Treatment of volatile organic compounds and other waste gases using membrane biofilm reactors: A review on recent advancements and challenges.

This article provides a comprehensive review of membrane biofilm reactors for waste gas (MBRWG) treatment, focusing on studies conducted since 2000. The first section discusses the membrane materials, structure, and mass transfer mechanism employed in MBRWG. The concept of a partial counter-diffusion biofilm in MBRWG is introduced, with identification of the most metabolically active region. Subsequently, the effectiveness of these biofilm reactors in treating single and mixed pollutants is examined. The phenomenon of membrane fouling in MBRWG is characterized, alongside an analysis of contributory factors. Furthermore, a comparison is made between membrane biofilm reactors and conventional biological treatment technologies, highlighting their respective advantages and disadvantages. It is evident that the treatment of hydrophobic gases and their resistance to volatility warrant further investigation. In addition, the emergence of the smart industry and its integration with other processes have opened up new opportunities for the utilization of MBRWG. Overcoming membrane fouling and developing stable and cost-effective membrane materials are essential factors for successful engineering applications of MBRWG. Moreover, it is worth exploring the mechanisms of co-metabolism in MBRWG and the potential for altering biofilm community structures.

Deciphering the influence of S/N ratio in a sulfite-driven autotrophic denitrification reactor.

Sulfur-based autotrophic denitrification is a cost-effective alternative to heterotrophic denitrification for nitrate removal due to no need of external organic carbon supply. Herein, sulfite-driven autotrophic denitrification (SDAD) was firstly established in a sequencing batch biofilm reactor treating high-strength nitrate-containing wastewater added by the sulfite. The nitrogen removal performance was mainly investigated under a molar ratio of sulfur-to­nitrogen (S/N) ranging from 0.44 to 3.07 in a total of 180-day operation. Long-term experiment showed the optimal of S/N was found to be 2.63, much close to the stoichiometric value, achieving the highest autotrophic denitrification rate and complete total nitrogen removal efficiency (TNRE) with 92.4 ± 0.3%. Cyclical trial confirmed nitrate reduction and sulfite oxidation simultaneously occurred along with sulfate formation. Meanwhile, nitrite accumulation was observed at a very low S/N conditions. Microbial community analysis identified that Sulfurovum, Thiobacillus, and Thermomonas as key denitrifying sulfur-oxidizing bacteria responsible for SDAD. Moreover, the dynamic shift in functional microorganisms affected by influent S/N was also detected. Finally, the metabolic pathway of SDAD process was unraveled via the cooperative encoding of sulfite oxidases (Sor, Apr, Sat) and nitrate-reducing genes. This study sheds light on a new sulfur-cycle autotrophic denitrification process for the bioremediation of nitrate-contaminated wastewater.

Accelerating anammox nitrogen removal in low intensity ultrasound-assisted ASBBR: Performance optimization, EPS characterization and microbial community analysis.

Efficient enrichment of slow-growing anammox species is essential for rapid start-up and stable operation of high-rate anammox reactors. Herein, a low intensity ultrasound (LIU) was introduced into anaerobic sequencing batch biofilm reactors (ASBBRs) to enhance anammox nitrogen removal from nitrogen-rich wastewater. Operation results demonstrated that the maximum total nitrogen (TN) removal efficiency of 91.5% were achieved under the optimal ultrasonic parameters (32.7 °C water temperature, 0.18 W/cm2 ultrasonic intensity and 25.7 min ultrasonication time). Moreover, significant increases of extracellular polymeric substances (EPS) components and contents were observed via the ultrasonication stimulation. A close correlation between nitrogen removal and shifts in transformation and intensity of spectrum peaks was also verified by three-dimensional excitation-emission matrix spectroscopy (3D-EEM) analysis. High-throughput sequencing revealed that the relative abundance of Candidatus Kuenenia as the key anammox consortium significantly increased after applying optimal ultrasonication condition. Furthermore, enhancement mechanisms and future prospect of the LIU-assisted anammox process was elucidated and discussed. This research provides a viable and promising acceleration strategy for anammox-based process in practice.

Optimizing anammox capacity for weak wastewater in an AnSBBR using aerobic activated sludge as inoculation.

