Nitrogen removal from fertilizer wastewater by ion exchange

Abstract

The wastewater treatment in the fertilizer factory in Kutina (Croatia) is carried out by an ion exchange process using strong acid cation and weak basic anion ion exchangers. The regeneration of cation exchange resin is performed by 56% HNO 3 while the anion resin regeneration is done by 16% ammonium hydroxide as an external regeneration process. The wastewater in the investigation period contained a high content of nitrogen in ammonium form (with an average of 325 mg l −1 N-NH 4 +) as well as nitrogen in nitrate form (with an average of 201 mg l −1 N-NO 3). After treatment, the wastewater contained 8.7 mg l −1 of ammonium nitrogen and 7.0 mg l −1 of nitrate nitrogen and with the conductivity of 150 μS cm −1 it is added into the cooling water system. As the nitrogen in collected wastewater is very high, the dilution is done prior to the ion exchange processing. The treated wastewater is a better choice for dilution process than decarbonisated water. In this case the exchange capacity of cation resin is higher by 9.3%. Four types of anion resin were used at the wastewater treatment plant. The influence of 2% HNO 3 on LEWATIT S 4428 ion exchange resin was examined under laboratory conditions. Due to the effect of 2% HNO 3 on LEWATIT S 4428 anion resin during 24 days the exchange capacity decreased from the initial 1.19 mol l −1 to a final 0.71 mol l −1. The dynamic contact of 2% HNO 3 with the same anion resin in the column results also in a decrease of the exchange capacity by 32%.This confirms the harmful influence of nitrogen acid on the nitrate binding capacity and resin stability. Four types of anion resins were used under industrial conditions. Under dynamic equilibrium the best results were obtained with the LEWATIT S 4428 resin.