Decentralised wastewater treatment systems – DEWATS

In contrast to Europe and North America where 95% of urban areas have conventional and centralised wastewater treatment systems, there are many countries where wastewater treatment systems are inadequate or do not even exist. Building a conventional sewerage system often proves difficult due to financial reasons and local conditions. As a result, more than 80% of the world’s wastewater is untreated when discharged to the environment. DEWATS are able to supply densely populated urban areas, as well as rural areas, with adequate wastewater treatment.

DEWATS offer good solutions, particularly to reduce the organic load from wastewater, which is the most significant problem for people and the environment.

The easy maintenance, low construction and operation coasts, and independence from urban infrastructure makes DEWATS suitable for poor urban and peri-urban areas, schools, hospitals, and small businesses with organic loads in their wastewater.

The DEWATS technology implemented by the BORDA network has proven itself for many years in Asia and Africa, and has become an integral part of various government sanitation programmes.

The DEWATS Technology

DEWATS do not have a standard design, but can adapted depending on the treatment requirements. For instance, municipal wastewater has different treatment needs than wastewater from hospitals. Another advantage lies in the simplicity of decentralised systems, which allows local people to be involved in construction and maintenance, as well as local construction materials to be used.

The heart of every DEWATS is the anaerobic baffled reactor (ABR), which unlike centralised wastewater treatment systems, treats the wastewater using anaerobic processes. This means that oxygen is not needed to break down the organic matter in wastewater. The resulting faecal sludge may be composted and used as a fertiliser. The treated wastewater itself, which is usually nutrient-rich, can also be used as irrigation water and fertiliser in agriculture. By reusing the products from wastewater treatment, it also becomes possible to close the water and nutrient cycles.

Typical DEWATS combine different wastewater treatment processes:

Primary treatment is done using sedimentation tanks, septic tanks or biogas plants. Secondary treatment uses the previously described anaerobic baffled reactors, while tertiary treatment uses an aerobic horizontal gravel filter. The final treatment step uses a purification tank.

The service package also includes a quality management system, monitoring and evaluation, so-called in-house-management, health and hygiene training, and an evaluation of the health impacts.

More information can be found in the Downloads.

Faecal Sludge Management – FSM

17% of the world’s population does not have access to sanitation. Those who do have access to simple sanitation mostly own pit latrines, the most common decentralised wastewater system in the world.

Particularly in urban areas, the lack of wastewater management leads to problems that endanger public health and pollute the environment. There is not enough space for new toilets, highly used toilets overflow, and informal service providers who collect faecal sludge often dispose it in the environment, such as the nearest river.

Faecal sludge management (FSM) is a multidisciplinary approach to develop solutions for this problem. It includes the technical side of creating customised sludge collection, transport, treatment, and recycling techniques; while also integrating a business model as an essential part of the concept. The aim of faecal sludge management is to include activities like service provision and facility maintenance, and to generate a sustainable income through sludge collection and treatment services. These systems should be replicable and adaptable to other locations. In Africa, BORDA cooperates with WSUP (Water and Sanitation for the Urban Poor) and implements unique FSM pilot systems in Zambia, Mozambique and Madagascar. In India, sponsored by the Bill & Melinda Gates Foundation, BORDDA supports the government and private sector in the citywide faecal sludge management.


Biogas can be produced from domestic wastewater, faeces, industrial wastewater with organic matter (for example, from tofu production), or from livestock and slaughterhouse waste.

A biogas plant is often installed with DEWATS to produce methane gas, which can be used for cooking or lighting. As a result, there are cost-savings for gas cartridges, firewood or and small side businesses can be operated, like catering services or restaurants. Using renewable energy, like biogas instead of firewood or other energy sources, helps to protect the climate and environment. Especially for poor families and school kitchens, using biogas brings substantial cost savings in everyday life. BORDA has pioneered the implementation and dissemination of these concepts since the 1970s.

As well, BORDA works in rural areas of Mali to make biogas usable to power Stirling engines.

Clean Production

In countries like Indonesia and the Philippines, BORDA works with small businesses in poor urban settlements and local governments for treating production wastewater and generating biogas. Many small- and medium-sized enterprises dispose untreated wastewater into the environment, and therefore, are threatened with closure. Through wastewater treatment, jobs can be saved, the environment can be protected, and biogas can produced as a sustainable source of energy. Enterprises which have worked successfully with DEWATS include slaughterhouses as well as noodle and tofu production sites.

Clean Hospitals

Many hospitals in BORDA’s partner countries do not treat their wastewater before discharging it to the environment. They pose a major threat to the health of local people who are exposed to the contaminated wastewater.

DEWATS are able to treat the hospital wastewater. In addition, biogas can be produced and used by the hospital, for instance in a canteen or for heating water needed to disinfect medical equipment.

Clean Settlements

To have a private toilet is a luxury for many people. Especially in Asia and Africa, many people have no access to basic sanitation, and 2.5 billion people worldwide do not have access to improved sanitation facilities.

Many poor urban settlements are not connected to centralised sewerage systems; wastewater flows directly into local surface water or groundwater and poses a serious threat to people and the environment. The local residents suffer from poor hygiene conditions, and particularly for women and children, the lack of basic sanitation is a major issue in daily life. With the construction of toilets, washing facilities and DEWATS, BORDA improves the situation of people living in poor urban areas. As a result, neighbourhoods become cleaner and healthier and the quality of life improves.

