Solar-powered algal production on vegetable processing industry wastewater at pilot scale

Abstract

Τhis paper proposed a sustainable treatment scheme for effluents from fruit and vegetable processing industries with high organic load that combined heterotrophic microalgae cultivation with microalgae spray drying producing end-products of commercial interest (biofertilisers and/or animal feed). A pilot plant was operated with feedstock from a fruit and vegetable processing industry and its final products were assessed. The pilot plant was powered by renewable energy (solar energy supported by biomass), which minimized the carbon footprint and operating costs of the process. Through the ultimate analysis of the produced algae, it was evident that in all cases it could be commercialized as a solid NPK organic fertilizer being in line with the respective EU and Spanish legislation framework. As far as the animal feed perspective is concerned, the end-product of the pilot plant could be efficiently included in the feed of various animals, substituting a significant part of the animal feed required. The results from the implementation were used for the design of a full-scale implementation of the innovative treatment scheme, proving that 1.26 ton/d of microalgae could be produced, which could be later used as fertiliser and/or animal feed from the daily wastewater production of a medium sized fruit and vegetable processing company. From an environmental perspective, the proposed solution provides a gold standard example of the circular economy concept, since 1.15 kg CO2 equivalent per kg of sludge avoided could be saved. Additionally, the use of renewable energy (solar and biomass) will result in a saving of 0.531 kg of CO2 emissions per kWh consumed. Conclusively, the proposed treatment scheme could meet circularity and sustainability since the end-products quality permits their integration into new value chains.