Moving bed membrane bioreactors for carbon and nutrient removal: The effect of C/N variation

Sludge reduction, nitrous oxide emissions, and phosphorus removal by oxic-settling-anaerobic (OSA) process: the effect of hydraulic retention time

This paper presents a study on reducing sewage sludge by an oxic-settling-anaerobic (OSA) pilot plant compared to the conventional activated sludge (CAS) process in view of resource recovery and moving towards plant carbon neutrality. The OSA plant was supplied with real wastewater and the anaerobic reactor was operated under two hydraulic retention times (HRT) (4 and 6 h). Greenhouse gas (GHG) emissions were monitored for the first time to determine the OSA process's production mechanism. The results highlighted that under the lowest HRT (4 h), the removal efficiencies of COD and PO4-P, increased from 75 to 89% and from 39 to 50% for CAS and OSA configurations, respectively. The observed yield coefficient was reduced from 0.58 gTSS gCOD-1 (CAS period) to 0.31 gTSS gCOD-1 (OSA period). A remarkable deterioration of nitrification efficiency under OSA configuration was obtained from 79% (CAS) to 27% (OSA with HRT of 6 h). The huge deterioration of nitrification significantly affected the GHG emissions, with the N2O-N fraction increasing from 1% (CAS) to 1.55% (OSA 4 h HRT) and 3.54% (OSA 6 h HRT) of the overall effluent nitrogen, thus suggesting a relevant environmental implication due to the high global warming potential (GWP) of N2O.

Pilot-scale investigation of performance and microbial community in a novel system combining fixed and suspended activated sludge

The conventional activated sludge (CAS) process is a widely used method for wastewater treatment due to its effectiveness and affordability. However, it can be prone to sludge abnormalities such as sludge bulking/foaming and sludge loss, which can lead to a decrease in treatment efficiency. To address these issues, a novel bag-based fixed activated sludge (BBFAS) system utilizing mesh bags to contain the sludge was developed for low carbon/nitrogen ratio wastewater treatment. Pilot-scale experiments demonstrated that the BBFAS system could successfully avoid the sludge abnormalities. Moreover, it was not affected by mass transfer resistance and exhibited significantly higher nitrogen removal efficiency, surpassing that of the CAS system by up to 78%. Additionally, the BBFAS system demonstrated comparable organic matter removal efficiency to CAS system. 16S rRNA gene high-throughput sequencing revealed that the bacterial community structure within the BBFAS system was significantly different from that of the CAS system. The bacteria associated with ammonium removal were more abundant in the BBFAS system than in the CAS system. The abundance of Nitrospira in the BBFAS could reach up to 6% and significantly higher than that in the CAS system, and they were likely responsible for both ammonia-oxidizing and nitrite-oxidizing functions. Clear stratification of microbial communities was observed from the outer to inner layers of the bag components due to the gradients of dissolved oxygen and other substrates. Overall, this study presents a promising approach for avoiding activated sludge abnormalities while maintaining high pollutant removal performance.

Optimization of moving bed biofilm reactors for the treatment of municipal wastewater

The properties of biocarriers significantly influence the performance of a moving bed-biofilm reactor (MBBR). This study aimed to assess the impact of media type, filling ratio, and hydraulic retention time (HRT) on biofilm formation and MBBR performance in both batch and continuous setups using real municipal wastewater. Two different media, high-density polyethylene (HDPE) and polypropylene (PPE), with varying surface area and properties were used. Biofilm growth and MBBR performance were monitored and optimized using response surface methodology. The effect of different media was investigated for three filling ratios of 20%, 40% and 60% and HRT of 4, 6 and 8 h. Results depicted a better biofilm growth on HDPE media in comparison to PPE carriers due to difference in media structure and surface properties. At all the conditions tested, HDPE media showed comparatively better performance for the removal of organic matter and nutrients than PPE media. The maximum organic matter removal efficiency was found as 77% and 75% at an HRT of 6 h and filling ratio of 40% for HDPE and PPE media, respectively. The ammonia removal was also found better for HDPE media due to its geometry and structure favoring the anoxic conditions with maximum removal of 89% achieved at 6-h HRT and 40% filling ratio. Overall, the system with HDPE media indicated more stability in terms of reactor performance than PPE carriers with variations in the operating conditions.

