Enrichment of soil mixed microbial cultures onto biochar as a proxy for landfarming techniques
Résumé
Estarreja soils are sinks of long-term contamination due to a Chemical Industrial Complex. We hypothesized that: (i) contaminated soils present microbial communities with better biodegradative performance compared to non-contaminated soils; (ii) such microbial communities can be cultivated ex situ to boost their effectiveness in environmental remediation; and (iii) biochar (pyrolysed biomass) can act as a biofilm carrier, thus allowing further field-scale spreading of the biocatalysts. Soils were sampled from two representative sites (contaminated and non-contaminated) across Estarreja and their microbial communities cultivated inside aerobic bioreactors fed-batch operated with glucose, thereafter progressively replaced with toluene. A third bioreactor was added with biochar to assess biofilm formation. A landfarming assay was performed with the bioactivated biochar in the contaminated soil spiked with glucose and toluene, and the respirometric response quantified. Both microbial C-biomass and respiration rate were systematically smaller in the contaminated soil (0.9 vs. 1.2 g-C kg-1 and 1.9 vs. 4.4 mg-C kg-1 h-1 respectively), resulting in a lower metabolic quotient yet anticipating a better carbon use efficiency. Indeed, the contaminated soil culture showed a higher COD removal efficiency (48-64% vs. 30-63%) when subjected to toxic conditions (>50% toluene feeding). Although biofilm development was not directly quantified, soil application of the bioactivated biochar resulted in 150% increase in both soil respiration and microbial C-biomass when compared to positive controls (abiotic biochar). These results anticipate the ability of contaminated soil microbial communities to perform effective environmental remediation as well as their capacity to form biofilms onto biochar, which is useful for landfarming techniques.