Efficiency of various biofilm carriers and microbial interactions with substrate in moving bed-biofilm reactor for environmental wastewater treatment

Integration of moving bed biofilm reactor and gravity-driven membrane bioreactor for decentralized domestic wastewater treatment: Efficiency and mechanistic insights

This study investigated the coupling of a moving bed biofilm reactor (MBBR) with a gravity-driven membrane bioreactor (GDMBR) for the long-term treatment of decentralized domestic wastewater. The results indicated that the introduction of MBBR significantly improved the stable flux of GDMBR (by 8 % - 22 %) and enhanced its resistance to the shock loading of influent quality. Such improvements were attributed to the reduction in extracellular polymeric substances (EPS) (by 30 % - 46 %), positive modifications to the membrane biofilm, and improvements in microbial richness and community composition. Compared to GDMBR control, the start-up period of MBBR-GDMBR systems was reduced by 6-15 days, owing to the beneficial effects of MBBR-derived microorganisms, which promoted microbial evolution within the GDMBR membrane biofilm, thereby accelerating the stabilization of filtration performance. Overall, this study provides valuable insights into shortening the start-up period of the GDMBR process, enhancing its resistance to external shock loads, and improving flux levels.

Rapid formation of partial denitrification biofilm using gas-liquid separation membrane as carrier: Performance and mechanism

Partial denitrification (PD) can ensure stable supply of electron acceptors for anaerobic ammonia oxidation, and biofilm is an effective method to prevent biomass loss, which are crucial for stable operation of PD. In this study, hydrophobic hollow-fiber gas-liquid separation membranes were placed in a denitrification sequencing batch reactor, and dense biofilms were formed within just 3 days. Confocal laser microscopy showed the preferential attachment of the protein (PN) content in extracellular polymeric substances (EPS) to the membrane surface, followed by exopolysaccharides. Further analyses showed the decrease in the types of signal molecules from six to two (i.e., C4-HSL, C6-HSL) due to negative pressure operation. Importantly, the concentration of C4-HSL increased dramatically with the increase in PN concentration, suggesting that negative pressure promoted the synthesis of C4-HSL signal molecules, which further mediated the secretion of PN for biofilm formation. In addition, biofilm formation was accompanied by nitrite accumulation, leading to successful achievement of PD. Furthermore, 60 % of nitrate-to-nitrite transformation ratio was obtained even when COD/N was increased from 4.5 to 5.0 and influent nitrate concentration was reduced to 25 mg/L. This confirmed the stability of PD, which was mainly attributed to a change in the microbial community and a decrease in nitrite reductase (Nir) activity, with microorganisms enriched through the gas-liquid separation operation exhibiting low Nir activity. This study provides a new method for rapid formation of biofilm for wastewater treatment and stable operation of PD.

Improving the shock resistance of anaerobic digestion under demand-oriented biogas production mode by using converter steel slag powder

Introducing flexible biogas production (FB) can result in instantaneous high-shock loads for anaerobic digestion system, posing risks to the system's stable operation. Steel slag, a typical metallurgical solid waste, has been demonstrated to enhance the buffering capacity of digestion systems, thereby increasing methane production and achieving 'waste treatment using waste'. However, its efficacy under high-shock loads in FB is uncertain. Pulse feeding experiments simulating FB were conducted to analyse the system's impact resistance with steel slag addition and investigate its enhancement mechanisms. The addition of steel slag improved the methane production rate under various shock conditions, with a particularly notable enhancement under concentration shock. This scenario also saw a significant increase in the generation of soluble chemical oxygen demand and its utilization by microorganisms. This can be attributed to the enrichment of hydrolytic bacterial phyla (Firmicutes) and genera (Gelria), with functional gene analysis revealing an increase in genes associated with Fe(III) reduction and CO2-to-methane pathways. The study results indicate that the role of steel slag as an alkaline, iron-rich material enhances system alkalinity, reduces inhibition from H2 partial pressure and boosts hydrogenotrophic methanogen activity, making it suitable as an exogenous enhancer for demand-oriented anaerobic digestion.

