Frequent Chemical Cleaning Research Articles

Optimizing full-scale MBR performance: A dual-phase approach for real-time air-scouring and permeate flow modifications

This study reports on an advanced fuzzy logic control system designed to optimize air-scour and permeate flow rates in membrane bioreactors, targeting enhanced energy efficiency and reduced fouling. Developed in two stages, the system integrates real-time monitoring of transmembrane pressure and permeability trends to adjust air-scour rates in response to fouling indicators. The initial simulations indicated potential for a 50 % reduction in air-scour rates, suggesting considerable energy savings. The second stage's refinements, based on empirical validations, yielded a more responsive system, albeit with more conservative operational adjustments for energy savings.Over eight months of full-scale testing, the advanced control system implemented in one of eight filtration lines exhibited lower fouling rates and maintained superior permeability values compared to the other lines. This performance translated into reduced chemical cleaning frequency, thereby affirming the system's efficiency in fouling management. These findings validate the application of fuzzy logic in MBR operations and offer a promising approach for energy-efficient and sustainable wastewater treatment.

Electrodeionization for Wastewater Reuse in Petrochemical Plants

This study investigated a hybrid membrane and electro-membrane separation process for producing demineralized water from tertiary petrochemical effluent, reusing it as feeding water for high-pressure boilers for steam generation. The effluents were treated in a pilot plant with a 1 m3 h−1 capacity by using a hybrid process of ultrafiltration (UF), reverse osmosis (RO), and electrodeionization (EDI). The physicochemical parameters of interest and maximum limits in industrial water were pre-determined by the industries. Operating parameters such as flow rate, pressure, percentage of recovery, and electric current were monitored, along with the frequency of chemical cleaning. The UF and RO systems operated with average permeate fluxes of 17 ± 4.06 L h−1 m−2 and 20.1 ± 1.9 L h−1 m−2, respectively. Under optimal operating conditions (flow rate of 600 L h−1, voltage of 22.2 ± 0.7 V, and electric current of 1.3 A), EDI produced high-quality water with an average electrical conductivity of 0.22 μS cm−1. Thus, the industrial water produced reached the quality required for reuse as make-up water for high-pressure boilers in the petrochemical industry. In addition, the specific energy consumption; the use of chemicals, spare materials, equipment; and labor costs were determined to support the technical feasibility study for implementing an industrial plant with a 90 m3 h−1 producing capacity. This resulted in a cost of USD 0.64 per cubic meter of demineralized water produced, a cost similar to values reported in the literature.

Emulsified oil fouling resistant cellulose acetate-MoS2-nanocomposite membrane for oily wastewater remediation

This study evaluated the performance stability of amphiphilic cellulose acetate-MoS2-nanocomposite membranes (CMN) on oil removal and flux, oil fouling trends, as well as MoS2's catalytic peroxidase-like efficiency for oily wastewater treatment. When H2O2 was present in the feed, the membrane consistently achieved oil removal rates as high as 83.12 %, with only <10 % flux decline over an 80-minute filtration. During longer-term filtration of 4–6 h, the CMN membrane also exhibited significantly lower overall flux decline rates compared to the neat membrane with flux decline rates of 16.27 %, which was half of the cellulose membrane flux of 39.38 %. The fouling resistant performance was underpinned by the generation of reactive oxygen species (ROS) via catalytic reactions of MoS2 and H2O2. Coumarin was use as ROS scavenging agent and confirmed that the ROS amount was affected by the MoS2 and H2O2 dosages. The CMN membrane achieved the oil removal to the permissible discharge limit for low concentration wastewater. As a low-pressure membrane, it offered advantages of less energy consumption and continuously operating mode without frequent chemical cleaning and desorption. These findings support the CMN membrane's potential as a promising solution for treating industrial oily wastewater.

