Ultrafiltration and nanofiltration in the pulp and paper industry using cross-rotational (CR) filters.

Ultra- and nanofiltration with high shear CR-filters have been utilized for cleaning of clear filtrates and effluents from the pulp and paper industry. The aim was to find out how different nanofiltration membranes operate at high shear conditions. The filtration efficiency of the membranes was evaluated by measuring flux, retention and fouling at various recovery and pH conditions. High fluxes (approximately 100 L/(m2h)) for nanofiltration membranes were measured when circulation waters from the paper machine were filtered at neutral conditions. In the filtration of discharge of external activated sludge treatment plants we measured fluxes around 150 L/(m2h) even at a concentration factor of 12. The best NF membranes removed over 80% of the organic carbon and of the conductivity and almost completely eliminated the color. With acidic waters fluxes and retentions were significantly lower. The NF270 membrane from Dow and the Desal-5 membranes from Osmonics had the highest flux and retention properties. However, the Desal-5 membrane lost its retention properties slowly, which restricts its use in the high shear CR-filter. CR-nanofiltration can be used in the pulp and paper industry without feed pre-treatment by ultrafiltration. This increases the attractiveness of high shear CR-nanofiltration.     

Performance of cellulose acetate - polyethersulphone blend membrane prepared using microwave heating for palm oil mill effluent treatment.

The objective of this research is to investigate the performance of blend cellulose acetate (CA)-polyethersulphone (PES) membranes prepared using microwave heating (MWH) techniques and then compare it with blend CA-PES membranes prepared using conventional heating (CH) methods using bovine serum albumin solution. The superior membranes were then used in the treatment of palm oil mill effluent (POME). Various blends of CA-PES have been blended with PES in the range of 1-5 wt%. This distinctive series of dope formulations of blend CA/PES and pure CA was prepared using N, N-dimethylformamide (DMF) as solvent. The dope solution was prepared by MW heating for 5 min at a high pulse and the membranes were prepared by phase inversion method. The performances of these membranes were evaluated in terms of pure water and permeate flux, percentage removal of total suspended solids (TSS), chemical oxygen demand (COD) and biochemical oxygen demand (BOD). The results indicate that blend membranes prepared using the microwave technique is far more superior compared to that prepared using CH. Blend membranes with 19% CA, 1-3% PES and 80% of DMF solvent were found to be the best membrane formulation.     

Study of antifouling modified ultrafiltration membrane based on the secondary treated water of urban sewage

Mixtures of polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA) containing hydrophilic ultrafiltration membranes were prepared by adding PVA (5 to 30%) to PVDF by the phase inversion method. The hydrophilic contact angle (CA), equilibrium water content, pure water flux and bovine serum albumin retention were studied to assess the membrane performance. The anti-fouling performance of modified membrane to the secondary treated water was evaluated by flux decline, washing recovery rate and fouling resistance analysis. Scanning electron microscopy showed that the cross-section structure of the membranes had finger-like pores, which were well developed and uniformly distributed, and the sub-layer structure was looser and more porous with the increasing content of PVA. The CA gradually decreased. The steady flux was 800 L/m(2) h from P15 to P30, and the BSA retention sharply declined. The ultrafiltration tests for secondary treated water indicated that the main fouling source of the modified membrane was the concentration polarization and cake layer resistance. After physical flushing, the flux recovery ratio of the membrane could reach 100% when the PVA content was 5-15%, which shows excellent anti-pollution performance and good prospects for use in processing wastewater from urban sewage.     

