The Yakama Nation Legends Casino, located in Toppenish, Wash., is a wholly owned operation of the Yakama Nation tribe. It features approximately 33,700 sq ft of gaming space. In 2015, the casino was in the midst of an expansion project that included a new hotel, spa, food court, buffet and additional gaming space. To accommodate the additional wastewater generated from these expanded facilities and services, the membrane bioreactor (MBR) wastewater treatment plant originally supplied by Ovivo (formerly Enviroquip) needed to be expanded from its current average daily flow of 180,000 gal per day (gpd) to 360,000 gpd.
The process flow of the original wastewater treatment plant (WWTP) was as follows: Influent wastewater flows through a 3-mm fine screen into an anoxic basin. From the anoxic basin, the wastewater is routed through a pre-aeration basin and into two parallel MBR basins. Effluent from the MBR units is conveyed through a medium-pressure ultraviolet disinfection unit into the permeate storage basins. Effluent is then conveyed for onsite turf irrigation or discharged to Wapato Irrigation Project (WIP) Drain No. 4, which drains to the Wanity Slough and then eventually flows to the Yakima River. Biosolids generated from the secondary treatment process are directed to the membrane thickening and aerobic digesters for stabilization. Digested sludge is dewatered using a belt filter press and then conveyed to a sludge dryer. The final biosolids product is Class-A quality and is land applied or disposed of on Yakama Nation lands.
The Solution
The original plant was designed and built with two process trains and four membrane trains. One process train and two flat plate membrane trains were kept in operation while the other train was used for permeate storage. The original plan was to populate the second train with new equipment when expansion of the facility was required. However, Ovivo’s advanced OV flat sheet membrane technology with higher packing density allowed for enough hydraulic capacity to handle the expansion needs while still utilizing only one process train and two membrane trains, thereby eliminating the cost of building new permeate storage tanks. In fact, the membrane replacement upgrade allowed the facility to handle 400,000 gpd, which is 2.2 times the original capacity, while utilizing only half of the plant footprint. This was achieved by implementing robust, self-healing flat sheet MBR technologies that are able to treat more flow in a smaller footprint.
The Results
To meet the tight timelines, project management expertise was applied. Equipment was staged and lined up in order of use. The owner bypassed all incoming wastewater to the city of Toppenish’s wastewater collection. During this plant shutdown, all the new equipment modifications were completed and commissioned in only 30 days. The timely modifications and commissioning ensured that the facility did not incur additional expenses of diverting flows. Furthermore, the use of existing tankage and connections allowed for a substantial reduction in overall project cost.