Unveiling the residual membrane foulants in full-scale MBR plant after chemically enhanced backwash: Insights into microbe-associated compounds

Membrane fouling is a main bottleneck that limits the stable operation of membrane bioreactors (MBRs). However, the nature of residual foulants over frequent chemical cleaning remain elusive. Herein, we collected fouled membranes from a large-scale MBR with the treatment capacity of 200, 000 m3/d and explored the culprit for the key components resistant to chemically enhanced backwash. During 155 days of operation, transmembrane pressure increasing highly linked to the characteristics of membranes and bio-cakes. Fourier-transform infrared microscopy deciphered that a part of polyvinylpyrrolidone in the structure of polyvinylidene fluoride hollow fiber membrane was removed by NaOCl after chemical backwash. The stubborn uronic acids were mostly responsible for irreversible fouling due to pore constriction and the resistance to NaOCl. The fouling-related genera f_Rhodocyclaceae and f_Anaerolineaceae prevailed in the bio-cakes. According to the network analysis, the negative and competitive interactions on the bio-cake contributed more to severe membrane fouling than the positive and cooperative interactions. The keystone taxa c_WS6 (Dojkabacteria) and c_Deltaproteobacteria, which involved in secreting polysaccharides and hydrolyzing refractory matters, accelerated the accumulation of organic foulants. Our findings help to elucidate the key contributors to membrane fouling and anti-cleaning in full-scale MBR, which provide new insights for future fouling control.

Renewable energy powered membrane technology: Impact of osmotic backwash on organic fouling during solar irradiance fluctuation

Organic fouling is a major issue of nanofiltration/reverse osmosis (NF/RO) membranes because it causes severe and usually irreversible flux decline. Consequently, NF/RO requires frequent chemical cleaning and/or replacement. In directly coupled photovoltaic (PV) powered NF/RO systems for brackish water desalination, solar energy fluctuations can induce a spontaneous osmotic backwash (OB) process, which may mitigate organic fouling. In this study, the feasibility of spontaneous OB as a self-cleaning method for organic fouling (humic acid with calcium) control under fluctuating conditions was evaluated with an online total organic carbon (TOC) analyser. The OB cleaning mechanisms with different solar energy fluctuating conditions, relevant feedwater chemistry (salinity, pH, and hardness) and membrane type (NF270 and BW30) were investigated. The visualisation of fouling layers by a helium ion microscope (HIM), a cryo scanning electron microscope equipped with a focused ion beam (FIB-SEM) and energy dispersive X-Ray spectroscopy (EDS) showed that partial foulants were removed by spontaneous OB, and the remaining layer was not uniform. Periodic solar irradiance step-response experiments’ results showed that spontaneous OB cleaning restored 46%–98% flux, depending on solar irradiance fluctuating conditions, feedwater chemistry, and membrane type. Specifically, low-level solar irradiance (i.e., more cloud coverage) and short operating time (i.e., high cleaning frequency) showed high OB cleaning efficiency. High salinity was found to enhance the OB performance but it was still ineffective for the enhanced organic fouling layer. Extremely pH (e.g. pH 2 or pH 12) weakened OB efficiency via a compact fouling layer/mixed fouling layer structures (calcite participation) in presence of calcium. Although spontaneous OB cleaning is promising to mitigate organic fouling, it is ineffective for severe organic fouling (e.g. 12.5 mM humic acid with 2.5 mM CaCl2). This work provides the contribution of process and water quality variables that make spontaneous OB effective for fouling control, which facilitates the further development and application of the OB technique in decentralised PV-NF/RO systems.

Improved separation performance of SS fiber nonwoven felt by the coating of a non-isotropic porous SS membrane layer

With excellent mechanical properties, large porosity, and permeability, stainless steel (SS) fiber nonwoven felt has outstanding application advantages in high-temperature filtration and purification. However, the pore size of the SS nonwoven felt, which is directly determined by the diameter of the produced fiber stacked inside, usually varies from tens of microns to several microns. Low filtration accuracy greatly limits its application in the fields of fine separation and purification. In this study, the separation performance of SS fiber nonwoven felt was improved by the coating of a non-isotropic porous SS membrane layer via the immersion precipitation phase inversion-sintering method. The effects of sintering temperature on pore structure, surface wettability, separation performance, and mechanical properties of the coated SS nonwoven felt were characterized by scanning electron microscope (SEM), water contact angle (WCA), water permeability, and tensile test, respectively. The results suggest that with the increase of sintering temperature from 1000°C to 1200°C, both porosity and pore size reduce gradually. The WCA value shows an increase from 31.4 to 62.3° and pure water flux shows a corresponding decrease from 2562 to 889 L . m−2 . h−1. The sintering temperature has a negative effect on the mechanical strength of the coated SS fiber nonwoven felt, which is mainly determined by the mechanical properties of the sintered SS fiber nonwoven felt substrate. The coated SS fiber nonwoven felt exhibits a long-term durable separation performance even after frequent combined physical washing and chemical cleaning when applied in the treatment of potato starch wastewater.

