Possibilities for the use of membrane processes for the pre-treatment of wastewater from the production of dried potato purée

Our research focused on the membrane separation of wastewater resulting from the production of dried potato purée. Our aim was to investigate possibilities for recycling obtained retentate back to the actual production process, and, consequently, for reducing wastewater pollution. This paper describes trials of MF and RO membrane filtration of starch wastewater. The treated water contained starch, in either granulated or gelatinized form, and solids (fine pieces of potato skins). The trials were conducted in either one or two stages. We used a pilot plant equipped with a ceramic membrane with a filtration area of 0.35 m² and pore sizes of 500 and 100 nm. We also tested an organic RO membrane (7410) in the laboratory.High permeate flux above 100 l/(m² h) was measured for the 100 nm membrane, but with considerable fouling. Filtration through this membrane resulted in high COD and BOD₅ rejection (approximately 60%), an effect which was increased by the subsequent RO filtration. The content of soluble carbohydrate, 0.011% in permeate (with 0.44% dry substance), was analyzed using high-performance anion-exchange chromatography coupled with pulsed amperometric detection.     

纳滤/反渗透膜处理重金属废水的性能

The performance of different nanofiltration （NF） and reverse osmosis （RO） membranes was studied in treating the toxic metal effluent from metallurgical industry. The characteristics and filtration behavior of the processes including the wastewater flux, salt rejection and ion rejection versus operating pressure were evaluated. Then the wastewater flux of RO membrane was compared with theoretical calculation using mass transfer models, and good consistency was observed. It was found that a high rejection rate more than 95% of metal ions and a low Chemical Oxygen Demand （COD） value of 10 mg·L^-1 in permeate could be achieved using the RO composite membrane, while the NF rejection of the salt could be up to 78.9% and the COD value in the permeate was 35 mg·L^-1. The results showed that the product water by both NF and RO desalination satisfied the State Reutilization Qualification, but NF would be more suitable for large-scale industrial practice, which offered significantly higher permeate flux at low operating pressure.     

Investigation of two ultrafiltration membranes for treatment of olive oil mill wastewater

In this study, a promising treatment method is given for the olive oil mill wastewater (OMWW). Although the same steps of this method have been used in different studies before, flow scheme is novel. The membrane filtration of pretreated OMWW was investigated by using two ultrafiltration membranes in this study. Pretreatment steps were pH adjustment (pH = 2) and cartridge filter filtration, and pH adjustment (pH = 6) and cartridge filter filtration. Each step of cartridge filter filtration was batch process and effluent from the filter was recycled back to OMWW tank. Pretreated OMWW was sent to feed vessel of experimental set-up. Recovery of olive oil in the OMWW was realized collecting it from the top of pretreated OMWW. Ultrafiltration membranes used were JW and MW membranes supplied by Osmonics. The effects of main operating parameters (transmembrane pressure, feed flow rate, pH and membrane type) on the permeate flux and membrane fouling were examined. The effectiveness of the different membranes and operating conditions was evaluated using retention coefficients calculated from COD and TOC of experimental studies. The highest permeate flux (25.9 l/m² h) was obtained using MW membrane under operational conditions of Qf = 200 l/h flow rate and TMP = 4 bar, while the highest removals were obtained at Qf = 100 l/h flow rate and TMP = 1 bar. COD, TOC, SS, oil and grease concentrations of MW membrane effluent were 6400 mg/l, 2592 mg/l, 320 mg/l, and 270 mg/l, respectively.     

Treatment of olive mill wastewater by the combination of ultrafiltration and bipolar electrochemical reactor processes

The main purpose of this study was to investigate the removal of the chemical oxygen demand (COD) from olive mill wastewater (OMW) by the combination of ultrafiltration with electrocoagulation process. Ultrafiltration process equipped with CERAVER membrane was used as pre-treatment for electrochemical process. The obtained permeate from the ultrafiltration process allowed COD removal efficiency of about 96% from OMW. Obtained permeate with an average COD of about 1.1 g dm⁻³ was treated by electrochemical reactor equipped with a reactor with bipolar iron plate electrodes. The effect of the experimental parameters such as current density, pH, surface electrode/reactor volume ratio and NaCl concentration on COD removal was assessed. The results showed that the optimum COD removal rate was obtained at a current density of 93.3 A m⁻² and pH ranging from 4.5 to 6.5. At the optimum operational parameters for the experiments, electrocoagulation process could reduce COD from 1.1 g dm⁻³ to 78 mg dm⁻³, allowing direct discharge of the treated OMW as that meets the Algerian wastewater discharge standards (<125 mg dm⁻³).     

