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Oily wastewater is becoming a concern worldwide due to its quantities and the presence of contaminants and its sustainable treatment should be cost-effective and meet all requirements so the contaminants are not transferred to the environment. The paper reviews the state-of-the- art in the oily wastewater treatment by electrochemical processes such as electrochemical advanced oxidation processes and electrocoagulation. Efficiency of oily wastewater treatment has been thoroughly investigated with its expression as a function of the main technological (process) parameters. Fe and Al electrodes, as well as their combination have proven to be very effective in oily wastewater treatment with slightly better performance of Al electrodes. Higher current densities and longer reaction times result with higher COD, TOC, turbidity, phenol and oil and grease removal efficiencies, but with resulting increase in wastewater temperature and energy consumption, so there is a strong need for the process optimization. There is a need for further research on the treatment efficiencies of different contaminants (heavy metals, total hydrocarbons, organic halogens, cyanides, etc.). A lack of research is presented on the treatment efficiency with electrodes of different materials as well as the analyses of the sludge production and its further treatment and use or disposal.

This article presents a pilot-plant study of the electroplating wastewater treatment by the processes of electroreduction with iron electrode plates, and electrocoagulation/ozonation with aluminum electrode set, followed by the process of ozonation. The initial effluent was found to be highly enriched in heavy metals and to possess the elevated levels of organic contaminants. The values of Cr(VI), Fe, Ni, Cu, Zn, Pb, TOC, and COD exceeded the upper permissible limits of 63, 220.2, 1.1, 7, 131.3, 1.7, 12.3, and 11.4 times, respectively. The heavy metal removal was forced either by the coagulation/flocculation using Fe(II), Fe(III), and Al(III) ions released into the treated solution by the electrochemical corrosion of the sacrificial iron and aluminum electrodes, or the precipitation of the metal hydroxides as well as co-precipitation with iron and aluminum hydroxides. The principle organic matter destruction mechanisms were ozone oxidation and the indirect oxidation with chlorine/hypochlorite formed by the anodic oxidation of chloride already present in the wastewater. Following the combined treatment, the removal efficiencies of Cr(VI), Fe, Ni, Cu, Zn, Pb, TOC, and COD were 99.94%, 100.00%, 95.86%, 98.66%, 99.97%, 96.81%, 93.24%, and 93.43%, respectively, thus complying with the regulated values.

The aim of this research was development of appropriate procedure for the treatment of landfill leachate taken from the Visevac, Mraclinska Dubrava and Piskornica sanitary landfills. Due to the complex nature of the effluents a combined treatment approach was applied. The pretreatment step included simultaneous treatment with calcium oxide and electrocoagulation/electrooxidation by stainless steel electrode set. The main treatment included electrocoagulation/electrooxidation using the set of stainless steel, iron and aluminum electrodes. The pretreatment allowed the destruction and/or coagulation of the high molecular weight organic substances as well as optimization of pH values for the formation of reactive oxidative species, and the transformation of NH(4)-N into volatile NH(3)-N. In the presence of added calcium oxide and electrochemically generated coagulant the removal of the fluorides, phosphates and heavy metals occur through the formation of poorly soluble fluorapatite, hydroxyl apatite, and various hydroxides. During the main treatment electrochemically generated reactive oxidative species carried out rapid decomposition of the organic matter and ammonia, resulting in the removal of COD from 74.9% to 94.2%, color from 98.8% to 99.7%, turbidity from 98.4% to 99.3%, suspended solids from 97.1% to 99.3%, and ammonia from 99.6% to 99.7%. Slightly better results for the removal efficiency of color, turbidity and suspended solids were obtained in the case of Piskornica landfill compared with the other two landfills, while the COD removal efficiency decreases in the following order: Piskornica >Mraclinska Dubrava >Visevac. This could be related to the age of the landfill, which increases in the same order. Consequently, with the increasing age of the landfill the degree of degradability of the organic matter reduces significantly. Applied treatment approach resulted in clear, colorless and odorless effluent with the values of all measured parameters significantly lower compared to the upper permissible limit for discharge into the environment.

The physical, chemical and genotoxic properties of the activated red mud and its waste mud remained after waste water treatment were studied. The sequential leaching of waste mud under different conditions was investigated, as well as the toxic effect of its water extract, in order to discover a safe way for the handling and disposal of this waste material. Furthermore, in order to reduce the amount of waste material, the possibility of its regeneration and re-usage was also studied. Heavy metals content and other parameters, as well as the genotoxicity of water extract of new coagulant produced for industrial waste water treatment, were investigated to confirm its non-toxicity before its commercial production and usage. For the toxicity investigation, two strains of Salmonella typhimurium, TA98 and TA100 were used as a test system. Tested samples were not cytotoxic or mutagenic for S. typhimurium TA98/TA100 in the presence/absence of the metabolic activation. Promising results were also obtained...

