Characterization of three industrial digestates and composts of digestates: Impacts of the composting step on the innocuousness of digestates

The use of treatment methods involving Anaerobic-Digestion (AD) is expanding rapidly for a wide range of organic waste in France/Europe. In addition to biogas, AD generates digestate, a partially stabilized/sanitized product. In the majority of cases digestate is recycled for agricultural use, whether in composted form or not. However, little is known about its effect and impact on soils and the agro-system. In this context DIVAGRO study was initiated in partnership (ADEME/INRA/VERI) with the aim to study three digestates and Composts of Digestates (CD).

Digestates studied were issued of the treatment of residual municipal solidwaste (biowastes), co-digestion (food processing wastes) and sludge (wastewater treatment). For Raw Digestates (RD) it appears that the agronomic characteristics are closely to raw-wastes put into AD (preservation of nutrients from raw-wastes), as well as to the process of AD implemented (HRT, thermo/mesophilic…). RD show a fertilizing value through the conservation of macro/micronutrients and nitrogen mineralization during AD. CD present almost similar agronomic characteristics to composts produced from other raw-wastes. Concerning the innocuousness of digestates and CD, heavy metals, organic compound and inert contents fulfill the French regulatory criteria (NFU44-051 or NFU44-095 for composts). Their spreading shouldn’t have any negative environmental impacts at short-term. Microbiological results show that a stabilization step by composting allows a reduction of salmonella. Finally, phytotoxicity tests show the phytotoxic character of one digestate and the absence of phytotoxicity of all the composts. Beneficial effects on germination and development of aerial parts of barley and watercress were even observed using CD.

https://www.wtert.eu/default.asp?Menue=1&ArtikelPPV=26158