ABSTRACT
The increasing awareness of natural resource depletion, the increasing demand of nutrients and energy for food production, and the more and more stringent nutrient discharge and fertilization levels have resulted in an increased attention for nutrient recovery from municipal and agricultural wastes. Anaerobic (co-)digestion is an established, environmentally friendly, and efficient technology to convert animal manure, sewage sludge, organic biological food/industrial wastes, and/or energy crops into renewable energy and digestates rich in bio-available (macro)nutrients. However, the further sustainable development of this technology is currently hindered, especially in high-nutrient regions, because the remaining digested wastes, i.e. digestates, cannot or only sparingly be returned to agricultural land in their crude form. This chapter aims to assess the fertilizer value of products recovered from digestate. Generic digestate characteristics and fertilizer quality specifications are inventoried, after which the agronomic and economic value of recovered products is evaluated according to their fertilizer properties. Finally, the fertilizer marketing potential of recovered products is discussed based on current market trends and prices. As such, this chapter provides useful guidance for worldwide revision of fertilizer regulations with respect to bio-based amendments.
