Sustainable Resort Infrastructure: Wastewater Utilization in Thermal Spa Complexes

A modern approach to the organization of wastewater disposal systems ensures the sustainable development of resort areas. Warm mineral springs (WMSs) located in suburban areas are not only recreational facilities for the population, but also sources of used mineral and communal wastewater. Preventing or reducing the discharge of pollutants in this type of liquid waste can reduce the anthropogenic impact on the environment. The article proposes a method for the chemical precipitation of ammonium ions in a mixture of mineral and domestic wastewater, and the production of struvite, a complex agricultural fertilizer. Three series of experiments were conducted: (1) on a model solution of ammonium ions; (2) on a mixture of a model solution and real mineral water; and (3) on real wastewater and spent mineral water taken from a thermal resort. As a result of an experiment with water samples at an initial concentration of no more than 85 mg/L, optimal doses of reagents were identified: 5.67 g/L of sodium hydrophosphate and 3.21 g/L of magnesium chloride to achieve a residual concentration of ammonium ions in purified water of no more than 1.5 mg/L at pH = 9–10. In the case of mixing of domestic wastewater and used mineral water, it was possible to reduce the use of magnesium chloride by 80%. At the same time it was possible to obtain the amount of sediment containing struvite, which is a valuable agricultural fertilizer. With the introduction of this technology, it is possible to reduce the expenses of reagents and reduce the damage caused by the discharge of liquid waste from a thermal resort, while the profit earned through the sale of fertilizer can partially offset the cost of wastewater disposal.