Insights into biofilm carriers for biological wastewater treatment processes: Current state-of-the-art, challenges, and opportunities

Journey of the swift nitrogen transformation: Unveiling comammox from discovery to deep understanding

COMplete AMMonia OXidizer (comammox) refers to microorganisms that have the function of oxidizing NH4+ to NO3- alone. The discovery of comammox overturned the two-step theory of nitrification in the past century and triggered many important scientific questions about the nitrogen cycle in nature. This comprehensive review delves into the origin and discovery of comammox, providing a detailed account of its detection primers, clades metabolic variations, and environmental factors. An in-depth analysis of the ecological niche differentiation among ammonia oxidizers was also discussed. The intricate role of comammox in anammox systems and the relationship between comammox and nitrogen compound emissions are also discussed. Finally, the relationship between comammox and anammox is displayed, and the future research direction of comammox is prospected. This review reveals the metabolic characteristics and distribution patterns of comammox in ecosystems, providing new perspectives for understanding nitrogen cycling and microbial ecology. Additionally, it offers insights into the potential application value and prospects of comammox.

Delignified porous wood as biofilm support for 1,4-dioxane-degrading bacterial consortium

Delignified porous wood samples were used as carriers for biofilm formation of a bacterial consortium with the ability to degrade 1,4-dioxane (DX). The delignification treatment of the natural wood resulted in higher porosity, formation of macropores, increase in surface roughness and hydrophilicity of the treated wood pieces. These superior properties of two types of treated carriers (respectively, A and B) compared to the untreated wood resulted in 2.19 ± 0.52- and 2.66 ± 0.23-fold higher growth of biofilm. Moreover, analysis of the fatty acid profiles indicated an increase in proportion of the saturated fatty acids during the biofilm formation, characterising an enhancement in rigidity and hydrophobicity of the biofilms. DX initial concentration of 100 mg/L was completely degraded (detection limit 0.01 mg/L) in 24 and 32 h using the treated A and B woods, while only 25.84 ± 5.95% was removed after 32 h using the untreated wood. However, fitting the DX biodegradation data to the Monod model showed a lower maximum specific growth rate for biofilm (0.0276 ± 0.0018 1/h) versus planktonic (0.0382 ± 0.0024 1/h), because of gradual accumulation of inactive cells in the biofilm. Findings of this study can contribute to the knowledge of biofilm formation regarding the physical/chemical properties of biofilm carriers and be helpful to the ongoing research on bioremediation of DX.

Coupling of gene regulation and carrier modification manipulates bacterial biofilms as robust living catalysts

The biofilm of an engineered strain is limited by slow growth and low yield, resulting in an unsatisfactory ability to resist external stress and promote catalytic efficiency. Here, biofilms used as robust living catalysts were manipulated through dual functionalized gene regulation and carrier modification strategies. The results showed that gene overexpression regulates the autoinducer-2 activity, extracellular polymeric substance content and colony behavior of Escherichia coli, and the biofilm yield of csgD overexpressed strains increased by 79.35 % compared to that of the wild type strains (p < 0.05). In addition, the hydrophilicity of polyurethane fibres modified with potassium dichromate increased significantly, and biofilm adhesion increased by 105.80 %. Finally, the isoquercitrin yield in the catalytic reaction of the biofilm reinforced by the csgD overexpression strain and the modified carrier was 247.85 % higher than that of the untreated group. Overall, this study has developed engineered strains biofilm with special functions, providing possibilities for catalytic applications.

Remediation of biochar-supported effective microorganisms and microplastics on multiple forms of heavy metals in eutrophic lake

In mineral-rich areas, eutrophic lakes are at risk of HMs pollution. However, few papers focused on the repair of HMs in eutrophic environment. Our study analyzed multiple forms of HMs, pore structure and microbial responses in the water-sediment system of eutrophic lake treated with biochar, Effective Microorganisms (EMs) or/and microplastics (MPs). As biochar provided an ideal carrier for EMs, the remediation of biochar-supported EMs (BE) achieved the greatest repairment that improved the bacterial indexes and greatly decreased the most HMs in various forms across the water-sediment system, and it also reduced metal mobility, bioavailability and ecological risk. The addition of aged MPs (MP) stimulated the microbial activity and significantly reduced the HMs levels in different forms due to the adsorption of biofilms/EPS adhered on MPs, but it increased metals mobility and ecological risks. The strong adsorption and high mobility of aged MPs would increase enrichment of HMs and cause serious ecological hazards. The incorporation of BE and MP (MBE) also greatly reduced the HMs in full forms, which was primarily ascribed to the adsorption of superfluous biofilms/EPS, but it distinctly depressed the microbial activity. The single addition of biochar and EMs resulted in the inability of HMs to be adsorbed due to the preferentially adsorption of dissolved nutrients and the absence of effective carrier, respectively. In the remediation cases, the remarkable removal of HMs was principally accomplished by the adsorption of HMs with molecular weight below 100 kDa, especially 3 kDa ∼100 kDa, which had higher specific surfaces and abundant active matters, resulting in higher adsorption onto biofilms/EPS.

Distribution characteristics of antibiotic resistance genes and microbial diversity in the inshore aquaculture area of Wenchang, Hainan, China

The rapid development of marine aquaculture has led to the increased use and release of antibiotics into the marine environment, consequently contributing to the emergence of antibiotic resistance. Information on antibiotic resistance in nearshore marine aquaculture areas remains limited, and research on the microbial composition and potential hosts of antibiotic resistance genes (ARGs) in marine aquaculture areas is scarce. This study used SmartChip real-time fluorescent quantitative PCR and qPCR to quantitatively analyze 44 ARGs and 10 mobile genetic elements (MGEs) genes in 12 sampling points in the nearshore aquaculture area of Wenchang. High-throughput sequencing of 16S rRNA was used to study microbial diversity in the study area, to clarify the correlation between ARGs, MGEs, and microbial diversity, and to determine the possible sources and potential hosts of ARGs. The results showed that a total of 37 ARGs and 8 MGEs were detected in the study area. The detection rate of 9 ARGs (aac(6')-Ib(aka aacA4)-02, catA1, cmlA, cfr, sul1, sul2, sulA/folP-01, tetC, tetX) was 100 %. The absolute abundance of ARGs in the 12 sampling points ranged from 2.75 × 107 to 3.79 × 1010 copies·L-1, and the absolute abundance of MGEs was 1.30 × 105 to 2.54 × 107 copies·L-1, which was relatively high compared to other research areas. ARGs and MGEs were significantly correlated, indicating that MGEs play an important role as a mediator in the spread of ARGs. At the phylum level, Proteobacteria and Cyanobacteria were the dominant bacteria in the study area, with HIMB11 and unidentifiedChloroplast being the dominant levels, respectively. Network analysis of ARGs and microorganisms (genus level) revealed that Cognatishimia, Thalassobius, Aestuariicoccus, Thalassotalea, and Vibrio were significantly correlated with multiple ARGs and were the main potential hosts of ARGs in the nearshore waters of Wenchang.

Optimizing waste molasses utilization to enhance electron transfer via micromagnetic carriers: Mechanisms and high-nitrate wastewater denitrification performance

The biological denitrification of high-nitrate wastewater (HNW) is primarily hindered by insufficient carbon sources and excessive nitrite accumulation. In this study, micromagnetic carriers with varying micromagnetic field (MMF) strengths (0.0, 0.3, 0.6, 0.9 mT) were employed to enhance the denitrification of HNW using waste molasses (WMs) as a carbon source. The results revealed that 0.6 mT MMF significantly improved the total nitrogen removal (TN) efficiency at 96.3%. A high nitrate (NO3--N) removal efficiency at 99.3% with a low nitrite (NO2--N) accumulation at 25.5 mg/L was achieved at 0.6 mT MMF. The application of MMF facilitated the synthesis of adenosine triphosphate (ATP) and stimulated denitrifying enzymes (e.g., nitrate reductase (NAR), nitrite reductase (NIR), and nitric oxide reductase (NOR)), which thereby promoting denitrification. Moreover, the effluent chemical oxygen demand (COD), tryptophan and fulvic-like substances exhibited their lowest levels at 0.6 mT MMF. Analysis through 16S ribosomal ribonucleic acid gene sequencing indicated a significant enrichment of denitrifying bacteria including Castellaniella Klebsiella under the influence of MMF. Besides, the proliferation of Acholeplasma, Klebsiella and Proteiniphilum at 0.6 mT MMF promoted the hydrolysis and acidification of WMs. This study offers new insights into the enhanced utilization of WMs and the denitrification of HNW through the application of MMF.