Sewage sludge minimisation by OSA-MBR: A pilot plant experiment

This study presents the excess sludge minimisation in a Membrane Bioreactor (MBR) system by an Oxic Settling Anaerobic (OSA) process. The pilot plant was fed with real wastewater and OSA was operated with two different hydraulic retention times (HRT), respectively 4 (Period II) and 6 h (Period III) and compared to an MBR (Period I). Multiple parameters/variables were monitored: sludge minimisation, nitrogen and carbon removal, membrane fouling, and biokinetic behaviour through respirometry. With respect to the current literature, greenhouse gas emissions were also here monitored, often neglected. Results demonstrated that combining MBR and OSA systems can significantly reduce excess sludge production (89.7%, in Period III and 59.7% in Period II, compared to Period I). However, Period III presented better PO4-P removal efficiencies but worse performances in the other parameters (COD, NH4 and Total Nitrogen). No substantial variation in membrane fouling was obtained over the experimental periods. Finally, the HRT increase in the anaerobic reactor promoted a N2O-N increase inside the unaerated reactors, highlighting the need for a trade-off between sludge minimisation and GHG emission.

Performance and mechanism of modified biological nutrient removal process in treating low carbon-to-nitrogen ratio wastewater

For solving the challenge of difficult nutrient removal, high running cost and CO₂ emission at low carbon-to-nitrogen (C:N) ratio, Bi-Bio-Selector for nitrogen and phosphorus removal (BBSNP) process was developed. Under parallel operation conditions, full-scale BBSNP was less influence by low C:N ratio (3.5-2) than Anaerobic-anoxic-aerobic (AAO) and achieved better nitrogen removal performance. The mechanism of performance advantage in BBSNP was analyzed by mass balance and high throughout sequencing. It demonstrated BBSNP developed unique microbial community at C:N ratio of 2. Higher abundance of Saccharibacteria, Ferruginibacter, Ottowia, Dokdonella, Candidatus_Nitrotoga and Nitrospira in BBSNP was responsible for better chemical oxygen demand (COD) utilization efficiency, denitrification, denitrifying phosphorus removal and nitrification. Meanwhile, under low C:N ratio, BBSNP could save 10% organic carbon and 15% oxygen requirement, reduce 53% running cost and 21% CO₂ emission, which had practical value in relieving energy crisis and carbon emission of wastewater treatment plants (WWTPs).

Modeling nitrous oxide emissions in membrane bioreactors: Advancements, challenges and perspectives

Membrane bioreactors (MBRs) have become a well-established wastewater treatment technology owing to their extraordinary efficiency and low space advantage over conventional activated sludge processes. Although the extended activated sludge models can predict the general trend of nitrous oxide (N₂O) emissions in MBRs, the simulation results usually deviate from the actual values. This review critically evaluates the recent advances in the modeling of N₂O emissions in MBRs, and proposes future directions for the development and improvement of models that better match the MBR characteristics. The quantitative impact of MBR characteristics on N₂O emissions is identified as a key knowledge gap demanding urgent attention. Accurately clarification of the N₂O emission pathways governed by MBR characteristics is essential to improve the reliability and practicability of existing models. This article lays a momentous foundation for the optimization of N₂O models in MBRs, and proposes new demands for the next-generation model. The contents will assist academics and engineers in developing N₂O production models for accurate prediction.

Roadmapping the Transition to Water Resource Recovery Facilities: The Two Demonstration Case Studies of Corleone and Marineo (Italy)

The current exploitation of freshwater, as well as the significant increase in sewage sludge production from wastewater treatment plants (WWTPs), represent nowadays a critical issue for the implementation of sustainable development consistent with the circular economy concept. There is an urgent need to rethink the concept of WWTPs from the conventional approach consisting in pollutant removal plants to water resource recovery facilities (WRRFs). The aim of this paper is to provide an overview of the demonstration case studies at the Marineo and Corleone WRRFs in Sicily (IT), with the final aim showing the effectiveness of the resources recovery systems, as well as the importance of plant optimization to reduce greenhouse gas (GHG) emissions from WRRFs. This study is part of the H2020 European Project “Achieving wider uptake of water-smart solutions—Wider-Uptake”, which final aim is to demonstrate the water-smart solution feasibility in the wastewater sector. The main project goal is to overcome the existing barriers that hamper the transition to circularity through the implementation of a governance analysis tool. The preliminary actions in the two demonstration cases are first presented, while, subsequently, the water-smart solutions to be implemented are thoroughly described, highlighting their roles in the transition process. The achieved preliminary results underlined the significant potential of WRRF application, a great chance to demonstrate the feasibility of innovative solutions in the wastewater sector to overcome the existing social, administrative and technical barriers.

