Struvite precipitation using continuous flow reactor

Abstract

Due to population rapid growth, fertilizer industries have to increase the production to ensure food security causing faster non-renewable resource depletion. However, organic wastewater (cow urine) commonly contains high amount in NH4+ and PO43- is still underutilized and causing eutrophication and unpleasant odour problem. Struvite precipitation, a common technique using for nitrogen and phosphorus recovery from wastewater,is proposed to recover the organic and renewable nutrients sources. Struvite precipitation process for nutrients recovery/removal from waste sources is beneficial not only providing slow-releasing and high-quality fertilizer but also reducing soil and water pollution from rich-nutrients wastewater. This research aimed to utilize the cow urine wastes as the raw material for the struvite precipitation, to determine the influence of the PO43-: Mg2+ concentration, and input flowrate on a continuous reactor to the struvite formation. Struvite was made using continuous method with variation of the PO43-: Mg2+ concentrations ratio of 1:1; 1:2 and 1:4 and the inlet flowrate of 8.2 mL/s and 15.8 mL/s. The results of this study show that the increase of MgCl2 addition and the higher flow rate could increase the P removal efficiency of struvite in reactors. The optimum phosphate removal efficiency at the flow rate of 8.2 mL/s is obtained at 80 mins with the percentage of 54%, while at the flow rate of 15.8 mL/s, 43% of P removal is obtained at 70 mins. The results from the kinetic study in the input flowrate was found that the higher the concentration ratio of PO43- and Mg2+, the greater the value of the reaction rate constant. However, for molar ratio 1:1 of PO43-: Mg2+, the greater the input flow rate, the smaller value of the reaction rate constant was obtained. From this study, it is revealed that the molar ratio of PO43-: Mg2+ and aeration rate affect significantly the struvite precipitation.