Pilot-scale hydrolysis bioreactors for VFA production

Plastics based on the petroleum industry are an environmental threat because they are non-degradable. Biodegradable plastic materials, for example polyhydroxyalkanoates (PHAs), are a good alterative that could be produced from volatile fatty acids (VFAs) by means of PHA-accumulating microorganisms. VFAs, as short-chain fatty acids, could be produced from biomass, like wastewater sludge. Wastewater sludge is another environmental problem with hazardous pollutants if it is not treated in the correct way. Treating wastewater sludge costs a lot of operating budgets of wastewater treatment plants (WWTPs). In this way, two environmental problems could be combined to be solved, i.e. the transition to biobased platics would reduce wastewater treatment costs. The object of this research was to build three 25 L pilot-scale hydrolysis bioreactors using dewatered digested sludge and wood chips (DSW), and feed to biogas sludges from LahtiAqua Ltd (FLA) and Labio Ltd (FL) under pH 7 conditions, selected from 500 mL laboratory-scale hydrolysis bioreactors based on VFAs results. DSW bioreactor produced a low VFA concentration of 16.5 mg/g VS in 2 days. The maximum production reached in FLA hydrolysis was 135.5 mg/g VS on day 4. A different situation occurred in the FL bioreactor, where the gradual increase of VFAs reached the maximum point of 204.6 mg/g VS on day 22. Low oxygen control appeared to be most appropriate in the FL bioreactor. Among the VFAs in the three bioreactors, acetic acid covered the largest proportion.