Production of Biogas and Astaxanthin from Fruit and Vegetable Wastes Using an Integrated System

Abstract

The use of fruit and vegetable wastes in biogas production is an attractive option, as it provides simultaneous waste treatment and energy production. The use of the CO2 in biogas for algae cultivation with a zero waste approach would make this process even more attractive. In this way, biogas enrichment, which is traditionally done using economically costly and non-environmentally friendly methods, would be improved, and algae cultivation would become more economical. In the first part of this study, the operation conditions for the biogas reactor and the algae reactor for astaxanthin production were optimized separately. Rates of up to 1.2 L CH4/day and yields up to 0.5 L CH4/g volatile solids were obtained with a 2.5 g dry matter/L day organic loading rate with an anaerobic bioreactor, and 5.1 mg/g astaxanthin was produced by air feeding. When it was decided that sufficient astaxanthin was produced, astaxanthin was obtained using vegetable oils (olive and nut), an environmentally friendly extraction method. In the second part of this study, the anaerobic bioreactor and the algae reactor were integrated, and 6 mg/g astaxanthin production was observed using fruit and vegetable wastes as the substrate for biogas production and the CO2 in biogas for cultivation of Haematococcus pluvialis and therefore astaxanthin production. The integrated system resulted in higher astaxhantin production with a zero waste approach. Moreover, the residual biomass remaining after extraction was fed back into the biogas reactor as a substrate, adopting a zero waste biorefinery approach.