Foulant characterization of the NF membranes with and without pretreatment of biologically treated wastewater.

In this study, different pretreatment methods such as ferric chloride (FeCl3) flocculation and powdered activated carbon (PAC) adsorption were evaluated in terms of their capability in removing effluent organic matter (EfOM) and the characteristics of the foulants on the NF membranes. A detailed experiment was conducted with two NF membranes (NTR 729HF with MWCO 700 daltons and LF 10 with MWCO 200 daltons). With pretreatment, the concentration of organic matter on the membranes decreased to 5.671 x 10(-3) (NTR 729HF) and 4.940 x 10(-3) (LF 10) mg EfOM/cm2 of membrane from 6.372 x 10(-3) (NTR 729HF) and 4.979 x 10(-3) (LF 10) mg EfOM/cm2 of membrane. The MW of the solute fraction of biologically treated sewage effluent (BTSE) ranged from 250 daltons to about 3573 (the most important being 250-520 daltons). The weight-averaged MW values of the foulants on the NTR 729HF membrane reduced from 304 daltons without pre-treatment to 208 daltons with pretreatment. In the case of EfOM, the small molecules (MW 300 to 500 daltons) are mainly responsible for the membrane fouling. Thus, the MW distribution of organic matter in the effluent and in the foulant can be used as a representative tool to evaluate the efficiency of pretreatment and NF and in the selection of their operating conditions.     

Tertiary treatment of biologically treated piggery wastewater using vibratory shear-enhanced RO membrane.

This study presents a good example for the tertiary treatment of biologically treated piggery wastewater using vibratory shear enhanced RO membrane (VSEP RO). Through a simple process combination, utilizing Bioceramic SBR(BCS) and VSEP RO, at Gimhae plant livestock wastewater is treated excellently to meet the strict effluent standards. Application of RO membrane directly to the biologically treated effluent has been successful without any pretreatment to reduce high suspended solids. The combination of VESP UF followed by RO filtration processes produced a higher recovery rate in the 3-week pilot test.     

混凝改善超滤膜过滤性能的研究

研究有机物的特性如亲、疏水性以及相对分子质量的大小对超滤膜通量的影响.着重考察混凝对有机物特性的影响以及改善超滤膜通量的效果.试验表明,超滤膜直接过滤原水时,主要截留疏水性有机物,从而造成膜通量的下降.投加硫酸铝25 mg/L和100 mg/L时,虽然TOC去除率仅为18.4%和48.2%,但明显提高了膜通量,这是由于混凝有效地去除小分子疏水性有机物的缘故.研究表明,膜通量的下降与膜截留疏水性有机物的多少有密切关系.     

Particle count and size alteration for membrane fouling reduction in non-conventional water filtration.

If coagulation is not completely successful and produces aggregates which are too small, fouling may increase. In some cases, a deep-bed filter could perhaps provide a solution. The paper examines these effects using experimental results for different waters. Activated sludge effluents, stormy seawater containing microalgae and spent filter backwash water (SFBW) were coagulated by alum or ferric chloride. Sand filtration tests were carried out. Tests were performed in a membrane filtration stirred cell, filtration pilot plant equipped with SDI analyzer (seawater) and pilot UF plant (SFBW). For activated sludge effluent, alum residual ratio curves of turbidity and total particle count (TPC) followed one another. With ferric chloride, low coagulant dosage showed negative turbidity removal. Contact granular filtration reduced membrane fouling intensity. Increasing the dose resulted in higher improvement in membrane flux. For seawater, a filter run period under storm conditions reached 35 hours with satisfactory filtrate quality. An iron chloride dose of 0.3 mg/l during normal conditions and 0.5 mg/l for stormy condition should be injected, mixed well before the filters, while maintaining 10 m/hr filtration rate and pH 6.8 value. For SFBW, alum flocculation pretreatment of SFBW was effective in reducing turbidity, TPC, viruses and protozoa. SFBW settling prior to flocculation did not enhance turbidity and TPC removal. The largest remaining particle fraction after alum flocculation was 3-10 microm in size, both Cryptosporidium and Giardia are found in this size range. Coagulation enhanced the removal of small size particles, a positive impact on reducing membrane fouling potential.     

