Compositional Microbial-Community Shift of Submerged Membrane Bioreactor Treating Hospital Wastewater at Varying Temperatures

Abstract

Stable and efficient performance of biological treatment plants requires optimization of treatment system operating parameters. Among the various operating parameters, temperature is an important factor that influences the treatment system microbial community, which is responsible for the efficient removal of organic pollutants. This study investigated the effect of temperature on the microbiome of a submerged membrane bioreactor (SMBR) treating hospital wastewater (HWW). Specifically, the effect of temperatures (T=20°C, 15°C, and 10°C) on the removal of pharmaceuticals from HWW was examined. The maximum removal of chemical oxygen demand (∼70%) and ammoniacal nitrogen (∼75%) in the SMBR occurred at 20°C. The suspended solids (SS) concentration in the SMBR decreased from 8.5 g L−1 SS at 20°C to 6.75 g L−1 SS at 15°C and to 5.2 g L−1 SS at 10°C. At the lowest temperature (10°C), there was moderate removal of ibuprofen, hydroxyl-ibuprofen estrone, and caffeine, but the removal of sulfamethoxazole, clarithromycin, diclofenac, hydroxy diclofenac, atenolol, venlafaxine, and desvenlafaxine was inhibited substantially relative to that at higher temperatures. The microbiome analysis indicated a reduction in the relative abundance of nitrifying bacteria (Nitrosospira, Rhodanobacter, and Sphingobium) at low temperatures, which appeared to be correlated with the decrease in performance. Analysis of the microeukaryote community revealed a massive decrease in the relative abundance of the ciliate population at the low temperature and an increase in the abundance of the fungal group (Basidiomycota and unclassified fungus). Despite the dominance of fungal groups at the lower temperature, the decreased SMBR performance suggests that those fungal groups did not play an important role in pharmaceutical degradation.