Water Resource Recovery Facilities (WRRFs): The Case Study of Palermo University (Italy)

The wastewater sector paradigm is shifting from wastewater treatment to resource recovery. In addition, concerns regarding sustainability during the operation have increased. In this sense, there is a need to break barriers (i.e., social, economic, technological, legal, etc.) for moving forward towards water resource recovery facilities and demonstration case studies can be very effective and insightful. This paper presents a new water resource recovery case study which is part of the Horizon 2020 EU Project “Achieving wider uptake of water-smart solutions—Wider Uptake”. The final aim is to demonstrate the importance of a resource recovery system based on the circular economy concept. The recovery facilities at Palermo University (Italy) are first presented. Afterwards, the resource recovery pilot plants are described. Preliminary results have underlined the great potential of the wastewater treatment plant in terms of resources recovery and the central role of the University in fostering the transition towards circular economy. The fermentation batch test highlighted a volatile fatty acids (VFAs) accumulation suitable for polyhydroxyalkanoates (PHAs) production. The results of static adsorption and desorption tests showed that the highest amount of adsorbed NH4+ was recorded for untreated and HCl-Na treated clinoptilolite.

Influence of volatile solids and pH for the production of volatile fatty acids: Batch fermentation tests using sewage sludge

The aim of this work was to study the effect of volatile suspended solid (VSS) and pH on volatile fatty acids (VFA) production from waste activated sludge (WAS) fermentation by means of batch tests. The final goal was to gain insights to enhance VFA stream quality, with the novelty of using WAS with high sludge retention time. Results revealed that the optimum conditions to maximize VFAs and minimize nutrients and non-VFA sCOD are a VSS concentration of 5.9 g/L and initial pH adjustment to pH 10. The WAS bacterial community structures were analysed according to Next Generation Sequencing (NGS) of 16S rDNA amplicons. The results revealed changes of bacterial phyla abundance in comparison with the batch test starting condition.

Ammonium adsorption, desorption and recovery by acid and alkaline treated zeolite

In this study, the suitability of zeolite as a possible medium for ammonium adsorption, desorption and recovery from wastewater was investigated. Specifically, batch adsorption and desorption studies with solutions enriched in NH₄⁺ were conducted employing zeolite to evaluate how the chemical treatment and contact time affect adsorption and desorption. Several experimental tests were carried out considering both untreated and treated zeolite. Untreated and HCl-Na treated zeolite adsorbed up to 11.8 mg NH₄⁺ g^-1 and showed the highest efficiency in recovering NH₄⁺ from aqueous solution. Regardless of pre-treatment, treatments with NaCl resulted in higher and faster adsorption of NH₄⁺ than treatments with CaCl₂ and MgCl₂.

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.

Effective removal of heavy metals from industrial effluent wastewater by a multi metal and drug resistant Pseudomonas aeruginosa strain RA-14 using integrated sequencing batch reactor

Sequencing batch reactor (SBR) is useful in removal of both non-biodegradable and biodegradable contaminants from wastewater. The main aim of the present investigation was to evaluate the potential of biocatalyst strain RA-14 on heavy metal removal under SBR. The selected strain was screened from the soil sediment contaminated with heavy metals. It was able to survive at different (Hg²⁺, Pb²⁺, Zn²⁺, Cu²⁺, Cd²⁺ and Ni²⁺) heavy metals (>500 ppm). The bacterial strain RA-14 showed maximum bioaccumulation potential than other strains. Heavy metal resistance patterns of Pb²⁺ > Cu² > Cd²⁺ > Hg²⁺, Ni²⁺ and Zn² was observed. Strain RA-14 was resistant to penicillin-G, nalidixic acid, ceftazidime, cefotaxime, kanamycin and ampicillin. The results revealed that bioaccumulation activities were improved at pH 7.0 (83.2 ± 1.8%), 40 °C (89.34 ± 3%) and affected at higher pH values and temperature. The results showed that contact time and initial Lead concentration was also affected Lead accumulation. The heavy metal tolerant strain RA-14 was further investigated towards heavy metal removal in SBR. Heavy metal was removed in SBR within 10 h of hydraulic retention time. Heavy metal removal was high at 2 mg/L (0.33 mg/L Cu²⁺, 0.33 mg/L Hg²⁺, 0.33 mg/L Pb²⁺, 0.33 mg/L Zn²⁺, 0.33 mg/L Cd²⁺ and 0.33 mg/L Ni²⁺) heavy metals. Total nitrogen, biological oxygen demand (BOD) and chemical oxygen demand (COD) of treated water in SBR was removed and the removal efficacy was 91.3 ± 2.1%, 97.6 ± 3.3%, and 94.3 ± 4.4%, respectively in 10 h hydraulic retention time. However, the efficiency of BOD, COD and total nitrogen content removal was decreased, due to the reduced metabolic process of bacteria after 10 h. The SBR reactor proved to be an efficient method for the treatment of various heavy metals from the wastewater.

