Treatment of tannery wastewater through the combination of a conventional activated sludge process and reverse osmosis with a plane membrane

Tannery wastewater contains high concentrations of organic matter (COD) with a significant percentage of refractory organic compounds, ammonium substances, salts (i.e. chloride and sulphate) as well as sulphur. Contaminants have to be removed in order to avoid significant environmental impacts. This paper presents the results obtained from a pilot scale study developed in the tannery district of Solofra in Southern Italy. It was aimed at evaluating the reuse of wastewater produced in the retanning process. The treatment process consisted of a biological treatment, as a pre-treatment, followed by a physico-chemical process (with a polymer as a coagulant) and reverse osmosis with a plane membrane. The biological pre-treatment was able to remove approx. 67% of COD, while the membrane system completed the purification process with the removal of the refractory organic compounds (chloride and sulphate). In the test carried out, the combination of a biological pre-treatment with a plane membrane system showed satisfactory results in terms of wastewater recovery and reuse in the tannery production cycle.     

Laboratory RO and NF processes fouling investigation by residence time distribution curves examination

The fouling phenomena of nanofiltration of calcium sulfate saturated feed solution in the presence of magnesium and carbonates as well as the reverse osmosis of saturated silica feedwater with magnesium chloride content at different pH levels, was investigated by analyzing the membrane residence time distribution curves (RTD) in our laboratory. The fraction of degraded membrane (parameter a), the fraction of active membrane area (parameter b) and the fraction of membrane blocked by impermeable layer (parameter c) as a function of permeate recovery was determined. It was found that not only surface blockage affects permeate efficiency, but also other factors, such as module retentate chamber pressure drop and osmotic pressure increase. The membranes RTD measurements as well as fouling, a, b and c parameters, gathered with ion-selective electrodes (chloride, calcium and cupric ion-selective) and appropriate tracer solutions (sodium chloride, calcium chloride and cupric nitrate) were compared with commonly used conductivity sensor and sodium chloride tracer solution. We found that both the tracer and detector type strongly affects membrane mean residence time and its variance, but at the same time no influence of detector and tracer type on membrane fouling a, b and c parameters was observed.     

Membrane application for recovery and reuse of water from treated tannery wastewater

Secondary treated tannery wastewater contains high concentrations of Total Dissolved Solids (TDS) and other residual organic impurities, which cannot be removed by conventional treatment method. A pilot plant membrane system with a designed processing capacity of 1 m³/h, comprising of nano and reverse osmosis (RO) membrane units, accompanied by several pre-treatment operations, was evaluated in order to further treat and reuse the tannery wastewater. The maximum TD S removal efficiency of the polyamide RO membrane was more than 98%. The permeate recovery of about 78% was achieved. The water recovered from the membrane system, which had very low TDS concentration, was reused for wet finishing process in the tanneries. The reject concentrate obtained from the operation was sent to solar evaporation pans. It was evident from the study that the membrane system can successfully be applied for recovery of water from secondary treated tannery effluent, provided a suitable and effective pretreatment system prior to membrane system is employed. Combining nano and RO membranes improved the life of the membranes and permeate recovery rate.     

Removal of heavy metals from wastewater by membrane processes: a comparative study

Wastewater containing copper and cadmium can be produced by several industries. The application of both reverse osmosis (RO) and nanofiltration (NF) technologies for the treatment of wastewater containing copper and cadmium ions to reduce fresh water consumption and environmental degradation was investigated. Synthetic wastewater samples containing Cu²⁺ and Cd²⁺ ions at various concentrations were prepared and subjected to treatment by RO and NF in the laboratory. The results showed that high removal efficiency of the heavy metals could be achieved by RO process (98% and 99% for copper and cadmium, respectively). NF, however, was capable of removing more than 90% of the copper ions existing in the feed water. The effectiveness of RO and NF membranes in treating wastewater containing more than one heavy metal was also investigated. The results showed that the RO membrane was capable of treating wastewater with an initial concentration of 500 ppm and reducing the ion concentration to about 3 ppm (99.4% removal), while the average removal efficiency of NF was 97%. The low level of the heavy metals concentration in the permeate implies that water with good quality could be reclaimed for further reuse.     

