Essential factors of an integrated moving bed biofilm reactor-membrane bioreactor: Adhesion characteristics and microbial community of the biofilm

How does carbon to nitrogen ratio and carrier type affect moving bed biofilm reactor (MBBR): Performance evaluation and the fate of antibiotic resistance genes

With the spread of antibiotic resistance genes (ARGs) in the environment, monitoring and controlling ARGs have become an emerging issue of concern in biological processes. Moving bed biofilm reactors (MBBR) have been gaining attention for application in wastewater treatment. Since the performance of MBBR depends on operational parameters and biocarriers, selection of suitable biocarriers and start-up conditions are vital for efficiency of MBBRs. This study investigates the effects of different carbon-to-nitrogen (C/N) ratios and carrier types on the fate of selected ARGs and microbial communities in four MBBR systems using two conventional (K3 and sponge biocarrier (SB)) and two modified carriers (Fe-Ca@SB and Ze-AC@SB). Results showed that the modified biocarriers achieved higher NH4-N removal and better simultaneous nitrification and denitrification (SND) performance (90%) at C/N of 20. However, as the C/N ratio decreased to 10 and 7, the performance of all bioreactors was approximately similar. Moreover, COD removal of 90% was achieved in all reactors regardless of C/N ratio and carrier type. Further studies on the fate of selected ARGs (tetA, blaTEM, ampR) showed that the C/N ratio could affect the abundance of target ARGs, especially for K3 biocarrier, with tetA being the most abundant gene. Also, as the C/N ratio decreased, intl1 was enriched using K3 and SB. However, for Ze-AC@SB, the increase in the abundance of ARGs and intl1 was the lowest making it a reliable carrier not only in MBBR performance but in the control of ARGs. Metagenomic studies showed that the C/N ratio and carrier type could alter the diversity and structure of the bacterial communities in different MBBR systems, with Proteobacteria being the most abundant phylum in all four systems.

Filtration performance of biofilm membrane bioreactor: Fouling control by threshold flux operation

Membrane fouling is the major factor that restricts the furtherly widespread use of membrane bioreactor (MBR). As a new generation of MBR, biofilm membrane bioreactor (BF-MBR) demonstrates high treatment efficiency and low sludge growth rate, however the filtration performance improvement and membrane fouling control are still the challenges for its further development. This work investigated the filtration performance using resistance in series model and membrane fouling control via threshold flux for BF-MBR. At first, the flux behavior and filtration resistance under various operating conditions, including agitation speed, membrane and TMP, were explored by resistance in series model. Because of the desirable anti-fouling capacity, UP100 and UP030 had the high threshold flux (100 and 90 L m-2 h-1) and low irreversible fouling resistance (1 and 1.3 × 10-10 m-1). Higher shear stress produced by higher agitation speed could reduce membrane fouling, while greatly promote the threshold flux (138 L m-2 h-1) and membrane cleaning efficiency (96%). Moreover, increasing shear stress or selecting membrane with large pore size could decrease the fouling rate and raise the threshold flux. As for TMP, high TMP reduced the removal rate for organic and nutrient, and enhanced the irreversible fouling. Besides, the aerobic-BF-MBR (101 L m-2 h-1 and 1.3 × 10-10 m-1) with lower foulant concentration had a better filtration performance than anoxic-BF-MBR (90 L m-2 h-1 and 1.5 × 10-10 m-1). Additionally, the long-term tests with 10 cycles were conducted to evaluate the industrial application value of BF-MBR (45-58 L m-2 h-1). This work provides the technical support for sustainable filtration performance of BF-MBR.

Pivotal role of intracellular oxidation by HOCl in simultaneously removing antibiotic resistance genes and enhancing dewaterability during conditioning of sewage sludge using Fe2+/Ca(ClO)2

Pre-acidification has been shown to be crucial in attenuating antibiotic resistance genes (ARGs) during the conditioning of sewage sludge. However, it is of great significance to develop alternative conditioning approaches that can effectively eliminate sludge-borne ARGs without relying on pre-acidification. This is due to the high investment costs and operational complexities associated with sludge pre-acidification. In this study, the effects of Fe2+/Ca(ClO)2 conditioning treatment on the enhancement of sludge dewaterability and the removal of ARGs were compared with other conditioning technologies. The dose effect and the associated mechanisms were also investigated. The findings revealed that Fe2+/Ca(ClO)2 conditioning treatment had the highest potential, even surpassing Fenton treatment with pre-acidification, in terms of eliminating the total ARGs. Moreover, the effectiveness of the treatment was found to be dose-dependent. This study also identified that the •OH radical reacted with extracellular polymeric substance (EPS) and extracellular ARGs, and the HOCl, the production of which was positively correlated with the dose of Fe2+/Ca(ClO)2, could infiltrate the EPS layer and diffuse into the cell of sludge flocs, inducing the oxidation of intracellular ARGs. Furthermore, this study observed a significant decrease in the predicted hosts of ARGs and MGEs in sludge conditioned with Fe2+/Ca(ClO)2, accompanied by a significant downregulation of metabolic pathways associated with ARG propagation, thereby contributing to the attenuation of sludge-borne ARGs. Based on these findings, it can be concluded that Fe2+/Ca(ClO)2 conditioning treatment holds great potential for the removal of sludge-borne ARGs while also enhancing sludge dewaterability, which mainly relies on the intracellular oxidation by HOCl.

Motility behavior and physiological response mechanisms of aerobic denitrifier, Enterobacter cloacae strain HNR under high salt stress: Insights from individual cells to populations

The motility behaviors at the individual-cell level and the collective physiological responsive behaviors of aerobic denitrifier, Enterobacter cloacae strain HNR under high salt stress were investigated. The results revealed that as salinity increased, electron transport activity and adenosine triphosphate content decreased from 15.75 μg O2/g/min and 593.51 mM/L to 3.27 μg O2/g/min and 5.34 mM/L, respectively, at 40 g/L, leading to a reduction in the rotation velocity and vibration amplitude of strain HNR. High salinity stress (40 g/L) down-regulated genes involved in ABC transporters (amino acids, sugars, metal ions, and inorganic ions) and activated the biofilm-related motility regulation mechanism in strain HNR, resulting in a further decrease in flagellar motility capacity and an increase in extracellular polymeric substances secretion (4.08 mg/g cell of PS and 40.03 mg/g cell of PN at 40 g/L). These responses facilitated biofilm formation and proved effective in countering elevated salt stress in strain HNR. Moreover, the genetic diversity associated with biofilm-related motility regulation in strain HNR enhanced the adaptability and stability of the strain HNR populations to salinity stress. This study enables a deeper understanding of the response mechanism of aerobic denitrifiers to high salt stress.

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).

