HORSEPOWER REQUIREMENTS FOR HIGH-SOLIDS ANAEROBIC-DIGESTION

Improved organic loading rates for anaerobic bioconversion of cellulos ic feedstocks are possible through high-solids processing. Additionall y, the reduction in process water for such a system further improves t he economics by reducing the overall size of the digestion system. How ever, mixing of high-solids materials is often viewed as an energy-int ensive part of the process. Although the energy demand for high-solids mixing may be minimized by improving the agitator configuration and r educing the mixing speed, relatively little information is available f or the actual horsepower requirements of a mechanically mixed high-sol ids digester system. The effect of sludge total solids content and dig ester fill level on mixing power requirements was evaluated using a no vel NREL laboratory-scale high-solids digester. Trends in horsepower r equirements are shown that establish the optimum parameters for minimi zing mixing energy requirements, while maintaining adequate solids ble nding for biological activity. The comparative relationship between la boratory-scale mixing energy estimates and those required for scaleup systems is also established.