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

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.

Feasibility of vertical ecosystem for sustainable water treatment and reuse in touristic resorts.

To counteract increasing water scarcity in the Mediterranean region, this study provides data on the efficiency of a decentralized, nature-based solution for hotel greywater (GW) treatment and reuse. A pilot plant of a constructed wetland called Vertical Ecosystem (vertECO), installed in a large hotel with GW separation, was operated continuously for 12 months. vertECO achieved a removal efficiency higher than 84.0% for COD and TSS and higher than 95.4% for turbidity and BOD5. The monitored physicochemical parameters in the effluent meet the requirements for many reuse purposes restricted in the water reuse legislation. Based on the pilot operation, an economic model was set to estimate its economic feasibility (CAPEX, OPEX and payback period of investment) at several treated volumes. The payback was calculated, at the water and energy prices of Spain and other countries, with a planned operation period of 20 years. The higher the water price, the lower was the payback period. Treated GW volumes of 10.5 and 20 m3/day correspond to payback periods for Spain of 10.1 years and 9.0 years, respectively. Finally, co-benefits of vertECO have been considered alongside economic terms, and compared with another intensive technology (i.e., membrane bioreactor).