Lagoon mixing is a critical component of wastewater treatment: Robust mixing keeps BOD-consuming microorganisms in contact with the dissolved and suspended organic matter and prevents sludge buildup. Mixing is especially critical for egg processing wastewater, which is notable for high BOD and suspended solids, floating proteins, and the potential for odors.
This video case study shows how Triplepoint helped Lakewood Wastewater Authority create a complete-mix lagoon to cope with high strength egg processing wastewater.
Case Study: Lagoon Mixing
Lake Odessa is a village of 2,000 residents halfway between Grand Rapids and Lansing, Michigan. The Lakewood Wastewater Authority handles their municipal wastewater treatment as well as effluent from a local industrial egg processor. The 0.65 acre, 1.4 million gallon flow equalization lagoon, outfitted with surface aerators, was not up to the task. The surface aerators struggled to mix the entire water column and could not maintain a sufficient lagoon DO for treatment. In 2012, the Michigan Department of Environmental Quality got involved, mandating that the effluent violation and odor problems be rectified.
Particular Challenges of an Egg Processing Lagoon
Egg processing can create large amounts of wastewater, which needs to be processed in a complete, cost-effective, and efficient manner. Some of this water is sanitizing washwater, which may contain cleaning chemicals. Some is contaminated with biological solids like fecal matter, feathers, shell fragments, and high protein egg contents from breakage. These substantial organic loads require high dissolved oxygen levels: Without sufficient lagoon DO, the bacteria and microorganisms do not have enough oxygen to break down the BOD. Moreover, egg processing wastewater tends to have high TSS, which must be kept in suspension. Without intense mixing, the solids will either settle to the bottom of the lagoon, or, in the case of egg proteins, float to the surface of the water. These floating proteins will build up and form a dense, buoyant sludge mat, which reduces lagoon capacity, damages the lagoon aeration system, and creates odor.
Purdue University’s Food Processing Environmental Assistance Center offers technical information on the demands of egg processing wastewater.
Lack of sufficient lagoon mixing caused problems at the Lakewood wastewater facility:
- Floating sludge: Due to ineffective aeration and mixing, the lagoon DO levels were extremely low, causing the lagoon to become septic. Solids rose to the surface and a floating sludge blanket over a foot thick in areas formed. The sludge blanket caused the surface aerators to malfunction, exacerbating the problem.
- Terrible odors: Complaints about lagoon odor were registered from over a mile away.
- High lagoon TSS and BOD: The lack of aeration halted treatment, causing high TSS and BOD levels.
The MARS Aerator Pilot
Rather than resorting to taking the lagoon offline and dredging it—a costly prospect—Lakewood decided to pilot-test twelve MARS Lagoon Aerators. The MARS lagoon aeration diffuser is ideal for egg processing wastewater treatment because it provides mixing and aeration in a single modular unit. The patented Double Bubble™ technology combines a fine bubble membrane for efficient oxygenation with a coarse bubble static tube aerator for intense turbulence and mixing to treat the entire water column. And because the MARS is installed at the bottom of the lagoon, floating egg proteins cannot escape the treatment area as they can with surface aerators.
The first challenge was to install the MARS aerators at the bottom of the lagoon—the sludge accumulation was so thick a 600 lb. concrete weight was required to break through. Once installed, the MARS Aerators made immediate improvements:
- Eliminated floating sludge: Within minutes, the sludge mat began to break up.
- Reduced objectionable odors: Within one day, odors were noticeably reduced.
- Improved mixing: The mixing intensity provided by the coarse bubble diffusion of each MARS aerator kept solids in suspension to promote biological digestion.
- Reduced TSS and BOD to required levels: Aeration provided by the fine bubble membrane improved DO levels, reducing TSS and BOD.
After the success of the pilot test, Lakewood added an additional 36 units to completely mix the lagoon. Fed air via three onshore 50hp blowers (one redundant), 48 MARS lagoon aerators now transfer 3,840 pounds of oxygen into the water per day. Furthermore, lagoon mixing improved greatly, with a complete turnover once every four minutes, keeping all sludge solids in suspension. Most importantly, the MARS aerators have kept the pond aerobic, with a strong dissolved oxygen content to maintain healthy BOD breakdown and keep odors at bay.
While all wastewater treatment lagoons require mixing and aeration, it is particularly critical in egg processing wastewater because of the high levels of BOD and TSS and the tendency for egg proteins to float, putting them out of reach of surface aeration.