Microwave Hydrothermal Carbonization of Human Biowastes

Abstract

The challenges of poor sanitation due to poor faecal sludge management, particularly in the developing and other remote regions of developed countries, are well documented. As a potential technological and complementary approach to managing human biowastes, microwave hydrothermal carbonization (M-HTC), a thermochemical process, was used in this study to convert human biowastes into a safe material without any foul odour. The process also recovered value-added products i.e. solid chars and liquid ammonia concentrate. Primary sewage and raw human faecal sludges were subjected to microwave heating at 160, 180 and 200 °C, at different residence times: 30, 60 and 120 min under autogenous pressure. As a result, up to 60 % energy densified chars were recovered from the raw biowastes. The calorific (higher heating) values of chars recovered after the process, particularly those from human faecal sludge, increased from 19.79 up to 25.01 MJ/kg. Also, up to 80 % ammonia was recovered in the liquid fraction of carbonized human biowastes. Solid char yield and other estimated physicochemical properties were observed to be dependent on both the reaction temperatures and residence times of the process. The results of this study show M-HTC is a potential value-added recovery process for managing human biowastes and further provides essential information useful for the design and optimization of a self-sustainable sanitation facility.