Anaerobic digesters continue to be a focus for processing wastewater solids to produce a renewable fuel source, digester gas. Effective mixing of the digester contents is important for process stability, maximizing gas production, minimizing scum and foam formation, and preventing solids deposition in the digester. Mixing requires electrical power which is often generated by coal-fired power plants. With the concern regarding electrical power cost and the interest in reducing greenhouse gas emissions, there is a renewed focus on reducing the power required for digester mixing. This paper reports the test results of a new mixing system called the Vertical Linear Motion Mixer (VLMM) manufactured by Enersave Fluid Mixer, Inc which was shown to have comparable performance to other more conventional mixing systems (impeller draft tube mixers) with substantially less electrical power needed. The test results represent testing conducted at the Ina Road Wastewater Reclamation Facility (WRF), located in Tucson, Arizona. One new mixer was retrofitted to a conventional "pancake" digester and compared to an identical digester using five impeller draft tube mixers.

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