Phosphorus recovery from hydroponics waste nutrient solution and its economic potential
Suhaib Malkawi, Dharmappa Hagare, Basant Maheshwari
Abstract
• Near-complete phosphorus recovery from hydroponic waste nutrient solutions (HWNS) at pH 9.5. • Phosphorus levels in HWNS observed to be as high as 70 mg/L with a median value of 20 mg/L. • Profitable recovery of phosphorus if its concentrations in HWNS are above 16 mg/L (Australia) or 12.4 mg/L (international). • Utilizing recovered calcium phosphate over commercial micro calcium phosphate fertilizer offers significant savings. • Study confirms the presence of amorphous calcium phosphate in the precipitate. Nutrient management, particularly phosphorus, is crucial for global food security due to its limited availability. This study investigates the extraction of phosphorus from hydroponic waste nutrient solutions (HWNS) using samples from various hydroponic farms. The results display elevated phosphorus levels, peaking at 70 mg/L and a median of 20 mg/L, in conjunction with a high median calcium concentration of 220 mg/L. This combination enhances the potential for efficient calcium phosphate precipitation. At a pH of 9.5, phosphorus removal reached consistently high levels, exceeding 94 % and achieving a median value of 97.6 %. The economic value of the recovered phosphorus was then compared to rock phosphates. Through chemical precipitation with micro-calcium phosphate, economic evaluations determined that to achieve production costs comparable to or below the market value of calcium phosphate, HWNS should contain a phosphorus concentration of at least 16 mg P/L and 12.4 mg P/L in the context of Australian and international markets, respectively.