Energy and Nutrient Recoveries from Faecal Sludge through Hydrothermal Carbonization Process

Abstract

Hydrothermal carbonization (HTC) is a thermal conversion process which can be applied to convert faecal sludge into a carbonaceous material called hydrochar. However, the HTC liquid by-product or process water (PW) still contains high concentrations of organic matters and nutrients. In this study, the HTC products such as hydrochar and PW were processed to produce a pellet fuel and fertilizer, respectively. The experimental results showed that pelletization of the hydrochar can produce an excellent pellet fuel. The hydrochar-pellet fuels were found to have energy content, bulk density and compressive strength of about 22-24 MJ/kg, 900-1000 kg/m³ and 8.0-8.5 kN/m², respectively. By applying the reduced pressure distillation, nutrient such as nitrogen (N) in the PW can be recovered in the ammonium sulphate ((NH₄)₂SO₄) form which can be utilized as an agricultural fertilizer. The experimental results showed that, at pH 11-13, temperature of 55 °C and reaction time of 60 min, N-removal and N-recovery efficiencies were found to be 99.8% and 53.4%, respectively. The results of this study demonstrated the technical feasibility of the HTC process for faecal sludge management which should result in environmental protection, health improvement and resource recovery, all leading to sustainable development.