In late summer 2011, the Navarro County Safety Rest Area, located on Texas Interstate 45, commissioned the Ovivo MPAC membrane bioreactor (MBR), providing onsite treatment for the generated wastewater of this heavily trafficked portion of Texas Highway.
The Texas Department of Transportation’s (TxDOT) new generation of Safety Rest Areas not only attract visitors to stop but also serve as cultural gateways to nearby communities. Although the Safety Rest Areas are designed to invite, inform and entertain, the basic objective is to see that travelers arrive safely to their destinations. Because Texas has the most roadways in the country (nearly 80,000 miles), highway safety is a top priority for TxDOT, and attractive, safe, efficient and clean rest area facilities are invitations to entice travelers to stop and rest.
These new Texas rest areas include high-tech play parks for children, native plants, walking trails, art and historical displays. Further, the Navarro County Safety Rest Area is located near the Richland Chambers Reservoir. In addition to the more visible attractions, TxDOT wanted a wastewater reuse facility to accompany these next-generation roadside safety rest areas.
Selecting Technology
Ovivo’s MBR system was selected for its effluent quality, small footprint, low maintenance, simple operation and flexibility. The maximum monthly flow was designed for 20,000 gal per day. Reuse consists of sending the MBR permeate back to the rest area toilets and urinals. And because the MBR effluent quality exceeds discharge requirements, surplus effluent can be discharged to the nearby Richland Creek during periods of high flow or lower visitor occupancy.
Given the heavy traffic often encountered on I-45, the system was expected to hit significant flow rates shortly after the rest area opened. By November 2012, as the rest area began to see a rise in motorists and other visitors, it became apparent that the original design, which included projections for ammonia loading, had been undersized. In other words, the plant, as originally designed, was not capable of treating the real world ammonia influent loads seen during Thanksgiving, 2012.
Fortunately for TxDOT and the thousands of motorists that visit this roadside attraction, Ovivo Field Service personnel were contacted and asked to review the situation. Working with TxDOT, it was determined that the incoming ammonia load was approximately 20% higher than originally anticipated, resulting in a system that was under-aerated for meeting the plant’s ammonia limit. Ovivo set off to work with the TxDOT engineering staff to determine additional aeration requirements for the system. In addition to evaluating the necessary oxygen required, Ovivo also performed an overall system check to confirm how the rest of the plant would behave when additional air is added.
After all the secondary possibilities were accounted for, such as alkalinity adjustment, possible recycle rate changes and air flow contingency, a plan of action was drawn up. Ovivo then executed a quick and efficient swap of the fine bubble aeration system (the existing blower arrangement meant that enough oxygen was available, but not enough diffuser area). Changes were completed and the plant was placed back online within 24 hours. Subsequently, effluent discharge from the plant soon met required state permit limits as intended and continues to do so today.
Flexibility & Reliability
The competitive cost, minimal system footprint and ability to produce reuse quality effluent within an outdoor-centric family environment demonstrates the quality of the Ovivo MBR system. But just as important, Ovivo’s Field Service staff proved to be as reliable and flexible as any support staff in the country. The Navarro County Safety Rest Area and Ovivo MBR system are on the forefront of sustainable Texas highways.
Christopher Lewis, M.S., P.E. is technology development manager for MBR systems at Ovivo. Lewis can be reached at [email protected] or 512.652.5825.