PHA accumulating bacteria selection in a SBR treating fermentation liquids of organic fraction of municipal solid waste

Abstract

Due to their biodegradability, biocompatibility, chemical-diversity, and being manufactured from renewable carbon resources, PHAs are considered one of the most promising biopolymers to serve as an alternative to synthetic thermoplastics. In this study is carried out the selection and accumulation of PHA accumulating biomass in two different reactors: a SBR, for selecting bacteria applying a selective pressure based on a carbon excess (feast) and limitation (famine), and an accumulation reactor, operated in batch, for maximizing PHA production. FL-OFMSW was the source of carbon and nutrients which enabled the integrated valorization of waste streams into valuable products. This substrate is composed by a mixture of VFA and N-NH4+ (8 – 9 g VFA/L and 2 – 4 g N-NH4+/L) and solid fraction. Sludge was collected from a secondary activated sludge system from a local wastewater treatment facility. The objectives for this work were to select PHA accumulating bacteria, to maximize PHA production, to promote nutrient removal from the effluent while PHA production was happening and to study FL-OFMSW affection into PHA accumulation. The F/f ratio obtained during experimentation was around 0.19 - 0.27 which ensure PHA accumulating bacteria selection. Influent characterization (VFA concentration) is essential for maintaining an optimal ratio for PHA accumulating bacteria selection. Maximum PHA accumulated per gram of TSS was 7.9% in the selection reactor and 37% in the accumulation reactor. Both results were obtained with synthetic mixture of acetic acid which suggested a possible affectation of the FL-OFMSW for PHA accumulation. Among the different possible limiting factors, ammonium concentrations seemed to be the most probable cause. Nutrient removal in the SBR reactor was possible controlling pH during the operation. Basic pH values (over 8.3) could promote high free ammonia concentrations in the rector which inhibits, directly, nitrifying activity. FL-OFMSW can be used as substrate for the process, nevertheless, due to its nutrient concentration, PHA accumulation and nutrient removal could be limited. For this reason, nutrient removal must be considered for increasing the overall yield of the process.