Background: Algaculture, like any form of agriculture, is highly sensitive to fertilizer or nutrient costs. A major roadblock to commercial algaculture is efficiently utilizing volatile nutrients, specifically carbon dioxide and ammonia, to feed microalgal cultures. These nutrients are typically plentiful in multiple agricultural and industrial waste streams and can potentially provide fertilizer or nutrients for large-scale microalgal cultivation. However, individual methodologies need to be developed for each type of waste stream to remove uncertainty in the assumption of yield and cost of production in microalgae cultivation systems.
Methods: This review focused on the use of waste nutrients used for cultivation of microalgae, specifically nutrients that are currently being underutilized or wasted. Those nutrients, carbon dioxide and ammonia, require special capture and/or handling steps in order for them to be used for microalgae cultivation. A variety of techniques, using carbon dioxide for pH control, mixing sumps, sparging, controlled dosing techniques and pond covers represent approaches used for handling and maximizing the use of available carbon dioxide and ammonia for microalgae cultivation.
Results: Efficient nutrient recycling has been shown to reduce fertilizer input costs, although this is highly dependent on the specific processes being employed, and the nutrient utilization efficiency. This review summarizes efforts to quantify and improve carbon dioxide and ammonia utilization in microalgal cultivation and to reduce overall volatilization and loss of these valuable nutrients. Practical methods of preventing volatilization and increasing gas transfer to the microalgae crop included: pH control, nutrient dosing and improving gas transfer efficiency.
Conclusion: Finding an economical nutrient source to drive microalgal biofuel production remains a key challenge. Wastewaters represent a relatively untapped source of nutrients for microalgae cultivation. Key nutrients in wastewaters are volatile (carbon dioxide and ammonia), potentially toxic, and require special handling approaches such as balancing pH, temperature, contact time, and contact surface area. Preliminary results suggest that these volatile nutrients can be effectively utilized for microalgal cultivation.