Used Water Treatment

"India faces a significant issue with untreated wastewater, as over 40,000 million litres are generated daily. "

This accounts for approximately 60 per cent of the total daily wastewater and is equivalent to the water needs of nearly 300 million individuals. India also struggles with water availability, posing a significant challenge for its residents.

One of the main reasons is the lack of treatment facilities in most areas of the country. The existing facilities, like centralized Sewage Treatment Plants (STPs), can only handle 44 per cent of the wastewater generated. These STPs also have high operational costs and maintenance problems, so the amount of wastewater meeting discharge standards may be even lower. This is a common issue for developing countries trying to ensure water security.

Treating wastewater can increase its potential for reuse, reducing the strain on freshwater sources and addressing public and environmental health concerns related to water pollution. Therefore, finding solutions to enhance wastewater treatment is necessary.

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What is DEWATS™

DEWATS™ is a wastewater treatment approach for households, communities, and institutes. It is nature-based and uses microorganisms and plants for treatment. These systems use gravity flows, reducing costs and eliminating the need for skilled labour. Treating wastewater close to the source eliminates piping and saves conveyance costs. It allows for water reuse for irrigation, toilet flushing, and gardening, conserving freshwater. Treated sludge can also be reused as a soil conditioner.

The Features of DEWATS™
  • The novelty of DEWATS™ is its simplicity
  • Implemented by incorporating the existing resources such as local materials
  • Less or no electricity, chemicals or skilled labor requirement, and does not lead to any odor problem
  • Long-lasting and reliable construction design
  • Can be easily contextualized and integrated with local landscape
  • Life cycle cost will be 50 percent lower compared to conventional treatment system

Accreditations for DEWATS™   

  • Dr. Mashelkar Committee: DEWATS™ is  one of the technologies accredited by the Dr. Mashelkar Committee, a committee set up by the Prime Minister’s Office to recommend clean technologies in India. (Link to the source page)
  • CPHEEO Manual: DEWATS™ has been mentioned in the Central Public Health and Environmental Engineering Organisation’s (CPHEEO) manual on Sewerage and Sewage Treatment. (Link to the source page)
  • Suchitwa Mission: Empaneled as Engineering Consultant for DPR preparation and handholding in project execution for Wastewater/ Septage Treatment projects taken up by the Local Self Gov. Institutions, Kerala. (Link to the source page)
  • DEWATS™ Trademark: DEWATS™  is a certified trademark of CDD under the Trade Marks Act, 1999 (Government of India)
  • Govt. of Kerala: Accreditation sanctioned to CDD India for Wastewater and Faecal Sludge Management, Water Body Rejuvenation and Solid Waste Management
  • UNESCO: ‘The United Nations world water development report 2019: leaving no one behind’ of the UNESCO World Water Assessment Programme recognizes the importance of DEWATS™ as a credible and necessary alternative to wastewater treatment in non-networked areas
Treatment Processes in DEWATS™

DEWATS is based on four treatment modules: 

  • Sedimentation and primary treatment in sedimentation ponds, Settler, or Imhoff tanks 
  • Secondary anaerobic treatment in Anaerobic baffled reactors or fixed bed filters
  • Advance Secondary or Tertiary aerobic treatment in constructed treatment wetlands (subsurface flow filters)
  • Post-treatment in polishing or aerobic ponds or conventional disinfection methods.

These four principal processes and systems are selected and designed as per the local context and considering the quantity and quality of influent wastewater, and the required effluent quality.

Components of a Typical DEWATS™ System

Grease and Grit Chamber: Used for removing oil and grease, it is installed in places like restaurants, milk dairies, etc., where the wastewater is likely to have large quantities of oil and grease. It is constructed such that the lighter grease floats and heavier grit settles at the bottom. 

