Reducing residual aluminum with carbon dioxide in drinking water treatment

This study evaluates the performance of carbon dioxide (CO 2 ) as a pH regulator for controlling residual aluminum (Al) in drinking water treated with polyaluminum chloride (PAC). Experimental results demonstrate that CO 2 dosing effectively lowers pH to the optimal range of 6.5–7.1, leading to a marked reduction in residual Al across different temperatures (15–25 ℃) and PAC dosages (10–60 mg/L). At 20 ℃, residual Al decreased from ≥ 0.30 mg/L under alkaline conditions (pH 8.35) to < 0.05 mg/L when adjusted with CO 2 to near-neutral pH. Turbidity removal also improved significantly, with minimum values reduced by more than 50 % compared to unadjusted conditions, and optimal performance achieved at 30–40 mg/L PAC. Compared with sulfuric acid, CO 2 -mediated pH regulation consistently achieved lower residual Al concentrations while minimizing sludge production and avoiding the introduction of sulfate ions. These findings highlight that CO 2 offers a safe, cost-effective, and environmentally sustainable alternative for pH adjustment in full-scale water treatment processes, ensuring improved water quality and reduced health risks associated with aluminum exposure.