Challenge

In 1998, a small Georgia community began operating a Sequencing Batch Reactor wastewater treatment plant (WWTP). Unique to the 1-mgd facility was the fact it was built without any biological solids handling equipment. Rising costs associated with handling the biosolids from an existing oxidation ditch facility was the motivating force behind the need to curb these costs as early as the design stage.  Because the town was far too familiar with the cost of sludge hauling, tipping fees, labor, and the rising costs of polymers and energy, it was determined to find a solution that would keep these costs to a minimum for their new facility.

Solution

The solution was found in the Siemens technology known as the Cannibal^™ solids reduction process.  The Cannibal process played a prominent role in the WWTP design from the onset.  The Cannibal process became operable in August 1998.   

The Cannibal process is unique in that it combines conventional activated sludge treatment with a smaller, separate sidestream system to recycle and restructure the bacterial population until all excess biological material is completely broken down and degraded. Through the Cannibal solids reduction process, routine biological wasting is eliminated. A portion of the return sludge is pumped to a sidestream bioreactor where the mixed liquor is converted from an aerobic-dominant population to a facultative-dominant population.  By carefully controlling the environment, aerobic bacteria are selectively destroyed in this sidestream reactor while enabling the low-yield, facultative bacteria to breakdown and utilize the remains of the aerobes and their byproducts.  

With the Cannibal process, mixed liquor from the sidestream bioreactor is not “wasted” from the plant, as it would occur in a typical digester.  The mixed liquor is recycled back to the main treatment process where the facultative bacteria, in turn, are out-competed by the aerobic bacteria and subsequently broken down in the alternating environments of the aerobic treatment process and the sidestream bioreactor.  A steady-state balance between selection and destruction is developed between the sidestream bioreactor and the main treatment process resulting in no net biological solids produced. 

Grit and other inert materials are removed from the process through the use of a patented solids separation module on the return sludge line. Without routine wasting this material would build-up in the plant.  An occasional purge will be required to remove the build-up of fines and the inerts that are not removed through the solids separation module.

Result

Since the Cannibal™ process came online, the plant has wasted biological solids only twice; once in the spring of 2003, after four years of operation, and again in April of 2004. Routine biological solids wasting has been eliminated. The result is a consistent, high quality effluent and an investment payback in less than 3 years.