Ammoniacal nitrogen removal and reuse: Process engineering design and technoeconomics of zeolite N synthesis

This investigation of Zeolite N synthesis addressed process flow design and manufacturing economics. Zeolite N is important as it has high selectivity and capacity for ammonium ions which means it has applications in wastewater treatment or nutrient management. The aim was to accelerate zeolite N use by developing an optimal economic model for zeolite N synthesis. Three process designs for 30 tonnes per day zeolite N production were evaluated; (1) No recycling of mother liquor or wash water; (2) recycling of mother liquor; (3) recycling of mother liquor and wash water. Recycling strategies reduced demand for KOH & KCl by 58% and 83%, respectively. Water consumption was lowest for the mother liquor/wash water recycling plant (c.f. 185 m3 per batch compared to 290 m3 per batch for base case). Similarly, wastewater generation was least when using the mother liquor/wash water recycling approach. Capital expenditure was similar for the three processes (A$14,190,750 to A$15,504,000). However, operational expenditure was considerably less when recycling mother liquor and wash water. The highest net present value (NPV) for zeolite N synthesis resulted from internal recycling of mother liquor and first stage wash water (A$85,813,532) resulting in a payback period of 2.44 years. Notably the assumed zeolite N selling price of A$2000 per tonne was less than the literature value of A$3067 per tonne which was suggested to be economically attractive. Sensitivity analysis indicated a break-even point of A$1300 per tonne of zeolite N and that zeolite price was the major factor controlling project viability.