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DEWATS-Decentralized wastewater treatment systems

November 23, 2008

WATER WISE

DEWATS to the rescue

S. VISHWANATH

A look at an efficient method of treating wastewater

Over 80 per cent of water consumed in flats and buildings comes out as wastewater. In un-sewered areas, the conventional practice has been to use a septic tank as the recipient of wastewater flows and the liquid effluents then emerging being led into soak pits or leaching trenches. This form of treatment is insufficient to render the outgoing effluents pollution free; in high water table areas, septic tanks can cause contamination of groundwater and surface water.

Cleaning septic tanks too is a cumbersome and unpleasant affair. There has been continuous work to find better systems of decentralised treatment of sewage. Domestic wastewater has a high percentage of nitrogen and carbonaceous materials as well as bacteria but is relatively simple to treat as compared to industrial wastewater. The world over, focus is on shifting to decentralised methods of treating wastewater which are simple to operate and economical too.

Low on maintenance

One approach being tried globally is called DEWATS or Decentralised Wastewater Treatment Systems. It aims to use local materials in design while following rigorous technical norms. It tries to be as low in energy intensity as possible and in favourable circumstances the whole treatment process of wastewater can be completely gravity driven without any energy requirement at all. This means that power cuts and load shedding or even accidental switching off of motors or pumps does not come into the picture at all, something which has been the bane of traditional wastewater treatment systems. Wastewater flows as low as 100 litres or 1 cubic metre to as high as 1,000 cubic metres can be handled by DEWATS systems. There is very little or no maintenance though the performance has to be monitored regularly.

A typical system for a domestic household consists of a primary treatment system consisting of a settling and floating tank, a secondary treatment system of an up-flow type baffled reactor which digests wastewater anaerobically, a tertiary treatment in subsurface horizontal flow sand filters with reed beds, and, finally, a polishing pond for oxygenation and UV disinfection from the sun’s rays.

Effective

The treatment of wastewater is highly effective and consistently meets pollution norms. Since the baffled reactors work very well, there is complete digestion of solids and usually there are no emptying or cleaning requirements unlike a septic tank. The quality of treated wastewater that emerges into the polishing pond is good enough for landscape applications. The reed bed system in the filter part can be a very good landscape feature with plants like canna offering a colourful and verdant look.

The DEWATS approach reports a 80 to 85 per cent reduction in BOD and COD, a 80 per cent reduction in phosphates and a 60 per cent reduction in ammonia from the input wastewater.

The Bremen Overseas Research Development Association (BORDA) ( www.borda.de) has been at the forefront of DEWATS research and outreach globally and has installed thousands of systems. More information is available on the website www.bord-sa.org where the Centre for Dewats Dissemination (CDD) is working.

www.rainwaterclub.org

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16 comments

  1. Hello sir,

    I am basically chemical engineer running consultancy in the field of waste management system, concern to this i am making entaire compus as a “Zero waste Compus” by handling Rain water harvesting, bore well recharge, solid waste treatment plants, water treatment plant. right now i am doing for engineering college ie Siddaganga Institute of Technology, Tumkur Karnataka state. from biomass i have put of Organic waste tratment plant and for watar treatment plant i have changed the existing plant into Dewat system we are recycling around 2 lakhs litree of water for landscape. next i am going for ” green house”
    i am very happey to read youre article and intrust towards the simple method of dewat system. please reply and be in touch.


  2. hi sir,i am lokeshwari studying in final year environmental engineering branch in vidya vardhaka college of eng. mysore.
    i am so impressed & curious abt dewat process,i am planning to do a project in dewat process,so i request u to kindly give suggetions abt dewat method.i hope u help us.
    thank you sir.


  3. thaks lokeshwari for reading my and yur intrest in this area reply to my mail id righit now i am imlimenting dewat system for one international residensial schoo, if you are inrested call me on my mobile sorry for the late reply because i havent got any message on my mail id please replay to my e mail my ph 81055-73163


    • What is your email and company name? I saw an article in The Hindu quoting your name but no details provided


  4. Dear Sir

    Kindly clarify whether DEWATS system is suitable for human excreta or is used only for grey water. Or in other words, are toilets also connected to the system & is the system capable of eliminating harmful pathogens & viruses from human excreta.


  5. Just looking into alternative treatment systems outside the traditional mound and septic system and came across this website. Question is; can this type of system be used in climates such as Canada where winter temperatures and ground temperature (naything under 1.5 meters) are below freezing for 6 months of the year. Are there any studies that have been done in this kind of climate.


  6. we have 300 person used water everyday can you tell me how to count tank capasity for wastewater treatment use dewats system anaerob ?


  7. hello sir…iam priyanka..i want 2 knw more abt dewats..so plz help me…


  8. Conversion Kit for existing septic tank to biogas generation unit is a concept.Please develop it.


  9. Iam interested in undergoing a training on DEWATTS Kindly giv me details


    • Please do get in touch with CDD Centre for Dewats Dissemination in Bangalore for more information on training on DEWATS.


  10. An intriguing discussion is definitely worth comment. There’s no doubt that that you ought to write more on this subject matter, it may not be a taboo matter but typically people do not discuss such issues. To the next! All the best!!


  11. interesting article !


  12. We are having Community Toilet Complexes comprising of 20-60 wc seats & 8-30 baths in each complex respectively..Wants to know about DEWATS treatment plants so that recycled water can be used for washing purposes.



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