For several years, NASSCO has worked with independent research groups to better understand potential health concerns regarding styrene used in the cured-in-place pipe lining process.
The first three phases of research focused on emissions from the cure process, while the primary objective of the Phase 4 study was to quantify the effects of residual styrene in cure water discharges from CIPP installations on secondary biological treatment processes typical of publicly owned treatment works in the continental U.S. The focus was on potential inhibition of biochemical oxygen demand removal and ammonia-nitrogen removal (nitrification).
The Phase 4 study included the following elements:
Literature review
A metadata review was conducted of published information about CIPP styrene-laden cure water causing bioinhibition at POTWs. More than 200 publications were reviewed; yet none of the data specifically addressed the study issue of concern.
Published information documented that styrene does not dissolve well into the water column and is easily volatilized from it, with odor noticeable at concentrations as low as 0.73 mg/L (compared to air where the odor threshold is approximately 100 parts per billion). Consequently, styrene half-life concentrations are suggested to be within a few hours of introduction to the water column. Finally, published information suggested that almost complete styrene removal was achieved following styrene adaptation of the treatment bacteria.
Questionnaire
A survey was developed to determine current perceptions and concerns about styrene resins and the CIPP process, particularly as it pertains to cure water discharges to POTWs. The questionnaire results suggested no direct impact of CIPP cure water discharge on POTWs, though there was anecdotal information suggesting isolated causal incidents.
Laboratory treatability study
Batch respirometry testing following OECD Method 209 (modified) was performed to assess the impact of different styrene concentrations on biomasses from three different advanced biological treatment plants with active nitrification, since these bacteria were anticipated to be most sensitive to the acute effects of styrene in the waste flow. The goal of the testing was to quantify: 1) the No Observed Effect Concentration, which was the styrene concentration threshold that had no negative effect on the treatment bacteria; and 2) Effect Concentrations as an extrapolated percentage of the treatment bacteria negatively affected, with EC50 (50% of bacteria negatively affected) reported.
Treatability study results
- NOEC and EC50: The NOEC for styrene was determined to be less than 2.3 mg/L for the three biomasses tested, noting that this does not account for mitigative effects of return activated sludge or continuous flow operations. The study quantified impacts on nitrification at styrene concentrations between 2.3 mg/L and 12 mg/L, while impacts on BOD removal occurred between 12 mg/L and 64 mg/L. The plotted testing data suggested the EC50 as greater than 105 mg/L. The range of NOEC and ECx provide quantifiable thresholds for risk evaluation and mitigation of cure water discharges to POTWs.
- Dilution and Resilience: Adjustments to recycled treatment process flows, such as increasing RAS flow, can enhance biomass resilience to styrene inhibition. The treatment plant recycle and treatment process residence times should be evaluated to determine if the 2.3 mg/L styrene concentration threshold is too conservative for a specific POTW.
Recommendations
- Styrene Cure Water Discharge Calculator. Using the NOEC as a conservative threshold, create a styrene concentration calculator for CIPP cure water discharges. This calculator is under development and will be made available for use at nassco.org.
- Styrene Cure Water Database. Develop a database of styrene concentrations in cure water through sampling programs and voluntary data sharing from installers and public agencies. NASSCO intends to make this information publicly available as anonymously sourced information.
For the full report and to learn more about styrene safety, visit nassco.org/safety.
About the Author
Sheila Joy is executive director of NASSCO. She can be reached at director@nassco.org.
