Specific Cake Resistance Research Articles

High efficiency filtration and optimization of pelletizing performance of fine hematite concentrate using sulfuric acid filter aid: Behavior and mechanism

Following the application of anionic reverse flotation to fine low-grade hematite ore, a significant challenge emerges with elevated slurry viscosity and heightened moisture content in the resulting filter cakes. To address the challenge of dewatering during the filtration process of fine hematite concentrate, the impact of sulfuric acid filter aid dosage and filtration temperature on the filtration performance of hematite concentrate was systematically investigated in this study. In addition, the effect of sulfuric acid filter aid on the preparation of hematite pellets was also studied. The results revealed a significant decrease from 1.10 × 1010 1/m2 to 5.7 × 109 1/m2 in the specific resistance of the hematite filter cake when the sulfuric acid dosage was 1.2 g/kg and the filtration temperature was 20 °C. The mechanism underlying the enhancement of filtration performance of fine hematite concentrate by sulfuric acid was summarized. Sulfuric acid compressed the double electric layer on the surface of hematite concentrate particles, reducing the surface zeta potential and causing the aggregation of fine particles into larger ones. This led to an increase in filter cake porosity and compression of the hydration film thickness on particle surfaces, facilitating easier removal of filtrate from the filter cake. The appropriate dosage of bentonite for pelletizing was not significantly affected by sulfuric acid filter aid. Sulfuric acid improved the porosity, drying rate, and burst temperature of hematite green pellets. While the compressive strength of preheated pellets from sulfuric acid-assisted filtration of hematite concentrate showed a slight decrease, the compressive strength of roasted pellets was significantly increased.

Salt removal from coal flotation product filter cakes using counter-current and displacement washing

Water reuse is a common practice to alleviate water scarcity concerns and mitigate their environmental footprint in coal processing facilities. Nevertheless, water reuse leads to the accumulation of various organic and inorganic substances, including salt and residual reagents in the processing water, potentially leading to the retention of soluble impurities within the coal product. Residual impurities may result in a reduction in the quality of coal products. Salt and moisture retention has become a common issue on-site, but there lacks a proper solution currently. To resolve this industrial problem, investigations were carried out for the effects of washing on removing inorganic impurities from the cake during filtration. Filter cakes were prepared from flocculated metallurgical coal in process water. Two washing methods were trialled namely counter-current washing and displacement washing. Regarding washing efficiency, counter-current washing tended to produce cakes with higher specific resistance, which caused longer filtration time. Displacement washing, however, showed increased filtration time, though to a lesser extent. In addition, washing with different washing liquid ratios for multiple wash cycles showed that the filtration time, specific cake resistance, and medium resistance increased with the number of wash cycles. The analysis of the filtrate indicated that utilising a strategy of displacement washing with a washing ratio of 1:20 yielded the most effective removal of salt. The filter cakes were analysed using the μCT imaging technique to gain insights into the pore structure of the cake at a microscopic level. There was a significant change in the cake structure, where the pore profile was more evenly distributed and smaller when the cake was washed by displacement washing.

Effect of Bulk Nanobubbles on the Flocculation and Filtration Characteristics of Kaolin Using Cationic Polyacrylamide

This study investigated the influence of bulk nanobubbles (NBs) on the flocculation and filtration behavior of kaolin suspensions treated with cationic polyacrylamide (CPAM). Traditionally, flocculation relies on bridging mechanisms by polymers like CPAM. The present work examines the possibility of combining NBs with CPAM to achieve more efficient kaolin separation. The settling behavior of kaolin suspensions with and without bulk nanobubbles was compared. The results with 2 mL CPAM and 300 s settling time revealed that bulk NBs significantly enhanced flocculation efficiency, with supernatant zone height reductions exceeding 50% compared to CPAM alone, indicating a faster settling rate resulting from bulk NBs. This improvement in the settling rate is attributed to NBs’ ability to reduce inter-particle repulsion (as evidenced by a shift in zeta potential from −20 mV to −10 mV) and bridge kaolin particles, complementing the action of CPAM. Additionally, the study demonstrated that bulk NBs improved dewatering characteristics by lowering the medium resistance and specific cake resistance during filtration. These findings pave the way for the utilization of bulk NBs as a novel and efficient strategy for kaolin separation in mineral processing, potentially leading to reduced processing times and lower operational costs.