Treatment of high-strength saline bilge wastewater by four pilot-scale aerobic moving bed biofilm reactors and comparison of the microbial communities

Four Pilot-scale Moving Bed Biofilm Reactors (MBBRs) were operated for the treatment of real, saline, bilge wastewater. The MBBRs were connected in pairs to create two system configurations with different filling ratios (20%, 40%) and were operated in parallel. The inflow organic loading rate (OLR) varied from 3.6 ± 0.2 to 7.8 ± 0.6 g COD L-1 d-1, salinity was >15 ppt and three hydraulic residence times (HRTs) were tested 48, 30 and 24 h. In both systems, the first-stage bioreactors (R1 and R3) eliminated the higher part of the organic load (57%-65%). The second-stage bioreactors (R2 and R4) removed an additional fraction (18%-31%) of the organic load received by the effluent of R1 and R3, respectively. The microbial communities of the influent wastewater, suspended, and attached biomass were determined using 16S rRNA gene amplicon sequencing analysis. The evolution of the microbial communities was investigated and compared over the different operational phases. The microbial communities of the biofilm presented higher diversity and greater stability in composition over time, while the suspended biomass exhibited intense and rapid changes in the dominance of genera. Proteobacteria, Bacteroidetes and Firmicutes were highly present in the biofilm. The genera Celeribacter, Novispirillum, Roseovarius (class: Alphaproteobacteria) and Formosa (class: Flavobacteriia) were highly present during all operational phases. Principal Component Analysis (PCA) was used to identify similarities between samples, exhibiting high relation of samples according to the series of the bioreactor (1st, 2nd).

Weak magnetic carriers reduce nitrite accumulation and boost denitrification at high nitrate concentrations by enriching functional bacteria and enhancing electron transfer

Biological denitrification is the dominant method for NO3- removal from wastewater, while high NO3- leads to NO2- accumulation and inhibits denitrification performance. In this study, different weak magnetic carriers (0, 0.3, 0.6, 0.9 mT) were used to enhance biological denitrification at NO3- of 50-2400 mg/L. The effect of magnetic carriers on the removal and mechanism of denitrification of high NO3- was investigated. The results showed that 0.6 and 0.9 mT carriers significantly enhanced the TN removal efficiency (>99%) and reduced the accumulation of NO2- (by > 97%) at NO3- of 1200-2400 mg/L 0.6 and 0.9 mT carriers stimulated microbial electron transport by improving the abundances of coenzyme Q-cytochrome C reductase (by 4.44-23.30%) and cytochrome C (by 2.90-16.77%), which contributed to the enhanced elimination of NO3- and NO2-. 0.6 and 0.9 mT carriers increased the activities of NAR (by 3.74-37.59%) and NIR (by 5.01-8.24%). The abundance of narG genes in 0.6 and 0.9 mT was 1.47-2.35 and 1.38-1.75 times that of R1, respectively, and the abundance of nirS genes was 1.49-2.83 and 1.55-2.39 times that of R1, respectively. Denitrifying microorganisms, e.g., Halomonas, Thauera and Pseudomonas were enriched at 0.6 and 0.9 mT carriers, which benefited to the advanced denitrification performance. This study suggests that weak magnetic carriers can help to enhance the biological denitrification of high NO3- wastewater.

Tracing and utilizing nitrogen loss in wastewater treatment: The trade-off between performance improvement, energy saving, and carbon footprint reduction

Biological nitrogen removal is widely applied to reduce the discharge of inorganic nitrogen and mitigate the eutrophication of receiving water. However, nitrogen loss is frequently observed in wastewater treatment systems, yet the underlying principle and potential enlightenment is still lacking a comprehensive discussion. With the development and application of novel biological technologies, there are increasing achievement in the deep understanding and mechanisms of nitrogen loss processes. This article reviews the potential and novel pathways of nitrogen loss, occurrence mechanisms, influential factors, and control strategies. A survey of recent literature showed that 3%∼73% of nitrogen loss beyond the nitrogen budget can be ascribed to the unintentional presence of simultaneous nitrification/denitrification, partial nitrification/anammox, and endogenous denitrification processes, under low dissolved oxygen (DO) and limited available organic carbon source at aerobic conditions. Key influential parameters, including DO, aeration strategies, solid retention time (SRT), hydraulic retention time (HRT), temperature and pH, significantly affect both the potential pathways of nitrogen loss and its quantitative contribution. Notably, the widespread and spontaneous growth of anammox bacteria is an important reason for ammonia escape at anaerobic/anoxic conditions, leading to 7%∼78% of nitrogen loss through anammox pathway. Moreover, the unwanted nitrous oxide (N2O) emission should also be considered as a key pathway in nitrogen loss. Future development of new nitrogen removal technologies is proposed to suppress the generation of harmful nitrogen losses and reduce the carbon footprint of wastewater treatment by controlling key influential parameters. Transforming "unintentional observation" to "intentional action" as high-efficiency and energy-efficient nitrogen removal process provides a new approach for the development of wastewater treatment.

Biofilm reactors for the treatment of used water in space:potential, challenges, and future perspectives

Water is not only essential to sustain life on Earth, but also is a crucial resource for long-duration deep space exploration and habitation. Current systems in space rely on the resupply of water from Earth, however, as missions get longer and move farther away from Earth, resupply will no longer be a sustainable option. Thus, the development of regenerative reclamation water systems through which useable water can be recovered from "waste streams" (i.e., used waters) is sorely needed to further close the loop in space life support systems. This review presents the origin and characteristics of different used waters generated in space and discusses the intrinsic challenges of developing suitable technologies to treat such streams given the unique constrains of space exploration and habitation (e.g., different gravity conditions, size and weight limitations, compatibility with other systems, etc.). In this review, we discuss the potential use of biological systems, particularly biofilms, as possible alternatives or additions to current technologies for water reclamation and waste treatment in space. The fundamentals of biofilm reactors, their advantages and disadvantages, as well as different reactor configurations and their potential for use and challenges to be incorporated in self-sustaining and regenerative life support systems in long-duration space missions are also discussed. Furthermore, we discuss the possibility to recover value-added products (e.g., biomass, nutrients, water) from used waters and the opportunity to recycle and reuse such products as resources in other life support subsystems (e.g., habitation, waste, air, etc.).

Polydopamine and calcium functionalized fiber carrier for enhancing microbial attachment and Cr(VI) resistance

The formation of biofilm determines the performance and stability of biofilm system. Increasing the hydrophilicity of the carrier surface could efficiently accelerate the attachment and growth of microorganisms. Here, the surface of polypropylene (PP) fiber carrier was modified with polydopamine (PDA) and calcium (Ca(II)) to enhance microbial attachment and toxicity resistance. The results of surface characteristic confirmed the self-polymerization of PDA and the chelation mechanism of Ca(II). Subsequently, the biofilm formation experiments were conducted in sequencing batch biofilm reactors using both normal and chromium-containing wastewater. The biofilm on the surface of the modified carrier exhibited better nitrogen removal and Cr(VI) reduction ability. The biomass of the modified carrier was significantly increased, and the maximum microbial attachment amounts in normal wastewater and chrome-containing wastewater were 1153.34 and 511.78 mg/g carrier, respectively. Furthermore, the confocal laser scanning microscope (CLSM) indicated that the modified carrier coated with PDA and Ca(II) were both biocompatible, and the cell activity was significantly increased. 16S rRNA sequencing results showed that the modified carrier efficiently enriched both denitrification bacteria (Thauera and Flavobacterium) and chrome-reducing bacteria (Simplicispira and Arenimonas) to improve system stability and Cr(VI) resistance. Microbial phenotype prediction based on BugBase analysis further verified the enrichment effect of modified carriers on microorganisms responsible for biofilm formation and oxidative stress resistance. Overall, this work proposed a novel functional carrier that could provide references for advancing the application of biofilm systems in wastewater treatment.

