Pilot-Scale Polyhydroxyalkanoate Production from Paper Mill Wastewater: Process Characteristics and Identification of Bottlenecks for Full-Scale Implementation

In this study, the suitability of paper industry wastewater for production of polyhydroxyalkanoate (PHA) was investigated in a pilot reactor in an industrial setting. The pilot plant was designed as a three-step process comprising (1) anaerobic fermentation for maximization of the volatile fatty acid (VFA) concentration, (2) enrichment of PHA-producing biomass, and (3) accumulation for maximization of the PHA content of the biomass. After fermentation, the paper mill process water contained a VFA fraction of 78% on a chemical oxygen demand (COD) basis. The length of the feast phase in the enrichment process stabilized at 45 min±4 min after 18 days of operation. At the end of the feast phase all VFA was consumed and the PHA content of the volatile suspended solids (VSS) was 0.50 g PHA/g VSS±0.05 g PHA/g VSS. The acquired microbial community was dominated by Plasticicumulans acidivorans, a PHA-producing microorganism previously found to dominate VFA-fed laboratory reactors. The maximum PHA content achieved after accumulation was 0.70 to 0.80 g PHA/g VSS. An overall PHA yield of 34% on a COD basis was achieved. Improving the VFA fraction in the product spectrum of the fermentation and minimization of acid and base consumption for pH control were identified as major bottlenecks.