Cleanup chlorinated ethene-polluted groundwater using an innovative immobilized Clostridium butyricum column scheme: A pilot-scale study

Bioremediation of trichloroethylene-contaminated groundwater using green carbon-releasing substrate with pH control capability

In this research, a sustainable substrate, termed green and long-lasting substrate (GLS), featuring a blend of emulsified substrate (ES) and modified rice husk ash (m-RHA) was devised. The primary objective was to facilitate the bioremediation of groundwater contaminated with trichloroethylene (TCE) using innovative GLS for slow carbon release and pH control. The GLS was concocted by homogenizing a mixture of soybean oil, surfactants (Simple Green™ and soya lecithin), and m-RHA, ensuring a gradual release of carbon sources. The hydrothermal synthesis was applied for the production of m-RHA production. The analyses demonstrate that m-RHA were uniform sphere-shape granules with diameters in micro-scale ranges. Results from the microcosm study show that approximately 83% of TCE could be removed (initial TCE concentration = 7.6 mg/L) with GLS supplement after 60 days of operation. Compared to other substrates without RHA addition, higher TCE removal efficiency was obtained, and higher Dehalococcoides sp. (DHC) population and hydA gene (hydrogen-producing gene) copy number were also detected in microcosms with GLS addition. Higher hydrogen concentrations enhanced the DHC growth, which corresponded to the increased DHC populations. The addition of the GLS could provide alkalinity at the initial stage to neutralize the acidified groundwater caused by the produced organic acids after substrate biodegradation, which was advantageous to DHC growth and TCE dechlorination. The addition of m-RHA reached an increased TCE removal efficiency, which was due to the fact that the m-RHA had the zeolite-like structure with a higher surface area and lower granular diameter, and thus, it resulted in a more effective initial adsorption effect. Therefore, a significant amount of TCE could be adsorbed onto the surface of m-RHA, which caused a rapid TCE removal through adsorption. The carbon substrates released from m-RHA could then enhance the subsequent dechlorination. The developed GLS is an environmentally-friendly and green substrate.

An innovative permeable reactive bio-barrier to remediate trichloroethene-contaminated groundwater: A field study

Permeable reactive bio-barrier (PRBB), an innovative technology, could treat many contaminants via the natural gradient flow of groundwater based on immobilization or transformation of pollutants into less toxic and harmful forms. In this field study, we developed an innovative PRBB system comprising immobilized Dehalococcoides mccartyi (Dhc) and Clostridium butyricum embedded into the silica gel for long-term treatment of trichloroethene (TCE) polluted groundwater. Four injection wells and two monitoring wells were installed at the downstream of the TCE plume. Without PRBB, results showed that the TCE (6.23 ± 0.43 μmole/L) was converted to cis-dichloroethene (0.52 ± 0.63 μmole/L), and ethene was not detected, whereas TCE was completely converted to ethene (3.31 μmole/L) with PRBB treatment, indicating that PRBB could promote complete dechlorination of TCE. Noticeably, PRBB showed the long-term capability to maintain a high dechlorinating efficiency for TCE removal during the 300-day operational period. Furthermore, with qPCR analysis, the PRBB application could stably maintain the populations of Dhc and functional genes (bvcA, tceA, and vcrA) at >108 copies/L within the remediation course and change the bacterial communities in the contaminated groundwater. We concluded that our PRBB was first set up for cleaning up TCE-contaminated groundwater in a field trial.

Improve Niche Colonization and Microbial Interactions for Organohalide-Respiring-Bacteria-Mediated Remediation of Chloroethene-Contaminated Sites