High-efficiency nitrogen and phosphorus removal for low C/N rural wastewater using a full-scale multi-stage A2O biofilm reactor combined with horizontal-vertical flow constructed wetlands system

Rural wastewater treatment faces significant challenges in achieving stable effluent quality due to factors such as temperature fluctuations, variations in water quality and quantity, and low carbon-to-nitrogen (C/N) ratios. This study developed a full-scale, non-membrane, multi-stage anaerobic-anoxic-oxic (MSA2O) biofilm reactor integrated with horizontal-vertical flow constructed wetlands (HVCWs), which was operated continuously for approximately 320 days with an average flow of 11.9 m3/d in a rural area of northern China. Key parameters were optimized: hydraulic retention time (HRT) of 21-32 h, aeration rate of 4.0 m3/h, carbon source dosing at 1.25 L/h, PAC dosing at 0.55 L/h, and mixed liquor reflux ratio at 200 %. The system demonstrated high removal efficiencies for COD (74.2 %), NH4+-N (93.4 %), TN (90.6 %), and TP (86.3 %), consistently meeting the class 1A of GB18918-2002, China (COD ≤50 mg/L, NH4+-N ≤ 5 mg/L, TN ≤ 15 mg/L, TP ≤ 0.5 mg/L), even under challenging conditions such as low C/N (3.3) and rainy seasons. More than 70 % of nitrogen and phosphorus were removed in the MSA2O system. Microbial analysis revealed the enrichment of many functional bacteria. Proteobacteria play a key role in denitrification and phosphorus removal. Actinomycetes, Acidobacteria, and Firmicutes to nitrogen fixation and organic matter degradation. Nitrosomonas dominated ammonia oxidation, while Dechloromonas and Accumulibacter significantly contributed to phosphorus uptake. Seasonal variations in microbial diversity enabled consistent and highly efficient nutrient removal. The HVCWs system contributed 16.3 % of total phosphorus removal through selected plant species and phosphorus-absorbing modified ceramsite, ensuring effluent polishing and stability. With low operational costs ($0.12/m3), the integrated system provides an effective and scalable solution for rural wastewater treatment, delivering high-quality effluent with minimal energy consumption.

Benefits of Immobilized Bacteria in Bioremediation of Sites Contaminated with Toxic Organic Compounds

Although bioremediation is considered the most environmentally friendly and sustainable technique for remediating contaminated soil and water, it is most effective when combined with physicochemical methods, which allow for the preliminary removal of large quantities of pollutants. This allows microorganisms to efficiently eliminate the remaining contaminants. In addition to requiring the necessary genes and degradation pathways for specific substrates, as well as tolerance to adverse environmental conditions, microorganisms may perform below expectations. One typical reason for this is the high toxicity of xenobiotics present in large concentrations, stemming from the vulnerability of bacteria introduced to a contaminated site. This is especially true for planktonic bacteria, whereas bacteria within biofilms or microcolonies have significant advantages over their planktonic counterparts. A physical matrix is essential for the formation, maintenance, and survival of bacterial biofilms. By providing such a matrix for bacterial immobilization, the formation of biofilms can be facilitated and accelerated. Therefore, bioremediation combined with bacterial immobilization offers a comprehensive solution for environmental cleanup by harnessing the specialized metabolic activities of microorganisms while ensuring their retention and efficacy at target sites. In many cases, such bioremediation can also eliminate the need for physicochemical methods that are otherwise required to initially reduce contaminant concentrations. Then, it will be possible to use microorganisms for the remediation of higher concentrations of xenobiotics, significantly reducing costs while maintaining a rapid rate of remediation processes. This review explores the benefits of bacterial immobilization, highlighting materials and processes for developing an optimal immobilization matrix. It focuses on the following four key areas: (i) the types of organic pollutants impacting environmental and human health, (ii) the bacterial strains used in bioremediation processes, (iii) the types and benefits of immobilization, and (iv) the immobilization of bacterial cells on various carriers for targeted pollutant degradation.

