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Technology Figure 3: Ultrasonic sludge disintegration Ultrasonic sludge disintegration is an excellent application for anaerobic digesters that have a short HRT (overloaded), low VS destruction, or even low gas production. Utilizing the ultrasonic reactor is an excellent way to help "supercharge" an anaerobic digester. Anaerobic Digestion Application Case Study: Bamberg WWTP, Germany The Bamberg WWTP is a traditional activated sludge plant having a 12-MGD design capacity, but was actually being loaded around 15 MGD, equating to an 18-day digestion time in the anaerobic digesters. The plant selected to use ultrasonic sludge disintegration to pretreat the sludge prior to entering the digester. The ultrasonic reactor was tested to determine if the technology could be used in lieu of building a new digester. Results: The ultrasonic reactor was tested for a four-month period where 30 percent of the TWAS flow was treated (as shown as one of the placement locations in Figure 2, going from the TWAS to the digester). After the testing period, the data showed the following: • Improved VS destruction from 42 to 54 percent • Digested sludge VS reduced from 60 percent (as percent of total solids) to 54 percent • Biogas production increase by 30 percent Due to the successful testing, the plant elected to keep the ultrasonic reactor and avoided the construction of a new digester. Ultrasonic Sludge Disintegration In BNR Applications In order to achieve complete nitrogen removal, the denitrification process must occur. Denitrification is the biological reduction of nitrate (NO3) into nitrogen gas by facultative heterotrophic microorganisms. There are three items required to achieve denitrification: 1) heterotrophic bacteria; 2) nitrate, which is used as an energy source by the microorganisms to metabolize and oxidize organic matter; and 3) organic matter, which serves as a food source for the heterotrophic bacteria to survive. Carbon requirements are a very important aspect of the denitrification process. As a rule of thumb, a 6:1 carbonto-nitrogen ratio is required to achieve complete nitrogen removal. Many wastewater treatment facilities find maintain34 wateronline.com ■ ing this ratio can be problematic, especially ones with solids handling processes that recycle excessive nitrogen back to the liquid treatment processes, which causes depletion of the carbon-to-nitrogen ratio. There are up to 200 wastewater treatment facilities in the U.S. that add methanol to achieve denitrification. Although the addition of methanol is common and relatively inexpensive, there are disadvantages such as increases in sludge loads and disposal costs, fluctuating prices (typically $1.50 to $3.50 per gallon), since most of it is imported, and dangerous handling, since methanol is flammable. Ultrasonic sludge disintegration is an excellent application for any wastewater treatment facilities that have BNR processes that are adding external carbon sources such as methanol or MicroC™ to achieve the denitrification process for complete nitrogen removal. Ultrasonic pretreatment technology causes the cell walls of microorganisms to rupture, which allows their cellular material to be available as an additional source of organic matter. Ultrasonic pretreatment technology provides an internal carbon source and prevents the addition of external carbon sources. There is substantial operating cost savings by preventing the addition of an external carbon source. It requires approximately 3.5 pounds of methanol to remove 1 pound of nitrogen. For example, a 5-MGD wastewater treatment facility will spend approximately $80,000 annually on methanol addition for every 10 mg/L of nitrogen (420 pounds/day of nitrogen) that needs to be removed, and this assumes a methanol cost of $1 per gallon. BNR Application Case Study: Datansha WWTP, Guangzhou, China The Datansha WWTP in Guangzhou, China, operates a conventional activated sludge process where they added methanol to achieve denitrification. In order to eliminate methanol addition, Datansha WWTP added an ultrasonic reactor downstream from the sludge thickener (as shown as one of the placement locations in Figure 2, going from the TWAS to the biological reactor). After the sludge passes through the ultrasonic reactor, it is fed into the bio-tanks of the activated sludge process and used as a carbon source to achieve denitrification. In comparison to methanol addition, by using the ultrasonic reactor at Datansha WWTP, there was a 20 to 30 percent increase in nitrogen removal, 80 percent cost savings, and sludge minimization of 15 percent. Bryen Woo is the aerobic digestion product manager at Ovivo and has held this position for seven years. He has a Bachelor of Science degree in civil engineering from California State University of Fullerton and is a registered professional civil engineer in the state of California. James Goldhardt has been working for Ovivo for over five years and is the anaerobic digestion group manager. He attended the University of Utah and graduated in mechanical engineering. Water Online The Magazine