Decentralized Wastewater Treatment Systems (DEWATS)
A Decentralised Wastewater System (DEWATS) refers to a decentralized, community-level wastewater treatment technology.
DEWATS is a technical approach to decentralized wastewater treatment in developing communities. The passive design uses physical and biological treatment mechanisms such as sedimentation, floatation, aerobic and anaerobic treatment to treat both domestic and industrial wastewater sources. DEWATS is designed to be affordable, low maintenance, use local materials, and meet environmental laws and regulations. DEWATS has service packages available for the sanitation needs of small and medium-sized enterprises including communities, schools, municipalities, agro-industry, emergency settlements, hospitals, hotels, and prisons.
This is a considered and implemented solution in developing countries including: Afghanistan, Bangladesh, Bhutan, Cambodia, Cuba, Ecuador, Haiti, India, Indonesia, Iraq, Lao People’s Democratic Republic, Lesotho, Mali, Mexico, Myanmar, Nepal, Nicaragua, Philippines, South Africa, Tanzania, Viet Nam, Zambia
This solution is implemented by Bremen Overseas Research & Development Association (BORDA)
Goal 6: Clean water and sanitation
Users seeking improved waste disposal, users with no sewer network or municipal treatment plant, users seeking passive wastewater treatment made from local materials
All materials used for construction are locally available.
Users can contact BORDA for information on service packages offered for DEWAT solutions.
As of 2017, more than 750 DEWATS plants were currently operating.
Flow rate of the equipment
Type of wastewater treatment process
How effective is the process at BOD removal?
How effective is the process at COD removal?
How effective is the process at NH4-N removal?
How effective is the process at total suspended solid removal?
How effective is the process at total phosphorus removal?
How effective is the process at fecal coliform removal?
The DEWAT functions as follows:
1. Primary treatment involving sedimentation and flotation
2. Secondary anaerobic treatment in fixed-bed reactors: baffled upstream reactors or anaerobic filters
3. Tertiary aerobic treatment in sub-surface flow filters
4. Tertiary aerobic treatment in polishing ponds
5. Systems can be designed to handle organic wastewater flows from 1-1000 m3 per day
6. Systems are built to be tolerant towards fluctuations in loads
Schematics illustrating processes employed by DEWAT systems
Experienced DEWATS experts facilitate comprehensive training programs for qualified staff of partner organizations and take on a supervisory role during the initial technical implementations.
Performance targets for DEWAT technologies are targeted at achieving the following advantages:
1. Providing treatment for domestic and industrial wastewater
2. Low primary investment costs as no imports are needed
3. Efficient treatment of daily wastewater flows up to 1000 m3
4. Modular design of all components
5. Tolerant towards inflow fluctuations
6. Reliable and long-lasting construction design
7. Expensive and sophisticated maintenance not required
8. Low maintenance costs
Testing performed to assess the average removal efficiencies for a DEWATS facility in Nepal consisting of an Anaerobic Baffled Reactor and Constructed Wetland: 96% TSS, 90% BOD, 90% COD, 70% NH4-N, 26% Total P, and 98% FC.
Nepal Environmental and Public Health Organization (ENPHO)
Sludge must be handled, treated and disposed of in accordance with hygiene and environmental standards.
DEWATS technical layouts can be optimized to provide a renewable energy source in the form of biogas.
Cardona, J., et al., 2010, DEWATS Capacity Building for Primary Schools in Jordan and Palestine, Water Practice and Technology, 5 (4).
Kerstens, K.M., et al., 2012, Evaluation of DEWATS in Java, Indonesia, Journal of Water, Sanitation and Hygiene for Development, 2 (4), pp. 254–265.
Reynaud, N., Buckley, C., 2015, Field-data on parameters relevant for design, operation and monitoring of communal decentralized wastewater treatment systems (DEWATS), Water Practice and Technology, 10 (4), pp. 787–798.
Singh, S., et al., 2009, Performance of an anaerobic baffled reactor and hybrid constructed wetland treating high-strength wastewater in Nepal—A model for DEWATS, Ecological Engineering, 35 (5), pp. 654-660.
Regulations vary by project location. A case study in Indonesia revealed over 90% of systems tested complied with Indonesian environmental regulations of BOD effluent less than 100 mg/L.
DEWAT technologies are evaluated for their capability to provide efficient treatment for domestic and industrial wastewater.
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