he growth of the livestock industry provides a valuable source of affordable, sustainable, and renewable bioenergy in the form of methane generated from the animal waste (biomass). Major environmental problems such as, water contamination, ammonia leaching, and methane emission could arise due to its improper disposal. Anaerobic digestion of animal wastes is a promising waste treatment technology to produce biogas (containing methane) in a controlled environment for utilization as an energy source. Amongst several design and mixing configurations of anaerobic digesters for treating animal waste bio gas-lift or recirculated digester are favorable for large scale operations. Mixing is an important parameter that affects the performance of biogas-lift anaerobic digesters. The findings in the literature on the effect of mixing on anaerobic digestion are contradictory and limited.

Anaerobic digesters are highly opaque three phase systems due the nature of the waste treated. Therefore, hydrodynamic studies have been carried out using noninvasive measurement technique such as computer automated radioactive particle tracking (CARPT). CARPT has been used to characterize the liquid flow behavior and understand mixing in a pilot scale (100 l active volume) biogas-lift anaerobic digester at different biogas recirculation rates used for treating bovine waste. Performance studies have been carried out at the same biogas flow conditions as the CARPT studies.

The energy efficiency of such systems in terms of the process power inputted for mixing and the energy generated from methane, is crucial for its economic viability. Hence, this study has been carried out understand mixing such that the performance of anaerobic systems can be optimized for methane production with minimal process power input. The key results and findings of this study will be discussed.