WARRENDALE, Pa., November 2, 2005 -- Siemens has announced that recent applications of the Cannibal® solids reduction process from its USFilter unit have shown a reduction in biosolids handling and dramatic reduction in costs associated with dewatering, power consumption and polymers as well as decreases or elimination of wet biosolids hauling. With more than 10 systems sold and another 20 in design, the Cannibal solids reduction process of the USFilter Envirex product line is proving to be an effective tool in eliminating routine biological solids wasting. By the end of 2006, at least 10 Cannibal plants (nine municipal and one industrial) will be operational, ranging in capacity from 0.75 million gallons per day (mgd) to 16 mgd.
Data from the field, R&D and several university studies have provided valuable insight. With this process, the biological solids yield is significantly reduced through a system of interchanging solids between aerobic and non-aerobic conditions. Screens and cyclones on the interchange recycle line then remove grit and other inert material from the process.
In one instance, a small community looking to expand its solids handling capability employed the Cannibal process to bypass the installation of a gravity thickener and belt press facilities. This saved more than $750,000 in capital and construction costs. Another community faced energy costs of nearly $0.16 per kWhr. By installing the Cannibal process, the power use in the side stream digester was reduced from 22 hours per day to just one hour per day.
In a first step, the sludge from the clarifier is pumped into a special separation module. Fine-mesh screens and a hydrocyclone separate all non-biodegradable contents such as trash, grit and inert particles. This fraction cannot be ‘digested’ by the treatment plant and is removed to the general landfill. Then part of this sludge is fed back to the aeration tank, the rest is transferred to an oxygen-limited sidestream bioreactor. The aerobic bacteria cannot survive in this environment and the population of facultative bacteria expands. Facultative bacteria are microbes that can live without oxygen, but use it if there is a sufficient supply. In the bioreactor, the aerobic bacteria are conditioned to increase biodegradability while the facultative bacteria break down and metabolize the remains of the aerobic bacteria strains. After the facultative bacteria have broken down the available biomass, the contents of the bioreactor are recycled back to the aeration tank.
In the oxygen-rich environment of the aeration basins, the facultative bacteria are out-competed by the aerobic bacteria population. As they slowly die off, their byproducts become food for the aerobic bacteria. A steady-state interchange of biological solids destruction and re-growth is established. The total number of bacteria remains the same so that no additional sludge is built up, reducing biological solids production by up to 90%.
The Cannibal process can be put into new facilities as easily as it can be incorporated into existing treatment plants. The process is compatible with any activated sludge technology. Five of the 11 sold systems pair the Cannibal process with other Envirex products, including the Orbal® in-series oxidation system, Verticel® aeration system and Vertical Loop Reactor (VLR®) biological treatment process. In California, USFilter’s Omniflo® sequencing batch reactor system precedes a Cannibal system.