Response of biofilm-based systems for antibiotics removal from wastewater: Resource efficiency and process resiliency

Biofilm-based systems have efficient stability to cope-up influent shock loading with protective and abundant microbial assemblage, which are extensively exploited for biodegradation of recalcitrant antibiotics from wastewater. The system performance is subject to biofilm types, chemical composition, growth and thickness maintenance. The present study elaborates discussion on different type of biofilms and their formation mechanism involving extracellular polymeric substances secreted by microbes when exposed to antibiotics-laden wastewater. The biofilm models applied for estimation/prediction of biofilm-based systems performance are explored to classify the application feasibility. Further, the critical review of antibiotics removal efficiency, design and operation of different biofilm-based systems (e.g. rotating biological contactor, membrane biofilm bioreactor etc.) is performed. Extending the information on effect of various process parameters (e.g. hydraulic retention time, pH, biocarrier filling ratio etc.), the microbial community dynamics responsible of antibiotics biodegradation in biofilms, the technological problems, related prospective and key future research directions are demonstrated. The biofilm-based system with biocarriers filling ratio of ∼50-70% and predominantly enriched with bacterial species of phylum Proteobacteria protected under biofilm thickness of ∼1600 μm is effectively utilized for antibiotic biodegradation (>90%) when operated at DO concentration ≥3 mg/L. The C/N ratio ≥1 is best suitable condition to eliminate antibiotic pollution from biofilm-based systems. Considering the significance of biofilm-based systems, this review study could be beneficial for the researchers targeting to develop sustainable biofilm-based technologies with feasible regulatory strategies for treatment of mixed antibiotics-laden real wastewater.

Strategic analysis on development of simultaneous adsorption and catalytic biodegradation over advanced bio-carriers for zero-liquid discharge of industrial wastewater

With rapid industrial development, millions of tons of industrial wastewater are produced that contain highly toxic, carcinogenic, mutagenic compounds. These compounds may consist of high concentration of refractory organics with plentiful carbon and nitrogen. To date, a substantial proportion of industrial wastewater is discharged directly to precious water bodies due to the high operational costs associated with selective treatment methods. For example, many existing treatment processes rely on activated sludge-based treatments that only target readily available carbon using conventional microbes, with limited capacity for nitrogen and other nutrient removal. Therefore, an additional set-up is often required in the treatment chain to address residual nitrogen, but even after treatment, refractory organics persist in the effluents due to their low biodegradability. With the advancements in nanotechnology and biotechnology, novel processes such as adsorption and biodegradation have been developed, and one promising approach is integration of adsorption and biodegradation over porous substrates (bio-carriers). Regardless of recent focus in a few applied researches, the process assessment and critical analysis of this approach is still missing, and it highlights the urgency and importance of this review. This review paper discussed the development of the simultaneous adsorption and catalytic biodegradation (SACB) over a bio-carrier for the sustainable treatment of refractory organics. It provides insights into the physico-chemical characteristics of the bio-carrier, the development mechanism of SACB, stabilization techniques, and process optimization strategies. Furthermore, the most efficient treatment chain is proposed, and its technical aspects are critically analysed based on updated research. It is anticipated that this review will contribute to the knowledge of academia and industrialist for sustainable upgradation of existing industrial wastewater treatment plants.

Effect of Membrane Pore Size on Membrane Fouling of Corundum Ceramic Membrane in MBR

Ceramic membrane has emerged as a promising material to address the membrane fouling issue in membrane bioreactors (MBR). In order to optimize the structural property of ceramic membrane, four corundum ceramic membranes with the mean pore size of 0.50, 0.63, 0.80, and 1.02 μm were prepared, which were designated as C5, C7, C13, and C20, respectively. Long-term MBR experiments showed that the C7 membrane with medium pore size experienced the lowest trans-membrane pressure development rate. Both the decrease and increase of membrane pore size would lead to more severe membrane fouling in the MBR. It was also interesting that with the increase of membrane pore size, the relative proportion of cake layer resistance in total fouling resistance was gradually increased. The content of dissolved organic foulants (i.e., protein, polysaccharide and DOC) on the surface of C7 was quantified as the lowest among the different ceramic membranes. Microbial community analysis also revealed the C7 had a lower relative abundance of membrane fouling associated bacteria in its cake layer. The results clearly demonstrated that ceramic membrane fouling in MBR could be effectively alleviated through optimizing the membrane pore size, which was a key structural factor for preparation of ceramic membrane.

Elucidating the performance of integrated anoxic/oxic moving bed biofilm reactor: Assessment of organics and nutrients removal and optimization using feed forward back propagation neural network

A lab-scale integrated anoxic and oxic (A/O) moving bed biofilm reactor (MBBR) was investigated for the removal of organics and nutrients by varying chemical oxygen demand (COD) to NH₄-N ratio (C/N ratio: 3.5, 6.75, and 10), hydraulic retention time (HRT: 6 h, 15 h, and 24 h), and recirculation ratio (R: 1, 2, and 3). The use of activated carbon coated carriers prepared from waste polyethylene material and polyurethane sponges attached to a cylindrical frame in the integrated A/O MBBR increased the attached growth biomass significantly. >95 % of COD removal was observed under the C/N ratio of 10 at an HRT of 24 h. While the low C/N ratio favored the removal of NH₄-N (∼98 %) and PO₄^3--P (∼90 %) with an optimal R of 1.75. Using the experimental dataset, to predict and forecast the performance of integrated A/O MBBR, a feed-forward-backpropagation-neural-network model was developed.

The Advancement in Membrane Bioreactor (MBR) Technology toward Sustainable Industrial Wastewater Management

The advancement in water treatment technology has revolutionized the progress of membrane bioreactor (MBR) technology in the modern era. The large space requirement, low efficiency, and high cost of the traditional activated sludge process have given the necessary space for the MBR system to come into action. The conventional activated sludge (CAS) process and tertiary filtration can be replaced by immersed and side-stream MBR. This article outlines the historical advancement of the MBR process in the treatment of industrial and municipal wastewaters. The structural features and design parameters of MBR, e.g., membrane surface properties, permeate flux, retention time, pH, alkalinity, temperature, cleaning frequency, etc., highly influence the efficiency of the MBR process. The submerged MBR can handle lower permeate flux (requires less power), whereas the side-stream MBR can handle higher permeate flux (requires more power). However, MBR has some operational issues with conventional water treatment technologies. The quality of sludge, equipment requirements, and fouling are major drawbacks of the MBR process. This review paper also deals with the approach to address these constraints. However, given the energy limitations, climatic changes, and resource depletion, conventional wastewater treatment systems face significant obstacles. When compared with CAS, MBR has better permeate quality, simpler operational management, and a reduced footprint requirement. Thus, for sustainable water treatment, MBR can be an efficient tool.

Calcium hypochlorite-coupled aged refuse promotes hydrogen production from sludge anaerobic fermentation

This work investigated the effect of calcium hypochlorite (CH) coupled aged refuse (AR) treatment on the enhanced hydrogen generation from sludge anaerobic dark fermentation (SADF). The enhanced mechanism was systematically revealed through sludge disintegration, organic matter biotransformation, and microbial community characteristics, etc. The experimental data showed that CH coupled AR increased the hydrogen yield to 18.1 mL/g, significantly higher than that in the AR or CH group alone. Mechanistic analysis showed that CH-coupled AR significantly promoted sludge disintegration and hydrolysis processes, providing sufficient material for hydrogen-producing bacteria. Microbiological analysis showed that CH-coupled AR increased the relative abundance of responsible hydrogen-producing microorganisms. In addition, CH-coupled AR was very effective in reducing phosphate content in the fermentation liquid and fecal coliforms in the digestate, thus facilitating the subsequent treatment of fermentation broth and digestate. CH coupled AR is an alternative strategy to increase hydrogen production from sludge.

