REUSE OF ALUM SLUDGE FOR PHOSPHORUS REMOVAL FROM MUNICIPAL WASTEWATER

Abstract

Municipal wastewater (MWW) is mostly rich in nutrients such as phosphorus (P), nitrites (NO2-), nitrates (NO32-) and ammonium (NH4+) etc. When discharged into water bodies, MWW cause algal growth resulting into eutrophication leading to taste and odor problems in drinking water supplies. P can be removed by chemical and biological processes but such processes are either costly or time consuming. Potable water supply facilities use alum for turbidity removal. The settled and dewatered alum sludge from water treatment facilities can effectively be used to remove P from MWW. In this study Orthophosphorus (OP) and Condensed phosphorus (CP) are taken as model pollutants as they were commonly found in MWW. Mojor objective of this work was to evaluate the effectiveness of waste alum sludge from various sources to remove P from MWW at optimum dose, mixing time and pH. Alum sludge was collected from two water treatment plants namely Rawal water treatment plant and Simli water treatment plant. Batch experiments were performed to determine P removal under equilibrium conditions i.e. sludge mass, contact time, pH and initial concentration. The maximum adsorption capacity (Qo) for Simli sludge was found to be 4.5 mg/g at 12g/L dose and 90 min contact time at 25+2oC. For Rawal sludge Qo was 1.53 mg/g at 30g/L dose and 80 contact time at 25+2oC. Experimental data were fitted on two adsorption isotherms models i.e. Langmuir and Freundlich adsorption isotherm to evaluate the P removal phenomenon by alum sludge. Langmuir adsorption isotherm was best fit (R2=0.99) while experimental data were less favorably fitted to Freundlich isotherm model. Results showed that pH significantly affect adsorption capacity and better removal is achieved in acidic range (pH 4.0-5.5). This study concluded that P removal was achieved by waste alum sludge through this cost effective and resource reuse method. Thus, reducing environmental hazards and burden of large quantities of waste alum sludge.