Study of thermochemical co-treatment of seafood byproducts and green waste towards alternative fertilizer production within Horizon2020 SEA2LAND

In recent years the expansion of the fish processing industry caused by the increase in seafood consumption has led to a considerable increase in by-products (up to 70%), causing important management problems due to their degree of degradability. However, they can be valorised as bioproducts for agriculture as they are rich in nutrients, especially nitrogen, and others, representing a good opportunity to mitigate the environmental problems associated with their disposal.

In this context, in the frame of SEA2LAND project, the possibility to recover bio-based fertilizer from molluscs and fish wastes has been studied. These wastes were collected, respectively, from the local companies Co.Pe.Mo. and Ittica del Conero, to be then applied in agriculture as soil improvers or organic fertilizers, which is completely in line with the objective set by the European Commission to reduce the use of non-renewable sources in fertilizer production by 30%. The valorization technologies which were experimentally investigated in this study consisted of pyrolysis and composting with biochar addition. Legislative requirements and international quality standards were also analysed and taken into account.

As first step, lab-scale pyrolysis was performed in order to analyze the biochar obtained from different sources and assess its compliance with quality standards. Tests were carried out by mixing gardening waste, commonly used in pyrolysis due to the lignocellulosic matrix, and fish by-products. Results showed non-significant differences in the char produced at a physical level, but at a chemical level, a significant increase in the nitrogen content in the pyrolysed biomass with higher percentages of fish by-products was observed. However, at the same time an increase in the nickel content, exceeding the threshold values given by quality standards was also obtained. Analyses were also performed on the bio-oil and syngas produced during pyrolysis to understand how the presence of lignocellulosic material can interact with the fish.

After that, fish by-products were composted in a 30-L reactor with forced aeration by adding 10% of biochar to improve process performance such as the increase in biological activity, reduction of odor and GHG emissions, and minimization of Nitrogen loss. The temperature inside the reactor, oxygen and carbon dioxide in exhausted gas were monitored online as an indication of microbial activity and control of aeration strategy. Composting mixture was sampled once per week to determine the degree of biological stability and control process performance. The ammonia emissions produced during the test were compared to other composting tests performed without the addition of biochar, showing a significant reduction. It was corroborated by performing nitrogen mass balances taht the addition of biochar within the feedstock to be composted significantly reduced emissions, thus increasing the nitrogen content within the final product, which can improve its value as Nfertilizer.