Biochar and microorganisms: a synergy for the sustainable treatment of contaminated waters and filters

Biochar is a carbon-rich material produced by pyrolysis of organic biomass and represents a sustainable, low-cost alternative to activated carbon (AC) as filter in water treatment. Bacteria establish biofilms on filter surface contributing to the filtering performance, but the mechanisms of their interaction and the communities developed on biochar filter are largely unexplored. Our work aimed, first, at investigating metabolic activity, composition and dynamics of microbial communities colonizing experimental filters (AC and biochar) applied in two groundwater treatment plants processing waters contaminated by different types of pollutants (aromatic hydrocarbons and ethers, or chlorinated compounds). Illumina sequencing, quantitative PCR and metagenomic shotgun sequencing were performed to analyze the microbial community development on filters applied at real scale in the two systems. Bacterial abundance remained stable over time, but community composition and functionality varied depending on the treatment plant and type of contamination. Enrichment of taxa associated with biofilm growth, stress resistance and organic contaminant degradation was observed on filters with similarity between AC and biochar in the same plant. Second, we evaluated the possibility to remove contaminants from end-life filters by exploiting microbial degradation abilities by applying synthetic consortia and adapted communities, assessing contaminant removal via GC-FID analysis. Biological treatment experiments showed a better performance of contaminant removal from biochar filters as compared to AC, together with a higher removal of aromatic hydrocarbons as compared to chlorinated compounds. In conclusion, biochar proves to be a valid alternative to AC in groundwater treatment plant supporting an effective development of microbial communities that can contribute to contaminants biodegradation and also a partial contaminants removal from waters, although further studies are needed to optimize the adsorption capacity. Additionally, our findings provide first indications on the potential of engineered microbial communities to decontaminate end-life filters.