The effects of biochar or activated carbon amendments on the fate of volatile petroleum hydrocarbons in an aerobic sandy soil

Abstract

The impact of biochar or activated carbon (AC) amendments on the biodegradation of a mixture of 12 volatile petroleum hydrocarbons ( VP Hs) in an aerobic sandy soil was investigated in batch microcosms and column experiments. The impacts of biochar amendments on nutrient availability and biogenic gases activity were also studied by batch microcosms. The maximum nutrient amount adsorbed by biochar (9 max) was very high.

Therefore, biochar amendments decreased the readily available nitrogen with increasing biochar application rate and contact period. Biogenic gas activities in biochar amended soils had varied responses because these activities were dependent on soil properties. The effects of sorbent amendment significantly depended on the compound chemical structure and type of sorbent material. In the batch microcosms, the AC and biochar amendments resulted in a large increase in the K values. The biodegradation of the water-dissolved OC fraction of most compounds was as fast or faster in the soil amended with activated carbon compared to the soil with or without biochar, but the strong sorption capacity of activated carbon, in particular, greatly reduced water-dissolved concentrations. The nutrient amendments accelerated the biodegradation of VPHs in the batch microcosms and nutrient availability was the main factor controlling the biodegradation rates of total petroleum hydrocarbons in sandy soil; whereas sorption was a secondary factor influencing the biodegradation of total petroleum hydrocarbons in biochar and activated carbon amended sandy soil. The biodegrada tion in sorbent amended columns was difficult to predict. The sorbent amendments decreased the availability of both VP Hs and nutrients. Therefore, the biodegradation rate was reduced. However, the petroleum hydrocarbon vapour migration and volatilization was also reduced, which increased the residence time of contaminants in the sorbent amended column. This means there was more time available to degrade the pollutants before they emanated from soil, and therefore the sorbent amendments may result in a greater amount of biodegradation, if considered over a certain distance and over a long time period. It is concluded that b iochar and activated carbon amendments are potentially a sustainable remediation strategy for dealing with volatile petroleum hydrocarbons pollution. These sorbents are able to reduce the risk of VPHs to biota and the also surrounding environments without using large scale, energy intensive and treatment processes.