The biological treatment of synthetic fracking fluid in an extractive membrane bioreactor: selective transport and biodegradation of hydrophobic and hydrophilic contaminants

Abstract

Hydraulic fracturing involves the use of horizontal drilling techniques and high-pressure liquid injections to stimulate the production of natural gas through the resultant micro-fracturing networks in tight formations. Hydraulic fracturing wastewaters (HFWs) often contain a diverse hydrocarbon profile, low molecular weight organic acids, and geogenic inorganic materials (salts) at low pH.

The diversity and variation of recalcitrant compounds within HFWs have made them difficult to remediate biologically due to the inhibitory effects imparted on microbial systems. Currently, there is a lack of effective remediation/disposal strategies capable of treating these heterogeneous wastes. This work proposes extractive membrane bioreactors (EMBs) as an innovative HFW treatment method. EMBs operate by selectively separating toxic waste streams from microbial systems preventing inhibition, while simultaneously sequestering and transporting the organic content via thermodynamic partitioning across polymer membranes.

Characterization of the suitability of various grades of Hytrel™ polymer tubing for EMB applications was undertaken based on polymer water content, molecular transport/retention, and thermodynamic affinity for a range of putative HFW components including acids, bases, salts, organic acids and other organic species. High water content polymers (=30% equilibrated water) were able to transport ionic species, facilitating the rapid transport of monovalent salts, while low water content polymers did not. A demonstration of the transport/retention capabilities of organic species and ions by low water content Hytrel™ tubing was exploited to concentrate dilute butyric acid, achieving a 220% concentration increase from initial dilute aqueous concentrations through chemical dissociation after 48 hours.

An EMB utilizing Hytrel™ 3548 tubing was employed for the biological treatment of frequently occurring, representative hydrophilic and hydrophobic organic contaminants at hyper-saline salt concentrations. A microbial consortium capable of degrading representative HFW compounds (benzene, phenol, methyl ethyl ketone (MEK) and acetic acid) was generated and identified using genetic sequencing. EMBs were then operated in both batch and continuous configurations, obtaining 99% biodegradation ofiii benzene and phenol after 72 hours, MEK biodegradation of =96% and acetic acid removal up to its ionization point. Successful treatment of synthetic hydraulic fracturing wastewater demonstrated the effectiveness in utilizing amphiphilic polymers in EMBs when treating complex fluids containing hydrophilic and hydrophobic organic fractions.