Molecular Microbiology Research 2024, Vol.14, No.2, 65-78 http://microbescipublisher.com/index.php/mmr 69 al., 2020). Designing SynComs tailored to the specific contaminants and environmental conditions of the site is essential. This involves selecting microbial strains with complementary metabolic capabilities to degrade a wide range of pollutants (Liang et al., 2022). Techniques such as metabolic modeling and high-throughput screening can aid in identifying optimal microbial combinations (Kehe et al., 2019). Methods for introducing SynComs to contaminated sites include soil injection, surface application, and mixing with soil amendments (Brune and Bayer, 2012). For groundwater contamination, permeable reactive barriers (PRBs) can be used to deliver SynComs directly into the aquifer (Wang et al., 2021). Continuous monitoring of microbial activity and pollutant degradation is necessary to evaluate the effectiveness of the SynComs. Parameters such as microbial population dynamics, pollutant concentrations, and environmental factors (e.g., pH, temperature) should be regularly measured. Maintenance may involve periodic re-inoculation and nutrient supplementation to sustain microbial activity (Kim et al., 2011). 5.2 Key field trials and large-scale applications Several field trials and large-scale applications have demonstrated the effectiveness of SynComs in environmental remediation. Permeable Reactive Barriers (PRBs) utilizing systems containing zero-valent iron (ZVI) have significantly reduced hexavalent chromium (Cr(VI)) contamination in groundwater in a large-scale study (Figure 1). The key to this technology lies in the reductive action of zero-valent iron, which transforms toxic hexavalent chromium into the less toxic trivalent chromium. During this process, significant changes occurred in the native microbial communities, reflecting not only their adaptation to the new environment but also their active role in the pollutant transformation process. This successful on-site application highlights the practical value and environmental adaptability of PRBs in the treatment of persistent organic pollutants (Wang et al., 2021). Figure 1 In situ remediation of Cr(VI) contaminated groundwater by ZVI-PRB and the corresponding indigenous microbial community responses (Adopted from Wang et al., 2021) Image caption: The PRB segment with 20% active reaction medium (ZVI) was able to successfully reduce Cr(VI) via chemical reduction from 27.29-242.65 mg/L to below the clean-up goal of 0.1 mg/L, and can be scaled-up under field conditions. The ZVI induced significant changes in the indigenous microbial community structure and compositions in the area of the PRB and those areas downgradient. The competitive growth among Cr(VI)-reducing bacteria (the reduced abundance of Hydrogenophaga, Pseudomonas, Exiguobacterium and Rhodobacter, along with the enrichment of Rivibacter and Candidatus_Desulforudis) were observed in PRB (Adopted from Wang et al., 2021).
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