Second-Generation Magnesium Phosphates as Water Extractant Agents in Forward Osmosis and Subsequent Use in Hydroponics

Abstract

The recovery of nutrients from wastewater streams for their later use in agricultural fertilization is an interesting approach. Wastewater recovered magnesium phosphate (MgP) salts were used in a forward osmosis (FO) system as draw solution in order to extract water and to produce a nutrient solution to be used in a hydroponic system with lettuces (Lactuca sativa, L.). Owing to the low solubility of the MgP salts (i.e., struvite, hazenite and cattiite) in water, acid dissolution was successfully tested using citric and nitric acids to reach pH 3.0. The dilution by FO of the dissolved salts reached levels close to those needed by a hydroponic culture. Ion migration through the membrane was medium to high, and although it did not limit the dilution potential of the system, it might decrease the overall feasibility of the FO process. Functional growth of the lettuces in the hydroponic system was achieved with the three MgP salts using the recovered water as nutrient solution, once properly supplemented with nutrients with the desired concentrations. This is an innovative approach for promoting water reuse in hydroponics that benefits from the use of precipitated MgP salts as a nutrient source.

Recent Studies of Membranes for Liquids Separation and Water Treatment

“…Forward osmosis is another prominent water treatment process that relies on the difference in osmotic pressure induced by different concentrations of the feed and draw solutions [ 17 ]. In a study by Mendoza et al, the forward osmosis technique was implemented using magnesium phosphate salts recovered from wastewater as the draw solution [ 18 ]. Nitric acid and citric acid were utilized to facilitate the dissolution of salts, including cattiite, struvite, and hazenite, as they show limited solubility in water.…”

“…Nitric acid and citric acid were utilized to facilitate the dissolution of salts, including cattiite, struvite, and hazenite, as they show limited solubility in water. This setup enabled water extraction to produce nutrient solutions [ 18 ]. Subsequently, the nutrient solutions were supplied as fertilizers to plants in a hydroponic system.…”

“…Subsequently, the nutrient solutions were supplied as fertilizers to plants in a hydroponic system. The results of the study showed the feasibility of functional growth of lettuce by utilizing recovered water as a source of nutrition [ 18 ].…”