Comparison of tertiary treatment by nanofiltration and reverse osmosis for water reuse in denim textile industry

The wastewaters resulting from different baths of a dyeing factory specialized in denim fabric are collected and treated by an activated sludge plant. This study investigated the coupling of activated sludge treatment with either nanofiltration (NF) or reverse osmosis (RO) to recycle water and reuse it in the process. We first conducted NF experiments with a HL membrane in different configurations: dead end and cross-flow for flat sheets and also in spiral wound form. Results on water permeation and salt rejection show that performances are configuration dependent. Then, for the study of the NF/RO textile wastewater treatment, experiments were conducted with spiral wound membranes in order to be closest to the industrial configuration. After analyzing the removal efficiencies of suspended solids and chemical oxygen demand (COD) of the treatment plant, we conducted NF experiments using an HL2514TF spiral wound membrane preceded by ultrafiltration (UF) treatment. We used as well an RO membrane (AG2514TF) to compare performances in water yield and quality for the same pumping costs. The results show that NF allows higher yield, while respecting the Tunisian standard of water reuse (COD < 90 mg L⁻¹). Above 9 bar, the TDS rejection reaches 60% and the hardness is lower than the factory constraint (100 mg L⁻¹ CaCO₃), allowing the reuse of the water in the process.     

A new systematic approach for water network design

This paper presents a systematic procedure involving two key steps for water minimization. In the first step, water targeting, the load problem table (LPT) has been used to establish the minimum water requirement for maximum water recovery and minimum wastewater generated. This table has been adapted from the load interval diagram (LID) recently proposed by El-Halwagi and Almutlaq (2004). In the next step, the design approach, designers can select the most practical network from a range of options, all of which can satisfy the raw water and wastewater targets. It is based on a special strategy of mixing the water sources in order to satisfy the given water demands, and on some guidelines about water distribution within a network. Several test problems are solved to illustrate the ease and applicability of the proposed methodology.     

Simultaneous methane production and wastewater reuse by a membrane-based process: evaluation with raw domestic wastewater

In this study, a membrane-based process was applied to simultaneously reclaim methane and generate reused water from raw domestic wastewater. The system was comprised of up-flow anaerobic sludge fixed bed (UAFB), anoxic sink (AS) and aerobic membrane bioreactor (MBR). The hydraulic retention time of UAFB (HRT(U)) was gradually shortened from 8h to 6h, 3h and to 1h, while the HRT of AS and MBR kept at 8 h. It is found that HRT(U) of 3h was more suitable for the balancing production of biogas and volatile fatty acids (VFAs), and the VFAs served as carbon source for denitrification. The trans-membrane pressure (TMP) of the MBR kept lower than 0.04 MPa without wash or change of membrane sheet, however, the scanning electron microscopy (SEM) analysis indicated that microbes attached to the inner-surface of membrane, causing irreversible fouling after 133-day operation. The denaturing gradient gel electrophoresis (DGGE) profiles of amplified 16S rDNA gene fragments proved that more functional bacteria and higher microbial diversity emerged at HRT(U) of 3h and 1h. Most bacteria belonged to Betaproteobacteria and were responsible for carbon and nitrogen removal.     

A/O MBR处理城市污水回用的中试研究

采用中试规模(36 m3/d)的缺氧-好氧膜生物反应器(A/O MBR)对城市污水处理回用进行了试验研究.试验结果表明,该工艺处理效果优良,系统对COD、氨氮、浊度、细菌的平均去除率分别为94%,98.3%,99.6%,lg6,出水浓度分别为18 mg/L,0.65 mg/L,0.06 NTU,4个/mL.出水水质优于城市杂用水水质标准(GB/T 18920-2002).该系统具有较强的抗冲击负荷能力.     

