[Effects of biochar covering on the release of pollutants from sediment]

In order to study the effects of biochar on the release of pollutants from sediment, Arundo donax, Phragmites australis, Arachis hypogaea and Zea mays were pyrolyzed into biochar. Biochar was used to cover the contaminated sediment in the simulated reactors. Concentrations of NH4(+) -N, NO3(-) -N, NO2(-) -N, COD and P4(3-) -P were continuously monitored, and the cumulative release amount and release rate were calculated. Besides that, the release amount of water-soluble NH4(+) -N and PO4(3-) -P from biochars were determined. In the blank control group, which was not covered with any kinds of biochar, the ammonia-nitrogen concentration of the overlying water reached a maximum value of 4.27 mg x L(-1) on the twenty-fifth day, and then stabilized at about 4.02 mg x L(-1). Ammonia-nitrogen concentrations of the treatment groups with the four kinds of biochar all maintained below 0.3 mg x L(-1) after 25 days. Particularly, the Phragmites australis treatment group showed the best ability to inhibit ammonia-nitrogen release, and the cumulative release amount of ammonia-nitrogen was reduced by 85.61%. The cumulative release amount of COD was reduced by 28.83% to 30%. Phosphate concentration of the Zea mays group was higher than that of the blank group. On the contrary, Arundo donax and Phragmites australis groups showed a great potential in the inhibition of phosphate release. Biochar released the majority of NH4(+) -N and PO4(3-) -P in the first 3 days. The release amount of NH4(+) -N from Arachis hypogaea group was larger than those of the other three groups, reaching 36.79 mg x kg(-1). Similarly, Zea mays group had the largest release of PO4(3-) -P, which was 70.64 mg x kg(-1). All suggest that biochar is a potential in-situ capping material to reduce the release of NH4(+) -N, COD and PO4(3-) -P in polluted sediments, and has the ability of applying to the remediation of sediment in the polluted water.