Sulfate radical-based oxidation of an alcohol ethoxylate (Brij30®) by the PS/UV-C process.

In this study, sulfate radical-based oxidation of an alcohol ethoxylate (AE) was explored by the persulfate (PS)/UV-C process. Poly(oxyethylene)(4)laurylether, commercially known as Brij30®, was used as a model AE. PS/UV-C oxidation of aqueous Brij30® (8-20 mg/L) was performed at initial PS concentrations varying between 0.50 and 6.50 mM and at initial pH values of 3.0 and 6.0. Results indicated that an increase in both initial PS and Brij30® concentrations did not have a significant effect on Brij30® removal efficiency and that Brij30® abatements of more than 90% could be achieved after 60 min of treatment time. Total organic carbon (TOC) removals were significantly improved with increasing initial PS concentrations for both initial pH values. On the other hand, an increase in initial Brij30® concentration had a negative effect on mineralization. By employing the competitive kinetic method, the second-order reaction rate coefficient of Brij30® with the sulfate radical (SO4 •-) was determined as 1.62 × 109 ± 3.5 × 107 M-1s-1. The second-order reaction rate constant of TOC, originating from Brij30® and reaction intermediates, was found to be 9.09 × 105 ± 2.91 × 105 M-1s-1 and 1.13 × 106 ± 0.46 × 106 M-1s-1 for pH values of 6.0 and 3.0, respectively. Toxicity of PS/UV-C treated aqueous Brij30® solutions towards Vibrio fischeri was also investigated to determine the possible toxic behavior of oxidation products.

A statistical experimental design approach for mineralization and detoxification of diethyl phthalate by H2O2/UV-C process.

In the present study, a three-factor central composite design (CCD) was implemented to evaluate the major factors (treatment time, initial H2O2 dose and initial diethyl phthalate (DEP) concentration) influencing the H2O2/UV-C treatment of aqueous DEP solution. Significant regression models for total organic carbon (TOC) removal and residual H2O2 concentration were derived using analysis of variance (ANOVA), which were found to be adequate to perform the process variables optimization. According to the applied ANOVA, treatment time (positive effect) and initial H2O2 dose (negative effect after an optimum value) were found to be significant on the H2O2/UV-C process performance. TOC removal efficiencies were enhanced with increasing initial H2O2 dose up to an optimum value, and further increases in H2O2 dose resulted in a decrease in TOC removals due to the hydroxyl radical scavenging effect. When initial H2O2 dose increased from 10 to 30 mM, the TOC removal efficiency improved from 41 to 100% for DEPo of 100 mg/L for treatment time of 50 min. Further increase in initial H2O2 dose to 50 mM decreased the TOC removal efficiency down to 38%. The results of toxicity assessments with Vibrio fischeri on aqueous DEP solutions subjected to H2O2/UV-C treatment revealed complete detoxification at the optimum conditions.

Pollution profile and biodegradation characteristics of fur-suede processing effluents.

This study investigated the effect of stream segregation on the biodegradation characteristics of wastewaters generated by fur-suede processing. It was conducted on a plant located in an organized industrial district in Turkey. A detailed in-plant analysis of the process profile and the resulting pollution profile in terms of significant parameters indicated the characteristics of a strong wastewater with a maximum total COD of 4285 mg L(-1), despite the excessive wastewater generation of 205 m3 (ton skin)(-1). Respirometric analysis by model calibration yielded slow biodegradation kinetics and showed that around 50% of the particulate organics were utilized at a rate similar to that of endogenous respiration. A similar analysis on the segregated wastewater streams suggested that biodegradation of the plant effluent is controlled largely by the initial washing/pickling operations. The effect of other effluent streams was not significant due to their relatively low contribution to the overall organic load. The respirometric tests showed that the biodegradation kinetics of the joint treatment plant influent of the district were substantially improved and exhibited typical levels reported for tannery wastewater, so that the inhibitory impact was suppressed to a great extent by dilution and mixing with effluents of the other plants. The chemical treatment step in the joint treatment plant removed the majority of the particulate organics so that 80% of the available COD was utilized in the oxygen uptake rate (OUR) test, a ratio quite compatible with the biodegradable COD fractions of tannery wastewater. Consequently, process kinetics and especially the hydrolysis rate appeared to be significantly improved.