The aim of this research was development of new system for the treatment of highly polluted wastewater (COD = 10240 mg/L; SS = 2860 mg/L) originating from vine-making industry. The system consisted of the main treatment that included electrochemical methods (electro oxidation, electrocoagulation using stainless steel, iron and aluminum electrode sets) with simultaneous sonication and recirculation in strong electromagnetic field. Ozonation combined with UV irradiation in the presence of added hydrogen peroxide was applied for the post-treatment of the effluent. Following the combined treatment, the final removal efficiencies of the parameters color, turbidity, suspended solids and phosphates were over 99%, Fe, Cu and ammonia approximately 98%, while the removal of COD and sulfates was 77% and 62%, respectively. A new approach combining electrochemical methods with ultrasound in the strong electromagnetic field resulted in significantly better removal efficiencies for majority of the measured parameters compared to the biological methods, advanced oxidation processes or electrocoagulation. Reduction of the treatment time represents another advantage of this new approach.

The aim of this work was the development and application of the pilot plant with the capacity of 1000 L/day for the purification of groundwater used for human consumption characterized with high concentration of arsenic and increased values of organic pollutants, ammonia, nitrites, color and turbidity. For that purpose, groundwater from the production wells supplying the towns Zrenjanin and Temerin (Vojvodina, Serbia) was used. Due to its complex composition, the purification system required the combination of the electroreduction/electrocoagulation, using iron and aluminum electrode plates with/without ozonation, followed by the electromagnetic treatment and the finally by the simultaneous ozonation/UV treatment. The electroreduction was used for the removal of nitrates, nitrites, and Cr(VI), while the removal of arsenic, heavy metals, suspended solids, color and turbidity required the application of the electrocoagulation with simultaneous ozonation. Organic contaminants and ammonia were removed completely in the last treatment step by applying the simultaneous ozonation/UV treatment. All measured parameters in the purified water were significantly lower compared to the regulated values. Under the optimum treatment conditions, the removal efficiencies for color, turbidity, suspended solids, total arsenic, total chromium, Ni(II), total copper, sulfates, fluorides, chemical oxygen demand, ammonia, nitrates, and nitrites were 100%. The removal efficiencies of the total manganese and iron were 85.19% and 97.44%, respectively, whilst the final concentrations were 4 and 7 μg/L, respectively.

A combined treatment approach using advanced oxidation, electrochemical methods and microwaves was developed and applied for the treatment of landfill leachate taken from Piskornica (Koprivnica, Croatia) sanitary landfill. Due to the complex nature of the effluent and extremely low bio-degradability (BOD(5)/COD ratio = 0.01) the purification of the leachate started with pre-treatment with ozone followed by simultaneous ozonation and electrocoagulation/electrooxidation using the set of iron and aluminum electrodes, and finally, the degradation of organic residue and ammonia with microwaves. Applied treatment approach resulted in clear, colorless and odorless effluent with the values of all measured parameters significantly lower compared to the upper permissible limit for discharge into the environment. The removal percentages of the parameters: color, turbidity, suspended solids, ammonia, COD and iron following the combined treatment were 98.43%, 99.48%, 98.96%, 98.80%, 94.17% and 98.56%, respectively.

The purpose of this work was development and application of the purification system suitable for the treatment of groundwater used for human consumption, satisfying following criteria: (a) no need for external addition of the chemicals ; (b) simultaneous removal of wide range of contaminants present in the treated water ; (c) low sensitivity to the changes in the composition of the treated water ; (d) high quality of treated water with regards to all measured parameters. Therefore the well water from the 60 m deep water layer situated near the city of Osijek (Eastern Croatia) with elevated values of heavy metals, color, turbidity, suspended solids, ammonia and organic contaminants was processed. Due to the complex composition of the treated water, the purification system required the combination of electroreduction/electrocoagulation, using iron and aluminum electrode plates followed by the simultaneous ozonation/UV treatment. The electroreduction/electrocoagulation approach was used for the removal of heavy metals, suspended solids, color and turbidity, while the organic contaminants and ammonia were removed by the ozonation/UV treatment. Allmeasured parameters in the purified water were significantly lower compared to the regulated values. Under the optimum treatment conditions, the removal efficiencies for color, turbidity, nickel and arsenic were 100%. The removal efficiencies of V, Cr, Mn, Fe, Cu, Zn, Pb, ammonia, fluorides, sulfates and COD were 94.5%, 96.0%, 98.3%, 99.6%, 99.7%, 97.8%, 96.7%, 96, 7%, 93.4%, 51.4%, 72.2% and 93.8%, respectively, increasing with the increased initial concentrations.