RO and NF membrane fouling and cleaning and pore size distribution variations

The variations of porosity parameters of some reverse osmosis (RO) and nanofiltration (NF) polyamide thin-film composite membranes were determined in order to explain the changes of membranes' performances caused by membrane fouling and chemical cleaning of the fouled membranes. The pore size distribution curves and the effective number of pores in the membrane surface indicated plugging of the tight network pores in the membrane surface and even their disappearance during fouling. The enlargement of the wider aggregate pores was responsible for the noticed reduction in salt rejection. The initial pore structure of the fouled RO membrane was restored by immediate chemical cleaning. A delay of chemical cleaning of the fouled membranes led to irreversible changes in the porous structure of both the RO and NF membranes, which were caused by a microbial activity.     

炼化污水抗污染反渗透膜回用处理中试研究

采用氧化混凝-复合过滤-反渗透组合工艺处理大庆炼化公司外排污水，考察了预处理系统的操作参数和抗污染反渗透膜组件性能的变化规律，为工程设计提供了基本参数。结果表明，预处理出水水质主要受过滤速度和絮凝剂加药量的影响，而膜污染是影响反渗透系统运行的主要因素。系统出水水质符合工业用水软化除盐设计规范。     

Incorporation of osmotic pressure in an integrated incremental model for predicting RO or NF permeate concentration

Consideration of concentration, recovery and osmotic pressure has been incorporated in a fully integrated diffusion based mass transfer model identified as integrated osmotic pressure model (IOPM). Osmotic pressure was incorporated into the model using correction coefficients that were calculated from boundary conditions, which were determined from the feed and concentrate streams osmotic pressures. Predicted permeate stream water quality using IOPM and the homogenous solution diffusion model (HSDM) were compared with and without consideration of osmotic pressure. IOPM was verified using independently developed data from full and pilot scale plants. The numerical simulation and statistical assessment show that osmotic pressure corrected models are superior to non-osmotic pressure corrected models, and that IOPM improved predictability of permeate stream water quality.     

The use of RO to remove emerging micropollutants following CAS/UF or MBR treatment of municipal wastewater

The removal of various organic micropollutants (OMPs), including six antibiotics (ERY, ROX, CLA, SMX, SMZ, and TMP), three pharmaceuticals (ibuprofen, salicylic acid, and diclofenac), one industrial product (BPA), and one hormone (cholesterol), was investigated in two pilot plants treating the same raw sewage of the Tel-Aviv WWTP. The effluent production by CAS-UF was 45 m³/h while that of MBR was 40 L/h. Each system's effluent constituted the feed for its RO, which comprised three RO steps after the CAS/UF and a semi-batch RO system after the MBR. Despite significant molecular differences between the selected OMPs, high removal rates were achieved after the RO stage (> 99% for macrolides, pharmaceuticals, cholesterol, and BPA, 95% for diclofenac, and > 93% removal of sulfonamides). However, low antibiotics concentrations and 28–223 ng/L residuals of ibuprofen, diclofenac, salicylic acid, cholesterol, and BPA in the MBR/RO and CAS-UF/RO permeates showed that although RO is an efficient removal solution, it cannot serve as an absolute barrier to OMPs. Therefore, additional treatment techniques should be considered to be incorporated aside the RO to ensure complete removal of such substances.     

某钢铁厂污水回用项目反渗透膜污染的分析和清洗

经过污堵物质的分析,采用了合适的复合药剂,利用成熟的膜清洗工艺流程对膜组件进行了清洗研究。     

Potential for reuse of high cellulose containing wastewater after membrane bioreactor treatment

