Dewats Model

DECENTRALIZED WASTEWATER TREATMENT SYSTEMS (DEWATS) FOR DOMESTIC SEWAGE

CENTRE FOR ENVIRONMENTAL PLANNING & TECHNOLOGY, AHMEDABAD

AN OVERVIEWy DEWATS are based on different natural treatment techniques,

put together in different combinations according to needs, possibilities, challenges and financial implications. y DEWATS provides treatment for wastewater flows ranging from 1m3 to 500 m3 per day from domestic and industrial sources. y Area of Application:y y y y y

Community Toilets at City Level WWT for small Townships and Colonies WWT and Sanitation for Slum Communities Institutions Small and Medium Scale Enterprises

y It guarantees permanent and continuous operation, however,

fluctuation in effluent quality may occur temporarily.1 Centre for Environmental Planning & Technology, Ahmedabad DEWATS for Domestic Sewage

DEWATS: DESIGN PRINCIPLEy Reliability; y Longevity; y Tolerance towards inflow fluctuation; y No sophisticated control and maintenance; y Treatment using methods that are designed to utilize natural

physical principles combined with biological activities of microorganisms y Improving quality of natural drains and water bodies

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Centre for Environmental Planning & Technology, Ahmedabad

DEWATS for Domestic Sewage

DEWATS AT A GLANCEy DEWATS mainly consists of three treatment phases:PHASE LEVEL OF TREATMENT Primary Treatment PHASE - I Secondary Treatment Anaerobic Filter PHASE - II Tertiary Treatment Planted Gravel Filter Anaerobic Ponds Post-treatment Facultative Aerobic Ponds Settler Baffled Reactor MODULE

PHASE III (OPTIONAL)

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DEWATS AT A GLANCEMODULE AREA REQUIREMENT 0.5m2/m3 of daily flow 1m2/m3 of daily flow 1m2/m3 of daily flow 30m2/m3 of daily flow 4m2/m3 of daily flow KIND OF WASTEWATER TREATED Treatment Quality (Approx. BOD Removal Rates) 25 to 50% SETTLER High % of settleable solids

BAFFLED REACTOR ANAEROBIC FILTER PLANTED GRAVEL FILTER ANAEROBIC PONDS

For all kinds of wastewater

70 to 90%

Low % of suspended solids and narrow COD/BOD ratio Low % of suspended solids and COD concentration below 500 mg/l

70 to 90%

70 to 95%

BOD content below 300 mg/l May be charged with strong wastewater, however, bad odor cannot be avoided reliably with higher loading rates

70 to 95%

FACULTATIVE AEROBIC PONDS4

25m2/m3 of daily flow

70 to 95%



DESIGN PARAMETERSy Data indispensable to the calculation and choice of right

DEWATS design are:y y y y y y y

Daily wastewater flow Hours of major wastewater flow or other data describing fluctuations Average COD values and range of fluctuations Average BOD values or average COD/BOD ratio Suspended solid content. Percentage of settleable solid pH Ambient temperature and temperature of wastewater at source

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ADVANTAGESREUSABILITY OF TREATMEN T PRODUCTS RESOURCE & COST EFFICIENCY LOW O & M COSTS

LANDSCAP E BENEFITS

DEWATS

EASY TO OPERATE & MAINTAIN

RELIABILIT Y& LONGEVITY MODULAR DESIGN

LIVELIHOO D OPPURTUN ITIES

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CONVEYANCEy Design according to terrain/topography y Simplified carriage and disposal network y No energy is required to carry the wastewater from source to y y y y

treatment unit No transmittance costs No health hazards due to leakages or mixing of pipelines Sewer network can also be decentralized Less maintenance

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REUSE POTENTIAL OF THE BY-PRODUCTSBIO-GAS

HEATING COOKING LIGHTING

BY PRODUCTS

TREATED WATER

GARDENING IRRIGATION FLUSHING

SLUDGE

COMPOSTING

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DEWATS MODULESy SETTLERy y y y y y

The Settler is made as sub-soil constructed tank with one partition wall. Two main treatment processes take place: Sedimentation/flotation and biological treatment Digestion process ensures the accumulated sludge is reduced and the remaining is stabilized. Storage volume for sludge is provided for 18 to 24 months Average reduction of BOD is between 25 and 50 %. The Settler is resistant to shock load and variable inflow mainly due to the following module of the system, i.e. the baffled reactor.

