Case Study: City of Yerington, NV
Yerington, Nevada, is a desert community of about 1,200 households in the western part of the state. Their wastewater is treated by an aerated lagoon system just north of town.
Frustrated by the high energy costs and consistent breakdown of their floating lagoon aerators, the city turned to Farr West Engineering in Reno for a solution. Farr West chose Triplepoint’s MARS aerators to upgrade Yerington’s lagoon system, which will save the city almost half a million dollars over ten years.
Floating Surface Aeration Pros and Cons
Energy consumption represents the highest operational cost for an aerated wastewater lagoon system. Many facilities use floating surface aerators, which have some benefits but are relatively inefficient and high maintenance.
Floating Lagoon Aerators: Advantages
- Portable; easy to install—Surface aerators float and are held by moorings with onshore anchors, so installing or moving the aerator is simple without dewatering.
- Good in Rough Environments—They are heavily resistant to corrosive wastewater, making them suitable for the most extreme environments.
- Good in Shallow Water—The shallower the water, the more directly affected the entire water column.
- Less Affected by Surfactants—Surfactants create a barrier to oxygen transfer. Surface aerators force bubbles into the water and churn them with a propeller, decreasing the influence of surfactants.
Floating Lagoon Aerators: Disadvantages
- High Maintenance—Constantly moving motors increase service requirements and the potential for breakdown and system downtime.
- Inefficient Aeration—Independent testing has shown floating surface aerators transfer just 1.25–2.25 pounds of oxygen per horsepower hour; diffused aerators can impart as much as 6–7 lb/hp-h. Floating aerators have higher power requirements and cost more to run.
- Limited Mixing; Ineffective in Deep Water—A surface aerator only mixes the water in its immediate vicinity, so “dead zones” develop where water stagnates and sludge accumulates.
- Trouble in Cold Weather—Water churned up by surface aerators freezes when exposed to cold ambient air, making motors prone to failure.
Yerington’s lagoon operators were experiencing the disadvantages of their floating surface aeration system, namely high maintenance and inefficient oxygen transfer, resulting in poor treatment and growing costs.
Upgrading to MARS
Farr West Engineering specified Triplepoint’s MARS aerators, which feature patented Double Bubble Technology™, combining the mixing capabilities of coarse bubbles with the superior oxygenation of fine bubbles in a modular, portable unit. MARS diffusers provide:
- Robust mixing—Coarse bubbles are released at the bottom of the static tube, creating a draft that pulls water and liquefied organic matter up from the floor, thoroughly churning and circulating the entire water column to keep solids in suspension and prevent sludge accumulation.
- Efficient aeration—Fine bubble diffusers surround the static tube, maximizing oxygen transfer efficiency while minimizing energy consumption.
- Easy installation—Self-weighted and portable, MARS aerators are quickly installed from the surface with no system downtime.
- Low maintenance—MARS have no submerged moving parts to clog or malfunction. The anti-fouling design, with self-checked diffusers and self-cleaning EPDM membranes, means maintenance is kept to a minimum.
- Energy efficiency—MARS aerators are 30–50% more energy efficient than surface aerators, reducing energy demands and expense.
Yerington’s lagoon system has a design flow of 0.345 MGD and a 1 MG, 15 foot deep treatment cell followed by a partially aerated polishing pond. The site had an identical parallel train that was unused, which allowed them to retrofit the empty parallel train with MARS units and discontinue flow to the existing train.
Twelve MARS aerators were installed in the primary cell to meet the daily oxygen demand of 495 lbs. Four MARS units were installed in the polishing cell. Air is supplied by an on-shore blower with VFD in the control panel.
The system was started up in early June 2016 and is affectionately referred to by operators as “our big Jacuzzi.” The city has ordered additional MARS units to help oxidize solids in a storage pond.
By replacing their floating lagoon aerators with MARS aeration, Yerington’s savings in reduced energy and maintenance costs will exceed $400,000 over ten years, and the facility is expected to break even in less than three.
For more on how efficient MARS aeration can save money and maintenance headaches, download our MARS brochure.