It is difficult to adequately treat wastewater with a high cellulose content with the traditional anaerobic and aerobic activated sludge processes. In this study we used microfiltration (MF) and reverse osmosis (RO) membranes combined with an anaerobic or aerobic activated sludge process to treat high cellulose containing wastewater for different hydraulic retention times (HRTs). The potential target applications for reuse of the treated wastewater are also compared. Six bioreactors, which were configured as anaerobic sequencing batch reactor (ANSBR), aerobic sequencing batch reactor (ASBR), aerobic membrane bioreactor (AMBR), AMBR plus RO (AMBR/RO), anaerobic activated sludge plus aerobic MBR (AOMBR), and AOMBR plus RO (AOMBR/RO), was operated in this study. The experiment results showed that, as expected, no effluents from the ASBR or the ANSBR could meet the Taiwan EPA criteria for effluent and wastewater reuse, no matter what the HRT was. However when the HRT was 12 h or more, the effluent from the AMBR and AOMBR processes did meet the criteria for effluent, but still did not meet the treated wastewater reuse criteria , primarily due to the color, total alkalinity, and total dissolved solid parameters. Finally, the effluents from the AMBR/RO and AOMBR/RO processes did meet the Taiwan criteria for both effluent and treated wastewater reuse when the HRT for the AOMBR/RO and AMBR/RO processes was equal to or longer than 12 h and 8 h, respectively. For the HRT of 4 h for both the AOMBR/RO and AMBR/RO process, and an HRT of 8 h for the AOMBR/RO process, neither the effluent criteria nor the treated wastewater reuse criteria were met.     

Removal of organics from aqueous solutions by commercial RO and NF membranes of characterized porosities

Removal of organic pollutants of petrochemical and agrochemical origin by some commercial reverse osmosis (RO) and nanofiltration (NF) membranes of characterized porosity was investigated. The rejection of organics was shown to depend on both the membrane properties like pore size, membrane material, membrane charge and solute characteristics such as molecule size, charge and polarity. The rejection of the small nonionized organic molecules by the tight pore membranes is influenced by both the sieving parameters (solute and pore size) and by the physicochemical interactions. The rejection of the same pollutants by the wider pore membranes is dominantly influenced by the physicochemical interactions. The rejection of pesticides is prevalently governed by the sieving mechanism based on the size of the solute molecule and the membrane pore size. However, the physicochemical effects cannot be totally neglected, and they can contribute to the rejection of some pesticides by certain membranes.     

印染废水处理与回用技术应用研究

采用气浮、膜生物反应器(MBR)与反渗透(RO)组合工艺,对某印染企业生产废水进行深度处理和回用。通过气浮、MBR去除有机污染物,利用RO系统去除剩余的有机物和盐分。实际运行结果表明,RO淡水水质可满足企业生产工艺用水要求,RO浓水水质达到了《污水综合排放标准》(GB 8978—1996)的三级标准。     

膜生物反应器废水处理组合工艺的研究进展

膜生物反应器（MBR）是近年来发展起来的一种新型的废水处理工艺,作者阐述了膜生物反应器的应用类型、机理以及应用现状,并对膜生物反应器组合工艺的特点、存在的问题和应用前景进行了分析评价。     

膜生物反应器在污水处理中膜污染及其防治

膜生物反应器在污水处理中的应用范围和规模虽然不断增加,然而,膜污染严重阻碍了膜生物反应器技术的推广应用。作者从膜的性质、料液性质以及膜分离的操作条件三个方面分析了膜污染的成因和膜污染过程,系统论述了膜污染在国内外的研究进展;另外还从改善膜本身的抗污染能力,变化混合液的特性,优化膜分离的操作条件和膜清洗四个方面介绍了膜污染的防治方法。     

New configuration of a membrane bioreactor for effective control of membrane fouling and nutrients removal in wastewater treatment

Excess aeration to membrane surface is common for controlling membrane fouling in a submerged membrane bioreactor (MBR) system, but significant energy is consumed for excess air production. Therefore, an alternative strategy for membrane fouling control is currently needed. A new configuration of MBR was proposed in this study to control membrane fouling effectively. To reduce biosolids concentration near the membrane surface, the position of the membrane module in MBR was elevated from the bottom to the top in the reactor. This could divide the reactor to two different zones: upper and lower zone. Air was not supplied at the lower zone whereas aeration was given to the upper zone where the membrane filtration was carried out. Biosolids concentration was reduced in the upper zone because the mixed liquor was settled down to the lower zone. Membrane fouling could be lessened in the upper zone due to the reduced biosolids concentration. Therefore, to verify if this new configuration of MBR could mitigate membrane fouling, the effect of changing vertical position of the membrane module in MBR on membrane fouling was investigated. Prior to verification the effect of elevation of membrane module on membrane fouling, influence of MLSS concentration on membrane fouling was investigated first. Transmembrane pressure (TMP) increase became steep as MLSS concentration increased. And the immersed membrane module was elevated from the bottom to the top of the MBR. When the upper membrane was located in the bioreactor, less membrane fouling was observed. This could demonstrate a possibility of new MBR design to control membrane fouling. In addition, reduced dissolved oxygen level in the returned sludge to anoxic tank could increase denitrification efficiency if this configuration is directly applied to biological nutrient removal processes.     

