UCLA

It is crucial to consider the impact of abiotic and biological remediation technologies on the microbial ecology to predict the success of short-term active treatments and long-term passive attenuation processes. In this research, three bioremediation strategies were tested individually or coupled with chemical remedies in bench- and pilot-scale studies for removing 1,4-dioxane and chlorinated volatile organic compounds (CVOCs), which are widespread co-occurring contaminants in soils and water resources across the U.S., attracting attention because of their potential carcinogenicities. In each project, amplification of taxonomic and functional genes by qPCR as well as metagenomics including high-throughput sequencing were applied to provide reliable information about microbial communities in the ecological matrices as they transitioned from 1,4-dioxane and CVOC contaminations to exposures from treatment technologies and degradation products.

A comprehensive multiple lines of evidence approach provided evidence of natural attenuation by microorganisms capable of metabolic or co-metabolic degradation of 1,4-dioxane within a large, diffuse plume. A pilot study of bioaugmentation with Pseudonocardia dioxanivorans CB1190 through direct injection as well as in-situ bioreactor was successfully conducted at a site impacted by 1,4-dioxane and CVOCs.

Bench-scale microcosms were established to inform pilot-scale ex-situ bioreactors and in-situ propane biosparging at an industrial site. 1,4-Dioxane co-metabolism by indigenous microbes was accelerated by biostimulation with propane and nutrients. Inoculations with CB1190 or propanotroph, Rhodococcus ruber ENV425, were eventually outcompeted by native microbes, but gene allocations for xenobiotics and lipid metabolism were enhanced and accompanied rapid 1,4-dioxane degradation rates.

Three synergistic treatment trains: oxidation & catalysis, oxidation & biodegradation, and catalysis & biodegradation, were applied to achieve nearly complete 1,4-dioxane removals even in the presence of inhibitory CVOCs. While oxidant- or nanocatalyst-tolerant microbes were dominant immediately after chemical processes, the microbial community thrived during the biodegradation in a deterministic process over time, presenting higher biodiversity that indicated a more stable community. The post-treatment community carried various functional potentials, such as degradation of CVOCs and aromatic hydrocarbons, as well as nitrogen fixation.

These mechanistic and quantitative data will be valuable for developing synergistic treatments that lead to savings in cost, energy, and substrate amendments for the remediation of contaminant mixtures.