Volatilization of Nitrogen from Dewatered Biosolids

Volatilization of N from biosolids applied to land lessens the risk of ground water contamination and reduces the amount available for plant uptake. This study determined rates of volatilization of NH + 4 -N from biosolids after surface-application. Biosolids from three sewage treatment plants (Cronulla, Liverpool, and Quakers Hill) in Sydney, Australia, were applied under controlled conditions to exclude leaching and plant uptake, and volatilization was calculated using a mass balance approach. Application rates supplied 100 to 168 g m -2 of total N including 20 to 67 g m -2 of NH + 4 -N. Most loss of N occurred within 1 wk of application; within 3 wk 71 to 81% of the NH + 4 -N applied had been lost. Subsequent changes in NH + 4 -N were small and there was little loss of organic N. The rapidity and magnitude of loss in both NH + 4 -N and total N suggests that N was primarily lost by volatilization, and that denitrification losses, involving slower biological processes, were minimal. Amounts of NH + 4 -N volatilized were proportional to amounts applied. Loss of applied NH + 4 -N did not increase with regular re-wetting, although loss of total N was increased, suggesting mineralization of organic N followed by gaseous loss. Volatilization, an important pathway for loss of N applied in biosolids, needs to be considered when calculating rates of biosolids application to protect ground water while providing nutritional benefit.