Dr. Joan Rose on panel for Congressional hearing examining public health issues related to U.S. wastewater treatment
WASHINGTON, D.C. — State and local water management officials along with wastewater management and pubic health experts, including Water Quality & Health Council chair Dr. Joan Rose, the Homer Nowlin Chair in Water Research at Michigan State University, testified at a Capitol Hill hearing on wastewater “blending.” The hearing, held April 13 before the House Water Resources and Environment Subcommittee, addressed public health and environmental issues regarding blending and its legality under the Clean Water Act (CWA). Testimony was heard about the inconsistencies and ambiguities in the conditions necessary to obtain blending permits in states across the country, which stems in large part from the lack of any final ruling by the U.S. Environmental Protection Agency (EPA) on the issue.
Blending is a method that has been used by some wastewater treatment plants since the 1970’s to address excess wet weather flows resulting from heavy rain or snow melts. This excess flow is diverted around the secondary, or biological, treatment system and recombined with the wastewater that has been treated before being discharged. The goal is a blended wastewater stream in a well-designed and operated treatment facility that meets secondary treatment standards and all relevant water standards.
Blending permits are issued by some states that require wastewater treatment plants to meet the relevant CWA standards before the plants discharge blended wastewater into a river or lake. Yet in other regions of the nation, states cannot issue permits that allow blending because the regional office of the EPA exercises a veto over the permit. The lack of uniform blending rules across the country has created considerable confusion as to when and where blending is legal is not.
The EPA issued a preliminary guideline in November 2003 that would allow authorities to release a blend of fully treated and partially treated sewage during peak flows. Yet the agency has delayed issuing final guidelines, which has only added to the difficulty in discerning the issue. As a result there is considerable eagerness for the EPA to issue final guidelines that finally provide national, uniform regulations.
According to Rep. John J. Duncan, Jr. (R-TN), Chairman of the House Water Resources and Environment Subcommittee, a balanced discussion on issues of when blending is appropriate and when it is not is needed to assure that public health is protected.
“We are misleading the public if we say that blending protects public health, relative to treating our sewage flows,” Dr. Rose testified. “We are adding back a larger concentration of contaminants from the untreated or partially treated flow and we are reducing the efficiency of the treatment.”
Dr. Rose stated that additional monitoring data was necessary to ensure that decisions made regarding wastewater infrastructure investments were based on water quality and health protection.
Wastewater Blending & Secondary Treatment
Municipal wastewater collection systems gather domestic sewage and additional wastewater from homes and send it to wastewater treatment plants for treatment and disposal. As a result, wastewater treatment systems must be properly designed to handle the volume of wastewater received, an essential component to public health and environmental protection.
Under the CWA, publicly owned wastewater treatment plants must meet a technology-based standard referred to as “secondary treatment.” Discharges from the plant must:
- Adhere to specific seven day and 30-day average effluent concentration limitations for total suspended solids (TSS) and biochemical oxygen demand (BOD);
- Reduce TSS and BOD by 85 percent (30-day average); and
- Maintain a neutral PH.
EPA regulations do not mandate specific treatment processes to meet secondary treatment and water quality standards. Therefore, many wastewater treatment plants use a combination of clarification, biological processes and chemical disinfection to achieve secondary treatment and meet water quality standards.
Physical removal through primary and secondary treatment and filtration are the most common way to reduce the parasitic risk for both Cryptosporidium and Giardia parasites, according to Dr. Rose.
“Primary treatment removes approximately 50 percent of the parasites in sewage. That is not good enough to protect public health,” Dr. Rose testified. “In secondary aerobic wastewater treatment, several specific studies including my own show that parasites Cryptosporidium and Giardia were reduced 92 to 99.9 percent.”
Analyzing Wastewater Blending Data
Unfortunately, very little data exists regarding the number of pathogens that would be found in sewage effluents if blending took place. Dr. Rose testified that she took a mathematical approach and examined the concentrations that might exist in blended effluents compared to fully treated effluents.
First, Rose used real monitoring data on average concentrations of viruses and parasites found in untreated, primary treated and secondary treated wastewater. To preserve the model’s integrity, Dr. Rose adjusted it to incorporate an example of a facility treatment design and blending practices along with human probabilities to infection based on a person swimming in proximity to discharge.
The following summarizes Dr. Rose’s findings:
- More than 99 percent of the loading of pathogenic viruses and protozoa resulted from the untreated/partially treated portion of the blended effluent. Risks associated with swimming in waters receiving blended flows were 100 times greater than fully treated wastewater for viruses.
- There were 13 times more viruses in primary treatment than secondary, four times more Cryptosporidium cysts in primary treatment than secondary and 4.8 times more Giardia cysts in primary treatment than secondary.
- Data from the Milwaukee wastewater treatment plant showed that Giardia cysts were elevated in blended effluent compared to water that was not blended.
Disinfection of wastewater with chlorine is critical to controlling viruses and bacteria, Dr. Rose stated. However, she added that Cryptosporidium is resistant to chlorination, with Giardia also shown to resist chlorine-based disinfection. Consequently, Rose’s conclusion in her Congressional testimony was that use of science-based risk assessment methods for addressing contaminants in water by the EPA is an appropriate approach toward developing rules that will ultimately protect public health.
“The wastewater treatment industry is one of the unsung heroes of public health, Rose confirmed. “EPA needs to develop treatment standards and ambient water quality criteria for the full range of pathogens that threaten public health. We need to examine advances in treatment, better disinfection and emerging contaminants.”
The views expressed by Dr. Rose in her testimony before the United States Congress are those of the speaker only and do not constitute those of the Water Quality and Health Council or the Chlorine Chemistry Division of the American Chemistry Council.