Technical guidelines for designing a decentralised waste water treatment system

This guidance document is intended to help with the implementation of a decentralised waste water treatment system (DWTS), and is based on the experience of several WaterAid country programmes and especially WaterAid Bangladesh.

A DWTS can be used to treat the waste water coming from houses and institutional settings, and represents an alternative to centralised treatment involving sewers and large treatment plants, and therefore large capital costs and running costs. A DWTS can be relatively compact, cheaper to install, and requires little maintenance and no energy input.

A DWTS typically consists of several elements: a septic tank, an anaerobic baffled reactor, an anaerobic filter, and a series of constructed wetlands. The exact dimensions and types of installations depend on many parameters, which are covered in this guideline.