Optimisation of the human solid waste treatment system to manage outputs in compliance with the ISO 30500

Abstract

Nearly half of the world’s population is still struggling with inadequate sanitation, especially where sewer systems are lacking. Non-sewered sanitation systems offer a sustainable alternative for human solid waste treatment. This research explores the torrefaction process for treating the solid fraction of human excreta. The study investigated the impact of torrefaction temperature and retention time on the quality of the solid char and liquid outputs through a series of experiments. Char quality was assessed using proximate and elemental analyses to determine composition, along with pathogen reduction tests for E. coli and C. perfringens. For the liquid output, chemical analyses were performed, including COD, TSS, TP, TN, and pH analysis. Results demonstrated that increasing torrefaction temperature from 150°C to 200°C resulted in a reduction of moisture content from 14% to 3% and a decrease in pathogen levels. As the temperature change was relatively small, there was small difference in elemental composition. Treatment at 250°C with 0.083 RPM resulted in a biochar with excellent terrified properties, including low moisture content (5%), increased hydrophobicity, improved grindability, and nearly full eradication of E. coli (<10 MPN/g). A novel rheology chart (RhS-0 to RhS-7) was developed to classify torrefied char based on its progressive transformation, including colour change (light brown, brown to black), increasing hydrophobicity, decreasing moisture and rising fixed carbon levels. This chart addresses a significant research gap by providing a systematic classification of torrefied char, a previously underexplored area. These findings contribute to advancing sustainable waste treatment technologies by providing a decentralised sanitation solution that aligns with ISO 30500 standards. Gates Foundation – INV - 053587