Combined membrane bioreactor (MBR) and reverse osmosis (RO) system for thin-film transistor-liquid crystal display TFT-LCD, industrial wastewater recycling.

In TFT-LCD industry, water plays a variety of roles as a cleaning agent and reaction solvent. As good quality water is increasingly a scarce resource and wastewater treatment costs rises, the once-through use of industrial water is becoming uneconomical and environmentally unacceptable. Instead, recycling of TFT-LCD industrial wastewater is become more attractive from both an economic and environmental perspective. This research is mainly to explore the capacity of TFT-LCD industrial wastewater recycling by the process combined with membrane bioreactor and reverse osmosis processes. Over the whole experimental period, the MBR process achieved a satisfactory organic removal. The COD could be removed with an average of over 97.3%. For TOC and BOD5 items, the average removal efficiencies were 97.8 and 99.4% respectively. The stable effluent quality and satisfactory removal performance were ensured by the efficient interception performance of the UF membrane device incorporated with biological reactor. Moreover, the MBR effluent did not contain any suspended solids and the SDI value was under 3. After treatment of RO, excellent water quality of permeate were under 5 mg/l, 2.5 mg/l and 150 micros/cm for COD, TOC and conductivity respectively. The treated water can be recycled for the cooling tower make-up water or other purposes.     

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.     

Removal of humic acid foulant from ultrafiltration membrane surface using photocatalytic oxidation process.

The experimental results indicated that without the TiO2 particles and PCO treatment, the permeate flux of ultrafiltration (UF) membrane declined to 40% of the initial permeate flux after 8 hours filtration. Feeding the humic acid solution with TiO2 particles dosage of 1 g/L with calcium ions into UF membrane, after the same filtration time and PCO reaction at 120 minutes, the permeate flux was increased to about 90% of the initial permeate flux. At longer PCO reaction times, a better water quality of UF permeate was observed. It has been found that with the coexistence of calcium ions in humic acid solution, the smaller molecular fragments of humic acid (HA) generated by PCO reaction may be transferred to the surface of TiO2 by means of adsorption. The humic acid adsorption by TiO2 in the presence of Ca2+ is also pH dependent. The adsorption rates were 21.0, 14.9 and 10.8 ppmTOC/gTiO2 for pH value of 4, 7 and 10 respectively. The combination of effects of PCO mineralization of humic acid into CO2 and adsorption of humic acid by TiO2 through the forming of HA-Ca(2+)-TiO2 aggregate particles were responsible for the removal of humic acid foulant from UF membrane surface.     

Assessing the removal potential of soil-aquifer treatment systems for bulk organic matter.

The fate of effluent organic matter (EfOM) during groundwater recharge was investigated by studying the removal behavior of four bulk organic carbon fractions isolated from a secondary effluent: Hydrophilic organic matter (HPI), hydrophobic acids (HPO-A), colloidal organic matter (OM), and soluble microbial products (SMPs). Short-term removal of the bulk organic fractions during soil infiltration was simulated in biologically active soil columns. Results revealed that the four organic fractions showed a significantly different behavior with respect to biological removal. HPI and colloidal OM were prone to biological removal during initial soil infiltration (0-30 cm) and supported soil microbial biomass growth in the infiltrative surface. Additionally, colloidal OM was partly removed by physical adsorption or filtration. HPO-A and SMPs reacted recalcitrant towards biological degradation as indicated by low soil biomass activity responses. Adsorbability assessment of the biologically refractory portions of the fractions onto powered activated carbon (PAC) indicated that physical removal is not likely to play a significantly role in further diminishing recalcitrant HPO-A, HPI and SMPs during longer travel times in the subsurface.     

在线混凝-超滤联用工艺用于小城镇给水的应用研究

采用在线混凝-超滤联用工艺对某水塘水进行中试研究.试验结果表明,将常规处理作为超滤的预处理时,膜压差增加迅速,无法保持稳定运行.将在线混凝作为超滤的预处理时,膜压差增加缓慢.通过比较不同的混凝剂抑制压差和去除有机物的效果,发现聚硫酸铁均优于聚氯化铝.次氯酸钠和高锰酸钾预氧化的试验结果表明,尽管高锰酸钾去除有机物和三氯甲烷生成潜能的效果较好,但膜压差增加较快.在线混凝-超滤联用工艺处理后出水的CODMn可低于3 mg/L.     

