Study on the effect of modified biochar materials on in situ remediation of contaminated sediments

To study the control effect of biochar material on the release of nitrogen, phosphorus and heavy metal pollutants, two kinds of polluted sediment samples were collected from the river network and lake in Jiaxing City. Four kinds of modified biochars were produced using reed as the biomass feedstock and FeCl₃, AlCl₃, MgCl₂ and KMnO₄ as modifiers, while unmodified biochar, activated carbon and Phoslock were used as reference materials. The control effects of the seven kinds of remediation materials on the release of ammonia nitrogen (NH₃-N), nitrate nitrogen ( NO${}_{ 3}^{-}$ -N) and total soluble nitrogen (DTN), orthophosphate ( P${\mathrm{O}}_4^{3-}$ -P), total soluble phosphorus (DTP) and heavy metal ions into the water from the two kinds of polluted sediments were analyzed. The results showed that after adding AlCl₃ modified biochar to the sediments, the concentrations of NH₃-N, DTN, P${\mathrm{O}}_4^{3-}$ -P, DTP, Ni, As released into the water from the two sediments could be reduced by 17.42%, 18.61%, 91.23%, 77.04%, 72.13%, 46.21%, respectively, at the most. After adding FeCl₃ modified biochar, the concentrations of P${\mathrm{O}}_4^{3-}$ -P, DTP and As released into the water from the two sediments could be decreased by 91.23%, 92.59% and 95.80%, respectively, but the concentrations of DTN and Ni in the water increased. After adding MgCl₂ and KMnO₄ modified biochar, the concentrations of nitrogen, phosphorus, Ni and As pollutants released into the water from the two sediments increased rather than decreased. In conclusion, AlCl₃ modified biochar could effectively fix phosphorus, Ni and As in sediments and thus be considered as a material for in situ remediation of contaminated sediment.