Advanced performance evaluation of a reverse osmosis treatment for oilfield produced water aiming reuse

Technology advancements and the increasing need for fresh water resources have created the potential for desalination of oil field brine (produced water) to be a cost-effective fresh water resource for beneficial reuse. At the mature oil and gas production areas in the northeast of Brazil, the majority of wells produce a substantial amount of water in comparison with oil production (more than 90%). At these fields, the produced water has to be treated on site only for oil and solids removal aiming re-injection. The aim of this work is to assess the quality of the produced water stream after a reverse osmosis desalination process in terms of physicochemical characteristics influencing reuse of the water for irrigation or other beneficial uses.     

污水深度回用装置反渗透膜的污染及化学清洗

结合水处理中常见的污染物种类,介绍了污水深度回用装置的反渗透膜污染情况及合理的化学清洗方案。     

Role of intermittent aeration in domestic wastewater treatment by submerged membrane activated sludge system

In this study, the treatment of domestic wastewater in a lab-scale submerged membrane activated sludge system (sMBR) was investigated under different aeration intervals. The COD concentration of the system effluent varied generally between 5 and 25 mg/l and the COD removal at the organic loads of 0.6-0.8 kg COD/m³.d was observed to be above 98%. The total phosphorus content of the filtrate was decreased to a level that was less than 1 mg/l under the aerobic conditions in which the aeration was continuously made. A dramatic increase in the total phosphorus content of filtrate was observed under the aerobic + anoxic conditions in which the aeration was made at differential intervals. The filtrate was free of suspended solid (SS) and total coliform bacteria and a percent removal of 100 was achieved in terms of these parameters. The influent turbidity removal was 97-99.8%. Generally, the removal of total Kjeldahl nitrogen (TKN) and ammonium nitrogen varied in the ranges of 87.8-99.1% and in the ranges of 89.4-99.8%, respectively. While the nitrate concentrations in the filtrate increased to 26.8 mg/l under the aerobic conditions, it was determined that this value was decreased to 2.4 mg/l under the aerobic + anoxic conditions.     

电镀废水处理及回用工程实例

采用混凝沉淀+水解酸化+膜生物反应器(MBR)+过滤+反渗透(RO)组合工艺,对某电镀企业生产废水进行深度处理和回用。首先通过混凝沉淀、生化和过滤去除重金属、有机物和悬浮物,然后利用RO系统去除剩余的有机物和盐分。实际运行结果表明,RO淡水水质可满足企业生产工艺用水水质要求,RO浓水水质达到了《电镀污染物排放标准》(GB 21900—2008)表2中的新建企业水污染物排放限值。     

无纺布膜生物反应器在洗浴废水再生处理中的应用

采用无纺布平板膜生物反应器对某高校游泳馆的洗浴废水进行处理,考察了无纺布膜生物反应器对洗浴废水的处理效果,并对该工艺进行了初步的技术经济分析。结果表明:无纺布膜生物反应器对洗浴废水处理效果良好,出水CODCr的质量浓度小于20 mg/L、BOD5的质量浓度小于5 mg/L、浊度小于1 NTU、NH3-N的质量浓度小于1 mg/L、LAS的质量浓度小于0.5 mg/L,各项指标均符合GB 18920—2002《城市污水再生利用城市杂用水水质》标准的要求。技术经济分析结果表明,采用无纺布膜生物反应器工艺可有效降低工程投资和运行成本。