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.     

A pilot study for reclamation of a combined rinse from a nickel-plating operation using a dual-membrane UF/RO process

A pilot study for reclamation of a combined rinse from a nickel-plating operation was conducted using a dual-membrane UF/RO process. The pilot plant has a product capacity of 1.5 m³/h. The OF unit, as a pre-treatment, was operated at 90% water recovery. The RO unit was operated with a 2:1 configuration in a feed-and-bleed mode with recirculation. Trial runs on various operating pressures and water recoveries were conducted and effect of feed pH on RO permeate quality was studied. Finding a critical pH value was explored to design the feed pH for RO process to treat this particular wastewater. A long-term run for the RO unit with an optimized 75% water recovery was later carried out to study the stability of the product and the fouling tendency of membranes. The cleaning-in-place methods were investigated for both OF and RO units. The pilot plant had successfully operated for 6 months at the time of reporting, consistently producing a high-quality product water (<95 μS/cm) at an overall water recovery of 67.5%. The quality of reclaimed water was better than town water used at the factory. The product water from the pilot plant was used as a substitute for town water for in-process rinsing at the factory with no detrimental effects for 3 months. The study has successfully developed a process for recycling a combined rinse water with conductivity up to 1700 μS/cm. The design data for a full-scale plant were obtained. An economic evaluation shows that a payback within 32 months is feasible at a treatment capacity of 20 m³/h.     

Threshold performance of a spiral-wound reverse osmosis membrane in the treatment of olive mill effluents from two-phase and three-phase extraction processes

A reverse osmosis (RO) treatment stage was examined for the complete depuration of the different effluents exiting the olive mill factories (OMW) working with diverse extraction procedures, that is, the two-phase and the three-phase extraction processes, respectively. In the present work, the modelization of batch RO purification of OMW by means of the relevant equations of the threshold flux theory for fouling control and plant dimension is addressed. Results show that higher threshold flux values (20.2–22.1% increase) and major feed recovery rates (80.2–85.0%) as well as very significant reduction of the long-term fouling index (27.3–52.7%) were achieved by using as pretreatment steps the following series of processes: pH-T flocculation, UV/TiO₂ photocatalysis, UF and NF in series. This leads to both lower energy and capital costs, in particular a reduction of the required membrane area in case of batch membrane processes equal to 22.3–44.8%. Accurate prediction of the rejection behavior was attained by the used leaky solution-diffusion model in all cases, with reflection coefficients (σ_COD) ranging from 0.86 to 1.0. The purified effluent streams are finally compatible with irrigation water quality standards (COD values below 1000 mg L⁻¹).     

Optimizing the coagulant dose to control membrane fouling in combined coagulation/ultrafiltration systems for textile wastewater reclamation

Optimal coagulation conditions need to be re-examined when coagulation is coupled to membrane filtration for wastewater treatment. This work focused on the optimization of coagulant dosing in order to control membrane fouling in ultrafiltration (UF), following coagulation for the reclamation of textile wastewater. The effects of pore size and coagulant types and dosages on flux decline were investigated using a stirred-cell UF unit. The flux was greatly enhanced for the UF membrane when a coagulant was added, whereas for the microfiltration (MF) membrane the flux decreased. This could be attributed to changes in the size of coagulated particles and their interaction with membrane pores. At a low dosage (e.g., 0.0371 mM as Al), the polyaluminum chloride (PACl) coagulant was found to control the flux decline most effectively for low ionic-strength wastewater. The optimal dose minimized the fouling and cake layer resistances, although it was sharp and dependent on influent composition. The cake layer protected the membrane from fouling, but it provided additional resistance to permeation. Analyses of turbidity, particle size, and membrane surface exhibited the characteristics of coagulated particles and their cake structures that are closely associated with flux behavior.     

