Membrane fouling characteristics and mitigation in a coagulation-assisted microfiltration process for municipal wastewater pretreatment

An advanced treatment process for 3-high wastewater discharged from crude oil storage tanks

The wastewater discharged from crude oil storage tanks (WCOST) contains high concentrations of salt and metal iron ions, and high chemical oxygen demand (COD). It belongs to "3-high" wastewater, which is difficult for purification. In this study, WCOST treatments were comparatively investigated via an advanced pretreatment and the traditional coagulation-microfiltration (CMF) processes. After WCOST was purified through the conventional CMF process, fouling occurred in the microfiltration (MF) membrane, which is rather harmful to the following reverse osmosis (RO) membrane unit, and the effluent featured high COD and UV254 values. The analysis confirmed that the MF fouling was due to the oxidation of ferrous ions, and the high COD and UV254 values were mainly attributable to the organic compounds with small molecular sizes, including aromatic-like and fulvic-like compounds. After the pretreatment of the advanced process consisting of aeration, manganese sand filtration, and activated carbon adsorption in combination with CMF process, the removal efficiencies of organic matter and total iron ions reached 97.3% and 99.8%, respectively. All the water indexes of the effluent, after treatment by the advanced multi-unit process, meet well the corresponding standard. The advanced pretreatment process reported herein displayed a great potential for alleviating the MF membrane fouling and enhanced the lifetime of the RO membrane system in the 3-high WCOST treatment.

New insights into membrane fouling during direct membrane filtration of municipal wastewater and fouling control with mechanical strategies

Direct membrane filtration (DMF) technology achieves energy self-sufficiency through carbon recovery and utilization from municipal wastewater. To control its severe membrane fouling and improve DMF technology, targeted research on fouling behaviour and mechanisms is essential. In this study, a DMF reactor equipped with a flat-sheet ceramic membrane was conducted under three scenarios: without control, with intermittent aeration, and with periodic backwash. This system achieved efficient carbon concentration with chemical oxygen demand below 50 mg/L in permeate. Membrane fouling was dominated by intermediate blocking and cake filtration. And reversible external resistance accounted for over 85 % of total resistance. Predominant membrane foulants were free proteins, whose deposition underlies the attachment of cells and biopolymers. Backwash decreased the fouling rate and increased fouling layer porosity by indiscriminately detaching foulants from the membrane surface. While aeration enhanced the back transport of large particles and microbial activity, causing a relatively thin and dense fouling layer containing more microorganisms and β-d-glucopyranose polysaccharides, which implies a higher biofouling potential during long-term operation. In addition, aeration combined with backwash enhanced fouling control fivefold over either one alone. Therefore, simultaneous operation of backwash and other mechanical methods that can provide shear without stimulating aerobic microbial activity is a preferred strategy for minimizing membrane fouling during DMF of municipal wastewater.

Strategies to improve membrane performance in wastewater treatment

Membrane technology has rapidly gained popularity in wastewater treatment due to its cost-effectiveness, environmentally friendly tools, and elevated productivity. Although membrane performance in wastewater treatment has been reviewed in several past studies, the key techniques for improving membrane performance, as well as their challenges, and solutions associated with the membrane process, were not sufficiently highlighted in those studies. Also, very few studies have addressed hybrid techniques to improve membrane performance. The present review aims to fill those gaps and achieve public health benefits through safe water processing. Despite its higher cost, membrane performance can result in a 36% reduction in flux degradation. The issue with fouling has been identified as one of the key challenges of membrane technology. Chemical cleaning is quite effective in removing accumulated foulant. Fouling mitigation techniques have also been shown to have a positive effect on membrane photobioreactors that handle wastewater effluent, resulting in a 50% and 60% reduction in fouling rates for backwash and nitrogen bubble scouring techniques. Membrane hybrid approaches such as hybrid forward-reverse osmosis show promise in removing high concentrations of phosphorus, ammonium, and salt from wastewater. The incorporation of the forward osmosis process can reject 99% of phosphorus and 97% of ammonium, and the reverse osmosis approach can achieve a 99% salt rejection rate. The control strategies for membrane fouling have not been successfully optimized yet and more research is needed to achieve a realistic, long-term direct membrane filtering operation.