Treatment of domestic sewage by a metal membrane bioreactor

A submerged flat metal MBR (membrane bioreactor) was used to treat synthetic domestic sewage in this study. The experiment was continued for 270 days and ran under two modes as AMBR (aerobic membrane bioreactor) and A/O-MBR (anoxic/aerobic membrane bioreactor) at a permeate flux of 0.4-1 m3/(m2 d). PVA (polyvinyl alcohol) gel beads were added to the aeration tank with a volume ratio of 10% at the end of the A/O-MBR mode. The mean COD and TN removal efficiencies achieved 96.69 and 32.12% under the AMBR mode, and those were 92.17 and 72.44% under the A/O-MBR mode, respectively. SND (simultaneous nitrification and denitrification) occurred at high MLSS (mixed liquor suspended solids) concentration. The metal membranes reduced effluent COD during filtration. The system ran stably for 115 days at a permeate flux of 0.8-1 m3/(m2 d) without changing membranes under the AMBR mode, but the membrane filterability decreased gradually under high MLSS or A/O-MBR mode, and the addition of PVA worsened the membrane filterability on the contrary. PSD (particle size distribution) and sludge fractions had evident influence on membrane fouling. The main fouling mechanism was cake formation under the AMBR mode, and that was pore blocking under the A/O-MBR mode.     

Effect of membrane characteristics on the performance of membrane bioreactors for oily wastewater treatment

Influence of membrane material and pore size on the performance of a submerged membrane bioreactor (sMBR) for oily wastewater treatment was investigated. The sMBR had a working volume of about 19 L with flat sheet modules at the same hydrodynamic conditions. Five types of micro- and ultra-polymeric membranes containing cellulose acetate (CA), cellulose nitrate (CN), polyamide (PA), polyvinylidene difluoride (PVDF) and polyethersulfone (PES) were used and their filtration performance in terms of permeability, permeate quality and fouling intensity were evaluated. Characterization of the membranes was done by performing some analysis such as pore size distribution; contact angle and scanning electronic microscopy (SEM) microphotograph on all membranes. The quality of permeates from each membrane was identified by measuring chemical oxygen demand (COD). The results showed more irreversible fouling intensity for membranes with larger pore size which can be due to more permeation of bioparticles and colloids inside the pores. Membrane characteristics have a major role in the preliminary time of the filtration before cake layer formation so that the PA with the highest hydrophilicity had the lowest permeability decline by fouling in this period. Also, the PVDF and PES membranes had better performance according to better permeate quality in the preliminary time of the filtration related to smaller pore size and also their better fouling resistance and chemical stability properties. However, all membranes resulted in the same permeability and permeate quality after cake layer formation. An overall efficiency of about 95% in COD removal was obtained for oily wastewater treatment by the membranes used in this study.     

Analysing mass balance of viruses in a coagulation-ceramic microfiltration hybrid system by a combination of the polymerase chain reaction (PCR) method and the plaque forming units (PFU) method.

Virus removal experiments using river water spiked with bacteriophages were conducted by an in-line coagulation-ceramic microfiltration hybrid system to investigate the effects of filtration flux (62.5 and 125 L/(m2 x h)) and type of virus (Qbeta and MS2) on virus removal. In addition, the mass balance of viruses through the hybrid system was analysed by quantifying the infectious and inactive viruses by a combination of the polymerase chain reaction (PCR) method and the plaque forming units (PFU) method. Even when the system was operated at high filtration flux (125 L/(m2 x h)), high virus removal (> 6 log) with short coagulation time (2.4 s) was successfully achieved by dosing polyaluminium chloride (PACI) at more than 1.08 mg-Al/L. Removal performances were different between Qbeta and MS2, although their diameters are almost the same: greater virus removal was achieved for MS2 at PACI dosing of 0.54 mg-Al/L, and for Qbeta at PACI dosing of more than 1.08 mg-Al/L. The combination of the PCR and PFU methods revealed that two phenomena, adsorption to/entrapment in aluminium floc and virucidal activity of PACI, partially account for the high virus removal in the coagulation-MF hybrid system.     

Membrane fouling and selectivity mechanisms in effluent ultrafiltration coupled with flocculation.

