N, P, K recovery from hydrolysed urine by Na-chabazite adsorption integrated with ammonia stripping and (K-)struvite precipitation.

This study investigated the recovery of K along with NH-N and PO-P from hydrolyzed urine by technical integration. The K adsorption capacities of biochar, clinoptilolite, artificial zeolite and chabazite were firstly compared. Due to the high K recovery efficiency and additional P recovery capacity, Na-chabazite was selected as the adsorbent in this study. Its kinetics and isotherm analysis indicated that the high molarity of NH-N seriously hindered the K adsorption onto Na-chabazite in synthetic hydrolyzed urine (SHU). However, this competition between NH and K got diminished when their molarity is the same, i.e. in the SHU after ammonia stripping (ASSHU). Based on this key finding, Na-chabazite adsorption was integrated with ammonia stripping and struvite precipitation under different configurations. Simultaneous ammonia stripping was inadequate to diminish the competitive effect of NH on K adsorption. Depending on the demand for fertilizer, two sequential configurations were recommended, respectively.