Fine bubble aeration is a popular method of wastewater lagoon treatment. A fine bubble lagoon aeration system is installed at the bottom and releases tiny bubbles that slowly rise to the surface of the water. Because the bubbles are so small, they rise relatively slowly and have a very large surface area, which maximizes oxygen transfer. But while fine bubble lagoon aeration provides excellent oxygen transfer efficiency, it’s not very good at providing mixing, which can lead to sludge buildup and insufficient treatment.
Our latest video case study takes a look at the upgrade of the lagoon system in Ponchatoula, Louisiana, which replaced its inadequate fine bubble lagoon aeration system with MARS units. Watch the video and read on for more information.
Case Study: Replacing Fine Bubble Lagoon Aeration
Ponchatoula, Louisiana, has over 7,000 residents and is located equidistant from Baton Rouge and New Orleans. It sits next to the Joyce Wildlife Management Area, a protected area of 34,000 acres of wetlands and swamps owned by the Louisiana Department of Wildlife and Fisheries.
Their lagoon facility’s fine bubble aeration system was not providing adequate treatment: sludge buildup had reduced the effective depth of the north cell to less than two feet. Dissolved oxygen levels were insufficient to treat the incoming BOD and the oxygen demand of the sludge, resulting in effluent violations.
Problems with Fine Bubble Lagoon Aeration
There are several different types of fine bubble aeration–check out our blog, Lagoon Fine Bubble Aeration: How to Choose the Best Option, for a review of common technologies and their pros and cons. Generally, despite fine bubble lagoon aeration’s superior oxygen transfer capability, it can have significant drawbacks:
Difficult to Install: Many traditional fine bubble aeration systems are either secured to fixed laterals at the bottom of the lagoon or hanging from floating laterals. With fixed laterals, the lagoon must be drained and desludged for the installation. You can expect this to be both costly and time consuming. With floating laterals, you’ll need to install the diffusers and laterals amphibiously—this can be a laborious and potentially hazardous process.
Fouling & Clogging: Any fine bubble aeration technology is susceptible to bacterial fouling, where bacteria form on the surface of the diffuser and impinge upon the orifices. This causes increased back-pressure and wear on the blower, thereby increasing energy and maintenance costs. In the case of perforated tube diffusers, orifices can get clogged and stop working entirely. This type of clogging is less of a concern for EPDM-based fine bubble diffusers.
In order to maintain system performance, operators must clean or replace fine bubble diffusers on a regular basis. This generally involves cleaning the diffuser surface with either a pressure washer or scrubbing it with a brush. In the case of completely clogged perforated tube diffusers, full replacement can be necessary. Depending on whether the lateral system is submerged or floating, this can be a time consuming and costly task.
Insufficient Mixing: The EPA defines the purpose of aeration as being twofold: 1) adding oxygen to the water, and 2) mixing the water so that microorganisms can come into contact with waste and break it down. As we’ve mentioned, fine bubble aerators are extremely efficient when it comes to transferring oxygen. However, fine bubbles alone are not as effective when it comes to mixing. Since fine bubbles are so small, they do very little to disrupt or displace water in large volumes. As a result, the fine bubbles rise through the water rather calmly, often allowing solids to settle. Fine bubbles can also fail to create the contact between microorganisms and nutrients that is necessary for a more efficient breakdown and overall water treatment. Over time this can lead to sludge buildup. Increased amounts of sludge result in less effective treatment overall, and the costly process of removing sludge from the wastewater lagoon. Read our article, Causes & Effects of Wastewater Lagoon Sludge Explained, for more about how damaging accumulated sludge can be to treatment efficiency.
The Solution: MARS Aeration
In May of 2015 the City of Ponchatoula was awarded the highest dollar award–$1 million–from Louisiana’s Community Development Block Grant Program. The funds were earmarked for the refurbishment of their nearly 50 year old wastewater treatment facility: desludging, building an earthen berm between the two main cells, and improving aeration.
Ponchatoula’s lagoon facility consists of two lagoons separated by a berm. Lagoon 2 is baffled into five individual cells: Cells 2A and 2D are aerated and Cells 2B, 2C, and 2E are facultative. Flow is 1.5 mgd.
Cell 2A, next to the berm, has a volume of 9.6 Mgal. Twenty-seven MARS aerators on surface laterals are attached to the existing positive displacement blower. Cell 2D, with a volume of 3.3 Mgal, has six MARS aerators, each attached with an individual weighted air line to a central positive displacement blower. A duckweed grid system assists in the uptake of ammonia and phosphorus; lagoon effluent is discharged into the wetlands to further remediate nutrients.
With the upgrade to MARS aeration, the overall treatment through the lagoon facility is 98%: from typical influent BOD of 75 mg/L to an effluent BOD of 1.4 mg/L.
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 percent more energy efficient than surface aerators, reducing energy demands and expense.
To learn more about how MARS can improve lagoon aeration efficiency, prevent sludge buildup, and save thousands of dollars in energy, operations, and maintenance costs, download our brochure or request a quote.