Organic matter and heavy metal removals from complexed metal plating effluent by the combined electrocoagulation/Fenton process.

In the present study, the treatment of metal plating wastewater containing complexed metals originating from the nickel and zinc plating process by electrocoagulation (EC) using stainless steel electrodes was explored. In order to improve the organic matter removal efficiency, the effect of H(2)O(2) addition to the electrocoagulation (the combined EC/Fenton process) application was investigated. For this purpose, a wide range of H(2)O(2) concentrations varying between 15 and 230 mM was tested. All EC and EC/Fenton processes were performed at an initial pH of 2.6 and at an optimized current density of 22 mA/cm(2). Although up to 30 mM H(2)O(2) addition improved the EC process performance in terms of organic matter abatement, the highest COD and TOC removal efficiencies were obtained for the combined EC/Fenton process in the presence of 20 mM H(2)O(2). Nickel and zinc were completely removed for all runs tested in the present study after pH adjustments. At the optimized operation conditions, the combined EC/Fenton process proved to be an alternative treatment method for the improvement of organic matter reduction as well as complexed metal removal from metal plating industry wastewater.

Application of struvite precipitation coupled with biological treatment to slaughterhouse wastewaters.

In this study, struvite precipitation coupled with an activated sludge process was applied to slaughterhouse wastewaters. Biological treatability characteristics of the wastewater were evaluated in a wide organic loading range of 0.06-0.42 g COD (g MLVSS)(-1)d(-1) to assess COD removal as well as the extent of nitrification. Results of biological treatment of raw wastewater indicated that COD removal varied between 88% and 99% and complete nitrification was achieved at 0.1 g COD (g MLVSS)(-1)d(-1) and lower organic loadings. Biological treatment of the struvite-precipitated sample, which required no nitrification, yielded 86% COD removal at the organic removal of 0.3 g COD (g MLVSS)(-1)d(-1). Struvite precipitation of both raw and biologically treated wastewater was at effective stoichiometric magnesium and phosphate doses to ammonia and between pH values of 9.0 and 9.5, providing ammonia concentrations of 20-30 mg N L(-1) in the effluent and being independent of initial concentrations. The application of struvite precipitation both prior to and after biological treatment resulted in similar effluent qualities and provided the additional benefit of having a high-rate activated sludge system instead of a low organic loading system with nitrification-denitrification. An additional benefit of struvite precipitation was the production of sludge which had recovery potential as a fertilizer. Among the tested treatment schemes, biological treatment following struvite precipitation seemed to be more advantageous in terms of process stability.

Bench-scale evaluation of treatment schemes incorporating struvite precipitation for young landfill leachate.

In this study, landfill leachate treatment technologies alternative to anaerobic treatment were experimentally investigated. The emphasis was placed upon nitrogen removal through the use of struvite precipitation. Treatment technologies studied included struvite precipitation, low pH (acidic) air stripping, and activated sludge. Dilution of landfill leachate was used as a means to obtain appropriate quality for feeding the activated sludge process in some instances. Five main treatment combinations were applied. The first and second schemes were struvite precipitation followed by activated sludge process which was fed on undiluted and diluted (1:5) effluents. The third scheme was dilution, activated sludge and struvite precipitation. The fourth alternative was acidic air stripping, struvite precipitation and activated sludge process. The fifth scheme was acidic air stripping, activated sludge and struvite precipitation. All treatment schemes provided comparable COD and ammonia removals, all being around 90%. The treatment schemes incorporating the acidic air stripping, however, was found to be the most advantageous in terms of both efficiency and volume and aeration requirements of the activated sludge process since over 80% COD could be removed in the stripping step. Of the fourth and fifth alternative schemes, the fourth was the most efficient, providing 95% removal of both COD and ammonia. Initial dilution of the leachate at a 1:5 ratio was the least effective one, yielding 90% or lower removals for COD and ammonia. The first scheme, namely application of struvite precipitation to raw leachate followed by activated sludge with or without dilution, proved to be a practical system, providing over 85% COD and 99% ammonia removals. High organic loading up to 0.8 g COD/g VSS day was found to be applicable within this scheme.