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Gas

SETTLERManhole

Manhole Inflow

Outflow Scum

Settling Particles

Sludge

Separation Chamber

Polishing Chamber

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DEWATS MODULESy ANAEROBIC BAFFLED REACTORy y y

y y y

y

The reactor consists of a series of chambers, in which the wastewater flows up-stream. Activated sludge is located at the bottom of each chamber. Influent wastewater is intensively mixed up with the sludge, inoculating it with anaerobic bacteria which decompose the pollutants. Progressive decomposition occurs in successive chambers The BOD reduction rate is 90 %. Pathogens reduction range between 40 75 %. The Baffled Reactor is resistant to shock load and variable inflow, the operation and maintenance is simple and no space is required since it is a sub-soil construction. Design depends on inflow BOD, temperature, retention time and up-flow velocity and effluent quality depends on the number of up-flow chambers.DEWATS for Domestic Sewage

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ANAEROBIC BAFFLED REACTORGas Manhole Manhole Manhole Manhole Manhole Manhole Manhole

Inflow Scum

Outflow

Sludge

Sedimentation

Inoculation of fresh wastewater with active sludge

Final Settler

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DEWATS MODULESy ANEROBIC FIXED BED FILTERy y y y y y

Treatment occurs in the absence of oxygen (anaerobic). Wastewater passes in a series of chambers through the filter material in up-flow form. The filter is made out of gravel, slag or plastic elements. To avoid plugging, pre-treatment (sedimentation) is necessary. Efficiency in terms of BOD removal ranges from 75% - 90%. De-sludging is needed only if excess activated sludge is generated

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ANAEROBIC FIXED BED FILTERGas Manhole Inflow Manhole Manhole Manhole Outflow

Sedimentation Tank

Filter Units Sludge

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DEWATS MODULESy PLANTED GRAVEL FILTERy y

y

y y y

The function of the PGF is mainly post treatment. Main removal mechanisms are biological conversion, physical filtration and chemical adsorption. Mechanisms of BOD removal are mainly aerobic. Planted Gravel Filter (PGF) is made of reed planted filter bodies consisting of graded gravel. Bottom slope is 1 %. The flow direction is mainly horizontal Reduction rate of BOD is between 75 - 90 %. Reduction of infective organisms is over 95 %. Operation and maintenance of the system is simple. The spatial requirements are compensated through pleasing landscapes. Flow rate, pollution load, Hydraulic retention time and temperature are the basic inputs for design.DEWATS for Domestic Sewage

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PLANTED GRAVEL FILTER

O2 Inflow

O2

O2

O2

Internal Water Level Manhole Central Outlet Shaft Final Outlet

Upper Sand Layer

Cross Distribution Trench filled with Rocks

Main Filter Body filled with Coarse gravel

Cross Perforated Pipe Collection connected to Trench filled Swivel Pipe for with Rocks Adjustable Height

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DEWATS MODULESy CONTROL PONDSy

The discharge from the planted gravel filter is passed into a fish pond for effluent quality control. The effluent of the pond can be used for irrigation of green areas of the site.

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COSTS Main Cost Components

(A) Administration (B) Planning and design18 Centre for Environmental Planning & Technology, Ahmedabad

(D) Annual cost (O&M) (C) ConstructionDEWATS for Domestic Sewage

COSTSy Cost of any treatment depends on:

Quality desired for effluent y Sophistication of treatment system y Reuse needsy

y It is difficult to give exact cost for a system because:

Construction cost varies from location to location and time to time y Land cost very tricky!!y

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COSTSy DEWATS has the potential of being more economical in

comparison to other realistic treatment options, because:DEWATS may be standardized for certain customer-sectors, which reduces planning cost. y DEWATS does use neither movable parts nor energy, which avoids expensive but quickly wearing engineering parts. y DEWATS is designed to be constructed with local craftsmen; this allows to employ less costly contractors which causes lower capital cost, as well, and later lesser expenses for repair.y

y DEWATS may be combined with natural or already existing

treatment facilities so that most appropriate solution may be chosen. y DEWATS has the least possible maintenance requirements which spares not only manpower for daily attendance but also highly paid supervisors or plant managers.20 Centre for Environmental Planning & Technology, Ahmedabad DEWATS for Domestic Sewage

CONSTRUCTIONy DEWATS are relatively simple structures that can be built by

reasonably qualified craftsmen or building contractors with the ability to read technical drawings. y Technical details of a design, which has been adapted to local conditions, should be based on the material that is locally available and the costs of such material. y Important materials are:Concrete for basement and foundation Brickwork or concrete blocks for wall Water pipes of 3 , 4 and 6 in diameter Filter material for anaerobic filters, such as cinder, rock chippings, or specially made plastic products y Properly sized filter material for gravel filters (uniform grain size) y Plastic foils for bottom sealing of filters and ponds y Gate valves of 4 and 6 diameter are necessary to facilitate desludging of tanks regularly.y y y y21



