Coarse bubble aeration for lagoons has fallen out of favor, mainly because of its inefficiency compared to fine bubble aeration. While coarse bubble aeration provides excellent mixing performance, it doesn’t transfer oxygen as well as fine bubble does, requiring higher energy expenditures.
This video case study shows how replacing coarse bubble aeration with Triplepoint’s MARS aeration allows a municipality to save money on energy and produce high quality effluent for beneficial reuse in irrigation.
Lagoon Case Study: Replacing Coarse Bubble Aeration
Tulelake, California, is a city of just over 1,000 residents near the Oregon border. Their lagoon system was out of compliance for biological oxygen demand (BOD), total suspended solids (TSS), and coliform; a consent order required them to correct these violations and convert to a zero discharge system from surface water discharge. Lagoon effluent would have to meet California’s Title 22 standards for agricultural reuse so it could be used to irrigate local farm fields.
The facility had coarse bubble aeration, which wasn’t doing the job: The lagoons had floating sludge mats and had accumulated multiple effluent violations and tens of thousands of dollars in fines. While coarse bubble aeration has many benefits, namely good mixing performance, durability, and resistance to surfactants, it has a number of drawbacks.
Problems with Coarse Bubble Aeration
- Inefficient Aeration: Bubble size is the single biggest factor in determining Standard Oxygen Transfer Efficiency (SOTE). Smaller bubbles have more contact area per volume of air and rise more slowly, making them more efficient at transferring oxygen than larger bubbles, which have less surface area and rise quickly. A typical coarse bubble diffuser may produce 1% of SOTE per foot of depth, while a typical fine bubble diffuser may produce about 2% SOTE per foot of depth.
- Difficulty Installing and Accessing: Most coarse bubble systems are anchored to the bottom of the lagoon, requiring the basin to be drained and sludge removed to allow installation and maintenance.
- Clogging Potential: If a coarse bubble diffuser isn’t equipped with backflow sealing, debris will clog the orifice when the air is switched off, causing backpressure issues, a drop in efficiency, and maintenance headaches.
For a closer look, read our article, Lagoon Coarse Bubble Aeration: Pros & Cons.
The Solution: MARS Lagoon Aeration
Twenty miles northwest of Tulelake, the South Suburban Sanitary District (SSSD) of Klamath Falls, Oregon, had successfully upgraded their coarse bubble system with MARS aeration, reducing their electrical and maintenance costs by over 40 percent. (Check out our case study, Facility maximizes lagoon aeration efficiency, saves money.) While SSSD’s system is much larger—four cells and a daily flow of 2.7 MGD—the MARS system is scalable to provide the required level of treatment for any lagoon application.
Tulelake’s lagoon facility has a design flow of 160,000 gpd and an average flow of 80,000 gpd of municipal wastewater. The rehabilitated facility has two 10-foot deep, 2 Mgal partial-mix aeration cells, one with an old wooden baffle, that will operate in series. An existing sand filter was converted to a redundant third treatment cell for surge events and to accommodate future growth. Cells 1 and 3 have full aeration capability so they can be run in parallel when necessary.
The MARS aerators on individual weighted air lines utilize the existing blowers and provide increased oxygen transfer at a higher energy efficiency while maintaining the mixing performance of a coarse bubble aeration system.
A Community Development Block Grant funded the purchase of 80 acres of land for two new storage ponds, which can hold up to 30 million gallons of effluent for the irrigation of adjacent farmland during the growing season. Tulelake is the first zero discharge agricultural reuse project in the region.
About MARS Aeration
Triplepoint’s MARS aerators, which feature patented Double Bubble Technology™, combine 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 maximize 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.
To learn more about how MARS can improve lagoon aeration efficiency and save thousands of dollars in energy, operations, and maintenance costs, download our brochure.