Characteristics of oxygen mass transfer and its impact on pollutant removal performance and microbial community structure in an aerobic fluidized bed biofilm reactor for treatment of municipal wastewater

Characterizing algal-bacterial symbiotic biofilms: Insights into coexistence of algae and anaerobic microorganisms

This study constructed an integrated algae/partial nitrification/anammox biofilm system and operated it for 240 days. The total nitrogen removal efficiency exceeded 90 %. The structure, compositions, and function of this symbiotic biofilm, which played a pivotal role in the system, were analyzed in detail. Microscope photos and fluorescence in situ hybridization both showed that bacteria and algae were well integrated. The dissolved oxygen gradient further confirmed that different functional microorganisms grew at varying depths within biofilm. Algae formed an oxygen-producing zone (0-0.48 mm), followed by ammonia oxidizing bacteria (AOB) consuming oxygen to form an oxygen-consuming zone (0.48-0.86 mm), and anaerobic ammonia oxidizing bacteria (AnAOB) removed nitrogen in anaerobic zone (>0.86 mm). Chlorella, Nitrosomonas and Candidatus_Kuenenia were identified as the dominant algae, AOB and AnAOB, with relative abundances of 11.80 %, 19.77 % and 3.07 %, respectively. This layered biofilm benefitted providing a suitable environment for various microorganisms to survive within a complex biofilm.

Rapid start-up and long-term stable operation of the anammox reactor based on biofilm process: Status, challenges, and perspectives

Anammox-biofilm processes have great potential for wastewater nitrogen removal, as it overcomes the slow growth and easy loss of AnAOB (anaerobic ammonium oxidation bacteria). Biofilm carrier is the core part of the Anammox-biofilm reactor and plays a key role in the start-up and long-term operation of the process. Therefore, the research on the biofilm carrier of Anammox-based process was summarized and discussed in terms of configurations and types. In the Anammox-biofilm process, fixed bed biofilm reactor is a relatively mature biofilm carrier configuration and has advantages in terms of nitrogen removal and long-term operational stability, while moving bed biofilm reactor has advantages in terms of start-up time. Although the long-term operational stability of fluidized bed biofilm reactor is good, its nitrogen removal performance needs to be improved. Among the different biofilm carrier categories, the inorganic biofilm carrier has an advantage in start-up time, due to the enhancement of the growth and metabolic of AnAOB by inorganic materials (such as carbon and iron). Anammox-based reactors using organic biofilm carriers, especially suspension carriers, are well-established and more stable in long-term operation. Composite biofilm carriers combine the advantages of several materials, but their complex preparation procedures lead to high costs. In addition, possible research directions for accelerating the start-up and keeping the long-term stable operation of Anammox reactor by biofilm process were highlighted. It is hoped to provide a possible pathway for the rapid start-up of Anammox-based process, and references for the optimization and promotion of process.

Under-loaded operation of an anaerobic-anoxic-aerobic system in dry and wet weather dynamics to prevent overflow pollution: Impacts on process performance and microbial community

Effects of low hydraulic loading rate (HLR) in dry weather and high HLR in wet weather on pollutant removal, microbial community, and sludge properties of a full-scale wastewater treatment plant (WWTP) were extensively studied to explore the risk of under-loaded operation for overflow pollution control. Long-term low HLR operation had an insignificant effect on the pollutant removal performance of the full-scale WWTP, and the system could withstand high-load shocks in wet weather. Low HLR resulted in higher oxygen and nitrate uptake rate due to the storage mechanism under the alternating feast/famine condition, and lower nitrifying rate. Low HLR operation enlarged particle size, deteriorated floc aggregation and sludge settleability, and reduced sludge viscosity due to the overgrowth of filamentous bacteria and inhibition of floc-forming bacteria. The remarkable increase in Thuricola and the contract morphology of Vorticella in microfauna observation confirmed the risk of flocs disintegration in low HLR operation.

Biofilm-based technology for industrial wastewater treatment: current technology, applications and future perspectives

The microbial community in biofilm is safeguarded from the action of toxic chemicals, antimicrobial compounds, and harsh/stressful environmental circumstances. Therefore, biofilm-based technology has nowadays become a successful alternative for treating industrial wastewater as compared to suspended growth-based technologies. In biofilm reactors, microbial cells are attached to static or free-moving materials to form a biofilm which facilitates the process of liquid and solid separation in biofilm-mediated operations. This paper aims to review the state-of-the-art of recent research on bacterial biofilm in industrial wastewater treatment including biofilm fundamentals, possible applications and problems, and factors to regulate biofilm formation. We discussed in detail the treatment efficiencies of fluidized bed biofilm reactor (FBBR), trickling filter reactor (TFR), rotating biological contactor (RBC), membrane biofilm reactor (MBfR), and moving bed biofilm reactor (MBBR) for different types of industrial wastewater treatment. Besides, biofilms have many applications in food and agriculture, biofuel and bioenergy production, power generation, and plastic degradation. Furthermore, key factors for regulating biofilm formation were also emphasized. In conclusion, industrial applications make evident that biofilm-based treatment technology is impactful for pollutant removal. Future research to address and improve the limitations of biofilm-based technology in wastewater treatment is also discussed.

