Attached-growth configuration outperforms continuously stirred tank anaerobic membrane bioreactors in alleviating membrane biofouling

Accounting for the microbial assembly of each process in wastewater treatment plants (WWTPs): study of four WWTPs receiving similar influent streams

We evaluated a unique model in which four full-scale wastewater treatment plants (WWTPs) with the same treatment schematic and fed with similar influent wastewater were tracked over an 8-month period to determine whether the community assembly would differ in the activated sludge (AS) and sand filtration (SF) stages. For each WWTP, AS and SF achieved an average of 1-log10 (90%) and <0.02-log10 (5%) reduction of total cells, respectively. Despite the removal of cells, both AS and SF had a higher alpha and beta diversity compared to the influent microbial community. Using the Sloan neutral model, it was observed that AS and SF were individually dominated by different assembly processes. Specifically, microorganisms from influent to AS were predominantly determined by the selective niche process for all WWTPs, while the microbial community in the SF was relatively favored by a stochastic, random migration process, except two WWTPs. AS also contributed more to the final effluent microbial community compared with the SF. Given that each WWTP operates the AS independently and that there is a niche selection process driven mainly by the chemical oxygen demand concentration, operational taxonomic units unique to each of the WWTPs were also identified. The findings from this study indicate that each WWTP has its distinct microbial signature and could be used for source-tracking purposes.IMPORTANCEThis study provided a novel concept that microorganisms follow a niche assembly in the activated sludge (AS) tank and that the AS contributed more than the sand filtration process toward the final microbial signature that is unique to each treatment plant. This observation highlights the importance of understanding the microbial community selected by the AS stage, which could contribute toward source-tracking the effluent from different wastewater treatment plants.

Predicting Anaerobic Membrane Bioreactor Performance Using Flow-Cytometry-Derived High and Low Nucleic Acid Content Cells

Having a tool to monitor the microbial abundances rapidly and to utilize the data to predict the reactor performance would facilitate the operation of an anaerobic membrane bioreactor (AnMBR). This study aims to achieve the aforementioned scenario by developing a linear regression model that incorporates a time-lagging mode. The model uses low nucleic acid (LNA) cell numbers and the ratio of high nucleic acid (HNA) to LNA cells as an input data set. First, the model was trained using data sets obtained from a 35 L pilot-scale AnMBR. The model was able to predict the chemical oxygen demand (COD) removal efficiency and methane production 3.5 days in advance. Subsequent validation of the model using flow cytometry (FCM)-derived data (at time t - 3.5 days) obtained from another biologically independent reactor did not exhibit any substantial difference between predicted and actual measurements of reactor performance at time t. Further cell sorting, 16S rRNA gene sequencing, and correlation analysis partly attributed this accurate prediction to HNA genera (e.g., Anaerovibrio and unclassified Bacteroidales) and LNA genera (e.g., Achromobacter, Ochrobactrum, and unclassified Anaerolineae). In summary, our findings suggest that HNA and LNA cell routine enumeration, along with the trained model, can derive a fast approach to predict the AnMBR performance.

Improving the performance of coupled solid carbon source biofilm carriers through pore-forming methods

Coupled solid carbon source biofilm carriers (CCBs) was usually utilized to enhance the treatment efficiency of low carbon/nitrogen (C/N) wastewater. However, current CCBs have low carbon release capacity because of its small inner mass transfer coefficient. Therefore, this study innovatively applied pore-forming methods to modify CCBs. After orthogonal selections, two porous CCBs, which were respectively prepared through circulating freezing pore-forming method (CCB2) and ammonium bicarbonate pore-forming method (CCB3), were proposed and further applied in sequencing batch moving bed biofilm reactors (SBMBBRs). The results indicated that circulating freezing pore-forming method could improve the mechanical strength and carbon source release rate of CCBs. In addition, CCB2 could significantly enhance the total nitrogen (TN) removal efficiency of SBMBBRs, when compared with the non-porous CCBs (i.e., CCB1). Further biofilm and simultaneous nitrification and denitrification (SND) rate calculation attributed this enhancement to the higher biofilm amount (i.e., 0.06 g g^-1 CCB) and the higher SND rate (i.e., 33.60%). Microbial community analysis reiterated these observations that CCB2 and CCB3 could accumulate Proteobacteria, Actinobacteriota and Nitrospirota, and also stimulate nitrification and denitrification associated pathways. More importantly, the cost calculation indicated CCB2 cost only 47.37% of CCB1 and 31.34% of CCB3, showing highly economic applicability. Overall, our results collectively proved that CCBs manufactured by circulating freezing pore-forming method could provide more carbon releasing points and microorganisms attaching positions, exhibiting effectively nitrogen removal when treating low C/N wastewater.

Biofilm formation as a method of improved treatment during anaerobic digestion of organic matter for biogas recovery

The efficiency of anaerobic digestion could be increased by promoting microbial retention through biofilm development. The inclusion of certain types of biofilm carriers has differentiated existing AD biofilm reactors through their respective mode of biofilm growth. Bacteria and archaea engaged in methanogenesis during anaerobic processes potentially build biofilms by adhering or attaching to biofilm carriers. Meta-analyzed results depicted varying degrees of biogas enhancement within AD biofilm reactors. Furthermore, different carrier materials highly induced the dynamicity of the dominant microbial population in each system. It is suggested that the promotion of surface contact and improvement of interspecies electron transport have greatly impacted the treatment results. Modern spectroscopy techniques have been and will continue to give essential information regarding biofilm's composition and structural organization which can be useful in elucidating the added function of this special layer of microbial cells.