Organic and detergent degradation in combined O3/UF for domestic laundry wastewater reclamation.

This paper focuses on the evaluation of organic and detergent degradation in a combined Ozone/UF system for domestic laundry wastewater reclamation. Formation of by-product was investigated by GC/MS for the reclaimed water. Ozone was injected into the raw wastewater in a 10 L contact tank and the wastewater was circulated through the membrane module for inner pressurized cross-flow filtration. The concentrate was returned back to the contact tank. The membrane used in this experiment was hollow fiber polysulfone UF membrane with MWCO 10,000. It has an effective filtration area of 0.06 m2. The experiment was carried out with intermittent ozone injection, 5 min injection and 10 min idling. Ozone was dosed at the concentration of 1.5 mg/L. The flux of the UF could be maintained at 0.24 m/d under filtration pressure 40-45 kPa and water temperature, 20-22 degrees C. The organic removal efficiency by the system was 90% in terms of COD. Ozone was considerably effective to degrade organics in the wastewater. Molecular weight of organics in the raw waste was mostly greater than 10,000 (72% of 950 mgCOD/L). However 86% of effluent COD (94-100 mg/L) was composed of organics smaller than MWCO 500 by ozone injection. No harmful by-products by ozone contact were detected from the analysis of treated water using GC/MS. It was identified that residual organics in the treated water were 1,1'-Oxybisbenzene, Octadecanoic acid, Squalene and Benzenmethanol, etc., which were additives contained originally in the detergent. Consequently the reclaimed water quality could be estimated safe enough to recycle for the rinsing cycle in a washing machine.     

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.     

Use of nanofiltration for potable water from an aquifer recharged with wastewater.

This paper presents the comparison of nine nanofiltration membranes to treat water coming from an aquifer recharged with wastewater and used as municipal supply in the Tula Valley, Mexico. The comparison was made based on (a) the amount of water produced; (c) the capability to produce a <1 mg TOC/L effluent without entirely eliminating salts, (b) the removal of specific organic and microbiological pollutants, and (c) the reduction of toxicity and mutagenicity from water. From the tested membranes, only four produce an effluent with <1 TOC mg/L, and three totally retained dibutyl phthalate, diethyl phthalate and hydroxytoluene butylate. Influent mutagenicity (Ames test) was negative but these was a certain degree of toxicity when Tetrahymena pyriformis was used as indicator. Toxicity was partially reduced by some of the NF membranes. The best membrane had a flux of 95 L m(-2)h(-1) and removal efficiencies of 98% for TOC, 92% for AUV(254), and 92% for TDS. The permeate had a final hardness of 76 mg/L and an alkalinity of 124 mg/L. Additionally, this membrane removed totally specific organic compounds, total and fecal coliforms and almost all the somatic coliphages.     

Hydrogen-dependent denitrification in an alternating anoxic-aerobic SBR membrane bioreactor.

A novel hydrogenotrophic denitrification system, which consisted of a sequencing batch membrane bioreactor, was evaluated for simultaneous removal of nitrate and soluble microbial products (SMP) from a synthetic groundwater feed. A hollow fiber membrane diffuser was used for bubble-less diffusion of hydrogen into the bioreactor under anoxic condition followed by aerobic SMP removal and biomass filtration. During the anoxic period, the nitrate loading of 0.328 kg N m(-3) d(-1) was completely denitrified to below detectable levels. A denitrification rate of 0.8 kg N m(-3) d(-1) was obtained at steady state biomass concentrations of 1,162 mg I(-1). During the aerobic period when biomass filtration was performed, 81% of SMP produced within the anoxic phase was retained by the membrane, 9% was biologically removed, 5% was passed through the membrane and 5% was discharged during the wasting of mixed liquor. The aerobic cycle was instrumental as it allowed for effective biomass filtration via membrane scouring and assisted in further reduction of effluent organic matter.     

Domestic wastewater reclamation by submerged membrane bioreactor with high concentration powdered activated carbon for stream restoration.

