PAA as a Pretreatment Alternative to Free Chlorine in a DBP Sensitive Application
Last Modified: Nov 07, 2018
- Aron Griffin, Jim DeWolfe - Hazen and Sawyer
- Sarah Restivo, Mark Stoner - Municipal Authority of Westmoreland County
The McKeesport WTP is a 10 MGD conventional WTP, owned by the Municipal Authority of Westmoreland County (MAWC) and located in McKeesport, PA. MAWC has initiated several treatment measures to decrease levels of DBPs, including implementation of tank aeration, but has still realized an upward trend in DBP concentrations. This trend has been attributed to changing source water quality, namely increased TOC concentrations and higher temperatures, two issues common with many municipalities. To combat this, MAWC is evaluating the use of peracetic acid (PAA) as a pre-oxidant in place of chlorine. PAA is a strong oxidant that exists in equilibrium with acetic acid, hydrogen peroxide, and water, and has been granted NSF 60 approval for water treatment. PAA has a higher oxidative potential than chlorine and does not form significant amounts of carcinogenic DBPs, primarily producing carboxylic acids which are largely benign. Unlike chlorine, PAA does not result in a consistent residual and therefore is only suitable for pre-oxidation, not as a final disinfectant.
A series of jar tests were performed to mimic the treatment processes at McKeesport WTP and evaluate the use of PAA vs pre-chlorine and sodium permanganate (NaMnO4). Initial tests determined the optimum oxidant dose for each oxidant based on raw water oxidant demand. These doses were then used to evaluate the treatment efficacy of each pre-oxidant based on reductions in turbidity, TOC, and UV-254. A simulated distribution system test was also performed to determine the impact of oxidant choice on DBP formation.
Use of PAA and NaMnO4 resulted in improved treatment performance when compared to pre-chlorine. Each pre-oxidant showed comparable reductions in turbidity, while PAA and NaMnO4 resulted in increased removal of TOC and increased UV-254 absorbance. Use of PAA and NaMnO4 resulted in significant decreases in both THMs and HAAs in the simulated distribution system test when compared to pre-chlorine. With PAA, average THM and HAA levels dropped 41% and 56% respectively, while with use of NaMnO4, THM and HAA levels were reduced by 30% and 58% respectively.
Based on the results of the jar tests, MAWC desires to proceed with pilot scale testing required for PADEP approval. Ongoing discussions with both Regional and Central PADEP offices will ensure development of a pilot plan in coordination with regulatory requirements. Initial cost estimates have found that use of PAA, in the case of MAWC, could result in significant cost savings (>50%) when compared to NaMnO4. Pending further testing, this effort may result in one of the first applications of PAA at a WTP in the country. With mounting concern over DBPs, PAA represents one potential strategy to reduce the water industry’s reliance on chlorine. Use of alternative oxidants will minimize the unintended formation of harmful chemical compounds during the treatment process and result in improvements to both human and environmental health.
For more information, please contact the author at email@example.com.
Hear about new publications with our email newsletter
Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.