Controllable and biocompatible 3D bioprinting technology for microorganisms: Fundamental, environmental applications and challenges

3D bioprinting is a new 3D manufacturing technology, that can be used to accurately distribute and load microorganisms to form microbial active materials with multiple complex functions. Based on the 3D printing of human cells in tissue engineering, 3D bioprinting technology has been developed. Although 3D bioprinting technology is still immature, it shows great potential in the environmental field. Due to the precise programming control and multi-printing pathway, 3D bioprinting technology provides a high-throughput method based on micron-level patterning for a wide range of environmental microbiological engineering applications, which makes it an on-demand, multi-functional manufacturing technology. To date, 3D bioprinting technology has been employed in microbial fuel cells, biofilm material preparation, microbial catalysts and 4D bioprinting with time dimension functions. Nevertheless, current 3D bioprinting technology faces technical challenges in improving the mechanical properties of materials, developing specific bioinks to adapt to different strains, and exploring 4D bioprinting for intelligent applications. Hence, this review systematically analyzes the basic technical principles of 3D bioprinting, bioinks materials and their applications in the environmental field, and proposes the challenges and future prospects of 3D bioprinting in the environmental field. Combined with the current development of microbial enhancement technology in the environmental field, 3D bioprinting will be developed into an enabling platform for multifunctional microorganisms and facilitate greater control of in situ directional reactions.

Biodegradation of 1,4-dioxane in a continuous-flow bioelectrochemical reactor by biofilm of Pseudonocardia dioxanivorans CB1190 and microbial community on conductive carriers

Bioelectrochemical degradation is an environmentally friendly, cost-effective and controllable way of providing electron acceptor to the microorganisms. A two-chamber continuous-flow bioelectrochemical reactor (BER) was developed in this study. The objective was to investigate the potential for enhancing the bioelectrochemical degradation of 1,4-dioxane (DX) by Pseudonocardia dioxanivorans CB1190 (CB1190) and microbial community biofilm on conductive and non-conductive carriers in low potentials (1.0-1.2 V) and currents (<2 mA). In the case of CB1190, biodegradation experiments at 1.0 V did not result in any observable change in DX removal efficiency (32.63 ± 2.48%) compared to the 0.0 V (31.69 ± 2.33%). However, the removal efficiency was much higher at 1.2 V (59.08 ± 0.86%). The higher removal at 1.2 V was attributed to an increase in dissolved oxygen (DO) concentration from 3.77 ± 0.33 mg/L at 0.0 V to 5.40 ± 0.11 mg/L at 1.2 V, which resulted from water electrolysis. In the case of microbial community, on the other hand, DX removal efficiency increased at 1.0 V (30.98 ± 1.10%) compared to 0.0 V (23.40 ± 1.02%) that can be attributed to a simultaneous increase in microbial activity from 2389 ± 118.5 ngATP/mgVSS at 0.0 V to 2942 ± 109 ngATP/mgVSS at 1.0 V. Analysis of the changes in microbial composition indicated enrichment of Alistipes and Lutispora at 1.0 V due to the ability of these genera to directly transfer electrons with conductive surface. On the other hand, no change was observed in the microbial community in the case of non-conductive carriers. Results of this study showed that electro-assisted biodegradation of DX at low potentials is possible through two different mechanisms (oxygen production and direct electron transfer with electrode) which makes this technique flexible and cost-effective. The novelty of this work lies in exploring the use of electrical assistance to enhance the biodegradation of DX in the presence of CB1190 and the microbial community. This study more specifically investigated lower potential than required water electrolysis potential, allowing microorganisms to be stimulated through mechanisms unrelated to oxygen generation.

Effects of regular zooplankton supplement on the bacterial communities and process performance of biofilm for wastewater treatment

Biofilm processing technologies were widely used for wastewater treatment due to its advantages of low cost and easy management. However, the aging biofilms inevitably decrease the purification efficiency and increase the sludge production, which limited the widely application of biofilms technologies in rural area. In this study, we proposed a novel strategy by introducing high-trophic organisms to prey on low-trophic organisms, and reduce the aged biofilms and enhance treatment efficiencies in rural wastewater treatment. The effect of three typical zooplankton (Paramecium, Daphnia, and Rotifer) supplement on the purification efficiency and biofilm properties in the contact oxidation process were investigated, and the reaction conditions were optimized by an orthogonal experiment. Under optimal conditions, the biofilms weight decreased 67.6%, the oxygen consumption rate of biofilms increased 9.4%, and wastewater treatment efficiency was obviously increased after zooplankton supplement. Microbial sequencing results demonstrated that the zooplankton optimize the contact oxidation process by altering the bacterial genera mainly Diaphorobacter, Thermomonas, Alicycliphilus and Comamonas. This research provides insight into mechanism of the zooplankton supplement in biological contact oxidation process and provides a feasible strategy for improving the rural sewage treatment technology.

A mini-review on indigenous microbial biofilm from various wastewater for heavy-metal removal - new trends

Biofilm, as a form of the microbial community in nature, represents an evolutionary adaptation to the influence of various environmental conditions. In nature, the largest number of microorganisms occur in the form of multispecies biofilms. The ability of microorganisms to form a biofilm is one of the reasons for antibiotic resistance. The creation of biofilms resistant to various contaminants, on the other hand, improves the biological treatment process in wastewater treatment plants. Heavy metals cannot be degraded, but they can be transformed into non-reactive and less toxic forms. In this process, microorganisms are irreplaceable as they interact with the metals in a variety of ways. The environment polluted by heavy metals, such as wastewater, is also a source of undiscovered microbial diversity and specific microbial strains. Numerous studies show that biofilm is an irreplaceable strategy for heavy metal removal. In this review, we systematize recent findings regarding the bioremediation potential of biofilm-forming microbial species isolated from diverse wastewaters for heavy metal removal. In addition, we include some mechanisms of action, application possibilities, practical issues, and future prospects.

Towards an understanding of the factors controlling bacterial diversity and activity in semi-passive Fe- and As-oxidizing bioreactors treating arsenic-rich acid mine drainage

Semi-passive bioreactors based on iron and arsenic oxidation and coprecipitation are promising for the treatment of As-rich acid mine drainages. However, their performance in the field remains variable and unpredictable. Two bioreactors filled with distinct biomass carriers (plastic or a mix of wood and pozzolana) were monitored during 1 year. We characterized the dynamic of the bacterial communities in these bioreactors, and explored the influence of environmental and operational drivers on their diversity and activity. Bacterial diversity was analyzed by 16S rRNA gene metabarcoding. The aioA genes and transcripts were quantified by qPCR and RT-qPCR. Bacterial communities were dominated by several iron-oxidizing genera. Shifts in the communities were attributed to operational and physiochemical parameters including the nature of the biomass carrier, the water pH, temperature, arsenic, and iron concentrations. The bioreactor filled with wood and pozzolana showed a better resilience to disturbances, related to a higher bacterial alpha diversity. We evidenced for the first time aioA expression in a treatment system, associated with the presence of active Thiomonas spp. This confirmed the contribution of biological arsenite oxidation to arsenic removal. The resilience and the functional redundancy of the communities developed in the bioreactors conferred robustness and stability to the treatment systems.