Efficient direct membrane filtration (DMF) of municipal wastewater for carbon recovery: Application of a simple pretreatment and selection of an appropriate membrane pore size

Considerable attention has been paid in recent years to the recovery and effective utilization of organic matter in municipal wastewater for the establishment of a circular economy. Direct membrane filtration (DMF) of municipal wastewater using microfiltration (MF) or ultrafiltration (UF) membranes to retain and concentrate the organic matter in municipal wastewater could be a practical option for this purpose. However, severe membrane fouling and high concentrations of organic matter remaining in the DMF permeate are concerns to be addressed. Application of a simple pretreatment using fixed biofilms was investigated to address these issues. In this study, experiments were carried out at an existing municipal wastewater treatment plant. A moving bed biofilm reactor (MBBR) process operated under a very short HRT of 1 h and DO concentration of 0.5 mg/L selectively degraded low-molecular-weight dissolved organic matter in municipal wastewater without degradation of membrane-recoverable suspended and colloidal organic matter. Application of the pretreatment did not reduce the amount of organic carbon recovered by DMF using an MF membrane (approximately 70% of the influent COD being recovered), while it dramatically mitigated the membrane fouling probably due to the alteration of characteristics of dissolved organic matter in wastewater. The pretreatment also reduced the concentration of organic matter in the DMF permeate by 41%: COD concentration in the DMF permeate was as low as 40 mg/L. With the established MBBR pretreatment, performances of MF (0.1 µm) and UF (molecular weight cut-off: 150,000) membranes for DMF were compared in parallel. It was found that the increase of the recoverable amount of organic matter by using UF was marginal (about 5%), whereas fouling in UF was much more severe than that in MF. The severe fouling in UF was caused by inorganic colloids such as FeS that could pass through MF membranes but be retained by UF membranes. Based on the results obtained in this study, it is concluded that MF is more suitable than UF for efficient DMF.

Online colloidal particle monitoring for controlled coagulation pretreatment to lower microfiltration membrane fouling at a potable water reuse facility

Fouling of microfiltration (MF)) membranes during water/wastewater treatment is predominantly caused by colloidal particles (size <1 µm) in the feed water. Until recently no online technology was available to directly measure the occurrence of colloidal particles in these waters. This study evaluated the viability of a novel online light scattering technology (Nanoparticle Tracking Analysis) to continuously monitor colloidal particles in the membrane feed water (a secondary-treated wastewater) for targeted removal by injecting coagulant at a dosage proportional to the measured concentration of colloidal particles. A diurnal variation was observed in the colloidal particle concentration in the feed water with the lowest concentration occurring at approximately 6 am and the highest concentration occurring after mid-day. The peak colloidal particle concentrations were 4 to 6 times higher than the lowest concentrations measured on the same day. Bench-scale studies were performed to develop a relationship between colloidal particle concentration and the optimum coagulant dosage required for their removal. Subsequently, a pilot-scale study was performed using two MF pilot units operated in parallel, one receiving targeted coagulant dosing and the other with no coagulant dosing, to demonstrate the effectiveness of targeted coagulant dosing in preventing membrane fouling. The pilot unit that received targeted coagulant dose experienced only 4 to 20% of the transmembrane pressure increase of the increase experienced by the pilot unit that received no coagulant. Evaluation of fouling resistance indicated that targeted coagulation improved flux by predominantly lowering the irreversible fouling. The filtrate water quality measured by colloidal particle concentration, chemical oxygen demand (COD), and turbidity were very similar for the two pilot units. This suggests that although the efficiency of particle and organic materials removal does not change with coagulant addition, the particles filtered by the membrane in the control unit contributed to membrane irreversible fouling, while in the coagulant-treated unit, the coagulated colloidal particles were removed away from the membrane into the backwash stream during the frequent backwash/air scour procedures.

Biogas Production from Concentrated Municipal Sewage by Forward Osmosis, Micro and Ultrafiltration

Direct application of anaerobic digestion to sewage treatment is normally only possible under tropical weather conditions. This is the result of its diluted nature and temperatures far from those suitable for anaerobic conversion of organic matter. Then, direct application of anaerobic treatment to sewage would require changing temperature, concentration, or both. Modification of sewage temperature would require much more energy than contained in the organic matter. Then, the feasible alternative seems to be the application of a pre-concentration step that may be accomplished by membrane filtration. This research studied the pre-concentration of municipal sewage as a potential strategy to enable the direct anaerobic conversion of organic matter. Three different membrane processes were tested: microfiltration, ultrafiltration and forward osmosis. The methane potential of the concentrates was determined. Results show that biogas production from the FO-concentrate was higher, most likely because of a higher rejection. However, salt increase due to rejection and reverse flux of ions from the draw solution may affect anaerobic digestion performance.

Enhancement of membrane fouling mitigation and trace organic compounds removal by electric field in a microfiltration reactor treating secondary effluent of a municipal wastewater treatment plant

Applying an electric field in the membrane filtration was an effective method to alleviate membrane fouling and enhance the trace organic compounds (TrOCs) removal. The secondary effluent of a municipal wastewater treatment plant was used as feed water to evaluate the performance of the electric field coupled microfiltration system. Applying a 1.25 V voltage reduced 22.9% membrane fouling by electrophoretic force, and the membrane fouling was alleviated by 70.8% at 3 V by electrochemical oxidation and electric field force. At 3 V, active chlorine and hydroperoxide generated on the electrodes and the acidic environment formed around the anode significantly inhibited the growth of microorganisms and their attachment on the membrane surface, and thus reduced the membrane fouling formed by microorganisms. Electrochemical oxidation also removed the protein in wastewater and changed the main organic components of membrane fouling from microorganisms, protein, and polysaccharide to humic substances and polysaccharide. Furthermore, the electrophoretic force and acidic environment reduced the electrostatic repulsion of humic substances and made them tend to aggregate and form hydrophilic porous fouling structures, which obviously lowered filtration resistance and showed significant membrane fouling mitigation. Also, the electric field effectively enhanced the removal of target TrOCs through electrochemical oxidation and electric field force improving the elimination of TrOCs from 8.5% ~ 26.1% at 0 V to 35.9% ~ 84.8% at 3 V.

