The effect of sewage sludge fertilization on the biomass yield of giant miscanthus and the energy balance of the production process

Abstract

The application of sewage sludge as fertilizer in the production of non-food crops is an environmentally sustainable approach to sewage sludge management. This article presents the results of a multidirectional analysis (agronomic and energy efficiency analysis) evaluating the effects of sewage sludge applied at rates equivalent to 100 and 160 kg N ha−1 on the production of giant miscanthus (Miscanthus × giganteus Greef and Deuter) in north-eastern Poland in 2013–2018. The optimal fertilizer rate was 160 kg N ha−1 regardless of nitrogen source (mineral fertilizers, sewage sludge), and it contributed to the achievement of the highest biomass yield (19.8 Mg ha−1 dry matter - DM) and the highest energy output (272–275 GJ ha−1). Energy demand was highest (19–24 GJ ha−1) in production technologies involving mineral fertilizers. The replacement of mineral fertilizers with sewage sludge decreased energy inputs in the production of giant miscanthus biomass by 32–34%. Energy gain was highest (259 GJ ha−1) when M. giganteus was supplied with sewage sludge at a rate equivalent to 160 kg N ha−1. The energy efficiency ratio peaked (24.7) in the production technology without fertilization. Energy efficiency was 43–52% higher when giant miscanthus plants were supplied with sewage sludge rather than mineral fertilizers.