Modeling, simulation, and characterization of spinning basket membrane module in recovery of proteins from synthetic wastewater

Membrane-based low-cost recovery of nutritional and therapeutic proteins from wastewater is regarded as a leap towards sustainability. However, membranes are heavily fouled by proteins, and thus, frequent chemical or hydrodynamic cleaning is needed even in the advanced dynamic shear-enhanced (DSE) filtration devices. This article presents the modeling, simulation, and characterization studies of a DSE system, namely the ‘Spinning Basket membrane’ (SBM) module with an inbuilt cleaning facility. The device has been established to be specifically suitable for the recovery of proteins from synthetic wastewater. It can perpetually regenerate the flux with its simple and, moreover, online cleaning facility. A two-parameter transient model, purely based on an analytical approach, has been developed to simulate the device. Moderately low deviation (±12 %) of the simulated flux from the corresponding experimental data obtained from ultrafiltration of synthetic wastewater unambiguously validates the proposed model. The present modeling strategy demonstrates how a DSE filtration system with highly complex modes of mass and momentum transfer could be easily simulated.

Reduction of long-term irreversible membrane fouling: A comparison of integrated and separated processes of MIEX and UF

In this study, the reductions of long-term irreversible membrane fouling in integrated and separated MIEX-UF processes were explored over a prolonged experimental period. The mechanism leading to the significant difference in membrane fouling behaviors of the two processes was systematically analyzed. The results show that the chemical cleaning frequency and the rate of chemically irreversible membrane fouling formation were decreased by 50% and 49%, respectively, in the integrated process compared to the separated process. Further analysis suggested that MIEX adsorption was unrelated to the different membrane fouling behaviors between the two processes. The effect of the resin layer on filtration and backwashing was the dominate mechanism leading to the more excellent anti-fouling performance of the integrated process. The stronger adhesion force of pollutants-MIEX enable the mixed cake layer formed in the integrated process to maintain good water permeability and easy to be removed by backwashing. The adhesion force of pollutants-MIEX was significantly affected by the saturation level of resin particles and less affected by resin regeneration. During the early period of long-term filtration experiment and the initial stage after every resin replacement, the low saturation degree of resin particles guaranteed the improved effect of the resin layer always existed.

Operational performance and cost analysis of PAC/ceramic MF for drinking water production: Exploring treatment capacity as a new indicator for performance assessment and optimization

A powdered activated carbon (PAC)/ceramic microfiltration (MF) pilot was operated (24/7) in a water treatment plant during 18 months, with water from different points of the treatment line (raw, ozonated with recirculated filter-backwash waters, ozonated/pre-coagulated, filtered), the testing including MF and PAC/MF. The optimization of PAC/MF operational performance, including PAC effect analysis and pretreatment required, and a cost analysis are herein presented. A new indicator was developed and explored for performance assessment and optimization, the treatment capacity (TCp), i.e. the design flowrate normalized to membrane area and intake pressure. As expected, a higher TCp was obtained with filtered water. Non-clarified waters required alum-coagulation pretreatment to minimize membrane fouling, and achieved similar TCp results among them. PAC addition (6–24 mg/L) did not promote membrane fouling and had no or a slight positive effect on TCp. TCp integrates all key aspects of process productivity and therefore constitutes a useful indicator to balance flux, energy consumption, backwash frequency and chemical cleaning frequency. The cost functions developed for PAC/MF yielded, for the best operating conditions found for the low-turbidity, low-dissolved organic content waters tested, a total cost of 0.07–0.11€/m3 for 100,000 m3/d, including investment and operation costs.

