Impact of additional carbon on poly-hydroxybutyrates (PHB) accumulation and nutrient removal in a sustainable anaerobic/anoxic/oxic (A2O) membrane bioreactor

Abstract

Recovering nutrient, energy, useful byproducts and reusing the treated wastewater may make a municipal wastewater treatment more sustainable. The approach employed in this study to increase the sustainability of wastewater treatment was to accumulate and harvest poly-hydroxybutyrates (PHB) in wastewater treatment plants. Additional carbon (acetate, supernatant of fermented sludge or thin corn stillage) was continuously fed along with synthetic municipal wastewater to a bench-scale anaerobic/anoxic/oxic (A2O) membrane bioreactor to promote PHB accumulation in the biomass. The impact of addition of carbon to the anaerobic tank or anoxic tank was also studied. PHB content in the range of 10% of dry biomass weight was achieved by adding 1000 mg-C/L acetate to either the anaerobic tank or anoxic tank. In addition, removal of total nitrogen and total phosphorus by the A2O MBR increased when acetate was added. Percent of nitrogen removal increased from 82.4% to 98%, and total phosphorus in effluent was reduced to as low as 0.4 mg/L. When supernatant of fermented sludge was added as additional carbon source, the PHB accumulation was about 4.2% of dry biomass weight. Adding supernatant of fermented sludge did not affect the effluent quality, and the total nitrogen and total phosphorus in the effluent were still within typical discharge limits. With thin corn stillage as an additional carbon source, a PHB content of 7.2% of dry biomass weight was obtained. However, use of corn stillage resulted in high TN, TP and COD in the effluent of the A2O MBR.