Challenge
In the State of California, an Indian tribe envisioned a world class casino, hotel and spa that would have the potential of becoming a premier recreational destination on the West Coast. In order to build this world-class facility, the reservation needed to make improvements and expand their wastewater treatment plant. Since the casino and resort would include a hotel with possible expansion opportunities in the future, it was concluded that a new wastewater treatment plant would be required to handle the increase in wastewater flow. A design/build approach was selected to construct a 0.75 million gallon per day (mgd) facility with a 900 mg/L BOD load.
The new treatment plant would also need to be designed to handle not only high strength wastewater, but also large weekly variations in flows and loadings due to the hotel and casino business. The tribe also wanted an efficient, easy to operate treatment plant that would meet their wastewater treatment objectives.
Solution
Due to limited land space and the requirement of an easy to operate treatment plant producing high quality effluent, an OMNIFLO® Sequencing Batch Reactor (SBR) was selected for the biological treatment process. Initial plans called for the installation of an aerobic digester and sludge drying beds for sludge handling. With the Tribe's concern regarding high energy costs for aerating an aerobic digester, a more energy efficient solution for sludge treatment was needed. It was found that a significant savings could be realized by combining the Cannibal® Solids Reduction System with the OMNIFLO® SBR. The Cannibal® System requires minimal aeration, which reduces energy requirements and also provides the benefit of greatly reducing the amount of solids for disposal. The final design of the facility included both of these treatment systems, or what is known as the OMNIFLO® Interchange Sequencing Batch Reactor (ISBR). This treatment system provides significant energy savings and reduces solids production.
For the biological treatment process, the plant includes a two-tank OMNIFLO® SBR with VARI-CANT® Jet Aeration that is operated by a flow proportional control system. The OMNIFLO® SBR system is a fill-and-draw, non-steady state activated sludge process in which one or more reactors are filled with wastewater during a discrete time period, and then operated in a batch treatment mode. The SBR accomplishes equalization, aeration and clarification in a timed sequence in a single reactor basin. By varying the operating strategy, aerobic, anaerobic or anoxic conditions can be achieved to encourage the growth of desirable microorganisms. Control over these conditions not only ensures high quality effluent, but allows for an ideal environment to control the growth of microorganisms and to promote effective solids reduction with the use of the Cannibal® solids reduction technology. The Cannibal® Solids Reduction system significantly reduces the biological solids produced by the wastewater treatment plant and decreases the costs associated with sludge wasting, stabilization and disposal.
Results
The wastewater treatment plant was started up in July 2004 and has exceeded expectations. The OMNIFLO® ISBR has consistently met all treatment performance objectives for energy savings and solids reduction. The facility uses less than 10% of the power for solids treatment than was planned with the proposed aerobic digester. Solids wasting from the plant has been minimal, with less than 0.1 pounds of biological solids wasted from the plant per pound of BOD treated. The control system keeps the entire treatment plant operating - balancing the proper conditions in both the SBR and the sidestream bioreactor. Optimal conditions are maintained for both effluent quality and minimizing solids production.
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