Effects of environmental conditions on the release of phosphorus from biochar

The biochar-water system was adopted as a model to investigate the effect of environmental factors (e.g., P species, retention time, coexisting anions, and nutrient salts) on P release. The results revealed that about 55wt.% P could be released in 3–4d, and the P release rate could be controlled by adjusting the environmental factors. The coexisting anions can enhance the P release due to the effect of ion exchange competition. The introduction of Hoagland nutrient solution led to the decrease in the release of P for the formation of precipitates between dissolved P and excessive Ca2+ and Mg2+. [Display omitted] •A novel method to mitigate the P depletion crisis by reuse of biochar was proposed.•The environmental factors influencing the P release were investigated in detail.•The mechanism of the release of different P species from biochar was provided. 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 2.2mgg−1 P in the form of inorganic orthophosphate and pyrophosphate was released from a raw biochar (contained 4.7mg Pg−1) at initial pH of 9.0 in the initial 8h. The release of orthophosphate was significantly enhanced from 0.64 to 1.35mgg−1 by the coexisting anions of Cl−, NO3- or SO42- due to the effect of ion exchange competition, while the release of pyrophosphate (P2O74-) 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 Ca2+ and Mg2+.