Cultivation of Brackish Water Microalgae for Pig Manure Liquid Digestate Recycling

Abstract

Sustainability and recycling of agricultural and animal husbandry waste are important. Pig manure contains relatively high concentrations of organic matter, such as nitrate-nitrogen, ammonia nitrogen, and phosphate, and a direct discharge can cause environmental pollution. This study successfully culturing four brackish water microalgae, including Tetraselmis chuii, Isochrysis galbana, Chlorella vulgaris, and Proteomonas sulcata, by using a diluted digestate solution of pig manure (NH3 concentration is lower than 10 mg/L). These microalgae can reach their highest cell concentration within 3–7 days of cultivation. The small microalgae, C. vulgaris and I. galbana, reached a cell density of 2.5 × 107 and 1.5 × 107, respectively, whereas lower cell densities were documented for large microalgae T. chuii (1.4 × 106) and P. sulcata (1.6 × 106). Our findings highlight the feasibility of sustainable treatment of animal manure using brackish water microalgae. These results provide opportunities to reduce freshwater usage and environmental pollutions, and support microalgae production for further aquaculture application.