有机纳滤膜处理酵母废水中试实验研究

为了降低酵母废水的COD值,并回收废水中有价值的成份,以达到最佳经济效益和满足环保要求,分别采用纳滤和反渗透工艺对废水进行了中试实验。实验表明经NF膜处理后的废水可100%回收酵母蛋白等成份,对色度具有>90%的去除率,浓缩液经处理后可制成干粉向市场销售,NF膜对COD去除率可从17000～22000mg/L降低至1000mg/L左右,大大减轻了后续生化处理的负荷,膜平均通量为15.0LMH以上,含固量浓缩倍数为4.45。经初步经济分析平均单位料液运行成本约为6.79元/吨,干粉成本约500元/吨,实验表明,以NF膜处理酵母废水是一种经济、可行的方法。     

Treatment of oily wastewater using low cost ceramic membrane: Comparative assessment of pore blocking and artificial neural network models

This work addresses the performance and modeling of the separation of oil-in-water (o/w) emulsions using low cost ceramic membrane that was prepared from inorganic precursors such as kaolin, quartz, feldspar, sodium carbonate, boric acid and sodium metasilicate. Synthetic o/w emulsions constituting 125 and 250 mg/L oil concentrations were subjected to microfiltration (MF) using this membrane in batch mode of operation with varying trans-membrane pressure differentials (ΔP) ranging from 68.95 to 275.8 kPa. The membrane exhibited 98.8% oil rejection efficiency and 5.36 × 10⁻⁶ m³/m² s permeate flux after 60 min of experimental run at 68.95 kPa trans-membrane pressure and 250 mg/L initial oil concentration. These experimental investigations confirmed the applicability of the prepared membrane in the treatment of o/w emulsions to yield permeate streams that can meet stricter environmental legislations (<10 mg/L). Subsequently, the experimental flux data has been subjected to modeling study using both conventional pore blocking models as well as back propagation-based multi-layer feed forward artificial neural network (ANN) model. Amongst several pore blocking models, the cake filtration model has been evaluated to be the best to represent the fouling phenomena. ANN has been found to perform better than the cake filtration model for the permeate flux prediction with marginally lower error values.     

Deacidifying rice bran oil by solvent extraction and membrane technology

Crude rice bran oil containing 16.5% free fatty acids (FFA) was deacidified by extracting with methanol. At the optimal ratio of 1.8:1 methanol/oil by weight, the concentration of FFA in the crude rice bran oil was reduced to 3.7%. A second extraction at 1:1 ratio reduced FFA in the oil to 0.33%. The FFA in the methanol extract was recovered by nanofiltration using commercial membranes. The DS-5 membrane from Osmonics/Desal and the BW-30 membrane from Dow/Film Tec gave average FFA rejection of 93–96% and an average flux of 41 L/m²·h (LMH) to concentrate the FFA from 4.69% to 20%. The permeate, containing 0.4–0.7% FFA, can be nanofiltered again to recover more FFA with flux of 67–75 LMH. Design estimates indicate a two-stage membrane system can recover 97.8% of the FFA and can result in a final retentate stream with 20% FFA or more and a permeate stream with negligible FFA (0.13%) that can be recycled for FFA extraction. The capital cost of the membrane plant would be about $48/kg oil processed/h and annual operating cost would be about $15/ton FFA recovered. The process has several advantages in that it does not require alkali for neutralization, no soapstock nor wastewater is produced, and effluent discharges are minimized.     

