Controlled anaerobic digestion of organic matter provides an effective means of stabilizing organic waste and it is currently widely used by the municipal/industrial waste treatment industry. Modern livestock production facilities typically contain large animal populations with resulting high production of organic waste. Transfer of anaerobic digestion technology as developed by the municipal/industrial waste treatment industry to livestock waste treatment is technically feasible with little design change required, but very few livestock producers are implementing the technology due to concerns over construction and operating costs;As one of the respiration products of the anaerobic bacteria involved in the digestion process is methane, anaerobic digesters should be net energy producers. That is, the energy required to operate a digester is, with prudent digester design, less than the energy content of methane produced. Anaerobic digesters operate best at elevated temperatures; one design temperature is 35(DEGREES)C and a second is 55(DEGREES)C. The major energy input in a digester is the heat required to bring influent liquid to design temperature. As digesters are operated at nearly constant volume, effluent flow rate essentially equals influent flow rate and an effluent to influent heat exchanger has great potential for reducing operating heat demands, and thus operating costs;A model concentric-tube counterflow heat exchanger with rotating augers in both the annulus and inner pipe was built to study this potential. It was tested using several different pseudoplastic liquids, including anaerobic digester effluents and influents. Viscometry measurements were done for each liquid to determine the effective viscosity necessary for developing convective heat transfer correlations. Effectiveness for the model for each different liquid was determined and effectiveness for selected prototypes was calculated in accordance with principles of similitude. Compared to a conventional concentric-tube heat exchanger, model test results show approximately a 10 fold increase in effectiveness for laminar flow and a 2 fold increase in turbulent flow.