Coagulants put phosphate-accumulating organisms at a competitive disadvantage with glycogen-accumulating organisms in enhanced biological phosphorus removal system

Enhanced biological phosphorus removal (EBPR) process is susceptible to the changed operation condition, which results in an unstable treatment performance. In this work, long-term effect of coagulants addition, aluminum salt for the reactor R₁ and iron salt for the reactor R₂, on EBPR systems was comprehensively evaluated. Results showed that during the initial 30 days' coagulant addition, effluent chemical oxygen demand and phosphorus can be reduced below 25 and 0.5 mg·L^-1, respectively. Further supply of metal salts would stimulate microbial extracellular polymeric substance excretion and induce reactive oxygen species accumulation, which destroyed the cell membrane integrity and deteriorated the phosphorus removal performance. Moreover, coagulants would decrease the relative abundance of Candidatus Accumulibacter while increase the relative abundance of Candidatus Competibacter, leading phosphors accumulating organisms in a disadvantage position. The results of this work might be valuable for the operation of chemical assisted biological phosphorus removal bioreactor.

Optimising the Flux Enhancer Dosing Strategy in a Pilot-Scale Anaerobic Membrane Bioreactor by Mathematical Modelling

Flux enhancers (FEs) have been successfully applied for fouling mitigation in membrane bioreactors. However, more research is needed to compare and optimise different dosing strategies to improve the filtration performance, while minimising the use of FEs and preventing overdosing. Therefore, the goal of this research is to develop an optimised control strategy for FE dosing into an AnMBR by developing a comprehensive integrated mathematical model. The integrated model includes filtration, flocculation, and biochemical processes to predict the effect of FE dosing on sludge filterability and membrane fouling rate in an AnMBR. The biochemical model was based on an ADM1, modified to include FEs and colloidal material. We developed an empirical model for the FE-induced flocculation of colloidal material. Various alternate filtration models from the literature and our own empirical models were implemented, calibrated, and validated; the best alternatives were selected based on model accuracy and capacity of the model to predict the effect of varying sludge characteristics on the corresponding output, that is fouling rate or sludge filterability. The results showed that fouling rate and sludge filterability were satisfactorily predicted by the selected filtration models. The best integrated model was successfully applied in the simulation environment to compare three feedback and two feedforward control tools to manipulate FE dosing to an AnMBR. The modelling results revealed that the most appropriate control tool was a feedback sludge filterability controller that dosed FEs continuously, referred to as ∆R20_10. Compared to the other control tools, application of the ∆R20_10 controller resulted in a more stable sludge filterability and steady fouling rate, when the AnMBR was subject to specific disturbances. The simulation environment developed in this research was shown to be a useful tool to test strategies for dosing flux enhancer into AnMBRs.

Enhanced membrane fouling control and trace organic compounds removal during microfiltration by coupling coagulation and adsorption in an electric field

Coupling electric field, coagulation, and powdered activated carbon (PAC) adsorption in the microfiltration (MF) process was an effective strategy for membrane fouling alleviation and trace organic compounds (TrOCs) elimination. In the electric field, the surface charges of bovine serum albumin (BSA) molecules and kaolin particles distributed along the direction of the electric field and formed electric dipoles, which lowered electrostatic repulsion between BSA-BSA, BSA-kaolin, and kaolin-kaolin, resulting in enhanced particle aggregation and turbidity reduction. Electrophoretic migration also strengthened the interaction between particles and polyaluminum chloride (PACl). Protein removal showed a significant linear correlation with the transmembrane pressure (TMP), and the slope variation of the fitting curves reflected the role of the electric field in the BSA removal and membrane fouling control. Under the synergistic function of electric field, coagulation, and PAC adsorption, the MF system achieved an 80.7% reduction on membrane fouling, an average BSA removal of 76.4%, and TrOCs elimination of 65.3%-81.7%. Electrochemical oxidation was the main contributor to the TrOCs removal when 2.5 V voltage was applied, and could also prolong the service life of PAC.