Settler: A closed tank of two or three chambers with 2-3 hours of retention time that traps a significant portion of heavier solids and floating particles while letting the rest pass into the subsequent modules of the system. It is a sedimentation tank in which settled sludge is stabilized by anaerobic digestion. The first chamber occupies about half the total volume because most of the sludge and scum accumulates here. The following chamber(s), provided to calm the turbulent liquid, are made of equal size and together occupy the other half of the tank volume. All chambers are normally of the same depth. Dissolved and suspended matter leaves the tank more or less untreated.

Biogas Digestor: An improvised sedimentation tank that acts as an alternative to the settler. It is suitable for wastewater with high organic content, which is decomposed by anaerobic digestion. Biogas generated during this process can be used as source of energy such as fuel, lighting.

Anaerobic Baffle Reactor (ABR): A closed tank with multiple chambers in series, connected with down-take pipes. The wastewater is passed in an up-flow fashion to establish contact with the sludge blanket formed at the bottom. The combination of sedimentation and anaerobic sludge digestion ensures the removal of suspended and colloidal particles of more easily biodegradable matters. The baffled reactor consists of minimum four chambers in series and can be integrated with anaerobic filter. Treatment performance ranges from 60-70 percent COD (70-80 per cent BOD) removal.

Anaerobic Filter: It consists of up-flow chambers connected in series, partially filled with filter media like cinder, gravel, rock aggregates, corrugated pipes, specially designed plastic media, etc. The anaerobically treated wastewater is forced to come into contact with active bacteria intensively. The biofilm formed on filter media traps and degrades finer suspended organic particles when wastewater passes through it. The quality of treatment in well-operated anaerobic filters is in the range of 70 – 90 percent BOD removal. 

Horizontal Gravel Filter: Can be Subsurface Flow Wetlands (SSF), Constructed Wetlands, or Root Zone Treatment Plants. Anaerobically treated wastewater is passed through graded filter media and roots of specific plants which help in the removal of remaining suspended solids and excess nutrients present in wastewater.  

Polishing Pond: Since Settler, ABR, and AF modules are operated in anaerobic conditions there will be the presence of pathogens in the wastewater after treatment to remove those pathogens a shallow pond that ensures aerobic treatment is constructed where pathogens are removed mainly due to exposure to natural ultraviolet rays in sunlight.

Treatment Efficiency of DEWATS™

Modules

HRT (hrs)

Efficiency (%)

Outlet BOD ranges (mg/L)

Settler

2-3

30-40

180-200

Anaerobic Baffled reactor

8-12

50-70

100-120

Anaerobic Filter

12-20

70-75

60-50

Planted Gravel Filter

24-36

85-90

30

Polishing pond

12-18

~95

<20



DEWATS™ at Different Scales

DEWATS™ was developed as a context appropriate technology for rural India as well as global South where availability of reliable electricity, funds and skilled human resource remain a challenge.  However, DEWATS™  being a versatile approach and can be adapted to various contexts and types of settlements. This is what makes the system suitable for a country like India. 

CDD’s experience over 15 years has allowed it to adapt and implement DEWATS™ at different scales – individual apartment complexes of different sizes, cluster of households, institutions, public toilet. It is constantly working on improving its system design by seeking to improve treatment efficiency, reduce area requirement and optimize costs. Additionally, there have been innovations like developing prefabricated systems which can be deployed more easily. In recent times, CDD has also been experimenting with DEWATS™ on larger scales for the purpose of water body rejuvenation.

DEWATS™ for City-level Sanitation

CDD has also used the DEWATS™ approach to improve sanitation at city-scale through the setting up of 10 Faecal Sludge Treatment Plants (FSTPs) as well as to rejuvenate one of the prominent lakes in the city of Bengaluru. 

The DEWATS™ approach lends itself to emerging narratives like city wide inclusive sanitation (CWIS), water sensitive urban design, resilient cities and circular economy. A detailed technical, socio-economic, ecological and cultural analysis is undertaken before commencing design. Our design principles enable us to develop an integrated and durable solution, which is key to the success of implemented systems. Over the years, we have been successful in establishing hundreds of treatment systems and supporting them with a feasible and sustainable business and operations plans. Continuous monitoring of these systems helps in upgradation of technology and enhancement of the performance of our systems to meet the necessary requirement for better applications. 