Process optimization is essential for improving the efficiency of anaerobic ammonium oxidation (anammox) process in a practical application. In this study, an anaerobic sequence biofilm batch reactor (AnSBBR) inoculated with aerobic activated sludge was chosen as an efficient mainstream anammox reactor for treating low-nitrogen wastewater. To optimize the AnSBBR-anammox process, eight different operation stages lasting for a total of 215 days were conducted by regulating key process parameters. Principal components analysis revealed significant effects of the substrate ratio (SR) and volumetric exchange ratio (VER) on anammox performance, while other parameters (cycle time, hydraulic retention time and nitrogen loading rate) played minor roles. The highest removal efficiencies for ammonia and total nitrogen, respectively, reached 99.8% and 95.3% under optimal conditions. High-throughput sequencing found the anammox species Candidatus Brocadia and Candidatus Kuenenia made up as much as 8.5% and 3.5%, respectively, of the microbial community. Redundancy analysis indicated that these taxa were also greatly influenced by operating parameters, particularly SR and VER. This research helps to decode the correlations among nitrogen removal capacity, process parameters and the microbial community to enhance anammox in an AnSBBR system.

Unravelling nitrogen removal and nitrous oxide emission from mainstream integrated nitrification-partial denitrification-anammox for low carbon/nitrogen domestic wastewater.

Stable supply of nitrite is often a major obstacle for achieving mainstream anammox due to washout failure of nitrite oxidizers (NOB) at low influent ammonia of municipal wastewater. In this study, an integrated nitrification, partial denitrification and anammox (INPDA) as a one-stage mainstream nitrogen removal alternative was established in a low-oxygen sequencing batch biofilm reactor treating synthetic sewage. The overall nitrogen removal and nitrous oxide (N2O) emission were mainly investigated at 50 mg/L NH4+-N influent with a low carbon/nitrogen (C/N) of 2.5. Continuous operation demonstrated that as high as 98.8% NH4+-N and 94.1% TN were removed in SBBR system. Cyclic experiment verified sequential completion of nitrification, partial denitrification and anammox were responsible for high-rate TN removal. During one typical cycle, the trend of N2O emission was characterized by firstly rapid rise, then fluctuant decrease followed by rapid decrease and finally slow disappearance. The maximum N2O emission rate reached up to 6.7 µg/(L·min) occurred at 75 min. High-throughput sequencing revealed the co-existence of nitrifying, denitrifying and anammox species and large detection of key functional genes (Hzs, Hdh, Hao, Nor) in an oxygen-limited SBBR, thereby highly correlating nitrogen removal and N2O emission characteristics. Nitrogen metabolic pathways analysis further suggest denitratation(NO3--N to NO2--N)-based anammox is a main route for mainstream nitrogen removal. Moreover, N2O might be generated by both hydroxylamine oxidation step in nitrification and also heterotrophic denitrification pathway. The research findings provide more deep understandings of enhanced nitrogen removal and mitigated N2O footprint from a single mainstream anammox-based system.

Performances and structures of functional microbial communities in the mono azo dye decolorization and mineralization stages.

Removal of azo dye from wastewater with biological method is a complicated process, including decolorization and mineralization. However, there is little understanding of the functional microbial community involved in the whole dye degradation process. In this study, a simplified model using anaerobic3-oxic2-sedimentaion reactor was proposed. Acid Orange and Methyl Orange were treated as model azo dyes. In each compartment, the degradation intermediates of azo dyes were identified with UV-Vis, FTIR, HPLC-MS and GC-MS, and the corresponding microorganisms were determined with 16S rDNA high throughput Miseq sequencing. Decolorization happened in anaerobic compartments, while mineralization of the resulted aromatic amines mainly occurred under aerobic circumstance. LEfSe analysis demonstrated that the microbial community compositions were significantly influenced by the chemical structures of substrates. With t-value biplot, the relationship between azo dye degradation and microbial community structure was proposed statistically. It was found that the functional microbial communities varied with the change of azo dye degradation intermediates. Besides, cleavage of benzene ring also happened under anaerobic circumstance. This may be due to the genera of Parabacteroides and Bacteroides, which exhibited significantly positive relationships with 1,4-Benzenediol. With the new model, the performances and structures of functional microbial communities for NN- reduction and aromatic amines mineralization were characterized and the reaction mechanism was explored.