Recent Progress and Challenges in Hollow Fiber Membranes for Wastewater Treatment and Resource Recovery

Membrane processes have been extensively employed in diverse applications, specifically in industrial wastewater treatment. The technological development in membrane processes has rapidly advanced and accelerated beyond its common principle and operation. Tremendous efforts have been made in the advancement of membrane materials, fabrication method, membrane modification and integration with other technologies that can augment the existing membrane processes to another level. This review presents the recent development of hollow fiber membranes applied in wastewater treatment and resource recovery. The membrane working principles and treatment mechanism were discussed thoroughly, with the recent development of these hollow fiber membranes highlighted based on several types of membrane application. The current challenges and limitations which may hinder this technology from expanding were critically described to offer a better perspective for this technology to be adopted in various potential applications.

Up-concentration processes of organics for municipal wastewater treatment: New trends in separation

Carbon neutrality is a pressing goal for the whole society. Over 20% of municipality electrical energy on public utilities was consumed by the operation of wastewater treatment plants (WWTPs). Up-concentration of organic matters and maximum energy recovery is essential for a more sophisticated municipal wastewater management. Chemical coagulation and biological adsorption have been used to achieve efficient carbon capture, while separation is an overlooked step. It may lead to poor effluent quality, as well as consume most of the time and volume. The introduction of new driving forces, such as pressure and magnetism, significantly improved the retention rate and speed, respectively. In this paper, recent works were comprehensively reviewed and a horizontal comparison was conducted from aspects of separation speed, retention rate, concentrate characteristics and economic costs. This review also discussed the selection of technologies under different conditions. Finally, the practical application, fouling mitigation with considering the value of the concentrate, identification of unique concentrate characteristics, and the establishment of an evaluation system was suggested as core issues for future researches. This review will promote the development of an energy-efficient wastewater treatment system with up-concentration processes.

Direct membrane filtration (DMF) for recovery of organic matter in municipal wastewater using small amounts of chemicals and energy

The recovery and utilization of organic matter in municipal wastewater are essential for the establishment of a sustainable society, such that these factors have drawn significant recent attention. The up-concentration of organic matter via direct membrane filtration (DMF), followed by anaerobic digestion, is advantageous over the treatment of the entire wastewater by an anaerobic process, such as an anaerobic membrane bioreactor (AnMBR). However, the occurrence of severe membrane fouling in the DMF is a problem. In this study, DMF was carried out at an existing wastewater treatment plant to attempt long-term operation. A combination of vibration of membrane modules, short-term aeration, and chemically enhanced backwash (CEB), with multiple chemicals (i.e., the alternative use of citric acid and NaClO), was found to be effective for the mitigation of membrane fouling in DMF. Furthermore, switching the feed from influents to effluents in the primary sedimentation basin significantly mitigated membrane fouling. In this study, in which microfiltration membrane, with a nominal pore size of 0.1 μm, was used, ∼75% of the organic matter in raw wastewater was recovered, with the volumetric concentration of wastewater by 50- or 150-fold. Organic matter recovered by DMF had significantly higher potentials for biogas production than the excess sludge generated from the same wastewater treatment plant. An analysis of the energy balance (i.e., the energy used for DMF and recovered by DMF) suggests that the proposed DMF can produce a net-positive amount of electricity of ∼0.3 kWh from 1 m³ of raw wastewater with a typical strength (chemical oxygen demand of 500 mg/L).

Microplastic particles in the aquatic environment: A systematic review

Microplastics (MPs) pollution has become one of the most severe environmental concerns today. MPs persist in the environment and cause adverse effects in organisms. This review aims to present a state-of-the-art overview of MPs in the aquatic environment. Personal care products, synthetic clothing, air-blasting facilities and drilling fluids from gas-oil industries, raw plastic powders from plastic manufacturing industries, waste plastic products and wastewater treatment plants act as the major sources of MPs. For MPs analysis, pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), Py-MS methods, Raman spectroscopy, and FT-IR spectroscopy are regarded as the most promising methods for MPs identification and quantification. Due to the large surface area to volume ratio, crystallinity, hydrophobicity and functional groups, MPs can interact with various contaminants such as heavy metals, antibiotics and persistent organic contaminants. Among different physical and biological treatment technologies, the MPs removal performance decreases as membrane bioreactor (> 99%) > activated sludge process (~98%) > rapid sand filtration (~97.1%) > dissolved air floatation (~95%) > electrocoagulation (> 90%) > constructed wetlands (88%). Chemical treatment methods such as coagulation, magnetic separations, Fenton, photo-Fenton and photocatalytic degradation also show moderate to high efficiency of MP removal. Hybrid treatment technologies show the highest removal efficacies of MPs. Finally, future research directions for MPs are elaborated.

