O. Tünay

Complexing agent and heavy metal removals from metal plating effluent by electrocoagulation with stainless steel electrodes.

In the present study, the treatability of a metal plating wastewater containing complexed metals originating from the nickel and zinc plating process by electrocoagulation using stainless steel electrodes was experimentally investigated. The study focused on the effect of important operation parameters on electrocoagulation process performance in terms of organic complex former, nickel and zinc removals as well as sludge production and specific energy consumption. The results indicated that increasing the applied current density from 2.25 to 9.0 mA/cm(2) appreciably enhanced TOC removal efficiency from 20% to 66%, but a further increase in the applied current density to 56.25 mA/cm(2) did not accelerate TOC removal rates. Electrolyte concentration did not affect the process performance significantly and the highest TOC reduction (66%) accompanied with complete heavy metal removals were achieved at the original chloride content ( approximately 1500 mg Cl/L) of the wastewater sample. Nickel removal performance was adversely affected by the decrease of initial pH from its original value of 6. Optimum working conditions for electrocoagulation of metal plating effluent were established as follows: an applied current density of 9 mA/cm(2), the effluents original electrolyte concentration and pH of the composite sample. TOC removal rates obtained for all electrocoagulation runs fitted pseudo-first-order kinetics very well (R(2)>92-99).

Hydroxide precipitation of complexed metals

Abstract In this study, theoretical analysis of the complexed metal treatment by conventional hydroxide precipitation is made. The analysis is aimed to evaluate the mechanism of ligand-sharing effect of metals which are added to wastewater to ensure effective removal of complexed heavy metals. Theoretical expression of the analysis is made using phase diagrams. Cadmium, copper and nickel are selected as heavy metals. EDTA, NTA and succinic acid are selected as organic complex formers of different strengths. Calcium is used as the ligand binding agent. Theoretical solutions are made for, single metal-single ligand system and several metal and ligand combinations in the closed system and single metal-single ligand in the open system. Theoretical solutions are interpreted considering the solubility, stability and ionization constants and their relative magnitudes. Experimental studies are conducted to check the theoretical predictions. Result indicate that high pH precipitation is applicable to the cases where organic ligand can be effectively bound by calcium or any other coagulant or pH adjustment agent thus freeing the heavy metal to form hydroxide or carbonate solids. Theoretical diagrams can be used to predict the favorable conditions for precipitation and as a guide to determine the operating conditions.

Electrocoagulation applications for industrial wastewaters: a critical review

Cost-effective methods are required to treat a wide range of wastewater pollutants in a diverse range of conditions. As compared with traditional treatment methods, electrocoagulation provides a relatively compact and robust treatment alternative in which sacrificial metal anodes initiate electrochemical reactions that provide active metal cations for coagulation and flocculation. The inherent advantage of electrocoagulation is that no coagulants have to be added to the wastewater and hence the salinity of the water does not increase after treatment. Electrocoagulation is a complex process involving a multitude of pollutant removal mechanisms operating synergistically. Although numerous publications have appeared in the recent past, the lack of a holistic and systematic approach has resulted in the design of several treatment units without considering the complexity of the system and process control mechanisms. Due to the fact that electrocoagulation is thought to be an enigmatic, promising treatment technology and a cost-effective solution for sustainable water management in the future, it will become increasingly important to provide a deeper insight into the pollutant removal mechanisms involved, kinetic modelling and reactor design. Considering the abovementioned facts, in this paper, industrial wastewater electrocoagulation applications have been reviewed with special emphasis placed on the major reaction mechanisms involved in these applications. Evaluation was based on specific pollutant parameters of the sector as well as operation costs including solid waste management, sacrificial electrode materials and electrical energy requirements.

Electrocoagulation of simulated reactive dyebath effluent with aluminum and stainless steel electrodes

Reactive dyebath effluents are ideal candidates for electrocoagulation due to their intensive color, medium strength, recalcitrant COD and high electrolyte (NaCl) content. The present study focused on the treatability of simulated reactive dyebath effluent (COD(o)=300 mg/L; color in terms of absorbance values A(o,436)=0.532 cm(-1), A(o,525)=0.693 cm(-1) and A(o,620)=0.808 cm(-1)) employing electrocoagulation with aluminum and stainless steel electrodes. Optimization of critical operating parameters such as initial pH (pH(o) 3-11), applied current density (J(c)=22-87 mA/cm(2)) and electrolyte type (NaCl or Na(2)SO(4)) improved the overall treatment efficiencies resulting in effective decolorization (99% using stainless steel electrodes after 60 min, 95% using aluminum electrodes after 90 min electrocoagulation) and COD abatement (93% with stainless steel electrodes after 60 min, 86% with aluminum electrodes after 90 min of reaction time). Optimum electrocoagulation conditions were established as pH(o) 5 and J(c)=22 mA/cm(2) for both electrode materials. The COD and color removal efficiencies also depended on the electrolyte type. No in situ, surplus adsorbable organically bound halogens (AOX) formation associated with the use of NaCl as the electrolyte during electrocoagulation was detected. An economical evaluation was also carried out within the frame of the study. It was demonstrated that electrocoagulation of reactive dyebath effluent with aluminum and stainless steel electrodes was a considerably less electrical energy-intensive, alternative treatment method as compared with advanced chemical oxidation techniques.

