Municipal wastewater treatment by purple phototropic bacteria at low infrared irradiances using a photo-anaerobic membrane bioreactor.

Light energy is one of the major costs for phototrophic systems. This study evaluated the photoreactor efficiency of purple phototropic bacteria anaerobic membrane bioreactor (PAnMBR) at low irradiance for the treatment of municipal wastewater. Infrared irradiance levels of 3.0 and 1.4 W/m2 produced by an infrared (IR) lamp emitting in the 800-900 nm wavelength range were investigated, with the ultimate goal of optimizing the irradiance energy demand. Experimental and modeling results demonstrated the ability of PPB to grow and treat raw municipal wastewater at the applied low irradiances, with effluent quality below target limits of TCOD˂50 mg/L, TN˂10 mg/L, and TP˂1 mg/L. While Monod kinetic parameters, km and Y, were determined to be lower than previous high-energy studies (1.9 mgCOD/mgVSS-d and 0.38 mgVSS/mgCOD, respectively), the photobioreactor performance were consistently maintained, indicating that energy cost associated with IR illumination can be reduced by up to 97%. To determine whether the treatment process could approach energy neutrality, subsequent anaerobic digestion experiments of the residual PPB biomass proved a potential for biogas recovery of up to 240 NmLCH4/gVSSadded, and a moderate biomass biodegradability of 41%. As a result, the net energy consumption of the process was estimated at 0.5 kWh/m3 of treated municipal wastewater, considering an energy demand for illumination of 0.67 kWh/m3 and an energy recovery attributed to the anaerobic digestion of 0.17 kWh/m3 from the excess PPB biomass wasted from PAnMBR.

Low temperature nutrient removal from municipal wastewater by purple phototrophic bacteria (PPB).

This study evaluated the performance of purple phototrophic bacteria (PPB) at temperatures of 22 °C and 11 °C in a membrane photobioreactor. PPB performance and Monod parameters were evaluated at 11 °C and were compared to PPB performance at 22 °C. At 22 °C, the optimum HRT with respect to meeting target limits of TCOD < 50 mg/L, TN < 10 mg/L, and TP < 1 mg/L was 9 h with ethanol supplementation at 300 mgCODL-1 noting that ethanol was only needed to meet the TN limit. However, at 11 °C, the photobioreactor achieved effluent TCOD, TN, and TP concentrations of 70 mg/L, 10 mg/L, and 1.2 mg/L respectively at 9 h HRT and 300 mgCOD/L ethanol addition. Monod kinetic parameters Ks, K, Y, and Kd were determined to be 20 mgCOD/L, 1.8 mgCOD/(mgVSS.d), 0.54 mgVSS/mgCOD, and 0.09 d-1 at 22 °C and 31 mgCOD/L, 1.2 mgCOD/(mgVSS.d), 0.51 mgVSS/mgCOD, and 0.07 d-1 at 11 °C respectively.