Organohalide-respiring bacteria (OHRB)-mediated reductive dehalogenation is promising in in situ bioremediation of chloroethene-contaminated sites. The bioremediation efficiency of this approach is largely determined by the successful colonization of fastidious OHRB, which is highly dependent on the presence of proper growth niches and microbial interactions. In this study, based on two ecological principles (i.e., Priority Effects and Coexistence Theory), three strategies were developed to enhance niche colonization of OHRB, which were tested both in laboratory experiments and field applications: (i) preinoculation of a niche-preparing culture (NPC, being mainly constituted of fermenting bacteria and methanogens); (ii) staggered fermentation; and (iii) increased inoculation of CE40 (a Dehalococcoides-containing tetrachloroethene-to-ethene dechlorinating enrichment culture). Batch experimental results show significantly higher dechlorination efficiencies, as well as lower concentrations of volatile fatty acids (VFAs) and methane, in experimental sets with staggered fermentation and niche-preconditioning with NPC for 4 days (CE40_NPC-4) relative to control sets. Accordingly, a comparatively higher abundance of Dehalococcoides as major OHRB, together with a lower abundance of fermenting bacteria and methanogens, was observed in CE40_NPC-4 with staggered fermentation, which indicated the balanced syntrophic and competitive interactions between OHRB and other populations for the efficient dechlorination. Further experiments with microbial source tracking analyses suggested enhanced colonization of OHRB by increasing the inoculation ratio of CE40. The optimized conditions for enhanced colonization of OHRB were successfully employed for field bioremediation of trichloroethene (TCE, 0.3-1.4 mM)- and vinyl chloride (VC, ∼0.04 mM)-contaminated sites, resulting in 96.6% TCE and 99.7% VC dechlorination to ethene within 5 and 3 months, respectively. This study provides ecological principles-guided strategies for efficient bioremediation of chloroethene-contaminated sites, which may be also employed for removal of other emerging organohalide pollutants.

Functional materials contributing to the removal of chlorinated hydrocarbons from soil and groundwater: Classification and intrinsic chemical-biological removal mechanisms

Chlorinated hydrocarbons (CHs) are the main contaminants in soil and groundwater and have posed great challenge on the remediation of soil and ground water. Different remediation materials have been developed to deal with the environmental problems caused by CHs. Remediation materials can be classified into three main categories according to the corresponding technologies: adsorption materials, chemical reduction materials and bioaugmentation materials. In this paper, the classification and preparation of the three materials are briefly described in terms of synthesis and properties according to the different types. Then, a detailed review of the remediation mechanisms and applications of the different materials in soil and groundwater remediation is presented in relation to the various properties of the materials and the different challenges encountered in laboratory research or in the environmental application. The removal trends in different environments were found to be largely similar, which means that composite materials tend to be more effective in removing CHs in actual remediation. For instance, adsorbents were found to be effective when combined with other materials, due to the ability to take advantage of the respective strengths of both materials. The rapid removal of CHs while minimizing the impact of CHs on another material and the material itself on the environment. Finally, suggestions for the next research directions are given in conjunction with this paper.

In situ reductive dehalogenation of groundwater driven by innovative organic carbon source materials: Insights into the organohalide-respiratory electron transport chain

In situ bioremediation using organohalide-respiring bacteria (OHRB) is a prospective method for the removal of persistent halogenated organic pollutants from groundwater, as OHRB can utilize H₂ or organic compounds produced by carbon source materials as electron donors for cell growth through organohalide respiration. However, few previous studies have determined the suitability of different carbon source materials to the metabolic mechanism of reductive dehalogenation from the perspective of electron transfer. The focus of this critical review was to reveal the interactions and relationships between carbon source materials and functional microbes, in terms of the electron transfer mechanism. Furthermore, this review illustrates some innovative strategies that have used the physiological characteristics of OHRB to guide the optimization of carbon source materials, improving the abundance of indigenous dehalogenated bacteria and enhancing electron transfer efficiency. Finally, it is proposed that future research should combine multi-omics analysis with machine learning (ML) to guide the design of effective carbon source materials and optimize current dehalogenation bioremediation strategies to reduce the cost and footprint of practical groundwater bioremediation applications.

Elucidating the Role of Biofilm-Forming Microbial Communities in Fermentative Biohydrogen Process: An Overview

Amongst the biofuels described in the literature, biohydrogen has gained heightened attention over the past decade due to its remarkable properties. Biohydrogen is a renewable form of H2 that can be produced under ambient conditions and at a low cost from biomass residues. Innovative approaches are continuously being applied to overcome the low process yields and pave the way for its scalability. Since the process primarily depends on the biohydrogen-producing bacteria, there is a need to acquire in-depth knowledge about the ecology of the various assemblages participating in the process, establishing effective bioaugmentation methods. This work provides an overview of the biofilm-forming communities during H2 production by mixed cultures and the synergistic associations established by certain species during H2 production. The strategies that enhance the growth of biofilms within the H2 reactors are also discussed. A short section is also included, explaining techniques used for examining and studying these biofilm structures. The work concludes with some suggestions that could lead to breakthroughs in this area of research.