Preparation of a new ceramic microfiltration membrane from mineral coal fly ash: Application to the treatment of the textile dying effluents

New microfiltration membranes from mineral coal fly-ash material are obtained using ceramic method. Paste from mineral coal fly ash (obtained by calcinations at 800 °C of non-grinded mineral coal) is extruded to elaborate a porous tubular configuration used as supports. The support heated at 1125 °C, shows an average pore diameter and porosity of about 4.5 μm and 51%, respectively. The properties in terms of mechanical and corrosion resistances are very interesting. The elaboration of the layer based on fly-ash powder (obtained by sintering at 700 °C of a finely grinded mineral coal) is performed by slip-casting method. The heating treatment at 800 °C leads to an average pore size of 0.25 μm. The water permeability determined of this membrane is 475 L/h m² bar. This membrane can be used for crossflow microfiltration. The application to the treatment of the dying effluents generated by the washing baths in the textile industry shows an important decrease of turbidity (inferior to 1 NTU), of chemical oxygen demand (COD) values (retention rate of about 75%) and a total color removal. The performances in term of permeate flux and efficiency were determined and compared to those obtained using a commercial alumina microfiltration membrane. Almost the same stabilised permeate flux was obtained (about 100 L h⁻¹ m⁻²). So, it seems that the prepared membrane is suitable for such wastewater treatment.     

Purification and Concentration of Caustic Mercerization Wastewater by Membrane Processes and Evaporation for Reuse

A membrane-based treatment strategy was developed for purifying the highly alkaline textile mercerization wastewater. 0.2-μm MF and 100 kDa UF membranes were evaluated as pretreatment alternatives before 10 kDa UF and 200 Da NF membranes. Turbidity was almost totally removed by both pretreatment options, while UF (100 kDa) showed higher COD retention than MF. In total recycle mode of filtration, fouling of both UF and MF membranes were 80% reversible by physical and almost totally reversible (≥ 97%) by chemical cleaning. In the second stage filtrations applied to the pretreated wastewater samples, NF could yield high (97-98%) COD retentions and low permeate COD concentrations (≤ 22 mg/L), while 10 kDa UF could only reduce the COD concentration to 150 mg/L. While no NaOH was lost in the MF+UF process, the use of NF as second stage resulted in 12-17% NaOH retention. The permeate flux in all second stage processes were stable, implying that the majority of the feed components that would cause fouling had been removed in the pretreatment stages. Permeate of the MF+NF sequence was concentrated by evaporation with no foaming problems, showing that the hybrid process can be applied to recycle a purified and concentrated caustic stream to the mercerization process.     

Experiment and calculation of filtration processes in an external-loop airlift ceramic membrane bioreactor

Air sparging is recognized as an effective way to increase permeate flux in membrane filtration processes. The application of air sparging with an external-loop airlift ceramic membrane bioreactor was studied at different gas flow rates, biomass concentrations and suction pressures. A 180% increase in permeate flux was obtained while filtering a 2 g/L activated sludge wastewater suspension with the airlift cross-flow operation for U_g=0.21 m/s. The mechanism of flux enhancement in the case of slug flow in tubular membrane was discussed. The region near the gas slug was divided into three different zones: falling film zone, wake zone and remaining liquid slug zone. Air sparging significantly lowered cake thickness and consequently cake resistances for the wake region and the falling film region. A novel model combining hydrodynamic of gas-liquid two-phase flow and cake resistance was developed to simulate the process. The model was validated with experimental data with an error of 8.3%.     

Experimental investigation and modeling hybrid nano-porous membrane process for industrial oily wastewater treatment

The aims of this work are to construct a pilot scale purification set-up using membrane process for Tehran Oil Refining Company desalter plant wastewater. The investigation was shown that the high amount of impurities in the feed was the main reason of low permeation flux. The nano-porous membrane-powdered activated carbon (NPM–PAC) was employed to settle this problem. Results demonstrated NPM alone was ineffective in removing TSS, COD, and TOC. In the NPM process the removal of COD and TOC are around 62.5 and 75.1%, respectively, and the steady permeation flux (SPF) is around 78.7 L/(m² h). Optimum PAC dosage, which leads to less deposit layer with high porosity on the membrane surface, could increase permeation flux up to 133.8 L/(m² h), the removal of COD and TOC, 78.1% and 90.4%, respectively, and also decreased steady fouling resistance (SFR) around 46.1%. Hermia's models were employed to investigate mechanism of preventing membrane fouling. After coagulation, the kinetic constants, K_b, K_i, K_s, and K_c, showed lower amounts when NPM filtration used alone. Thus, a NPM–PAC hybrid membrane system has the potential to be an effective method to improve NPM removal efficiency in high percentages as well as to improve membrane fouling and permeation flux in desalter plant.     

