Challenge

Like many businesses and municipalities, the City of Lebanon, Oregon was faced with cutting operating costs to meet the demands of tighter budgetary restrictions. In response to this challenge, Lebanon officials met with their locally-based contract operating partner, CH2M Hill OMI, to explore cost-saving options that could be implemented at the city’s wastewater treatment facility (WWTF).

Knowing that a decrease in the biosolids produced by the WWTF would directly result in a reduction in disposal, equipment and labor expenditures, the team decided to install a Cannibal® solids reduction system from Siemens Water Technologies.

Solution

Prior to the Cannibal installation, the Lebanon facility was designed for a wet weather flow of 8 million gallons per day (MGD) and featured two single-stage aeration tanks that operated in parallel. Biosolids were processed through a gravity thickener for stabilization in two aerobic digesters before being distributed to surrounding agricultural fields.

One of the benefits of the Cannibal system is its ability to be integrated into existing infrastructure, which lowers construction costs. During the Lebanon installation, one of the existing aerobic digesters was converted to an interchange bioreactor while the aeration basins were modified to run in series with two small anoxic selector tanks at the influent end of each basin. Together, these improvements minimized the growth of biosolids through an interchange recycle flow between the aeration basins and the interchange bioreactor.

The final phase of the installation was the construction of a new building to house the Cannibal solids separation module, which consists of an ultra-fine mesh rotary drum screen and hydro-cyclones.

Results

Since the installation of the Cannibal system in late 2008, the Lebanon WWTF has experienced a more than 80% reduction in hauled biosolids, from an average of more than 2.3 million lbs. to less than 400,000 lbs. The cost savings resulting from this reduction have been significant. Solids hauling frequency has greatly decreased and, in turn, so has the amount of time plant personnel spend managing biosolids disposal.