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INTRODUCTION
Resource-oriented sanitation (ROS) has been increasingly considered as a substitute for current wastewater treatment systems in developing countries because it helps fulfill the sixth Sustainable Development Goal (SDG-6) (Han et al. 2016; Han & Hashemi 2017). Source-separated urine that can be used as fertilizer forms the basis of these systems (Hashemi & Han 2017a). However, the production of urine odor at the collection and storage stages tends to make these systems unpopular and hinders their widespread acceptance (SANItaryRecycling ESCHborn 2012; Hashemi & Han 2017b).
The separation of urine at its source has a long history, especially in Asia. Korea practiced urine separation and utilization as fertilizer from the Silla dynasty to the Joseon dynasty (57 BC-1897 AD), using special closed urine jars called yogang and ojum-janggun. Although there is no evidence of any particular practice for odor prevention, these jars could act as sealed anaerobic storages, used for storing source-separated urine (Han & Kim 2014; Han & Hashemi 2017). Ancient Persians used vinegar and baking soda as a means to remove odors from materials contaminated with urine (Menocal et al. 2000). A Persian chemist named Zaryab transferred this knowledge to the Europeans during his stay in Andalusia in the ninth century (Holod 1992). A scientific investigation of the application of the mentioned ancient practices may be helpful for improving the acceptability of ROS systems.
Foods and drugs have a substantial impact on the smell of fresh urine (Hashemi & Han 2017b). In stale urine, odor can be caused by a number of odorous compounds, such as ammonia, trimethylamine, and various types of volatile fatty acids (Zhang et al. 2013; Hashemi et al. 2016). To control odor, managing ammonia is important because of its notably higher concentration compared to other odorous compounds (Wolrath et al. 2005).
Following excretion, urea (CH4N2O) is the predominant component of fresh urine after water (Udert et al. 2006). As soon as urine is excreted from the human body, urea is converted to ammonia (NH3) by the enzyme urease via the reaction presented in Equation (1). This process usually lasts 15-20 days until the urine stabilizes, meaning that no more NH3 is produced (Hashemi et al. 2016):
Then, NH3 reacts with water and increases the pH of the urine, as demonstrated...