Recent advancements in the treatment of palm oil mill effluent (POME) using anaerobic biofilm reactors: Challenges and future perspectives

Palm oil is the most utilized vegetable globally which is mostly produced in countries such as Malaysia, Indonesia and Thailand. The great amount of POME generation from palm oil mills is now a threat to the environment and require a suitable treatment of POME to reduce the organic strength in accordance with the standard discharge limit before releasing to the environment. Currently, the technology to combine the anaerobic process and biofilm system in bioreactors have produced a fresh idea in treatments of high strength wastewater like POME. Anaerobic biofilm reactor is a convincing method for POME treatment due to its significant advantages over the conventional biological treatments consisting of anaerobic, aerobic and facultative pond systems. Overall, integrated anaerobic-aerobic bioreactor (IAAB) can remove more than 99% of chemical oxygen demand (COD), biochemical oxygen demand (BOD) and total suspended solids (TSS) with the combination of anaerobic and aerobic digestion for POME treatment. It has better performance as compared to up-flow anaerobic sludge blanket (UASB) and up-flow anaerobic filter (UAF) with 80% and 88-94% COD removal efficiency respectively. Anaerobic pond was found to perform well also by removing 97.8% of COD in POME but require long retention time and larger land. Hence, this study aims to provide intensive review of the performance of the anaerobic biofilm reactor in treating POME and the recent advancements in this technology. The limitations and future perspectives in utilization of anaerobic biofilm reactor during its operation in treating POME are discussed.

Integrated moving bed biofilm reactor with partial denitrification-anammox for promoted nitrogen removal: Layered biofilm structure formation and symbiotic functional microbes

Partial denitrification/anaerobic ammonia oxidation (anammox) (PD/A) is currently an advanced nitrogen removal process. This study developed a PD/A system in a moving bed biofilm reactor. Results showed that the nitrogen removal efficiency reached 76.60% with a COD/NO₃-N of 2.0, and the contribution of anammox was 88.01%. Further analysis showed that the biocarriers could form layered pH and dissolved oxygen structures to promote the aggregation of different functional bacteria at various depths, thus stabilizing the coupled process. Microbial structure analysis showed that the abundance of Saccharimonadales, responsible for denitrification, increased from 0% to 36.27% between day 0 and day 120, while the abundance of Candidatus Jettenia, responsible for anammox, decreased from 10.41% to 2.20%. The synergistic effect of Saccharimonadales and Candidatus Jettenia enabled stable and efficient removal of nitrogen. This study proposed a novel configuration of the PD/A process and provided a theoretical basis for its promotion and application.

Recent advances in biological removal of nitroaromatics from wastewater

Various nitroaromatic compounds (NACs) released into the environment cause potential threats to humans and animals. Biological treatment is valued for cost-effectiveness, environmental friendliness, and availability when treating wastewater containing NACs. Considering the significance and wide use of NACs, this review focuses on recent advances in biological treatment systems for NACs removal from wastewater. Meanwhile, factors affecting biodegradation and methods to enhance removal efficiency of NACs are discussed. The selection of biological treatment system needs to consider NACs loading and cost, and its performance is affected by configuration and operation strategy. Generally, sequential anaerobic-aerobic biological treatment systems perform better in mineralizing NACs and removing co-pollutants. Future research on mechanism exploration of NACs biotransformation and performance optimization will facilitate the large-scale application of biological treatment systems.

A review of ammonia removal using a biofilm-based reactor and its challenges

Extensive growth of industries leads to uncontrolled ammonia releases to environment. This can result in significant degradation of the aquatic ecology as well as significant health concerns for humans. Knowing the mechanism of ammonia elimination is the simplest approach to comprehending it. Ammonia has been commonly converted to less hazardous substances either in the form of nitrate or nitrogen gas. Ammonia has been converted into nitrite by ammonia-oxidizing bacteria and further reduced to nitrate by nitrite-oxidizing bacteria in aerobic conditions. Denitrification takes place in an anoxic phase and nitrate is converted into nitrogen gas. It is challenging to remove ammonia by employing technologies that do not incur particularly high costs. Thus, this review paper is focused on biofilm reactors that utilize the nitrification process. Many research publications and patents on biofilm wastewater treatment have been published. However, only a tiny percentage of these projects are for full-scale applications, and the majority of the work was completed within the last few decades. The physicochemical approaches such as ammonia adsorption, coagulation-flocculation, and membrane separation, as well as conventional biological treatments including activated sludge, microalgae, and bacteria biofilm, are briefly addressed in this review paper. The effectiveness of biofilm reactors in removing ammonia was compared, and the microbes that effectively remove ammonia were thoroughly discussed. Overall, biofilm reactors can remove up to 99.7% ammonia from streams with a concentration in range of 16-900 mg/L. As many challenges were identified for ammonia removal using biofilm at a commercial scale, this study offers future perspectives on how to address the most pressing biofilm issues. This review may also improve our understanding of biofilm technologies for the removal of ammonia as well as polishing unit in wastewater treatment plants for the water reuse and recycling, supporting the circular economy concept.