Physicochemical profiles of mixed ruminal microbes in response to surface tension and specific surface area

Introduction

In ruminants, a symbiotic rumen microbiota is responsible for supporting the digestion of dietary fiber and contributes to health traits closely associated with meat and milk quality. A holistic view of the physicochemical profiles of mixed rumen microbiota (MRM) is not well-illustrated.

Methods

The experiment was performed with a 3 × 4 factorial arrangement of the specific surface area (SSA: 3.37, 3.73, and 4.44 m2/g) of NDF extracted from rice straw and the surface tension (ST: 54, 46, 43, and 36 dyn/cm) of a fermented medium in a fermentation time series of 6, 12, 24, 48 h with three experimental units. Here, we used three rumen-fistulated adult Liuyang black goats as the rumen liquid donors for this experiment.

Results

It was found that increasing SSA decreased the average acetate/propionate ratio (A/P, p < 0.05) and increased the molarity of propionate (p < 0.05). Increasing ST decreased total volatile fatty acid (tVFA) concentration (p < 0.01). Greater SSA increased (p < 0.01) MRM hydrophobicity, whereas increasing ST increased MRM cell membrane permeability (p < 0.01). The neutral detergent fiber digestibility (NDFD, r = 0.937) and tVFA (r = 0.809) were positively correlated with the membrane permeability of MRM.

Discussion

The surface tension of the artificial medium and substrate-specific surface area had a significant influence on MRM's fermentation profiles, hydrophobicity, and permeability. The results suggest that physical environmental properties are key in regulating rumen fermentation function and homeostasis in the gastrointestinal tract ecosystem.

An innovative design and development of up-flow compact constructed wetland for sewage treatment

The growing demand for sustainable sewage treatment requires technologies that overcome the limitations of energy-intensive and chemical-dependent systems. This study presents an innovative solution addressing both environmental and operational challenges with the design and development of an Up-flow Compact Constructed Wetland (UCCW) based Sewage Treatment Plant (STP). This system integrates preliminary, primary, secondary, and tertiary treatment units into a single setup. The performance of UCCW based STP was evaluated over 720 days under different Hydraulic Retention Times (HRTs), considering seasonal variations in both rectangular and circular configurations. The system achieved significant pollutant removal as Total Suspended Solids (96%), Chemical Oxygen Demand (86%), Biochemical Oxygen Demand (90%), Total Nitrogen (70%), Total Phosphorus (65%), and Fecal Coliforms (99%) at a 36-h HRT. These parameters meet discharge standards, except FC, which requires disinfection for safe reuse and recycling. Further, Response Surface Methodology (RSM) and Monte Carle Simulation of UCCW based STP confirmed optimal and reliable performance at a 36-h HRT. Compared to conventional treatment technologies, the UCCW based STP demonstrated higher efficiency, a smaller footprint (1m2/KLD), better operational flexibility, cost-effectiveness, and minimal operation & maintenance to make it sustainable for decentralised treatment.

Dynamics of antibiotic resistance genes and bacterial community structure within substrate biofilms

Biofilms that develop on the surface of substrates are critical for treating wastewater. The accumulation of antibiotic resistance genes (ARGs) within these biofilms is particularly noteworthy. Despite their importance, studies that focus on biofilms attached to substrate surfaces remain scarce. This investigation explored the prevalence and succession of ARGs and microbial dynamics in biofilms on different substrates (ceramic, biomass filter, and steel slag) versus water biofilms over a year. Results showed distinct differences in ARG profiles between water and substrate biofilms. Multidrug ARGs constituted 39.14-46.73% of all ARGs in the substrate biofilms, with macrolide ARGs making up 11.98-14.52%. Seasonal variations influenced the diversity of the ARGs, notably increasing during the spring. The neutral community model suggested that the ARG assembly was dominantly driven by stochastic process. Proteobacteria, Actinobacteria and Campylobacter emerged as the predominant phyla within these biofilms. The microbial community distribution was predominantly influenced by ammonium nitrogen (NH4+-N) (R2 = 0.4113), temperature and total nitrogen (TN). Notably, temperature exerted a critical impact on the microbial community distribution (P = 0.001), identifying it as the principal factor for spatial arrangement. Furthermore, the structural variations of ARGs were primarily driven by total organic carbon (TOC) (R2 = 0.3988), temperature, oxidation-reduction potential (ORP) and NH4+-N. Our findings provided new insights into the optimization of substrate selection and ecological management to manage ARG enrichment, offering a promising strategy for aquatic ecological restoration and pollution control.