Membrane Bioreactor with External Side-Stream Membranes and High Cross Flow Velocity to Treat Municipal Wastewater

In this work, a pilot unit using side-stream MBR configuration was operated in BioFlow mode (i.e. no back pulse) and BioPulse mode (with intermittent back pulses) to treat municipal wastewater with relatively low MLSS. The results showed that the trans-membrane pressure (TMP) was less in the case of BioPulse over the whole period of system operation compared to that of BioFlow mode. However, the energy consumption per unit volume of permeated water is slightly higher in the case of BioFlow mode (3.4 kW.hr/m3) than that in the case of BioPulse mode (3.2 kW.hr/m3). Therefore, operation in BioPulse is preferable due to stable TMP caused by nearly fully recoverable fouling type, which results in lower chemical cleaning frequency. The MBR unit showed steady performance at a flux of 60 L/m2.hr. The system could achieve good water quality that satisfies Iraqi standards requirements for wastewater reuse or discharge to water resources

Assessing pretreatment and seawater reverse osmosis performance using an ATP-based bacterial growth potential method

Various bacterial growth potential (BGP) methods have been developed recently to monitor biofouling in seawater reverse osmosis (SWRO) systems such as assimilable organic carbon and bacterial regrowth potential. However, the relationship between these methods and biofouling in SWRO desalination plants has not yet been demonstrated. In this research, an attempt is made to investigate if a correlation exists between BGP of SWRO feed water and the chemical cleaning frequency in SWRO plants using an ATP-based BGP method employing an indigenous microbial consortium. Using ATP-based BGP method at 5 different seawater locations showed low variations of bacterial yield.The BGP method was applied to assess the pretreatment performance of three full-scale SWRO plants with different pretreatment processes. Dual media filtration (DMF) showed the highest BGP removal (>50%) in two SWRO plants. Removal of BGP and hydrophilic organic carbon in dissolved air floatation combined with ultrafiltration was similar to the removal achieved with DMF in combination with inline coagulation. For the three SWRO plants investigated, a higher BGP in SWRO feed water corresponded to a higher chemical cleaning frequency. However, more data is required to confirm if a real correlation exists between BGP and biofouling in SWRO plants.

Comparison of the effects of ozone, biological activated carbon (BAC) filtration and combined ozone-BAC pre-treatments on the microfiltration of secondary effluent

The effects of ozonation (O3), biological activated carbon (BAC) filtration and combined O3 and BAC (O3-BAC) pre-treatments on the microfiltration (MF) treatment of secondary effluent using a polyvinylidene fluoride (PVDF) membrane were studied. The permeability of the membrane was quantified and compared to the removal of humic substances (HS), biopolymers (BPs), dissolved organic carbon (DOC), absorbance at 254 nm (UVA254), and colour by these pre-treatments. The apparent molecular weight distribution (AMWD) was determined to further characterise the secondary effluent before and after each treatment. The unified membrane fouling indices (UMFI) after O3, BAC and the O3-BAC pre-treatments were also determined to evaluate the relative effectiveness of different pre-treatments on fouling reduction. The overall removal of colour and UVA254 in the MF of the O3 pre-treated secondary effluent was found to be 83% and 52% respectively, compared to 75% and 47% respectively for MF with BAC pre-treatment and 38% and 14% respectively without pre-treatment. The O3-BAC pre-treatment yielded the highest normalized permeability after 100 min of operation (0.76) and the lowest UMFI (1 × 10−3 m2/L). This result indicates that the O3-BAC pre-treatment could reduce the frequency of chemical cleaning and may extend the membrane lifetime.

Recent developments in biofouling control in membrane bioreactors for domestic wastewater treatment

• Biofouling is a long-standing problem in MBR for wastewater treatment. • Recent advances in anti-biofouling technologies in MBR are critically reviewed. • Integration of MBR with hybrid approach can mitigate biofouling effectively. • Biofouling properties are compared between aerobic and anaerobic MBR systems. • Biofouling is controlled by functionalized media in particle-sparged MBR. Biofouling is a long-standing problem in membrane bioreactors (MBRs) for domestic wastewater treatment because it deteriorates membrane permeability, thus demanding frequent chemical cleaning which can shorten membrane life-time. Recently, several anti-biofouling strategies have been suggested under scientific and engineered attentions from aerobic or anaerobic MBR systems. Nevertheless, researches are still needed to better understand biofouling and develop novel approaches to control this inevitable phenomenon. In this review, recent advances and emerging issues associated with biofouling control in aerobic and anaerobic MBR technologies are critically discussed. Existing challenges and future research perspectives are also addressed to achieve MBR sustainability with biofouling control. This also suggests that integration of MBR with hybrid approach could effectively enhance MBR performance in terms of biofouling mitigation. Future works should elucidate biofouling behavior in integrated MBRs more clearly for sustainable wastewater treatment applications.