Pilot study for reclamation of secondary treated sewage effluent

A pilot study for reclamation of secondary treated sewage effluent in Singapore was conducted using a MF/RO system with the capacity of 20 m³/d. A 0.1 μm MF membrane from Asahi and RE-4040-FL RO membrane from Saehan were used in this study. The pilot plant consists of six spiral-wound RO elements. The RO train was configured in single stage. The pilot plant was designed with automatic control system and it was operated continuously (24 h) during the study. Trial runs on various flux rates of the RO membrane at different operating pressures were conducted over 3 months. The pilot results showed that the optimal operation flux rate of the RO membrane ranged from 10 to 15 gal/f²/d (GFD) for this application. The normalized flux after CIP was 97% of the initial one. At a flux rate of 10 GFD and water recovery of 50%, the average operating pressure of 57 psi was noted corresponding to a high normalized flux of 38 L m⁻² h⁻¹ MPa⁻¹ at 25°C. Rejections of the RO membrane in terms of conductivity, TOC, ammonium and nitrate were higher than 96%,97%,90% and 85%, respectively. It was concluded that the RO permeate quality in terms of conductivity, turbidity, TOC, ammonium, nitrate, hardness, total bacteria and total coliform matched the quality of high-grade water (NEWater) for use in the electronics industry.     

工业污水处理水再生处理初步研究

通过在聚合氯化铝絮凝处理焦化工业污水处理水的过程中引入一种精细化学品作絮凝增效剂,对焦化工业污水处理水进行再生处理。实验表明,絮凝过程中加入絮凝增效剂能大大提高焦化工业污水处理水色度和COD去除率;单独使用聚合氯化铝絮凝时,色度去除率为64．3％,COD去除率为47．3％,引入絮凝增效剂后,色度去除率可以提高到90％,COD去除率可以提高到55．7％,使焦化工业污水处理水的COD由200mg／L降低到88mg／L,色度由600度降低到55度。     

含硒废水处理方法的小试研究

随着工农业的发展,水体遭受硒污染的情况越来越严重,水体中硒超标的现象也日趋普遍。含硒工业废水主要来源于生产硒和应用硒的行业,如冶炼含硒金属矿石、炼油、火力发电、制造硫酸、颜料及特种玻璃等行业。对炼厂污水水质进行详细的硒含量分析,并对炼厂污水进行混凝实验及活性炭吸附实验,为含硒废水的处理提供参考。实验结果表明,只采用三氯化铁溶液作为混凝剂的混凝实验对硒等污染物的去除效果较好,硒的去除率在活性炭吸附实验中的去除效果相对较差,粉末活性炭、煤质颗粒活性炭、柱状活性炭中,柱状活性炭的去除效果较好。     

Removal of fluoride from electronic industrial effluentby RO membrane separation

The electronics industry generates large amounts of fluoride-containing effluents. The objective of this studyis to study the feasibility of applying reverse osmosis (RO) membrane separation to reduce fluoride load to less than 1 kg/d. The effect of transmembrane pressure on the removal of fluoride ion has been investigated in detail, and the design parameters of a small RO separation unit were estimated. The present study indicated that the rejection of fluoride ion is typically higher than 98%, considering that the RO membrane was fully regenerated after each set of experiments. The effect of upstream concentration on the required mechanical pressure was determined by estimating the theoretical osmotic pressure of the feed solution. For industrial effluents, the process developed in this work allows us to reduce the treated volume from 6 m³/d to 0.36 m³/d without any pretreatment or adding additional compounds. The cost of the designed RO separation plant (€76,000) is much less than that of the conventional treatment (€533/m³) that deals mainly with volumes rather than specific     

Feasibility study for reclamation of a secondary treated sewage effluent mainly from industrial sources using a dual membrane process

A feasibility study for reclamation of a secondary treated sewage effluent mainly from industrial sources (60%) in Singapore has been conducted using a dual membrane UF-RO process. The pilot system had a treatment capacity of 2 m³/h. The UF unit and RO unit were operated at 70–80% and 40% water recovery, respectively. Six-month run for the pilot was carried out to study the stability and fouling tendency of membranes.

