Obrada otpadnih voda od pranja brodova kombinacijom fizičko-kemijskih metoda

The aim of this study was to investigate the effi ciency of (1) chemical precipitation by calcium oxide, (2) coagulation/flocculation 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 efficient, but their combination yielded a significantly 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 efficiencies 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 final effluent. Our results suggest that the combined treatment of marina wastewaters with calcium oxide followed by ferric chloride is efficient, cost-effective, and user-friendly.Radi smanjenja toksičnosti otpadnih voda koje nastaju pranjem brodova premazanih bojama protiv obraštaja primijenjene su tri metode obrade: (1) kemijsko taloženje s pomoću kalcijeva oksida, koagulacija/flokulacija s pomoću željezova klorida (FC) i (3) kombinacija ovih dviju metoda. Sve tri metode dale su zadovoljavajuće rezultate u uklanjanju boje, mutnoće, kroma, željeza, bakra, cinka i olova. Koncentracije teških metala niže od graničnih vrijednosti postignute su nakon tretmana s 1 g CaO ili 2,54 mg Fe3+ dodanog u obliku FeCl3×6H2O ili kombinacijom od 0,25 g CaO i 5,08 mg Fe3+ na 50 mL otpadne vode. Optimalne vrijednosti uklanjanja boje, mutnoće, Cr, Fe, Cu, Zn odnosno Pb s pomoću CaO (1,50 g na 50 mL) bile su 99,07 %, 99,54 %, 86,97 %, 96,77 %, 97,81 %, 98,76 % odnosno 84,10 %, dok su u slučaju željezova klorida te vrijednosti iznosile 98,76 %, 99,85 %, 78,99 %, 97,35 %, 96,77 %, 98,53 % odnosno 78,99 %. Značajno viši stupanj uklanjanja postignut je kombinacijom navedenih dvaju pristupa čime je postignuta maksimalna učinkovitost uklanjanja i to 99,41 % boje, 100,00 % mutnoće, 97,87 % kroma, 99,09 % željeza, 99,90 % bakra, 99,46 % cinka i 98,33 % olova. Za boju, krom, bakar, cink i olovo učinkovitost uklanjanja raste ovim redoslijedom: FC <CaO <CaO + FC dok za mutnoću i željezo raste u ovom nizu: CaO <FC