Biofilm application for anaerobic digestion: a systematic review and an industrial scale case

Biofilm is a syntrophic community of microorganisms enveloped by extracellular polymeric substances and displays remarkable adaptability to dynamic environments. Implementing biofilm in anaerobic digestion has been widely investigated and applied as it promotes microbial retention time and enhances the efficiency. Previous studies on anaerobic biofilm primarily focused on application in wastewater treatment, while its role has been significantly extended to accelerate the degradation of lignocellulosic biomass, improve gas-liquid mass transfer for biogas upgrading, or enhance resistance to inhibitors or toxic pollutants. This work comprehensively reviewed the current applications of biofilm in anaerobic digestion and focused on impacting factors, optimization strategies, reactor set-up, and microbial communities. Moreover, a full-scale biofilm reactor case from Norway is also reported. This review provides a state of-the- art insight on the role of biofilm in anaerobic digestion.

Chitosan-casein as novel drug delivery system for transferring Phyllanthus emblica to inhibit Pseudomonas aeruginosa

This study investigated the ability of Phyllanthus emblica encapsulated within chitosan-coated casein (CS-casein-Amla) nanoparticles to inhibit the growth of multi-drug-resistant Pseudomonas aeruginosa (P. aeruginosa) bacteria and prevent the formation of biofilms. The MDR strains underwent screening, and the morphological characteristics of the resulting nanoparticles were assessed using SEM, DLS, and FTIR. In addition, the efficacy of encapsulation, stability, and drug release were evaluated. The PpgL, BdlA, and GacA biofilm gene transcription quantities were quantified by quantitative real-time PCR. Simultaneously, the nanoparticles were assessed for their antibacterial and cytotoxic effects using the well diffusion and MTT procedures. CS-casein-Amla nanoparticles with a size of 500.73 ± 13 nm, encapsulation efficiency of 76.33 ± 0.81%, and stability for 60 days at 4 °C (Humidity 30%) were created. The biological analysis revealed that CS-casein-Amla nanoparticles exhibited strong antibacterial properties. This was shown by their capacity to markedly reduce the transcription of PpgL, BdlA, and GacA biofilm genes at a statistically significant value of p ≤ 0.01. The nanoparticles demonstrated decreased antibiotic resistance compared to unbound Amla and CS-casein. Compared to Amla, CS-casein-Amla nanoparticles showed very little toxicity against HDF cells at dosages ranging from 1.56 to 100 µg/mL (p ≤ 0.01). The results highlight the potential of CS-casein-Amla nanoparticles as a significant advancement in combating highly resistant P. aeruginosa. The powerful antibacterial properties of CS-casein-Amla nanoparticles against P. aeruginosa MDR strains, which are highly resistant pathogens of great concern, may catalyze the development of novel antibacterial research approaches.

Enhancement of livestock wastewater treatment by a novel wooden-modified biocarrier

Intensive livestock wastewater poses threat to ecosystem. A novel wooden-modified biocarrier was applied in this study to enhance the livestock wastewater treatment in anoxic-aerobic systems. Compared to the ordinary polyethylene (PE) biocarrier, the novel wooden-modified biocarrier improved the biomass owing to its rough surface and porous side wall, and had better nitrogen removal ability. The biomass of wooden-modified biocarrier was 6.3 ± 1.1 and 36.4 ± 17.0 times that of PE biocarrier in anoxic and aerobic condition, respectively. The removal rates of ammonia nitrogen and total nitrogen of this novel biocarrier on specific biofilm's aera eventually stabilized at 0.64 ± 0.10 and 0.94 ± 0.21 g N/m2/d, respectively. Notably, this wooden-modified biocarrier was conducive to increase nitrogen removal by simultaneous nitrification and denitrification to some extent. The biofilm on novel modified biocarrier had higher extracellular polymeric substances (EPS) contents than activated sludge (AS), and the proportions of polysaccharides (PS) in EPS from biocarrier were more than those from AS. Compared to PE biocarrier and AS, the wooden-modified biocarriers enhanced the enrichment of nitrifying and denitrifying bacteria, and promoted the membrane transport and aerobic nitrogen metabolism. This study confirmed the superiority of wooden-modified biocarrier and provided reference for the treatment of high concentration sewage in full-scale project.

