A Texas city deploys an innovative hybrid technology to resolve a long-standing lagoon solids accumulation and restore permit compliance.
In 2011, the Texas city of Celeste experienced severe solids accumulation in its wastewater treatment lagoon, causing dramatic loss of retention time and significant discharge permit exceedances. Strong odors forced neighbors a mile or more downwind to close their windows.
Celeste, a city of 800, 10 miles northwest of Greenville in Hunt County, addressed the issue with an innovative hybrid aeration and digestion technology. After a year in operation, the process eliminated the solids buildup and enabled the plant to restore permit compliance.
Nick of time
Celeste’s leaders were just days away from investing more than $150,000 to mechanically dredge a section of one wastewater lagoon when they learned about a more affordable alternative that promised long-term, environmentally sustainable results.
“We were literally about to sign the contract to dredge the pond when we got the call from Blue Frog,” says Mayor Larry Godwin. “They explained how their system would save us money and keep us from having to continuously dredge the lagoons. We decided to take a closer look. I’m glad we did.”
The Blue Frog System (Absolute Aeration) is a hybrid technology that uses biological processes to enhance organic solids digestion. Known as biodredging, the process selects for the indigenous bacteria that are in the lagoon and already adapted to local conditions and the wastewater substrate.
The bacteria form synergistic anaerobic biofilms in tight, mineral-based granules, forming a granular sludge bed reactor over the entire bottom of the lagoon. Surface biosolids are delivered to the bed, liquefied and then turned into gas by the bacteria immobilized in and on the granules.
Produced gas rises and gently mixes the water column, continuously feeding the granules to increase their productivity. Once the granular sludge bed reactor is established, bacteria grow and die in direct response to the level of nutrients coming into the lagoon.
This organic biological control is well suited for the natural fluctuations in flow that characterize municipal wastewater lagoons. In addition, biological control is more cost-effective than traditional oxygen-adding strategies that require significant horsepower to drive aeration blowers.
In Celeste, the design strategy was to digest recalcitrant solids that had built up over 30 years at the bottom of the lagoons and to keep up with the incoming solids daily to eliminate buildup, ultimately increasing the pond’s retention time. The system was also designed to meet the monthly permitted discharge requirements of 30 mg/L BOD and 90 mg/L TSS.
The city has two wastewater treatment lagoons. Pond 1 has an asymmetric depth, 8 feet at the inlet and 4.5 to 5 feet at the outlet. Pond 2 is 5 feet deep. The average flow is 95,000 gpd.
Wastewater treatment lagoon optimization requires a thorough understanding of what is happening chemically, physically and biologically inside. Water chemistry changes with loading, dissolved oxygen, temperature, sunlight or other influences, bringing corresponding changes in the lagoon’s microbial ecosystems. These changes alter the quality of the water.
The Blue Frog System was delivered in June 2012. The process began by installing an engineered floating boom called a continuously stirred tank reactor, used to create hydraulic walls to redirect horizontal flowing water down to the anaerobic zone.
The CSTR functions as an engineered tank that concentrates bacteria and solids at the bottom of the lagoon. Placed over the inflow, it serves as a flow equalization tank, a selector tank that selects for sludge-digesting bacteria, and an incubation tank that produces a large population of high-quality microbes.
The Blue Frog team had to be creative during installation to build around the high levels of accumulated solids. The CSTR was temporarily redesigned to the current solids levels and retrofitted six months after the solids were reduced.
Within weeks of installation, the Blue Frog units had noticeably reduced the solids. In six months, they had eliminated more than 50 percent of the organic solids. Within the first year, the ponds were essentially sludge-free. Incoming organic waste was digested before it could settle, and the neighbors could safely open their windows again.
The Blue Frog team continues to work with the city, charting monthly data and using the lagoons as a test site for new advancements. Effluent BOD and TSS consistently remain below the permitted limits.
“It’s been four years since we installed the Blue Frog System, and our lagoons look and smell as good as any public lake in the state,” says Mark Coles, city employee. “Where there was nothing but a filthy, stinking pool of sludge, there’s now clear water.”
As federal and state regulators enact more restrictive regulations, pressure is increasing to replace lagoons with activated sludge plants. Still, lagoons are a cost-effective way to treat wastewater and can be revitalized with emerging technologies.
The results in Celeste demonstrate that proactive municipalities can make changes to resolve wastewater treatment problems. Current technology can be an important way to optimize lagoon systems to achieve effluent quality comparable to activated sludge systems.
About the author
Chip Bettle is a co-inventor of Blue Frog technology and executive vice president of engineering for Absolute Aeration of Greeley, Colorado. He can be reached at email@example.com.