Sustainable Algal Cultivation by Effective Utilization of MSW Digestate Slurry and Biogas By-Products—An Advanced Approach Towards Carbon Fixation and Generation of Biofuels

Abstract

With the increasing popularity of generating biogas from Municipal Solid Waste (MSW), large volumes of digested slurry/digestate liquid are being discharged into sewers without recovering the large nutrient content within. Conversion of digestate nutrients to algal biofuel and its further conversion of residues to biogas can now concentrate three value-added by-products from MSW namely: biogas, algal biofuel and nutrient-rich residue. Microalgae with their faster growth rates and high lipid accumulation capability offer the potential to serve as feedstock for biofuel production. The process of biofuel production from algae is environment-friendly as the fuel produced is degradable, non-toxic and potentially carbon neutral. Algal biofuels offer an immense potential for replacing fossil fuels when algal cultivation is carried out in a sustainable manner. This study attempts to develop a sustainable process of biofuel production from algae wherein biogas slurry and CO2 from biogas are used as substrates reducing the potential carbon emissions and mutually benefit. Mixotrophic cultivation of microalgae was carried out with biogas slurry (as nutrient source) to evaluate its potential to replace conventional media since biogas slurry contains dissolved nutrients emerging from the substrate during digestion. Algae grown in biogas slurry-based system showed a 90% higher productivity than the media based system. Utilization of CO2 generated from biogas plant by algae as a carbon source can aid simultaneously in carbon fixation and biogas improvement. This paper also describes the other advantages as algal grazer management when slurry from MSW biogas plants is used for algal cultivation.