The operational performance of a 10 m3/day demonstration scale hybrid ion exchange (IEX) process to remove and recover nutrients from wastewater has being tested for the last 2 years. For the selective removal of ammonia and phosphorus from the wastewater a synthetic zeolite and hybrid anion exchanger (HAIX) were used, with empty bed contact times of 5 and 10 min, respectively. To ensure the economic feasibility of the process, the regenerant solutions were managed carefully, including re-using and recycling back to the process after the nutrients were recovered. The synthetic zeolite removed up to 89% of the initial NH4-N and nitrogen recovery took place after the regenerant (KCl 10%) reached 450 mg NH4-N/L, i.e., after 6 cycles of adsorption and regeneration. The HAIX underwent over 60 cycles without any loss in capacity. The NaOH 2% regenerant solution reached a concentration of 750 mg PO4-P/L following 8 consecutive cycles and the phosphorus was recovered by precipitation as hydroxyapatite after the addition of calcium hydroxide. The hydroxyapatite recovery process was investigated more in detail: different variables such as Ca:P ratio, pH, ideal mixing and time were optimized. The characterization of the recovered product indicated low level of impurities (heavy metals and hazardous pollutants) with potential re-use in chemical and agricultural industries. This project is part of H2020 SMART-PLANT that aims at scaling-up low-carbon footprint material recovery techniques in existing WWTPs.
Key themes: phosphorus recovery