Volatile fatty acids production from sewage organic matter by combined bioflocculation and anaerobic fermentation

[Display omitted] •Bioflocculation – anaerobic VFA system shows high potential for organic recovery.•High-loaded MBR bioflocculation concentrated more than 75% of sewage COD.•At an SRT of 5days VFA yield was 15% of sewage COD, but more than 24% is feasible. This work aims at exploring the feasibility of a combined process bioflocculation to concentrate sewage organic matter and anaerobic fermentation to produce volatile fatty acids (VFA). Bioflocculation, using a high-loaded aerobic membrane bioreactor (HL-MBR), was operated at an HRT of 1h and an SRT of 1day. The HL-MBR process removed on average 83% of sewage COD, while only 10% of nitrogen and phosphorus was removed. During anaerobic fermentation of HL-MBR concentrate at an SRT of 5days and 35°C, specific VFA production rate of 282mg VFA-COD/g VSS could be reached and consisted of 50% acetate, 40% propionate and 10% butyrate. More than 75% of sewage COD was diverted to the concentrate, but only 15% sewage COD was recovered as VFA, due to incomplete VSS degradation at the short treatment time applied. This shows that combined process for the VFA production is technologically feasible and needs further optimization.