Performance and microbial community of MBBRs under three maintenance strategies for intermittent stormwater treatment

Maintaining microbial activities is a critical problem for biological treatment processes of stormwater runoff because of its intermittent nature. In this study, the suitability of the moving bed biofilm reactor (MBBR) was assessed for stormwater treatment by long-term dry - rainy alternation operation. Three strategies to maintain microbial activities during the dry period, including keeping idle (MBBR_I), introducing river water throughout the period (MBBR_C), and ahead of a rainy day (MBBR_M), were investigated. COD and NH₄⁺-N removal efficiencies declined linearly from 94.2 % and 94.7 % to 51.7 % and 64.6 %, respectively, after the 61-day operation with microbial activity and biomass decreased. Introducing river water adversely affected the process performance as MBBR_C presented the highest declining rates of COD and NH₄⁺-N removal efficiencies. Most genera in MBBRs decayed and their microbial communities developed towards individualization, especially in MBBR_M because of its highest environmental variability. Keeping idle slightly alleviated the performance decline and formed a more stable microbial community structure. However, significantly deteriorating performance in all MBBRs after the long-term operation indicated that MBBRs were unsuitable for treating stormwater independently of intermittent nature.

Effects mechanism of bio-carrier filling rate on rotating biofilms and the reactor performance optimization method

Benefited from the massive filling bio-carriers, the packed cage rotating biological contactors (RBCs) have better performance and application potentiality in wastewater treatment. Investigating the effects mechanism of bio-carrier filling rate is crucial for such reactors management. In this study, the pollutants removal performance, biofilms physical characteristics, and microbial communities of the biofilms under a series of bio-carrier filling rates were analyzed. The results shown, the pollutant removal rate and amount were quite different under different filling rates, and biofilms structure and microbial composition were the main factors affecting the pollutants removal performance. With the increasing filling rates, the biofilms were more mass increased (dry weight from 0.066 to 0.148 g/per carrier), thicker (from 340.30 to 850.84 μm) and lower dense (from 0.068 to 0.060 g/cm³). The microbial community composition of those biofilms was also quite different at the genus level. The effects mechanism of bio-carrier filling rate can be summarized: the filling rates affect the physical and biological characteristics of biofilms, which will further affect the microenvironment and microbial distribution in biofilms, and then determines the pollutant metabolic rate and metabolic pathway. This study will contribute to design better bio-carrier filling rate according to different wastewater treatment scenario, and promote the performance optimization of packed cage RBCs.

Synergic role of ferrate and nitrite for triggering waste activated sludge solubilisation and acidogenic fermentation: Effectiveness evaluation and mechanism elucidation

Enhancing anaerobic treatment efficiency of waste activated sludge (WAS) toward preferable resource recovery would be an important requirement for achieving carbon-emission reduction, biosolids minimization, stabilization and security concurrently. This study demonstrated the synergic effect of potassium ferrate (PF) and nitrite on prompting WAS solubilisation and acidogenic fermentation toward harvesting volatile fatty acids (VFAs). The results indicated the PF+NaNO₂ co-pretreatment boosted 7.44 times and 1.32 times higher WAS solubilisation [peak soluble chemical oxygen demand (SCOD) of 2680 ± 52 mg/L] than that by the single nitrite- and PF-pretreatment, respectively, while about 2.77 times and 2.11 times higher VFAs production were achieved (maximum VFAs accumulation of 3536.25 ± 115.24 mg COD/L) as compared with the single pretreatment (nitrite and PF)-fermentations. Afterwards the WAS dewaterability was improved simultaneously after acidogenic fermentation. Moreover, a schematic diagram was established for illustrating mechanisms of the co-pretreatment of PF and nitrite for enhancing the VFAs generation via increasing key hydrolytic enzymes, metabolic functional genes expression, shifting microbial biotransformation pathways and elevating abundances of key microbes in acidogenic fermentation. Furthermore, the mechanistic investigations suggested that the PF addition was conducive to form a relatively conductive fermentation environment for enhancing electron transfer (ET) efficiency, which contributed to the VFAs biotransformation positively. This study provided an effective strategy for enhancing the biodegradation/bioconversion efficiency of WAS organic matters with potential profitable economic returns.

Removal of Escherichia coli from domestic sewage using biological sand filters: Reduction effect and microbial community analysis

The recycling of sewage is an economical option to solve the water resource pressure. However, to avoid health risks to humans, pathogens in sewage must be removed before reuse. In this study, a biological sand filter (BSF) was used to remove pathogen indicator Escherichia coli (E. coli) from sewage. The biolayer (schmutzdecke layer) formation process of BSFs, operation performance, factors affecting E. coli removal and microbial community structure were evaluated. The results of schmutzdecke layer culture showed that a large number of microorganisms were attached to the upper medium of BSFs. At the same time, the BSFs could reduce both conventional contaminants and E. coli. The E. coli removal experiments revealed that the removal rate of E. coli was about 96.1% at higher effective medium depth (50 cm), the removal rate was about 95% when set hydraulic loading rate (HLR) to 0.16 m³/m²/h and the removal efficiency reached 93.6% at lower influent bacteria concentration. Finally, the microbial community analysis indicated that different BSFs had similar microbial structure, and the microbial abundance in the schmutzdecke layer was higher than that in the bottom layer in the same BSFs. Besides, Biological action played a significant role in the removal of E. coli, including the bacteriolysis of Bdellovibrio and the competition between other bacteria and E. coli. In summary, BSF was a promising technology for removing E. coli from sewage.

Metagenomic insights into the effects of various biocarriers on moving bed biofilm reactors for municipal wastewater treatment

Preferable biocarrier is vital for start-up and operation of moving bed biofilm reactor (MBBR). Effects of three separate biocarriers - PPC, PU, and PP on MBBRs were systematically investigated including nutrients removal performances, biomass attachment, microbial community, and relevant functional genes. Results showed that three biocarriers achieved similar removal efficiencies for chemical oxygen demand (COD) and total phosphorus (TP), though much higher biomasses were found attached onto PPC and PU carriers. PPC and PU performed better than PP for ammonia nitrogen (NH₄⁺-N) removal. However, PPC exhibited the greatest and most reliable denitrifying efficiency, mainly due to stronger simultaneous nitrification and denitrification during better micro-anoxic-environment created within PPC carriers than others. Further studies by 16S rRNA gene and metagenomic sequencing analysis uncovered the bacterial diversity and structures, and relevant functional genes for nitrogen-transformation and pathways of nitrogen metabolisms, which laid the biological basis for the best performances via biocarrier PPC. This study inspired a feasible approach for municipal wastewater treatment through PPC filled MBBR.

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.

Recent advances in attached growth membrane bioreactor systems for wastewater treatment

To tackle membrane fouling and limited removals of pollutants (nutrients and emerging pollutants) that hinder the wide applications of membrane bioreactor (MBR), attached growth MBR (AGMBR) combining MBR and attached growth process has been developed. This review comprehensively presents the up-to-date developments of media used in both aerobic and anaerobic AGMBRs for treating wastewaters containing conventional and emerging pollutants. It also elaborates the properties of different media, characteristics of attached biomass, and their contributions to AGMBR performance. Conventional media, such as biological activated carbon and polymeric carriers, induce formation of aerobic, anoxic and/or anaerobic microenvironment, increase specific surface area or porous space for biomass retention, improve microbial activities, and enrich diverse microorganisms, thereby enhancing pollutants removal. Meanwhile, new media (i.e. biochar, bioaugmented carriers with selected strain/mixed cultures) do not only eliminate conventional pollutants (i.e. high concentration of nitrogen, etc.), but also effectively remove emerging pollutants (i.e. micropollutants, nonylphenol, adsorbable organic halogens, etc.) by forming thick and dense biofilm, creating anoxic/anaerobic microenvironments inside the media, enriching special functional microorganisms and increasing activity of microorganisms. Additionally, media can improve sludge characteristics (i.e. less extracellular polymeric substances and soluble microbial products, larger floc size, better sludge settleability, etc.), alleviating membrane fouling. Future studies need to focus on the development and applications of more new functional media in removing wider spectrum of emerging pollutants and enhancing biogas generation, as well as scale-up of lab-scale AGMBRs to pilot or full-scale AGMBRs.

