Challenge

Arid El Paso, Texas, needed a plan to reuse treated wastewater in the face of dwindling fresh water supplies from its aquifer, and scarce precipitation.

The utility sought viable technologies to install at its Fred Hervey Water Reclamation Plant, so that the treated effluent would meet drinking water standards and could be injected into the groundwater aquifer as recharge water. In that way, the community could maintain adequate levels of potable water.

Solution

The utility installed a process to treat up to 10 million gallons of sewage a day, including screening, degritting, primary clarification, flow equalization, biophysical treatment using powdered activated carbon, secondary clarification, filtration and disinfection.

The biophysical process is a two-stage PACT® system, supplied by Siemens Water Technologies. Combining adsorption on powdered activated carbon with activated sludge, the PACT system is the heart of the reuse system. It removes most organics and all nitrogen compounds.

Results

Full scale operation commenced in 1985. Since then, the reuse plant has operated without a discharge permit violation, and has met or exceeded design parameters.

The treated water meets US Environmental Protection Agency water standards and is well within state standards for drinking water quality. 

• Effluent BOD less than 3 milligrams per liter
• Effluent COD less than 10 mg/l
• Effluent TKN less than 1 mg/l
• Effluent NH₃-N less than 0.2 mg/l
• Effluent THM less than 0.1 mg/l

The effluent is pumped to the aquifer through a system of ten recharge wells. Some of it is used by industry.

Cost per treatment was about $1.60 per 1,000 gallons (year 2000 figures).