Quantifying the Effect of COD to TN Ratio, DO Concentration and Temperature on Filamentous Microorganisms’ Population and Trans-Membrane Pressure (TMP) in Membrane Bio-Reactors (MBR)

Using moderate populations of filaments in the biomass of Membrane Bio-Reactors (MBRs) is a biological anti-fouling method which has been increasingly applied over the last few years. This study aims to quantify the effect of COD to TN ratio, Dissolved Oxygen (DO) concentration and temperature on filaments’ population and Trans-Membrane Pressure (TMP) in a pilot-scale MBR, with a view to reducing membrane fouling. The novelty of the present work concerns the development of a mathematical equation that correlates fouling rate (dTMP/dt) with the population of filamentous microorganisms, assessed by the Filament Index (FI), and with the concentration of the carbohydrate fraction of Soluble Microbial Products (SMPc). Apart from TMP and SMPc, other fouling-related biomass characteristics, such as sludge filterability and settleability, were also examined. It was shown that at high COD to TN ratio (10:1), low DO concentration in the filaments’ tank (0.5 ± 0.3 mg/L) and high temperature (24–30 °C), a moderate population of filaments is developed (FI = 1–2), which delays the TMP rise. Under these conditions, sludge filterability and settleability were also enhanced. Finally, TMP data analysis showed that the fouling rate is affected by FI and SMPc concentration mainly in the long-term fouling stage and increases exponentially with their increase.

Prediction the performance of multistage moving bed biological process using artificial neural network (ANN)

Complexity, uncertainty, and high dynamic nature of nutrient removal through biological processes (BPs) makes it difficult to model and control these processes, forcing designers to rely on approximations, probabilities, and assumptions. To cope with this difficult task and perform an effective and well-controlled BP operation, an artificial neural network (ANN) algorithm was developed to simulate, model, and control a three-stage (anaerobic/anoxic and MBBR) enhanced nutrient removal biological process (ENR-BP) challenging real wastewater. The effect of surface area loading rate (SALR), organic matters (OMs), nutrients (N & P), feed flow rate (Q_feed), hydraulic retention time (HRT), and internal recycle flow (IRF) on the performance of the ENR-BP to fulfil rigorous discharge limitations were evaluated. Experimental data was used to develop the appropriate architecture for the AAN using iterative steps of training and testing. Significant removals of chemical oxygen demand (COD) (89.2 to 98.3%), NH₄⁺ (88.5 to 98.9%), and total phosphorus (TP) (77.9 to 99.9%) were achieved at a total HRT of 13.3 h (HRT_Z-1 = 3 h, HRT_Z-2 = 6 h and HRT_Z-3 = 5.3 h) and an IRF value of 1.75. The ENR-BP treatment mechanism relies on the use of OMs as a source of energy for phosphorus bio-uptake and the simultaneous nitrification and denitrification (SND) of nitrogen compounds. The removal efficiencies in the proposed ENR-BP were four fold higher than the suspended growth process and in the same order of magnitude of 5-stage Bardenpho-MBBR. The developed ANN-based model provides an efficient and robust tool for predicting and forecasting the performance of the ENR-BP.

