The role of microbial diversity and composition in minimizing sludge production in the oxic-settling-anoxic process

© 2017 Elsevier B.V. The oxic-settling-anoxic (OSA) process, which involves an aerobic tank attached to oxygen- and substrate-deficient external anoxic reactors, minimizes sludge production in biological wastewater treatment. In this study, the microbial community structure of OSA was determined. Principal coordinate analysis showed that among the three operational factors, i.e., (i) redox condition, (ii) external reactor sludge retention time (SRText), and (iii) sludge interchange between aerobic and anoxic reactors, redox condition had the greatest impact on microbial diversity. Generally, reactors with lower oxidation-reduction potential had higher microbial diversity. The main aerobic sequencing batch reactor of OSA (SBROSA) that interchanged sludge with an external anoxic reactor had greater microbial diversity than SBRcontrol which did not have sludge interchange. SBROSA sustained high abundance of the slow-growing nitrifying bacteria (e.g., Nitrospirales and Nitrosomondales) and consequently exhibited reduced sludge yield. Specific groups of bacteria facilitated sludge autolysis in the external reactors. Hydrolyzing (e.g., Bacteroidetes and Chloroflexi) and fermentative (e.g., Firmicutes) bacteria, which can break down cellular matter, proliferated in both the external aerobic/anoxic and anoxic reactors. Sludge autolysis in the anoxic reactor was enhanced with the increase of predatory bacteria (e.g., order Myxobacteriales and genus Bdellovibrio) that can contribute to biomass decay. Furthermore, β- and γ-Proteobacteria were identified as the bacterial phyla that primarily underwent decay in the external reactors

Effects of operational disturbance and subsequent recovery process on microbial community during a pilot-scale anaerobic co-digestion

© 2019 This study investigated changes in microbial community structure and composition in response to operational disturbance and subsequent process recovery by inoculum addition. Amplicon sequencing of 16S rRNA and mcrA marker genes on the Illumina Miseq platform was used for microbial community analysis. The results show that imbalance among core microbial groups caused volatile fatty acid accumulation and subsequent deteriorated biogas production (decreased by 45% of daily volume) and methane content (57% of the total abundance) and reduction of acetogenic and methanogenic microbes (they accounted for <9% and <3% of the total abundance, respectively). Acetogens and methanogens were replenished by inoculum addition to recover digester performance. Although digester performances were similar in stable (prior to disturbance) and post recovery phases, the microbial community did not return to the original state, suggesting the existence of functional redundancy in the community

Osmotic versus conventional membrane bioreactors integrated with reverse osmosis for water reuse: Biological stability, membrane fouling, and contaminant removal

© 2016 This study systematically compares the performance of osmotic membrane bioreactor – reverse osmosis (OMBR-RO) and conventional membrane bioreactor – reverse osmosis (MBR-RO) for advanced wastewater treatment and water reuse. Both systems achieved effective removal of bulk organic matter and nutrients, and almost complete removal of all 31 trace organic contaminants investigated. They both could produce high quality water suitable for recycling applications. During OMBR-RO operation, salinity build-up in the bioreactor reduced the water flux and negatively impacted the system biological treatment by altering biomass characteristics and microbial community structure. In addition, the elevated salinity also increased soluble microbial products and extracellular polymeric substances in the mixed liquor, which induced fouling of the forward osmosis (FO) membrane. Nevertheless, microbial analysis indicated that salinity stress resulted in the development of halotolerant bacteria, consequently sustaining biodegradation in the OMBR system. By contrast, biological performance was relatively stable throughout conventional MBR-RO operation. Compared to conventional MBR-RO, the FO process effectively prevented foulants from permeating into the draw solution, thereby significantly reducing fouling of the downstream RO membrane in OMBR-RO operation. Accumulation of organic matter, including humic- and protein-like substances, as well as inorganic salts in the MBR effluent resulted in severe RO membrane fouling in conventional MBR-RO operation

An Osmotic Membrane Bioreactor-Membrane Distillation System for Simultaneous Wastewater Reuse and Seawater Desalination: Performance and Implications

© 2017 American Chemical Society. In this study, we demonstrate the potential of an osmotic membrane bioreactor (OMBR)-membrane distillation (MD) hybrid system for simultaneous wastewater reuse and seawater desalination. A stable OMBR water flux of approximately 6 L m-2 h-1 was achieved when using MD to regenerate the seawater draw solution. Water production by the MD process was higher than that from OMBR to desalinate additional seawater and thus account for draw solute loss due to the reverse salt flux. Amplicon sequencing on the Miseq Illumina platform evidenced bacterial acclimatization to salinity build-up in the bioreactor, though there was a reduction in the bacterial community diversity. In particular, 18 halophilic and halotolerant bacterial genera were identified with notable abundance in the bioreactor. Thus, the effective biological treatment was maintained during OMBR-MD operation. By coupling biological treatment and two high rejection membrane processes, the OMBR-MD hybrid system could effectively remove (>90%) all 30 trace organic contaminants of significant concern investigated here and produce high quality water. Nevertheless, further study is necessary to address MD membrane fouling due to the accumulation of organic matter, particularly protein- and humic-like substances, in seawater draw solution

The fate of trace organic contaminants during anaerobic digestion of primary sludge: A pilot scale study

