Anaerobic digestion of animal waste: Effect of mode 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).…”

“…In summary, there is no specific measurement of power requirement for optimum methane production in any particular anaerobic system and it is very much related to the type of wastewater itself whether it is diluted or concentrated. However as a general rule, minimal mixing is the best mode of mixing as confirmed by many studies (Karim et al, 2005a;Karim et al, 2005b;Karaparju et al, 2007;). …”

“…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.…”

“…In terms of power requirement for digesters mixing system, there is no specific value enforced, however US Environmental Protection Agency (EPA) recommended the power input of 0.20-0.30 HP/1000 cu ft (5.26-7.91 W/m 3 ) of the digester content (Karim et al, 2005a). In general, the mixing power requirement is very much related to the type of wastewater in terms of total solid contents as confirmed byvarious studies (Karim et al, 2005a;Karim et al, 2005b). For the dilute cow manure of 5% total solids, the influence of mixing was insignificant in terms of biogas productivity for the mixed and unmixed digesters (Karim et al, 2005a).…”

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.…”