Anaerobic digestion of animal waste: Waste strength versus impact of mixing

Influential Parameters on Biomethane Generation in Anaerobic Wastewater Treatment Plants

“…Generally for large scale applications, agitator or mixer system is commonly used to mix substrate homogenously inside the bioreactor and to provide a good contact between microorganisms and the substrate. All previously published articles on the effects of mixing on the stability and methane production reported similar observations which led to a consistent conclusion that vigorous mixing that is turbulent flow in nature is unsuitable for microorganisms growth and consequently results in an unsatisfactory methane production (Stafford, 1982;Stroot et al, 2001;Karim et al, 2005a;Karim et al, 2005b;Kaparaju et al, 2007;. This is basically due to the effect of high shear force on separating the hydrolytic bacteria from their substrate (Stafford, 1982).…”

“…There is only a limited number of studies found specifically focused on the effects of mixing on the treatment efficiency and biogas production using various types of organic wastes including cow manure, palm oil mill effluent (POME), animal waste, municipal solid waste, primary sludge and fruit and vegetable wastes (Stafford, 1982;Stroot et al, 2001;Karim et al, 2005a;Karim et al, 2005b;Kaparaju et al, 2007;). Adequate mixing is very important in order to achieve successful anaerobic treatment of organic rich wastewater.…”

The Research on Optimization of the Multiphase Flow Field of Biogas Plant by Using CFD Software

“…From the figure, the velocity vectors distribution is relatively even, and the majority of kinetic energy is found in high area. At the initial stage of fermentation, as most feedstock float in the high area, the kinetic energy concentrating in the high area can help to mix up the slurry out of gravity and enhance the fermentation efficiency [16]. However, as the total kinetic energy is not abundant in this condition, a higher inlet velocity is considered.…”

“…25 L·L , unable to continue to ascend, while Karim [16] stated by experiment that the digesters mixed by slurry recirculation, impeller, and biogas recirculation produced approximately 29%, 22% and 15% more biogas than unmixed digester, respectively, which verified that the hydraulic mixing is the best method. In author's previous quantitative description on the effect of several models of hydraulic mixing with CFD software, the bottom inflow mixing was stated as the best in hydraulic mixing, and the high dispersed outlets [16] were optimized. However, the in-depth study of the inlet velocity of hydraulic mixing has not been reported.…”

Effect of Mixing Driven by Siphon Flow: Parallel Experiments Using the Anaerobic Reactors with Different Mixing Modes

“…Since mixing has been shown to have a large positive impact on digestion efficiency, most commercial large-scale digesters have a continuous mixing system. The effect of mixing on anaerobic digestion has been investigated from several perspectives [6][7][8][9]. The most notable positive effects of mixing are: (1) the dispersion of the substrate for better contact with microorganisms; (2) making the sludge temperature uniform and (3) the reduction of scum and deposits formation.…”