Advanced treatment by chemical oxidation of pulp and paper effluent from a plant manufacturing hardboard from waste paper.

This study attempts to evaluate the applicability of chemical oxidation processes to polish biologically treated effluent of a plant manufacturing hardboard from waste paper to comply with the discharge limit of 120 mg l(-1) chemical oxygen demand (COD). In the first step, a chemically assisted settling was applied. The optimum results were obtained with alum plus lime with the alum dose of 200 mg l(-1). In the second step, chemically assisted settling effluent was fed into an activated sludge system and over 80% COD removal was achieved. In the last step of the experimental study, a series of ozone oxidation and Fenton oxidation methods were tested to remove residual COD. Ozone oxidation provided 80% COD removal. An ozone dose of 40 mg min(-1) with a reaction time of two hours was found to be optimum. Catalytic ozonation by using ferric iron, as well as high pH ozonation, Fenton process and H2O2/O3 oxidation did not prove to be more efficient than plain ozonation under these study conditions.

The effect of the textile industry dye bath additive EDTMPA on colour removal characteristics by ozone oxidation.

In this study, the effects of the phosphonic acid based sequestering agent EDTMPA used in the textile dye baths on colour and organic matter removal by ozone oxidation was experimentally investigated. Procion Navy HEXL dyestuff that has been commonly used for the reactive dyeing of cellulose fibers was selected as the model component. The organic matter oxidation by ozone was determined to obey the pseudo-first order kinetics as they are treated singly or in combination. COD removal rates obtained from pseudo-first order reaction kinetics showed that oxidation of Navy HEXL alone (0.0947 L/min) was faster than that of EDTMPA (0.0171 L/min) and EDTMPA with dye (0.0155 L/min) at pH 3.0. It was also found that reaction rates of single EDTMPA removal and EDTMPA and dye mixture removal increased as the reaction pH was increased from 3.0 to 10.5.

Effect of Fenton's treatment on the biodegradability of chromium-complex azo dyes.

Pretreatment of an acid dyebath effluent bearing a new generation chromium complex azo dyestuff (C0 = 350 mg/L) with Fenton's reagent was investigated. Preliminary optimisation (baseline) experiments were conducted to determine the Fe2+, H2O2 concentrations and pH required to the highest possible COD and colour removals. Kinetic studies were carried out at varying temperatures (20 degrees C < T < 70 degrees C) to establish a relationship between COD abatement and H2O2 consumption. The activation energy found for catalytic H2O2 decomposition (Ea = 9.8 kJ/mol) appeared to be significantly less than that of fermentative (Ea = 23 kJ/mol) and of thermal (Ea = 76 kJ/mol) H2O2 decomposition, implying that H2O2 decomposition during the Fenton's reaction occurs more spontaneously. The experimental studies indicated that approximately 30% COD and complete colour removal could be achieved under optimised Fenton pretreatment conditions (Fe2+ = 2 mM; H2O2 = 30 mM; pH = 3; at T = 60 degrees C). Long-term activated sludge experiments revealed that although the raw and pretreated acid dyebath effluent contained practically the same amount of "readily biodegradable" COD (inert COD fraction < or = 10%), biodegradation of the chemically pretreated acid dye effluent proceeded appreciably faster than that of the untreated acid dyebath effluent.