Study on the performance of a new type of combined packing biofilm reactor treating wastewater

The present work investigates the performance of a biofilm reactor filled with a new type of combined packing used to treat wastewater and explores a new technology approach for the application of coral sand and waste non-woven fabric. The combined packing was made of coral sand and waste non-woven fabric, which was used as a biofilm carrier to treat sewage. The experimental results showed that the removal efficiencies of COD, NH4+-N and TN in the biofilm reactor containing the combined packing were 92.9%, 72.9% and 63.2%, respectively. The maximum removal efficiencies of COD, NH4+-N and TN in the biofilm reactor containing single packing were 89.0%, 63.4% and 55.2%, respectively. The properties of the combined packing were characterized by Fourier Transform Infrared (FTIR), specific surface area, SEM and dehydrogenase activity. Infrared analysis showed that there were hydroxyl, carboxyl and carbonyl groups on the surface of coral sand and non-woven fabric which were beneficial for biofilm growth and wastewater treatment. The large pores in the interior of coral sand and non-woven fabric could provide a comfortable environment for microbes to grow and reproduce. The dehydrogenase activity of the biofilm on the surface of coral sand in the third biofilm reactor was 49.91 μgTF·g-1·h-1, which was significantly higher than that of the other two biofilm reactors. The new type of combined packing is suitable for biofilm carriers with low cost, which can be applied to actual sewage treatment projects. This study provides a reference for the practical application of the technique.

Ceramsite made from remediated soil: A risk assessment of its potential role serving as urban street cushion

To promote the reuse of remediated soil (RS) and facilitate the cleanup of rainwater in sponge city, we investigated the effects of ceramsite made from RS serving as urban street cushion. Ceramsite was prepared by RS or pollution-free soil (PS) and showed no difference in physical properties. Compared with gravel, ceramsite had purification effects on effluents, reducing the content of chemical oxygen demand, total nitrogen, and ammoniacal nitrogen. However, the content of total phosphorus and the concentration of Cr(VI) and arsenic slightly increased in ceramsite groups, inferring potential risk. Microbial community analysis proved that ceramsite promoted microbial growth and increased microbial diversity. A long-term risk assessment indicated that ceramsite was good at fixing heavy metals during leaching process. Taken together, ceramsite prepared from RS could serve as excellent urban street cushion with little potential risk to surroundings.

Improved simultaneous nitrification-denitrification in fixed-bed baffled bioreactors treating mariculture wastewater: Performance and microbial community behaviors

As mariculture develops, wastewater treatment becomes crucial. In this study, fixed-bed baffled reactors (FBRs) packed with carbon fiber (CFBR) or polyurethane (PFBR) as biofilm carriers were used for mariculture wastewater treatment. Under salinity shocks between 0.10 and 30.00 g/L, the reactors showed efficient and stable nitrogen removal capacities, and the maximum NH₄⁺-N removal rates were 107.31 and 105.42 mg/(L·d) for CFBR and PFBR, respectively, with an initial NH₄⁺-N concentration of 120.00 mg/L. Further, in the independent aerobic chambers of the FBRs for nitrogen removal, taxa enrichment varied depending on the biofilm carrier, and the assembly process was more deterministic in CFBR than in PFBR. Two distinct clusters representing the spatial distribution of the adhering and deposited sludge in CFBR and the front and rear compartments in PFBR were noted. Furthermore, microbial interactions were more numerous and stable in CFBR. These findings improve the application prospects of FBRs in mariculture wastewater treatment.

Enhanced aquaculture wastewater treatment in a biofilm reactor filled with sponge/ferrous oxalate/biochar composite (Sponge-C2FeO4@NBC) biocarriers: Performance and mechanism

Fabricating low-cost and efficient biofilm carriers for moving bed biofilm reactors in wastewater treatment is crucial for achieving environmental sustainability. Herein, a novel sponge biocarrier doped with NaOH-loaded biochar and nano ferrous oxalate (sponge-C₂FeO₄@NBC) was prepared and evaluated for nitrogenous compounds removal from recirculating aquaculture systems (RAS) wastewater by stepwise increasing ammonium nitrogen (NH₄⁺-N) loading rates. The prepared NBC, sponge-C₂FeO₄@NBC, and matured biofilms were characterized using SEM, FTIR, BET, and N₂ adsorption-desorption techniques. The results reveal that the highest removal rates of NH₄⁺-N reached 99.28 ± 1.3% was yielded by the bioreactor filled with sponge-C₂FeO₄@NBC, with no obvious nitrite (NO₂^--N) accumulation in the final phase. The reactor packed with sponge-C₂FeO₄@NBC biocarrier had the highest relative abundance of functional microorganisms responsible for nitrogen metabolism than in the control reactor, confirmed from 16S rRNA gene sequencing analysis. Our study provides new insights into the newly developed biocarriers for enhancing RAS biofilters treatment performance in keeping water quality within the acceptable level for the rearing of aquatic species.

Mariculture affects antibiotic resistome and microbiome in the coastal environment

Antibiotics are increasingly used and released into the marine environment due to the rapid development of mariculture, resulting in spread of antibiotic resistance. The pollution, distribution, and characteristics of antibiotics, antibiotic resistance genes (ARGs) and microbiomes have been investigated in this study. Results showed that 20 antibiotics were detected in Chinese coastal environment, with predominance of erythromycin-H₂O, enrofloxacin and oxytetracycline. In coastal mariculture sites, antibiotic concentrations were significantly higher than in control sites, and more types of antibiotics were detected in the South than in the North of China. Residues of enrofloxacin, ciprofloxacin and sulfadiazine posed high resistance selection risks. β-Lactam, multi-drug and tetracycline resistance genes were frequently detected with significantly higher abundance in the mariculture sites. Of the 262 detected ARGs, 10, 26, and 19 were ranked as high-risk, current-risk, future-risk, respectively. The main bacterial phyla were Proteobacteria and Bacteroidetes, of which 25 genera were zoonotic pathogens, with Arcobacter and Vibrio in particular ranking in the top10. Opportunistic pathogens were more widely distributed in the northern mariculture sites. Phyla of Proteobacteria and Bacteroidetes were the potential hosts of high-risk ARGs, while the conditional pathogens were associated with future-risk ARGs, indicating a potential threat to human health.

Removal performance and dissolved organic matter biodegradation characteristics in advection ecological permeable dam reactor

In this present study, an advection ecological permeable dam (AEPD) based on a biofilm reactor was established to investigate pollution control performance and dissolved organic matter (DOM) bio-degradation. The AEPD achieved optimal efficiency-chemical oxygen demand, 6-53 mg/L; total nitrogen concentration, 1.47-6.89 mg/L; total phosphorus concentration, 0.53-3.93 mg/L, and increases in values for ultraviolet-visible parameters-SUVA₂₅₄, from 0.392 to 0.673-1.438; E4/E6, from 1.09 to 1.11-1.26; A_240-400, from 12.06 to 13.09-19.95; and A_253-203, from 0.03 to 0.04-0.23. This showed that DOM degradation promoted its humification, aromatisation, and unsaturation as well as increased the number of polar functional groups in the organic aromatic rings of DOM. Synchronous fluorescence and parallel factor analyses indicated that AEPD could effectively degrade tyrosine-like and tryptophan-like compounds, which showed the most significant decrease in fluorescence intensity. Additionally, AEPD displayed some stable dominant bacterial genera (e.g. Proteobacteria_unclassified, Bacteroidetes_unclassified, Gemmobacter, Pseudofulvimonas, Flavobacterium, Pseudomonas, and Nitrospira), although their relative abundance differed under variable hydraulic loading rates. This research provided further technical support for the application of AEPD in the treatment of water environment pollution.