High fouling-resistance of polyamide desalination-membrane modified with PEI/PAH polyelectrolyte multilayers

Membrane fouling is a persistent problem in reverse osmosis (RO) process which leads to higher operating pressure, quality deterioration, and frequent chemical cleaning of the membranes. The objective of this paper is to prepare a fouling-resistant RO desalination membrane while keeping high salt rejection and permeate flux. Polyamide (PA) membranes were prepared and modified using spin assisted Layer-by-Layer assembly of polyelectrolytes (PEI/PAH), characterized and tested in a cross-flow desalination setup. The effect of preparation conditions (number of coating layers, concentration and pH of the polyelectrolyte solutions) on the performance of the membrane was also investigated. SEM micrographs showed that the surface of the PA membrane is rough and has typical ridge and valley structure. However, images of the modified membranes showed smoother surfaces as the number of polyelectrolyte bilayers was increased which was verified using the AFM analysis. In addition, contact angle measurements suggested that the surfaces of the modified membranes became more hydrophilic due to the presence of hydrophilic hydroxyl and amine groups. Permeation results showed comparable salt rejection under saline feed water of 2000ppm. 50 bilayer modified membrane having 110mg/L of polyelectrolyte solution, possess permeability of 0.83L/m2hbar with 95% salt rejection. However, 27 bilayer modified membrane having 200mg/L of polyelectrolyte solution, possess greater permeability of 1.78L/m2hbar with 96% salt rejection. Fouling experiments showed that after three hours of filtration, functionalized membranes retained more than 88% of water flux compared to pristine polyamide membrane which suffered from more than 42% flux drop.

Impact of operations and cleaning on membrane fouling at a wastewater reclamation facility

Effects of operational changes on membrane fouling were evaluated for a wastewater reclamation facility. The focuses were on addition of a coagulant (ferric chloride) versus no addition and an accidental high chlorine (sodium hypochlorite) dose. Two membrane modules with different service ages, 3 years versus 9 months, were compared. Fouling rates ranged between 2 and 3 times higher during no ferric chloride addition. Chemical cleaning frequency was reduced by approximately 5 times during ferric chloride addition for older membranes, while it did not change for newer membranes. High chlorine dose had slightly improved membrane permeability for newer membrane, and reduced the transmembrane pressure (TMP) for both older and newer membranes. Chemical wash with enzymatic detergents substantially improved membrane permeability and reduced TMP for both older and newer membranes. Fouling index values indicated that coagulant addition had greater impact on performance recovery for older membranes than newer membranes. Successful and economical operation of membranes depends on fouling rate, which in this study was found to be a function of flux, membrane age, pretreatment, and cleaning type and frequency.

Estimating design parameters for sustainable operation of a membrane bioreactor treating s-triazine herbicide

An Ametryn (an s-triazine herbicide) fed laboratory-scale membrane bioreactor (MBR) was studied for 214 days under sub-tropical conditions (20–22 °C) for evaluating its treatment/operating performance and to consolidate the previous findings and establish the design parameters. Ten short-term critical flux tests were carried out at different stages of the study and the Critical Flux Values (CFV) varied from 6 to 33 L/m2h for the experiments carried out under intermittent suction mode. Two numerical models were used to estimate the “critical times”, which is useful to establish the chemical cleaning frequency of membrane modules and to assess the key kinetic parameters required to design a pilot/full scale MBR. The study also confirmed the overall fluctuation of the components of polymeric substances (proteins and carbohydrates of extra-cellular polymeric substances (EPS) and soluble microbial products (SMP)) in the MBR due to the addition of different concentrations of Ametryn (0–4 mg/L).

Kinetic evaluation of nitrification performance in an immobilized cell membrane bioreactor.

