Sustainable Microalgae Cultivation for Biogas Production: A Technical and Economic Analysis
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Microalgae cultivation using waste streams as nutrient source in industrial scale is anunconventional, and so far untapped, process pathway to produce microalgae biomass. The mainadvantage of this approach is the fact no resources are spent on nutrients, which make up for themajor part of the conventional production costs. The main limitation is that culture medium is directlyinfluenced by the available in-site waste streams, which limits the application of this to industrialprocesses with nutrient-rich and toxin free waste streams. There is also a degree of limitation withrespect to specific nutrient concentration towards cultivation optimization. Optimization of biomassproductivity implies knowledge about the behavior of each specific microalgae strain towardsprocess parameters such as illumination, temperature, oxygen gas concentration in the culturemedium, nutrient availability, pH value, hydraulic retention time, mixing and heavy metal presence.The use of the cultivated microalgae to produce methane through anaerobic digestion also putemphasis on the specific chemical composition of microalgae.This study was done in partnership with Biokraft AS and it integrated in the innovation projectsin business and industry COMPLETE. The purpose of this study is to investigate the effect of theaforementioned parameters in microalgae cultivation and find out patterns to act as general guidelinesfor process optimization. It also an objective of the this work to evaluate laboratory and pilot-scaleapplications of conventional and wastewater-based microalgae cultivation towards the establishmentof an industrial-scale cultivation model, whose profitability under a set of conditions will becalculated and evaluated.The produced work highlights that there is interest in the scientific community about theadvantages of using wastewater-based microalgae cultivation systems, especially because of theirpotential as a biological wastewater treatment with reduce energetic consumption. It was also foundthat the cultivation technology that best suits the specific needs of this project is an internallyilluminated photobioreactor that will keep production steady and independent from the variable solarirradiance in Norway. Furthermore, it was found that the most cost-effective solution for harvestingthe cultivated biomass is electrocoagulation.