Anaerobic Biodegradation of Chloroform and Dichloromethane with a Dehalobacter Enrichment Culture

Abstract

Chloroform (CF) and dichloromethane (DCM) are among the more commonly identified chlorinated aliphatic compounds found in contaminated soil and groundwater. Complete dechlorination of CF has been reported under anaerobic conditions by microbes that respire CF to DCM and others that biodegrade DCM. The objectives of this study were to ascertain if a commercially available bioaugmentation enrichment culture (KB-1® Plus CF) uses an oxidative or fermentative pathway for biodegradation of DCM; and to determine if the products from DCM biodegradation can support organohalide respiration of CF to DCM in the absence of an exogenous electron donor. In various treatments with the KB-1 ® Plus CF culture to which 14 C-CF was added, the predominant product was 14 CO 2 , indicating that oxidation is the predominant pathway for DCM. Recovery of 14 C-DCM when biodegradation was still in progress confirmed that CF first undergoes reductive dechlorination to DCM. 14 C-labeled organic acids, including acetate and propionate, were also recovered, suggesting that synthesis of organic acids provides a sink for the electron equivalents from oxidation of DCM. When the biomass was washed to remove organic acids from prior additions of exogenous electron donor and only CF and DCM were added, the culture completely dechlorinated CF. The total amount of DCM added was not sufficient to provide the electron equivalents needed to reduce CF to DCM. Thus, the additional reducing power came via the DCM generated from CF reduction. Nevertheless, the rate of CF consumption was considerably slower in comparison to treatments that received an exogenous electron donor. IMPORTANCE Chloroform (CF) and dichloromethane (DCM) are among the more commonly identified chlorinated aliphatic compounds found in contaminated soil and groundwater. One way to address this problem is to add microbes to the subsurface that can biodegrade these compounds. While microbes are known that can accomplish this task, less is known about the pathways used under anaerobic conditions. Some use an oxidative pathway, resulting mainly in carbon dioxide. Others use a fermentative pathway, resulting in formation of organic acids. In this study, a commercially available bioaugmentation enrichment culture (KB-1 ® Plus CF) was evaluated using carbon-14 labelled chloroform. The main product formed was carbon dioxide, indicating the use of an oxidative pathway. The reducing power gained from oxidation was shown to support reductive dechlorination of CF to DCM. The results demonstrate the potential to achieve full dechlorination of CF and DCM to nonhazardous products that are difficult to identify in the field.

Water recycling public toilets based on onsite electrochemical wastewater treatment

“…Surprisingly the values in the ABR where such CFM treated water was recycled remained at a value of 1–10 mg L −1 . It has been reported that anaerobic conditions favor biodegradation of chloroform 25 and additionally CFM is highly volatile, thus these factors may justify the low ABR values in the closed loop. The high CFM values produced by the ECR are thus not due to an accumulation effect.…”

Metaproteomics reveals methyltransferases implicated in dichloromethane and glycine betaine fermentation by ‘Candidatus Formimonas warabiya’ strain DCMF

“…At contaminated sites in particular, it may enhance bioremediation, as the production of hydrogen, acetate, and ethanol can both stimulate microbial blooms or serve as secondary substrates for co-metabolism ( Horvath, 1972 ; Wrighton et al, 2014 ). Outside of necromass studies, similarly “self-feeding” mixed cultures have been described for dechlorination of trichloromethane and DCM ( Wang et al, 2022 ), chlorobenzene ( Liang et al, 2013 ), and 3-chlorobenzoate ( Dolfing, 1986 ; Dolfing and Tiedje, 1987 ). Consumption of dead biomass can also remineralize or liberate important nutrients including nitrogen, phosphorous, trace elements, and cobalamins ( Head et al, 2006 ; Christie-Oleza et al, 2017 ).…”

Remediation of chloroform in fine‐textured soil using zero‐valent iron

“…Microbial reductive dechlorination (halorespiration) requires carbon and electron sources to dechlorinate chlorinated solvents, using them as electron acceptors. However, halorespiration is mostly carried out by specialized bacteria not common in the environment (Wang et al, 2022). Application of nanoscale zero‐valent iron (Fe 0 ) has been used in soil and groundwater remediation (Jin et al, 2018; Lv et al, 2020; Zhu et al, 2021), where it acts as a reducing agent donating electrons to transform halogenated contaminants into less toxic forms.…”