Microplastics in the environment: Occurrence, perils, and eradication

Microplastics (MPs) with sizes < 5 mm are found in various compositions, shapes, morphologies, and textures that are the major sources of environmental pollution. The fraction of MPs in total weight of plastic accumulation around the world is predicted to be 13.2% by 2060. These micron-sized MPs are hazardous to marine species, birds, animals, soil creatures and humans due to their occurrence in air, water, soil, indoor dust and food items. The present review covers discussions on the damaging effects of MPs on the environment and their removal techniques including biodegradation, adsorption, catalytic, photocatalytic degradation, coagulation, filtration and electro-coagulation. The main techniques used to analyze the structural and surface changes such as cracks, holes and erosion post the degradation processes are FTIR and SEM analysis. In addition, reduction in plastic molecular weight by the microbes implies disintegration of MPs. Adsorptive removal by the magnetic adsorbent promises complete elimination while the biodegradable catalysts could remove 70-100% of MPs. Catalytic degradation via advanced oxidation assisted by S O 4 • - or O H • radicals generated by peroxymonosulfate or sodium sulfate are also adequately covered in addition to photocatalysis. The chemical methods such as sol-gel, agglomeration, and coagulation in conjunction with other physical methods are discussed concerning the drinking water/wastewater/sludge treatments. The efficacy, merits and demerits of the currently used removal approaches are reviewed that will be helpful in developing more sophisticated technologies for the complete mitigation of MPs from the environment.

Fouling Mitigation by Cationic Polymer Addition into a Pilot-Scale Anaerobic Membrane Bioreactor Fed with Blackwater

Cationic polymers have proven to be suitable flux enhancers (FEs) in large-scale aerobic membrane bioreactors (MBRs), whereas in anaerobic membrane bioreactors (AnMBRs) research is scarce, and so far, only done at lab-scale. Results from MBRs cannot be directly translated to AnMBRs because the extent and nature of membrane fouling under anaerobic and aerobic conditions are different. Our research focused on the long-term effect of dosing the cationic polymer Adifloc KD451 to a pilot AnMBR, fed with source-separated domestic blackwater. A single dosage of Adifloc KD451 at 50 mg L^-1 significantly enhanced the filtration performance in the AnMBR, revealed by a decrease in both fouling rate and total filtration resistance. Nevertheless, FE addition had an immediate negative effect on the specific methanogenic activity (SMA), but this was a reversible process that had no adverse effect on permeate quality or chemical oxygen demand (COD) removal in the AnMBR. Moreover, the FE had a long-term positive effect on AnMBR filtration performance and sludge filterability. These findings indicate that dosing Adifloc KD451 is a suitable strategy for fouling mitigation in AnMBRs because it led to a long-term improvement in filtration performance, while having no significant adverse effects on permeate quality or COD removal.

Precoating membranes with submicron super-fine powdered activated carbon after coagulation prevents transmembrane pressure rise: Straining and high adsorption capacity effects

Commercially available powdered activated carbon (PAC) with a median diameter of 12-42 μm was ground into 1 μm sized superfine PAC (SPAC) and 200 nm sized submicron SPAC (SSPAC) and investigated as a pretreatment material for the prevention of hydraulically irreversible membrane fouling during a submerged microfiltration (MF) process. Compared with PAC and SPAC, SSPAC has a high capacity for selective biopolymer adsorption, which is a characteristic found in natural organic matter and is commonly considered to be a major contributor to membrane fouling. Precoating the membrane surface with SSPAC during batch filtration further removes the biopolymers by straining them out. In lab-scale membrane filtration experiments, an increase in the transmembrane pressure (TMP) was almost completely prevented through a precoating with SSPAC based on its pulse dose after coagulation pretreatment. The precoated SSPAC formed a dense layer on the membrane preventing biopolymers from attaching to the membrane. Coagulation pretreatment enabled the precoated activated carbon to be rinsed off during hydraulic backwashing. The functionality of the membrane was thereby retained for a long-term operation. Precoating the membranes with SSPAC after coagulation is a promising way to control membrane fouling, and efficiently prevents an increase in the TMP because of the straining effect of the SSPAC and the high capacity of the SSPAC to adsorb any existing biopolymers.

Direct membrane filtration for wastewater treatment and resource recovery: A review

Direct membrane filtration has shown great potential in wastewater treatment and resource recovery in terms of its superior treated water quality, efficient nutrient recovery, and sustainable operation, especially under some scenarios where biological treatment is not feasible. This paper aims to give a comprehensive review of the state-of-the-art of direct membrane filtration processes (including pressure-driven, osmotic-driven, thermal-driven, and electrical-driven) in treating different types of wastewater for water reclamation and resource recovery. The factors influencing membrane performance and treatment efficiency in these direct membrane filtration processes are well illustrated, in which membrane fouling was identified as the main challenge. The strategies for improving direct membrane filtration performance, such as physical and chemical cleaning techniques and pretreatment of feed water, are highlighted. Towards scaling-up and long-term operation of direct membrane filtration for effective wastewater reclamation and resource recovery, the challenges are emphasized and the prospects are discussed.

