CHALLENGES OF ALUM RECOVERY FROM DRINKING WATER TREATMENT SLUDGE USING ELECTROLYSIS METHOD

Aluminum sulfate was used as coagulant in the coagulation process in drinking water treatment plant (DWTP) to remove various types of contaminants from the raw water. Acidification was applied for alum recovery from sludge, but it was a nonselective process. It was followed by an electrolysis to separate the aluminum from impurities. This study aims to evaluate the efficiency and challenges of the electrolysis in the alum coagulant recovery from drinking water treatment sludge (DWTS). The dried DWTS was acidified using sulfuric acid at pH 3 and then separated in centrifugation to get the acidified alum sludge solution. The electrolysis was conducted using carbon (C)/silver (Ag), platinum (Pt)/platinum (Pt), and platinum (Pt)/stainless stell (SS A304) electrodes with current density of 25, 29.17, and 12.5 mA/cm², respectively. The electrolysis was performed in a batch recirculation reactor without membrane, using cation exchange membrane (CEM), and anion exchange membrane (AEM). Chemical oxygen demand (COD) value was measured using titrimetric method. The metals (Al, Fe, Mn, Zn, Pb, Cu, and Cr) in the deposited matter at the cathode were weighed and analyzed by Inductively Coupled Plasma (ICP). The results showed that the use of CEM in the electrolysis with Pt/SS A304 electrodes increased the alum recovery up to 67.56% that was pure of organic contaminants. The challenges in alum coagulant recovery from DWTS using electrolysis method were the differences of the raw water quality during wet and dry seasons, the appropriate electrical current density, the electrode materials, the potential value at the anode and cathode, and the use of the ion exchange membrane in the electrolysis.