MAINTENANCEy Permanent wastewater treatment that does not include some y y

y

y

degree of maintenance is inconceivable. DEWATS is designed such that maintenance is reduced to the minimum. DEWATS nonetheless reduces maintenance to the nature of occasional routine work. Anaerobic Tanks would need to be de-sludged at calculated intervals (usually 1 to 3 years) due to the sludge storage volume having been limited to these intervals. In case of Anaerobic Filters, the general practice is to remove the filter media, wash it and clean it outside and put it back after this cleaning. This may be necessary every 5 to 10 years. Planted Gravel Filter gradually loose their treatment efficiency after 5 to 15 years, depending on grain size and organic load.y

The same media may however be re-used after washing.

y Pond systems require the least maintenance. De-sludging may

not be necessary for 10 to 20 years. Normally, an occasional control of the inlet and outlet structures should be sufficient.22 Centre for Environmental Planning & Technology, Ahmedabad DEWATS for Domestic Sewage

TRAINING FOR OPERATIONy DEWATS is designed in such a way that maintenance is

reduced to the minimum. y It would be best to explain the treatment process to the most senior person available, as he is likely to be the one to give orders to the workers in case of need. y In case the educational qualifications of the on site staff is low, the engineer who designed the plant or the contractor who constructed the plant should provide service personnel, who may come to the site once a year or at times of need. y In case of housing colonies, the members of the permanent staff can be trained under an extensive training programme.

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COMPARATIVE STUDYS R. N O ITEM CONVENTIO NAL ACTIVATED SLUDGE PROCESS CONVENTI ONAL TRICKLING FILTER FACULTATI OXIDATI VE ON AERATED DITCH LAGOON WASTE STABILISAT ION PONDS UASB REACT OR PROCE SS DEWAT S

1 BOD removal (%) 2 Land Requirement (m2/capita excluding post treatment) 3 Energy Requirement KWH/Person /Year24

85-92

80-90

95-98

75-85

75-85

75-85

75-95

0.18-0.25

0.20-0.30

0.150.20

0.30-0.40

2.0-2.8

0.150.20

1.5-2

12-15

7-11

16-19

12-15

nil

-

nil




4 Equipment

Aerators, pumps, scrapers, Thickener, Digester, Dryer, Gas equipment

Trickling recycle pumps, sludge scrappers, thickeners, digester equipment s,

Aerator Aerators recycle pimps

nil

Pumps Gas , gas ion equip ment collecti equipm ent if the biggas is to be reused collect on

Requirement recycle

filter arms, s,

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Simple 5 Level of Supervision Skilled Skilled Skilled Semiskilled r than Simplest activat ed sludge 6 Capital /MLD lakhs) O&M Cost/MLD/Y ear (in lakhs) 1.5 0.75 1.25 1.25 0.72 cost (in 35 25 15 9 24 Simples t

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CASESTUDY 1: DEWATS FOR SUN DIVINE - 4y PROJECT BACKGROUND:y y y y y y y y

Sun Divine 4 is a luxury residential complex at SG Road. There are no municipal sewage lines placed in the area yet. Type of Project: Residential (24 units, G+2) Developers: Sun Housing Corporation No. of Occupants: 144 residents (6 per unit) Source of water: Bore well (6 and 700 deep) Sources of Wastewater: Kitchen, Toilets Considering a consumption of 200 lpcd and 80% of it as sewage generation per head, Total Sewage Generation at site: 24 m3

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SALIENT FEATURESPARAMETER Number of Treatment Plants Source Design Capacity No. of Users Peak Flow VALUE 1 Unit in the proposed common plot area 24 Kitchens, 87 Toilets 24 m3 144 8h

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MODULE S ADOPTEDBIOGAS SETTLER Digester Volume Gas Volume Area of Construction BAFFLE D REACTOR Volume Area of Construction PLANTED GRAVEL FILTER Volume Area of Construction Filter Material Used Plants COLLECTION TANK Volume Area of Construction29

18 m3 5.6m3 19 m2 43.4 m3 40 m2 44 m2 110 m2 Gravel Colacasia, Canna Indica 12 m3 4 m2DEWATS for Domestic Sewage


