Water security and sustainable water resource management have become urgent global issues due to increasing water shortages and frequent droughts. To address these challenges, various alternative methods for utilizing existing water resources have been implemented, including wastewater recycling, rainwater catchment, and the use of seawater. In islands, seawater can be utilized for various purposes, such as desalination and flushing toilets. 

With funding support from the Guam Waterworks Authority and the Guam Hydrogeologic Survey (Guam Public Law 24-247), WERI conducted research on water security and sustainability, focusing on the use of seawater for flushing toilets—a promising technique to conserve freshwater resources. Literature reviews indicate that toilet flushing accounts for a significant proportion of household water consumption, ranging from 29% to 47%. 

Currently, Guam’s wastewater treatment plants handle 59% of household wastewater, while the remaining 41% of households use septic tanks, which are expected to be eventually connected to sewage lines. The main pollutants in septic tanks are ammonium, typically ranging from 20 to 55 mg/L. Consequently, ammonium and other ions, such as chloride, would significantly increase in wastewater if septic tank connections and seawater-flushing toilet systems were implemented. Some reports indicate that Guam’s wastewater treatment plants occasionally experience ammonium levels in effluent as high as 24.9 mg/L. Thus, controlling ammonium levels in wastewater treatment plants is a major concern in Guam. 

Nitrification, a biological oxidation process that converts ammonia to nitrite (nitritation) and then nitrite to nitrate (nitratation), is the most critical process for determining wastewater treatment efficiency. The metabolisms of nitrifying bacteria, such as Nitrosomonas and Nitrobacter, are largely responsible for nitrification.