Denitrification processes and microbial communities in a sequencing batch reactor treating nanofiltration (NF) concentrate from coking wastewater

Responses of microbial interactions and functional genes to sulfamethoxazole in anammox consortia

Sulfamethoxazole (SMX) has been widely detected in various environments and its potential environmental risks have caused great concerns. However, the impact mechanism of SMX on microbial interactions among anammox consortia remain unknown. A long-term exposure experiments (140 d) was carried out to systematically examine the influence of SMX (0-1000 μg/L) on the anammox system, especially microbial network dynamics and variations of key metabolic genes. Results showed that anammox system could adapt to SMX below 500 μg/L and maintain a high nitrogen removal efficiency (NRE) of 85.35 ± 2.42%, while 1000 μg/L SMX significantly decreased the abundance of functional microbes and deteriorated denitrification performance with NRE dropped to 36.92 ± 15.01%. Co-occurrence network analysis indicated that 1000 μg/L SMX decreased the interactions between Proteobacteria and Chloroflexi and limited AnAOB from playing an important role as central nodes in the subnetwork of Planctomycetes. Metagenomics analysis found that genes associated with nitrogen removal (i.e., hdh, hzs, nirS, and hao) showed lower expression level after addition of SMX, while SMX-related ARGs (sul1 and sul2) increased by 1.22 and 2.68 times. This study provided us a relatively comprehensive perspective in response of microbial interactions and metabolic activity to various SMX concentrations.

Microbial community and performance of a partial nitritation/anammox sequencing batch reactor treating textile wastewater

Implementation of onsite bioremediation technologies is essential for textile industries due to rising concerns in terms of water resources and quality. Partial nitritation-anaerobic ammonium oxidation (PN/A) processes emerged as a valid, but unexplored, solution. In this study, the performance of a PN/A pilot-scale (9 m3) sequencing batch reactor treating digital textile printing wastewater (10-40 m3 d-1) was monitored by computing nitrogen (N) removal rate and efficiencies. Moreover, the structure of the bacterial community was assessed by next generation sequencing and quantitative polymerase chain reaction (qPCR) analyses of several genes, which are involved in the N cycle. Although anaerobic ammonium oxidation activity was inhibited and denitrification occurred, N removal rate increased from 16 to 61 mg N g VSS-1 d-1 reaching satisfactory removal efficiency (up to 70%). Ammonium (18-70 mg L-1) and nitrite (16-82 mg L-1) were detected in the effluent demonstrating an unbalance between the aerobic and anaerobic ammonia oxidation activity, while constant organic N was attributed to recalcitrant azo dyes. Ratio between nitrification and anammox genes remained stable reflecting a constant ammonia oxidation activity. A prevalence of ammonium oxidizing bacteria and denitrifiers suggested the presence of alternative pathways. PN/A resulted a promising cost-effective alternative for textile wastewater N treatment as shown by the technical-economic assessment. However, operational conditions and design need further tailoring to promote the activity of the anammox bacteria.

Simultaneous enhancement of nitrate removal flux and methane utilization efficiency in MBfR for aerobic methane oxidation coupled to denitrification by using an innovative scalable double-layer membrane

Endevours on the enhancement of nitrate removal efficiency during methane oxidation coupled with denitrification (AME-D) has always overlooked the role of membrane employed. It would be highly beneficial to enrich the biomass content and to manage biofilm on the membrane, in the utilization of methane and denitrification. In this study, an innovative and scalable double-layer membrane (DLM) was designed and prepared for a membrane biofilm reactor (MBfR), to simultaneously enhance nitrate removal flux and methane utilization efficiency during aerobic methane oxidation coupled with the denitrification (AME-D) process. The DLM allowed quick bacterial attachment and biomass accumulation for biofilm growth, which would be then self-regulated for well distribution of functional microbes on/within the DLM. Upon a high biofilm density of over 70 g-VSS m^-2 achieved on the DLM, the methane utilization efficiency of the MBfR was enhanced significantly to over 1.3 times than the control MBfR with conventional polypropylene membrane. The MBfR employed DLM also demonstrated the maximum nitrate removal flux of 740 mg-NO₃^--N m^-2 d^-1 that was approximately 1.64 times of that in control MBfR at continuous-mode operation. This DLM indeed favored the enrichment of Type II aerobic methanotrophs of Methylocystaceae, and methanol-utilization denitrifiers of Rhodocyclaceae that preferentially utilize methanol as the cross-feeding intermediates to promote the methane utilization efficiency, and thus to enhance the nitrate removal flux. These results raised from new designed DLM confirmed the importance of membrane surface properties on the effectiveness of MBfR, and offered great potential to address challenging problems of MBfRs during engineering application.

Influence of salinity cycles in bioreactor performance and microbial community structure of membrane-based tidal-like variable salinity wastewater treatment systems

A membrane bioreactor and two hybrid moving bed bioreactor-membrane bioreactors were operated for the treatment of variable salinity wastewater, changing in cycles of 6-h wastewater base salinity and 6-h maximum salinity (4.5 and 8.5 mS cm^-1 electric conductivity, which relate to 2.4 and 4.8 g L^-1 NaCl, respectively), under different hydraulic retention times (6, 9.5, and 12 h) and total solids concentrations (2500 and 3500 mg L^-1). The evaluation of the performance of the systems showed that COD removal performance was unaffected by salinity conditions, while BOD₅ and TN removals were significantly higher in the low-salinity scenario. The microbial community structure showed differences with respect to salinity conditions for Eukarya, suggesting their higher sensitivity for salinity with respect to Prokarya, which were similar at both salinity scenarios. Nevertheless, the intra-OTU distribution of consistently represented OTUs of Eukarya and Prokarya was affected by the different salinity maximums. Multivariate redundancy analyses showed that several genera such as Amphiplicatus (0.01-5.90%), Parvibaculum (0.27-1.19%), Thiothrix (0.30-1.19%), Rhodanobacter (2.81-5.85%), Blastocatella (0.21-2.01%), and Nitrobacter (0.80-0.99%) were positively correlated with BOD₅ and TN removal, and the ecological roles of these were proposed. All these genera were substantially more represented under low-salinity conditions (10-500% higher relative abundance), demonstrating that they might be of importance for the treatment of variable salinity wastewater. Evaluation of Eukarya OTUs showed that many of them lack a consistent taxonomic classification, which highlights the lack of knowledge of the diversity and ecological role of Eukaryotes in saline wastewater treatment processes. The results obtained will be of interest for future design and operation of salinity wastewater treatment systems particularly because little is known on the effect of variable salinity conditions in wastewater treatment.