Electrospinning micro-nanofibers immobilized aerobic denitrifying bacteria for efficient nitrogen removal in wastewater

Electrospinning micro-nanofibers with exceptional physicochemical properties and biocompatibility are becoming popular in the medical field. These features indicate its potential application as microbial immobilized carriers in wastewater treatment. Here, aerobic denitrifying bacteria were immobilized on micro-nanofibers, which were prepared using different concentrations of polyacrylonitrile (PAN) solution (8%, 12% and 15%). The results of diameter distribution, specific surface area and average pore diameter indicated that 15% PAN micro-nanofibers with tighter surface structure were not suitable as microbial carriers. The bacterial load results showed that the cell density (OD₆₀₀) and total protein of 12% PAN micro-nanofibers were 107.14% and 106.28% higher than those of 8% PAN micro-nanofibers. Subsequently, the 12% PAN micro-nanofibers were selected for aerobic denitrification under the different C/N ratios (1.5-10), and stable performance was obtained. Bacterial community analysis further manifested that the micro-nanofibers effectively immobilized bacteria and enriched bacterial structure under the high C/N ratios. Therefore, the feasibility of micro-nanofibers as microbial carriers was confirmed. This work was of great significance for promoting the application of electrospinning for microbial immobilization in wastewater treatment.

Mainstream deammonification at ambient temperature treating real sewage by a plug-flow fixed-bed reactor based on zeolite/tourmaline-modified polyurethane carriers

A plug-flow fixed-bed reactor (PFBR) with zeolite/tourmaline-modified polyurethane (ZTP) carriers (PFBR_ZTP) was constructed to realize mainstream deammonification for real domestic sewage treatment. The PFBR_ZTP and PFBR were operated for 111 days treating aerobically pretreated sewage in parallel. A higher nitrogen removal rate of 0.12 kg N·(m³·d)^-1 was achieved in PFBR_ZTP despite lowering the temperature (16.8-19.7 ℃) and fluctuating water quality. Meanwhile, it was indicated that anaerobic ammonium oxidation dominated (64.0 ±13.2%) in PFBR_ZTP, by nitrogen removal pathway analysis and high anaerobic ammonium-oxidizing bacteria (AnAOB) activity (2.89 mg N·(g VSS·h)^-1). And, the lower protein/polysaccharides (PS) ratio further indicated a better biofilm structure in PFBR_ZTP owing to a higher abundance of microorganisms relevant to PS and cryoprotective EPS secretion. Furthermore, partial denitrification was an important nitrite supply process in PFBR_ZTP based on low AOB activity/AnAOB activity ratio, higher Thauera abundance and a remarkably positive correlation between Thauera abundance and AnAOB activity.

Photocatalytic degradation of reactive dyes using natural photo-smart pigment-A novel approach for waste water re-usability

The present study is aimed at an efficient photocatalytic degradation of industrially important reactive dyes using phycocyanin extract as a photocatalyst. The percentage of dye degradation was evidenced by a UV-visible spectrophotometer and FT-IR analysis. The degraded water was checked for its complete degradation by varying pH from 3 to 12. Furthermore, the degraded water was also analyzed for water quality parameters and was found to meet industrial wastewater standards. The calculated irrigation parameters like magnesium hazard ratio, soluble sodium percentage, and Kelly's ratio of degraded water were within the permissible limits, which enables its reusability in irrigation, aquaculture, as industrial coolants, and domestic applications. The calculated correlation matrix shows that the metal influences various macro-, micro-, and non-essential elements. These results suggest that the non-essential element lead can be effectively reduced by increasing all the other micronutrients and macronutrients under study except sodium metal.

The role of anthraquinone-2-sulfonate on intra/extracellular electron transfer of anaerobic nitrate reduction

To improve the electron (e^-) transfer efficiency, exogenous redox mediators (RMs) were usually employed to enhance the denitrification efficiency due to the electron shuttling. Previous studies were mainly focused on how to improve the extracellular electron transfer (EET) by exogenous RMs. However, the intracellular electron transfer (IET), another crucial e^- transfer pathway, of biological denitrification was scarcely reported, especially for the relationship between the denitrification and IET. In this study, Coenzyme Q, Complexes I, II and III were determined as the core components in the IET chain of denitrification by using four specific respiration chain inhibitors (RCIs). Anthraquinone-2-sulfonate (AQS) partially recovered the IET of denitrification from NO₃^--N to N₂ gas when the RCIs were added. Specifically, the generations of N₂ gas were improved by 9.68%-18.25% in the experiments with RCIs and AQS, comparing to that with RCIs. nrfA gene was not detected by reverse transcription-polymerase chain reaction, suggesting that Klebsiella oxytoca strain could not conduct dissimilatory nitrate reduction to ammonium. Nitrate assimilation was considered as the main NH₄⁺-N formation way of K. oxytoca strain. The two e^- transfer pathways of denitrification were constructed and the roles of AQS on the IET and EET of denitrification were specifically discussed. The results of this study provided a better understanding of the e^- transfer pathways of denitrification, and suggested a potential practical use of exogenous RM on bio-treatment of nitrate-containing wastewater.

Phosphorus-rich biochar modified with Alcaligenes faecalis to promote U(VI) removal from wastewater: Interfacial adsorption behavior and mechanism

Phosphorus-rich biochar (PBC) has been extensively studied due to its significant adsorption effect on U(VI). However, the release of phosphorus from PBC into solution decreases its adsorption performance and reusability and causes phosphorus pollution of water. In this study, Alcaligenes faecalis (A. faecalis) was loaded on PBC to produce a novel biocomposite (A/PBC). After adsorption equilibrium, phosphorus released into solution from PBC was 2.32 mg/L, while it decreased to 0.34 mg/L from A/PBC (p < 0.05). The U(VI) removal ratio of A/PBC reached nearly 100%, which is 13.08% higher than that of PBC (p < 0.05), and it decreased only by 1.98% after 5 cycles. When preparing A/PBC, A. faecalis converted soluble phosphate into insoluble metaphosphate minerals and extracellular polymeric substances (EPS). And A. faecalis cells accumulated through these metabolites and formed biofilm attached to the PBC surface. The adsorption of metal cations on phosphate further contributed to phosphorus fixation in the biofilm. During U(VI) adsorption by A/PBC, A. faecalis synthesize EPS and metaphosphate minerals by using the internal components of PBC, thus increasing the abundance of acidic functional groups and promoting U(VI) adsorption. Hence, A/PBC can be a green and sustainable material for U(VI) removal from wastewater.

Superior nitrogen removal and efficient sludge reduction via partial nitrification-anammox driven by addition of sludge fermentation products for real sewage treatment

Efficient retention and enrichment of anammox bacteria (AnAOB) are essential for the application of municipal wastewater anammox. Herein, an innovative process for highly enriching AnAOB within suspended carrier was developed in a single-stage anaerobic/oxic/anoxic reactor with 5.5 % carrier filling ratio for real sewage. Addition of sludge fermentation products promoted stable maintenance of partial nitrification (nitrite accumulation rate > 90.0 %) and achieved efficient external sludge reduction (27.6-37.9 %). Continuous nitrite supply and carrier addition promoted AnAOB enrichment (2.4 × 1011 gene copies/g dry sludge). Candidatus Brocadia was the predominant bacteria in carriers (18.6 %). The average effluents of total inorganic nitrogen (TIN) and NH4+-N were 1.9 and 0.8 mg/L with removal rates of 97.0 % and 98.7 %. In the anoxic stage, TIN removal rate reached 71.5 %, and the proportion of anammox to nitrogen removal accounted for 82.7 %. This study broadens the application of mainstream sewage anammox and the resource utilization of waste activated sludge.