This paper provides the information on the optimum conditions of the treatment process of the boat pressure washing wastewater (BPWW) by the combination of the ozonation and electrochemical (EC) methods developed on the laboratory and pilot plant scale. The initial effluent was highly enriched in heavy metals and elevated levels of organic contaminants. The concentrations of V, Cr, Fe, Cu, Zn, TOC, and COD exceeded the upper permissible limits of 22, 20, 6, 112, 17, 4, and 2 times, respectively. The main mechanisms of the organic matter destruction were the ozone oxidation and the indirect oxidation with chlorine/hypochlorite formed by the anodic oxidation of chloride already present in the wastewater. The heavy metal removal was forced by the coagulation/flocculation using Fe(2+), Fe(3+), and Al(3+) ions released into the treated solution by electrochemical corrosion of the sacrificial stainless steel and aluminum electrodes. At the optimum conditions obtained with the pilot plant, the removal efficiencies of the parameters V, Cr, Fe, Ni, Cu, Zn, Pb, TOC, and COD were 100.00 %, 99.35 %, 99.51 %, 87.31 %, 99.83 %, 99.65 %, 100.00 %, 88.46 %, and 76.28 %, respectively. All the parameters in the final effluent were in agreement with regulated values. The advantages of this system compared to its physico-chemical counterparts are as follows: (1) no need for the external addition of flocculating agents since they are electrochemically generated inside the treatment tank; (2) minimal pH changes during the treatment process not requiring pH adjustment by acids/basis; (3) a significantly lower amount of sludge since only Fe and Al ions were released in the solution; (4) flocs formed by the electrocoagulation can be easily separated by the filtration due to their higher stability, lower content of the bound water and larger surface compared to chemical flocs; (5) the final EC effluent is clear, colourless and odourless, containing the less total dissolved solids and organics, thence more suitable for the reuse compared to the one obtained by the standard chemical treatment.

The aim of this research was development of appropriate procedure for treatment of landfill leachate taken from old sanitary landfill Piskornica (Koprivnica, Croatia). Due to complex nature of the effluent a combined treatment approach was applied. Samples were treated with calcium oxide followed by ferric chloride and finally with clinoptilolite. The optimum amount of treating agents and contact time were determined. Application of calcium oxide (25 g/L, 20 min. contact time) resulted in the reduction of color, turbidity, suspended solids and ammonia for 94.50%, 96.55%, 95.66% and 21.60%, respectively, while the removal efficiency of Cr (VI), Fe, Ni, Cu, Zn and Pb was 75.00%, 95.34%, 56.52%, 78.72%, 73.02% and 100.00%, respectively. After addition of ferric chloride (570 mg Fe(3+)/L, 20 min. contact time) removal efficiency of color, turbidity, suspended solids and ammonia increased to 96.04%, 99.27%, 98.61%, and 43.20%, respectively. Removal of ammonia (81.60%) increased significantly after final adsorption onto clinoptilolite (25 g/L, 4 h contact time). Removal of COD after successive treatment with calcium oxide, ferric chloride and clinoptilolite was 64.70%, 77.40% and 81.00%, respectively.

Water extracts genotoxicity of the coagulant produced from industrial waste (red mud and waste base) and its waste mud remained after waste water treatment by the coagulation/flocculation process were studied. Tests were conducted in order to confirm nontoxicity of this new product prior to commercial production and usage and also to recommend a safe way for a handling and disposal of the remaining waste material. The toxicity investigation included (i) determining frequency of the cell survival, (ii) the Ames assays, (iii) micronucleus assay, and (iv) cell proliferation kinetics (expressed as mitotic index). These techniques were also employed in toxicity testing of the different concentrations of metal salts, zinc chloride, and lead nitrate in this case since these two elements were present in high concentrations in the waste water intended for the purification with the new coagulant. Mixture of metal salts in the concentrations that represent maximum allowed values for water extracts of technological waste was also tested. Two strains of Salmonella typhimurium, TA98, and TA100 were used for determining cytotoxicity and for the Ames test, while the cytogenetic investigations were performed on human peripheral blood lymphocytes. Water extracts of the coagulant and its waste mud did not induce a significant increase of the micronuclei in human peripheral blood lymphocytes. They also did not disturb lymphocyte proliferation kinetics in vitro. As regards lead nitrate it proved not to be cytotoxic on bacterial strains in the tested concentration range (1-100 mg/L), whereas zinc chloride showed cytotoxic effect for the concentrations above 25 mg/L. The Ames test results for the noncytotoxic concentrations of these metals were negative. Comparing to the negative control a significantly higher number of the micronuclei was determined after the treatment of the whole blood with 100 mg/L of zinc chloride, as well as with 10 and 100 mg/L of lead nitrate. A linear, dose dependent increase was obtained for both salts. Similar results were obtained on the basis of the mitotic index.