Microbial community structures and antibiotic biodegradation characteristics during anaerobic digestion of chicken manure containing residual enrofloxacin

To explore the interaction between the residual antibiotic in animal manure and biological treatment, the effect of enrofloxacin (ENR) on the anaerobic digestion of chicken manure, and biodegradation rate of ENR was studied under the condition of actual residual ENR content of 0, 8, 16 and 32 mg/kg·TS. The results showed that the addition of ENR increased the total biogas production, especially 8 mg/kg·TS promoted the anaerobic reaction obviously, and the corresponding cumulative biogas production was increased by 15.33%. However, in the presence of 32 mg/kg·TS, the biogas production rate was reduced and the peak period of biogas production was delayed. The results of enzyme activities determination and 16S rRNA sequencing showed that ENR had different effects on archaea and bacteria. The residual ENR could promote hydrolysis reactions in the anaerobic system, but could inhibit acetoclastic methanogens, and the relative abundance of Methanosaeta declined by 7.22‒12.41%. The first-order kinetic model showed that the half-life period of ENR in the anaerobic digestion system was 9.16‒10.83 days, and the biodegradation rate exceeded 80% after the treatment. This study can bring important information for the management of animal manure in the future.

Biofilm formation of Ancylobacter sp. TS-1 on different granular materials and its ability for chemolithoautotrophic As(III)-oxidation at high concentrations

The oxidation of arsenic (As) is a key step in its removal from water, and biological oxidation may provide a cost-effective and sustainable method. The biofilm-formation ability of Ancylobacter sp. TS-1, a novel chemolithoautotrophic As oxidizer, was studied for four materials: polypropylene, graphite, sand, and zeolite. After seven days under batch mixotrophic conditions, with high concentrations of As(III) (225 mg·L^-1), biofilm formation was detected on all materials except for polypropylene. The results demonstrate As(III)-oxidation of TS-1 biofilms and suggest that the number of active cells was similar for graphite, sand, and zeolite. However, the biofilm biomass follows the specific surface area of each material: 7.0, 2.4, and 0.4 mg VSS·cm^-3 for zeolite, sand, and graphite, respectively. Therefore, the observed biofilm-biomass differences were probably associated with different amounts of EPS and inert biomass. Lastly, As(III)-oxidation kinetics were assessed for the biofilms formed on graphite and zeolite under chemolithoautotrophic conditions. The normalized oxidation rate for biofilms formed on these materials was 3.6 and 1.0 mg·L^-1·h^-1·cm^-3, resulting among the highest reported values for As(III)-oxidizing biofilms operated at high-As(III) concentrations. Our findings suggest that biofilm reactors based on Ancylobacter sp. TS-1 are highly promising for their utilization in As(III)-oxidation pre-treatment of high-As(III) polluted waters.

The Influence of Different Operation Conditions on the Treatment of Mariculture Wastewater by the Combined System of Anoxic Filter and Membrane Bioreactor

The mariculture wastewater treatment performance for the combined system of anoxic filter and membrane bioreactor (AF-MBR) was investigated under different hydraulic retention times (HRTs), influent alkalinity, and influent ammonia nitrogen load. The results showed that the removal efficiencies of TOC and total nitrogen were slightly better at the HRT of 8 h than at other HRTs, and the phosphate removal efficiency decreased with the increase of HRT. With the increase of influent alkalinity, the removal of TOC and phosphate did not change significantly. With the increase of influent alkalinity from 300 mg/L to 500 mg/L, the total nitrogen removal efficiency of AF-MBR was improved, but the change of the removal efficiency was not obvious when the alkalinity increased from 500 mg/L to 600 mg/L. When the influent concentration of ammonia nitrogen varied from 20 mg/L to 50 mg/L, the removal efficiencies of TOC, phosphate, and total nitrogen by AF-MBR were stable. An interesting finding was that in all the different operation conditions examined, the treatment efficiency of AF-MBR was always better than that of the control MBR. The concentrations of NO₃⁻-N in AF-MBR were relatively low, whereas NO₃⁻-N accumulated in the control MBR. The reason was that the microorganisms attached to the carrier and remained fixed in the aerobic and anoxic spaces, so that there was a gradual enrichment of bacteria characterized by slow growth in a high-salt environment. In addition, the microorganisms could gather and grow on the carrier forming a biofilm with higher activity, a richer and more stable population, and enhanced ability to resist a load impact.

Preparation and performance evaluation of novel magnetic porous carriers in fluidized bed bioreactor for wastewater treatment

Biofilm process is a promising wastewater treatment technology and biofilm carrier (biocarrier) is regarded as the core of this process. However, the traditional commercial biocarriers have their inherent drawbacks, therefore, the development of new-type biocarrier to enhance wastewater treatment efficiency is significantly important to biofilm-based reactors. In this study, based on radical suspension polymerization, a novel kind of magnetic porous carriers (PMCs) was prepared by modifying the porous polymer carriers (PPCs) with inorganic particles, and then applied in a fluidized bed bioreactor (FBBR) with a low packing ratio of 10 % (v/v) to synthetic wastewater treatment. The results showed that this novel biocarrier possesses paramagnetism with saturation magnetization of 1.01emu/g, low density (1.26 g/cm³), excellent hydrophilicity (surface water contact angle approaching zero) and rough surface. Besides, compared with the PPCs, the developed PMCs have larger pores (up to 50 μm or more), in which the larger-sized microbes are able to colonize. Moreover, as compared to the PPCs-based FBBR, the PMCs-based reactor achieved shorter time (7 days) for biofilm formaiton and significantly enhanced NH₃-N removal efficiency ( nearly 20 % increase at the level of influent NH₃-N concentration about 100 mg/L). High-throughput sequencing (HTS) results indicated that this new biocarrier could promote biodiversity and improve the abundance of Nitrosomonadales (the functional bacteria for ammonia removal in the bio-system), thus enhancing the ammonification process. Therefore, the developed PMCs could be preferable biocarriers for biofilm formation and provide an alternative to the traditional suspended biocarrier, demonstrating a promising potential, even at a lower filling ratio, to enhance the pollutants removal performance.

