Scalability of combining microalgae-based biofuels with wastewater facilities: A review

The feasibility of growing microalgae-based biofuels has been broadly researched by taking advantage of municipal wastewater as the source of nutrients. Significant progress has been made by indentifying algae genera capable of growing in wastewater, such as Chlorella, Haematococcus, Scenedesmus, Chlamydomonas, and Chloroccum. Additionally, municipal wastewater, taken at different stages of the treatment process, has been evaluated as the growth media. By comparing the lipid productivities of microalgae grown in centrate, obtained from the dewatering of sludge, secondary treated wastewater, and raw wastewater, the most promising results have been observed when the centrate has been used as the source of nutrients. The growth-rate limiting nutrients for microalgae were reported to have their highest concentration in the centrate out of the overall wastewater treatment process, up to 134 mg·l− 1 and 212 mg·l− 1 for nitrogen and phosphorous, respectively. To evaluate the scalability of growing microalgae in such substrate, further considerations are taken into account in the present research. Such considerations are the uniqueness of the wastewater treatment facility, wastewater characteristics and production, potential inhibitors, and the presence of biological nutrient removal (BNR) operations in the process, which are required by the Environmental Protection Agency (EPA) to meet the latest wastewater discharge permits. Moreover, the most suitable computational and experimental methods to predict the growth of microalgae in wastewater and lipid synthesis will be assessed in depth.