Effects of environmental conditions on the release of phosphorus from biochar.

Biochar, the byproduct from fast pyrolysis of waste biomass, is widely used as a soil conditioner. The phosphorus in biochar is not only a P source for plant growth, but also an important factor caused the eutrophication of water. Here, the effects of environmental conditions on the release of different P species from biochar in a biochar-water system were investigated. About 2.2 mg g(-1) P in the form of inorganic orthophosphate and pyrophosphate was released from a raw biochar (contained 4.7 mg P g(-1)) at initial pH of 9.0 in the initial 8h. The release of orthophosphate was significantly enhanced from 0.64 to 1.35 mg g(-1) by the coexisting anions of Cl(-), NO3(-) or SO4(2-) due to the effect of ion exchange competition, while the release of pyrophosphate (P2O7(4-)) was not influenced by the introduction of anions which might be attributed to the formation of stable complexes. The introduction of Hoagland nutrient solution led to the decrease in release of P due to the formation of precipitates between dissolved P and excessive Ca(2+) and Mg(2+).