Effect of dissolved oxygen concentration on activated sludge bacterial community and oxygen uptake rate in a SBR using co-produced oxygen from a PEM hydrogen electrolyser

A laboratory-scale sequential batch reactor (SBR) was operated for 5 months on artificial wastewater using co-produced oxygen from a hydrogen proton exchange membrane (PEM) electrolyser. High chemical oxygen demand (COD) removal (>80–85 %) was achieved consistently using a Food to Microorganism (F/M) ratio as high as 1. The effect of dissolved oxygen (DO) concentration, ranging from 1 to 8 mg/L, on COD removal and oxygen uptake rate (OUR) was evaluated. DO concentration was shown to influence bacteria respiration as OUR values increased across the DO range studied. OUR increased linearly from 4.24 to 9.23 mgO2/L/h/g of MLSS with DO concentration of 1 to 8 mg/L respectively, however no effect on COD removal was observed. Microorganism communities were characterized, and significant variation in bacteria communities distribution was observed when increasing the DO concentration along with a decrease in bacteria diversity. The dominant phylum observed during this study were Proteobacteria, Bacteroidetes, and Candidatus Sacharibacteria. Aeration energy expenditures were estimated to be two times lower than for a similar air SBR when keeping DO concentration below 5 mg/L.