Characterization of Alum Sludge from Surabaya Water Treatment Plant, Indonesia

Abstract

A conventional water treatment plant (WTP) typically involves coagulation-flocculation processes to remove suspended particles and colloids in raw water. The process generates a large volume of alum sludge with high aluminum content, which is discharged into a river with improper treatment. The sludge may cause a potential risk to human health, and disrupt the life of river biota. The aims of this study were to determine the physical and chemical characteristics of alum sludge from Surabaya WTP, and to compare them with those of alum sludge from other plants in Indonesia and developing countries. The alum sludge sample was obtained from the Surabaya WTP in Indonesia. The results showed that the alum sludge had a pH value of 7.47, volatile solids of 12,696 mg/L, total suspended solids of 12,511 mg/L, chemical oxygen demand (COD) 9666.7 mg/L, biochemical oxygen demand (BOD) 1082.5 mg/L, and sludge volume index 114.18 mL/g. The sludge had high aluminum and iron concentrations. The aluminum content of the sludge was 1194 mg/L, iron 515 mg/L, chromium 0.217 mg/L, and copper 0.559 mg/L. Having a BOD/COD ratio of 0.1, the alum sludge contained high level of nonbiodegradable organic matter.

Recovery of Alum Sludge by using Membrane-Based Electrochemical Process

“…Reactions in the anode compartment: is highly soluble in the cathode compartment (Liu et al, 2010). Therefore, in the case of CEM application, alum was recovered as Al(OH) 3, and soluble Al(OH) 4 ion in the cathode compartments in all electrode distance set-up.…”

“…9, with aluminum hydride as the recovered Al products (Adhikari, 2008). Therefore, in the case of AEM application, alum was recovered in the cathode compartment as as Al(OH) 3, soluble Al(OH) 4 and AlH 3 precipitates. The formation of precipitates may also release protons, causing a decrease of pH.…”

“…6). In addition, the form of recovered aluminum as Al(OH) 4 complex compound was obtained as the solution in the cathode compartment after 10-hour electrochemical process (t-10), i.e., 3.23% and 50.13% applying CEM with 0.2 cm and 1 cm electrode distance, respectively. The aluminum recovery in the electrochemical process applying AEM at both electrode distance of 0.2 cm and 1 cm was determined by the percentage of aluminum hydroxide and aluminum hydride deposited at the cathode, i.e., 7.96% and 24.95%, respectively (Fig.…”

“…In the electrochemical process applying CEM with 1 cm electrode distance shows that the recovery of aluminum was mostly formed as Al(OH) 4 because the pH of the electrolyte in the cathode compartment was up to 11.67 at the end of the process. Aluminum recovery as hydroxide precipitate at the cathode had a small portion due to the formation of the Al(OH) 4 ions that lead to the redissolved aluminum (Liu et al, 2010). The possible formation of aluminum hydride may also lead to redissolved alumnium as the Al(OH) 4 ions at higher pH (Adhikari, 2008).…”

“…and inorganic ions (such as calcium, silica, etc. ), which then act as impurities (Barakwan et al, 2019). High concentration of organic impurities in the recovered alum coagulant may lead to the high formation potential of trihalomethane during the final chlorination stage of further water treatment (Sarkar et al, 2010;Keeley et al, 2016).…”