Decentralised Wastewater Treatment (DEWAT)

Decentralised wastewater treatment systems have enormous potential in contributing to the development of sustainable environmental sanitation concepts and are in line with the Bellagio Principles. As engineers, we are called upon to provide technologies that are reliable, easy to operate and affordable to use. This task is a difficult one that requires an interdisciplinary approach that takes into account local conditions.

Adapted from Otterpohl R.

The conventional wastewater management approach

The conventional wastewater management concept, consisting of a water-borne wastewater collection system leading to a central treatment plant, has been successfully applied over many decades in densely populated areas of industrialised countries and contributed to a great extend to the improvement of hygienic conditions in these areas. However, the appropriateness of this model in the context of developing world cities must be questioned, given the urgent need for affordable, sustainable infrastructure. During the last decade, various researchers and institutions, including the World Bank, have started to consider the decentralised wastewater management approach as an alternative to conventional centralised systems, but theses approaches have struggled to gain acceptance. The main arguments against decentralisation of wastewater management are based on financial concerns and issues of treatment efficiency. This might be partly true, but it cannot be denied that the decentralised approach has great potential and could serve to complement existing centralised systems.

Why choosing a decentralised approach?

Apart from its proven benefits, the centralised wastewater management system is nothing else than a transportation system for human excreta and industrial wastes to a central discharge place or a treatment unit. Using valuable drinking water as transport medium, these systems are wasteful not only of water but also of human waste elements that can be easily treated and reused. Centralised wastewater management systems reduce wastewater reuse opportunities and increase the risk to humans and the environment in the event of system failures. Conversely, the decentralised wastewater management concept is better suited to translate Bellagio Principles No 3 (perceiving human excreta and wastes as potential resources) and No 4 (solving sanitation issues as close as possible to the source of waste generation) into practice. Furthermore the decentralised wastewater management concept:

• broadens the technology options and permits tailoring the solutions to the prevailing conditions;
• minimises the freshwater requirements for waste transportation;
• reduces the risks associated with system failure;
• increases wastewater reuse opportunities; and
• permits incremental development and investment in the community wastewater system.