Optimization of heavy metal removal from aqueous solution using groundwater treatment plant sludge (GWTPS)

A groundwater treatment plant in Chicha, Kelantan, produces 5 tonne of sludge daily that requires off site disposal. The sludge contains high concentration of iron and manganese. This study determines the feasibility of reusing the groundwater treatment plant sludge (GWTPS) for heavy metal removal. This study focused on finding the optimum condition for zinc and copper removal through adsorption and precipitation process using GWTPS. The effectiveness of GWTPS as a recycled adsorbent was evaluated using batch study. Batch study were conducted by shaking 100 mL of samples in the orbital shaker at various initial pH of adsorbate, contact time, dosage of GWTPS and initial concentration of adsorbate. The initial and final concentration of heavy metal residue was measured using atomic absorption spectrophotometer (AAS). The optimum pH for both heavy metal removal was found to be between pH 2 and pH 2.5. Approximately 2000 mg/L dosage of GWTPS was required to remove Zn(II) and Cu(II) by adsorption, while higher dosage of 2000 mg/L to 8000 mg/L was required for precipitation to remove metal effectively from solution. The results indicated that 100% of Zn(II) and Cu(II) was removed at initial concentration of 10 mg/L and 65 mg/L of Zn(II) and Cu(II), respectively. At initial concentration of Zn(II) and Cu(II) of 100 mg/L, approximately 19% and 25% of Zn(II) and Cu(II) was removed from solution, respectively. The optimum adsorption contact time varied from 75 to 180 min for removal by adsorption, while contact time varied from 90 to 480 min for removal by precipitation, depending on the initial concentration of adsorbate.