Characterization and mitigation of the fouling of flat-sheet ceramic membranes for direct filtration of the coagulated domestic wastewater

Ceramic membranes allow a high filtration flux with a low fouling propensity. Direct filtration of municipal wastewater using flat-sheet ceramic membranes (FSCM) is an attractive and promising technology for wastewater treatment and resource recovery. Urgent need is to determine the fouling behavior of FSCM and its optimal cleaning strategy in direct filtration applications. This study was conducted on pre-coagulation of sewage with FeCl₃ (20 mg Fe/L) or polyaluminum chloride (15 mg Al/L), followed by FSCM filtration at around 1.0 m/d (as high as 41.7 L/m²-h in flux). The results showed that the coagulation-FSCM filtration removed chemical oxygen demand and total phosphorus by up to 90.0% and 99.9%, respectively. The pollutants (organics and nutrients) in the sewage influent were concentrated into the sludge for potential resource recovery. Without pre-coagulation, foulants easily entered the membrane pores, causing rapid membrane fouling. Chemically enhanced coagulation greatly decreased the membrane fouling rate by aggregating various foulants into flocs. Fouled membranes were effectively renewed by physical means, such as water flushing and sonication, or a short period of chemical backwashing with NaOH, HCl or oxidizing agents. The study revealed the fouling mechanisms of FSCM in sewage filtration and developed effective cleaning strategies for its long-term operation.

Conversion of municipal wastewater-derived waste to an adsorbent for phosphorus recovery from secondary effluent

The sustainable management and recirculation of phosphorus resources are essential to our human lives. In this work, phosphorus removal and recovery from secondary effluent were achieved using municipal wastewater-derived materials as adsorbents. Through modification with 0.5 M NaOH for 30 min, iron containing sludge that originated from the coagulation pretreatment of municipal wastewater was successfully converted to phosphorus adsorbent. The maximal adsorption capacity of the prepared adsorbent was estimated to be 22 mg-P/g, and the adsorption performance remained stable in the pH range of 5-8. FeO(OH) was identified as the key adsorption site, and the ligand exchange mediated chemical adsorption was the main mechanism for phosphorus removal by the prepared material. Moreover, a laboratory-scale continuous-flow adsorption column experiment showed that the surplus phosphorus in secondary effluent could be readily reduced to <0.1 mg/L. By pyrolysis of P-laden alkali-treated iron sludge under oxygen limited conditions, the phosphorus was recovered and successfully applied to support wheat growth. This work provides valuable information for both the sustainable management of phosphorus streams in wastewater and cyclic utilization of waste sludge.

A Review on the Mechanism, Impacts and Control Methods of Membrane Fouling in MBR System

Compared with the traditional activated sludge process, a membrane bioreactor (MBR) has many advantages, such as good effluent quality, small floor space, low residual sludge yield and easy automatic control. It has a promising prospect in wastewater treatment and reuse. However, membrane fouling is the biggest obstacle to the wide application of MBR. This paper aims at summarizing the new research progress of membrane fouling mechanism, control, prediction and detection in the MBR systems. Classification, mechanism, influencing factors and control of membrane fouling, membrane life prediction and online monitoring of membrane fouling are discussed. The research trends of relevant research areas in MBR membrane fouling are prospected.

Pretreatment of ceramic membrane microfiltration in wastewater reuse: A comparison between ozonation and coagulation

To determine the most efficient pretreatment for ceramic membrane filtration (CMF) of primary clarifier effluent (PE), the effectiveness of ozonation and coagulation was investigated from the viewpoint of both virus removal and mitigation of membrane fouling. Our results showed virus removal by coagulation to be more efficient as a CMF pretreatment, whereas ozonation showed better efficiency when used as a CMF posttreatment. The effect of ozonation and coagulation on ceramic membrane fouling was investigated during short-term operation. With the use of coagulation before CMF (PACl + CMF), irreversible fouling resistance was 0.5 × 10¹¹ m^-1 at a dosage of 150 mg/L of polyaluminum chloride (PACl), which was 10 times lower than when ozonation was used as a pretreatment to CMF (O₃+CMF) (0.7 × 10¹² m^-1 at 50 mg-O₃/L). This result indicates coagulation to be more efficient than ozonation for mitigating ceramic membrane fouling. Based on these results, the process sustainability of PACl + CMF was then investigated during longer-term operation. At a dosage of 150 mg/L of PACl, the PACl + CMF process could be sustainably operated for 120 h without any need for chemically enhanced backwashing, which was twice as long as for PACl dosages of 50 and 100 mg/L. Coagulation is thus a more efficient pretreatment for CMF of PE from the viewpoint of both virus removal and mitigation of ceramic membrane fouling. The hygienic safety of reclaimed water can be further improved if ozonation is used as a CMF posttreatment.

Membrane Surface Patterning as a Fouling Mitigation Strategy in Liquid Filtration: A Review

Membrane fouling is seen as the main culprit that hinders the widespread of membrane application in liquid-based filtration. Therefore, fouling management is key for the successful implementation of membrane processes, and it is done across all magnitudes. For optimum operation, membrane developments and surface modifications have largely been reported, including membrane surface patterning. Membrane surface patterning involves structural modification of the membrane surface to induce secondary flow due to eddies, which mitigate foulant agglomeration and increase the effective surface area for improved permeance and antifouling properties. This paper reviews surface patterning approaches used for fouling mitigation in water and wastewater treatments. The focus is given on the pattern formation methods and their effect on overall process performances.

