Utilization of waste nitrogen for biofuel production in China

Nitrogen (N) is the limiting factor for current biofuel production. Enormous quantities of waste N from agricultural, industrial and domestic use have been lost to the environment resulting in serious negative consequences. In this study, we discuss biofuel production using waste N (BPWN) on untilled or marginal land. Taking China as an example, the total waste N lost to surface water was estimated at 11.3 Tg N (1 Tg = 1012 g) in 2008, accounting for 40% of total fertilizer N applied to Chinaʹs cropland. The total potential biofuel produced by waste N was estimated at 16,436.3 PJ year−1 (1 PJ = 1015 J), accounting for ∼20% of Chinaʹs total energy consumption, or five times Chinaʹs total gasoline demand in 2008. t energy balance (Output–Input) of BPWN is 570 GJ ha−1 year−1 (1 GJ = 109 J) in China, about 15–30 times that of current major biofuel production systems (e.g. corn, switchgrass, low-input high-diversity grassland). The feasibility analysis shows that, although the land resources for BPWN are not sufficient in one-fifth of Chinaʹs provinces if considering all of the potential waste N supply, the total maximum land requirement is only 17.5% of Chinaʹs total untilled land resource. Further research on the imbalance between land requirement and waste N supply on the regional and local scales will help to refine the estimate of biofuel production potential.