Promoting the remediation of contaminated soils using biochar in combination with bioaugmentation and phytoremediation techniques.

Pollutants in soils are detrimental to ecosystems and agricultural production and may also be a pressing threat to human health. In this context, biochar could be used as part of nature-based solutions to remediate polluted areas. In this work, a series of innovative biochar-based strategies were tested in a soil contaminated by hydrocarbons C > 12 and copper (Cu) to investigate their effectiveness in soil decontamination and revegetation potential. Specifically, biochar was applied to soil alone (SB) or combined with bioaugmentation (SBB) and/or phytoremediation (SBP and SBBP) techniques. Overall results showed that after nine months (T9) biochar added to soil increased hydrocarbon degradation to 66.7% with respect to control soil (46%, natural attenuation). Moreover, the biochar in combination with a microbial consortium and/or plants significantly increased hydrocarbon removal by up to 90%. Concurrently, the fraction of Cu associated with organic matter, characterized by low bioavailability, increased significantly (1.4-2-fold) when biochar was applied. Soil microbial abundance increased over time in all conditions, reaching highest values in SBB and SBBP. This was associated with the higher levels of available phosphorus in the soil. The consortium's presence enhanced plant growth compared to SB. On the contrary, plants grown on contaminated soil alone were not able to survive until the end of the experiment. Overall, the results of this work make a significant contribution to the understanding of the interaction of biochar with contaminants, plants and microorganisms, providing a useful tool for future brownfield revegetation/remediation programs.