A detailed investigation has concluded that the Dec. 10-11 accidental discharge of non-hazardous treated wastewater from Cornell's digester of animal remains was caused by programming issues that were traced to the digester's manufacturer.

Investigators concluded that the amount of hydrolysate effluent -- a brine-like fluid from the chemical digestion of animal remains -- in the digester when the spill occurred was about 1,600 gallons, about half the amount originally reported. This effluent had been diluted with some 90,000 gallons of potable rinse water, and most of the spill ended up in Ithaca's sewer system. A significant amount of hydrolysate remained in the digester, the investigators believe, and never left the facility.

Cornell and State University Construction Fund staff conducted the review to determine the root cause of the discharge from the Cornell College of Veterinary Medicine's digester, a 7-foot-wide sealed reactor that uses chemicals and heat to safely treat animal remains. The digester serves as a more environmentally friendly alternative to the incinerator it replaced last spring.

"The system we're using to handle animal remains was selected after a thorough review by university and community members," said Alfonso Torres, the College of Veterinary Medicine's associate dean for public policy. "It is state-of-the-art technology that is safe, environmentally friendly and is used worldwide."

Working with the digester's manufacturer, Cornell has already implemented and tested a number of corrective actions and will continue to closely monitor the digester as operations resume, Torres added.

"Initially, we thought the discharge was the result of a mechanical failure, but now we know it was 100 percent a series of programming problems," said Paul Jennette, the Vet College's biosafety engineer.

The spill occurred after a digester manufacturer's representative remotely made a change Dec. 9 to the digester's control program to clear a drainage problem with a load. The representative assumed that the program would automatically reset the following day, which it failed to do. And because Cornell was not notified that he had altered the program, Cornell's operating staff had no reason to expect the following cycle to fail, Jennette said.

As a result, on Dec. 10 a load of animal remains completed its initial heat and chemical treatment cycle, but then due to the representative's alteration, the hydrolysate failed to drain prior to a rinse cycle. Potable rinse water then overfilled the digester; more than half the spill flowed down a sanitary sewer connection intended to collect condensed water vapor, and the rest flowed up into the building's ventilation ducts, through several vents and into floor drains that led to the city's sewer. When an air duct gave way under the water's weight, some wastewater also entered a floor hole and drained into a dumpster below and outside into storm drains that run into Fall Creek, Jennette said.

Testing by an independent, state-certified laboratory support the conclusion that most of the hydrolysate discharged went to the Ithaca Area Wastewater Treatment Facility and that the portion that entered the storm sewer system did not exceed New York State Department of Environmental Conservation water quality standards in Fall Creek.

Corrective actions that have been implemented and tested include:

In addition, the digester's vent is being rerouted to the facility's wastewater storage tank, in case wastewater is discharged through the vent again.

A test run of the new measures Dec. 16-17 determined that the digester was working properly and the system returned to full operation Dec. 20.

A community meeting will take place Jan. 4 at 4:30 p.m. in S1007 Schurman Hall on Cornell's campus.