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

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 s^-1 (1.7 ft s^-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 s^-1 (1 ft s^-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.