Performance and dye-degrading bacteria isolation of a hybrid membrane process

Textile dyeing wastewater contains harmful compounds, which are toxic to both marine organisms and human beings if it discharged into an aquatic environmental without suitable treatment. In this study, the wastewater containing the azo dye, Reactive Black 5 (RB5), was partially treated in an anaerobic sequencing batch reactor which was further treated either in an aerobic membrane bioreactors (AOMBR) or in combined aerobic membrane bioreactor/reverse osmosis (AOMBR/RO) process. The results showed that in the anaerobic sequencing batch reactor the RB5 dye was degraded to form aromatic amine intermediate metabolites, which were further mineralized in the AOMBR. It was also observed that although all effluents from the AOMBR and AOMBR/RO processes met the Taiwan EPA's effluent criteria, irrespective of which membranes were used in the aerobic tank, the effluent from the AOMBR/RO process met the criteria for reuse for toilet flushing, landscaping, irrigation, and cooling water purposes, where as the AOMBR effluent only met the criteria for cooling water due to incomplete color removal. Five anaerobic high dye-degrading bacteria were isolated, which were identified to be the same species of Lactococcus lactis by 16S rRNA sequencing. The L. lactis showed complete degradation of RB5 and further studies showed that it can also able to degrade Reactive Red 120 and Reactive Yellow 84 efficiently within 6 h.     

水和废水中氯苯的气相色谱分析方法研究

本文研究了水和废水中氯苯的萃取及分析方法。采用气相色谱法、大口径毛细管柱分离氯苯,以ECD进行检测,得到了良好的分离效果和较高的灵敏度,方法的检出限可达0.01mg/L。本方法完全能满足环境样品分析的要求。     

表面处理行业废水的治理与回用标准化探讨

直接排放表面处理废水将严重污染环境,彻底治理废水是表面处理行业生存和发展的必由之路。为了解决企业废水处理所面临的困难、规范废水治理技术、促进我国表面处理行业废水处理水平,建立完整的废水治理与回用标准体系已成为表面处理行业亟待解决的问题。阐述了建立表面处理废水治理和回用标准的必要性及标准化应遵行的原则,着重介绍了标准化体...     

A strategy for the optimization and economic evaluation of an ORC system for energy recovery

Abstract

A strategy for the performance prediction and economic evaluation of an ORC (organic Rankine cycle) system for power conversion is studied. Different assumptions and system boundaries are used to understand the constraints of the boundaries as well as their effects on the evaluation results. A series of methods, including cost estimation, operation’ research, sensitivity analysis and optimal design of heat exchangers, is employed in evaluating this thermal to power conversion system. It is found that the resultant variations in the economic evaluation, no matter what economic index is used, are mostly depending on the input parameters and the unpredictable variables at the preliminary design stage. The analysis strategy, the detailed procedures as well as the computer programs, is presented with a 400°F, 2.5 ×10⁷ Btu/hr flue gas recovery case as an illustration. This study shows a large variation of payback period ranging from 5 to 15 years, depending on different assumptions, operating conditions, and system boundaries. This analysis recommends a more conservative approach to evaluate an energy recovery project to avoid an inappropriate judgement of an engineering design project.     

Potable water recovery from As, U, and F contaminated ground waters by direct contact membrane distillation process

In this study, the feasibility of the direct contact membrane distillation (DCMD) process to recover arsenic, uranium and fluoride contaminated saline ground waters was investigated. Two types of membranes (polypropylene, PP; and polytetrafluoroethylene, PTFE) were tested to compare the permeate production rates and contaminant removal efficiencies. Several experiments were conducted to study the effect of salts, arsenic, fluoride and uranium concentrations (synthetic brackish water with salts: 1000-10,000 ppm; arsenic and uranium: 10-400 ppb; fluoride: 1-30 ppm) on the desalination efficiency. The effect of process variables such as feed flow rate, feed temperature and pore size was studied. The experimental results proved that the DCMD process is able to achieve over 99% rejection of the salts, arsenic, fluoride and uranium contaminants and produced a high quality permeate suitable for many beneficial uses. The ability to utilize the low grade heat sources makes the DCMD process a viable option to recover potable water from a variety of impaired ground waters.     