Insights into the Development of Phototrophic Biofilms in a Bioreactor by a Combination of X-ray Microtomography and Optical Coherence Tomography

As productive biofilms are increasingly gaining interest in research, the quantitative monitoring of biofilm formation on- or offline for the process remains a challenge. Optical coherence tomography (OCT) is a fast and often used method for scanning biofilms, but it has difficulty scanning through more dense optical materials. X-ray microtomography (μCT) can measure biofilms in most geometries but is very time-consuming. By combining both methods for the first time, the weaknesses of both methods could be compensated. The phototrophic cyanobacterium Tolypothrix distorta was cultured in a moving bed photobioreactor inside a biocarrier with a semi-enclosed geometry. An automated workflow was developed to process µCT scans of the biocarriers. This allowed quantification of biomass volume and biofilm-coverage on the biocarrier, both globally and spatially resolved. At the beginning of the cultivation, a growth limitation was detected in the outer region of the carrier, presumably due to shear stress. In the later phase, light limitations could be found inside the biocarrier. µCT data and biofilm thicknesses measured by OCT displayed good correlation. The latter could therefore be used to rapidly measure the biofilm formation in a process. The methods presented here can help gain a deeper understanding of biofilms inside a process and detect any limitations.

Biological and Physiochemical Methods of Biofilm Adhesion Resistance Control of Medical-Context Surface

The formation of biofilms on medical-context surfaces gives the EPS embedded bacterial community protection and additional advantages that planktonic cells would not have such as increased antibiotic resistance and horizontal gene transfer. Bacterial cells tend to attach to a conditioning layer after overcoming possible electrical barriers and go through two phases of attachments: reversible and irreversible. In the first, bacterial attachment to the surface is reversible and occurs quickly whilst the latter is permanent and takes place over a longer period of time. Upon reaching a certain density in the bacterial community, quorum sensing causes phenotypical changes leading to a loss in motility and the production of EPS. This position paper seeks to address the problem of bacterial adhesion and biofilm formation for the medical surfaces by comparing inhabiting physicochemical interactions and biological mechanisms. Several physiochemical methodologies (e.g. ultrasonication, alternating magnetic field and chemical surface coating) and utilizing biological mechanisms (e.g. quorum quenching and EPS degrading enzymes) were suggested. The possible strategical applications of each category were suggested and evaluated to a balanced position to possibly eliminate the adhesion and formation of biofilms on medical-context surfaces.

Enhanced nitrogen removal by simultaneous nitrification-denitrification and further denitrification (SND-DN) in a moving bed and constructed wetland (MBCW) integrated bioreactor

With the main objective of improving the removal of nitrogen from domestic wastewater and more sustainably, a moving bed and constructed wetland (MBCW) integrated bioreactor was fabricated and evaluated with continuous and intermittent aeration operations. The hybrid system achieves average removal efficiencies up to 90.4 ± 0.8% of chemical oxygen demand (COD), 91.8 ± 1.2% of ammonia nitrogen (NH₄⁺-N), and 77.0 ± 2.6% of total nitrogen (TN), respectively, through a simultaneous nitrification-denitrification and further denitrification (SND-DN) process. This occurs through an intermittent aeration operation followed by continuous aeration with a dissolved oxygen (DO) of 4.0 mg L^-1 due to the complementary and coordinated action of mixed biocarriers. It has resulted in the improvement of the efficiency of SND from 5.9 to 35.3% and in the removal via wetland for DN, between 2.42 and 2.45 g m^-2·d^-1, respectively. The analysis of extracellular polymeric substances (EPS) and high-throughput sequencing demonstrated the enhanced SND mechanism and the evolution of microbial species within the biofilm structure. The total relative abundance of nitrifying bacteria, more aggregated outside the biofilm, decreased by 7.66% compared to denitrifying bacteria, mostly accumulated inside, which increased by 5.49%, respectively.

17β-Estradiol removal routes by moving bed biofilm reactors (MBBRs) under various C/N ratios

This study evaluated the contribution of biotic and abiotic routes to the 17β-estradiol (E2) removal in moving bed biofilm reactors (MBBRs), and uncovered the interrelation between the E2 removal routes and biofilm characteristics, which was not researched in previous literature. Three MBBRs with different C/N ratios (0 for C/N₀; 2 for C/N₂; and 5 for C/N₅) were operated in continuous mode. A 65-day degradation demonstrated that the MBBRs had high potential to remove E2 regardless of the C/N (E2 removal greater than 99% for all MBBRs; P > 0.05). Further batch tests showed that the E2 removal mainly resulted from heterotrophic activities for all MBBRs, accounting for approximately 85% for all MBBRs (P > 0.05), followed by nitrification (10-11%) and adsorption (4-5%). Importantly, lower adhesive force likely led to higher E2 adsorption onto biofilms. Besides, enhanced ammonia oxidizing rate (AOR) was consistent with the high contribution of nitrification to the E2 attenuation. Importantly, heterotrophic activity was positively correlated with its contribution to E2 removal (r = 0.99, P < 0.05). To sum, the results obtained in this study helped to understand the E2 removal routes in nitrifying biofilm systems.

Intertidal wetland sediment as a novel inoculation source for developing aerobic granular sludge in membrane bioreactor treating high-salinity antibiotic manufacturing wastewater

This study proposed a novel approach of cultivating aerobic granular sludge (AGS) using intertidal wetland sediment (IWS) as inoculant in MBR for saline wastewater treatment. Granulation was observed in IWS-MBR during start-up, with increased sludge particle size (3.1-3.3 mm) and improved settling property (23.8 ml/g). The abundant inorganic particulates (acted as nuclei) and distinctive microbial community in IWS contributed to the granules formation. With the help of AGS, IWS-MBR system exhibited excellent TOC reduction of 90.3 ± 6.1% and significant TN reduction of 31.2 ± 5.0%, while the control MBR (Co-MBR) only showed 58.9 ± 7.2% and 10.4 ± 2.7%, respectively. Meanwhile, membrane fouling was mitigated in IWS-MBR, with a longer filtration cycle of 21.5 d, as compared with that of 8.9 d for Co-MBR. Microbial community analysis revealed that abundant functional bacteria associated with granulation and pollutants removal were enriched from IWS and set the basis for AGS formation and the superior treatment performance.

Recent progress in integrated fixed-film activated sludge process for wastewater treatment: A review

Integrated fixed-film activated sludge (IFAS) process is considered as one of the leading-edge processes that provides a sustainable solution for wastewater treatment. IFAS was introduced as an advancement of the moving bed biofilm reactor by integrating the attached and the suspended growth systems. IFAS offers advantages over the conventional activated sludge process such as reduced footprint, enhanced nutrient removal, complete nitrification, longer solids retention time and better removal of anthropogenic composites. IFAS has been recognized as an attractive option as stated from the results of many pilot and full scales studies. Generally, IFAS achieves >90% removals for combined chemical oxygen demand and ammonia, improves sludge settling properties and enhances operational stability. Recently developed IFAS reactors incorporate frameworks for either methane production, energy generation through algae, or microbial fuel cells. This review details the recent development in IFAS with the focus on the pilot and full-scale applications. The microbial community analyses of IFAS biofilm and floc are underlined along with the special emphasis on organics and nitrogen removals, as well as the future research perspectives.

