Recovery of coagulants via acid treatment in potabilization sludges and their reuse in raw and urban wastewaters

Conventional water treatment plants have used aluminum-based coagulant solutions to remove colloidal substances and other suspended particles from raw water. During this process, a byproduct known as water treatment sludge (WTS) is generated that is typically discharged without prior treatment, causing serious environmental problems for surface waters and nearby ecosystems. Studies have been conducted to evaluate its potential reuse in various processes such as agriculture, construction material manufacturing, pollutant absorption, and its reuse as a coagulant. This study evaluated the recovery of aluminum via acid treatment in WTS from a drinking water treatment plant (DWTP) that supplies water for a population of 413,484 inhabitants, using different pH levels and mixing speeds. The efficiency of the recovered coagulants was evaluated for the removal of color and turbidity in raw and wastewater. The main results showed a maximum aluminum recovery at a pH of 1.5 with values up to 810.5 mg Al/L, with pH being the most influential factor in the process. The removal of color and turbidity of 95.84 and 97.06% were achieved in wastewater and 69.78 and 69.73% in raw water, respectively. The recovered coagulant could be used in DWTPs and in chemically enhanced primary treatment for sewage treatment.