Synthesis and characterization of cellulose acetate-polysulfone blend microfiltration membrane for separation of microbial cells from lactic acid fermentation broth

This work is focused on synthesis and characterization of a polymer blend microfiltration membrane for separation of microbial cells from lactic acid fermentation broth in a continuous process. The membranes were prepared by blending hydrophilic cellulose diacetate (CA) polymer with hydrophobic polysulfone (PSF) polymer in wet phase inversion method. Polymers were blended in N-methyl-2-pyrrolidone (NMP) solvent (70 wt.%) where polyethylene glycol was added as a pore former. The membranes were characterized in terms of morphology, porosity, flux and microbial separation capability. The best prepared membrane with PSF/CA weight ratio of 25/75 yielded a pure water flux of 1830 LMH (liter/m² h) and a fermentation broth flux of 1430 LMH at around 1.5 bar TMP (trans-membrane pressure). The membrane was successful in complete retention of microbial cells from the broth in a continuous crossflow membrane module integrated with the fermentor.     

A study on submerged rotating MBR for wastewater treatment and membrane cleaning

A submerged rotating membrane bioreactor (SRMBR), with a rotatable, rounded, flat-sheet Poly(vinyldiene fluoride) (PVDF) membrane module fixed on hollow axes and moved by an electromotor, was used for wastewater reclamation. It was found that the effluent COD became stable and lower than 20 mg/L after one day running. The equilibrium permeate flux increased from 42.5 to 47.5 L/m²·h with the rotation speed increasing from 15 r/min to 25 r/min. Prolonging relaxation time could alleviate membrane fouling and enhance the flux. Finally, membrane cleaning was studied. The results showed that flushing the membrane surface with water, water/NaOH and water/NaOH/HCl recovered permeate flux to 48.4%, 83.5% and 90.2% of that of the initial operation, respectively.     

陶瓷纳滤膜处理淋浴污水及膜的清洗

采用无机陶瓷纳滤膜对淋浴污水进行分离特性试验，重点探讨了膜通量随时间的衰减情况以及操作压差、污水温度和pH值等操作参数对淋浴污水处理效果和膜通量的影响；并就陶瓷膜的污染对膜的清洗方法进行了初步研究。研究结果表明，陶瓷纳滤膜对淋浴污水中COD、TOC和浊度均有一定的去除效果，用水洗＋碱洗＋酸洗的综合清洗方法可以获得较好的清洗效果     

The effect of transmembrane pressure and pH on treatment of paper machine process waters by using a two-step nanofiltration process: Flux decline analysis

In this work, the treatment of paper machine whitewater obtained from paper production by using loose and tight Nanofiltration (NF) membranes in a lab-scale plant with a plate and frame module was investigated. The NF membranes were evaluated for fouling, flux decline due to concentration polarization and their suitability for removing of components present in wastewater. The loose NF membrane was used for the first step under different transmembrane pressure (8 to 32 bars) and pH (3, 5.6 and 10) values. The best filtration performances were provided under a pressure of 32 bar and a pH of 5.6. The fouling mechanism at different transmembrane pressures and pH values was investigated by “Hermia's model”. Also, fouling on pores and on the surface of NF membranes was characterized by Scanning electron microscopy (SEM) and contact angle measurements, respectively. For the advanced treatment of permeate obtained from the loose NF membrane that provided the lowest fouling and flux decline, a tight NF membrane was used in the second step. Even better retentions were achieved from experiments with this NF membrane. Results obtained in this study showed that the combination loose and tight NF membranes achieved reuse of paper machine white water for use as shower water of paper machine.     

Flat-plate submerged membrane bioreactor for the treatment of higher-load graywater

Graywater treatment has been the focus when topics of decentralized treatment systems are discussed. In this paper, the treatment of higher-load graywater, a mixture of washing machine and kitchen sink wastewater, was investigated. A 10 L lab-scale submerged membrane bioreactor (subMBR) was operated with a flat-plate membrane for 87 days. Permeate was intermittently withdrawn at constant transmembrane pressure (TMP) induced by water level difference and without pump requirement. The pollutants' removal and membrane behavior were monitored. The COD removal was around 96% and a permeate COD of about 26 mg L^− 1 was obtained. The total linear alkylbenzene sulfonate (LAS) removal achieved was > 99%, indicative of its non-inhibited degradation even at influent concentration of 30.8 mg L^− 1. The subMBR was operated at almost stable and constant flux of 0.22 m³ m^− 2 d^− 1 at a mean HRT of 13.6 h.     