Comparison of electrocoagulation, coagulation and the fenton process for the treatment of reactive dyebath effluent.

In this paper, experimental studies were performed on a simulated reactive dyebath effluent to compare coagulation-flocculation and Fenton's oxidation with electrocoagulation using stainless steel (SS 304) and aluminium electrodes in terms of colour and COD removals as well as AOX formation potential and improvement of biological treatability. Results have indicated that FeCl3 and alum coagulation had little effect on colour removal whereas comparable colour removal efficiencies with those of electrocoagulation with steel electrodes and Fenton's oxidation were attained by FeSO4 coagulation. Almost complete colour removals accompanied with 77% COD abatement were obtained by both electrocoagulation with steel electrodes and Fenton's oxidation under optimised reaction conditions. Although electrocoagulation with aluminium electrodes yielded very limited colour removal and produced a high amount of sludge upon extended reaction time, this application brought about a marked improvement in biodegradability.

Nitrogen recovery by urea hydrolysis and struvite precipitation from anthropogenic urine.

Human urine is a source of nutrients and has a significant potential for recycle of nitrogen. Recently, much research focused on separate collection and treatment of human urine. Recovery of nutrients from human urine requires hydrolysis of urea into ammonia and subsequent removal of ammonia and sometimes phosphorus. This study attempted to evaluate urea hydrolysis of human urine in both untreated fresh samples and urease added urine samples. Recovery of nutrients by struvite precipitation on pre-hydrolysed samples was also assessed on undiluted and 1:1 diluted samples. Results of urea hydrolysis on untreated urine samples indicated that the process was slow and pH exerted a significant effect on the process. No hydrolysis occurred above pH 10. From pH 2 to 7.5, 25% of urea could be hydrolysed in 30 d. Urease added hydrolysis with the enzyme doses 25-49 mg L(-1) was a rapid process providing complete conversion into ammonia in 1.5 h. Struvite precipitation conducted on enzyme hydrolysed urine sample proved to be an efficient process and ammonia removals up to 95% were obtained. Struvite precipitation also provided 50% organic nitrogen removal.

Nitrogen removal from tannery wastewater by protein recovery.

Nitrogen removal from wastewaters has gained importance in recent years. In this paper protein precipitation and recovery potential of leather tanning industry wastewaters were experimentally evaluated. A protein profile for all sources was prepared. Liming was determined to be the most important protein source. Composite samples were made up to assess the protein precipitation applications. Isoelectric pH precipitation yielded around 50% protein removal between the optimum pH interval of 2.1-3.8. FeCl3 proved to be a very effective means of protein removal providing over 60% efficiency. Polyelectrolyte precipitation did not yield satisfactory results. Magnesium ammonium phosphate precipitation followed by acid precipitation of protein provided 85% ammonia removal in addition to 50% protein removal.

Factors affecting colour removal from reactive dye bath by ozonation.

A reactive dye bath sample containing a mixture of dyes was ozonated and colour removal was obtained in a relatively short time of 30 min at 605 mgl-1 of ozone utilisation. The factors affecting ozonation were assessed by comparing the results of dye bath and synthetic samples. Results from dye bath and synthetic dye solution ozonation were found to be significantly different. NaCl and Na2CO3 were determined to have a slight effect only on the initial rate of ozonation. However, the effect of the chelating agent in terms of both time and ozone dose was significant and explained the differences between the results of the dye bath and dye solution ozonation.

Assessment of magnesium ammonium phosphate precipitation for the treatment of leather tanning industry wastewaters.

