Effect of Pine Waste and Pine Biochar on Nitrogen Mobility in Biosolids

Humanity produces similar to 27 kg of dry matter in biosolids per person per year. Land application of biosolids can improve crop production and remediate soils but may result in excessive nitrate N (NO3--N) leaching. Carbonaceous materials can reduce the environmental impact of biosolids application. We aimed to ascertain and compare the potentials for Monterey pine (Pinus radiata D. Don)-sawdust-derived biochars and raw sawdust to reduce NO3--N leaching from biosolids. We used batch sorption experiments 1: 10 ratio of material to solution (100 mg kg(-1) of NH4+ or NO3-) and column leaching experiments with columns containing biosolids (2.7% total N, 130 mg kg(-1) NH4+ and 1350 mg kg(-1) NO3-) mixed with soil, biochar, or sawdust. One type of low-temperature (350 degrees C) biochar sorbed 335 mg kg(-1) NH4+, while the other biochars and sawdust sorbed < 200 mg kg(-1) NH4+. None of the materials sorbed NO3-. Biochar added at rates of 20 to 50% reduced NH4+-N (< 1% of total N) leaching from columns by 40 to 80%. Nitrate leaching (< 7% of total N) varied little with biochar form or rate but was reduced by sawdust. Incorporating dried sawdust with biosolids showed promise for mitigating NO3--N leaching. This effect likely is due to sorption into the pores of the biochar combined with denitrification and immobilization of N rather than chemical sorption onto surfaces.