Student-Designed Cover Speeds Waste Treatment Process, Cuts Costs

July 21, 1998

GAINESVILLE — A heat-trapping sewage tank cover designed by University of Florida engineering students speeds up the treatment process at wastewater treatment plants, a development that already has led to substantial savings at a Gainesville plant.

The large, plastic cover fits atop so-called “digesters,” large round tanks used to break down sewage sludge. It has so accelerated treatment at Gainesville Regional Utilities’ (GRU) Kanapaha Water Reclamation Facility the utility has dropped plans to spend at least $1.2 million for a new digester, GRU officials said.

“We’re able to run the digester at higher temperatures and achieve treatment that allows us to actually run the system at almost double the normal (speed),” said Robert McVay, assistant general manager of waste/wastewater systems at GRU.

Wastewater plant operators use microorganisms to treat wastewater. The organisms multiply as they feed, creating thousands of gallons of sludge daily. The sludge must be treated in the digesters — the process also involves using microorganisms — to remove pathogens. It is then used as fertilizer.

Two years ago, a group of students designed a cover that raises the temperature inside digesters by trapping heat generated by the microorganisms. The students did the work as part of the College of Engineering’s Integrated Product and Process Design Program (IPPD), which pairs student teams with corporate or government sponsors for yearlong design projects.

“This was just one of many projects we do through the IPPD program,” said Spyros Svoronos, a chemical engineering professor and associate chair of the chemical engineering department who served as the faculty coach on the project.

The added heat speeds up the microorganisms’ activity inside the digester, boosting the rate of pathogen removal. Using results from two scaled-down digesters built to test the concept, the students also came up with a computer model that predicts the temperature of the sludge, enabling operators to predict treatment times.

“Other methods increased the temperature more, but it was important to be able to control the heat within an optimal range and to provide a cost-effective solution,” said Mary Alford, a member of the student design team, graduate student in environmental engineering and engineering intern at GRU.

In past summers, the average temperature of the sludge at the Kanapaha plant was about 80 degrees Fahrenheit. This summer, the temperature of the sludge in the covered digester has averaged 98 degrees Fahrenheit. An 18-degree increase in temperature generally doubles the reaction rate, meaning the covered digester is treating about twice as much sludge as the uncovered ones. With the Kanapaha facility generating about 70,000 gallons of sludge daily, the device has alleviated the need for a planned sixth digester to cope with rising volumes of waste, McVay said.

McVay said the use of the cover to speed up the treatment process appears to be unique in the industry. Other utilities are interested in the results, Alford said.

“They’ve been used for odor control and they’ve been used for other reasons, but never has anyone, as far as I know, used a cover in combination with a computer program to predict temperature for treatment purposes,” McVay said.