© 2018 A pilot-scale study was conducted to investigate the fate of trace organic contaminants (TrOCs) during anaerobic digestion of primary sludge. Of the 44 TrOCs monitored, 24 were detected in all primary sludge samples. Phase distribution of TrOCs was correlated well with their hydrophobicity (>67% mass in the solid phase when LogD > 1.5). The pilot-scale anaerobic digester achieved a steady performance with a specific methane yield of 0.39–0.92 L/gVSremoved and methane composition of 63–65% despite considerable variation in the primary sludge. The fate of TrOCs in the aqueous and solid phases was governed by their physicochemical properties. Biotransformation was significant (>83%) for five TrOCs with logD 1.5 were poorly removed under anaerobic conditions. Sorption onto the solid phase appears to impede the biodegradation of these TrOCs

Aerobic membrane bioreactors and micropollutant removal

© 2020 Elsevier B.V. All rights reserved. Membrane bioreactor (MBR) has become a credible alternative to conventional treatment technology especially for water reuse and to enhance the removal of micropollutants from municipal wastewater. Numerous large-scale MBR plants have been commissioned over the last few years. In general, MBR can produce better effluent in terms of both basic water quality and concentration of micropollutants than conventional wastewater treatment processes. Micropollutant removal from the liquid phase by MBR is governed mostly by biodegradation and adsorption to sludge. Factors governing these removal mechanisms include physicochemical properties of the micropollutant (e.g., hydrophobicity and molecular structure), configuration of the biological process, and operating parameters (e.g., pH, temperature, solid retention time, and dissolved oxygen concentration or redox condition). A notable research gap in the current literature is the lack of insight into the microbial community of the biological reactor. With molecular biology research tools such as next-generation sequencing becoming more accessible to water researchers, techniques to regulate the microbial community to enhance micropollutant removal by MBR can be expected in the near future

Bacterial community dynamics in an anoxic-aerobic membrane bioreactor - Impact on nutrient and trace organic contaminant removal

The bacterial community in different redox regimes of an anoxic-aerobic MBR under different operating conditions was investigated using pyrosequencing. With internal recirculation (IR) between the anoxic and aerobic reactors, the bacterial communities in these reactors were highly similar in structure and phylogenetic relationship, indicating IR as a key driving force shaping the bacterial communities that are responsible for the core function in the system. Without IR, each redox condition sustained the growth of distinct bacterial communities according to their oxygen requirement, and the anoxic community presented a low capacity of nutrient and trace organic contaminant (TrOC) removal. Higher bacterial diversity under longer sludge retention time (SRT) was evident; however, except for a few TrOCs, removal efficiency of TOC, TN and TrOCs were the same irrespective of the SRT. The presence of TrOCs induced shifts in bacterial communities, and a correlation between bacterial communities and TrOC transformation was noted. The important candidates for TrOC biotransformation were the taxa within Proteobacteria, particularly Methylophilales and Myxococcales. Other bacterial groups potentially contributing to TrOC biotransformation were those related to nitrogen removal, such as Rhodocyclales and Plantomycetes. In contrast, the detected members of Cytophagaceae (Bacteroidetes) appeared not to contribute to TrOC biotransformation

Impact of anaerobic co-digestion between sewage sludge and carbon-rich organic waste on microbial community resilience

© 2018 The Royal Society of Chemistry. This study examines the changes in microbial community diversity and structure in response to anaerobic co-digestion (AcoD) between sewage sludge and a carbon-rich organic waste. Biomass samples were collected at different carbon-rich co-substrate mixing ratios to cover a large range of organic loading rate (OLR) for microbial community analysis by amplicon sequencing of 16S rRNA and mcrA marker genes on the Illumina Miseq platform. The results show a reduction in community diversity (i.e. richness and evenness) and a shift in community structure as the OLR increased due to the addition of the carbon-rich co-substrate. Despite the decrease in community diversity, biogas production increased proportionally to the increase in OLR of up to 3.03 kg COD per m3 per day (corresponding to 171% OLR increase compared to anaerobic digestion of only sewage sludge). Further OLR increase led to the collapse of biogas production as well as significant reduction in both the microbial diversity and methanogenic population. The methanogenic community was more sensitive to the increase in OLR compared to hydrolytic and fermentative bacteria. These results show that there is an OLR threshold at which the function and resilience of the anaerobic ecosystem could be maintained. Beyond this threshold, the enrichment of hydrolytic and fermentative bacteria, as well as inhibition of methanogenic community, can cause anaerobic digestion failure

Biological performance and trace organic contaminant removal by a side-stream ceramic nanofiltration membrane bioreactor

This study evaluated the performance of a side-stream ceramic nanofiltration membrane bioreactor (NF-MBR) system with respect to basic water quality parameters as well as trace organic contaminant (TrOC) removal efficiency. The results show a stable biological performance of the continuous NF-MBR system with high effluent quality (total organic carbon  3) were well removed (>85%), except diazinon (59 ± 7%). Hydrophilic compounds containing electron donating groups were also well removed (>90%). By contrast, hydrophilic compounds containing electron withdrawing groups were poorly removed (8–54%). Most of the 40 TrOCs investigated in this study did not accumulate in the sludge. Only three hydrophobic compounds, namely amitriptyline, triclosan and triclocarban showed considerable accumulation in sludge (>500 ng g−1). Mass balance indicated biodegradation/transformation as the most significant TrOC removal mechanism by this NF-MBR