Taking the Broad View on Disinfection Practice
The public health and environmental benefits of practicing water and wastewater disinfection in the United States are very clear. Historically, disinfection was synonymous with chlorination for both water and wastewater treatment systems. During this time, the disinfectant of choice was gaseous chlorine. This disinfectant was easy to dose and control, did an effective job and greatly improved public health. Over time, however, many laws, regulations, and other issues have influenced water and wastewater disinfection practice in the United States, resulting in a new analysis of current and proposed methods.
The Clean Water Act (1972 and 1977) established the basis for regulating pollutant discharges into the waters of the United States and surface water quality. This act has been modified by numerous revisions and amendments since it was enacted in 1972. The National Pollutant Discharge Elimination System (NPDES) permit program (authorized by the Clean Water Act) regulates point sources that discharge pollutants into waters of the United States in an attempt to control water pollution. Disinfection of treated sanitary wastewater and stormwater (through Combined Sewer Overflows) is a key unit process used by the wastewater treatment industry to meet NPDES permit requirements and protect the receiving water, which also protects downstream drinking water treatment plant intakes from harmful pollutants.
The implementation of the Risk Management Plan (RMP) by the USEPA for the storage of hazardous chemicals (June 1999) and the Occupational Safety and Health Administration (OSHA) Process Safety Management Standard of Highly Hazardous Chemicals, Explosives and Blasting Agents (29 CFR 1910.119) have had a significant effect on disinfection practice in the United States relating to the water and wastewater disinfection industry in the United States. As a result of these regulations, a large percentage of water and wastewater disinfection in this country has now been changed from gaseous chlorine to some form of sodium hypochlorite or other disinfectant. Two articles in this issue, by Birkel et al. and Jones et al., describe the experiences of wastewater treatment plants that have decided to switch to hypochlorite.
The Stage 1 Disinfection and Disinfectant By Product Rule was promulgated in 1998. This regulation set limits for allowable levels of disinfectant by products (Trihalomethanes and Haloacetic acids) in drinking water treatment, storage and distribution systems. As a result of this regulation many drinking water disinfection systems are altering their disinfection practice (e.g., changing from free chlorine to chloramines). Wastewater collection and treatment systems have also begun to use non-chemical means of disinfection (e.g., Ultraviolet light) as their disinfection system of choice in order to avoid producing disinfection byproducts.
Many emerging disinfection technologies are available to engineers when designing and improving wastewater treatment plants. Some of these technologies are taken directly from drinking water applications, some are new developments and others are combinations of the conventional physical or chemical unit processes. The design and operation of emerging disinfection technologies can be quite challenging as there may not be significant information available to assist utility management staff with the operation and maintenance of these systems. Operators who have emerging systems need to work closely with the respective vendors to determine the appropriate operating conditions.
On September 11, 2001, the possibility of an international terrorist attack within the continental United States became a reality. The most spectacular and horrific terrorist attacks in the United States have been directed at constructed facilities and infrastructure noted for their high human populations (e.g., the World Trade Center in New York City, the Pentagon, the Alfred P. Murrah Federal Building in Oklahoma City). However, these are not the only high-risk facilities that remain vulnerable. Among the most critical infrastructure areas needing protection are potable water treatment, storage and distribution systems and wastewater collection and treatment systems. The aftermath of hurricane Katrina allowed the country to begin to understand the impact on a community (e.g., businesses, hospitals, etc.) when they could not use the drinking water or wastewater system.
Congress included a drinking water component in PL 107-188, the “Public Health Security and Bioterrorism Preparedness and Response Act”, passed in June 2002. This legislation required drinking water systems serving more than 3,300 people to conduct a vulnerability assessment to help them determine their vulnerability to various threats, including intentional contamination. In addition, this legislation required utilities to prepare an emergency response plan, or revise an existing plan, incorporating the results of the vulnerability assessment. As a result of this drinking water regulation, many wastewater treatment facilities also performed vulnerability assessments and updated their emergency response plans.
Recent terrorist attacks in Iraq have combined explosives and chlorine cylinders. These attacks have resulted in a heightened awareness of the placement of any chlorine cylinders used for water or wastewater disinfection. Many suppliers have begun to take an inventory of all chlorine cylinders in use by their customers. Because of the security risks many utilities may stop using 150 pound chlorine cylinders for their chlorination processes. One article in this issue, by Kroll et al., takes a look at the drawbacks associated with switching from free chlorine.
Water and wastewater treatment plant designers and operators must consider all of the potential impacts when planning the operational philosophy for these critical infrastructure systems. Sometimes, one must look beyond daily processes and operations in an effort to envision oncoming regulations and occurrences that may impact the design and operation of drinking water and wastewater disinfection systems in the future.
Leonard Casson, Issue Editor
Department of Civil and Environmental Engineering, University of Pittsburgh