Nutrient recovery from high-salinity dairy wastewater through the cultivation of acclimatized microalgae

Large-scale farms with concentrated animal feeding operations generate significant volumes of dairy livestock wastewater (LWW) that are rich in nutrients and salinity, and its improper management can quickly deteriorate natural environments. Here, we cultivated two microalgae, Chlorella protothecoides and Chlamydomonas reinhardtii, in filtered dairy LWW to achieve nutrient recovery from high-salinity dairy wastewater. Under 1000-7000 lux using 25-100 % LWW, we observed high removal of 86.8-95.3 % dissolved total nitrogen, 75.5-92.0 % dissolved organic nitrogen, 98.3-99.8 % NH4+-N, and 57.2-100 % total phosphorus, with moderate removal of 12.1-67.5 % for dissolved organic carbon and 2.49-33.4 % for total 19 metal(loid)s. Notably, the aromaticity of LWW dramatically reduced under higher light intensity and low rainwater dilution levels, while organic nitrogen utilization was markedly enhanced when light intensity exceeded 3000 lux. We found the highest values of 5.33-6.52 g/L for biomass yields, 37.9-42.0 % for protein contents, and 22.2-27.6 % for lipid contents. Total fatty acids (TFAs) contained 89.5-100 % C16-C18, predominantly C16:0, C18:1, and C18:2. Lipid accumulation was significantly enhanced under higher light intensities, though C. reinhardtii exhibited a greater sensitivity to higher LWW proportions compared to C. protothecoides, which favored lower rainwater dilution levels for increased TFA accumulation. Our study indicated that these two microalgae, when cultivated in filtered dairy LWW rich in nutrients and salinity, are promising feedstock candidates for biodiesel production.