Influence of N-rich material in valorization of industrial eggshell by co-composting

Industrial eggshell (ES) is an animal by-product (ABP) involving some risk if not properly managed. Composting is a possible treatment approved for its safe use. This study aims to assess the influence of using N-rich material (grass clippings (GC)) to improve co-composting of ES mixtures for reaching sanitizing temperatures imposed by the ABP regulation from the European Union. Two sets of mixtures (M-1 and M-2) were investigated, each containing industrial potato peel waste, GC and rice husks at 3:1.9:1 and 3:0:1 ratios by wet weight. In each set, ES composition ranged from 0% to 30% (w/w). Co-composting trials were performed in self-heating reactors for 25 days, followed by maturation in piles. Results showed that only M-1 trials attained temperatures higher than 70 degrees C for nine consecutive hours, but N-losses by stripping on average were four- to five-fold higher than M-2. In the absence of N-rich material, biodegradability of mixtures was low' to moderate' and organic matter conversion was impaired. Physical, chemical and phytotoxic properties of finished composts were suitable for soil improvement, but M-1 took 54 more days to achieve maturity. In conclusion, co-composting ES with N-rich materials is important to assure the fulfilment of sanitizing requirements, avoiding any additional thermal treatment.