Versatile enhancement for anaerobic moving bed biofilm (AnMBBR) treating pretreated landfill leachate by hydrochar: Energy recovery, greenhouse gas emission reduction and underlying microbial mechanisms

Hydrochars were prepared from fruit peels (HC-1) and vegetable waste (HC-2), and combined with fiber spheres, respectively, to form homogeneous biocompatible carriers, which were used for anaerobic moving bed biofilm reactor (AnMBBR) to enhance anaerobic digestion (AD) performance and energy recovery of landfill leachate treatment. Compared with the control AnMBBR with conventional fiber spheres as carriers, the chemical oxygen demand (COD) removal efficiency of the AnMBBR with HC-2 increased from 75 % to 88 %, methane yield increased from 77.7 mL/g-COD to 155.3 mL/g-COD, and achieved greenhouse gases (GHG) emission reductions of 1.74 t CO2 eq/a during long-term operation. HC-2-fiber sphere biocarriers provided more sites for attached-growth biomass (AGBS) and significantly enhanced the abundance of functional microbial community, with the relative abundance of methanogenic bacteria Methanothrix increased from 0.03 % to over 24.4 %. Moreover, the gene abundance of most the key enzymes encoding the hydrolysis, acidogenesis and methanogenesis pathways were up-regulated with the assistance of HC-2. Consequently, hydrochar-assisted AnMBBR were effective to enhance methanogenesis performance, energy recovery and carbon reduction for high-strength landfill leachate treatment.

Effects of a novel sawdust-modified carrier on performance, bioaccumulation and microbial community of sequencing batch reactor

The impact of a novel sawdust-modified carrier on the performance of aerobic sequencing batch reactor (SBR) was examined. Compared with the conventional polyethylene (PE) carrier, the sawdust-modified carrier had coarse surface and porous side wall, which was beneficial for the rapid formation of biofilm. The biomass of sawdust-modified carrier was 3.4 ± 0.7 times more than those of PE carrier at the end of this study. The biofilm gotten from suspended carrier had higher extracellular polymeric substances (EPS) concentrations than activated sludge (AS). The EPS from biofilm contained higher proportions of polysaccharides compared to those from AS. The SBR with addition of sawdust-modified carrier exhibited higher ammonia nitrogen removal efficiency (84.8%) than the one with addition of conventional PE carrier (73.1%) in a typical cycle at 12 h. The volumetric nitrification rates of modified carrier were higher than those of conventional PE carrier. High throughput sequencing revealed that sawdust-modified carriers exhibited greater microbial richness and diversity compared with traditional PE carriers. Saccharimonadales was the most predominant genus that removed organic matter under aerobic condition, whereas Nitrospira was the dominant nitrifying genus. The present study verifies the advantage of sawdust-modified carrier, which has the potential for the full-scale application in the future.

Biofilm formation and microbial interactions in moving bed-biofilm reactors treating wastewater containing pharmaceuticals and personal care products: A review

The risk of pharmaceuticals and personal care products (PPCPs) has been paid more attention after the outbreak of COVID-19, threatening the ecology and human health resulted from the massive use of drugs and disinfectants. Wastewater treatment plants are considered the final stop to restrict PPCPs from wide spreading into the environment, but the performance of conventional treatment is limited due to their concentrations and characteristics. Previous studies have shown the unreplaceable capability of moving bed-biofilm reactor (MBBR) as a cost-effective method with layered microbial structure for treating wastewater even with toxic compounds. The biofilm community and microbial interactions are essential for the MBBR process in completely degrading or converting types of PPCPs to secondary metabolites, which still need further investigation. This review starts with discussing the initiation of MBBR formation and its influencing parameters according to the research on MBBRs in the recent years. Then the efficiency of MBBRs and the response of biofilm after exposure to PPCPs are further addressed, followed by the bottlenecks proposed in this field. Some critical approaches are also recommended for mitigating the deficiencies of MBBRs based on the recently published publications to reduce the environmental risk of PPCPs. Finally, this review provides fundamental information on PPCPs removal by MBBRs with the main focus on microbial interactions, promoting the MBBRs to practical application in the real world of wastewater treatment.

