Treatment of human waste in small-scale facilities: a prospective review

A sustainable approach to the small-scale treatment of portable toilet and septic tank waste is in need to minimise the associated public health and environmental risks. Treatment of human wastes is highly regulated by legislation in many countries given the high content of organic components and pathogens. In conventional wastewater treatment plants, sewage undergoes a series of treatment stages (primary, secondary and tertiary) before effluent discharge. Delivering this approach on a small scale, to meet demands of temporary events, public gatherings or remote locations provides benefits in reducing transport and bulk handling. For a small-scale treatment process to effectively work, the process steps need to be simplified and minimised. The potential of a new treatment scheme is reviewed where the first step is the solid-liquid fraction separation, followed by anaerobic digestion (AD) of the solid fraction, including energy recovery in a combined heat and power unit. The liquid fraction undergoes a series of filtration and disinfection steps to comply with effluent regulations. Digestate from AD is burned on site to provide local domestic/office heating. This has a great potential for application in different locations where inputs may be sporadic, such as outdoor festivals, disaster response scenarios and construction sites.