Ozonation of textile effluents and dye solutions under continuous operation: Influence of operating parameters

Ozonation experiments were carried out under continuous operation in a bubble column. The effect of several parameters (inlet dye concentration, applied ozone dose, pH and conductivity) in colour and TOC removal of an acid dye solution was investigated with the aim to optimize the operation conditions. The ozone consumption was measured in each experiment. Ozonation was found to be effective for decolourisation of an acid dye; however, it only has a slight effect on TOC removal. Increasing the inlet dye concentration leads to a decrease in the decolourisation efficiency and an increase in the ozone consumption. The decolourisation increases with the applied ozone dose. Colour removal efficiencies for different ozone doses were between 76 and 100%. In the pH range 5-9, the decolourisation efficiency decreases with pH only when buffered solutions were used. The presence of salt decreases the decolourisation efficiency. Several dyes of different classes were also studied and ozonation was found to be effective for decolourisation but considerably less efficient for TOC removal. Under the conditions tested, only the disperse and sulphur dyes presented a colour removal lower than 86%. Practical application of this process was validated by treating two industrial textile effluents collected after two different biological treatments.     

超滤膜法城市污水深度处理中水回用中试试验研究

以高碑店污水处理厂二级出水为处理对象，建立日产中水500t的超滤中试试验装置，研究膜法城市污水深度处理中水回用的工艺和操作条件，考察所能达到的技术经济指标，掌握放大规律，为万吨级工业装置和系统的设计提供基础数据．试验装置连续运行了约2500h，膜性能稳定，产水水质达到生活杂用水标准(CJ．25．1—89)。     

Improvement of paint effluents coagulation using natural and synthetic coagulant aids

The coagulant iron chloride and the flocculants Polysep 3000 (PO), Superfloc A-1820 (SU) and Praestol 2515 TR (PR) have been used in this study to show the efficiency of coagulation flocculation process in the chemical precipitation method for the removal of organic and colouring matters from the paint industry wastewater. This study also includes the amount of produced sludge. The results indicate that FeCl(3) is efficient at pH range 8-9 and at optimal dose of 650 mgl(-1). Iron chloride allows the removal of 82% of chemical oxygen demand (COD) and 94% of colour. However, sequential addition of coagulant and polymeric additives enhance clearly pollutant removal and produces less decanted sludge compared to the results obtained when the coagulant is used alone. The removal efficiency of COD reaches 91% and that of colour 99%. Coagulation-biflocculation process is more effective than the coagulation-monoflocculation one. The sequential addition of iron chloride, Polysep 3000 (cationic flocculant) and Praestol 2515 TR (anionic flocculant) seems to be the most suitable combination for the treatment of the paint industry wastewaters.     

Development and optimization of dark Fenton oxidation for the treatment of textile wastewaters with high organic load

The examination of the effectiveness of the chemical oxidation using Fenton's reagent (H(2)O(2)/Fe(2+)) for the reduction of the organic content of wastewater generated from a textile industry has been studied. The experimental results indicate that the oxidation process leads to a reduction in the chemical oxygen demand (COD) concentration up to 45%. Moreover, the reduction is reasonably fast at the first stages of the process, since the COD concentration is decreased up to 45% within four hours and further treatment time does not add up to the overall decrease in the COD concentration (48% reduction within six hours). The maximum color removal achieved was 71.5%. In addition, the alterations observed in the organic matter during the development of the process, as indicated by the ratios of COD/TOC and BOD/COD and the oxidation state, show that a great part of the organic substances, which are not completely mineralized, are subjected to structural changes to intermediate organic by-products.     

