The ion exchange loop stripping (ILS) process was developed to recover nitrogen in form of ammonium (NH4+) from the liquid phase of mechanical sludge dewatering at a municipal wastewater treatment plant. NH4+ removal is based on the principle of ion exchange on natural zeolite (main mineral is clinoptilolite) and a subsequent regeneration with caustic soda. Besides nitrogen, phosphorus is another essential nutrient, which is present in wastewater and is degraded unused at wastewater treatment plants. In this work, the NH4+ exchange mechanism was kinetically modeled at laboratory scale to define potential optimization approaches for the existing ILS process. Based on the exchange kinetics, a process for simultaneous recovery of ammonium (NH4+) and phosphate (PO43-) from aqueous solutions using natural zeolite was developed. The PO43- removal mechanism was identified as a surface precipitation reaction of PO43- ions and the calcium ions (Ca2+), which were desorbed from zeolite due to NH4+ ion exchange. Here, the pH of the solution is the rate-controlling parameter in the surface precipitation of Ca2+ and PO43-. Experiments carried out, that zeolite loadings up to 6.78 mg PO43- g-1 and 15.92 mg NH4+ g-1 were reached and after regeneration 75% of the dissolved PO43- were recovered, respectively. It was further shown that simultaneous removal of PO43- had no effect on NH4+ removal onto zeolite. The results in the laboratory show that simultaneous recovery of NH4+ and PO43- using natural zeolite is possible and thus represents a great potential for the stepwise scale up of the ILS process to the ILSplus process.
|Translated title of the contribution||Process Development for Simultaneous Recovery of Ammonium and Phosphate from Wastewater|
|Publication status||Published - 2022|
Bibliographical noteno embargo
- wastewater treatment
- nutrient recovery