Theme: 02. Assessing Remediation Effectiveness

Topic Area: 02h. Optimizing Remedial Systems

Formatted Title:

Microbial and Inorganic Fouling Control in Groundwater Extraction and Treatment: Pilot Studies of Agents’ Efficacy and Fate

Background/Objectives:

Microbial and inorganic fouling can pose major challenges in operations of groundwater remediation system extraction and treatment. Pipeline and unit operations microbial and inorganic fouling can lead to process upsets through reduced extraction rates, system fouling, reduced operating time, and increased maintenance costs. Extraction and discharge conditions may provide scenarios under which it is advantageous to consider treatment options that reduce disinfection byproduct formation, are effective through non-oxidative pathways, mitigate inorganic deposition, and are effective in pre-treatment or early treatment stages.

Approach/Activities:

Two pilot tests were conducted to determine the efficacy and fate of two biological control agents (non-oxidizing and oxidizing) and five inorganic deposit control agents. Pilot tests included field- and laboratory-scale analysis. The field study included a biocide demand analysis and a deposit control study from two aquifer units with differing properties (microbial communities, ORP, and inorganic compounds). The laboratory study investigated the likely deposition of the subject reagents in the following treatment operations: oxidant media filters, and granular activated carbon filters as well as reagent UVT interferences. The two biological control agents included: Tetrakis (hydroxymethyl) phosphonium sulfate (THPS – non-oxidative) and peracetic acid (PAA - oxidizing). PAA is a widely used biocide seeing expanding application in various markets as an alternative to common inexpensive halogen-bearing options. THPS is widely applied in remedial and oilfield applications, where less expensive oxidizing biocides are ineffective due to certain water quality parameters. The five deposit control agents included: Ethylenediaminetetraacetic acid (EDTA), citric acid, a terpolymer, Etidronic acid (HEDP), and sodium metasilicate.

Results/Lessons Learned:

Results of the pilot tests for the biocides provided insights into the differing microbial control efficacies, demand in differing groundwater conditions, and fate in groundwater treatment unit processes. Differences in microbial community control between PAA and THPS were recorded, with strong correlations in residual concentrations of the subject reagents. Demand of the subject reagents in differing groundwater conditions was recorded, with high ORP/inorganic groundwater increasing PAA demand while THPS was insensitive. Results from the deposit control agents provided insights into chelation/complexation with the oxidative biocide PAA, efficacy in reducing inorganic oxidation from the biocide PAA, and fate in groundwater treatment unit processes. The deposit control reagents showed differing chelation/complexation responses and removal responses in oxidant media and carbon filters. The results of the pilot studies can assist designers and engineers that are investigating methods in mitigating microbial fouling and inorganic deposit formation in groundwater extraction and treatment cases.

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Brad Horn