The characteristics of the raw feed indicated that ammonia-N was consistently high at 30–50 mg/L. Very high fluctuations in iron (0.3–3.7 mg/L), turbidity (1–27.1 NTU) and TOC (3.2–56.7 mg/L) were observed. Nitrate was low at <0.2 mg/L. The results of the study showed that dosage of alum in the UF process significantly reduced organic foulants and phosphate scalants. The polymeric RO membrane could tolerate organics from industrial wastewater and performed >96% salt rejection at the end of the study after 6 months. The study concluded the dual membrane process was capable of reclaiming the sewage effluent mainly from industrial sources for industrial use.     

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。     

Reuse of reverse osmosis membranes in advanced wastewater treatment

In areas where tap water has a high salt content, wastewater is not appropriate for reuse in agriculture, particularly for sensitive crops. One alternative is reduction, via desalination, of the brackish character to the secondary effluent. A filtration stage is also required before desalination. On the other hand, used reverse osmosis membranes can be recycled and used as filters in the advanced treatment stage in order to reduce suspended matter contained in the secondary effluent—one advantage being the environmental recovery of solid waste. Used membranes can be treated with strong chemical oxidants to peel off the active separation layer in order to transform them into microfiltration or ultrafiltration elements. Preliminary tests have been carried out with 8″ elements, aimed at comparing membrane performance before and after the peeling process. An index denoted as peeling effectiveness (high flux, high salt passage) is used for comparison. It was soon observed that potassium permanganate was more effective than others, together with sodium hydroxide. Doses around 1000 mg/L KMnO₄ provided the best results. It was also concluded that membrane cleaning, done with sodium bisulphite prior to peeling, was better when recirculating the cleaning solution around the membrane rather than soaking it. Next steps in the research will test the actual filtration capability of the peeled membranes in actual wastewater.     

Performance evaluation of pretreatment processes in integrated membrane system for wastewater reuse

A series of lab-scale filtration experiments were performed under various operating conditions to investigate the fouling behavior of microfiltration (MF) membranes when employing two different pretreatment methods. The secondary effluents from a biologically advanced treatment process were fed to each hybrid system, consisting of coagulation-flocculation-MF (CF-MF) and ozonation-MF processes. All experiments were carried out using a stirred-cell system, which consisted of polyvinylidene difluoride (PVDF) MF membranes with a 0.22 μm pore size. When MF membrane was used alone without any pretreatment, the permeate flux dropped significantly. However, in the case of employing polyaluminium chloride (PACl) coagulation and ozonation as a pretreatment, the extent of flux decline rates was enhanced up to 88 and 38%, respectively. In the CF-MF hybrid system, the removal efficiencies of COD and total phosphorus were significantly enhanced at a coagulant dose above 30 mg/L. With ozonation, more than 90% of the color was removed even at a low dosage of ozone (5 mg/L). Therefore, ozonation would be strongly recommended as a pretreatment in terms of removing organic matter. The permeate water quality by ozonation-MF process was in good compliance with the guidelines for wastewater reuse proposed by South Korean Ministry of Environment.     

A comparison between catalytic ozonation and activated carbon adsorption/ozone-regeneration processes for wastewater treatment