Reducing pollution from the deliming–bating operation in a tannery. Wastewater reuse by microfiltration membranes

This paper presents experimental results from the implementation of two measures aimed at reducing the nitrogen concentration in a tannery wastewater. Specifically, this research has focused on the wastewater from the deliming/bating operations. The proposed measures are the replacement of ammonium salts by carbon dioxide in the deliming process and the reuse of wastewater and chemicals after membrane filtration of the deliming/bating liquor. The experimental study covered different wastewater pretreatment alternatives and experiments with two membranes (with different separation properties): one in the range of microfiltration (MF) and one in the range of the ultrafiltration (UF). Results of the pretreatment study indicated that neither settling nor protein precipitation were feasible. Only a security filtration prior to membrane filtration was recommended. The tested MF membrane was selected due to the higher flux (around 25 L/(m² h)) in comparison with the UF membrane. The MF permeate was successfully reused in the deliming/bating process. The delimed leather quality was excellent according to both visual and organoleptic inspection from process technicians and phenolphthalein test, confirming the technical feasibility of the proposal. Globally, the implementation of the above mentioned two measures resulted in 53% total nitrogen reduction.     

The Study on the Ceramic Membrane Wastewater Reuse System with Pre-Ozonation and Coagulation

A new wastewater reuse system using ozonation, coagulation and MF ceramic membrane (0.1 μm) filtration was developed. The testing was performed using secondary effluent treated at the wastewater treatment plant (WWTP) in Tokyo, Japan. The volume of treated water by the pilot study equipment is about 90 m³/day. The combination of pre-ozonation and coagulation processes achieves continuous stable membrane filtration with flux of 4m³/m²/day (167 LMH). A stable membrane filtration could be maintained by controlling ozone dosing rate depending on secondary effluent (raw water) quality fluctuation. The COD (Mn) removal ratio in raw water was 50 to 60%, and the color removal ratio satisfied 80% or higher. The quality of the treated water that was obtained from our pilot study was better than the California's standards.     

Membrane choice for wastewater treatment using external cross flow tubular membrane filtration

Systematic investigations of activated sludge separation were conducted using membrane filtration. To accomplish this, different organic tubular membranes with different separation limits and diameters were examined. Furthermore, from the results obtained in the initial tests, an appropriate membrane was chosen for a long-term test. The investigations determined that for biomass separation by the tubular membranes in the tested system, neither the membrane material nor the separation limit within a range of 1 μm to 20,000 Da had a significant influence on the filtration characteristics. It was recognized that the application of a tubular membrane with a diameter of less than 8 mm is problematic, because high flow velocities were needed to prevent blockage of the membrane. When the flow velocity was in the range of 1 to 4 m/s, a linear relation between flux and velocity was found. This showed the potential for controlling the membrane filtration process and externally influencing the permeate rate. An average retention of TOC was about 75%. The retention of TOC was not significantly influenced by the nominal pore sizes of the membranes (except for the membrane WFNX 0505) which were tested here. The ultrafiltration membrane WFS 0120 (Stork) was prominent in the long-term test due to its very high flux, germfree permeate with a MWCO (molecular weight cut-off) of 100,000 Da, and was not blocked with a diameter of 14.4 mm, also at lower flow velocities. The results of the long-term test supported the hypothesis that a meaningful application of such a module concept is possible in a filtration plant for the preparation of samples or for the rejection of the biomass in small sewage treatment plants.     

Study on backwash wastewater from rapid sand-filter by monolith ceramic membrane

To verify the feasibility of membrane micro-filtration process to treat the sand-filter backwash wastewater and the sediment sludge withdrawn from the coagulation-flocculation-settling tank, a multi-lumen monolith ceramic membrane module was applied in a test pilot plant. The ceramic membrane filtration was operated very stably at the filtration flux of 4 m/day when the sand-filter backwash wastewater was fed. The membrane filtration was also operated very stably at the flux of 2 m/day when the mixture of the sand-filter backwash wastewater and the sediment sludge was fed. The level of these substances in the membrane filtrate was very low and met drinking water standards.