| Summary: | Chemical toilets are becoming more and more common. Large volumes of chemical toilet sewage (CTS) are generated in popular tourist destinations, where waste conveyance and treatment systems are not an option, which necessitates new methods for neutralizing such waste. Anaerobic digestion is, potentially, one such solution. The aim of the present study was to test the treatability of chemical toilet sewage (CTS) co-fermented with maize silage biomass using anaerobic digestion (AD). It was found that CTS does not impair AD, as long as the fluid used to dilute the feedstock does not contain more than 30% CTS. Biogas yield reached 400 cm<sup>3</sup>/gVS, and the biogas produced contained 57 ± 2.6% CH<sub>4</sub> methane. Higher doses of CTS inhibited anaerobic digestion. This inhibition was directly linked to CTS toxicity, which reduced methanogen populations. This, in turn, slowed down VFA-to-biogas conversion, triggered VFA accumulation, and ultimately increased FOS/TAC and decreased pH.
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