Circular concepts for biowaste and crop fertilization management

The current growth of global population and rising living standards require an increment of crop production and consequently of fertilizer consumption. This increase in fertilization, together with the decoupling of crop and livestock farms, has led to a transition from a circular and sustainable nutrient use towards a linear and inefficient nutrient transfer along the agrifood chain. Moreover, the production of nitrogen and phosphorous fertilizers is critical and poses significant environmental impact. Livestock and municipal biowastes, annually produced in huge quantities, present a high nutrient content and hold significant potential to reduce our dependency on synthetic fertilizers. However, their use as such presents several limitations and can imply nutrient losses during storage and application. Therefore, these biomass wastes can be treated by composting, pyrolysis and anaerobic digestion. After giving an overview of the three processes, this review article goes into detail on the technologies to optimize the anaerobic digestion performance. Particular attention is paid to substrate pre-treating processes and digestate post-treatment methods, targeting nutrient recovery and recycling. An example for application of these concepts is given within the European project ECONUTRI, aiming to optimize the recovery of nutrients from anaerobic digestate in form of struvite, a slow-release fertilizer.