HIGH RATE ANAEROBIC DIGESTION WITH MECHANICAL SHEAR – A CASE STUDY AT THE CALDWELL, ID WWTP
The mechanical shearing of the recycled stream for anaerobically digested biosolids has been successfully demonstrated as a means of enhancing mesophilic anaerobic digestion (Muller, 2003). When shear energy is applied in an internal recycle loop, stabilized biosolids are disintegrated and a fraction of the material associated with the anaerobic sludge floc is rendered available for further degradation. The result is enhanced degradation of material that would otherwise be refractory within the SRT of the digester, which can lead to a decrease in solids to be disposed as well as, a corresponding increase in gas production. The study reported here investigated the use of shear energy as a means of increasing the loading of volatile solids in anaerobic digesters at the Caldwell, ID Wastewater Treatment Plant. This consisted of a full-scale test program lasting six months. The results indicated that mechanical shearing of anaerobic digester sludge has the potential of generating significant savings to a treatment plant in terms of both capital cost and operating cost of sludge disposal. The results indicated that application of shear allowed increase in volatile solids loading without compromising the quality of the end products and fulfilling the Class B requirements of land application. The direct benefit in capital cost saving is due to the high level of stabilization using less digester volume. Reduction in total and volatile solids can result in significant operating cost savings. Additionally, this process enhances the potential for revenue generation by a treatment plant in the form of increased gas production.
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Document Type: Research Article
Publication date: 01 January 2004
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