Fluidized-Bed Bioreactor Applications for Biological Wastewater Treatment: A Review of Research and Developments

Wastewater treatment is a process that is vital to protecting both the environment and human health. At present, the most cost-effective way of treating wastewater is with biological treatment processes such as the activated sludge process, despite their long operating times. However, population increases have created a demand for more efficient means of wastewater treatment. Fluidization has been demonstrated to increase the efficiency of many processes in chemical and biochemical engineering, but it has not been widely used in large-scale wastewater treatment. At the University of Western Ontario, the circulating fluidized-bed bioreactor (CFBBR) was developed for treating wastewater. In this process, carrier particles develop a biofilm composed of bacteria and other microbes. The excellent mixing and mass transfer characteristics inherent to fluidization make this process very effective at treating both municipal and industrial wastewater. Studies of lab- and pilot-scale systems showed that the CFBBR can remove over 90% of the influent organic matter and 80% of the nitrogen, and produces less than one-third as much biological sludge as the activated sludge process. Due to its high efficiency, the CFBBR can also be used to treat wastewaters with high organic solid concentrations, which are more difficult to treat with conventional methods because they require longer residence times; the CFBBR can also be used to reduce the system size and footprint. In addition, it is much better at handling and recovering from dynamic loadings (i.e., varying influent volume and concentrations) than current systems. Overall, the CFBBR has been shown to be a very effective means of treating wastewater, and to be capable of treating larger volumes of wastewater using a smaller reactor volume and a shorter residence time. In addition, its compact design holds potential for more geographically localized and isolated wastewater treatment systems.     

Treatment of textile wastewaters by electrocoagulation using iron and aluminum electrodes

Treatment of textile wastewaters by electrocoagulation using iron and of aluminum electrode materials has been investigated in this paper. The effects of relevant wastewater characteristics such as conductivity and pH, and important process variables such as current density and operating time on the chemical oxygen demand (COD) and turbidity removal efficiencies have been explored. Furthermore, the electrode and energy consumptions for each electrode have been calculated. The results show that iron is superior to aluminum as sacrificial electrode material, from COD removal efficiency and energy consumption points.     

Aerobic decolourization of the indigo dye-containing textile wastewater using continuous combined bioreactors

An aerobic bioprocess was applied to Indigo dye-containing textile wastewater treatment aiming at the colour elimination and biodegradation. A combined aerobic system using continuous stirred tank reactor (CSTR) and fixed film bioreactor (FFB) was continuously operated at constant temperature and fed with the textile wastewater (pH: 7.5 and total chemical oxygen demand (COD): 1185 mg l(-1)). The CSTR is a 1l continuous flow stirred tank reactor with a 700 ml working volume, and operated with a variable wastewater loading rate (WLR) from 0.92 to 3.7 g l(-1) d(-1). The FFB is a 1.5l continuous flow with three compartments packed with a rippled cylindrical polyethylene support, operated with a variable WLR between 0.09 and 0.73 g l(-1) d(-1). The combined two bioreactors were inoculated by an acclimated microbial consortium and continuously operated with four total WLR. This system presented high COD elimination and colour removal efficiencies of 97.5% and 97.3%, respectively, obtained with a total hydraulic retention time (HRT) of 4 days and total WLR of 0.29 g l(-1) d(-1). The effects of WLR on absorption phenomena on the yield of conversion of substrate on biomass (R(TSS/COD)) and on the yield of conversion of substrate on active biomass (R(VVS/COD)) are discussed. The increase of WLR and the decrease of HRT diminished the performances of this system in terms of decolourization and COD removal explained by the sloughing of biofilm, and the washout phenomena.     

Highly dealuminated Y zeolite as efficient adsorbent for the hydrophobic fraction from wastewater treatment plants effluents

In this work we report that highly dealuminated zeolite Y is a hydrophobic material that is able to remove selectively fatty acids and hydrocarbon compounds from the effluent of an urban wastewater treatment plant (UWTP). This adsorbent capability of zeolite Y could lead to an improved quality of UWTP effluents. Typical domestic wastewaters contain detergents, soaps and surfactants that are only partially removed in conventional UWTP. In the present work using an effluent from a UWTP located at Ribarroja del Turia (Valencia, Spain) containing 10 ppm of total organic carbon, we have been able to retain by adsorption on the dealuminated Y zeolite up to 16 and 60% of the organic matter of the effluent at pH values 7.2 and 4, respectively. Characterization of the adsorbed organic matter by Fourier transformed infrared (FT-IR), ¹H NMR and GC–MS after derivatization has shown that the zeolite adsorbs selectively the hydrophobic compounds of the effluent.     

