Effects of the Organic Loading Rate on Polyhydroxyalkanoate Production from Sugarcane Stillage by Mixed Microbial Cultures.

Stillage is an abundant wastewater from the sugarcane ethanol industry. It is rich in fermentable substrates and presents low-nutrient content, constituting a promising substrate for polyhydroxyalkanoate (PHA) production by mixed microbial cultures (MMC). This work assessed the enrichment of a PHA-accumulating MMC from acidified sugarcane stillage in a sequencing batch reactor under increasing organic loading rates (OLR) and no external nutrient supplementation. The OLR was increased from 1.0 to 7.1 kg COD m-3 day-1 in four steps. A PHA-producing MMC with high storage response was selected in all experimental conditions. The volumetric biomass productivity and the maximal PHA storage capacity increased continuously with the OLR, reaching 0.061 g VSS L-1 h-1 and 0.49 g PHA g VSS-1, respectively. The highest observed PHA storage yield (0.60 g CODPHA g COD.t-1) and specific PHA storage rate (0.169 g CODPHA g of CODX h-1) were obtained for the OLR of 4.5 kg COD m-3 day-1. The PHA produced was a co-polymer of 3-hydroxybutyrate (86-77%mol) and 3-hydroxyvalerate (14-23%mol). The performance of the biomass enrichment was comparable to those attained with other agro-industrial wastewaters, indicating the potential of acidified sugarcane stillage as a feedstock for MMC PHA production.