Clean Schools

In many countries, schools have very poor or no toilets at all for the students. Girls especially will often miss school when there is no access to safe toilets. BORDA and its partners work closely with schools in Afghanistan, Indonesia, Laos, Cambodia, Tanzania, Zambia, Lesotho and South Africa to improve the situation for children. Our solution for schools has several components:

  • A technical component with the construction of child-friendly toilets, biogas plants to generate energy for cooking in the school kitchens, and a decentralised wastewater treatment system (DEWATS).
  • A social component with hygiene education for students and teachers because regular handwashing with soap can prevent many diseases.
  • A management component to develop internal school processes for maintaining the facilities and providing hygiene education.

School should not make children sick. But to equip schools with toilets and DEWATS as well as provide hygiene education to students and teachers, money is needed. Donations are welcome to improve the situation of schools in poor urban areas.

Basic Sanitation in Humanitarian Emergencies and Transitional Aid

The question of what happens to wastewater and faecal sludge not only arises in development cooperation, but also in emergency situations like refugee camps. BORDA is increasingly bringing knowledge and experience in basic sanitation to humanitarian emergencies and transitional aid. There are fundamental differences between development cooperation, which focuses on sustainable and long-term projects, and humanitarian relief, which focuses on saving lives in an emergency. Humanitarian aid is done generally for a shorter period and is limited to areas directly affected by the emergency, and the priority is to alleviate the suffering of the affected population in situations that suddenly occur – whether they are natural disasters or human-made causes.

There are also permanent emergency situations like refugee camps which last – instead of months – for several years.

In these situations, the experience of long-term development cooperation is becoming increasingly important. Central to BORDA’s work, are proven concepts for basic sanitation with wastewater treatment and faecal sludge management.

In close contact with local governments and humanitarian organizations, BORDA provides training programs and DEWATS systems that cover a wide range of modules for different needs and can be used even under difficult conditions. BORDA has it been used in various fields in the basic humanitarian supplies, among others in Indonesia and India. Currently BORDA works in special initiatives in Mali and northern Iraq.

Health Impact Evaluation – HIE

BORDA’s aim is to improve of the living conditions of disadvantaged groups. But how can you measure the improvement of living conditions?

For a long time it was usual in development cooperation to monitor and evaluate projects based on performance, for example by counting the number of toilets constructed. However, counting does not give information about whether the toilets are actually used and if the living conditions of the users have been improved.

Therefore, BORDA asks in the Health Impact Evaluation whether the users are satisfied with the project, the cleanliness of the community has improved, and the incidence of diseases has decreased. With these and many other questions, BORDA can understand the impact of its projects on public health and socioeconomic development.


Infrastructure Planning for Urban Settlements

To comprehensively and sustainably plan sanitation infrastructure for a city, geographic information about the current supply and disposal infrastructure is needed. In this way, wastewater and waste treatment systems can be customised to meet the needs of the people. Mapping cities or districts is done using specialised geographic information systems and includes identifying existing water and wastewater treatment systems as well as the supply and disposal patterns of the population. Aspects of consumption, population distribution, and land use are also included in the mapping. In India, Indonesia and Tanzania experts are busy working in close cooperation with local authorities on this important and challenging task.

Link zu CDD . Citywide planning

Decentralised Water Supply

The water supply in mountain areas is often problematic. Power for electrically operated water pumps is not available. Women and girls, especially, have to travel long and arduous distances to fetch water for household and agricultural use.

Globally on average, women and children cover distances of 10-15 km each day to collect water and transport up to 15 kg each way.

In addition, if there is a lack of regular rainfall, the harvest of the local people is threatened along with their basic food supply and source of income.

To provide a more reliable water supply for the residents of mountain areas, hydraulic rams can be installed in rivers. The hydraulic ram is water-driven and powered by the kinetic energy (energy of motion) of a river. Energy from fossil fuels are not needed for the water supply. With such a ram, elevations of more than 100 metres can be reached to ensure a continuous water supply in mountain areas. Between 3,000-45,000 litres of water can be supplied daily, depending of the course of the river, the size of the pump, the flow rate, and the elevation that has to be overcome. The hydraulic ram is virtually maintenance-free and does not need professional support.

In China and northern India, BORDA has successfully installed over 600 hydraulic rams and supplied more than 400.000 people with fresh water. On average, the agricultural output in the regions increased by 20%. The local governments have taken over the programme and continued it on their own initiative. Since 2001, the technology, expertise and production has been transferred to Vietnam. In the first two years, more than 40 villages were equipped with a decentralised, continuous water supply.

Decentralised Energy Generation

In remote mountain areas, a connection to power plants is not possible. A lack of energy for lighting, heating or electric tools complicates the economic development of a region.

With small water turbines, the situation can be improved in remote mountain areas. Kinetic energy (energy of motion) of rivers is used to generate electricity.

Homes can be supplied with lighting, as well water mills, saws or butter making machines can be powered. As a result, there can be more employment opportunities for villagers.

The turbines are installed in collaboration with the future users. Professional care is not necessary due to the low maintenance needs of the turbines.

BORDA has already installed these water turbines in remote mountain regions in India, China and Vietnam.

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