Continuous acidogenic fermentation: Narrowing the gap between laboratory testing and industrial application

This study explored the potential of acidogenic fermentation of sewage sludge (SS) in an 80 L automatized pilot scale platform. A high-rate VFA production was obtained at HRT 5 d and pH 9, with a volatile fatty acid (VFA) yield of 336 mg VFA g^-1 VS and a VFA productivity of 2.15 kg VFA m^-3 d^-1. During co-fermentation of SS with OFMSW, a reversible pH shift from pH 9 to pH 6, evidenced a higher acidogenic activity which promoted the butyrate metabolic pathway, with 13.97 g COD L^-1 of butyric acid and a VFA peak 23.2 g COD L^-1. The results show the degree of flexibility of mixed culture fermentation systems, where other pH control methods other than steady control could be used to enhance the fermentation process. Ultrafiltration was a feasible technology to obtain a VFA rich permeate where 12.3-26.6 g COD L^-1 could be recovered.