No abstract

Nitrification can increase levels of soluble lead in potable water by reducing pH. The magnitude of the pH drop depends on the initial alkalinity and extent of nitrification. At 100 mg/L alkalinity as CaCO3, complete nitrification did not significantly decrease pH (pH stayed >7.5) or increase lead contamination of water for lead pipe, but at 15 mg/L alkalinity, nitrification decreased the pH by 1.5 units (pH reduced to <6.5) and increased soluble lead contamination by 65 times. Lower pH values from nitrification also leached 45% more lead and 81% more zinc from leaded brass connected to PVC pipes relative to the same situation for copper pipes. Particulate lead leaching was high but did not vary dependent on nitrification. While nitrification also produces nitrite and nitrate and reduces inorganic carbon and dissolved oxygen, these factors did not significantly impact lead leaching in this work.

Bench‐scale experiments determined the germicidal effects of varying dosages of polychromatic ultraviolet (UV) radiation on oocysts of Cryptosporidium parvum. C. parvum oocysts suspended in treated surface water were irradiated with polychromatic light emitted by either a medium‐pressure, continuous‐wave UV lamp or a pulsed‐UV lamp then assayed with human cell culture techniques. Experiments conducted using pulsed‐UV doses of ≥ 16 mJ/cm2 provided > 2‐log inactivation of suspended oocysts of C. parvum. Experiments at lower UV dosages established a dose‐response relationship with both the medium‐pressure and pulsed‐UV lamps. When disinfection results from both light sources were compared on an equivalent dosage basis, no statistical difference in disinfection power was found between the medium‐pressure and pulsed‐UV lamps. Results from both lamps showed that UV doses as low as 7.5 and 11 mJ/cm2 provided inactivation of infectious oocysts of C. parvum at rates of 1 log (90%) and 2 log (99%), respectively. The authors also examined UV disinfection of heterotrophic bacteria and Escherichia coli. They found the response of heterotrophic bacteria to be statistically different from that of C. parvum, whereas E. coli's response to UV light did not statistically differ from that of C. parvum. This suggests that E. coli may be a surrogate organism for C. parvum disinfection provided by UV technologies.

in simulated distribution systems (annular reactors). The annular reactors were placed in two parallel trains at the effluent of a full-scale treatment plant: one train received chlorinated water, and the other received chloraminated water. Each train was composed of two annular reactors in series. The upstream annular reactor received water with a disinfectant residual, and the downstream annular reactor received dechlorinated or dechloraminated water. In warm water (17-22 o C) and in the absence of a disinfectant residual, the dihalogenated HAA species degraded in the downstream annular reactors of both trains (by ~75% in the chlorinated train and ~60% in the chloraminated train). These HAAs were not degraded, however, in cold water (12-14 o C) or in the presence of a disinfectant residual. The THMs and the trihalogenated HAAs were not observed to degrade under the experimental conditions (i.e., 12-h retention time in each annular reactor).