Ultrasonic coupled bioleaching pretreatment for enhancing sewage sludge dewatering: Simultaneously mitigating antibiotic resistant genes and changing microbial communities

In this study, ultrasonic as a pretreatment coupled with bioleaching was used to enhance sludge dewaterability. Changes in microbial diversity and antibiotic resistant genes (ARGs) were studied during the combined treatment process. The results show that under optimal conditions, combined ultrasonic and bioleaching treatment led to decreases in the specific resistance of filtration and bioleaching time by 7.59% and 12.5%, respectively, compared with single bioleaching process. Using high pressure filtration system, the water content of sludge cake treated by the combined treatment was decreased to 58.04%, which was 10.04% lower than bioleaching sludge. After combined treatment, the microbial diversity and the total number of bacteria in the sludge decreased significantly, which caused the decreases in the absolute abundance of sulfonamide and tetracycline ARGs by 1.56-1.58 and 0.34-1.23 log units, respectively. However, the decrease in the total bacterial biomass was greater than the decrease in the number of potential hosts carrying the tetracycline ARG, resulting in an increase in the relative abundance of tetracycline gene. Furthermore, this study proposed a mechanism of the dewatering and ARGs, involving the combined ultrasonic and bioleaching treatment: Firstly, ultrasonic cavitation causes extracellular polymeric substances (EPS) to fall off the surface of sludge; Secondly, this faster and directly makes bacteria cells affected by bio-acidification and bio-oxidation. In this case, the cells could be more easily destroyed by the combined ultrasonic and bioleaching treatment, compared with individual bioleaching treatment; As a result, stronger dewaterability and more removal rates of ARGs were achieved under the combined treatment. The economic analyses showed that the combined ultrasonic and bioleaching treatment is a more practical and economical technique for achieving deep dewatering of sludge.

Comparative Study of Denitrifying-MBBRs with Different Polyethylene Carriers for Advanced Nitrogen Removal of Real Reverse Osmosis Concentrate

Nitrogen (N) remains a great challenge in wastewater treatment while attempts to remove N has continuously been a research point for decades. In this study, the long-term performance of four identical-shape denitrification MBBRs (moving bed biofilm reactors) with four different configurations of cylindrical polyethylene as carriers (Φ25 × 12, Φ25 × 4, Φ15 × 15, and Φ10 × 7 mm) for advanced N removal of real reverse osmosis concentrate was investigated in great detail. The N of the real concentrate can be effectively removed by denitrification MBBRs when the pH, temperature, hydraulic retention time (HRT), C/N ratio, and filling rate are 7.50–8.10, 24~26 °C, 12 hours, 6.6, and 50%, respectively. The results showed that the MBBR with the Φ15 × 15 poly-carrier had the best removal efficiency on NO₃^-–N (78.0 ± 15.8%), NO₂^-–N (43.79 ± 9.30%), NH₄⁺–N (55.56 ± 22.28%), and TN (68.9 ± 12.4%). The highest biomass of 2.13 mg/g-carrier was in the Φ15 × 15 poly-carrier was compared with the other three carriers, while the genes of the Φ15 × 15 poly-carrier reactor were also the most abundant. Proteobacteria was the most abundant phylum in the system followed by Bacteroidetes and then Firmicutes. The entire experiment with various parameter examination supported that Φ15 × 15 poly-carrier MBBR was a promising system for N removal in high strength concentrate. Despite the lab-scale trial, the successful treatment of high strength real reverse osmosis concentrate demonstrated the reality of the treated effluent as possible reclaimed water, thus providing a good showcase of N-rich reverse osmosis concentrate purification in practical application.

Revealing microbial mechanism associated with volatile fatty acids production in anaerobic acidogenesis of waste activated sludge enhanced by freezing/thawing pretreatment

This study investigated the association of volatile fatty acid (VFA) production with microbial mechanism in waste activated sludge (WAS) anaerobic acidogenesis enhanced by freezing/thawing (F/T) pretreatment. WAS solubilization was enhanced with 955.4 ± 10.0 mg/L soluble chemical oxygen demand (SCOD) release by a 50-h F/T pretreatment at -24 °C. The highest level of VFAs (4852 ± 156 mg COD/L) was obtained after a 12-day fermentation. Moreover, phyla of Proteobacteria, Bacteroidetes, Firmicutes, and Ignavibacteriae played vital roles in VFA generation, while high genera abundance of Clostridium, Macellibacteroides, Prevotella, and Megasphaera were positively associated with high yields of short-chain (C2-C5) fatty acids. A schematic diagram was drawn to illustrate the microbial mechanism of enhanced VFA generation by F/T pretreatment during WAS fermentation. This study provides an in-depth exploration of promoting bio-resource recycling from WAS with a low-cost approach (specially in high latitudes) and bring about some new thinking on future WAS management.

Additional function of pasteurisation pretreatment in combination with anaerobic digestion on antibiotic removal

Pasteurisation pretreatment (PP) in combination with anaerobic digestion (PPAD) is one of the best ways for sterilisation of pathogenic microorganisms in manure. However, the effect of antibiotic residues in manure on PPAD has not been studied. This study investigated the function of PPAD on antibiotic removal and the effect of antibiotic on PPAD performance. Results demonstrated that chlortetracycline (CTC) and oxytetracycline (OTC) concentrations decreased from 17.236 and 183.446 to 0 and 17.348 mg/kg·TS using PPAD, respectively. PPAD for swine manure containing CTC and OTC increased methane production from 244.0 ± 7.6 to 254.0 ± 6.1 mL/g·VS and reduced technical digestion time (T₈₀) from 30 to 25 days compared with AD process. Moreover, PPAD affected only archaeal communities, whereas PP affected bacterial/archaeal communities. Thus, PPAD can be used to treat antibiotic-containing manure and reduce the negative effects of antibiotics.

Microbial community succession and its correlation with reactor performance in a sponge membrane bioreactor coupled with fiber-bundle anoxic bio-filter for treating saline mariculture wastewater

The application of MBR in high saline wastewater treatment is mainly constrained by poor nitrogen removal and severe membrane fouling caused by high salinity stress. A novel carriers-enhanced MBR system was successfully developed for treating saline mariculture wastewater, which showed efficient TN removal (93.2%) and fouling control. High-throughput sequencing revealed the enhancement mechanism of bio-carriers under high saline condition. Bio-carriers substantially improved the community structure, representatively, nitrifiers abundance (Nitrosomonas, Nitrospira) increased from 2.18% to 9.57%, abundance of denitrifiers (Sulfurimonas, Thermogutta, etc.) also rose from 3.81% to 14.82%. Thereby, the nitrogen removal process was enhanced. Noteworthy, ammonia oxidizer (Nitrosomonas, 8.26%) was the absolute dominant nitrifiers compared with nitrite oxidizer (Nitrospira, 1.13%). This supported the finding of shortcut nitrification-denitrification process in hybrid system. Moreover, a series of biomacromolecule degraders (Lutibacterium, Cycloclasticus, etc.) were detected in bio-carriers, which could account for the mitigation of membrane fouling as result of EPS and SMP degradation.

A simple way to improve a conventional A/O-MBR for high simultaneous carbon and nutrient removal from synthetic municipal wastewater

In this study, two anoxic-oxic membrane bioreactor (A/O-MBR) systems, i.e. conventional and biofilm anoxic-oxic-membrane bioreactors (C-A/O-MBR and BF-A/O-MBR, respectively), were operated in parallel under conditions of complete sludge retention for the purposes of comparing system performance and microbial community composition. Moreover, with the microbial communities, comparisons were made between the adhesive stage and the suspended stage. High average removal of COD, NH4+-N and TN was achieved in both systems. However, TP removal efficiency was remarkably higher in BF-A/O-MBR when compared with C-A/O-MBR. TP mass balance analysis suggested that under complete sludge retention, polyurethane sponges that were added into the anoxic tank played a key role in both phosphorus release and accumulation. The qPCR analysis showed that sponge biomass could maintain a higher level of abundance of total bacteria than the suspended sludge. Meanwhile, AOB and denitrifiers were enriched in the suspended sludge but not in the sponge biomass. Results of illumina sequencing reveal that the compacted sponge in BF-A/O-MBR could promote the growth of bacteria involved in nutrient removal and reduce the amount of filamentous and bacterial growth that is related to membrane fouling in the suspended sludge.