This study focuses on the practical application of high concentration powdered activated carbon coupled membrane bio-reactor to domestic wastewater reclamation. The study was conducted in three parts, such as analysis of secondary domestic wastewater effluent, design and operation parameter evaluation and reclaimed water quality estimation for stream restoration. The organic concentration was 25.2-80.2 mgCOD(Cr)/L for the effluent of three domestic wastewater treatment plants. Around 50-75% of the COD was low molecular substances less than 1,000 which were quite biodegradable. The sawdust PAC was estimated to be proper adsorbent for the organics in the secondary effluents. Its Freundlich constant, K value was 5.847 and 1/n, 0.36. Using a system consists of single reactor with high concentration PAC (80 g/L) and submerged hollow fiber MF membrane module with nominal pore size of 0.1 microm, design and operation parameters were obtained, such as HRT of the bioreactor (2.5 hr), PAC concentration (80 g/L), the initial flux (less than 0.5 m/day) and intermittent suction cycle (12 min. suction and 3 min. idling). Organic removal by the system was high enough to produce reclaimed water for urban stream restoration The effluent organic concentration was at the level of 2 mg/L in terms of TOC (around 5 mg/L as COD(Cr)). Substances with molecular weight cut off < 1,000 were removed mostly by adsorption and biodegradation. Those above 1,000 were rejected at PAC cake layer on the membrane and gradually degraded by microorganisms during extended contact.     

The removal of residual organic matter from biologically treated swine wastewater using membrane bioreactor process with powdered activated carbon.

The objective of this study was to characterize the mechanisms of the COD removal in the membrane bioreactor (MBR) process with powdered activated carbon (PAC) addition and to determine its optimal operation, for the removal of residual organic matters (ROM) from biologically treated swine wastewater. The MBR process with PAC showed higher removal efficiency of chemical oxygen demand (COD(Mn)) than that without PAC. When the average COD(Mn) concentration of the influent was 217 mg/L, the average COD(Mn) concentration of the permeate from the MBR with PAC was about 41.5 mg/L, indicating an approximate removal efficiency of 81%. On the other hand, the average COD(Mn) concentration of the permeate from the MBR without PAC was 172 mg/L. The PAC dosage estimated to obtain the above removal efficiency was about 0.74 g per litre of influent. Among the total residual organics removed by PAC-added MBR, 46.5% was removed by PAC adsorption, 20.8% by biodegradation, 4.4% by membrane separation, and 9.3% by enhanced microorganism activity. From these results, the MBR process with PAC was considered as a very useful treatment process for the reduction of COD(Mn) in biologically treated swine wastewater.     

Combined chemical biological treatment of bleached eucalypt kraft pulp mill effluent.

Effectiveness of ozonation before and after biological treatment for removal of recalcitrant organic matter in bleached kraft pulp effluents was compared. Two industrial ECF bleached eucalypt kraft pulp effluents (E1 and E2) were pretreated with 100 mg O3/L. Raw and pretreated effluents were treated biologically in bench-scale sequencing batch reactors, under constant conditions. Following biological treatment, effluents were post-treated with 100 and 200 mg O3/L. Effluent pretreatment increased effluent biodegradability by 10% in E1 and 24% in E2. Combined O3-biological treated led to small but significant increases in COD, BOD and lignin removal over biological treatment alone, but pretreatment had no significant effect on effluent colour and carbohydrate removal. Ozone pretreatment did not affect biological activity during treatment of effluent E1 but resulted in a 38% lower specific oxygen uptake rate in effluent E2. At an equivalent dose of 100 mg/L, pre-ozonation produced better quality effluent than post-ozonation, especially with regard to COD and colour. Likewise, when an equivalent dose of 200 mg/L was applied, splitting the dose equally between pre- and post-treatments was more efficient than applying the entire dose in the post-treatment. The potential for combined chemical-biological treatment to improve effluent quality has been confirmed in this study.     