Two methods based on the use of granular activated carbon (GAC) and ozone to remove organic compounds from water have been investigated. Both methods have been applied to degrade an aqueous solution of gallic acid and a secondary effluent from a wastewater treatment plant (WWTP). One of the methods, namely catalytic ozonation, implies simultaneous ozonation and adsorption onto GAC. This process takes advantage of the oxidizing power of ozone and the adsorption capacity of GAC but also of the catalytic transformation of ozone into secondary oxidants on the GAC surface. The efficiency of catalytic ozonation was compared to those of single adsorption and single ozonation. It was found that the catalytic process highly improves the conversion of total organic carbon (TOC) and makes a more efficient use of ozone than the single ozonation process. To illustrate the reusability of the catalyst, the GAC was reused four times through a series of consecutive experiments. No loss of catalytic activity was observed when treating the WWTP effluent but some deactivation could be appreciated when treating the aqueous solution of gallic acid. This deactivation could be attributed to some porosity destruction and surface oxidation produced as a result of reactions of aqueous ozone on the GAC surface. The other method investigated is an adsorption-regeneration process (namely GAC/O₃-regeneration) that comprises two steps: dynamic adsorption onto GAC and further regeneration of the spent GAC with gaseous ozone. The adsorption stage of the GAC/O₃-regeneration experiments was carried out in a continuous flow adsorption column and breakthrough curves were obtained. It was observed that the GAC used in this work adsorbed gallic acid very efficiently but exhibited limited capacity to remove chemical oxygen demand (COD) from the WWTP effluent. The optimum ozone dose to regenerate the spent GAC after gallic acid adsorption was found to be about 0.4 g O₃/g GAC, with results showing around 90% regeneration efficiency. As a result of incomplete regeneration, the GAC adsorption capacity progressively decreased with the number of adsorption–regeneration cycles. The GAC/O₃-regeneration method was not successful at treating the WWTP effluent as low adsorption uptake was observed. Moreover, the GAC became damaged after regeneration because of excessive oxidation of its surface.     

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.     

Chemical cleaning of reverse osmosis membranes used for treating wastewater from a rolling mill process

An analysis of fouling material and the effects of chemical cleaning were examined for a reverse osmosis (RO) membrane, which was used for the treatment of wastewater from a rolling mill process in the steel industry. The bulk foulant accumulated in the membrane module consisted mainly of CaSO₄·2H₂O, and the organic contaminants were contained at a very low level. The test pieces obtained from the exhausted RO membrane module (spiral-wound type) were used to examine chemical cleaning with the following solutions: acid and alkaline solutions with EDTA added, 50% methanol, and 10% ethyleneglycol monobutyrate (EGMB). Although a major component of the fouling material was calcium salt, the acid or alkaline solution containing EDTA did not promote the effective recovery of the water flux. On the other hand, cleaning with 50% methanol or 10% EGME solution increased the water flux significantly. The atomic force microscopy images of the membrane surface indicated that relatively large particles accumulated at the surface of the fouled membranes, and the large particles remained even after acid or alkaline cleaning. In the case of EGMB cleaning after alkaline cleaning, large particles did not remain, and uniform and fine particles were observed. The results that calcium salt, a major fouling material, was not removed effectively with the acid and alkaline solution may be due to trace organic materials in the fouling layer that act as a binder for inorganic fouling materials.     

TiO2-photocatalysis as a tertiary treatment of naturally treated wastewater

Solar TiO₂-photocatalysis was applied to waters from a natural wastewater treatment plant located in the Universidad de Las Palmas de Gran Canaria. Degussa P-25 TiO₂ and its mixture with activated carbon (AC–TiO₂) were used as catalysts. The presence of ozone and certain ions such as phosphates on the photocatalytic degradation of organic matter was also studied.

Disinfection experiments have provided interesting results, particularly when using the catalyst AC–TiO₂ and ozone, since total disinfection was achieved in less than 60 min. No bacterial reappearance at 24 or 48 h was observed. Additionally, this catalyst gave important TOC and some ions concentrations reductions.

Studies in catalyst reuse revealed that the catalyst AC–TiO₂ showed almost no deactivation.     