Nutrients removal in overloaded WWTP by intermittently aerated IFAS: Effects of biofilm carrier and intermittent aeration cycle

Updating of the current Urban Waste Water Treatment Directive (91/271/EEC) will demand stricter regulations for nutrients removal. In this frame, wastewater treatment plants (WWTPs) of small-to-medium potential will face new challenges for achieving process intensification. Integrating intermittent aeration (IA) and integrated fixed-film activated sludge (IFAS) technologies could be a promising solution to meet such requirements. This study analyzed how IA cycles affected nutrients removal in IFAS reactors with different biofilm carriers (e.g., plastic and sponge media). The plants responses to different carbon/nitrogen/phosphorous (C/N/P) ratios were evaluated while operating under low sludge retention time (SRT) to simulate overloaded conditions. A short IA cycle (1 h) with an aeration/not aeration ratio of 2:1 enabled high organic carbon and nitrification performances when operating at high C/N/P (11.8/1/1), whereas low denitrification and phosphorous removal yields were obtained because of the short not-aerated phase. Decreasing C/N ratio (8.8/1/1) without changing the IA cycle resulted in nitrification worsening because of the reduced metabolic kinetics of biofilm. Under such load conditions, a higher IA cycle (2 h) was necessary to improve process performance. A longer not-aerated phase was also positive for denitrification and phosphorous removal because of the establishment of anoxic and anaerobic environments within the bulk and inner biofilm layers. Besides, results suggested that sponge carriers offered advantages over plastic ones, enabling a higher biofilm retention capacity, better nutrient removal, as well as robustness and resilience to operating condition changes. This would result in simpler management systems for implementing the IA process, thus reducing process complexity and costs.

A review on the application of biochar as an innovative and sustainable biocarrier material in moving bed biofilm reactors for dye removal from environmental matrices

Dye decolorization through biological treatment techniques has been gaining momentum as it is based on suspended and attached growth biomass in both batch and continuous modes. Hence, this review focused on the contribution of moving bed biofilm reactors (MBBR) in dye removal. MBBR have been demonstrated to be an excellent technology for pollution extraction, load shock resistance, and equipment size and energy consumption reduction. The review went further to highlight different biocarrier materials for biofilm development this review identified biochar as an innovative and environmentally friendly material produced through the application of different kinds of reusable or recyclable wastes and biowastes. Biochar as a carbonized waste biomass could be a better competitor and environmentally friendly substitute to activated carbon given its lower mass costs. Biochar can be easily produced particularly in rural locations where there is an abundance of biomass-based trash. Given that circular bioeconomy lowers dependency on natural resources by turning organic wastes into an array of useful products, biochar empowers the creation of competitive goods. Thus, biochar was identified as a novel, cost-effective, and long-term management strategy since it brings about several essential benefits, including food security, climate change mitigation, biodiversity preservation, and sustainability improvement. This review concludes that integrating two treatment methods could greatly lead to better color, organic matter, and nutrients removal than a single biological MBBR treatment process.

