Biological Treatment of Hydraulic Fracturing Produced Water

摘要

Hydraulic fracturing enables the enhanced recovery of hydrocarbons from shale formations while generating large volumes of produced water, i.e. wastewater from hydraulic fracturing. Treatment of produced water for reuse or final disposal is challenged by both high salinity and the presence of organic compounds. This dissertation is focused on the biological treatment of produced water using a mixed-culture biofilm approach to remove the available electron donors and therefore, potentially limit microbial growth, biocide use, and fouling of wells (during reuse) and membranes (during treatment prior to final disposal). Conventional activated sludge treatments are intolerant of high salinity, thus a biofilm approach was proposed to provide a more robust treatment method for high salinity produced waters. First, a preliminary evaluation on COD biodegradation (as acetate and guar gum) in synthetic and real produced waters was performed. Biodegradation was mainly driven by salinity; however, microbial activity was observed at salt concentrations as high as 100,000 mg/L TDS. Next, the effect of glutaraldehyde (GA), a commonly used biocide in hydraulic fracturing, on biodegradation of organic chemicals that are commonly used in fracturing fluids, is investigated. Results demonstrated that glutaraldehyde can affect the observed lag period and half-lives of the compounds, depending on the compound. Finally, the biodegradation of produced waters were evaluated in seven samples from different wells. Results showed a negative correlation between salinity and biodegradation rates. Moreover, variable biodegradation rates were observed at the same salt concentration. Finally, a Ra-226 biosorption was evaluated in synthetic and real produced waters to determine the efficacy of Ra-226 removal by a halophilic microalga D. salina.udThis study contributes to the understanding of biological treatment applicability in produced water management. The proposed biofilm approach could further encourage the use of similar approaches in produced water treatment and possibly in other industrial wastewaters containing high salinity and toxic chemicals. The evaluation of the biocide effect on biodegradation can enhance the understanding and accuracy of environmental model predictions for bio-treatment, bio-remediation, and pollution transport. Ultimately, this dissertation will contribute to more sustainable and economical produced water management strategies.