BOAT PRESSURE WASHING WASTEWATER TREATMENT WITH CALCIUM OXIDE AND/OR FERRIC CHLORIDE

The aim of this study was to investigate the effi ciency of (1) chemical precipitation by calcium oxide, (2) coagulation/fl occulation by ferric chloride (FC), and (3) the combination these two methods in reducing the toxicity of wastewater generated by boat pressure washing. All three methods gave satisfactory results in the removal of colour, turbidity, Cr, Fe, Cu, Zn, and Pb. The concentrations of heavy metals were lowered below national limits with 1 g of CaO, 2.54 mg of Fe3+ in the form of FeCl3×6H2O, and the combination of 0.25 g of CaO and 5.08 mg of Fe3+ per 50 mL of wastewater. Both CaO (1.50 g per 50 mL of wastewater) and FC proved effi cient, but their combination yielded a signifi cantly better performance: 99.41 %, 100.00 %, 97.87 %, 99.09 %, 99.90 %, 99.46 % and 98.33 % for colour, turbidity, Cr, Fe, Cu, Zn, and Pb respectively. For colour, Cr, Cu, Zn, and Pb removal effi ciencies increased in the following order: FC<CaO<CaO+FC, while this order for turbidity and Fe was as follows: CaO<FC<CaO+FC. As expected, all three methods increased the concentration of total dissolved solids in the fi nal effl uent. Our results suggest that the combined treatment of marina wastewaters with calcium oxide followed by ferric chloride is effi cient, cost-effective, and user-friendly