Characterization of Biofilm Microbiome Formation Developed on Novel 3D-Printed Zeolite Biocarriers during Aerobic and Anaerobic Digestion Processes

Background: Aerobic or anaerobic digestion is involved in treating agricultural and municipal waste, and the addition of biocarriers has been proven to improve them further. We synthesized novel biocarriers utilizing zeolites and different inorganic binders and compared their efficiency with commercially available biocarriers in aerobic and anaerobic digestion systems. Methods: We examined BMP and several physicochemical parameters to characterize the efficiency of novel biocarriers on both systems. We also determined the SMP and EPS content of synthesized biofilm and measured the adherence and size of the forming biofilm. Finally, we characterized the samples by 16S rRNA sequencing to determine the crucial microbial communities involved. Results: Evaluating BMP results, ZSM-5 zeolite with bentonite binder emerged, whereas ZSM-5 zeolite with halloysite nanotubes binder stood out in the wastewater treatment experiment. Twice the relative frequencies of archaea were found on novel biocarriers after being placed in AD batch reactors, and >50% frequencies of Proteobacteria after being placed in WWT reactors, compared to commercial ones. Conclusions: The newly synthesized biocarriers were not only equally efficient with the commercially available ones, but some were even superior as they greatly enhanced aerobic or anaerobic digestion and showed strong biofilm formation and unique microbiome signatures.

Enhanced nitrogen removal in mainstream deammonification systems at ambient temperature by novel modified carriers and differentiation of microbial community transformation

Zeolite-modified polyurethane (ZP) carriers and zeolite/tourmaline-modified polyurethane (ZTP) carriers were proposed to enhance mainstream deammonification. The system with ZTP carriers was rapidly established in 28 days with a nitrogen removal rate (NRR) of 0.150 kg N·(m³·d)^-1. Moreover, the facilitative effect of tourmaline was suggested by the highest humic acid peak intensity and more balanced potential activity. Besides, SEM-EDS analysis revealed carrier characteristic improvement was achieved in both novel carriers while maintaining an excellent spatial structure. Moreover, the microbial analysis suggested that both modified carriers support the substrate supply to anaerobic ammonium oxidizing bacteria (AnAOB) by enhancing dissimilatory nitrate reduction to ammonium and partial denitrification under nitrate accumulation conditions. Nevertheless, the ZTP system had a greater advantage over maintaining the original AnAOB (Candidatus Jettenia) and ammonium oxidizing bacteria (Nitrosomonas) abundance. Overall, this study provides ZTP carriers with great potential for facilitating the establishment of mainstream deammonification at full-scale WWTPs.

A review on algal-bacterial symbiosis system for aquaculture tail water treatment

Aquaculture is one of the fastest growing fields of global food production industry in recent years. To maintain the ecological health of aquaculture water body and the sustainable development of aquaculture industry, the treatment of aquaculture tail water (ATW) is becoming an indispensable task. This paper discussed the demand of environmentally friendly and cost-effective technologies for ATW treatment and the potential of algal-bacterial symbiosis system (ABSS) in ATW treatment. The characteristics of ABSS based technology for ATW treatment were analyzed, such as energy consumption, greenhouse gas emission, environmental adaptability and the possibility of removal or recovery of carbon, nitrogen and phosphorus as resource simultaneously. Based on the principle of ABSS, this paper introduced the key environmental factors that should be paid attention to in the establishment of ABSS, and then summarized the species of algae, bacteria and the proportion of algae and bacteria commonly used in the establishment of ABSS. Finally, the reactor technologies and the relevant research gaps in the establishment of ABSS were reviewed and discussed.

Mixotrophic denitrification processes in basalt fiber bio-carriers drive effective treatment of low carbon/nitrogen lithium slurry wastewater

Lithium battery slurry wastewater was successfully treatedby using basalt fiber (BF) bio-carriers in a biological contact oxidation reactor. This resulted in a significant reduction of COD (93.3 ± 0.5 %) and total nitrogen (77.4 ± 1.0 %) at 12 h of HRT and dissolved oxygen (DO) of 0-1 mg/L. The modified Stover-Kincannon model indicated that the total nitrogen removal rate was 4.462 kg/m3/d in R-BF while the substrate maximum specific reaction rate (qmax) in the Monod model was 0.323 mg-N/mgVSS/d. A stable internal environment was established within the bio-nest. Metataxonomic analysis revealed the presence of denitrification and decarbonization bacteria, combined heterotrophic nitrification-aerobic denitrification bacteria, nitrite-oxidizing bacteria, and ammonia-oxidizing bacteria. Functional analysis displayed changes related to (aerobic)chemoheterotrophy, nitrogen respiration, nitrate reduction, respiration/denitrification of nitrite, and nitrate in R-BF. The study proposes a novel approach to achieve denitrification for the treatment of lithium slurry wastewater at low C/N conditions.

Immobilization of Biomass Materials for Removal of Refractory Organic Pollutants from Wastewater

In the field of environmental science and engineering, microorganisms, enzymes and algae are promising biomass materials that can effectively degrade pollutants. However, problems such as poor environmental adaptability, recycling difficulties, and secondary pollution exist in the practical application of non-immobilized biomass materials. Biomass immobilization is a novel environmental remediation technology that can effectively solve these problems. Compared with non-immobilized biomass, immobilized biomass materials have the advantages of reusability and stability in terms of pH, temperature, handling, and storage. Many researchers have studied immobilization technology (i.e., methods, carriers, and biomass types) and its applications for removing refractory organic pollutants. Based on this, this paper reviews biomass immobilization technology, outlines the mechanisms and factors affecting the removal of refractory organic pollutants, and introduces the application of immobilized biomass materials as fillers for reactors in water purification. This review provides some practical references for the preparation and application of immobilized biomass materials and promotes further research and development to expand the application range of this material for water purification.

Global review of macrolide antibiotics in the aquatic environment: Sources, occurrence, fate, ecotoxicity, and risk assessment

The extensive use of macrolide antibiotics (MCLs) has led to their frequent detection in aquatic environments, affecting water quality and ecological health. In this study, the sources, global distribution, environmental fate, ecotoxicity and global risk assessment of MCLs were analyzed based on recently published literature. The results revealed that there are eight main sources of MCLs in the water environment. These pollution sources resulted in MCL detection at average or median concentrations of up to 3847 ng/L, and the most polluted water bodies were the receiving waters of wastewater treatment plants (WWTPs) and densely inhabited areas. Considering the environmental fate, adsorption, indirect photodegradation, and bioremoval may be the main attenuation mechanisms in natural water environments. N-demethylation, O-demethylation, sugar and side chain loss from MCL molecules were the main pathways of MCLs photodegradation. Demethylation, phosphorylation, N-oxidation, lactone ring hydrolysis, and sugar loss were the main biodegradation pathways. The median effective concentration values of MCLs for microalgae, crustaceans, fish, and invertebrates were 0.21, 39.30, 106.42, and 28.00 mg/L, respectively. MCLs induced the generation of reactive oxygen species, that caused oxidative stress to biomolecules, and affected gene expression related to photosynthesis, energy metabolism, DNA replication, and repair. Moreover, over 50% of the reported water bodies represented a medium to high risk to microalgae. Further studies on the development of tertiary treatment technologies for antibiotic removal in WWTPs, the combined ecotoxicity of antibiotic mixtures at environmental concentration levels, and the development of accurate ecological risk assessment models should be encouraged.

Experimental and optimization studies on phycoremediation of dairy wastewater and biomass production efficiency of Chlorella vulgaris isolated from Ganga River, Haridwar, India

Dairy wastewaters (DWW) are rich in several pollutants, including high biochemical oxygen demand (BOD) and chemical oxygen demand (COD), and their unsafe disposal may cause damage to the environment. In this study, Chlorella vulgaris (identified as NIES:227 strain based on 28s rRNA sequencing) was isolated from the freshwater habitat of the Ganga River at Haridwar, India, and further tested for its efficacy in treating DWW. The phycoremediation experiments were conducted using three different DWW concentrations (0, 50, and 100%), operating temperatures (20, 25, and 30 °C), and light intensities (2000, 3000, and 4000 lx) using response surface methodology. Results showed that after 16 days of experiments, a significant (P < 0.05) reduction in BOD (96.65%) and COD (87.50%) along with a maximum biomass production of 1.757 g/L was achieved using 57.72% of dairy industry wastewater, 24.16 °C of reactor temperature, and 3874.51 lx of light intensity. The RSM models had coefficient of determination (R²) values above 0.9459 with a minimum difference between measured and predicted responses. Therefore, the findings of this study suggest that the isolated C. vulgaris can be effectively used to treat dairy wastewater along with significant production of algal biomass which can be further used for the generation of low-cost biofuel and other materials.