High rate membrane bioreactor (MBR) systems operated at extremely low sludge ages (superfast membrane bioreactors (SFMBRs)) are inefficient to achieve nitrogen removal, due to insufficient retention time for nitrifiers. Moreover, frequent chemical cleaning is required due to high biomass flux. This study aims to satisfy the nitrification in SFMBRs by using sponge as carriers, leading to the extension of the residence time of microorganisms. In order to test the limits of nitrification, bioreactor was run under 52, 5 and 2 days of carrier residence time (CRT), with a hydraulic retention time of 6 h. Different degrees of nitrification were obtained for different CRTs. Sponge immobilized SFMBR operation with short CRT resulted in partial nitrification indicating selective dominancy of ammonia oxidizers. At higher CRT, simultaneous nitrification-denitrification was achieved when accompanying with oxygen limitation. Process kinetics was determined through evaluation of the results by a modeling study. Nitrifier partition in the reactor was also identified by model calibration.

Antibiofilm activity of biomolecules: gene expression study of bacterial isolates from brackish and fresh water biofouled membranes

AbstractMembrane biofouling is a common and emerging problem, where cells get cemented and create problems in industrial process. Frequent chemical cleaning used for the treatment of biofouled membrane shortens the membrane life time and creates ‘stress’ to existing microflora to trigger more exopolysaccharides production, which becomes the principle cause of biofouling. To understand safe and environmentally feasible antifouling strategies, key biofilm forming representative bacteria isolated from brackish and fresh water biofouled membranes were subjected to natural agents, such as vanillin (0.05–0.4 mg/mL) and salicylic acid (0.1–0.7 mg/mL). Salicylic acid (0.7 mg/mL) was found to be effective against only

Fertiliser drawn forward osmosis process: Pilot-scale desalination of mine impaired water for fertigation

The pilot-scale fertiliser driven forward osmosis (FDFO) and nanofiltration (NF) system was operated in the field for about six months for the desalination of saline groundwater from the coal mining activities. Long-term operation of the FDFO-NF system indicates that simple hydraulic cleaning could effectively restore the water flux with minimal chemical cleaning frequency. No fouling/scaling issues were encountered with the NF post-treatment process. The study indicates that, FDFO-NF desalination system can produce water quality that meets fertigation standard. This study also however shows that, the diffusion of solutes (both feed and draw) through the cellulose triacetate (CTA) FO membrane could be one of the major issues. The FO feed brine failed to meet the effluent discharge standard for NH4+ and SO42+ (reverse diffusion) and their concentrations are expected to further increase at higher feed recovery rates. Low rejection of feed salts (Na+, Cl−) by FO membrane may result in their gradual build-up in the fertiliser draw solution (DS) in a closed FDFO-NF system eventually affecting the final water quality unless it is balanced by adequate bleeding from the system through NF and re-reverse diffusion towards the FO feed brine. Therefore, FO membrane with higher reverse flux selectivity than the CTA-FO membrane used in this study is necessary for the application of the FDFO desalination process.

Long-term operation of biological activated carbon pre-treatment for microfiltration of secondary effluent: Correlation between the organic foulants and fouling potential

The impact of long-term (>2 years) biological activated carbon (BAC) treatment for mitigating organic fouling in the microfiltration of biologically treated secondary effluent was investigated. Correlation between the organic constituents and hydraulic filtration resistance was investigated to identify the major components responsible for fouling. Over two years operation, the removal efficiency for dissolved organic carbon (DOC) by the BAC treatment was fairly consistent (30 ± 3%), although the reduction in UVA254 gradually decreased from 56 to 34%. BAC treatment effectively decreased the organic foulants in the effluent and so contributed to the mitigation of membrane fouling as shown by reduction in the unified membrane fouling index (UMFI). BAC consistently removed biopolymers whereas the removal of humic substances decreased from 52 to 25% after two years of BAC operation, and thus led to a gradual decrease in UMFI reduction efficiency from 78 to 43%. This was due to gradual reduction in adsorption capacity of the activated carbon as confirmed by analysis of its pore size distribution. Hence humics also played an important role in membrane fouling. However, there was a good correlation between protein and carbohydrate contents with hydraulically reversible and irreversible filtration resistance, compared with UVA254, turbidity and DOC. Although the mitigation of membrane fouling decreased over time, this study demonstrated that the long-term use of BAC pre-treatment of biologically treated secondary effluent prior to microfiltration has potential to reduce the need for frequent chemical cleaning and so increase membrane life span.