Effects of Chitin Purity and Proppant Loading on the Bioremediation of Chloroethenes

Hydraulic fracturing (or fracking) of substrates and proppants into contaminated soils is a developing, but understudied, practice of stimulating in situ bioremediation. In this work, three different purities of the substrate crab shell chitin (SC-20, SC-40, and SC-80), two proppant loadings (sand:chitin mass ratios of 5∶1 and 15∶1), and three chloroethene concentrations (1 and 10 mg∕L trichloroethene, and 1:5 mg∕L cis-1,2-dichloroethene) were experimentally and statistically examined to determine their effects on halorespiration. The least refined crab shell, SC-20, produced the greatest variety of electron donors, converted the highest percentage of contaminant mass to ethene, and supported a significantly greater Dehalococcoides population than the other substrates. Although influent chloroethene concentration and proppant loading did not significantly affect halorespiration (p-values > 0:079), decreasing the proppant loading from 15∶1 to 5∶1 increased the longevity of electron-donor production. These results indicate that funds need not be expended for purification of crab shell substrates, and that SC-20 should be used with proppant loadings of 5∶1 or lower to maximize the duration of electron-donor production at sites with potential biodegradation rate limitations. DOI: 10.1061/(ASCE)EE.1943-7870.0000541. © 2012 American Society of Civil Engineers. CE Database subject headings: Remediation; Biological processes; Groundwater pollution; Soil pollution; Solvents; TCE. Author keywords: Halorespiration; Trichloroethene; TCE; Crab shell; Fracking.