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 51 and 151), 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 151 to 51 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 51 or lower to maximize the duration of electron-donor production at sites with potential biodegradation rate limitations.