Research on the factors affecting the product filtration efficiency in mineral processing plants

Filtration is a long-standing process but the technology has changed slowly, mainly based on the increase in filtration pressure and changes in the characteristics of filter media. The problem is high moisture remains product, requiring more expensive technologies (thermal drying) and long processing times. In the mineral processing industry, not only concentrates but also tailings need to be dewatered. The test samples were Cam Duong apatite concentrated and tailing ore, Ta Phoi copper concentrated and Sin Quyen tailing ore, Cua Ong fine coal, and Dak Nong red mud. All samples’ properties have been defined by sieving analyses, SEM method, and gravitational density measurement. Then, samples were experimented with using the Nutsche high-pressure filtration in the variable operational parameters. While the sludge concentration affected the specific resistance, the filter cake height and filtration pressure did not affect as much. At the suitable condition (homogeneous filter cake, 1 bar pressure difference, and 50 grams solid weight), the specific resistance and residual moisture content of the filter cake are around 2.5x10-12÷1.5x10-13 m-2, 15÷25%, respectively. Through the test results, some recommendations are mentioned in order to perfect the process and scale up for industrial production.

The application of chitosan quaternary ammonium salt to replace polymeric aluminum ferric chloride for sewage sludge dewatering

Inorganic coagulants such as poly aluminum ferric chloride (Al/Fe) are applied conventionally to sewage sludge dewatering and can be retained in the sludge cake, causing its conductivity to increase and generate secondary pollution. To reduce these disadvantages, there is a need to develop alternative, more sustainable chemicals as substitutes for conventional inorganic coagulants. In the present investigation, the application of a polymeric chitosan quaternary ammonium salt (CQAS) is explored as a complete, or partial, replacement for Al/Fe in the context of sludge dewatering processes. Laboratory experiments using digested sewage sludge showed that CQAS could effectively substitute for over 80 % of the Al/Fe inorganic coagulant in the sludge dewatering process. This substitution resulted in a reduction of sludge cake conductivity by more than 50 %. Simulation of sludge dewatering curves and imaging of the sludge surface indicated that the addition of CQAS led to an increase in nanosized pores, and a decrease in the specific resistance of the sludge filter cake as the dosage of Al/Fe decreased to around 30 %. The variations of fluorescence emission, quantum yield and carboxylic and amino groups, suggested that the chelating of Al/Fe decreased due to the bridging effects of CQAS. The CQAS had different flocculation bridging effects on various EPS fractions, which varied the amount of protein chelated with Al/Fe in each fraction. This study provides new information about the benefits of replacing conventional inorganic coagulants with natural organic polymers for sewage sludge dewatering, in terms of reduced sludge cake conductivity and greater dry solids content.

Integrated Filtration and Washing Modeling: Optimization of Impurity Rejection for Filtration and Washing of Active Pharmaceutical Ingredients.

A digital design tool that can transfer material property information between unit operations to predict the product attributes in integrated purification processes has been developed to facilitate end-to-end integrated pharmaceutical manufacturing. This work aims to combine filtration and washing operations frequently using active pharmaceutical ingredient (API) isolation. This is achieved by coupling predicted and experimental data produced during the upstream crystallization process. To reduce impurities in the isolated cake, a mechanistic model-based workflow was used to optimize an integrated filtration and washing process model. The Carman-Kozeny filtration model has been combined with a custom washing model that incorporates diffusion and axial dispersion mechanisms. The developed model and approach were applied to two systems, namely, mefenamic acid and paracetamol, which are representative compounds, and various crystallization and wash solvents and related impurities were used. The custom washing model provides a detailed evolution of species concentration during washing, simulating the washing curve with the three stages of the wash curve: constant rate, intermediate stage, and diffusion stage. A model validation approach was used to estimate cake properties (e.g., specific cake resistance, cake volume, cake composition after washing, and washing curve). A global systems analysis was conducted by using the calibrated model to explore the design space and aid in the setup of the optimization decision variables. Qualitative optimization was performed in order to reduce the concentration of impurities in the final cake after washing. The findings of this work were translated into a final model to simulate the optimal isolation conditions.

