge.


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Table 5.1.4.1 (a) Recycled Water Quali ty

Standard

Microbiological Sanitary

Faecal

Coli-

form

Intestinal

Enterococci

Helminthes

Ova

pH

BOD5

(ATU)

Total

Suspended

Solid

Ammonia

Nitrogen

Total

Phosphorus

Turbidity

Residual

Chlorine

Dissolved

Oxygen

MAC

MAC

MAC

Average

MAC

MAC

MAC

MAC

MAC

Average

Average

CFU/100ml

CFU/100ml

Number/1

mg/l

mg/l

mg/l

mg/l

NTU

mg/l

mg/l

P1 General reuse 100 40 < 16 to8

10 10 - - 50.5 to

1. 1

P2Restricted

reuse1000 200 < 1

6 to8

10 20 - - 100.5 to

1. 1

P3 Marine 1000 - 06 to9

50 50 2 2 75 1 > 3

Notes:General reuse involves frequent and uncontrolled exposure of the general public toRecycled Water and Restricted reuse involves infrequent and controlled public

exposure to Recycled Water

Notes:CFU = Colony Forming Units; NTU = Nephelometric Turbidity Unit; mg/l =milligrams per liter

Notes:MAC = Maximum allowable concentration; Average Arithmetic Mean of thesamples taken in any calendar month must comply with the standard

Notes:

Marine and land discharges are also subject to Federal and Emirate laws detailed inAnnex A3 and A4. Any system discharging to land percolation should consider P1as a minimum acceptable standard unless a site specific assessment in conjunctionwith relevant authorities determines otherwise.

b) The need for the disinfection of Recycled Water will depend upon theexact application of the Recycled Water. Some applications require fulldisinfection with residual chlorine providing ongoing protection. Otherapplications may need only UV disinfection or no disinfection at all.

c) By its very nature, sewage contains many types of bacteria, viruses andother potentially harmful micro-organisms. These micro-organisms posea particular threat to human health and therefore consideration must begiven to the possible need for disinfection of the Recycled Water prior touse.


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d) Micro-organisms can enter the human body through three possiblepathways:

i. Injection, i.e. through a cut or abrasionii. Ingestion (swallowing) of contaminated materialiii. Inhalation of air containing contaminated particles

f) Infection via injection can occur when Recycled Water comes intocontact with an area of unprotected skin. Sewage treatment plantoperators and other workers who deal with Recycled Water are routinelyexposed to this risk but are given appropriate training and equipment(i.e. PPE) to protect them against it. If the Recycled Water is used in anapplication where only suitably trained staff are likely to come intocontact with the Recycled Water, then disinfection of the Recycled Watermay not be deemed necessary. If however untrained persons (such as

the general public) are likely to come into contact with the RecycledWater (for example, in a water body used for swimming and otherrecreational purposes), then disinfection is necessary.

g) Infection via ingestion occurs when contaminated material is swallowed.This may occur if the Recycled Water is used for irrigation of food crops,particularly those intended for direct (i.e. raw) consumption. A riskassessment should be carried out in these circumstances. If the risk isconsidered significant, then the Recycled Water should be disinfected.

h) Infection via inhalation can occur if the Recycled Water is passedthrough a small orifice, thereby producing aerosols of contaminateddroplets. Spray irrigation is an example of such a process and in thesecircumstances the Recycled Water should normally be disinfected.

i) Table 5.1.4.2 indicates those activities that pose a risk of infection andtherefore may require the disinfection of Recycled Water by chlorineinjection to render the effluent virtually harmless and to control thegrowth of algae in the system. A chlorine residual of 0.5 mg/l at the outletof the irrigation system should be available. Disinfection of RecycledWater for reuse as irrigation water by the dosing of chlorine, chlorinedioxide or sodium hypochlorite shall produce a residual chlorineconcentration of at least 0.5 mg/l in the Recycled Water.

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Section 5 Recycled Water Rev: 02 March . 2011 Page 7 of 14

Table 5.1.4.2 Activi ties posing a risk of infection from Recycled Water

Appl ication

Injection Ingestion Inhalation

Workers Public Workers Public Workers Public

Irrigation of

grass verges

Irrigation of non-

food crops

Irrigation of rootvegetables

Irrigation of

salad

vegetables

Spray irrigation

Ornamental

ponds

Recreational

lakes

Irrigation of

school playing

fields

Fountains

5.1.5 RECYCLED WATER USE IN IRRIGATION

Where Recycled Water is used for irrigation purposes the following additional

Requirements apply:

a) The Recycled Water must meet the standards set out in table 5.1.5.1derived from Annex 1 of WHO 2006 Guidelines for the safe use ofWastewater in Agriculture

b) the Disposal Licensee must define the agronomic value of the RecycledWater by specifying, amongst other things the:


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I. Typical range of total and available nitrogen, phosphorus andpotassium; and

