Abstract
Declining earth resources, rising ore cost and increasing pollution are calling for recycling of wastewater in the context of the circular economy. In particular, urine is a potential source of phosphorus (P) and potassium (K), yet currently available methods for P and K recovery are limited in efficiency. Here, we designed an electrochemical crystallization system using sacrificial magnesium anodes to recover P and K in the form of K-struvite (MgKPO4·6H2O) from simulated urine at low (P/K = 0.25) and high (P/K = 0.6) phosphate levels, respectively. Results show optimal recoveries of 88.5% for P and 35.4% for K in the form of rod-shaped K-struvite at 3.5 mA/cm2, though higher current density reduced recovery due to side reactions and pH increase. Seeding prefabricated struvite crystals at 1.6 g/L into urine enhanced the recovery of K by 14.7% and of P by 23.7% compared to the control group. Overall, our findings show that electrochemical crystallization is promising to recover K-struvite fertilizers.
Highlights
As the world's population continues to grow, the demand for food will increase by about one third by 2050 (Fukase et al 2020)
Adding prefabricated struvite crystals at 1.6 g/L into urine enhanced the recovery of K by 14.7% and of P by 23.7% compared to the control group
We firstly tested the electrochemical recovery of P and K from simulated urine with K/P ratio of 1/0.25 (Fig. 2a, b, c)
Summary
As the world's population continues to grow, the demand for food will increase by about one third by 2050 (Fukase et al 2020). Since the raw materials of traditional fertilizers are derived from ore and are non-renewable, the development of new technologies to recover these nutrients from the environment as alternative fertilizers has attracted widespread attention (Flores et al 2017). Urine is rich in nutrients and is the source of more than 50% of phosphorus and 80% of potassium in municipal wastewater, even though it makes up only 1% of total wastewater volume (Yan et al 2021). Extracting urine elements before urine reaches municipal wastewater would both lower the load of sewage plants and produce valuable fertilizers (Badeti et al 2021). Urine storing for more than 6 months can be used directly in agricultural production, this technique is limited by the need for storage space, odor treatment during storage, and high transportation costs (Udert et al 2012), calling for the development of new technologies
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