Potential by-products from the production of algal biodiesel include the capture of carbon, the generation of biogas through anaerobic digestion, the generation of bioethanol through fermentation of carbohydrates, the production of feeds for aqua­culture, the production of animal feeds rich in protein and carbohydrates (~60% protein), and the production of a high-grade, protein-rich material (~90% protein). In the case of fermentation or digestion of the algal cell debris, the recycling of N and P media components can be used to decrease media costs.

Williams and Laurens (2010) considered the scenarios of biogas formation, preparation of animal feed, and preparation of high-grade, protein-rich material. They highlighted the uncertainty and process specificity of costing these options and noted the requirement for improved knowledge in this area. The 60% protein feed was valued at US$750 tonne-1 based on FAO (Food and Agriculture Organization) statistics. Relating it to the value of soya meal containing 45% protein, a value of US$500 tonne-1 was proposed. In comparison, the high-grade, protein-rich material was valued at US$900 tonne-1. Biodiesel was estimated at a value of US$125 bbl-1. Using this estimate, positive scenarios were found at protein feed values of US$350 tonne-1 and above, and protein-rich extracts at US$600 tonne-1 and above. Under the conditions used, anaerobic digestion was not cost effective; however, the high energy requirement to maintain the digester temperature was a result of the temperate environment, and revised analysis is required for warmer climates where the performance of biodigesters is well documented.