Characterization of Solid Digestates: Part 2, Assessment of the Quality and Suitability for Composting of Six Digested Products

Abstract

The aim of this research was to characterize six organic solid digestates in order to discuss their potential direct agricultural utilisation or their further valorization through an aerobic post-treatment. The studied digestates came from four different sources: waste water treatment sludge, food-processing wastes, agricultural solid wastes and source-selected organic fraction of municipal solid wastes. Physico-chemical, biochemical and biological characteristics showed that a direct use of digestates and application on land as soil amendment or fertilizer is not recommended according to current standards. A posttreatment appeared thus to be necessary in order to obtain commercial amendments or fertilizers. A composting posttreatment of these digestates would assure their full biological stabilization as these organic residues still contain residual biodegradability and present sometimes phytotoxic risks. The prediction of operational parameters showed that the composting post-treatment of these digestates will probably lead to a limited rise in temperature, require moderate aeration supply and last less than a typical composting treatment of organic wastes.

Studies on the Chemical Stabilisation of Digestate from Mechanically Recovered Organic Fraction of Municipal Solid Waste

“…Due to its potentially low quality, opportunities to apply digestate produced from mixed MSW to land are limited [3]. In addition, few studies were found concerning the characterisation of digestate from mixed MSW, but efforts have been made to characterise similar wastes and find consistent applications [4][5][6][7][8].…”

A comparative cost analysis for using compost derived from anaerobic digestion as a peat substitute in a commercial plant nursery

“…This treatment generates two products, namely biogas containing methane (CH 4 ) and a digested material by-product (digestate) (Restrepo et al, 2013). However, although the digestate has potential as a fertilizer, it can also present some undesirable characteristics, such as odor, in association with high volatile fatty acid contents, viscosity, high humidity and potential phytotoxicity and pathogenic microorganisms (Teglia et al, 2011). Composting the solid fraction of the digestate can be a feasible method not only for managing these materials but also for improving the quality of the endproduct.…”

Organic Xenobiotics

“…Digestates are either directly applied to the soil or are treated before (solid-liquid separation, drying, dilution, filtration, composting) (Möller and Müller 2012). Many questions regarding the quality of biogas digestates as a fertilizer source are still unanswered such as pathogen transfer, organic contaminations and high ammonium availability (Goberna et al 2011;Teglia et al 2011). The direct application of digestates without post-treatment is often not recommended (Teglia et al 2011).…”

“…Many questions regarding the quality of biogas digestates as a fertilizer source are still unanswered such as pathogen transfer, organic contaminations and high ammonium availability (Goberna et al 2011;Teglia et al 2011). The direct application of digestates without post-treatment is often not recommended (Teglia et al 2011). Moreover anaerobic digestion of animal manures may cause a lower P availability in the digestate (Güngör and Karthikeyan 2008).…”