Simultaneous nitrification-denitrification in biofilm systems for wastewater treatment: Key factors, potential routes, and engineered applications

Simultaneous nitrification-denitrification (SND) is an advantageous bioprocess that allows the complete removal of ammonia nitrogen through sequential redox reactions leading to nitrogen gas production. SND can govern nitrogen removal in single-stage biofilm systems, such as the moving bed biofilm reactor and aerobic granular sludge system, as oxygen gradients allow the development of multilayered biofilms including nitrifying and denitrifying bacteria. Environmental and operational conditions can strongly influence SND performance, biofilm development and biochemical pathways. Recent advances have outlined the possibility to reduce the carbon and energy consumption of the process via the "shortcut pathway", and simultaneously remove both N and phosphorus under specific operational conditions, opening new possibilities for wastewater treatment. This work critically reviews the factors influencing SND and its application in biofilm systems from laboratory to full scale. Operational strategies to enhance SND efficiency and hints to reduce nitrous oxide emission and operational costs are provided.

Nitrogen removal characteristics of biofilms in each area of a full-scale AAO oxidation ditch process

Plastic carriers were installed in different areas of a full-scale anaerobic/anoxic/aerobic (AAO) oxidation ditch process, and the dynamics of nitrogen removal, biofilm morphologies, and microorganism species were investigated. The results showed that the biofilm at the front of the aerobic area (dissolved oxygen [DO] = 0.93 mg L^-1) provided the best denitrification, with specific nitrate and nitrite reduction rates of 10.16 and 3.78 mg·(g·h)^-1, respectively. The biofilm in the middle of the aerobic area (DO = 1.27 mg L^-1) exhibited the best nitrification performance, with a maximum specific ammonia oxidation rate of 3.21 mg·(g·h)^-1. The biofilm at the end of the aerobic area (DO = 0.01 mg L^-1) exhibited the highest anammox potential with a maximum specific anammox rate of 0.67 mg·(g·h)^-1. No correlation was observed between the specific nitrogen removal rates and abundance of nitrogen-removing microorganisms at the genus level. Biofilm denitrification during the process was primarily completed by heterotrophic denitrifying bacteria (Thauera, Acinetobacter, Hyphomicrobium, and Thermomonas). Aerobic denitrifying bacteria (0.19% Thauera and 0.34% Hyphomicrobium) were identified as the main denitrifying bacteria in the middle of the aerobic area. The dominant nitrifying microorganisms in the middle of the aerobic area were Nitrosomonas (0.50%) and Nitrospira (1.04%). A biofilm in the end of the aerobic area exhibited specific anammox potential, which may have been related to the dominance of 0.024% Candidatus Brocadia. Kinetic analysis revealed that adding plastic carriers to the front and middle of the aerobic area contributed to stable nitrogen removal efficiency.

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.

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.

Manipulating Bacterial Biofilms Using Materiobiology and Synthetic Biology Approaches

Bacteria form biofilms on material surfaces within hours. Biofilms are often considered problematic substances in the fields such as biomedical devices and the food industry; however, they are beneficial in other fields such as fermentation, water remediation, and civil engineering. Biofilm properties depend on their genome and the extracellular environment, including pH, shear stress, and matrices topography, stiffness, wettability, and charges during biofilm formation. These surface properties have feedback effects on biofilm formation at different stages. Due to emerging technology such as synthetic biology and genome editing, many studies have focused on functionalizing biofilm for specific applications. Nevertheless, few studies combine these two approaches to produce or modify biofilms. This review summarizes up-to-date materials science and synthetic biology approaches to controlling biofilms. The review proposed a potential research direction in the future that can gain better control of bacteria and biofilms.

Medium-chain fatty acids production from carbohydrates-rich wastewater through two-stage yeast biofilm processes without external electron donor addition: Biofilm development and pH impact

The production of medium-chain fatty acids (MCFAs) is considered promising for carbon resource recovery from waste streams. However, a large quantity of external electron donors are often required, causing great cost and environmental impact. Therefore, in this study, a two-stage technology was developed to produce MCFAs from carbohydrate-rich wastewater without external electron donor addition, with the biofilm development and pH impact being explored. Stage I aimed at converting organics into ethanol and a yeast biofilm reactor is innovatively applied. The results showed that the yeast biofilm could quickly form on carriers with steady-state thickness reaching 50-200 μm. However, the attachment of yeast biofilm was weak at the initial stage so that the violent turbulence should be avoided during operation. The polyurethane foam was the most suitable for yeast biofilm development among the tested carriers, as evidenced by the highest ethanol production, accounting for 74.2% of soluble organics. The Nakaseomyces was the main fungal genus in the steady-state biofilm, while lactic acid bacteria were also developed, resulting in lactate and acetate production. In Stage II, the yeast biofilm reactor effluent was applied for MCFA production at different pH (5-8). However, the MCFA production selectivity was significantly affected by pH, with 65.2% at pH of 5 but decreasing substantially to 3.0% at pH of 8. Both the microbial and electron transfer efficiency analysis suggested that mildly acidic pH can promote the electron transfer from ethanol toward the chain elongation process instead of its excessive oxidation. Thus, if conditions of online extraction or microbial tolerance permit, a lower pH should be recommended for Stage II in the developed technology as well as other ethanol-based MCFA production process. This is a conceptual study that eliminated external electron donor addition in MCFAs production and provide a sustainable and reliable way in carbon resources recovery.

An assessment of the purification performance and resilience of sponge-based aerobic biofilm reactors for treating polluted urban surface waters

Pollutants are continuously released into surface waters, which decrease the dissolved oxygen (DO) concentration and leads to the formation of black-odorous water, especially in slow-flowing urban lakes and enclosed small ponds. In situ treatment by artificial aeration or water cycling, coupled with biofilm, can address this problem without occupying large amounts of land. In this study, we designed a novel sponge-based aerobic biofilm reactor (SABR) and evaluated its performance in purifying urban surface water under different conditions. In the urban lake water treatment, the continuous inflow results revealed that the NH₄⁺-N and NO₂^--N concentrations in the effluent were stable and remained lower than 0.10 mg/L and 0.05 mg/L, respectively. Abrupt increases in the NH₄⁺-N and NO₂^--N concentrations in the influent and sudden increases in the NH₄⁺-N and NO₂^--N concentrations in the effluent were observed, and only 4 to 8 days were required for the concentrations to decline below 0.10 mg/L and 0.05 mg/L, respectively. Increases in the polyurethane sponge filling ratios in the SABRs can reduce the DO concentration but do not affect NH₄⁺-N removal. When no biodegradable organic matter was present in the enclosed surface water, the degradation time of NH₄⁺-N from 14.22 to 0.10 mg/L was only 9 days when SABRs were combined with water cycling, which was shorter than the time needed by water cycling alone (16 days), and most of the NH₄⁺-N was converted to NO₃^--N. When massive amounts of biodegradable organic matter were present in the enclosed surface water, 22 days were required to remove the NH₄⁺-N when SABRs were combined with water cycling. Our results indicated that organic matter could be used as a carbon source to eliminate the produced NO₃^--N in SABRs. Therefore, the newly developed bioreactor provides an effective approach for treating N-polluted urban surface waters.