Membrane filtration is adequate for producing disinfected clear water suitable for various kinds of applications. However, fouling of membranes is the main limitation. The scope of the present study is to examine the effect of iron coagulation of primary wastewater effluent on membrane filtration, in parallel to fouling characterization of the iron itself. The fouling of ultrafiltration membranes by colloidal iron hydroxide-oxide has been studied by measuring the pore streaming potential of PES UF membrane. pH 5.5 (charge neutralization zone) provided better removal and lower fouling intensity than pH 7.8 (sweep coagulation zone), but the internal clogging at acidic pH was higher. Fouling of the membrane as measured by flux reduction was usually accompanied by a positive change in zeta potential and iso-electric point (IEP) of the membrane. An initially large change in zeta potential (without charge reversal) was seen even after relatively small amounts of iron solution were filtered through the membrane. A control experiment showed this is not due to iron adsorption equilibrium, but should probably be attributed to fouling. Change in zeta potential, can be used as an indicator for commencement of fouling even for small flux reductions. UF membrane critical flux after iron filtration can be evaluated more accurately by zeta potential than pressure drop or change in iron concentration.     

Evaluation of a MF membrane system composed of pre coagulation-sedimentation and chlorination for water reuse.

In this research, we investigated the variation of transmembrane pressure and permeate water quality in pre-coagulation and sedimentation with iron based coagulant, and chlorination of feed water for PVDF (Polyvinylidene fluoride) based MF membrane filtration. NaCIO was fed to the membrane module at a dosage of 0.5 mg/L and maintained during filtration. To observe the effect of raw water, three types of raw and processed waters, including river surface water, coagulated water and coagulated-settled water, were employed. In the case of river surface water, the transmembrane pressure increased abruptly in 500 hours operation. On the contrary, no significant increase in transmembrane pressure was observed for coagulated water and coagulated-settled water for 1200 hours operation. The turbidity of permeate was lower than the detection limit for all applied waters. The removal efficiency for humic substances in coagulated water and coagulated-settled water was approximately ten times higher than that in surface river water. And, the removal efficiency for TOC and DOC was approximately two times higher than that in surface river water. From the results of the operation, it can be observed that it is possible to maintain stable operation at 0.9 m(3)/m(2)-day filtration flux through a combination of pre-coagulation and pre-chlorination. However, the water quality of permeate was the best when the pre-coagulation-sedimentation process was combined with pre-chlorination. With respect to fouling reduction and operation efficiency increase in membrane filtration, the pre-coagulation/sedimentation process is a promising alternative.     

Mullite ceramic membranes for industrial oily wastewater treatment: experimental and neural network modeling

In this paper, results of an experimental and modeling of separation of oil from industrial oily wastewaters (desalter unit effluent of Seraje, Ghom gas wells, Iran) with mullite ceramic membranes are presented. Mullite microfiltration symmetric membranes were synthesized from kaolin clay and alpha-alumina powder. The results show that the mullite ceramic membrane has a high total organic carbon and chemical oxygen demand rejection (94 and 89%, respectively), a low fouling resistance (30%) and a high final permeation flux (75 L/m2 h). Also, an artificial neural network, a predictive tool for tracking the inputs and outputs of a non-linear problem, is used to model the permeation flux decline during microfiltration of oily wastewater. The aim was to predict the permeation flux as a function of feed temperature, trans-membrane pressure, cross-flow velocity, oil concentration and filtration time, using a feed-forward neural network. Finally the structure of hidden layers and nodes in each layer with minimum error were reported leading to a 4-15 structure which demonstrated good agreement with the experimental measurements with an average error of less than 2%.     

