A critical review on current urea removal technologies from water: An approach for pollution prevention and resource recovery

Urea is the key nitrogenous waste product generated in the urea cycle in ureotelic animals. Apart from that, urea and its derivatives are manufactured on a large scale for various industrial and agricultural purposes. Due to these sources, urea contamination is reported across various industries. However, since the scale and nature of these industries vary, urea contamination level within these contexts differs accordingly. Among the available urea removal methods for contaminated water, only a few technologies have been applied in real-world situations, and the majority are still at the laboratory scale. Hence, selecting suitable remediation technology for an existing or novel context should be based on a critical evaluation of all the existing technologies. Moreover, moving towards sustainable practices, urea removal from contaminated water simultaneously provides water and nutrient recovery opportunities. Hence, this review critically assesses all the available urea removal technologies, including adsorption, hydrolysis, advanced oxidation, membrane separation, and biological removal, in terms of urea removal mechanisms, applied technologies, and advantages and disadvantages. Furthermore, insights into future urea removal research and resource recovery are also presented.