Wastewater treatment using moving bed biofilm reactor technology: a case study of ceramic industry

Biological approaches and coagulation are frequently used to reduce the chemical oxygen demand (COD) for treatment of ceramic effluent water. The technology known as the moving bed biofilm reactor (MBBR) can accomplish this goal. Further, the process of emulsification-aided innovative MBBR using biosurfactants can be proposed for ceramic effluent treatment. In a step-by-step upgrading scheme, biosurfactants and a consortia of halophilic and halotolerant microbial culture was utilized for the treatment of the effluent water. Over the course of 21 days, a progressive decrease in COD of up to 95.79% was achieved. Over the next 48 h period, the biochemical oxygen demand (BOD) was reduced by 98.3%, while total suspended solids (TSS) decreased by 79.41%. With the use of this innovative MBBR technology, biofilm formation accelerated, lowering the COD, BOD, and TSS levels. This allows treated water to be used for further research on recycling it back into the ceramics sector and repurposing it for agricultural purposes. PRACTITIONER POINTS: Implementation of modified MBBR technology for the treatment of effluent water. Biosurfactants could reduce in the organic and inorganic loads. Increase in MLSS values with COD removal observed. The plant operations without the use of chemical coagulants was effective with biosurfactants. Biofilm formation on carriers was scraped and the presence of surfactin and rhamnolipid was confirmed.

Microbial community analysis of membrane bioreactor incorporated with biofilm carriers and activated carbon for nitrification of urine

The integration of powdered activated carbon and biofilm carriers in a membrane bioreactor (MBR) presents a promising approach to address the challenge of long hydraulic retention time (HRT) for nitrification of hydrolysed urine. This study investigated the effect of the incorporation in the MBR on microbial dynamics, focusing on dominant nitrifying bacteria. The results showed that significant shifts in microbial compositions were observed with the feed transition to full-strength urine and across different sludge growth forms. Remarkably, the nitrite-oxidizing bacteria Nitrospira were highly enriched in the suspended sludge. Simultaneously, ammonia-oxidizing bacteria, Nitrosococcaceae thrived in the attached biomass, showing a significant seven-fold increase in relative abundance compared to its suspended counterpart. Consequently, the incorporated MBR displayed 36% higher nitrification rate and 40% HRT reduction compared to the conventional MBR. This study provides valuable insights on the potential development of household or building scale on-site nutrient recovery from urine to fertiliser.

Fate of the biofilm chips overflowed from a wastewater treatment plant

In February 2018 over 100 millions of polyethylene biofilm chips overflowed from a wastewater treatment plant located at Capaccio Paestum (Italy) and due to the Thyrrhenian Sea currents, in few days they invaded the coasts of Campania, Lazio and Tuscany. During the following months the diffusion involves all the coasts of the western Mediterranean, including Spain, France and Tunisia. Samples of chips were recovered mainly along the Latium coasts (Italy) during the last 6 years. Following the exposure of the biofilm chips to the environmental conditions, the effect of natural weathering on polyethylene have been studied. The following annual decreases were evaluated: thickness 9.5 μm, diameter 18.5 μm and weight 3.7 mg while the average value of the size of all recovered items (n = 60) are: thickness = 2.936 ± 0.0406 mm, diameter = 44.349 ± 0.1266 mm and weight = 1.1593 ± 0.0248 g. Considering the weight loss, it was calculated that the complete mineralization of the disks will occur in 310 years producing about 0.5 tons of microplastics per year. FTIR analysis was used to investigate the change of chemical structure of the polyethylene. The Carbonyl index (CI), Vinyl index (VI) and Hydroxyl normalized absorbance peak were used to evaluate the polymer degradation while Scanning Electron Microscopy (SEM) was used to characterize the surface of the polymer samples. It was observed that erosion/degradation increases with time spent in the environment, above all from the last two years. The static contact angle was always >90° confirming that the surface of the biofilm chip is hydrophilic. The Oxygen/Carbon ratio increase with time: 0.18 and 0.27 has been found for 2018 and 2023 disks respectively confirming the progressive oxidative process. From TGA analysis a slightly reduction of decomposition temperature has been evaluated.

