Mitigating ammonia nitrogen deficiency in dairy wastewaters for algae cultivation

•Limiting factor to algae growth is the ammonia nitrogen deficiency in dairy wastewaters.•Mixing dairy wastewater with slaughterhouse wastewater balanced the nutrient profile.•Algae biomass yield on mixed wastewater had been improved to 1.32–2.66g/L.•Algal grown on mixed wastewater had high protein content (55.98–66.91%). This study demonstrated that the limiting factor to algae growth on dairy wastewater was the ammonia nitrogen deficiency. Dairy wastewaters were mixed with a slaughterhouse wastewater that has much higher ammonia nitrogen content. The results showed the mixing wastewaters improved the nutrient profiles and biomass yield at low cost. Algae grown on mixed wastewaters contained high protein (55.98–66.91%) and oil content (19.10–20.81%) and can be exploited to produce animal feed and biofuel. Furthermore, algae grown on mixed wastewater significantly reduced nutrient contents remained in the wastewater after treatment. By mitigating limiting factor to algae growth on dairy wastewaters, the key issue of low biomass yield of algae grown on dairy wastewaters was resolved and the wastewater nutrient removal efficiency was significantly improved by this study.