II. The salinity of the Recycled Water by providing information on theparameters identified in Table A2.1 (B).

Table 5.1.5.1 Irrigation criteria for trace elements

Parameter UnitMaximum allowable

concentration

Aluminum mg/l 5

Arsenic mg/l 0.1

Beryllium mg/l 0.1

Cadmium mg/l 0.01

Chromium mg/l 0.1

Cobalt mg/l 0.05

Copper mg/l 0.2

Fluoride mg/l 1

Iron mg/l 5

Lead mg/l 5

Lithium mg/l 2.5

Manganese mg/l 0.2

Molybdenum mg/l 0.01

Nickel mg/l 0.2

Selenium mg/l 0.02Vanadium mg/l 0.1

Zinc mg/l 2

Table 5.1.5.2 Salinity parameters

Parameter Unit

Electrical conductivity (dS/m @ 25oC)

Total dissolved solids (TDS) mg/l

Sodium adsorption ratio (SAR) meq/l

Sodium (Na+) meq/l

Chloride (Cl-) meq/lBoron mg/l

Bicarbonate (HCO3-) mg/l


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5.1.6 INFRASTRUCTURE

a) The infrastructure required by ADSSC to provide Recycled Water whichis suitable for irrigation consists of:

i. A treatment process (normally the in-place sewage works)ii. A disinfection process (most Recycled Water needs to be

disinfected prior to use)iii. Reservoirs for storage. These are specified in greater detail later.iv. Connections to allow Recycled Water to be removedv. A facility to overflow to watercourse/sea

b) As stated in Section 5.1.3, ADSSC have no responsibilities beyondensuring that the Recycled Water meets chemical and biological quality

standards and that facilities exist for safe delivery to the Public GardensDepartment of the Abu Dhabi Municipality.

5.2 DESIGN REQUIREMENTS

5.2.1 DISINFECTION

Irrigation water is often used in close proximity to workers and the generalpublic. Clearly, this poses a risk of infection by biological pathogenscontained within the Recycled Water. There are applications therefore thatrequire the disinfection of Recycled Water. There are two options: chemicaldisinfection or the use of ultraviolet light.

5.2.1.1 CHEMICAL DISINFECTION

a) Chemical disinfection of Recycled Water shall consist of a duty/standbysystem dosing chlorine, chlorine dioxide or sodium hypochlorite. Thesystem shall be installed on the inlet to the Recycled Water holding tankat the treatment works and shall be sized to dose the maximum flowentering the tank. Chlorine monitors shall be installed on the outlet ofthe Recycled Water Holding Tank and an alarm shall be raised if thechlorine level drops below 0.5 mg/l. For full details of the equipmentstandards see the ADSSC Standard Specification 15150 Disinfection.

b) In addition secondary chlorination would also be required to ensure a

residual chlorine of 0.5 mg/l at the point of transfer. A similar monitoringsystem as above should also be installed at the point of transfer.

5.2.1.2 ULTRAVIOLET DISINFECTION

a) Ultraviolet disinfection is not suitable for applications that require 100%pathogen kill and is therefore of limited application for Recycled Waterdisinfection. If used, the uv plant should meet the followingspecifications:


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i. The ultraviolet disinfection phase should consist of at least two units

arranged in a duty/standby configuration.ii. On-line monitoring of the upstream suspended solids/turbidity

content of the influent shall be carried out.iii. Continuous monitoring of the uv dose supplied shall be installed.

b) The UV disinfection will also have to meet the requirements set out inADSSC Standard Specification 15150 Disinfection in addition to theabove.

5.2.2 STORAGE TANKS (UP TO 2,000 m3CAPACITY)

These tanks will normally constructed in reinforced concrete. The tanksshould be gravity fed, should be equipped with a suitable inlet and overflow

and (in the cases where chemical disinfection is used) should be covered.The tanks should be equipped with facilities for withdrawing large volumes ofRecycled Water by tanker. Should the sewage works be adjacent to afacility that is likely to have an ongoing and significant need for irrigationwater, then ADSSC will consider installing direct pipework to this facility.Under normal circumstances this will not be the case and ADSSC will informthe designers and constructors of sewage treatment works of any specificrequirements of this sort prior to any contract being awarded. See standardand typical drawings of such tanks for further details.

5.2.2.1 CONFIGURATION

a) Rectangular or square depending on plan area of allocated site.

b) Two equal compartments.

c) Sloping floor to outlet at a gradient of 1 in 70.

d) Internal height 3m.

e) Roof supported on columns to suit structural design.

5.2.2.2 INLET ARRANGEMENT

a) Splitting chamber to provide separate feed, normally 400mm diameter,

to each compartment with appropriate valves and fitting.

b) Ball float valve in each compartment for automatic water level control.

5.2.2.3 OVERFLOW AND WASHOUT

a) Separate pipework and valves to each compartment with discharge to acommon collection chamber for disposal to watercourse or sea.

5.2.2.4 ACCESS


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a) Covers above ball float valves to afford access for maintenance andpossible removal.

b) Water level check facility to each compartment.

c) Lockable covers.

5.2.2.5 VENTILATION

a) Two number required. One no. to each compartment with integraldeodoriser and mosquito screen.