Treatment of phthalic acid esters by electrocoagulation with stainless steel electrodes using dimethyl phthalate as a model compound

In this study, treatment of phthalates by electrocoagulation employing stainless steel electrodes was investigated using dimethyl phthalate (DMP) as a model compound. DMP was completely destructed within 30 min up to the high initial concentration of 100mg/L while total mineralization was also obtained within a couple of hours. The applied current density of 22.5 mA/cm(2) and electrolyte (NaCl) concentrations varying between 1000 and 1500 mg/L as chloride resulted in the highest treatment performance. The initial solution pH (2-6) had practically no effect on the process efficiency. Desorption experiments and the reaction rates obtained for DMP, COD and TOC abatements appeared to be a strong evidence of an oxidative removal mechanism. DMP removal fitted first order kinetics. COD and TOC removals began after the total DMP removal and also fitted first order kinetics. Activated sludge inhibition experiments revealed that toxicity could be significantly reduced by electrocoagulation application.

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.

An OUR-based approach to determine the toxic effects of 2,4-dichlorophenoxyacetic acid in activated sludge

This study uses the oxygen uptake rate (OUR) measurement to measure toxicity effects of 2,4-dichlorophenoxyacetic acid (2,4-D) on activated sludges fed with the wastewater from a small domestic wastewater treatment plant and peptone-based synthetic wastewater. Two 2l lab-scale batch reactors were run in parallel with the same F/M ratios (0.4 mg COD per mg VSS per day) to assess the inhibition effects of 2,4-D concentrations between 25 and 75 mg l(-1) considering at least a 100% dilution rate, as compared with a pesticide industry effluent containing 20,000-40,000 mg l(-1) COD, reaches a central treatment plant. It was noted that the OUR was decreased to 15 and 30%, respectively, when adding 75 mg l(-1) of 2,4-D to the domestic and synthetic reactors. Meanwhile, the addition of 25 plus 50 mg l(-1) of 2,4-D in sequence to the domestic wastewater reactor did not significantly affect the OUR profile. The OUR-based inhibition definition has been used in this research since the OUR methods have been frequently used and cited in the literature to study toxicity effects. However, the origin of the sludge used in the testing is also important. Synthetic wastewater may simulate the toxicity studies but with a higher response than actual systems, since the microorganisms are considerably becoming substrate-selective.

Characterization and Treatment of Textile Printing Wastewaters

Textile printing is becoming an important wastewater source as the water-based materials replace the organic solvents. The wastewaters originating from this operation are often strong and may contain toxics, although their volume is quite low. In this study, a textile printing plant was evaluated to assess pollution characteristics and treatment alternatives. Rotation printing wastewaters were found to be relatively diluted compared with other printing wastewaters, having a COD of around 800 mg l−1 and responded with a high efficiency to both chemical precipitation and biological treatment. On the other hand, tube and item printing wastewaters contained solvents as well as high COD and TKN. Chemical treatment and aeration used as a pretreatment resulted in over 90 % COD removal together with high degree of color and solvent removal. Biological treatment following pretreatment resulted in an effluent COD of 250-500 mg l−1. Nitrogen removal in the pretreatment stage was also assessed using magnesium ammonium phosphate (MAP) precipitation and air stripping. Results of the study were evaluated considering alternative treatment schemes.

Removal of Color and COD from a Mixture of Four Reactive Azo Dyes Using Fenton Oxidation Process

Abstract This study was designed to decolorize and to reduce COD content in a mixture of four reactive dyes, i.e., Remazol Black 5 (RB5), Remazol Red RB (RR), Remazol Yellow 84 (RY), Remazol Brilliant Blue (RB) using Fenton Oxidation Process (FOP). Optimum pH, temperature, and the doses of FeSO4 and H2O2 were determined. Experiments were conducted on the samples containing a total concentration of 100 mg L−1 (RB + RY), 200 mg L−1 (RB5 + RR), 300 mg L−1 (RB5 + RR + RB + RY), and 400 mg L−1 (RR + RB + RY) dyes considering their actual application doses in dyehouses. Optimum pH was observed as 2.5 at 30°C using 400 mg L−1 FeSO4 and 800 mg L−1 of H2O2 resulting in more than 96% COD and 99% Pt-Co unit of color removal for the mixture of RB5 and RR. The optimum conditions determined were 4.0 pH, 50°C, and 500 mg L−1 FeSO4 applying 1000 mg L−1 H2O2 for the mixture of (RB5 + RR + RB + RY). A 100 mg L−1 solution of a mixture of RB and RY at equal amounts was oxidized using 200 mg L−1 FeSO4 and 300 mg L−1 H2O2 at 3.0 pH and 50°C.

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)−1d−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)−1d−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)−1d−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.