SYSTEM IN BRIEFy The wastewater shall be channeled from all the sources and

collected in the settler. y The treatment system would consist of 4 modules: Biogas settler, Baffled reactor, Planted gravel filter and Collection Tank.Fixed dome tunnel shaped biogas settler is a sedimentation tank which also improves settling performance. Biogas is formed due to the digestion of settled organic particles under anaerobic condition. y Baffle reactor (8 chambers) would ensure anaerobic degradation of suspended and dissolved solids by mixing fresh wastewater with an active sludge blanket. y Planted gravel filter would be used as tertiary treatment unit where aerobic and facultative degradation of dissolved organic and pathogen removal would occur. y A collection tank shall be used to store the treated water.y30 Centre for Environmental Planning & Technology, Ahmedabad DEWATS for Domestic Sewage

OPERATION & MAINTENANCEy The wastewater treatment plant will be operated and

maintained by the permanent staff at the residential colony. A regular schedule shall be followed for maintenance, like periodical check of sewer line systems, removal of sludge in settler and in baffle reactor. In the planted gravel filter regular harvesting of plants is done and the filter media is washed once in five years. y Cost incurred for operation and maintenance per annum would be approximately rupees 5,000/-

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REUSE OPTIONSy Reuse of treated water for gardening y Reuse of biogas for common lighting y Sludge can be transformed into good manure through

composting.

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CASESTUDY 2: DEWATS FOR SUN DIVINE - 1y PROJECT BACKGROUND:y y y y y y y y

Sun Divine 1 is a residential complex near Sola over bridge. Municipal sewage lines have been placed in the area a few months back. Type of Project: Residential (144, Highrise) Developers: Sun Housing Corporation No. of Occupants: 720 residents (5 per unit) Source of water: Bore well (4 and 800 deep) Sources of Wastewater: Kitchen, Toilets Considering a consumption of 135 lpcd and 80% of it as sewage generation per head, Total Sewage Generation at site: 78 m3

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SALIENT FEATURESPARAMETER Number of Treatment Plants Source Design Capacity No. of Users Peak Flow VALUE 1 Unit in the proposed common plot area 144 Kitchens, 432 Toilets 24 m3 720 8h

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MODULE S ADOPTEDBIOGAS SETTLER Digester Volume Gas Volume Area of Construction BAFFLE D REACTOR Volume Area of Construction PLANTED GRAVEL FILTER Volume Area of Construction Filter Material Used Plants COLLECTION TANK Volume Area of Construction35

18 m3 5.6m3 19 m2 43.4 m3 40 m2 44 m2 110 m2 Gravel Colacasia, Canna Indica 12 m3 4 m2DEWATS for Domestic Sewage


SYSTEM IN BRIEFy The wastewater shall be channeled from all the sources and

collected in the settler. y The treatment system would consist of 4 modules: Biogas settler, Baffled reactor, Planted gravel filter and Collection Tank.Fixed dome tunnel shaped biogas settler is a sedimentation tank which also improves settling performance. Biogas is formed due to the digestion of settled organic particles under anaerobic condition. y Baffle reactor (8 chambers) would ensure anaerobic degradation of suspended and dissolved solids by mixing fresh wastewater with an active sludge blanket. y Planted gravel filter would be used as tertiary treatment unit where aerobic and facultative degradation of dissolved organic and pathogen removal would occur. y A collection tank shall be used to store the treated water.y36 Centre for Environmental Planning & Technology, Ahmedabad DEWATS for Domestic Sewage

OPERATION & MAINTENANCEy The wastewater treatment plant will be operated and

maintained by the permanent staff at the residential colony. A regular schedule shall be followed for maintenance, like periodical check of sewer line systems, removal of sludge in settler and in baffle reactor. In the planted gravel filter regular harvesting of plants is done and the filter media is washed once in five years. y Cost incurred for operation and maintenance per annum would be approximately rupees 5,000/-

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REUSE OPTIONSy Reuse of treated water for landscaping; y Reuse of biogas for common area lighting; y Sludge can be transformed into good manure through

composting.

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TYPICAL THUMBRULE COSTSCONSTRUCTION COST Settler ABR/AF PGF Running Cost De-sludging Labor Reference: CDD Society Rs/m3 OF WASTEWATER TREATED 7000 15000 16000 Rs (Units Given) 4000 (for 10m3) 3000 (monthly salary)

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COST CALCULATIONSCASE STUDY -1: SUN DIVINE-4 BAFFLE D REACTOR PLANTED GRAVEL FILTER

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Dewats Model