Feasibility Study on Windrow Co-composting to Recycle Industrial Eggshell Waste

The main objective of this study was to evaluate the feasibility of recycling large quantities of industrial eggshell waste through turned windrows composting in order to obtain a value-added soil improver. For that, four different formulations were tested to produce stable composts with adequate properties to be further used for agronomic applications such as amendment in soils with acid characteristics and/or with low calcium concentration. The eggshell waste is mainly an inorganic animal by-product, and thus its co-composting was conducted with farm wastes (horse and chicken manures) and grass clipping. The windrows were aerated periodically and monitored during 50 days regarding temperature, moisture, pH, conductivity, and carbon/nitrogen ratio (C/N). The thermophilic phase lasted for 10-20 days. At the end, moisture, pH, electrical conductivity, organic matter, C/N ratio, and toxic heavy metals (Cd, Cr, Pb, Cu, Ni, Zn) were determined. The microbiological assessment involved total mesophilic heterotrophic bacteria, total coliform bacteria, thermotolerant coliform bacteria, E. coli and spores of sulphite-reducing clostridia. The assessment of maturity based on germination index and stability by using Dewar selfheating test and respirometry showed that all the composts were mature and stable, with adequate properties for agronomic applications. This study evidenced that large quantities (up to 30 % in weight) of eggshell waste may be converted into calcium-rich marketable compost by thermophilic windrows composting.