Potential Environmental Benefits from Blending Biosolids with Other Organic Amendments before Application to Land.

Biosolids disposal to landfill or through incineration is wasteful of a resource that is rich in organic matter and plant nutrients. Land application can improve soil fertility and enhance crop production but may result in excessive nitrate N (NO-N) leaching and residual contamination from pathogens, heavy metals, and xenobiotics. This paper evaluates evidence that these concerns can be reduced significantly by blending biosolids with organic materials to reduce the environmental impact of biosolids application to soils. It appears feasible to combine organic waste streams for use as a resource to build or amend degraded soils. Sawdust and partially pyrolyzed biochars provide an opportunity to reduce the environmental impact of biosolids application, with studies showing reductions of NO-N leaching of 40 to 80%. However, other organic amendments including lignite coal waste may result in excessive NO-N leaching. Field trials combining biosolids and biochars for rehabilitation of degraded forest and ecological restoration are recommended.

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

Humanity produces ∼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 (NO-N) leaching. Carbonaceous materials can reduce the environmental impact of biosolids application. We aimed to ascertain and compare the potentials for Monterey pine ( D. Don)-sawdust-derived biochars and raw sawdust to reduce NO-N leaching from biosolids. We used batch sorption experiments 1:10 ratio of material to solution (100 mg kg of NH or NO) and column leaching experiments with columns containing biosolids (2.7% total N, 130 mg kg NH and 1350 mg kg NO) mixed with soil, biochar, or sawdust. One type of low-temperature (350°C) biochar sorbed 335 mg kg NH, while the other biochars and sawdust sorbed <200 mg kg NH. None of the materials sorbed NO. Biochar added at rates of 20 to 50% reduced NH-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 NO-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.

The effect of lignite on nitrogen mobility in a low-fertility soil amended with biosolids and urea.

Lignite has been proposed as a soil amendment that reduces nitrate (NO3(-)) leaching from soil. Our objective was to determine the effect of lignite on nitrogen (N) fluxes from soil amended with biosolids or urea. The effect of lignite on plant yield and elemental composition was also determined. Batch sorption and column leaching experiments were followed by a lysimeter trial where a low fertility soil was amended with biosolids (400 kg N/ha equivalent) and urea (200 kg N/ha equivalent). Treatments were replicated three times, with and without lignite addition (20 t/ha equivalent). Lignite did not reduce NO3(-) leaching from soils amended with either biosolids or urea. While lignite decreased NO3(-) leaching from an unamended soil, the magnitude of this effect was not significant in an agricultural context. Furthermore, lignite increased cumulative N2O production from soils receiving urea by 90%. Lignite lessened the beneficial growth effects of adding biosolids or urea to soil. Further work could investigate whether coating urea granules with lignite may produce meaningful environmental benefits.