Distribution characteristics of N-acyl homoserine lactones during the moving bed biofilm reactor biofilm development process: Effect of carbon/nitrogen ratio and exogenous quorum sensing signals

Carbon/nitrogen (C/N) ratios play an important role in biological wastewater treatment processes, with quorum sensing (QS) coordinating biological group behaviors. However, the relationship between them remains unclear. This study investigated the effects of varying C/N ratios and exogenous QS signals on the distribution characteristics of AHLs in Moving Bed Biofilm Reactors during the biofilm development process. Results show that C10-HSL and C12-HSL were the dominant AHLs, with the highest concentrations observed in the reactor with a C/N ratio of 10, followed by C/N ratios of 20 and 4. With varying C/N ratios, the biofilm microbial community structure changed significantly, which may contribute to significant differences in the distribution of AHLs. Furthermore, with the addition of a QS strain Sphingomonas rubra sp. nov., the pollutant removal efficiency of the reactor was not significantly improved and a reversible change in community composition was temporarily observed.

Denitrification and microbial community in MBBR using A. donax as carbon source and biofilm carriers for reverse osmosis concentrate treatment

In this study, raw Arundo donax (A. donax) pieces were applied as carbon source and biofilm carriers for denitrification in a lab-scale moving bed biofilm reactor (MBBR) for the treatment of reverse osmosis concentrate gathered from local wastewater reuse plant. At stable phase (about 60 days), efficient denitrification performance was obtained with 73.2% ± 19.5% NO₃^--N average removal and 8.10 ± 3.45 g N/(m³·day) NO₃^--N average volumetric removal rate. Mass balance analysis showed that 4.84 g A. donax was required to remove 1 g TN. Quantitative real-time PCR analysis results showed that the copy numbers of 16S r-RNA, narG, nirS, nosZ and anammox gene of carrier biofilm and suspended activated sludge in the declination phase (BF2 and AS2) were lower than those of samples in the stable phase (BF1 and AS1), and relatively higher copy numbers of nirS and nirK genes with lower abundance of narG and nosZ genes were observed. High-throughput sequencing analysis was conducted for BF2 and AS2, and similar dominant phyla and classes with different abundance were obtained. The class Gammaproteobacteria affiliated with the phylum Proteobacteria was the most dominant microbial community in both BF2 (52.6%) and AS2 (41.7%). The PICRUSt prediction results indicated that 33 predictive specific genes were related to denitrification process, and the relative abundance of 18 predictive specific genes in BF2 were higher than those in AS2.

Optimized aeration strategies for nitrogen removal efficiency: application of end gas recirculation aeration in the fixed bed biofilm reactor

Aeration strategy played an important role in reactor performance. In this study, when superficial upflow air velocity (SAV) decreased from 0.16 to 0.08 cm s^-1, low dissolved oxygen concentration (DO) of 2.0 mg L^-1 occurred in reactor. The required depth for anoxic microenvironment in biofilm decreased from 902.3 to 525.9 μm, which enhanced the growth of denitrifying bacteria and total nitrogen (TN) removal efficiency. However, decreasing aeration intensity resulted in insufficient hydraulic shear stress, which led to weak biofilm matrix structure. Mass biofilm detachment and reactor deterioration then occurred after 87 days of operation. An end gas recirculation aeration strategy was proposed to separately manipulate DO and aeration intensity. Low DO and high aeration intensity were simultaneously achieved, which enhanced the metabolism of denitrifying bacteria (such as Flavobacterium sp., Pseudorhodobacter sp., and Dok59 sp.) and EPS-producing bacteria (such as Zoogloea sp. and Rhodobacter sp.). Consequently, high TN removal performance (82.1 ± 2.7%) and stable biofilm structure were achieved.

Pre-coagulation coupled with sponge-membrane filtration for organic matter removal and membrane fouling control during drinking water treatment

A new hybrid system was developed in this study for the treatment of drinking water consisting of pre-coagulation using polyaluminium chloride (PACl) and membrane filtration (MF) with sponge cubes acting as biomass carriers (P-SMF). When compared to a conventional MF (CMF) and a MF after coagulation by utilizing PACl (P-MF), better removal of nutrients, UV₂₅₄ and dissolved organic carbon (DOC) (>65%) was obtained from the P-SMF. The accumulation of biopolymers (including polysaccharides and proteins), humic substances, hydrophilic organics, and other small molecular weight (MW) organic matter in the CMF led to the most severe membrane fouling coupled with the highest pore blocking and cake resistance. Pre-coagulation was ineffective in eliminating small MW and hydrophilic organic matter. Conversely, the larger MW organics (i.e. biopolymers and humic substances), small MW organics and hydrophilic organic compounds could be removed in significantly larger quantities in the P-SMF by PACl coagulation. This was achieved via adsorption and the biodegradation by attached biomass on these sponges and by the suspended sludge. Further analyses of the microbial community indicated that the combined addition of PACl and sponges generated a high enrichment of Zoolgloea, Amaricoccus and Reyranella leading to the reduction of biopolymers, and Flexibacter and Sphingobium were linked to the degradation of humic substances. Moreover, some members of Alphaproteobacteria in the P-SMF may be responsible for the removal of low MW organics. These results suggest that the pre-coagulation process coupled with adding sponge in the MF system is a promising technology for mitigating membrane fouling.

Start-up evaluations and biocarriers transfer from a trickling filter to a moving bed bioreactor for synthetic mariculture wastewater treatment

Mariculture wastewater treatment by nitrification requires a long start-up time due to high salinity stress. This study aimed to verify the faster start-up of a trickling filter (TF) compared to a moving bed bioreactor (MBBR) treating synthetic mariculture wastewater, and to investigate the feasibility of transferring mature biocarriers from the TF to a new MBBR (TF-MBBR). The nitrogen removal performance, biofilm physicochemical properties and microbial communities were investigated. The results obtained showed that, the TF started up 41 days faster than the MBBR, despite the richer microbial diversity in the latter. Lower biofilm roughness and protein content as well as higher adhesive force and polysaccharide content in the TF were obtained compared to the MBBR. Adhesive force was found to be negatively correlated with roughness (r = -0.630, p = 0.069). Transmittance assigned to amide II (1538 cm^-1) and amid III (1243 cm^-1) through Fourier transform infrared spectroscopy (FTIR) determination was only obtained in the TF, which was likely related to the faster start-up. Nitrosomonas and Nitrospira were detected as the predominant nitrifiers in both reactors. In addition, the new MBBR, incubated with the mature biocarriers transferred from the TF, had a satisfactory nitrification performance with no lag time. Interestingly, the transfer action increased the microbial diversity and made the biofilm physicochemical characteristics shift toward those of the MBBR. Taken together, the study confirmed that MBBR nitrification start-up can be accelerated via TF and biocarrier transfer.

