Effect of pH on the anaerobic dechlorination of chlorophenols in a defined medium

Abstract

Anaerobic dehalogenation of aromatic compounds is a well-documented phenomenon. However, the effects of operating parameters such as pH have received little attention despite their potential impact on treatment processes using dehalogenating organisms. In this work the effect of pH on the dehalogenation of 2,4,6-trichlorophenol (2,4,6-TCP) was studied using defined media containing one of several non-fermentable buffering agents (MOPS, TRICINE, BI-CINE, CHES), and no chloride ions. The dechlorination process was followed by monitoring the disappearance of 2,4,6-TCP, as well as the appearance of its dehalogenation products, i.e., 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP), and chloride ions. The results indicate that dechlorination occurs only if the pH is within the range 8.0-8.8. The newly formed 2,4-DCP was also dehalogenated in the process. However, even within this pH range dechlorination ceased when all 2,4,6-TCP and 2,4-DCP was converted to 4-CP. Stoichiometric amounts of all dehalogenation products (including chloride) could be recovered at any stage during the process. In addition, the biomass concentration was measured. After an initial lag phase, it appeared that the rate of dechlorination per unit biomass (proportional to the C1-concentration divided by the biomass concentration) went through a rapid increase and then remained constant throughout the process. This indicates that the dechlorinating organim(s) either make up the entire population or constitute a stable fraction of it.

Effect of yeast extract on growth kinetics during aerobic biodegradation of chlorobenzoic acids

“…Because no inhibitory effect was apparent this time, the Monod model [Eq. (4)] was used to regress the data. The corresponding values of pmax and K, are also given in Table I.…”

“…In the first type, p increased as a function of S and approached an asymptotic value for large values of S. The data showing this trend were analyzed using a Monod kinetic expre~sion~*~': (4) where pmax and Ks were obtained from a nonlinear regression of the experimental values using a modified Levenberg-Marquardt method. 1671' This approach was preferred to the traditional Lineweaver-Burke plotting5 of Up vs. 1/S that puts too much emphasis on the low-substrateconcentration data points.…”

Kinetics of the sequential dechlorination of 2,4,6-trichlorophenol by an anaerobic microbial population

“…Analytical Method A Waters HPLC system was used for the determination of phenol and all chlorophenols. Details of the analytical procedure are reported elsewhere Armenante et al, 1993).…”

“…The rate of dechlorination under such conditions is actually greatest for more heavily chlorinated compounds, and it slows down as the chlorophenoi molecules become more dechlorinated. Previous investigations have shown that the aromatic ring is not attacked under anaerobic conditions (Kafkewitz et al, 1992;Armenante et al, 1993;Togna et aL, 1995). However, to date little quantitative information on the dehaiogeuation rates of chlorophenols by anaerobic cultures is available, and no kinetic parameters have been obtained.…”

“…The total mass of all the combined chlorophenols remains constant throughout the process, and stoichiometric amounts of chloride ion have been recovered. Further anaerobic dchalogenation of 4-MCP to phenol is typically either small or negligible (Armenante et aL, 1993;Togna et aL, 1995). Anaerobic degradation of phenol is negligible during the time period required for the 2,4,6-TCP and 2,4-DCP dehalogenation process to be completed.…”