Mass production of Arthrospira platensis on the livestock manure for use as a protein source in animal feed

The biotechnological applications of Arthrospira platensis require intensive cultivation for mass production, taking into consideration the economic perspectives. The livestock manure was tested for the cultivation of A. platensis EG5 for economic production of biomass and protein. The manure concentrations of 1.6, 3.2, 6.4 and 12.8 g L^-1 significantly increased (P ≤ 0.5) the biomass by 19.6, 44.9, 29.8, and 18.8 %, compared to the control Zarrouk’s medium. Meanwhile, the control medium supported protein production more than manure media but with a nonsignificant difference (P ≤ 0.05) with the manure concentrations of 3.2 and 6.4 g L^-1, where it reached 50±5.4 and 49.6±4.0 g 100g^-1 dry biomass compared to 53.5±6.6 g 100g^-1 for control medium. The metals; Fe, Zn, Cu, Mg and Mn were measured in A. platensis EG5 cultivated on different manure media and their concentration range was in good agreement with many animal feed requirements as reported by NRC. The biomass and protein productivity of A. platensis EG5 on a continuous open pond system using manure medium (3.2 g L^-1) was studied for three continuous culturing cycles and maintained mean biomass of 1.11, 1.42 and 1.35 kg m^-3 and protein content of 48.5, 52 and 56 g 100g^-1 for the 1^st, 2^nd, and 3^rd harvested biomass. The biomass of A. platensis EG5 cultivated on manure medium was a good source of the essential amino acids; arginine, leucine, isoleucine, lysine, methionine, phenylalanine, threonine, and valine with concentrations comparable to the amino acids requirements of many animals as reported by the NRC. In conclusion, the cultivation of A. platensis EG5 on livestock manure for biomass and protein production maintained promising results. Therefore, we would recommend future detailed studies on using the manure commercial-scale cultivation of microalgae as a protein source to enhance the nutritional quality of fish and animal diets economically and sustainably.