Committee Report: Disinfection at large and medium-size systems

As a followup to its surveys of 1979 and 1989, the Disinfection Systems Com mittee conducted a survey in 1998 of disinfection practices at large and me dium (i.e., those serving 10,000 or more people) systems using both surface water and groundwater supplies. Chlorine, either as gas or hypochlorite, r emained the predominant choice for primary disinfection. Moderate increases were seen in the use of alternative forms of chlorine such as chloramines, chlorine dioxide, and ozone. Based on the results of this survey, large an d medium systems appear well-prepared to meet the new Stage I disinfection by-product requirements, and many appear to be capable of meeting the propo sed Stage 2 requirements if they are implemented in their current form. The se systems also appear to be meeting existing Surface Water Treatment Rule (SWTR) and pending Interim Enhanced SWTR turbidity and disinfection C x T r equirements. But, based on data submitted by only about half of the respond ents, almost 10 percent may have to further enhance treatment to meet Stage 1 total organic carbon removal requirements.