Horsepower Requirements for High Solids Anaerobic Digestion

C. J. Rivard, B. D. Kay, D. H. Kerbaugh, N. J. Nagle, M. E. Himmel

Research output: Contribution to journalArticlepeer-review

14 Scopus Citations


Improved organic loading rates for anaerobic bioconversion of cellulosic feedstocks are possible through high-solids processing. Additionally, the reduction in process water for such a system further improves the economics by reducing the overall size of the digestion system. However, mixing of high-solids materials is often viewed as an energy-intensive part of the process. Although the energy demand for high-solids mixing may be minimized by improving the agitator configuration and reducing the mixing speed, relatively little information is available for the actual horsepower requirements of a mechanically mixed high-solids digester system. The effect of sludge total solids content and digester fill level on mixing power requirements was evaluated using a novel NREL laboratory-scale high-solids digester. Trends in horsepower requirements are shown that establish the optimum parameters for minimizing mixing energy requirements, while maintaining adequate solids blending for biological activity. The comparative relationship between laboratory-scale mixing energy estimates and those required for scale-up systems is also established.

Original languageAmerican English
Pages (from-to)155-162
Number of pages8
JournalApplied Biochemistry and Biotechnology - Part A Enzyme Engineering and Biotechnology
Issue number1
StatePublished - 1995

NREL Publication Number

  • NREL/JA-422-6662


  • anaerobic digestion
  • high solids
  • Horsepower
  • mixing


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