Dissimilatory sulfate reduction in an anaerobic biofilm reactor for tofu processing wastewater treatment: Bacterial community and their functional genes.

Dissimilatory sulfate reduction (DSR) is the key sulfur cycle that transforms sulfate to sulfide. This process leads to odour issues in wastewater treatment. However, few studies have focused on DSR during treating food processing wastewater with high sulfate. This study investigated DSR microbial population and functional genes in an anaerobic biofilm reactor (ABR) treating tofu processing wastewater. The tofu processing wastewater is a common food processing wastewater in Asia. The full-scale ABR was operated for over 120 days in a tofu and tofu-related products manufacturing factory. Mass balance calculations based on the reactor performance indicated that 79.6-85.1 % of the sulfate was transformed into sulfide irrelevant to dissolved oxygen supplementation. Metagenomic analysis revealed 21 metagenome-assembled genomes (MAGs) containing enzymes encoding DSR. The biofilm contained the complete functional genes of DSR pathway in the full-scale ABR, indicating that biofilm could process DSR independently. Comamonadaceae, Thiobacillus, Nitrosomonadales, Desulfatirhabdium butyrativorans, Desulfomonile tiedjei were the dominant DSR species in the ABR biofilm community. Dissolved oxygen supplementation directly inhibited DSR and mitigated HS- production. It was also found that Thiobacillus contained all the function genes encoding every necessary enzyme in DSR, and thus Thiobacillus distribution directly correlated to DSR and the ABR performance.

Identification of dissimilatory nitrate reduction to ammonium (DNRA) and denitrification in the dynamic cake layer of a full-scale anoixc dynamic membrane bioreactor for treating hotel laundry wastewater.

Identification of dissimilatory nitrate reduction to ammonium (DNRA) and denitrification in the dynamic cake layer of a full-scale anoixc dynamic membrane bioreactor (AnDMBR) for treating hotel laundry wastewater was studied. A series of experiments were conducted to understand the contributions of DNRA and canonical denitrification activities in the dynamic cake layer of the AnDMBR. The dynamic cake layer developed included two phases - a steady transmembrane pressure (TMP) increase at 0.24 kPa/day followed by a sharp TMP jump at 1.26 kPa/day four to five days after the AnDMBR start-up. The nitrogen mass balance results showed that canonical denitrification was predominant during the development of the dynamic cake layer. However, DNRA activity and accumulation of bacteria equipped with a complete DNRA pathway showed a positive correlation to the development of the dynamic cake layer. Our metagenomic analysis identified an approximately 18% of the dynamic cake layer bacterial community has a complete DNRA pathway. Pannonibacter (1%), Thauera (0.8%) and Pseudomonas (3%) contained all genes encoding for funcional enzymes of both DNRA (nitrate reductase and DNRA nitrite reductase) and denitrification (nitrate reductase, nitrous oxide reductase and nitric oxide reductase). No other metagenome-assembled genomes (MAGs) possessed a complete cononical denitrification pathway, indicating food-chain-like interactions of denitrifiers in the dynamic cake layer. We found that COD loading rate could be used to control DNRA and canonical denitrification activities during the dynamic cake layer formation.

Core carbon fixation pathways associated with cake layer development in an anoxic-oxic biofilm-membrane bioreactor treating textile wastewater.

Microbial carbon fixation pathways have not yet been adequately understood for their role in membrane case layer formation processes. Carbon fixation bacteria can play critical roles in either causing or enhancing cake layer formation in some autotrophic-prone anoxic conditions, such as sulfur-cycling conditions. Understanding the microbes capable of carbon fixation can potentially guide the design of membrane biofouling mitigation strategies in scientific ways. Thus, we used meta-omics methods to query carbon fixation pathways in the cake layers of a full-scale anoxic-oxic biofilm-MBR system treating textile wastewater in this study. Based on the wastewater constituents and other properties, such as anoxic conditions, sulfide-reducing and sulfur-oxidizing bacteria could co-exist in the membrane unit. In addition, low-light radiation conditions could also happen to the membrane unit. However, we could not quantify the light intensity or total energy input accurately because the whole experimental setup was a full-scale system. Potentially complete carbon fixation pathways in the cake layer included the Calvin-Benson-Bassham cycle, Wood-Ljungdahl pathway, and the 3-hydroxypropionate bicycle. We discovered that using aeration could effectively inhibit carbon fixation, which resulted in mitigating membrane cake layer development. However, the aeration resulted in the 3-hydroxypropionate bicycle pathway, presumably used by aerobic sulfur-oxidizing prokaryotes, to become a more abundant carbon fixation pathway in the cake layer under aerobic conditions.