The utilization of marine aquaculture sludge in a biodrying process has demonstrated its efficacy as a viable feedstock. This technology offers a dual advantage by unlocking two alternative valorization pathways for the sludge. On one front, it enables the production of a valuable solid organo-mineral fertilizer. Simultaneously, the process output material can be subjected to combustion in a biomass boiler, generating energy while preserving the phosphorus (P) and potassium (K) content, in the resultant ashes. These residual ashes can be ultimately valorized as a plant-available source of these essential elements. The results of the work developed indicate that the obtained solid material aligns with the nutrient (4.77 % of P) and organic carbon (11.9 %) requisites of the specific Product Function Category (PFC 1(B)(I)) outlined in the EU Fertilizing Products Regulation (EU 2019/1009), making it suitable for use as an organo-mineral fertilizer. In terms of energy evaluation, the balance reveals a net energy gain (368.1 kWh/t) when burning the obtained solids after deducting the energy invested in the biodrying process.

Our know-how about biodrying technology applied to aquaculture sludges can help industrial stakeholders in its satisfactory implementation. First, the addition of a bulking agent (i.e. wood chips) is advised to adjust the porosity and moisture content of the bulk mixture that must be in the range of 50-60%. We propose a temperature-dependent (<35, 35-45, 45-55, 55-70 and >70ºC) aeration regime according to the organic matter content of the sludge (0.5, 0.6, 0.8, 1 and 1.5 L min-1 kgVS-1, respectively for each temperature range). Finally, the efficient combustion in the biomass boiler can be enhanced by the complementary addition of conventional biomass fuel materials (i.e. wooden pellets) with similar heating values.

Figure 1: Biodrying reactor.

 

Figure 2: Raw wastewater solid fraction (left) and biodried product (right).