BACKGROUND: The performance of microalgal and bacterial systems devoted to wastewater treatment might be limited by the poor settling of microalgal biomass and the inhibition of nitrifying bacteria under high irradiance conditions. This work implemented a photo-sequencing batch bioreactor (PSBR) treating medium- and low-strength wastewaters. The impact of a short settling time on the formation of microalgal–bacterial aggregates (MABAs) was evaluated. Moreover, online photosynthetically active radiation (PAR) measurements at the bottom of the PSBR were used to identify potential nitrifying activity inhibition. RESULTS: A chemical oxygen demand removal efficiency of up to 88% was obtained for the medium- and low-strength wastewaters. Photoinhibition of the nitrifying activity was observed at PAR values from 73 to 480 μmol m−2 s−1, and it was confirmed under non-limiting dissolved oxygen conditions. The PSBR operating conditions, including a short settling time (30 min) and treatment of medium-strength wastewater, favored the rapid formation of MABAs in only 19 days, with a biomass settling velocity (vs) of 0.74 m h−1. The microalgal genera Acutudesmus, Desmodesmus, and Chlorella were predominant in the MABAs. Experimental estimation of the light extinction coefficient (λ = 0.056 m2 g−1 total suspended solids) allowed the simulation of light penetration profiles at different reactor liquid depths and biomass concentrations. CONCLUSION: A short settling time favors the rapid formation of MABAs in PSBR-type reactors treating medium-strength wastewater. Online monitoring and simulation of light penetration is a valuable tool to determine photoinhibition of the nitrifying activity in microalgal and bacterial systems.
All Science Journal Classification (ASJC) codes
- General Chemical Engineering
- Renewable Energy, Sustainability and the Environment
- Fuel Technology
- Waste Management and Disposal
- Organic Chemistry
- Inorganic Chemistry