In unconventional fields, hydraulic fracturing is a requirement, not an option. Whether the water used in fracking is recycled produced water or freshwater, it must be treated to remove bacteria to minimize equipment damage. One 100-barrel-per-minute frac water disinfection system meets the increasing need for cost-effective, nontoxic, next generation ultraviolet (UV) systems that can be used to treat produced water and freshwater. The self-contained mobile unit eliminates toxic biocides that may be included in some frac fluids.
The Treatment Technology
This system is based on a patented UV technology named UVX, providing 14 times greater bacterial inactivation power per cubic foot and eight times greater bacterial inactivation power per watt than conventional UV disinfection systems. Its compact size is a key advantage, enabling the system to be used on the frac pad while meeting the need for large amounts of highly disinfected water.
The system consists of six parallel sets of chambers. In each UVX chamber, proprietary medium pressure lamps produce UVC radiation to inactivate bacteria in the water (see Figure 1). In each chamber, water flows through a series of sub-chambers, each of which illuminate the water. The water flow is optimized to create sequential vortices. The high degree of parallelism provides inherent redundancy because water may be redirected through the remaining five chamber sets by closing a valve if a lamp were to fail in one of the chambers. The chamber system is optimized to minimize energy use while achieving high bacteria kill rates. Its performance was modeled and optimized using computational fluid dynamics software. Extensive onboard instrumentation and computer control ensure failsafe operation. By circulating the water in each sub-chamber, the distribution of bacteria is narrowed, and the efficiency of bacterial inactivation is increased dramatically over conventional UV disinfection systems. Medium-wavelength UV light prevents photoreactivation of inactivated bacteria in treated water. The biocidal action of UV light is complemented by a small amount of peracetic acid (PAA) for residual disinfection. The PAA is produced in the trailer by mixing a combination of powdered, nontoxic and non-hazardous precursors into an onboard freshwater tank. PAA is approved by the U.S. Food & Drug Administration for washing fresh fruit and vegetables at a concentration of 4.8 parts per million. The UVX system uses PAA at an even lower concentration for both initial disinfection and residual disinfection. PAA does not interfere with other frac chemicals and is effective as a residual disinfectant against self-reducing bacteria, iron-reducing bacteria and acid-producing bacteria.
The UVX system is integrated into a single semitrailer with an external generator to allow all-weather operation. Integrated heaters enable operation at temperatures as low as 25 F. Integrated ballast cooling allows operation up to 110 F outside. The single trailer configuration enables the UVX unit to get close to the water source and rapidly rig up and rig down. The trailer is designed with sufficient internal room to enable lamp changes and preventive maintenance on the system in the protected trailer environment during any weather condition. The semitrailer has an integrated operator area providing access to the flow hardware and the electronic system controls. The UVX system is designed to allow regular, rapid cleaning of the protective quartz sleeves surrounding the lamps in the field between frac jobs. The manifold's design permits the rapid replacement of any system lamp without needing to remove water from the system in the unlikely event of a lamp failure. The intake manifold has a strainer to prevent foreign material from entering the system. The UVX system has an integrated ground fault interruption system with immediate interruption of lamp current if the unit senses a ground fault. An uninterruptible power supply with battery backup powers the ground fault interruption system and other key components of the control system to protect the system from power surges or power loss. An on-site field test laboratory based on Environmental Protection Agency (EPA) standard methods was developed to alleviate the logistical challenges of obtaining field samples and transporting them to an independent EPA-certified laboratory at a controlled temperature within seven hours of sampling. This lab is complete with an incubator, sterile titration apparatus, and EPA-approved IDEXX QuantiTray multi-well incubation system for heterotrophic plate count analysis.
The UV treatment system has consistently achieved more than 99.95 percent bacterial inactivation rates during freshwater fracs and turbid produced water fracs at flow rates of more than 90 barrels per minute. It has produced excellent results in the Marcellus Shale, the Permian Basin and the Anadarko Basin, proving the system's effectiveness in different reservoirs. Test results were verified through duplicate sample sets sent to certified independent laboratories and analyzed by membrane filtration. The UVX system, tested by the University of Arizona at Tucson, has also demonstrated a greater than 99.999993 percent bacterial inactivation. The system also eliminates exposure to hazardous biocides such as glutaraldehyde and tetrakis (hydroxymethyl) phosphonium sulfate and any associated health and safety issues. Unlike biocides and oxidants, the UVX disinfected water does not break down or crosslink the guar or the friction reducer used in the frac water.