Application of reverse osmosis to reduce pollutants present in industrial wastewater

Reverse osmosis (RO) is increasingly used as a separation technique in chemical and environmental engineering; desalination, selective separation and wastewater treatment are well established examples. Treatment by RO reduces high levels of dissolved salts but has certain limitations in the removal of organics from chemical industry effluents. We describe a comparative study of four different polyamide membranes that were tested for their ability to reduce the concentrations of pollutants in a synthetic effluent stream containing acrylnitrile and three inorganic species (sulphate, ammonium and cyanide). The pH value of the solution plays an important role in the ionization of the different species and, subsequently, in their rejection. The membranes were checked using a 3×10⁻³ m² flat cell where the permeated and concentrated currents were recirculated to the feed reservoir. In a preliminary set of experiments the pH of the feeding solution was 9.0. The rejection percentage of sulphate ion was high in all the membranes tested (96% to 99.4%) regardless of the working pressure. Ammonium rejection values were between 72.3% and 83.9%, while acrylnitrile rejection was low (10.5% to 28.8%) compared with the results obtained for the other pollutants. Cyanide rejection was negative for all membranes tested except for HR95PP, which produced a rejection percentage of 16.5%. The same membrane also produced higher rejection percentages for cyanide and acrylnitrile than the other membranes. Finally, this membrane was selected to study the influence of the feed stream pH on the rejection of ammonium and cyanide ions. The study concluded that cyanide and ammonium could not be acceptably eliminated in a single step operation when they are simultaneously present in industrial wastewater. The results pointed to the need to carry out several steps at different pH values to reduce the level of both pollutants in the studied wastewater.     

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.     

Spiral-wound membrane reverse osmosis and the treatment of industrial effluents

Reverse osmosis (RO) is increasingly used as a separation technique in chemical and environmental engineering where desalination, selective separation and wastewater treatment are well established examples. Treatment by RO reduces high levels of dissolved salts but has certain limitations when used for the removal of organic compounds from effluents of the chemical industry. The spiral-wound membrane element is the most widely used membrane device because it has a high membrane surface area to volume ratio, it is easy to replace and can be manufactured from a wide variety of materials. This work forms part of a wider research project aimed at recovering products and reducing the concentration of pollutants in wastewater by using membrane process. The synthetic effluent stream that was treated contained an organic product (acrylnitrile) and four inorganic species (sulphate, ammonium, cyanide and sodium). It was found that the pH value ofthe solution plays an important role in the ionization of the different species and, subsequently, in their retention. The object of this study was to reduce the concentration of pollutants to the levels of mentioned regulations concerning discharges, using a pilot plant with a spiral-wound membrane element (0.56 m² surface area) and a polyamide membrane, which was previously selected. The RO measurements were carried out in a closed-loop controlled-pressure system, with the solution being constantly fed through the spiral-wound membrane. The rejection percentage of sulphate ion was high in the two treatments assayed, regardless ofthe operational pH and sequence of steps followed. The degree to which NH₄⁺ and CN⁻ were eliminated was strongly dependent on the pH of the feed stream. Ammonium ion, too, was strongly eliminated regardless ofthe sequence ofthe steps, while the best results with CN⁻ were obtained when the first step had a nearly neutral pH and the second a pH of 11.0. Acrylnitrile showed low rejection percentages in all the steps carried out.     

Performances of RO and NF processes for wastewater reuse: Tertiary treatment after a conventional activated sludge or a membrane bioreactor

Wastewater reclamation requires processes and technologies having the ability to reduce the presence of micropollutants which are not wholly treated in conventional WWTP. Due to the complexity of membrane-solute interactions and the diversity of secondary treatment effluent (STE) matrices, deeper investigations are required to identify the major foulant species and more specifically their behaviour at high concentration in real waters. This study investigates the rejection and fouling potential of nanofiltration (NF) and low-pressure reverse osmosis (RO) membranes with two STEs sampled from i) a conventional activated sludge process coupled with ultrafiltration (CAS-UF) and from ii) a membrane bioreactor MBR (AquaRM^®, SAUR (France)). Whatever the origin of the effluent, RO seems to be the best solution to prevent pollution of tertiary effluents (expected result) but also to obtain low fouling levels. The different composition and molecular weight distribution of MBR and CAS-UF effluents can explain the different fouling behaviours that were observed.