Anaerobic Reactor Filling for Phosphorus Removal by Metal Dissolution Method

A commonly indicated drawback of anaerobic wastewater treatment is the low effectiveness of phosphorus removal. One possibility to eliminate this disadvantage is the implementation of active fillings that contain admixtures of metals, minerals, or other elements contributing to wastewater treatment intensification. The aim of the research was to present an active filling produced via microcellular extrusion technology, and to determine its properties and performance in anaerobic wastewater treatment. The influence of copper and iron admixtures on the properties of the obtained porous extrudate in terms of its functional properties was also examined. The Barus effect increased with the highest content of the blowing agent in the material from 110 ± 12 to 134 ± 14. The addition of metal powders caused an increase in the extrudate density. The modification of PVC resulted in the highest porosity, amounting to 47.0% ± 3.2%, and caused the tensile strength to decrease by about 50%. The determined values ranged from 211.8 ± 18.3 MPa to 97.1 ± 10.0 MPa. The use of the filling in anaerobic rectors promoted COD removal, intensified biogas production, and eliminated phosphorus with an efficiency of 64.4% to 90.7%, depending on the type of wastewater and applied technological parameters.

Enhancement of wastewater treatment performance using 3D printed structures: A major focus on material composition, performance, challenges, and sustainable assessment

In order to enhance the performance and sustainability of wastewater treatment technologies, researchers are showing keen interest in the development of novel materials which can overcome the drawbacks associated with conventional materials. In this context, 3D printing gained significant attention due to its capability of fabricating complex geometrics using different material compositions. The present review focuses on recent advancements of 3D printing applications in various physicochemical and biological wastewater treatment techniques. In physicochemical treatment methods, substantial research has been aimed at fabricating feed spacers and other membrane parts, photocatalytic feed spacers, catalysts, scaffolds, monoliths, and capsules. Several advantages, such as membrane fouling mitigation, enhanced degradation efficiency, and recovery and reusability potential, have been associated with the aforementioned 3D printed materials. While in biofilm-based biological treatment methods, the use of 3D printed bio-carriers has led to enhanced mass transfer efficiency and microbial activities. Moreover, the application of these bio-carriers has shown better removal efficiency of chemical oxygen demand (∼90%), total nitrogen (∼73%), ammonia nitrogen (95%), and total phosphorous (∼100%). Although the removal efficiencies were comparable with conventional carriers, 3D printed carriers led to ∼40% reduction in hydraulic retention time, which could significantly save capital and operational expenditures. This review also emphasizes the challenges and sustainability aspects of 3D printing technology and outlines future recommendations which could be vital for further research in this field.

Unravelling capability of two-stage thermophilic anaerobic membrane bioreactors for high organic loading wastewater: Effect of support media addition and irreversible fouling

This study investigated the effects of adding polyvinyl alcohol (PVA) beads on the performance of methanogenic reactors and the fouling behavior of a two-stage thermophilic anaerobic membrane bioreactor (ThAnMBR) for treating wastewater at a feed chemical oxygen demand (COD) of 10 g/L. The PVA-added methanogenic reactor exhibited stable operation performance and offered a relatively low volatile fatty acid concentration effluent with a higher COD removal than the system without PVA addition. The predominant microbial communities in both methanogenic reactors were similar and were assigned to the genus Methanosaeta, followed by Clostridia, which was the predominant genus in the hydrolytic reactor. Ultrafiltration in the PVA-added system offered higher effluent quality and lower fouling resistance. The system was able to operate with hydraulically removable fouling, without any chemical cleaning requirements; however, an elevated flux caused the system to suffer from hydraulically irreversible fouling. PVA beads exhibit their structural stability over long-term operation.

Combination Therapies for Biofilm Inhibition and Eradication: A Comparative Review of Laboratory and Preclinical Studies

Microbial biofilms are becoming increasingly difficult to treat in the medical setting due to their intrinsic resistance to antibiotics. To combat this, several biofilm dispersal agents are currently being developed as treatments for biofilm infections. Combining biofilm dispersal agents with antibiotics is emerging as a promising strategy to simultaneously disperse and eradicate biofilms or, in some cases, even inhibit biofilm formation. Here we review studies that have investigated the anti-biofilm activity of some well-studied biofilm dispersal agents (e.g., quorum sensing inhibitors, nitric oxide/nitroxides, antimicrobial peptides/amino acids) in combination with antibiotics from various classes. This review aims to directly compare the efficacy of different combination strategies against microbial biofilms and highlight synergistic treatments that warrant further investigation. By comparing across studies that use different measures of efficacy, we can conclude that treating biofilms in vitro and, in some limited cases in vivo, with a combination of an anti-biofilm agent and an antibiotic, appears overall more effective than treating with either compound alone. The review identifies the most promising combination therapies currently under development as biofilm inhibition and eradication therapies.

Quantification of human enteric viruses as alternative indicators of fecal pollution to evaluate wastewater treatment processes

We investigated the potential use and quantification of human enteric viruses in municipal wastewater samples of Winnipeg (Manitoba, Canada) as alternative indicators of contamination and evaluated the processing stages of the wastewater treatment plant. During the fall 2019 and winter 2020 seasons, samples of raw sewage, activated sludge, effluents, and biosolids (sludge cake) were collected from the North End Sewage Treatment Plant (NESTP), which is the largest wastewater treatment plant in the City of Winnipeg. DNA (Adenovirus and crAssphage) and RNA enteric viruses (Pepper mild mottle virus, Norovirus genogroups GI and GII, Rotavirus Astrovirus, and Sapovirus) as well as the uidA gene found in Escherichia coli were targeted in the samples collected from the NESTP. Total nucleic acids from each wastewater treatment sample were extracted using a commercial spin-column kit. Enteric viruses were quantified in the extracted samples via quantitative PCR using TaqMan assays. Overall, the average gene copies assessed in the raw sewage were not significantly different (p-values ranged between 0.1023 and 0.9921) than the average gene copies assessed in the effluents for DNA and RNA viruses and uidA in terms of both volume and biomass. A significant reduction (p-value ≤ 0.0438) of Adenovirus and Noroviruses genogroups GI and GII was observed in activated sludge samples compared with those for raw sewage per volume. Higher GCNs of enteric viruses were observed in dewatered sludge samples compared to liquid samples in terms of volume (g of sample) and biomass (ng of nucleic acids). Enteric viruses found in gene copy numbers were at least one order of magnitude higher than the E. coli marker uidA, indicating that enteric viruses may survive the wastewater treatment process and viral-like particles are being released into the aquatic environment. Viruses such as Noroviruses genogroups GI and GII, and Rotavirus were detected during colder months. Our results suggest that Adenovirus, crAssphage, and Pepper mild mottle virus can be used confidently as complementary viral indicators of human fecal pollution.

Bacterial biofilm and extracellular polymeric substances in the moving bed biofilm reactor for wastewater treatment: A review

Among the several biofilm-based bioreactors, moving bed biofilm reactors (MBBR) have been extensively used for wastewater treatment due to low operational costs, technical feasibility, and stability. Biofilm forming strains, e.g., Stenotrophomonas maltophila DQ01, achieved 94.21% simultaneous nitrification and denitrification (SND) and 94.43% removal of total nitrogen (TN) at a cycle time of 7 h, and a biofilm consortium consisting of Chryseobacteriumsp. andRhodobactersp. achieved 86.8% removal of total organic carbon (TOC) at hydraulic retention time (HRT) of 24 h using lab-scale MBBR. Modifications in the surface properties of the biocarrier materials achieved 99.5 ± 1.1% chemical oxygen demand (COD) and 93.6 ± 2.3% NH₄⁺-N removal, significantly higher than the conventional commercial carrier. This review article summarizes the application of MBBR technology for wastewater treatment. The importance of bacterial biofilm and extracellular polymeric substances (EPS), anammox-n-DAMO coupled processes, and carrier surface modifications in MBBR technology have also been discussed.