Global decentralisation or "scalping" wastewater treatment can help solve water shortages and environmental issues

Decentralised wastewater treatment is frequently used worldwide in those locations where additional water supply and shortages of potable water make reuse of highly treated wastewater more acceptable. Treating wastewaters is often are less costly than developing other potable water supplies. In addition, decentralised facilities can reduce the overall cost of transporting sewage and provide for localized treatment of industrial and agricultural wastes.

Historically, centralization of wastewater treatment has been driven by the need to ensure compliance with regulatory requirements. Recognizing that the numerous treatment facilities that have been constructed over time were either not meeting current standards or were creating a financial burden to operate and maintain, the industry moved towards consolidation. However, the decision to centralize facilities to meet environmental goals did not anticipate, in most instances, the ever increasing resource value of wastewater effluent.

While this subject may not be directly relevant to the NZ environment these global trends demonstrate factors which may be useful for smaller communities in NZ and will provide an insight into issues being faced in other parts of the world. These learnings could be adapted for the NZ environment. This paper will discuss several drivers for decentralised wastewater treatment, and present several case histories of various wastewater treatment plants around the world, including design criteria, effluent standards, and other descriptive information.