Responses of microbial structures, functions, metabolic pathways and community interactions to different C/N ratios in aerobic nitrification

The responses of microbial structures, functional profiles and metabolic pathways during nitrification to four C/N ratios (0, 5, 10 and 15) were investigated in four parallel SBRs denoted as S₀, S₅, S₁₀, S₁₅. Results indicated that microbial diversities were affected by C/N ratios, while the same dominant taxa were observed, mainly including Proteobacteria, Betaproteobacteria, Rhodocyclales, Rhodocyclaceae, Zoogloea. The unique biomarkers were identified in each sludge sample through LEfSe analysis. Functional genera/enzymes responsible for removing organics and nitrogen coexisted in four SBRs at different abundances, except for that ammonia oxidizing bacteria (AOB) Nitrosomonas (0.33%-0.66%) and ammonia monooxygenase (amo) (9.4 × 10^-7-2.8 × 10^-6) were only detected in S₀. Moreover, PICRUSt analysis indicated similar overall patterns of metabolic pathways in four sludge samples. The network analysis revealed that total nitrogen removal positively correlated with hcp (Spearman's ρ of 0.853), and ammonia oxidizing rate was associated with amo (Spearman's ρ of 0.096).

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.

Optimizing nutrient removal of moving bed biofilm reactor process using response surface methodology

The potential of 3-stages process (anaerobic, anoxic and moving bed biofilm reactor (MBBR)) for organic matter and nutrient removals from secondary WWTP effluents at various hydraulic retention time (HRT) and nitrate recycle ratio (R) was investigated. Percentage removals of total nitrogen (%TNremoval) and phosphorous (%TPremoval) were optimized using response surface methodology (RSM). Under optimized conditions (HRTtotal = 12.8 hr and R = 1.5) significant chemical oxygen demand removal (%CODremoval), %TNremoval and %TPremoval of 95.5%, 96.2%, 94.70% were attained. The MMBR effectively reduced organic matter and nutrient under low HRT and R. %TNremoval was improved by increasing the HRTR2 up to 1.5 h at R ≤ 2. Bio-uptake of phosphorus and nitrate is controlled by release of secondary phosphorous. Reactors demonstrated stable biofilm characteristics except for a slight decrease in biofilm thickness due to flow-shear stress. The 3-stages process performed four times higher than suspended growth process and similar to 5-stage Bardenpho-MBBR.

Moving bed biofilm reactor as an alternative wastewater treatment process for nutrient removal and recovery in the circular economy model

Over the last years, an increasing concern has emerged regarding the eco-friendly management of wastewater. Apart from the role of wastewater treatment plants (WWTPs) for wastewater and sewage sludge treatment, the increasing need of the recovery of the resources contained in wastewater, such as nutrients and water, should be highlighted. This would allow for transforming a wastewater treatment plant (WWTP) into a sustainable technological system. The objective of this review is to propose a moving bed biofilm reactor (MBBR) as a novel technology that contributes to the circularity of the wastewater treatment sector according to the principles of circular economy. In this regard, this paper aims to consider the MBBR process as the initial step for water reuse, and nutrient removal and recovery, within the circular economy model.

Enhancing treated wastewater effluent characteristics using hybrid biofilm/activated sludge process - a case study

This paper documents the results of 12 months of monitoring of an upgraded hybrid moving bed biofilm reactor-conventional activated sludge wastewater treatment plant (MBBR-CAS WWTP). It also targets the assessment of the increment of the hydraulic load on existing treatment units with a zero construction and land cost. The influent flow to the plant was increased from 21,000 m³ d^-1 to 30,000 m³ d^-1, 40% of the existing CAS reactor volume was used for the MBBR zone with a carrier fill fraction of 47.62% and with Headworks Bio ActiveCell™ 515 used as media; no modifications were made for the primary and secondary tanks. The hybrid reactor showed high removal efficiencies for biochemical oxygen demand (BOD₅), chemical oxygen demand (COD) and total suspended solids (TSS), with average effluent values recording 33.00 ± 8.87 mg L^-1, 52.90 ± 9.65 mg L^-1 and 29.50 ± 6.64 mg L^-1 respectively. Nutrient removals in the hybrid modified biological reactor were moderate compared with carbon removal despite the high C/N ratio of 12.33. Findings in this study favor the application of MBBR in the upgrading of existing CAS plants with the plant BOD₅ removal efficiency recording an increase of about 5% compared with the plant before upgrade and effluent values well within the legal requirements.

