Lebanon Express writer

The city of Lebanon invested in two projects this summer to improve the way the city handles treated sewage, both solid and liquid, at the city's wastewater treatment plant. One reduces biosolids and the other helps effluent mix into the river better.

The total cost of the two projects is over $6 million, $4.3 million for biosolids design and build and $1.8 million for effluent installation.

The biosolids, or "cannibal" project, is expected to reduce the amount of solids that remain after sewage is treated by 80 percent, "which is fantastic," said Senior Engineer Rob Emmons.

In the past, the city stored sludge - the solid biodegradable material produced by the wastewater treatment process - from fall to spring, then trucked it out to be spread on farm fields during the summer. In each of the last couple of years, storage space for sludge at the plant on Tennessee Road has maxed out. The cannibal process decreases the amount of sludge needing to be stored.

The new process starts with a drum screen of a fine mesh that will filter out any remaining small pieces of trash and inert material such as plastics. The next step involves a patented bioreactor vessel that encourages the growth of an organism that eats sludge.

"That's where the bulk of the reduction comes," Emmons said.

The cannibal process also reduces ammonia content in the effluent, helping the city meet Oregon Department of Environmental Quality (DEQ) rules.

Along with a new building for the cannibal equipment, the city also is replacing aerators, which mix air into the raw sewage in the first step of the treatment process.

The cannibal project will result in a cost savings for the city because of the net reduction in biosolids and some energy savings as well, Emmons said.

The contract for the biosolids project was issued without competitive bidding because the equipment is available only from Siemens Corp. and CH2M Hill/OMI operates the city's wastewater treatment plant. The project is financed through a tax exempt lease by Siemens Financial.

The second project of the summer replaces the system that discharges effluent into the river.

Effluent - the liquid stream of treated sewage - is chlorinated to kill bacteria, then dechlorinated to remove chlorine, which can be toxic to fish in high concentrations. The Oregon Department of Environmental doesn't want more than trace amounts to enter the river. The city is well above current chlorine limits.

Effluent has been piped from the treatment plant eastward to a point about 30 feet from the river. From there it forms a small creek and enters the river at one location, hugging the bank for up to 400 yards as it mixes with river water.

In August, a contractor working for the city lowered a diffuser into the river. Effluent is piped to the diffuser, which has 11 ports through which the effluent enters the river, mixing more quickly with river water in a shorter distance. The new process helps the warmer temperatures of the effluent come down to river temperature more quickly, meeting another DEQ goal.

Money for the effluent project came from a sewer capital projects account and a loan from the Department of Environmental Quality clean water revolving fund.

The contractor was R & G Excavating of Scio.