Feasibility of using pretreated swine wastewater for production of water spinach (Ipomoea aquatic Forsk.) in a hydroponic system

Based on sufficient pollutants in pretreated swine wastewater (PSW), this study aimed to explore feasibility of growing water spinach (WS) in a hydroponic system using PSW as a liquid fertilizers in a hydroponic system. The tolerance values of WS to Cu(Ⅱ), Zn(Ⅱ), total phosphorus (TP), and ammonium-N (NH₄ ⁺-N) in culture solution were found to be 0.5, 2.0, 150, and 300 mg·L⁻¹, respectively, in the hydroponic systems. The fresh stem-leaf production of WS in undiluted PSW increased by 38.9% compared to the control group (Formula B of leafy vegetable solution culture in South China Agricultural University), and the concentration of nutrients (chlorophyll a, chlorophyll b, β-carotene, and sugar) of WS was also higher than the control group. The concentration of Pb(Ⅱ), Hg(Ⅱ), As(Ⅴ), and Cr(Ⅱ) in WS was all below the safety standard content for agriculture production in China. After 20 d hydroponic culture, the NH₄ ⁺-N, TP, Cu(Ⅱ), and Zn(Ⅱ) concentration in PSW significantly decreased to 19.77 (<80), 3.32 (<8.0), 0.15(<2.0), and 0.54 (<5.0) mg·L⁻¹, corresponding to removal rate of 87.91%, 92.38%, 64.29%, and 49.53%, respectively, which met the national discharge standard of livestock wastewater in China.