Exploiting Biofilm Characteristics to Enhance Biological Nutrient Removal in Wastewater Treatment Plants

Biological treatments are integral processes in wastewater treatment plants (WWTPs). They can be carried out using sludge or biofilm processes. Although the sludge process is effective for biological wastewater systems, it has some drawbacks that make it undesirable. Hence, biofilm processes have gained popularity, since they address the drawbacks of sludge treatments, such as the high rates of sludge production. Although biofilms have been reported to be essential for wastewater, few studies have reviewed the different ways in which the biofilm properties can be explored, especially for the benefit of wastewater treatment. Thus, this review explores the properties of biofilms that can be exploited to enhance biological wastewater systems. In this review, it is revealed that various biofilm properties, such as the extracellular polymeric substances (EPS), quorum sensing (Qs), and acylated homoserine lactones (AHLs), can be enhanced as a sustainable and cost-effective strategy to enhance the biofilm. Moreover, the exploitation of other biofilm properties such as the SOS, which is only reported in the medical field, with no literature reporting it in the context of wastewater treatment, is also recommended to improve the biofilm technology for wastewater treatment processes. Additionally, this review further elaborates on ways that these properties can be exploited to advance biofilm wastewater treatment systems. A special emphasis is placed on exploiting these properties in simultaneous nitrification and denitrification and biological phosphorus removal processes, which have been reported to be the most sensitive processes in biological wastewater treatment.

Removal of azimsulfuron and zoxamide using a tapered variable diameter biological fluidized bed combined with electrochemistry: Mass fraction division, energy metabolism activity and carbon emissions

The performance of the combination system of tapered variable diameter biological fluidized bed (TVDBFB) with electrochemistry (EC) was evaluated for removing azimsulfuron and zoxamide under different temperatures and influent concentrations. Maximum removal efficiency of azimsulfuron and zoxamide could reach 94% and 98% under higher influent concentration (about 780 mg/L). As temperature decreased from 32 ℃ to 8 ℃, the mS_e increased from 48% to 56%, and the mS_o and mS_xv decreased from 30% to 22% and 27% to 24%, respectively. As the influent COD equivalent concentration of azimsulfuron and zoxamide enhanced from 260 mg/L to 780 mg/L, the K_d increased from 0.06 d^-1 to 0.23 d^-1. Temperature and influent concentration were main influencing factors of DHA, ATP and ETS. Increasing aeration in TVDBFB and HRT in EC under shock conditions could improve azimsulfuron and zoxamide removal efficiency, however, it was also accompanied by higher carbon emissions.

Comparison of nitrogen removal efficiency and microbial characteristics of modified two-stage A/O, A2/O and SBR processes

The low temperature of sewage in north China results in low performance of biological treatment at municipal wastewater treatment plants (MWTPs), especially in biological nitrogen removal. A modified two-stage A/O process with an embedded biofilm was proposed to enhance nitrogen removal. The operation performance of a pilot test was compared with an A²/O and SBR process at existing MWTPs to investigate the resistance to low temperature. The microbial communities for the three processes were compared based on the metagenomics results of 16sDNA high-throughput sequencing from activated sludge. The modified A/O resulted in a higher average removal of COD (90.12%) than A²/O (85.23%) and SBR (83.03%), especially of small-molecule organic compounds (< 500 Da) and macromolecular refractory organics (> 5 k Da); the TN removal rate of A2/O, SBR and the modified A/O was also increased from 74.47%, 70.63% and 78.46%, respectively. High-throughput sequencing revealed increased microbial diversity and an abundance of denitrifying functional bacteria was observed in the modified A/O process at low temperatures. The abundance of nitrite oxidation bacteria (NOB) including Nitrosomonas and Nitrospira, the amount was 1.76% and 2.34% in modified A/O, respectively, whereas NOB only accounted for 1.82% in A²/O and 1.35% in SBR.

A novel low temperature aerobic technology with electrochemistry for treating pesticide wastewater: Compliance rate, mathematical models, economic and environmental benefit analysis

In this study, a novel combination system of the tapered variable diameter biological fluidized bed (TVDBFB) with electrochemistry (EC) has been developed and its performances are investigated at different seasons. The results showed that the COD removal efficiency of TVDBFB increased from 61% to 67% and compliance rate increased from 84% to 88% when the carrier packing rate increased from 15% to 30% and temperature was 12 ℃. However, COD removal efficiency and compliance rate increased to 87% and 100% when EC was a post treatment unit. The mathematical models could fit well with the attached biomass, which can be applied to reflect and predict the biomass per unit carrier under different conditions, and the EC removal of COD follow the first-order reaction kinetic model. The economic and environmental benefit analysis indicated that TVDBFB and EC were feasible for treating pesticide wastewater.