5.2.3 STORAGE TANKS (UP TO 5,000 m3CAPACITY AND ABOVE)

a) Constructed in reinforced concrete or steel. See Section 5.2.2 for furtherspecifications.

5.2.3.1 CONFIGURATION

a) Rectangular with actual dimensions dependent on capacity required,land availability and shape. Length to breath breadth ratiorecommended as 1.5:1.

b) One compartment.

c) Sloping floor to outlet end at 1 in 200.

d) Maximum height above ground 5m (check with Planning Departmentrestriction).

e) Roof supported on columns to suit structural design.


a) Single feed pipe under reservoir and up through floor terminating in abell-mouth 150mm above floor level. Control inflow through valve oninlet pipe with remote operation at distribution centre.

5.2.3.3 OVERFLOW AND WASHOUT

a) Overflow level at 100mm above top water level connected to outfall anddesigned to be capable of passing maximum inflow. Washout at floorlevel in bell-mouth and connected to same outfall. Washout usually300mm diameter. The washout shall be installed at outlet end ofreservoir with a manual valve. The overflow shall have neither valve norother constriction

5.2.3.4 ACCESS


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a) Lockable covers.

b) Openings sufficient to afford suitable access for men and equipment andover all pipe entries and exits to facilitate inspection.

c) Ladders at each access openings.

d) Staircase access to roof with hand railing.

5.2.3.5 VENTILATION

a) 150mm diameter pipe with integral deodoriser and mosquito meshprovided for every 400m of roof.

5.2.3.6 WATER LEVEL INDICATION

a) Manometer tube 80mm diameter fixed to outside of reservoir wall withflip-type colour indicators and relayed to distribution centre.

5.2.4 PIPEWORK

5.2.4.1 HYDRAULIC DESIGN

a) Design of Recycled Water mains should be based on equations such asManning, Colebrook-White and Hazen Williams. Pipe roughness factorsshall be as follows:

i. Manning n = 0.0075ii. Colebrook-White ks = 0.15mm (for velocity 1.1 to

1:8m/sec)ks = 0.3mm (for velocity less than1.1m/sec)

iii. Hazen Williams 140 for pipe diameters >500mm135 for pipe diameters


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a) 12% system loss is to be allowed.

5.2.4.4 VALVE CHAMBERS

a) Isolation Valves

i. Valves shall be installed at strategic locations to enable isolation ofportions of the network.

ii. Valves shall be provided at cross connections between primary /secondary mains and secondary distribution mains.

iii. Valves shall be provided at irrigation T-connection pipe.iv. Maximum spacing shall be 500m in green areas.

b) Air Release Valves shall be installed at:

i. All high points.ii. Changes in grade.iii. Minimum 500m spacing.iv. Selected locations to assist emptying the main.

c) Washout Valves

i. Washout facilities shall be installed at the low points.

5.2.4.5 FLOWMETERS

a) Flowmeters shall be provided at suitable locations to monitorconsumption and irrigation efficiencies.

5.2.4.6 OTHER FEATURES

a) Minimum Cover

i. Without protection 1.2m (depth to top of pipe)ii. With protection 0.5m (depth to top of protection)

b) Pipe bedding: Refer to the standard drawings

c) Pipeline protection: Use of concrete slab, where required.

d) Thrust blocks.

i. Refer to the standard drawings.ii. Check manufacturers recommendations for maximum bend without

restraint.iii. Wherever possible, blocks shall take the form of a cradle wedged

against the undisturbed trench side and design based on the safebearing pressure of the ground.

iv. Piling may be required to achieve support from the ground at depth,subject to results of soils investigation.

v. Arrangement should not impede flexibility or expansion.


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vi. Check for friction factor of safety 1.5, sliding factor of safety 2.0,overturning factor of safety 2.0 and bearing capacity.

e) Marker Posts are to be provided at bends, features and crossings.

5.2.5 PUMPING STATIONS

Pumping stations for treated sewage effluent will be dry well (closed)pumping stations, drawing Recycled Water from storage tanks / reservoirs.The overall approach to Recycled Water pumping station design, generallayout and mechanical / electrical requirements is similar to sewage effluentpumping stations and shall be as per Section 3.4. The major aspects thatcan differ are:


a) The system between the reservoirs and the pumps is continuous withouta break to atmosphere. The suction head on the pipes shall be directlyrelated to the reservoir level.

5.2.5.2 INLET CONTROL

a) Pressure sensors / relays shall be installed on the suction side of thepumps to signal the pumps to trip in the event of a set maximumnegative pressure being exceeded.

5.2.5.3 PUMP SELECTION

a) Double entry split casing type with double entry impellers are preferred.

b) Construction materials for the parts in contact with the effluent shall beresistant to corrosion from the chlorine content.

5.2.5.4 OUTLET CONTROL

a) The design shall maintain a fixed pressure head to allow pump speed /flow characteristics to develop.

b) Bypass line to the pressure control shall be provided with pressuresustained by partial closure of a valve.

c) Pressure sensing / relays shall be installed on the delivery main.

END OF SECTION

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