Microbial communities developed in membrane photo-bioreactors performance for domestic wastewater reclamation

Membrane photobioreactors (MPBRs) combine ultrafiltration membranes and phototrophic-heterotrophic-nitrifying culture growth in an interesting process for wastewater treatment that promotes the circular economy. This technology has been investigated to improve the reclamation process of primary and secondary effluents from real domestic wastewater treatment facilities. Microorganism cultures were developed in lab-scale reactors from indigenous microbial consortium under various operating conditions. Culture samples from stable biological suspensions and several strains of heterotrophic nitrification–aerobic denitrification bacteria and fungi were isolated. A total of 140 viable strains of microorganisms were identified and associated with physical-chemical properties of the feedwater and suspensions but also, with the operational conditions, to identify differences in structural composition of the developed consortia. The bacterial community exhibited significantly higher abundance and richness compared to the fungi and plantae communities, encompassing a total of 12 phyla and 43 genera. Proteobacteria were the most dominant phylum, with relative abundances of 71 % and 69 %, respectively. However, the genus composition varied greatly among the different treatments. According to diversity measurements, all suspensions fed with secondary effluents exhibited significantly lower richness, abundance, and diversity than those cultivated with primary effluents. The main factor influencing microbial community composition was the C/N ratio for most secondary effluents, whereas the ammonium‑nitrogen loading rate was determinant for primary effluents. • Hydraulic retention time of 2 days was optimal for increasing biomass productivity • Ammonium assimilation by biomass predominated at the highest organic loading rate • Relevant nitrification at low organic loading rates • 140 strains of microorganisms were isolated from the photobioreactors • Primary sewage allowed for the most abundant and richest culture suspensions