Performance and bacterial community of moving bed biofilm reactors with various biocarriers treating primary wastewater effluent with a low organic strength and low C/N ratio

A laboratory-scale sequencing batch reactor (SBR) and two moving bed biofilm reactors (MBBRs) with different types of biocarriers were operated to treat the effluent of chemically enhanced primary sedimentation (CEPS). Due to the low organic strength and low carbon/nitrogen ratio of the CEPS effluent, COD and NH₄⁺-N were effectively removed by the MBBRs but not by the SBR. Of the two MBBRs, MBBR2 filled with LEVAPOR biocarrier cubes performed even better than MBBR1 filled with K3 polystyrene biocarriers. The continuous decline of the sludge concentration in the SBR and the high and stable biomass content in MBBR2 contributed to their performances. High-throughput sequencing analysis showed that the reactors had selective effects on the bacterial community structure. Principal coordinate analysis indicated the different dynamic successions in the three reactors. Network analysis showed different community composition and diversity that were highly suggestive of different bacterial interactions among the three bioreactors.

Fouling Mitigation and Wastewater Treatment Enhancement through the Application of an Electro Moving Bed Membrane Bioreactor (eMB-MBR)

High operational cost due to membrane fouling propensity remains a major drawback for the widespread application of membrane bioreactor (MBR) technology. As a result, studies on membrane fouling mitigation through the application of integrated processes have been widely explored. In this work, the combined application of electrochemical processes and moving bed biofilm reactor (MBBR) technology within an MBR at laboratory scale was performed by applying an intermittent voltage of 3 V/cm to a reactor filled with 30% carriers. The treatment efficiency of the electro moving bed membrane bioreactor (eMB-MBR) technology in terms of ammonium nitrogen (NH₄-N) and orthophosphate (PO₄-P) removal significantly improved from 49.8% and 76.7% in the moving bed membrane bioreactor (MB-MBR) control system to 55% and 98.7% in the eMB-MBR, respectively. Additionally, concentrations of known fouling precursors and membrane fouling rate were noticeably lower in the eMB-MBR system as compared to the control system. Hence, this study successfully demonstrated an innovative and effective technology (i.e., eMB-MBR) to improve MBR performance in terms of both conventional contaminant removal and fouling mitigation.

Integrated fixed-film activated sludge membrane bioreactors versus membrane bioreactors for nutrient removal: A comprehensive comparison

This research elucidates the pollutants (nutrients and carbon) removal performance and nitrous oxide (N₂O) emissions of two pilot plants. Specifically, a University of Cape Town (UCT) Membrane Bioreactor (MBR) plant and an Integrated Fixed Film Activated Sludge (IFAS)-UCT-MBR plant were investigated. The plants were fed with real wastewater augmented with acetate and glycerol in order to control the influent carbon nitrogen ratio (C/N). The short-term effect of the inlet C/N ratio variation (C/N = 5 mgCOD/mgN and C/N = 10 mgCOD/mgN) on the behaviour of both plants was investigated. The results showed that the IFAS-UCT-MBR configuration provided the best performance in terms of pollutants removal at the two investigated C/N ratios. Furthermore, the lowest N₂O emission (with respect to the influent nitrogen) was observed in the IFAS-UCT-MBR configuration, thus suggesting a potential beneficial effect of the biofilm in the emission reduction. However, the membrane of the IFAS-UCT-MBR showed a greater fouling tendency compared to the UCT-MBR configuration. This result, likely related to the biofilm detached from carriers, could seriously affect the indirect GreenHouse Gas emissions due to the increase of the energy requirement for permeate extraction with the increase of membrane fouling.

Greenhouse gas emissions from membrane bioreactors: analysis of a two-year survey on different MBR configurations

This study aimed at evaluating the nitrous oxide (N₂O) emissions from membrane bioreactors (MBRs) for wastewater treatment. The study investigated the N₂O emissions considering multiple influential factors over a two-year period: (i) different MBR based process configurations; (ii) wastewater composition (municipal or industrial); (iii) operational conditions (i.e. sludge retention time, carbon-to-nitrogen ratio, C/N, hydraulic retention time); (iv) membrane modules. Among the overall analysed configurations, the highest N₂O emission occurred from the aerated reactors. The treatment of industrial wastewater, contaminated with salt and hydrocarbons, provided the highest N₂O emission factor (EF): 16% of the influent nitrogen for the denitrification/nitrification-MBR plant. The lowest N₂O emission (EF = 0.5% of the influent nitrogen) was obtained in the biological phosphorus removal-moving bed-MBR plant likely due to an improvement in biological performances exerted by the co-presence of both suspended and attached biomass. The influent C/N ratio has been identified as a key factor affecting the N₂O production. Indeed, a decrease of the C/N ratio (from 10 to 2) promoted the increase of N₂O emissions in both gaseous and dissolved phases, mainly related to a decreased efficiency of the denitrification processes.