Decontamination of Bacillus spores adhered to iron and cement-mortar drinking water infrastructure in a model system using disinfectants

摘要

Decontamination of Bacillus spores adhered to common drinking water infrastructure surfaces was evaluated using a variety of disinfectants. Corroded iron and cement-mortar lined iron represented the infrastructure surfaces, and were conditioned in a 23 m long, 15 cm diameter (75 ft long, 6 in diameter) pilot-scale drinking water distribution pipe system. Decontamination was evaluated using increased water velocity (flushing) alone at 0.5 m sec⁻¹ (1.7 ft sec⁻¹), as well as free chlorine (5 and 25 mg L⁻¹), monochloramine (25 mg L⁻¹), chlorine dioxide (5 and 25 mg L⁻¹), ozone (2.0 mg L⁻¹), peracetic acid 25 mg L⁻¹) and acidified nitrite (0.1 mol L⁻¹ at pH 2 and 3), all followed by flushing at 0.3 m sec⁻¹ (1 ft sec⁻¹). Flushing alone reduced the adhered spores by 0.5 and 2.0 log10 from iron and cement-mortar, respectively. Log10 reduction on corroded iron pipe wall coupons ranged from 1.0 to 2.9 at respective chlorine dioxide concentrations of 5 and 25 mg L⁻¹, although spores were undetectable on the iron surface during disinfection at 25 mg L^-1. Acidified nitrite (pH 2, 0.1 mol L⁻¹) yielded no detectable spores on the iron surface during the flushing phase after disinfection. Chlorine dioxide was the best performing disinfectant with >3.0 log10 removal from cement-mortar at 5 and 25 mg L^-1.The data show that free chlorine, monochloramine, ozone and chlorine dioxide followed by flushing can reduce adhered spores by >3.0 log10 on cement-mortar.