Indexed on: 21 Sep '11Published on: 21 Sep '11Published in: Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering
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.