Life cycle environmental impacts of alkaline regulator substitution in electroplating wastewater treatment

Physicochemical methods, which are essential for treating highly toxic industrial wastewater, remain underexplored in terms of emissions reduction compared to biological methods. This work examines two electroplating wastewater treatment processes: an old process using sodium hydroxide as the hydroxide ion source and a new process that partially substitutes sodium hydroxide with low-cost calcium hydroxide. Life cycle assessment results demonstrate that the substitution improves environmental performance across all but one impact categories. Significant reductions in the categories of ammonia nitrogen (55.7 %), chemical oxygen demand (54.6 %), and volatile organic compounds (62.4 %) are attributed to the use of key chemicals, offering a clear pathway for emissions reduction. However, reducing impacts in categories like global warming potential and primary energy demand is more challenging due to the balanced contribution of multiple inventory items. Field data highlight that calcium hydroxide not only reduces sodium hydroxide consumption but also decreases the use of other resources like sodium hypochlorite, activated carbon, and electricity, resulting in substantial environmental benefits. Among them, global warming potential is reduced from 15.3 kg CO₂ eq/ton of water to 11.7 kg CO₂ eq/ton of water, a decrease of 23.5 %. This study demonstrates the multifunctionality of chemicals like calcium hydroxide in improving treatment efficiency and reducing life cycle environmental impacts. It provides insights into advancing and optimizing industrial wastewater treatment processes.