Today over two billion people around the world do not have access to improved sanitation facilities. Haphazard disposal of human excreta and wastewater is degrading the environment and causing serious health risks, particularly for the poor in developing countries. With rapid and unsystematic urbanisation, discharge of untreated sewage in to the rivers has become a common practice. The condition of Bagmati River in Kathmandu is a glaring example of this trend. Experiences from cities in developing countries of Asia and elsewhere have shown that large centralised sewage treatment systems are expensive and difficult to construct and operate. In this context, decentralised wastewater treatment system (DEWATS) can complement conventional treatment systems for more sustainable and effective service. Although there are few DEWATS plants in Nepal and the region, there is a need to rapidly scale up the application of these systems. This requires knowledge and skills in designing, developing and maintaining these systems.

Decentralised Wastewater Treatment Systems (DEWATS)

DEWATS is an approach for treatment of wastewater generated from domestic and industrial processes.  It is based on different natural water treatment  techniques comprising of some basic treatment modules, which are combined according to specific requirements depending on the characteristics of the wastewater to be treated, the desired quality of the treated wastewater and technical specificities.

DEWATS units can be designed for treatment of wastewater flow ranging from <1 to 1,000 m3 per day. DEWATS has certain advantages over the centralised systems. It is easily workable, simple, its on-site treatment modules require minimal operation and maintenance, it requires no mechanical parts and less sewerage network. All these features also allow for substantial cost savings.

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