某富营养化池塘夏季温室气体通量的昼夜变化

为揭示富营养化浅水池塘昼夜性的温室气体通量特征,利用DLT-100温室气体分析仪高采样频率的优势,通过48 h的在线观测,获得了宜昌野猪林池塘夏季CH4和CO2扩散和冒泡释放的昼夜性通量数据。观测点F点水气界面总CH4和CO2通量分别约为595.2,1 450.8 mg/(m2·d),CH4和CO2气泡排放量分别占到总排放量的99.7%和3.0%。观测期内冒泡存在高度时间变异性,最大的一次CH4冒泡释放速率为424.28 mg/(m2·h),占2 d内总气泡释放量的35.75%,而大多数时段的CH4冒泡速率低于20.0 mg/(m2·h)。监测期内CH4和CO2扩散通量的最高值分别为各自最低值的6.0和6.5倍。监测表明,富营养化浅水池塘夏季CH4通量非常高,且主要以冒泡方式释放;而CO2通量明显响应于浮游植物光合作用和呼吸作用交替的新陈代谢作用,存在昼夜性的变化规律。     

Denitrification rate and carbon source consumption in full-scale wastewater filtration.

In response to new demands for increased removal of nitrogen and phosphorus, the Henriksdal and Bromma treatment plants, with hydraulic loads of 283,000 and 148,000 m3/d, respectively, built filtration steps as a final process step in the plants. The denitrification rates in a full-scale and in a pilot plant filter are calculated to 13.1 and 21.3 g (NO3+NO2)-N/(m3 x h), respectively, in the total filter bed after 2.5-24.2 and 16.0-28.0 h of operational time, and 6.4 and 18.7 g (NO3+NO2)-N/(m3 x h), respectively, after 1.0 and 0.1-0.9 h of operational time. In composite samples, the denitrification rate in the total filter bed is 10-20 g (NO3+NO2)-N/(m3 x h) in the full-scale filter. The average values for k = deltaCODf/deltaC(T) are 1.6 and around 3 in the total filter bed in steady state and in the beginning of the experiments, respectively, both in the full-scale and in the pilot plant study. The carbon source costs for reducing the concentration of nitrate nitrogen in the Bromma plant from 12 to 8 mg/l in the effluent are 117,400 EUR and 147,400 EUR with methanol and ethanol, respectively, as a carbon source.     

温度对两种固定化硝化菌硝化反应的影响

通过包埋固定化硝化菌颗粒和生物接触氧化法在不同温度条件下的硝化反应速率测定试验,发现在28℃时两个反应器均达到最大硝化速率,分别为40 mgN/(L.h)和31 mgN/(L.h);温度降至8℃时,硝化速率分别为18 mgN/(L.h)和8 mgN/(L.h),包埋固定化硝化菌在低温条件下显示出明显的优势。温度为20~32℃时,包埋硝化菌处理高氨氮废水很容易形成亚硝酸型硝化。     

Optimising the operation of a MBR pilot plant by quantitative analysis of the membrane fouling mechanism.

In order to optimize some operational conditions of MBR systems, a MBR pilot plant equipped with a submerged hollow fibre membrane module was employed in this study. The pilot MBR was fed with real municipal wastewater and the filtration flux, backwashing interval, aeration frequency and temperature were varied. A filtration flux below 25 I/m2h is generally recommended, at below this flux, the MBR operated at sub-critical flux conditions, the filter cake was minimized and membrane fouling was mainly attributed to the membrane pore blocking. Moreover, the membrane fouling, at below 25 I/m2h, was more reversible to backwashing; above this value, backwashing became less efficient to clean the membrane. Less frequent backwashing (e.g. 600 s filtration/45 s backwashing) decreased the amount of fouling irreversible to backwashing and its performance was superior to that of frequent backwashing (e.g. 200 s filtration/15 s backwashing). The MBR suffered more fouling at low temperature conditions (e.g. at 13-14 degrees C) than at high temperature conditions (e.g. at 17-18 degrees C). A conceptual model was built up and successfully interpreted this temperature effect.     

