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43 monooxygenases (SIDMO), specifically propane SDIMOs and THF SDIMOs thought to be responsible for catalyzing the degradation of 1,4-dioxane (Li et al., 2019).
Applying cometabolism to biologically active filtration (BAF) is an attractive, low cost option for carbon-based potable reuse plants and even drinking water plants employing biofiltration. THF and propane were tested as suitable cometabolites for the removal of 1,4-dioxane in BAFs operated at an indirect potable reuse (IRP) facility.
Materials and methods
The BAF pilot received water from an upstream IPR facility. The water was secondary clarifier effluent from a 5-stage bardenpho wastewater treatment plant that had then undergone enhanced coagulation, flocculation, sedimentation, and ozonation. The BAF pilot contained 4 filters operated in parallel and at a constant empty bed contact time of 10 min. Each filter was 5 ft of exhausted carbon (Calgon 816) atop 1 foot of common filter sand. Each filter backwashed when the turbidity exceeds 0.15 NTU or 3m of head loss across the filter.
1,4-Dioxane and THF were measured using EPA 522. Propane was analyzed using a modified RSK 175 method by Eurofins Analytical.
Results and discussion
The first cometabolite tested was THF. For the first portion of the study (Days 0-321), the 1,4-dioxane dose was 10 µg/L, which was subsequently decreased to 5 µg/L on day 218. One BAF during this portion of the study was used as a control, receiving no cometabolite. One BAF received a THF dose was 50 µg/L. Consistent removal of 1,4-dioxane averaging 45% was observed during this period at both concentrations of 1,4-dioxane. It is worth noting the THF dose took some time to optimize, and was started low before increasing to 50 µg/L. THF was completely removed to below the method detection limit of 0.06 µg/L throughout the entire study. The control BAF saw an average of 20%
removal of 1,4-dioxane during this period. Figure 1.1 shows the percent removal of 1,4-dioxane compared to the dose of THF during the first portion of this experiment. Figure 1.2 compares the percent removals of 1,4-dioxane in the control BAF and the THF BAF.
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Figure 1.1. The addition of THF resulted in the cometabolic removal of 1,4-dioxane in BAF during days 0-321. The solid horizontal line denotes the change in influent 1,4-dioxane concentrations from 10 µg/L to 5 µg/L. Figure 1.2.
The percent removal of the control BAF and the THF BAF are compared.
The second cometabolite tested was propane. During this portion of the experiment, (Days 328-839) propane was fed to the previously control BAF and the THF BAF was used for comparison. Propane was fed at a range of doses, from 1 mg/L to 4 mg/L. The THF dose was decreased to 25 µg/L. The 1,4-dioxane dose was initially 5 µg/L, and was then decreased to 1 µg/L on day 601. Finally, the supplementation of dioxane was stopped on day 727, and the background concentrations of 1,4-dioxane in the source water was tested. The concentration of 1,4-1,4-dioxane was typically 0.3-0.4 µg/L during this phase.
The THF BAF, continued to remove on average 45% of the 1,4-dioxane over the entire portion of this phase. When THF was not added, usually do to a chemical feed error, no 1,4-dioxane was removed.
The SDIMO that THF induce do not remain active in the BAF without the cometabolite present. This is surprising after the long period (multiple years) of sustained 1,4-dioxane removal this BAF demonstrated. Figure 2 shows the dose of THF compared to the percent removal of 1,4-dioxane during this portion of the experiment.
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Figure 2. The addition of THF resulted in the cometabolic removal of 1,4-dioxane in BAF during days 328-790. Days 790-850 are included to show the loss of removal without cometabolite removal. The solid horizontal line denotes the change in influent 1,4-dioxane concentrations from 5 µg/L to 1 µg/L. The dashed line denotes the change in influent 1,4-dioxane concentrations from 1 µg/L to 0.3 µg/L.
The propane BAF removed 60% of 1,4-dioxane on average during days 601-833. Propane feed issues from days 328-601 showed either no removal of 1,4-dioxane or unsteady, small removals. Once the propane feed issues were resolved, the BAF removed 1,4-dioxane very well, sometimes even as high as 80% removal. Again, the 1,4-dioxane concentration began at 5 µg/L, was dropped to 1 µg/L, and finally 0.3-0.4 µg/L. Sustained removal of 1,4-dioxane was maintained during these changes. Similar to THF, propane was always removed to below the method detection limit, in this case 5 µg/L within the BAF. Also, similar to the THF BAF, 1,4-dioxane removal was not sustained if propane was not being fed. Figure 3 shows the dose of propane compared to the percent removal of 1,4-dioxane.
Figure 3. The addition of propane resulted in the cometabolic removal of 1,4-dioxane in BAF during days 328-790.
Days 790-850 are included to show the loss of removal without cometabolite removal. The solid horizontal line denotes the change in influent 1,4-dioxane concentrations from 5 µg/L to 1 µg/L. The dashed line denotes the change in influent 1,4-dioxane concentrations from 1 µg/L to 0.3 µg/L.
While both cometabolites show positive results, propane was chosen for installation at a full-scale 1 MGD IPR facility in Suffolk, VA. This includes the addition of propane to the feed for two full-scale BAFs with two others serving as controls. The propane feed system is now in startup, with preliminary full-scale data likely available at the time of the conference.
46 References
Cordone, L., Carlson, C., Plaehn, W., Shangraw, T. and Wilmoth, D. 2016. Case Study and Retrospective: Aerobic Fixed Film Biological Treatment Process for 1,4-Dioxane at the Lowry Landfill Superfund Site. Remediation Journal 27(1), 159-172.
Deng, D., Li, F. and Li, M. 2018. A Novel Propane Monooxygenase Initiating Degradation of 1,4-Dioxane by Mycobacterium dioxanotrophicus PH-06. Environmental Science & Technology Letters 5(2), 86-91.
DiGuiseppi, W., Walecka-Hutchison, C. and Hatton, J. 2016. 1,4-Dioxane Treatment Technologies. Remediation Journal 27(1), 71-92.
EPA 2014 Technical fact sheet: 1, 4‐Dioxane, Office of Solid Waste and Emergency Response US Environmental Protection Agency.
Li, F., Deng, D. and Li, M. 2019. Distinct catalytic behaviors between two 1, 4-dioxane-degrading monooxygenases:
kinetics, inhibition, and substrate range. Environmental science & technology 54(3), 1898-1908.
Lippincott, D. 2015. Bioaugmentation and Propane Biosparging for In Situ Biodegradation of 1,4-Dioxane. Groundwater Monitoring & Remediation 35(2), 81-92.
Mahendra, S., Petzold, C.J., Baidoo, E.E., Keasling, J.D. and Alvarez-Cohen, L. 2007. Identification of the intermediates of in vivo oxidation of 1 ,4-dioxane by monooxygenase-containing bacteria. Environ Sci Technol 41(21), 7330-7336.
Otto, M. and Nagaraja, S. 2007. Treatment technologies for 1, 4‐Dioxane: Fundamentals and field applications. Remediation Journal: The Journal of Environmental Cleanup Costs, Technologies & Techniques 17(3), 81-88.
Presenting Author
Hannah M.B. Stohr
Virginia Tech/Hampton Roads Sanitation District
Is the presenting author an IWA Young Water Professional? Y
Hannah is a third year PhD student at Virginia Tech doing research on indirect potable reuse with Hampton Roads Sanitation District. She received her Bachelor’s in Science in Chemical Engineering from the University of Kansas.
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