Application of multicriteria decision analysis to jar-test results for chemicals selection in the physical-chemical treatment of textile wastewater

Jar-test is a well-known tool for chemicals selection for physical-chemical wastewater treatment. Jar-test results show the treatment efficiency in terms of suspended matter and organic matter removal. However, in spite of having all these results, coagulant selection is not an easy task because one coagulant can remove efficiently the suspended solids but at the same time increase the conductivity or increase considerably the sludge production containing chemicals and toxic dyes. This makes the final selection of coagulants very dependent on the relative importance assigned to each measured parameter. In this paper, the use of multicriteria decision analysis (MCDA) is proposed to help on the selection of the coagulant and its concentration in the physical-chemical wastewater treatment, since textile wastewater contains hazardous substances. Therefore, starting from the parameters fixed by the jar-test results, these techniques will allow to weight these parameters, according to the judgements of wastewater experts, and to establish priorities among coagulants. Two well-known MCDA techniques have been used: analytic hierarchic process (AHP) and preference ranking organization method for enrichment evaluations (PROMETHEEs) and their results were compared. The method proposed has been applied to the particular case of textile wastewaters. The results obtained show that MCDA techniques are useful tools to select the chemicals for the physical-technical treatment.     

Process development for the removal and recovery of hazardous dye erythrosine from wastewater by waste materials-Bottom Ash and De-Oiled Soya as adsorbents

Erythrosine is a water-soluble xanthene class of dye. It is widely used as colorant in foods, textiles, drugs and cosmetics. It is highly toxic, causes various types of allergies, thyroid activities, carcinogenicity, DNA damage behaviour, neurotoxicity and xenoestrogen nature in the humans and animals. The photochemical and biochemical degradation of the erythrosine is not recommended due to formation of toxic by-products. The present paper is an attempt to remove erythrosine from wastewater using adsorption over Bottom Ash-a power plant waste and De-Oiled Soya-an agricultural waste. Under the batch studies, effect of concentration of dye, temperature, pH of the solution, dosage of adsorbents, sieve size of adsorbents, etc., have been studied for the uptake of the dye over both adsorbents. The adsorption process verifies Langmuir and Freundlich adsorption isotherms in both the cases and based on the data different thermodynamic parameters have been evaluated. Batch studies also include kinetic measurements, rate constant study, mass transfer behaviour and establishment of mechanistic pathway for both the cases. For the bulk removal of the dye column operations have been carried out and breakthrough capacities of the Bottom Ash and De-Oiled Soya columns have been calculated. Attempts have also been made for the recovery of the adsorbed dye from exhausted columns by eluting dilute NaOH and more than 90% of the dye was recovered.     

Separation of IPA/water mixtures by pervaporation: sorption and pervaporation results

Homogeneous membranes were prepared by blending polyvinyl alcohol (PVA) with polyacrylic acid (PAA) and furthermore the blend membrane is cross-linked covalently through an ester linkage formation between a hydroxyl group of PVA and carboxyl group of PAA. These membranes were evaluated for separation of azeotropic isopropyl alcohol (IPA)/water mixtures by pervaporation, that is, a vacuum applying membrane process. The overall and preferential sorption of IPA/water mixtures in cross-linked membranes were determined to investigate the influence of PVA/PAA ratio and of liquid mixture composition. Pervaporation characteristics were also determined as a function of PVA/PAA ratio and of the feed mixture composition. With increasing PAA content in the membranes, solubilities and fluxes decreased and selectivities increased. Because of polarity, water permeated preferentially through the membranes. Sorption results showed the same tendency as pervaporation results.