Study on the mechanism of hydrodynamic manipulation of floc structure to achieve high-flux of coagulation macro-filtration for the rapid removal of Aphanizomenonflos-aquae

Coagulation-filtration hybrid process has been widely used in algae removal treatment to improve the water quality and alleviate the membrane fouling. However, the intricate interplay of how floc structure induced by coagulation hydraulic shear influences the cake layer and filtration performance in coagulation macro-filtration of microalgae remains unexplored. In this study, a novel coagulation filtration with macro-pore of 75 μm was first adopted for the rapid removal of Aphanizomenonflos-aquae, and the floc structure was artificially manipulated through various velocity gradients to explore the effect mechanism of the coagulation hydrodynamic shear on the macro-filtration performance from the perspectives of floc characteristics (size and fractal dimension) and cake layer structure (thickness and roughness). The results showed that an optimal average flux of 31257.64 ± 2776.28 L·m−2·h−1 can be achieved at a manipulated appropriate velocity gradient (19 s−1), which is 1.1–2.3 times the flux achieved at higher or non-velocity gradients. The flocs formed at low velocity gradient were large and loose, while those formed at high velocity gradient were small and compact. Subsequently, the cake layer stacked by loose flocs was thicker and coarser than that by compact flocs, and exhibited a lower specific cake resistance, yielding a higher average flux. Moreover, a theoretical model for average flux was developed by introducing the velocity gradient, which directly elucidates how hydrodynamic shear affects floc characteristic, cake structure and filtration flux for the coagulation macro-filtration of Aphanizomenonflos-aquae. This study lays a theoretical foundation for the optimization of coagulation macro-filtration performance of microalgae and provides a new solution for the large flux removal of cyanobacteria by artificially regulating the coagulation hydrodynamic shear.

Analytical and numerical modelling of the effect of filter medium resistance on the mechanical dewatering of wastes and industrial filter cakes

A nonlinear model is proposed to predict the effect of filter medium resistance on the filter cake compression and dewatering at constant pressure. This model is based on the Darcy-Terzaghi-Shirato filtration-compression equations presented in material coordinates and modified to consider the power-law pressure dependence of the specific cake resistance α. Above mentioned model is extended to consider the filter medium resistance Rmintroducing the number of Biot, Bi=αavWRm.Local profiles of compressive pressure and filter cake characteristics, as well as consolidation ratio and cake dryness, are simulated and compared for different moderately and highly compressible filter cakes (silica, activated sludge, Baker’s yeast, and CaCO3) based on the analytical and numerical solutions of the model. It is shown that the behavior of cake compression and dewatering significantly depends on the filter medium resistance Rm, especially at the small numbers of Bi≤1.

Assessment of denitrification efficiency and membrane fouling potential in a sulfur-driven membrane bioreactor treating effluent from biological treatment

In this study, any remaining nitrate not eliminated during a biological treatment process with a low C/N ratio was effectively removed using sulfur powder in an autotrophic denitrification membrane bioreactor. Moreover, particular attention was given to investigating the potential for membrane fouling in a sulfur-based denitrification reactor, with a comparative analysis to conventional activated sludge in an aerobic membrane bioreactor. At an influent nitrate concentration of 320 mg/L, the removal efficiency reached 94–98 % within a 4-hour hydraulic retention time and at a reactor temperature of 30 °C. The sulfur-based denitrification reactor exhibited soluble microbial products concentration and specific cake resistance values of 38.3 mg/L and 1.4 × 1013 m/kg, respectively, which were 5.47 and 2.26 times higher than those of conventional activated sludge. Furthermore, it was observed that the supernatant from the sulfur-based denitrification reactor resulted in more significant fouling within the membrane surface.

Oily cold rolling mill sludge conditioned by quicklime to improve dewatering performance: optimization and mechanism study.

Dewatering is critical to oily cold rolling mill (CRM) sludge treatment. Therefore, finding an efficient, energy-saving, and applicable dewatering technology for oily CRM sludge is still urgent. This study investigated the performance of quicklime as a conditioning agent for oily CRM sludge conditioning and dewatering. The interactive effects of quicklime dosage, temperature, and time on filter cake's specific resistance to filtration (SRF) and the dewatering rate of oily CRM sludge were studied by response surface methodology (RSM). The optimal parameters for conditioning oily CRM sludge were quicklime dosage of 18.7%, temperature of 54 °C, and time of 43.3 min, which resulted in filter cake SRF of 0.50 × 1010 m/kg and dewatering rate of 61.2%. The viscosity of oily CRM sludge could be reduced by 90% after conditioned with quicklime, which caused by the neutralization or hydrolysis of high viscosity organic matter in the oil phase with quicklime to produce low viscosity organic matter. The study indicated the excellent performance of quicklime as a conditioning agent for oily CRM sludge treatment and provided an effective route for the recycling of the oily CRM sludge for steel production.