Differential ATR FTIR spectroscopy of membrane fouling: Contributions of the substrate/fouling films and correlations with transmembrane pressure

This study examined the formation of fouling films deposited on the surface of a polyethersulfone (PES) membrane during the filtration of alginate solutions with various ionic strengths. Membrane fouling was characterized by changes of the transmembrane pressure (TMP) and ex situ measured attenuated total reflectance (ATR) Fourier-transform IR (FTIR) spectra at varying stages of filtration runs. The ATR spectra that comprise the vibration bands characteristic of the PES substrate and the deposited film were processed taking into the gradual weakening of the PES substrate-specific bands, whose intensity was shown to depend on the wavenumber of IR radiation and the thickness of the deposited layer. Strongly linear correlations between ratios of first derivatives intensity and wavenumbers of the PES reference lines were established. Calculations of the PES bands' attenuation coefficients allowed determining the apparent thickness and ATR FTIR vibrations of the fouling films per se. Strong correlations between TMP development and ATR-determined apparent thickness of the fouling layers were observed. The intensity of ATR absorbance at 3200 cm^-1 was linearly correlated with TMP development for small TMP values before the point of rapidly developing failure of the hydraulic permeability of the system was reached.

Mitigated membrane fouling and enhanced removal of extracellular antibiotic resistance genes from wastewater effluent via an integrated pre-coagulation and microfiltration process

Antibiotic resistance genes (ARGs) have been regarded as an emerging pollutant in municipal wastewater treatment plant (WWTP) effluents due to their potential risk to human health and ecological safety when reused for landscape and irrigation. Conventional wastewater treatment processes generally fail to effectively reduce ARGs, especially extracellular ARGs (eARGs), which are persistent in the environment and play an important role in horizontal gene transfer via transformation. Herein, an integrated process of pre-coagulation and microfiltration was developed for removal of ARGs, especially eARGs, from wastewater effluent. Results show that the integrated process could effectively reduce the absolute abundances of total ARGs (tARGs) (>2.9 logs) and eARGs (>5.2 logs) from the effluent. The excellent performance could be mainly attributed to the capture of antibiotic resistant bacteria (ARB) and eARGs by pre-coagulation and co-rejection during subsequent microfiltration. Moreover, the integrated process exhibited a good performance on removing common pollutants (e.g., dissolved organic carbon and phosphate) from the effluent to improve water quality. Besides, the integrated process also greatly reduced membrane fouling compared with microfiltration. These findings suggest that the integrated process of pre-coagulation and microfiltration is a promising advanced wastewater treatment technology for ARGs (especially eARGs) removal from WWTP effluents to ensure water reuse security.

Direct filtration for the treatment of the coagulated domestic sewage using flat-sheet ceramic membranes

Direct membrane filtration (DMF) is considered as a promising technology for municipal wastewater treatment. We utilized an innovative application of flat-sheet ceramic membranes (FSCM) for DMF for the rapid treatment of domestic sewage. Coagulation was applied before FSCM filtration to increase the pollutant removal and to mitigate membrane fouling. This coagulation-FSCM filtration can significantly reduce the pollutant load on the downstream treatment and concentrate organics and nutrients into sludge to facilitate resource recovery. Using polyaluminum chloride (PACl) based FSCM filtration, approximately 90.0% of the chemical oxygen demand (COD) and 99.0% of the phosphorus (P) were removed from the sewage influent and retained in the concentrated sludge, with less than 25.0 mg/L COD left in the effluent. Long-term operation of the PACl-based FSCM filtration stably maintained a high flux of 41.7 L/m²-h (LMH, or 1.0 m/d). The fouled membranes were cleaned chemically every 3-5 d, and the membrane permeability could almost be completely recovered using chemical backwash for only 10 min with a diluted acidic, alkaline, chlorine or H₂O₂ solution. The novel FSCM process will fundamentally advance wastewater treatment technology. It can be readily modularized and installed as simple add-on units to upgrade and retrofit existing wastewater treatment systems.

Integration of Green Energy and Advanced Energy-Efficient Technologies for Municipal Wastewater Treatment Plants

Wastewater treatment can consume a large amount of energy to meet discharge standards. However, wastewater also contains resources which could be recovered for secondary uses under proper treatment. Hence, the goal of this paper is to review the available green energy and biomass energy that can be utilized in wastewater treatment plants. Comprehensive elucidation of energy-efficient technologies for wastewater treatment plants are revealed. For these energy-efficient technologies, this review provides an introduction and current application status of these technologies as well as key performance indicators for the integration of green energy and energy-efficient technologies. There are several assessment perspectives summarized in the evaluation of the integration of green energy and energy-efficient technologies in wastewater treatment plants. To overcome the challenges in wastewater treatment plants, the Internet of Things (IoT) and green chemistry technologies for the water and energy nexus are proposed. The findings of this review are highly beneficial for the development of green energy and energy-efficient wastewater treatment plants. Future research should investigate the integration of green infrastructure and ecologically advanced treatment technologies to explore the potential benefits and advantages.

