Water use and its recycling in microalgae cultivation for biofuel application

• Water recycling in microalgae cultivation enhanced the growth of microalgae.
• Presence of extracellular product may enhance bacterial growth.
• Harvesting method affects the water reusability.
• Water reuse resulted in positive energy.
• Reuse of water can reduce nutrient related energy requirement.

Microalgal biofuels are not yet economically viable due to high material and energy costs associated with production process. Microalgae cultivation is a water-intensive process compared to other downstream processes for biodiesel production. Various studies found that the production of 1 L of microalgal biodiesel requires approximately 3000 L of water. Water recycling in microalgae cultivation is desirable not only to reduce the water demand, but it also improves the economic feasibility of algal biofuels as due to nutrients and energy savings. This review highlights recently published studies on microalgae water demand and water recycling in microalgae cultivation. Strategies to reduce water footprint for microalgal cultivation, advantages and disadvantages of water recycling, and approaches to mitigate the negative effects of water reuse within the context of water and energy saving are also discussed.