Predictive model of constant rate expression for dewatering of semi-solid materials

Nonlinear predictive model of constant rate expression is developed for dewatering semi-solid materials and industrial filter cakes. Nonlinear consolidation equation is expressed on the base of a power-law θ-function linearising Darcy law. Analytical solutions of consolidation equation are obtained under the constant rate condition. Presented model permits obtain the local solid and liquid pressure profiles during constant rate solid–liquid expression, as well as the internal distributions of liquid flow rate, local specific cake resistance and void ratio. Proposed analytical model and numerical simulations were used in worked examples for the highly compressible filter cakes of silica and activated sludge, as well as for the moderately compressible filter cake of CaCO3. It is shown that the value of applied expression rate is determinant for the process efficiency. Expression rate should be very low in case of highly compressible filter cakes of silica and activated sludge to avoid very rapid pressure rise and excessively high expression pressure. Obtained results permit verify and confirm Shirato’s hypothesis that internal structure of filter cake compressed under the instantaneous pressure in a constant rate operation is practically the same as that compressed under such a pressure in a constant-pressure operation.

Effect of operating parameters on the sludge settling characteristics by treatment of the textile dyeing effluent using electrocoagulation

Abstract This study invested the impact of the operational parameters (pH, Current Density (CD) and Electrode Gap (EG)) on the sludge generated after electrocoagulation treatment of textile dyeing effluent (TDE) by studying sludge settleability and filterability characteristics of EC generated sludge. Electrocoagulation treatment evaluated at laboratory scale with aluminum as electrode material at operating condition of parameters of pH, CD and EG. (pH-5.5, CD-105.12 A/m2 and EG-2.5 cm). Under these operating conditions, maximum COD reduction was achieved 88.45 % and maximum color reduction was about 66.92 %. Settling characteristics of TDE was studied by sludge volume index (SVI) and Centrifugal settleability index (CSI). From disposal point of view, filterability characteristic was also studied by simple gravity filtration method. Specific cake resistance, α (m/kg), filter medium resistance, R m(m−1) was also studied. The specific cake resistance was found in the order of 38.4 × 1013 >34.13 × 1013 >22.25 × 1013 >11.19 × 1013 >7.30 × 1013 (m/kg) at the pH 9.5, 7.5, 1.5, 5.5 and 3.5 respectively. While filter medium resistance was found to be 111.22 × 109, 92.28 × 109, 82.33 × 109, 41.38 × 109 and 13.87 × 109 m−1 at pH 7.5, 9.5, 3.5, 5.5 and 1.5 respectively.

Influence of Oil Content on Particle Loading Characteristics of a Two-Stage Filtration System

Filter media may encounter aerosols mixed with solid and oil ingredients from various sources, such as industries, transportation, and households, in the air purification process, while the influence such oil content has on the loading performance of single-stage and two-stage filtration systems is under-reported. Thus, this study aims to evaluate oil fraction effects on the loading performance of single-stage and two-stage filtration systems. First, to reveal the oil–solid mixed particle deposition mechanisms, the filter media parameters, i.e., specific cake resistance ε and cake porosity K2, were tested, indicating that a slight amount of oil can increase the dust holding capacity (DHC) of filters by forming a more porous cake, while an excess of oil results in reduced DHC by forming impermeable liquid films on the solid skeleton. Further two-stage experimental results indicate that the effectiveness of a pre-stage filter can be significantly affected by the properties of incoming aerosol and main-stage filters. The utilization of a pre-stage filter unintentionally deteriorated the service lifetime of the main-stage filter when challenged with contaminants with certain oil particles. This counter-intuitive negative phenomenon is due to the special loading behaviors of oil–solid mixed particles. The existing pre-stage filters allow a higher fine oil particle fraction to reach the main-stage downstream, while the induced cake filtration scenario leading to a film clogging scenario adversely reduced the lifetime of the main-stage filter. The findings suggest that the feasibility of a pre-stage in the filtration system requires compressive evaluations according to the specific oil-coated contaminants.

