Biodegradation of tetrachloroethene by chitin fermentation products in a continuous flow column system

The ability of chitin fermentation products to promote tetrachloroethene (PCE) reduction was evaluated in a continuous-flow column system to identify how different electron donors affect reductive dechlorination. Natural chitin fermentation products were initially used to support PCE reduction. Acetate (3.5mM) was the dominant fermentation product, followed by propionate (0.1mM), butyrate (0.1mM), and hydrogen (100nM). After chlorinated ethene concentration profiles reached pseudo steady state, the ability of individual fermentation products (acetate, acetate+propionate, propionate, or formate) to support PCE reduction was evaluated. None of the fermentation products tested stimulated dechlorination as well as the suite generated from chitin (k_PCE=6.9day^-1); however, acetate-stimulated PCE dechlorination the best (k_PCE=5.3day^-1), followed by formate (k_PCE=2.4day^-1), acetate+propionate (k_PCE=1.8day^-1), and propionate (k_PCE =1.2day^-1). Similar trends were observed for the PCE daughter products trichloroethene and dichloroethene. Free energies of individual fatty acid reactions were calculated and shown to be useful predictors of dechlorination performance, except for the case of acetate+propionate. Hence, acetate is the dominant fatty acid controlling dechlorination in the chitin-enhanced system, propionate appears to have an inhibitory effect when present with acetate alone, and other unidentified nutrients produced during chitin fermentation likely contribute to dechlorination activity as well.