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Evolution of DEWATS™: DEWATS™ Plus, Hybridization

Since DEWATS™ is a nature-based solution, it might be a challenge to meet recent stringent discharge standards prescribed by Central Pollution Control Board (CPCB) in 2017. Hence the hybridization of DEWATS™ with conventional technologies may be adopted to achieve the desired results in terms of nutrient (N,P) and pathogen reduction, as well as for area optimization. The following are the units which are being used for the purpose of hybridization.

Vortex: A vertically positioned cylindrical tube with a funnel-shaped bottom where a continuous swirling motion causes an oxygenation effect. The system can be scaled – up or down, according to varying wastewater volumes and is exceptionally energy efficient compared to conventional operated treatment plants 

ECO2 Aeration Tank: A second economic alternative to conventional aerators, the ECO unit is used to aerate, circulate, and de-gasify smaller volumes of water. It is placed submerged within the water body at a depth ranging from 0.5 to 1 meter (about 0.2 mts above the bottom surface clamped to a cement block). 

Sand and Carbon Filter: This is used at the polishing stage for removal of suspended solids and pathogens that are left out. 

The sand media traps all suspended matter while the activated carbon filter removes unwanted contaminants from wastewater including micropollutants such as chlorine, methane, organic compounds, and even any unpleasant taste and odor

Vertical flow constructed wetland: This is a planted filter bed that is drained at the bottom. Wastewater is poured or dosed onto the surface from above using a mechanical dosing system. The water flows vertically down through the filter matrix to the bottom of the basin where it is collected in a drainage pipe. The important difference between a vertical and horizontal wetland is not simply the direction of the flow path, but rather the aerobic conditions.

Today DEWATS™ is a proven technology, which has been implemented in over 17 countries. CDD Society, its trainees, and partner organizations have implemented over 400 DEWATS™ systems across India, which treat 15,000 million litres of wastewater, generated by 2 lakh people every day.

DEWATS™ Sector of Application

Schools
  • Spartan School (Chennai)
  • Silver Oak School (Bangalore)
  • Harvest International School (Bangalore)
Factories
  • Positive Labels (Bangalore)
  • Gokuldas Images (Bangalore)
  • Kamal Solar Factory (Bangalore)
Apartments
  • Padma Sai Enclaves (Madurai, Tamil Nadu)
  • Housing Apartments (Thilothu, Bihar)
  • Pristine Temple Tree Apartments ( Bengaluru, Karnataka)
Colleges/Universities
  • Colleges/Universities Indian Institute of Technology (Gandhinagar)
  • MVJ College of Engineering (Bangalore) Kathmandu University (Nepal)
Communities
  • Ullalu Bus stand (Bangalore)
  • Sunga Cimmunity (Thimi, Nepal)
  • Mahajan Nagar Community (Nagpur)
Food Processing Units
  • Shyam Rice Mills (Palwal, Haryana)
  • Saria Rice Mills (Haryana)
  • Alternative (Bangalore, Karnataka) ​
Hospitals
  • Seven Hills Hospital (Mumbai)
  • Arvind Eye Hospital (Pondicherry)
  • Dhulikhel Hospital (Nepal) ​
Housing Colonies
  • VBHC (Chennai)
  • Singanayakanahalli Housing Colony (Bangalore)
  • Good Earth (Bangalore) ​
Institutions
  • Friends of Camphill (Bangalore)
  • Avatar Meher Baba Trust (Meherabad)
  • Association of People with Disability
Disaster Relief
  • Kadampadi (22 communities) and Kuttiyadiyur – post the 2004 Tsunami Rehabilitation of flood affected colonies – Madapura and Galibeedu – in Coorg ​
Water Body Rejuvenation
  • Mahadevapura Lake (Bengaluru)
  • Sadarmangala Lake (Bengaluru)