Impacts of operating conditions on specific cake resistance in dead-end microfiltration process

In the present work, the fouling behavior and the corresponding specific cake resistance of polyethersulfone microfiltration membrane fouled by using different solutions (bovine serum albumin solution, sodium alginate solution, humic acid and activated sludge suspension) under different operating conditions, transmembrane pressure (TMP), concentration (C), stirred speed (ω) and temperature (T) were systematically investigated. The ensuing results showed that the proposed equation can be used to accurately calculate instantaneous specific cake resistance (α). The average specific cake resistance increased with increasing operating pressure, concentration, and stirred speed, while it decreased with increasing operating temperature. The average specific cake resistance of sodium alginate (SA) was larger and the sequence was SA>HA>BSA>AS.

Ultrasonication-assisted fouling control during ceramic membrane filtration of primary wastewater under gravity-driven and constant flux conditions

This study investigated the feasibility of using ultrasonication as a ceramic microfiltration membrane fouling control strategy during gravity-driven membrane (GDM) filtration and constant flux filtration of primary municipal wastewater. The fouling model fitting curves revealed that initial intermediate pore blocking was dominant in the GDM system, followed by cake filtration; while cake filtration was dominant during constant flux filtration with a continuously increasing pattern. In the GDM system, periodic ultrasonication cleaning achieved higher cake resistance reduction (∼60 % vs ∼ 26 %) and led to lower specific cake resistances (0.2–2.0 × 107vs 29.6–59.3 × 107 m/mg) compared to periodic backwash. Ultrasonication-facilitated fouling mitigation effectiveness was related to cake properties (such as cake foulant density and porosity) and improved with extending ultrasonication duration. The foulant examination indicated that ultrasonication may result in porous cake nature by cake expansion and facilitate detaching particulate foulants and soluble organics (such as biopolymers) from the membrane. Cost analysis revealed that with commercial ceramic membranes, ultrasonication-facilitated GDM systems are economically feasible for treating wastewater at a household scale (∼1.1 EUR/m3 water), while ultrasonication-facilitated constant flux filtration systems are favorable at a small-community scale (∼0.5 EUR/m3 water). Furthermore, it was predicted that the use of low-cost recycled ceramic membranes would allow GDM systems as economical decentralized wastewater treatment processes due to their lower water production cost (∼0.16 EUR/m3 water) with easy operation and maintenance.

Special features of microbial cake under high pressure conditions in microfiltration

Here, cell separation from microbial suspensions (gram-negative bacterium Escherichia coli, gram-positive bacterium Lactococcus lactis, and yeast Saccharomyces cerevisiae) was performed by dead-end microfiltration. From the results of three types of experiments, namely constant-rate and constant-pressure filtration, and constant-pressure consolidation, it was revealed that the microfiltration behaviors of microbial suspensions can be described on the basis of the pressure dependences of the average void ratio and specific resistance of the microbial cake. However, under high-pressure conditions, we found that the cake structure of Escherichia coli was changed, and the calculations were inconsistent with constant-rate filtration data. The data, such as constant-rate filtration behaviors, spectra of filtrate, electron micrographs of filter cake, and constant-pressure consolidation behaviors, indicated the possibility of cellular destruction of Escherichia coli under pressures above 700 kPa. In contrast, this phenomenon was not observed at pressures of up to 1000 kPa in yeast with different cell envelope compositions. Cellular destruction affected the filtration performance, and since intracellular water was discharged, the dehydration characteristics of the cake changed significantly. The findings on the properties of microbial cakes under high pressure obtained in this study are useful for improving the efficiency of filtration operations for microbial suspensions and dehydration operations for biological sludge.

Valorising Nutrient-Rich Digestate as a Waste-Based Media for Microalgal Cultivation: Bench-Scale Filtration Characterisation and Scale-Up for a Commercial Recovery Process