Wastewater Treatment Using Membrane Bioreactor Technologies: Removal of Phenolic Contaminants from Oil and Coal Refineries and Pharmaceutical Industries

Huge amounts of noxious chemicals from coal and petrochemical refineries and pharmaceutical industries are released into water bodies. These chemicals are highly toxic and cause adverse effects on both aquatic and terrestrial life. The removal of hazardous contaminants from industrial effluents is expensive and environmentally driven. The majority of the technologies applied nowadays for the removal of phenols and other contaminants are based on physio-chemical processes such as solvent extraction, chemical precipitation, and adsorption. The removal efficiency of toxic chemicals, especially phenols, is low with these technologies when the concentrations are very low. Furthermore, the major drawbacks of these technologies are the high operation costs and inadequate selectivity. To overcome these limitations, researchers are applying biological and membrane technologies together, which are gaining more attention because of their ease of use, high selectivity, and effectiveness. In the present review, the microbial degradation of phenolics in combination with intensified membrane bioreactors (MBRs) has been discussed. Important factors, including the origin and mode of phenols' biodegradation as well as the characteristics of the membrane bioreactors for the optimal removal of phenolic contaminants from industrial effluents are considered. The modifications of MBRs for the removal of phenols from various wastewater sources have also been addressed in this review article. The economic analysis on the cost and benefits of MBR technology compared with conventional wastewater treatments is discussed extensively.

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.

Anaerobic Membrane Bioreactor (AnMBR) for the Removal of Dyes from Water and Wastewater: Progress, Challenges, and Future Perspectives

The presence of dyes in aquatic environments can have harmful effects on aquatic life, including inhibiting photosynthesis, decreasing dissolved oxygen levels, and altering the behavior and reproductive patterns of aquatic organisms. In the initial phase of this review study, our aim was to examine the categories and properties of dyes as well as the impact of their toxicity on aquatic environments. Azo, phthalocyanine, and xanthene are among the most frequently utilized dyes, almost 70–80% of used dyes, in industrial processes and have been identified as some of the most commonly occurring dyes in water bodies. Apart from that, the toxicity effects of dyes on aquatic ecosystems were discussed. Toxicity testing relies heavily on two key measures: the LC50 (half-lethal concentration) and EC50 (half-maximal effective concentration). In a recent study, microalgae exposed to Congo Red displayed a minimum EC50 of 4.8 mg/L, while fish exposed to Disperse Yellow 7 exhibited a minimum LC50 of 0.01 mg/L. Anaerobic membrane bioreactors (AnMBRs) are a promising method for removing dyes from water bodies. In the second stage of the study, the effectiveness of different AnMBRs in removing dyes was evaluated. Hybrid AnMBRs and AnMBRs with innovative designs have shown the capacity to eliminate dyes completely, reaching up to 100%. Proteobacteria, Firmicutes, and Bacteroidetes were found to be the dominant bacterial phyla in AnMBRs applied for dye treatment. However, fouling has been identified as a significant drawback of AnMBRs, and innovative designs and techniques are required to address this issue in the future.

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.

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.

Boron Derivatives Accelerate Biofilm Formation of Recombinant Escherichia coli via Increasing Quorum Sensing System Autoinducer-2 Activity

Boron is an essential element for autoinducer-2 (AI-2) synthesis of quorum sensing (QS) system, which affects bacterial collective behavior. As a living biocatalyst, biofilms can stably catalyze the activity of intracellular enzymes. However, it is unclear how boron affects biofilm formation in E. coli, particularly recombinant E. coli with intracellular enzymes. This study screened different boron derivatives to explore their effect on biofilm formation. The stress response of biofilm formation to boron was illuminated by analyzing AI-2 activity, extracellular polymeric substances (EPS) composition, gene expression levels, etc. Results showed that boron derivatives promote AI-2 activity in QS system. After treatment with H3BO3 (0.6 mM), the AI-2 activity increased by 65.99%, while boron derivatives increased the biomass biofilms in the order H3BO3 > NaBO2 > Na2B4O7 > NaBO3. Moreover, treatment with H3BO3 (0.6 mM) increased biomass by 88.54%. Meanwhile, AI-2 activity had a linear correlation with polysaccharides and protein of EPS at 0−0.6 mM H3BO3 and NaBO2 (R2 > 0.8). Furthermore, H3BO3 upregulated the expression levels of biofilm formation genes, quorum sensing genes, and flagellar movement genes. These findings demonstrated that boron promoted biofilm formation by upregulating the expression levels of biofilm-related genes, improving the QS system AI-2 activity, and increasing EPS secretion in E. coli.