Biodegradability enhancement of municipal landfill leachate

The method of enhancing the biodegradability of landfill leachate via air stripping followed by coagulation/ultrafiltration （UF） processes is introduced. In this study, the air stripping process obtained a removal efficiency of 88.6% for ammonia nitrogen （NH3-N）, at an air-to-liquid ratio （A/L） of 3 300 （pH = 11） and after 18 h of stripping. The single coagulation process increased the BOD （biological oxygen demand）/COD （chemical oxygen demand） ratio by 0.089 with a FeCl3 dosage of 570 mg/L, at pH 7.0, and the single UF process increased the BOD/COD ratio from 0.049 to 0.311. However, the combination of coagulation and UF increased the BOD/COD ratio from 0.049 to 0.423, and the final BOD, COD, NH3-N, and colour of the leachate were 1 023 mg/L, 2 845 mg/L, 145 mg/L, and 2 056, respectively, when a 3 kDa molecular weight cut-off （MWCO） membrane was used at an operating pressure of 0.7 MPa. In the ultrafiltration process, the average solution flux （Jv）, concentration multiple （Mc）, and retention rate （R） for the COD were 107.3 L/（m^2·h）, 6.3, and 84.2%, respectively.     

Influence of module configuration and hydrodynamics in water clarification by immersed membrane systems.

Different immersed membrane systems were compared according to the module configuration. Filtering concentrated aqueous suspensions under constant permeate flux, the hydraulic performances of the systems were evaluated and compared through parameters such as critical permeate flux notion and trans-membrane pressure variation rates. Operational variables were membrane size and module fibre density, aeration inside or outside the fibre network, suspension concentration and physico-chemical conditioning. When using hollow fibres including a possible air injection inside the fibre network, results pointed out the positive role of the aeration on the fouling control. But too high a fibre density did not allow an optimal control when the aqueous suspension was very concentrated. On the other hand, when working with capillary membranes showing sufficient space between fibres, the major parameters were the transversal suspension flow circulation through the fibre network and the FeCl3 conditioning of the suspension. Experimental results show a possible working at a 0.07 m3 x m2 x h(1) permeate flow rate under low TMP evolutions, 0.02 Pa/s, even if the filtration was operated under high concentrated suspension, 5kgSS/m3.     

Membrane filtration for tertiary treatment of biologically treated effluents from the pulp and paper industry.

Discharge waters from activated sludge processes in the pulp and paper industry and from a municipal wastewater treatment plant were filtered with various nanofiltration (NF) and low pressure reverse osmosis (RO) membranes. The purpose was to study flux, retention, and permeate quality after membrane filtration by using a high shear (CR-250/2) filter. The suitability of the achieved permeates for reuse at the industrial site is also discussed. The NF permeate was practically free from colour and organic compounds but contained significant amount of inorganic compounds e.g. chloride ions, especially when a high amount of sulphate containing discharge waters were filtered, in which case a low pressure RO membrane was needed to successfully remove monovalent anions. Organic compounds were almost completely retained by NF and RO membranes and organic carbon in the permeate was less than 10 mg/dm3 on average. The achieved permeate can easily be reused in paper production. Nanofiltration has a significantly higher flux and also a lower fouling tendency than reverse osmosis but it passes through monovalent ions when there is a high sulphate concentration in the water. Therefore, RO might be needed in such cases to produce excellent process water.     

The relationship between critical flux and fibre movement induced by bubbling in a submerged hollow fibre system.

Bubbling has been used to enhance various processes. In this paper we deal with the effect of bubbling on submerged hollow fibre membranes, where bubbling is applied to prevent severe membrane fouling. Previous work with submerged hollow fibres has observed that significant fibre movement can be induced by bubbling and that there is a qualitative relationship between fibre movement and filtration performance. Therefore, the aim of the present research has been to analyse the link between bubbling, fibre movement and critical flux, identified as the flux at which the transmembrane pressure (TMP) starts to rise. Tests were performed on vertical isolated fibres with a model feed of yeast suspension. The fibres were subject to steady bubbling from below. The parameters of interest were the fibre characteristics, such as tightness, diameter and length, as well as feed concentration. The results confirmed that the critical fluxes are affected by the fibre characteristics and feed concentration. Higher critical flux values can be achieved by using loose fibres, smaller diameters and longer fibres. The enhancement is partially linked to fibre movement and this is confirmed by improved performance when fibres are subject to mechanical movement in the absence of bubbling.     