Cultivating microalgae requires a nitrogen and phosphorous feed source. Anaerobic digestion waste (digestate) provides a cheap sustainable feedstock for these materials. Previous studies have successfully demonstrated the feasibility of nutrient recovery and subsequent algae growth. There is now a need to fully characterise digestate filtration to improve our understanding of this process prior to its commercialisation. In this work, digestate filtration is characterised at bench scale using frontal (dead-end) filtration and a 100 kDa MWCO ultrafiltration membrane. Our experiments demonstrated rapid cake formation causing significant flux decline. The steady-state permeate flux for digestate was 2.4 to 4.8 L m−2 h−1, a reduction of ~90% compared to clean water flux. The specific cake resistance was ~1015 m kg−1 and the compressibility index 1.07. A series of four filtration and cleaning cycles showed 90% flux recovery following a clean water wash. Digestate filtration was then evaluated at a commercial scale using crossflow and the KOCH ABCOR® tubular membrane (100 kDa MWCO). The results were similar to those at the bench scale, i.e., rapid initial fouling leading to a period of steady-state flux (approximately 7 L m−2 h−1). The commercial membrane was flushed with water and diluted bleach after each use, and a digestate permeate flux decline of only 4.8% over a 12-month active use period was observed. The present research provides bench scale characterisation and demonstrates the commercial scale operation of anaerobic digestate filtration using ultrafiltration. The overall filtration performance was excellent, and the process can now be scaled to any operational capacity.

Effects of Viscosity on Submerged Membrane Microfiltration Systems.

Submerged microfiltration has a wide range of applications in water and wastewater treatment. Membrane fouling is a major problem, resulting in a severe decline in flux, high energy consumption and frequent membrane cleaning and replacement. The effect of viscosity was not previously studied under controlled conditions to relate it to the air scour. Hence, this study investigated the effect of viscosity on membrane fouling during the operation of submerged membrane microfiltration by adding predetermined amounts of glycerol to a kaolin clay suspension. The addition of glycerol increased the viscosity (from 0.001 to 0.003 Pa·s), resulting in a 3-fold higher transmembrane pressure (TMP) development. An increased airflow (air scour) rate by 3 fold (from 0.6 m3/m2/h to 1.8 m3/m2/h), reduced TMP development by 65%. Membrane fouling quickly developed during the initial stage of microfiltration operation. Therefore, special precautions to control fouling during the early stages of filtration could significantly enhance the operation of the microfilter. Higher airflow caused a reduction in average specific cake resistance, whereas higher viscosity increased this value.

An approach to highly efficient filtration of methane hydrate slurry for the continuous hydrate production

A continuous process for gas hydrate production is of great significance to hydrate–based technologies. In this study, filtrating hydrate particles from hydrate slurries, which is a key step for continuous hydrate production based on water–in–oil emulsion, was systematically studied. The specific resistances of the hydrate cakes formed from different emulsions and under different pressure drops were measured. The results showed that the specific resistance of the hydrate cake increased with the increase of the pressure drop in two stages, and it increased much more rapidly in the second stage. Increasing the concentrations of Span 20, TBAB and PE would increase the specific resistance. The resistances of the hydrate cakes formed with Span 20 + TBAB were much higher than that with Span 20 or Span 20 + PE. Calculation results suggested that only when TBAB with concentration ≥0.25 wt% was used as the anti–agglomerant, the filtration rate could not meet the requirement of a hypothetical production task. An approach that involves filtration mediums, additives and pressure drops was proposed to efficiently filtrate hydrate slurries for continuous hydrate production. Based on the results, a process for continuous hydrate production from water–in–oil emulsion was proposed.

A multi-functional rinsing model based on cake properties for predicting rinsing efficiency and calculating energy consumption in MBR

The model establishment is of great significance to realize the automatic operation of membrane bioreactor (MBR). In this study, a multi-functional rinsing model based on the variation of cake properties was established to predict the instantaneous fouling resistance/rinsing efficiency (η) of 0.1 μm PAN membranes fouled with activated sludge suspension and calculate the energy consumption (W) for cake removal. The results showed that the model predictions had good agreements with experimental data (R2>0.960). Meanwhile, the cake thickness (L)/porosity (εc) decreased while the specific cake resistance (r) increased in the ringing process. And the cake with smaller εc and larger r was more difficult to remove. In addition, the transition points of W (uw) and η (uη) were determined (uw < uη). And the variation trend of η and W could be divided into three stages: (i) η increased rapidly while W increased slowly before uw; (ii) η increased slowly while W increased rapidly in the range from uw to uη; (iii) η increased slightly while W increased more rapidly after uη. The suitable cross-flow velocity range (uw < u < uη) and the suitable working region were determined after weighing W and η, which can be used to select optimal rinsing conditions in the actual MBR.