Magnesium ammonium phosphate (MAP) precipitation has a potential for ammonium removal from industrial wastewaters. Application basis of this recent method of treatment has not been fully determined. In this study application of MAP precipitation to leather tanning wastewaters has been experimentally evaluated. Five alternative places of MAP precipitation in leather tanning wastewater treatment scheme tested were; instead of plain settling, after plain settling, after polyelectrolyte added plain settling, within the chemical precipitation and after biological treatment. Among these alternatives MAP application instead of plain settling and within the chemical precipitation were found to be most favourable and efficient by reducing the nitrogen load to the level of nutrient requirement in the biological stage. pH 9.0-9.5 and stoichiometric magnesium and phosphate doses were determined to be optimum conditions for MAP precipitation.

Assessment of source-based nitrogen removal alternatives in leather tanning industry wastewater.

Nitrogen is an important parameter of leather tanning wastewaters. Magnesium ammonium phosphate (MAP) precipitation is a chemical treatment alternative for ammonia removal. In this study, a detailed source-based wastewater characterisation of a bovine leather tannery was made and nitrogen speciation as well as other basic pollutant parameter values was evaluated. This evaluation has led to definition of alternatives for source-based MAP treatment. MAP precipitation experiments conducted on these alternatives have yielded over 90% ammonia removal at pH 9.5 and using stoichiometric doses. Among the alternatives tested liming-deliming and bating-washing was found to be the most advantageous providing 71% ammonia removal.

Effect of chemical treatment on soluble residual COD in textile wastewaters.

The effect of chemical treatment on the magnitude of soluble residual COD in the biological treatment effluent is investigated for knit fabric finishing wastewater. Bentonite is selected for its potential to remove soluble COD together with color and particulate components. Chemical treatment using bentonite, when applied prior to biological treatment removes around 40% of the biodegradable as well as soluble inert COD initially present in the wastewater. As a chemical post-treatment, it acts as a polishing step, removing particulate matter and a minor portion of around 20% of the remaining soluble COD. These findings suggest chemical pre-treatment as a better alternative for the optimization of soluble COD removal.

Ozonation application in activated sludge systems for a textile mill effluent.

The study investigates the effect of partial ozonation of textile wastewater, both at the inlet (pre-ozonation) and the outlet (post-ozonation) of biological treatment, for the optimization of COD and color removals, both typical polluting parameters associated with the textile industry. Pre-ozonation provides at optimum contact time of 15 minutes 85% color removal, but only 19% COD reduction. Removal of the soluble inert COD fraction remains at 7%, indicating selective preference of ozone for simpler compounds. Post-ozonation is much more effective on the breakdown of refractory organic compounds and on color removal efficiency. Ozonation after biological treatment results in almost complete color removal and a 14% soluble inert COD reduction. The polishing effect of post-ozonation also proves quite attractive from an economical standpoint, involving approximately 50% of the ozone utilization at the same ozone flux rate and contact time, yet providing a lower soluble residual COD level.

A scientific approach to wastewater recovery and reuse in the textile industry.

Wastewater recovery and reuse in industries requires all the basic steps of quality management. It should involve a comprehensive in plant survey of processes with wastewater generation, identification of recoverable streams, and treatment requirements for reuse. It should equally undertake evaluation of wastewater quality remaining after segregation of the recovered portion, with specific emphasis on technological implications of appropriate treatment and compliance with effluent limitations. In this study, all these factors were experimentally assessed and evaluated for a knit fabric processing textile plant.

Effect of ozonation on the biological treatability of a textile mill effluent.

Ozonation applied prior to biological processes, has proved to be a very effective chemical treatment step mostly for colour removal when soluble dyes are used in textile finishing operations. Its impact on biological treatability however has not been fully evaluated yet. This study evaluates the effect of ozonation on the quality of wastewater from a textile mill involving bleaching and reactive dyeing of cotton and synthetic knit fabric. The effect of ozonation on COD fractionation and kinetic coefficients defining major biological processes is emphasised. The results indicate that the extent of ozone applied greatly affects the remaining organic carbon composition in the wastewater. The relative magnitude of different COD fractions varies as a function of the ozone dose. Ozonation does not however exert a measurable impact on the rate of major biological processes.