Formatted Title
Sustainable Bioremediation of 1,4-Dioxane Using Membrane Biofilm Reactors
Background/Objectives
1,4-Dioxane is a groundwater contaminant that is a growing concern and is commonly associated with chlorinated solvent plumes. Removal of 1,4-dioxane using traditional physical-chemical water treatment technologies can be difficult, and many existing groundwater pump and treat (P&T) systems are not equipped to remove chlorinated solvents and 1,4-dioxane. While advanced oxidation processes (AOPs) can reliably destroy 1,4-dioxane, other treatment methods are emerging – with bioremediation serving as a reliable, safe, sustainable, and economical alternative to AOPs. Bioreactors are an attractive option for retrofitting existing P&T systems when 1,4-dioxane treatment is required, or as a technology to incorporate into new construction. The focus of ESTCP project (ER22-7226) is the biodegradation of 1,4-dioxane using propane as a primary substrate in an aerobic membrane biofilm reactor (MBfR). The objectives of this project are to demonstrate the effectiveness of the technology to destroy 1,4-dioxane in groundwater to below relevant regulatory standards and compare MBfRs to AOPs on the basis of economics and sustainability.
Approach/Activities
This project combines two previously demonstrated remedial technologies: propane-mediated biodegradation of 1,4-dioxane and MBfRs. Biodegradation of 1,4-dioxane typically occurs via aerobic pathways. Engineered bioremediation approaches have been implemented at the pilot-scale and full-scale and have commonly utilized propane as a primary substrate. Using gaseous species to foster biologically mediated reactions in conventional engineered bioreactors can be challenging, specifically related to achieving adequate gas transfer. An MBfR eliminates this challenge by utilizing pressure-controlled gas-transfer membranes by providing gaseous substrate directly to the biofilm via membrane diffusion. Gas supply to the biofilm is driven by the concentration gradients induced via biochemical demand, making the MBfR a self-regulating system. The first phase of this project initiates with bench-scale testing to configure commercially available membranes for 1,4-dioxane biological treatment. A field demonstration will then be conducted at Arnold Air Force Base, in Tennessee, to gather the data required to take this technology to full scale.
Results/Lessons Learned
Work to date has focused on quantification of oxygen and propane fluxes through two types of commercially available membranes. Additionally, bench-scale MBfRs have been operating to degrade 1,4-dioxane in the presence of two types of bioaugmentation cultures and under various operating conditions. Initial bench-scale MBfR results demonstrate 93% to 99.9% 1,4-dioxane removal when provided at high concentrations (e.g., 1 mg/L to ~60 mg/L) as the sole carbon source. Propane-mediated cometabolic tests resulted in ~50% to >99% removal of 1,4-dioxane, starting at approximately 100 µg/L, to less than 5 µg/L for various configurations and operating conditions. The molar ratio of 1,4-dioxane to propane has been varied between 1:200 to nearly 1:30000 to test treatment sensitivity and identify optimal operating conditions for the future field demonstration at Arnold Air Force Base.