Combined chlorine is effective in reducing fecal coliforms to what level?

Combined chlorine, which includes chloramines formed when chlorine reacts with ammonia in water, is effective for disinfection purposes, specifically in reducing fecal coliform levels in wastewater. Research and guidelines from health and environmental authorities indicate that combined chlorine can sustainably reduce fecal coliform concentrations to levels around 200 mg/L or less, which is essential for meeting certain water quality standards before discharge or reuse.

The effectiveness of combined chlorine is influenced by factors such as concentration, contact time, and the presence of other water constituents. While lower concentrations of chloramines may have disinfection potential, achieving substantial reductions in fecal coliform levels typically necessitates maintaining the combined chlorine concentration around the 200 mg/L threshold to ensure adequate efficacy without excessive chemical residuals that could harm aquatic life or violate regulatory limits.

Understanding this threshold is vital for water treatment practices and wastewater management, as it aligns with public health goals to minimize pathogens in water systems.