Use of Bacteria to Recover Coagulant from Water Treatment Residue and Reuse for Turbidity Removal from Water

Abstract

Aluminum is present in significant concentrations in water treatment residue (WTR), a waste product obtained during turbidity removal in drinking water treatment. This study aimed at exploring the potential for recovery of coagulant from WTR using Acidithiobacillus ferroxidans (ATF) and reusing the recovered coagulant (RC) for turbidity removal from water. The activity of ATF was measured by monitoring the pH and Al recovery (in %, AlR%). The effects of two factors (WTR and sulfur dose) on the activity of ATF were studied using central composite design (CCD) and response surface methodology (RSM). The results indicated that the bacteria activity decreased with an increase in WTR dose. The results also revealed that the sulfur dose does not have a significant effect on the ultimate AlR%; however, it significantly reduced the time required for achieving AlR%. ANOVA analysis indicated that the obtained model and factors were significant. The maximum AlR% around 70.9% was obtained with 10 g/L of WTR dose and 8 g/L of sulfur dose. The RC was reused for the turbidity removal from lake water and synthetic turbid water (STW) and compared with the turbidity removal achieved with 1% (w/v) aluminum sulfate. The doses of RC to bring the turbidity <5 NTU in lake water and STW were found to be 0.75 and 1 mL/L respectively. To obtain similar turbidity level, the dose required with aluminum sulfate was 2.5 and 1.5 mL/L for lake water and STW, respectively. There was no significant change in the pH and sulfate and metal concentrations in the effluent treated with RC. The results obtained indicate that the RC is efficient in turbidity removal. The RC, therefore, has potential to reduce the demand for fresh alum for water treatment purposes and provide an alternative use of a waste material.