A comparison study of in-situ coagulation and magnetic ion exchange (MIEX) as pre-treatments for ultrafiltration: Evaluating effectiveness of organic matters removals and fouling mitigation

This work was designed to compare the effectiveness of in-situ coagulation and MIEX as pre-treatments prior to ultrafiltration (UF) to improve organic matter (OM) removal and mitigate membrane fouling. Three kinds of OMs, i.e. salicylic acid (SA), humic acid (HA) and bovine serum albumin (BSA) were employed. The experimental results show that coagulation-UF led to most effective removal of HA (almost 90%), while the SA was uncoagulated and least removable, with the rejection rate of about 55%. Conversely, MIEX present superior ability for removing SA, contributing to additional efficiency of 71.95-77.21% than UF alone. Proper dosage of Al-based coagulants could alleviate flux loss, especially in the cases of HA and BSA. Increasing coagulant dose resulted in continuous decrement of irreversible resistance (R_ir), which dominated the membrane fouling development by the SA water. For HA and BSA waters, alternatively, variations of R_r determined the flux declines. Floc compact degree was the decisive factor for R_r for coagulated SA; while for HA and BSA, R_r was most related to the floc size and foulant-foulant interaction. MIEX was most effective for alleviating flux loss when treating the hydrophilic SA with small molecules and for all the cases, MIEX exerted little influence on the R_r values.

Actinia-like multifunctional nanocoagulant for single-step removal of water contaminants

Current technologies for water purification are limited by their contaminant-specific removal capability, requiring multiple processes to meet water quality objectives. Here we show an innovative biomimetic micellar nanocoagulant that imitates the structure of Actinia, a marine predator that uses its tentacles to ensnare food, for the removal of an array of water contaminants with a single treatment step. The Actinia-like micellar nanocoagulant has a core-shell structure and readily disperses in water while maintaining a high stability against aggregation. To achieve effective coagulation, the nanocoagulant everts its configuration, similar to Actinia. The shell hydrolyses into 'flocs' and destabilizes and enmeshes colloidal particles while the core is exposed to water, like the extended tentacles of Actinia, and adsorbs the dissolved contaminants. The technology, with its ability to remove a broad spectrum of contaminants and produce high-quality water, has the potential to be a cost-effective replacement for current water treatment processes.

Dynamic membrane for micro-particle removal in wastewater treatment: Performance and influencing factors

Dynamic membranes (DMs) have been of great interest in recent years because they can reduce energy consumption and costs during wastewater treatment. Dynamic membranes are a promising technology for the removal of low-density, non-degradable micro-particles, such as plastics, which are an increasingly prevalent wastewater contaminant. These micro-particles are not easily removed via conventional sedimentation and result in increased operation and maintenance costs in downstream unit processes. In this study, DMs were formed on a 90 μm supporting mesh through filtration of a synthetic wastewater. The impact of influent flux (solid flux) and influent particle concentration on DM performance was investigated. The effluent turbidity was reduced to <1 NTU after 20 mins of filtration, verifying the effective removal of micro-particles by the DM. Transmembrane pressure (TMP) and total filtration resistance increased linearly with filtration time, and were highly correlated (R² > 0.998). TMP ranged from 80 to 180 mm of water head, and total filtration resistance ranged from 2.89 × 10^-9 m^-1 to 6.52 × 10^-9 m^-1 during DM filtration. In general, an increase in influent flux and influent particle concentration corresponds with increasing TMP and filtration resistance, as well as a rapid reduction in effluent turbidity due to swift formation of a DM on the supporting mesh.

Prediction of membrane fouling using artificial neural networks for wastewater treated by membrane bioreactor technologies: bottlenecks and possibilities

Membrane fouling is a major concern for the optimization of membrane bioreactor (MBR) technologies. Numerous studies have been led in the field of membrane fouling control in order to assess with precision the fouling mechanisms which affect membrane resistance to filtration, such as the wastewater characteristics, the mixed liquor constituents, or the operational conditions, for example. Worldwide applications of MBRs in wastewater treatment plants treating all kinds of influents require new methods to predict membrane fouling and thus optimize operating MBRs. That is why new models capable of simulating membrane fouling phenomenon were progressively developed, using mainly a mathematical or numerical approach. Faced with the limits of such models, artificial neural networks (ANNs) were progressively considered to predict membrane fouling in MBRs and showed great potential. This review summarizes fouling control methods used in MBRs and models built in order to predict membrane fouling. A critical study of the application of ANNs in the prediction of membrane fouling in MBRs was carried out with the aim of presenting the bottlenecks associated with this method and the possibilities for further investigation on the subject.