Direct Potable Reuse of Wastewater

Water is essential to our societies and mankind. Currently, 844 million people across the globe lack access to potable water. By 2025, it is projected that half of the world population will be in a region of water stress.5 The water crisis is often thought of as a problem limited to places that have always struggled to have clean water, but it is now affecting new areas such as the southwest United States. With increasing population demands and drought, the feasibility of direct potable reuse (DPR) of wastewater is being considered. According to an EPA report in 2017, there are only four operational or planned DPR facilities in the United States. Of these, the El Paso Advanced Water Purification Facility will be the only one to send treated water directly into the distribution system without blending or continuation onto conventional treatment.1 As demand and water costs increase, we believe that the implementation of our DPR process for wastewater effluent is a viable option for many communities. The primary contaminants in wastewater treatment plant (WWTP) effluent that must be targeted for potable reuse are organics, bacteria, pathogens, viruses, and suspended and dissolved solids. Our process consists of ozone treatment, granular activated carbon (GAC) treatment, a cartridge particulate filter, ultrafiltration, reverse osmosis, and ultraviolet disinfection. Ozone is used to kill microorganisms in the secondary WWTP effluent before it enters the rest of the system to prevent bio-fouling on the equipment. GAC is used to remove the majority of organic contaminants. A cartridge filter is between the GAC and ultrafiltration (UF) to prevent plugging of the UF membrane. Ultrafiltration is used as pretreatment for the reverse osmosis unit. UF was chosen for its ability to remove pathogens and viruses. Reverse osmosis will remove dissolved solids, a necessary step for the contaminated water to become potable. The final step is disinfection by ultraviolet treatment to ensure no live pathogens reach distribution. Experiments were performed to determine if this combination of steps could effectively treat contaminated water. The necessary treatment must be able to reduce the total dissolved solids (TDS) level from 1,200 parts per million to less than 500 parts per million and reduce TOC from 10 parts per million to less than 0.1 parts per million. Fecal bacteria such as coliform must not be present for the water to be considered potable.15 A full size plant was designed based on the needs of a community of 5,000, using an average water demand of 100 gallons per person per day.18 The Poo Pig Sooie team has found Silver City, New Mexico (population ≈ 10,000) to be an ideal city for implementation of the DPR process. This plant would be able to supplement 50% of the potable water (equivalent to a city with a population of 5,000) demands of the city for as little as $1.27 per 1,000 gallons