Naturally illuminated photobioreactors for resource recovery from piggery and chicken-processing wastewaters utilising purple phototrophic bacteria

Resource recovery from wastewater, preferably as high value products, has become an integral part of modern wastewater treatment. This work presents the potential to produce single cell protein (SCP) from pre-settled piggery wastewater (PWW) and meat chicken processing wastewater (CWW), utilising anaerobic purple phototrophic bacteria (PPB). PPB were grown as biofilm in outdoors 60 L, 80 L and 100 L flat-plate reactors, operated in sequential batch mode. PPB biofilm was recovered from reactor walls at a total solid (TS) content similar to 90 g center dot L-1, and the harvested biomass (depending on the wastewater) had a consistent quality, with high protein contents (50-65%) and low ash, potentially applicable as SCP. The COD, N and P removal efficiencies were 71 +/- 5.3%, 22 +/- 6.6%, 65 +/- 5.6% for PWW and 78 +/- 1.8%, 67 +/- 2.7% and 37 +/- 4.0% for CWW, respectively, with biofilm areal productivities up to 14 g TS center dot m(-2)center dot d(-1). This was achieved at ammonium-N concentrations over 1.0 g center dot L-1 and temperatures up to 55 degrees C and down to 6 degrees C (daily fluctuations of 20-30 degrees C). The removal performances and biomass productivities were mostly dependent on the bioavailable COD in the form of volatile fatty acids (VFA). At sufficient VFA availability, the irradiance became limiting, capping biofilm formation. Harvesting of the suspended fraction resulted in increased productivities and recovery efficiencies, but lowered the product quality (e.g., containing undesired inerts). The optimum between quantity and quality of product is dependent on the wastewater characteristics (i.e., organic degradable fraction) and potential pre-treatment. This study shows the potential to utilise sunlight to treat agri-industrial wastewaters while generating protein-rich PPB biomass to be used as a feed, feed additive or feed supplement.

Automated summary

This study demonstrates the potential of utilizing anaerobic purple phototrophic bacteria to produce single cell protein from piggery and chicken processing wastewater. The harvested biomass has high protein contents and can be used as a high-quality feed. The biofilm reactors showed efficient removal of COD, N, and P, with high productivities.