Organic colloids and their influence on low-pressure membrane filtration.

Wastewater treatment by low-pressure membrane filtration (MF and UF) is affected to a large extent by macromolecules and colloids. In order to investigate the influence of organic colloids on the membrane filtration process, colloids were isolated from a wastewater treatment plant effluent using a rotary-evaporation pre-concentration step followed by dialysis. Stirred cell tests were carried out using redissolved colloids, with and without additional glass fiber filtration. After constant pressure membrane filtration of 190 L/m2, the initial flux had declined by 50% for colloids > 6-8 kD (glass fiber filtered) with a hydrophilic MF membrane and for colloids > 12-14 kD (glass fiber filtered) with a hydrophobic MF membrane. For the non-filtered colloidal solutions, the flux decline was even steeper with the flux being below 10% of the initial flux after 190 L/m2 were passed through the membranes. As with larger particles, colloids form a filtration cake layer on top of the membrane surface when used as isolates without prior filtration. This filtration cake is easily removed during backwashing. However, polysaccharides as a macromolecular component of the colloid isolate cause severe fouling by the formation of a gel layer on the membrane surface that is difficult to remove completely.     

Treating wastewater with high oil and grease content using an Anaerobic Membrane Bioreactor (AnMBR). Filtration and cleaning assays

An Anaerobic Membrane Bioreactor (AnMBR) pilot plant was studied to improve certain operational conditions of AnMBRs that treat high oil and grease wastewaters discharged from a snacks factory. A comparison of its performance and behavior was made with an upflow anaerobic reactor throughout the first eight weeks of its operation. Raw snack food wastewater was characterized by oil and grease concentrations of up to 6,000 mg/l, with chemical oxygen demand (COD) and biological oxygen demand (BOD(5)) concentrations of up to 22,000 and 10,300 mg/l, respectively. The AnMBR achieved COD removal efficiencies of 97% at an organic loading rate (OLR) of 5.1 kg COD/m(3) d. The filtration flux, and the suction, backwash and relaxation times for each cycle were all varied: an 11 min filtration time involving 10 s pre-relaxation, 20 s backwash and 70 s post-relaxation was finally selected. The filtration flux for long-term operation was between 6.5 and 8.0 l/m(2) h. The study also tested physical cleaning strategies such as intensive backwashing cycles and extended relaxation mode, and different chemical cleaning methods, such as chemically enhanced backwash on air and chemical cleaning by immersion.     

Evaluation of the importance of various operating and sludge property parameters to the fouling of membrane bioreactors

A single-fibre microfiltration system was employed to investigate the importance of various operating and sludge property parameters to the membrane fouling during sludge filtration. The sludge was obtained from a submerged membrane bioreactor (SMBR). A series of comparative and correlative filtration and fouling tests were conducted on the influence of the operating variables, sludge properties and the liquid-phase organic substances on the membrane fouling development. The test results were analysed statistically with Pearson's correlation coefficients and the stepwise multivariable linear regression. According to the statistical evaluation, the membrane fouling rate has a positive correlation with the biopolymer cluster (BPC) concentration, sludge concentration (mixed liquor suspended solids, MLSS), filtration flux and viscosity, a negative correlation with the cross-flow velocity, and a weak correlation with the extracellular polymeric substances and soluble microbial products. BPC appear to be the most important factor to membrane fouling development during the sludge filtration, followed by the filtration flux and MLSS concentration. The cross-flow rate also is important to the fouling control. It is argued that, during membrane filtration of SMBR sludge, BPC interact with sludge flocs at the membrane surface to facilitate the deposition of the sludge cake layer, leading to serious membrane fouling.