Energy and nutrient recovery from anaerobic co-digestion of malting wastewater and microalgae biomass

This study aimed to investigate the impact of the ratio of Spirulina maxima biomass to inoculum on the anaerobic co-digestion of malting wastewater using upflow anaerobic sludge blanket pilot-scale reactors. The AD process occurred in mesophilic conditions, lasting for 369 h. The experimental conditions included three groups: (1) malting wastewater (control); (2) malting wastewater with an 80:20 inoculum/Spirulina maxima ratio; (3) malting wastewater with a 60:40 inoculum/Spirulina maxima ratio. The 60:40 inoculum/Spirulina maxima ratio demonstrated superior performance, generating 6.7 times more biomethane compared to both the control and the 80:20 inoculum/Spirulina maxima ratio. This condition achieved a chemical oxygen demand removal efficiency of 76%. Furthermore, the digestate generated did not exhibit phytotoxicity towards lettuce and barley. Therefore, co-digestion digestates can be effectively utilized in agriculture. Co-digestion was also found to be efficient in simultaneously treating co-digestion, generating biomethane, and producing biofertilizer. This work emphasizes a promising and sustainable approach to valorizing waste and effluents, which has positive impacts on bioenergy generation and food production. It promotes the principles of the circular economy and sustainability in agriculture.