Organic structure impact on gypsum converting communities grown on sewage

In order to assess a viable carbon source for the bioconversion of waste gypsum, we examined if the organic makeup of municipal sewage sludge affects sulfate reduction and methanogenesis. We compared an environmental microbial community (EMC) from an abandoned sulfur mine in Sicily, Italy, and an indigenous sewage microbial community (ISMC), in two sludge mixes: effluent amended with partially digested or undigested sludge. All reactors showed comparable rates of sulfate reduction ($\sim$10-15 mM sulfide by day 32), gypsum dissolution, alkalinity generation and chemical oxygen demand (COD) removal. However, CH$_4$ production was significantly suppressed in treatments combining enriched microbial communities with partially digested sludge, with an 88.9\% reduction compared to all other groups.