Phosphate Removal from Wastewater by Mineral Wool Filters

Abstract

According to the United Nations, eutrophication is the most prevalent water quality problem. Developing countries especially are struggling to manage the increasing volume of untreated wastewater. A preliminary study of a Dutch-Indian partnership, developing universal watermanagement (LOTUSHR), has shown some indication of ortho-phosphate removal by mineral wool. The objective of this research is to understand the ortho-phosphate removal mechanism of mineral wool used for wastewater treatment. It was hypothesized that mineral wool dissociates ions due to biologically mediated pH changes, which subsequently interact with ortho-phosphate, forming minerals and removing ortho-phosphate from wastewater. First of all, the chemical composition of mineral wool was determined. Secondly, the dissolution of mineral wool was quantified by batch experiments at different pH and phosphate concentrations. Furthermore, geochemical modeling with PHREEQC was used to analyze the thermodynamic potential of wastewaters to precipitation, not containing mineral wool. Additionally, the phosphate removal rates of a flow-through experiment, using mimicked Indian Drain Water and mineral wool, was compared with PHREEQC simulations. Results showed that based on chemical analysis mineral wool contains: 188.0 g/kg silicon, 187.6 g/kg calcium, 79.3 g/kg aluminum, 43.1 g/kg iron, among other elements. The mineral wool showed no significant dissolution of ions under different pH and phosphate concentrations. Therefore, the hypothesis was rejected, as the mineral wool did not release ions when stressed with different pH. Consequently, biological conversion will not facilitate ion release from the mineral wool either. The mineral wool did show a self-buffering effect, due to its alkaline properties. Furthermore, with use of PHREEQC, amorphous tricalcium phosphate was characterized as the major mineral phase. In conclusion, the hypothesis formulated was rejected. This research performed did not lead to the identification of the removal mechanism responsible for the ortho-phosphate removal from wastewater by mineral wool filters.