Toxicity reduction in an industrial nitro-aromatic wastewater plant: an assessment and a proposed improvement

In this study, the performance of a typical Chinese industrial nitro-aromatic wastewater project (operational capacity: 3,000 m(3)d(-1)) was evaluated using chemical properties and toxicity data. Additionally, the relationship between the removal of organic pollutants and toxicity reduction was investigated throughout the whole-process wastewater treatment. Current advanced treatment reduced the dissolved organic carbon by 40% compared with biologically treated wastewater effluent (BTWE), but the acute toxicity and early life-stage toxicity increased significantly. For instance, the acute toxicity of the current advanced treated wastewater was 450% greater than that of the untreated BTWE. With the aim of effectively decreasing the toxicity of the effluent, several efficient adsorption technologies were assessed and compared for further treatment of BTWE. Coagulation and/or oxidation coupled with activated carbon adsorption, hypercrosslinked resin adsorption, or MIEX(?) technology was helpful for improving chemical indices and reducing toxicity. Among these adsorption treatment technologies, hypercrosslinked resin adsorption was more effective at removing most of the toxicants than MIEX(?) technology, and it also had better regeneration efficiency and mechanical properties compared with activated carbon. Therefore, hypercrosslinked resin adsorption may be a promising technology for enhancing organic pollutant removal and toxicity reduction of BTWE from nitro-aromatic factories.     

Treatment of slaughterhouse plant wastewater by using a membrane bioreactor

The use of a membrane bioreactor (MBR) for removal of organic substances and nutrients from slaughterhouse plant wastewater was investigated. The chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) concentrations of slaughterhouse wastewater were found to be approximately 571 mg O2/L, 102.5 mg/L, and 16.25 mg PO4-P/L, respectively. A submerged type membrane was used in the bioreactor. The removal efficiencies for COD, total organic carbon (TOC), TP and TN were found to be 97, 96, 65, 44% respectively. The COD value of wastewater was decreased to 16 mg/L (COD discharge standard for slaughterhouse plant wastewaters is 160 mg/L). TOC was decreased to 9 mg/L (TOC discharge standard for slaughterhouse plant wastewaters is 20 mg/L). Ammonium, and nitrate nitrogen concentrations of treated effluent were 0.100 mg NH4-N/L, and 80.521 mg NO3-N/L, respectively. Slaughterhouse wastewater was successfully treated with the MBR process.     

Pharmaceutical rejection by membranes for wastewater reclamation and reuse.

Various membranes, which have different materials and nominal molecular weight cut-offs (MWCO), were compared in terms of rejection of ibuprofen and removal of effluent organic matter (EfOM) from membrane bioreactor (MBR), because pharmaceutical compounds contain a potential risk and EfOM is the precursor of carcinogenic disinfection by-products when reusing for drinking water source. To provide equivalent comparison with respect to hydrodynamic condition, mass transfer parameter, J0/k ratio, was used. A tight-UF membrane with a molecular weight cut off of 8,000 daltons exhibited 25 approximately 95% removal efficiencies of ibuprofen with a molecular weight of 206 with and without presence of EfOM(MBR). EfOM(MBR) caused the reduction of ibuprofen removal efficiency for UF membrane. Rejection of EfOM(MBR) by UF and NF membranes ranged 29 approximately 47% and 69 approximately 86%, respectively. UF membrane could successfully remove ibuprofen at lower J0/k ratio range (< or = 1) in organic free water but could not efficiently reject ibuprofen with a relatively hydrophilic EfOM(MBR) (SUVA < or = 3).     

Behaviour of heavy metals during tertiary bio-filtration.

More stringent water quality parameters in the Annex of the Water Framework Directive 2000/60/EC led to the introduction of "Maximum Tolerable Risk concentrations" (MTR-values) in the national legislation in The Netherlands (Vierde Nota Waterhuishouding). The MTR-values give limitations for the concentrations of e.g. heavy metals (HM's) but also for nutrients: Ntot < 2.2 mg/l, Ptot <0.15 mg/l. Investigations of HM removal during denitrifying flocculation filtration are conducted on the effluent of a typical modern Dutch WWTP. Because of low concentrations of HM's in the feed water, a cocktail of copper, nickel and zinc chloride (approximately equal 150-200 microg/l) is dosed before filtration. Preliminary jar tests and filtration tests with media filtration in pilot-scale and lab-scale are conducted. The results show high removal of nickel and zinc during jar tests with dosing of powdered activated carbon. During filtration tests at pilot-scale the bounded fraction of copper and zinc is highly removed. All three HM's are removed in the lab-scale activated carbon filter. After dosing, nickel is found mainly in the dissolved form, but it is removed in the lab-scale activated carbon filter. The removal of HM's via adsorption subsequently leads to a discussion on the toxicity of HM's and their bio-availability.