El Paso sets example for water reclamation
In the early 1980's, the residents of El Paso, Texas, watched water levels in their aquifer decline year after year. The city depended upon the Hueco Bolson aquifer, shared with a city double the size of El Paso, for about 60% of its water. The El Paso Public Service Board devised a plan to maintain adequate levels of fresh drinking water through a wastewater reuse programme, leading to the building of the Fred Hervey Water Reclamation Plant.The plant restores sewage to drinking water quality. Up to 37.85Ml/d of sewage (1580m3/h) are processed from El Paso's northeast section, including water from toilets, showers, and kitchens. Sewage is treated to drinking water standards. The complete process includes both wastewater and water treatment processes: screening, degritting, primary clarification, flow equalization, two-stage PACTRegistered system treatment, lime treatment, two-stage recarbonization, sand filtration, ozonation, granular activated carbon filtration, chlorination, and storage. Two parallel 18.925Ml/d treatment trains make up the 37.85Ml/d system. Primary sludge is digested anaerobically, and with the chemical sludge, placed into drying beds. Thereafter, dried solids are disposed of in a monofill.
The PACT process, supplied by USFilter's Zimpro Products, is at the heart of the reuse system, using powdered activated carbon and bacteria in an aerobic treatment process. Physical adsorption and biological assimilation occur simultaneously, enabling synergistic treatment to occur. The process removes most organics and all nitrogen compounds.
Full-scale operation of the plant began in 1985. Since then, the plant has been operating without a discharge permit violation, and has met or exceeded design parameters since start-up. The current unit cost for treatment is about $1.60 per 3785l.
The water meets the US EPA's water standards and is well within State/Federal standards for several parameters.
The effluent water is used for industrial purposes, as well as for aquifer re-charge, through a system of ten recharge wells, each reaching down 245m. It takes about two years for the injected water to migrate to the potable water wellheads.
For every 10 years the plant performs at its capacity, the life of the Hueco Bolson is extended one year.
Writing in Pipeline, Robert G. Boyd asserts that, with fewer and fewer sources of potable water in the US, "Wastewater reclamation and reuse will become more of a necessity than a novelty." The city of El Paso serves as an example for all in efficiently re-using water.