Lake Wister Water Treatment
Shelyn Gehle, Whitney Lisenbee, Rebecca Purvis, Maggie Wyatt
PVIA stands for the Poteau Valley Improvement Authority. The PVIA treats and distributes water to about 80% of Le Flore County in Oklahoma. Le Flore County is located in east-central Oklahoma. Efforts were focused in Wister, OK, where Lake Wister is located (Figure 1). On average, six million gallons of water a day (MGD) are pumped out of Lake Wister for treatment and distribution through the drinking water supply system. The maximum capacity for the treatment plant is twelve MGD. The intake is located in Quarry Island Cove (Figure 2) on the northeast side of the lake. The cove contains about 2 percent of the total volume of the lake, totaling 1418 ac-ft, and the depth across the cove is on average fifteen feet. Our design will be implemented in Quarry Island Cove, allowing for the water to be treated before being pumped to the treatment plant.
Lake Wister has a very high level of dissolved phosphorus, which is released from the lake bedrock, with little to no contribution from agricultural runoff. Phosphorus is the limiting nutrient for algal growth. Therefore, an increase in phosphorus concentration results in an increased level of algae within the lake. A high level of phosphorus within the lake can create a eutrophic environment, where oxygen is limited and algae blooms encourage fish kills or other detrimental conditions. To ensure that the lake is mesotrophic, rather than eutrophic, the phosphorus level needs to be below 24 µg/L (Appendix A). One way to monitor the phosphorus level within the lake is to quantify the chlorophyll-A level, which is a component of algae photosynthesis. There are no standards for phosphorus, but the Oklahoma Department of Environmental Quality (ODEQ) has set the chlorophyll-A standard to not exceed 10 µg/L.
Scope of Work
Our project objective is to create an Alum Microfloc Curtain. Essentially, this curtain is created by a line of aeration components on the bottom of the lake with an alum component placed over the top. The aeration components move air bubbles from the bottom to the lake surface while alum is injected above the aeration system. The curtain provides direct contact between the alum and phosphorus laden water as the alum is brought to the surface. The mixing creates a flocculation precipitant that settles to the bottom of the lake to form a protective barrier against the re-suspension of dissolved phosphorus from the sediments. This curtain will allow for a continuous decrease in phosphorus concentration in the water as it enters the cove. The reduction in phosphorus will in turn reduce the algae and cyanobacteria (blue-green algae) levels. The reduction in algae will also help reduce the level of toxic disinfection by-products in the treated outflow. Disinfection by-products are the result of chlorine reacting with the organic matter, such as dead algae, in the water treatment process. This in-lake treatment will help the PVIA keep Lake Wister under the state standards for chlorophyll-A.