The valorisation of Anaerobic digestion (AD) waste streams into algal biomass to produce a protein alternative to soybeans could have significant commercial and environmental value. It has the benefit of alleviating the pressure of disposal of nutrient-rich digestate that is rich in N, P and trace metals, while potentially reducing the cost of microalgae production. Currently, the use of soybean protein in animal feed has significant negative environmental issues and high carbon footprint associated with its use. This study investigates three types of AD to grow Phaeodactylum tricornutum Bohlin microalgae. The results found that the crude protein in all concentrations of CW and FW digestates were found to produce a significantly higher concentration of crude protein in comparison to the F/2 control. In addition, CW 1% and PW 1% formulations were found to have favourable fatty acid profiles, which has significant health benefits in the livestock industry. There was no significant difference in the total fatty acids (TFA) found in CW 1% and PW 1% digestates compared to the F/2 control, which was in the range of 243.4 to 269.4mg/g (dry weight). The other formulations produced a significantly lower (p< 0.05) concentration of TFA compared to the control. CW 1% was found to be richer in omega-3, Eicosapentaenoic acid (EPA), compared to PW 1%, however, no significant difference was found between the EPA concentration of CW 1% and the F/2 control. Overall, in terms of highest TFA and crude protein, CW 1% digestate was found to perform the best out of all the digestates tested, and outperformed the F/2 control in terms of crude protein. The P. tricornutum grown in digestate was also found to bioaccumulate higher levels of calcium. P. tricornutum grown in CW 1% digestate could offer an alternative viable locally grown protein source for the animal feed industry, with the added advantage of being rich in EPA and calcium.
McDowell, D., Dick, J. TA., Eagling, L., Julius, M., Sheldrake, G. N., Theodoridou, K., & Walsh, P. J. (2020). Recycling Nutrients from Anaerobic Digestates for the cultivation of Phaeodactylum tricornutum: A Feasibility study. Journal of Algal Research, 48, . https://doi.org/10.1016/j.algal.2020.101893