Effects of individual and combined zinc oxide nanoparticle, norfloxacin, and sulfamethazine contamination on sludge anaerobic digestion

This work investigated the individual and combined effects of zinc oxide, norfloxacin, and sulfamethazine on sludge anaerobic digestion-associated methane production, protein and carbohydrate metabolism, and microbial diversity. Norfloxacin and sulfamethazine (500 mg/kg) did not inhibit methane production, but inhibited its production rate. Zinc oxide nanoparticles with antibiotics inhibited hydrolysis, fermentation, and methanogenesis over varying digestion periods. Complex pollution had a greater impact on methane production than zinc oxide alone, with acute, synergistic toxicity to methanogenesis over short periods. Complex pollution also had varying effects on bacterial and archaeal communities during digestion. These results aid understanding of the toxicity of emerging contaminants in sludge digestion, with the potential to improve pollution removal and reduce associated risks.

Preparation and characterization of a new hydrophilic and biocompatible magnetic polypropylene carrier used in wastewater treatment

This paper employed a blending method to prepare a new hydrophilic and biocompatible magnetic polypropylene carrier (HBMPC) and pure polypropylene carrier (PPC). Mechanical strength, magnetic induction on surface, microstructure, hydrophilicity and biocompatibility of HBMPC were measured, characterized and investigated respectively. The results showed that mechanical strength of PPC and HBMPC was not much different; magnetic induction on the surface of HBMPC was 4-6 mT; HBMPC had relatively large surface roughness and specific surface; average water content of PPC and HBMPC was 47.1% and 64.7%, respectively; contact angle of PPC and HBMPC was 88.7° and 58.5°, respectively; adsorption capacity of HBMPC and PPC to microorganism was 5.40E + 05 and 5.70E + 04 cfu (g·h)^-1, respectively. It took about 15 days for PPC to succeed in biofilm culturing while it took only 12 days for HBMPC. COD and [Formula: see text] removal efficiencies of PPC and HBMPC on the 15th day of biofilm formation were 80.5%, 90.5%, 63.7% and 85.4%, respectively; and growth status of microorganism adhering to the surface of HBMPC was better than that of PPC, biomass on single HBMPC and PPC after succeeded in biofilm culturing was 43.9 and 27.4 mg, respectively. All of these indicated that HBMPC had excellent hydrophilicity and biocompatibility.

The characteristic evolution of soluble microbial product and its effects on membrane fouling during the development of sponge membrane bioreactor coupled with fiber bundle anoxic bio-filter for treating saline wastewater

Membrane fouling mitigation was observed during the development of novel sponge membrane bioreactor coupled with fiber bundle anoxic bio-filter (AF-MBMBR). Soluble microbial product (SMP) was found to be positively correlated with membrane fouling. To further clarify the mechanism of fouling mitigation, the effects of bio-carriers (sponge and fiber bundles) on characteristics and fouling potential of SMP were investigated. Characterization of SMP implied that as a consequence of employing bio-carriers, tyrosine and tryptophan in SMP significantly decreased, instead relative proportions of humic and fulvic acids increased. Meanwhile, batch filtration tests demonstrated that fouling potential of SMP was significantly alleviated, flux decline caused by filtrating SMP decreased from 84.5% to 60.1%. Further analysis on foulants and filtrate revealed that proteins performed high adhesion propensity on membrane while humic and fulvic acids mainly can pass through the membrane; this finding could well explain the mitigation of SMP fouling potential induced by bio-carriers.

Influence of carrier media physical properties on start-up of moving attached growth systems

Five carrier media with different shapes (spherical and cylindrical), sizes, voidage and protected surface areas (112-610 m²/m³) were studied in a pilot scale moving bed biofilm reactor (MBBR). This study aimed at assessing start-up duration using biofilm formation rates. Results indicated that the spherical media required shorter periods to achieve stable biofilm formation rates associated with chemical oxygen demand (COD) (15-17 days), compared to cylindrical high surface area media (23-24 days). Protected surface area presented weaker correlations with the biofilm formation rate for COD (R² = 0.83) and ammonia removal (R² = 0.76). However, good correlations were observed with a combination of the media physical factors: dimensionality (Di), voidage (Voi), and hydraulic efficiency (HE) strongly correlated with biofilm formation rates for heterotrophic (R² = 0.95) and nitrifying bacteria (R² = 0.92). This study proposes that the media physical properties can contribute to shortening start-up, contributing to improved removal rates and fast commissioning of MBBRs.

Enhancing microalgae biofilm formation and growth by fabricating microgrooves onto the substrate surface

Attachment of cells to substrate surface is the premise for biofilm formation. To shelter microalgae cells from fluid shear stress and offer larger areas for microalgae attachment, the inerratic microgrooves, which can act as anchor points that offer larger areas for microalgae attachment and induce vortex to protect cells from hydraulic shear stress, were designed and fabricated into substrate surface. The results indicated that the shear stress on the surface with V-grooves was weaker than that on the surface with U-grooves, and 45° V-grooves with the width of 200 μm were benefit for cells attachment. The initial attachment time was shortened to 50 min under the hydraulic shear stress of 0.02 Pa compared to that of 135 min on the surface without microgrooves. Subsequently, the biofilm biomass concentration on the surface with 45° V-grooves increased by 14.29% to 165.84 g m^-2 compared with that on flat substrates.

Membrane fouling mechanism of biofilm-membrane bioreactor (BF-MBR): Pore blocking model and membrane cleaning

Biofilm membrane bioreactor (BF-MBR) is considered as an important wastewater treatment technology that incorporates advantages of both biofilm and MBR process, as well as can alleviate membrane fouling, with respect to the conventional activated sludge MBR. But, to be efficient, it necessitates the establishment of proper methods for the assessment of membrane fouling. Four Hermia membrane blocking models were adopted to quantify and evaluate the membrane fouling of BF-MBR. The experiments were conducted with various operational conditions, including membrane types, agitation speeds and transmembrane pressure (TMP). Good agreement between cake formation model and experimental data was found, confirming the validity of the Hermia models for assessing the membrane fouling of BF-MBR and that cake layer deposits on membrane. Moreover, the influences of membrane types, agitation speeds and transmembrane pressure on the Hermia pore blocking coefficient of cake layer were investigated. In addition, the permeability recovery after membrane cleaning at various operational conditions was studied. This work confirms that, unlike conventional activated sludge MBR, BF-MBR possesses a low degree of membrane fouling and a higher membrane permeability recovery after cleaning.

Antibiotic degradation and microbial community structures during acidification and methanogenesis of swine manure containing chlortetracycline or oxytetracycline

Anaerobic digestion (AD) has been applied to animal manure stabilization, and antibiotics is frequently found in animal manure. However, antibiotic degradation and microbial community structures during two-stage AD (acidification and methanogenesis) remain poorly understood. This experiments on two-stage anaerobic swine manure digesters were performed to investigate the degradation mechanisms and effects of chlortetracycline (CTC) and oxytetracycline (OTC) on microbial community structures. Results showed that acidification and methanogenesis showed good degradation performance for manure containing CTC and OTC at 60 and 40 mg/kg·TS, respectively. CTC and OTC were degraded by 59.8% and 41.3% in the acidogenic stage and by 76.3% and 78.3% in the methanogenic stage, respectively. CTC and OTC negatively affected bacterial community in methanogenic and acidogenic stages, respectively. They also adversely influenced the archaeal species in the methanogenic stage. Two-stage AD was proposed to treat manure containing antibiotics and to reduce the negative effects of antibiotics on AD.