Decentralising sanitation – the experience of DES
Submitted by: Jonathan Ramayia, Friday, February 1, 2013
“The Decentralised Waste Water Treatment (DEWATS) system is necessitated by problems experienced in sanitation throughout the world, in particular the developing world where there is inadequate financial resources and skills to deal with the demand of conventional waste water treatment systems and where authorities battle financially to connect citizens to the formal sewer system”, says Sandile Mbatha Programme Director of NGO, Decentralised Environmental Solutions (DES). Although the system has mainly been tested in rural and peri-urban communities, the DES Programme Director is convinced that this pioneering technology in the field of water treatment is suitable for most applications, be it industrial, or gated communities in Durban, within the limitations of the nature of wastewater the system can treat.
DEWATS is a decentralised approach for treating organic sewage at source without depending on conventional municipal wastewater treatment plants. Instead waste water is channelled into a prefabricated box or container located underground and undergoes a number of treatment processes that ultimately results in water that may be utilised for irrigation purposes. The DEWATS technology has been tested by DES and the Bremen Overseas Research and Development Organisation (BORDA) in collaboration with eThekwini Municipality, and the University of KwaZulu-Natal’s leading researchers in the Newlands and KwaMashu areas in Durban. The main purpose is to test the system against local conditions and to set parameters for safe reuse aspects of the treated effluent.
Water treatment through DEWATS
The Newlands/Mashu DEWATS treatment plant was installed in 2010 and currently connected to 85 households in that area. “For the purposes of testing the plant, sewage from these 85 households was diverted to feed the DEWATS system. It then goes through a series of treatment chambers called anaerobic baffled reactors (ABRs)”” says Mbatha.
Four important treatment processes are undertaken through the DEWATS system, which include the following:
- Primary treatment and sedimentation also known as settler
- Secondary treatment anaerobic treatment in fixed bed or baffled upstream reactors
- Tertiary aerobic/anaerobic in subsurface flow filters (planted gravel filter)
- Tertiary aerobic treatment in ponds
As the diagram shows, each treatment process relies on the settling of sludge as well as a process whereby microorganisms ‘feed’ on sludge thereby breaking it down and making it less polluted, or treated. A number of filter units along the module as well as a planted gravel filter outside of the module work as post-treatment stages to bring wastewater to acceptable chemical standards for irrigation. The DEWATS system can provide treatment for wastewater flows up to 1000 m3/day and is said to achieve pollution reduction of up to 90% from pre-DEWATS levels.
The system has important environmental benefits, explains Mbatha, “through DEWATS we are looking at closing the nutrient cycle in dealing with sanitation, where the final nutrient rich effluent is within acceptable levels for reuse in urban agriculture. In the case of your regular municipal sanitation solutions the treated wastewater is often disposed into water bodies and an opportunity to reuse the nutrients missed.”
DES has set up a number of community and food gardens in the area around the DEWATS plant which aims to fulfil one of its goals in addressing food security. The gardens could eventually be irrigated by the treated water of the DEWATS plant and tests are currently being undertaken to ascertain the health and hygiene parameters for the reuse of treated wastewater, “there are ongoing trials on irrigating with treated wastewater currently being conducted by UKZN but this is currently only happening under a controlled environment. The tests are to establish soil and plant response to treated effluent and associated health risks”. If tests show that this could be viable, this will allow communities to kick start a food garden programme in their communities without needing to fork out for a high water bill or high expenditure costs for industrial fertilisers.
“Technical efficiency does not guarantee community acceptance. There needs to be a balance between the two, DES tries to educate the community on the DEWATS project and how it can be beneficial to their livelihoods”, says Mbatha. In particular, the idea of using waste water for watering food gardens is not always an easy idea for people to accept, says Mbatha. Where DES fits in is their closeness to the community which has been established over time, “we try to include communities in the development process. Since 1994, NGOs have lost an important space within the development arena and in many ways local government has taken over this role. NGOs in the sanitation sector often don’t have a platform to effect development and aren’t always aware of what’s on the market and what’s going on. What DES is trying to do is to bridge the information gap in what the Municipality and other important thinkers are doing in sanitation since the Municipality might not always be in the position to engage with the communities directly”. Mbatha notes that “if members of the community are included in the development process from the start they would more likely be supportive of the technology, which is what we have done with DEWATS where members of the community have been educated about the project”.
Universal Application of DEWATS and Way Forward
DEWATS is not just for indigent and rural communities as some developments in places like Kloof still use septic tanks and would be ideal candidates for installation of a DEWATS system, as would other gated-communities, notes Mbatha. “I think it would give some of these golf estates and gated communities ‘green status’, because they could use the treated wastewater to water the greens and their wastewater would not be channelled into the river system or to the ocean”.
In spite of this, Mbatha agrees that the programme was designed with poorer communities in mind, and will spend much of the year developing a business plan on how to manage an agricultural project based on the re-use of effluent from the DEWATS system. The idea is to foster entrepreneurs in the local community who will one day be able to sell their own fruit and vegetables which was irrigated from ‘DEWATS treated water’.
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