Anaerobic
Digestion or
Anaerobic Degradation
is a process where microorganisms break down biodegradable material in
the absence of oxygen to process waste and release energy (methane). The anaerobic processes can be managed in a
"digester" (an airtight tank) or a covered lagoon (a pond used to
store animal waste) for waste treatment. The primary benefits of anaerobic
digestion are nutrient recycling, waste treatment, and odor control. In
very large systems, the biogas production is generally captured and then
recycled for use in for other unit operations within a treatment plant.
The methane gas that
evolves from a digester has been used to generate electricity. This
electricity has been used for general plant operation or to supplement the
energy requirements for blowers used for diffusers used in aeration. The
methane has also been used to heat the facilities or to warm the contents of the
digester itself, which generally results in higher gas production.
There are numerous types
of anaerobic digesters that are available. Some of these anaerobic digester use top
entering mixers. Defining the mixing requirement for an anaerobic
digesters of a closed tank system will be dependent upon the process
requirements of the system used and the type of containment vessel used.
Viscosity studies of
various sludge's indicate that they are special pseudo-plastic shear thinning
non-Newtonian
slurries. This sizing and mixer selection procedure is based upon general assumptions about sludge
characteristics. Viscometer readings that determining shear rate vs.
viscosity, which are typically used for flow evaluation (tank turnovers), should
be somewhat tempered as sludge has very unusual visco-elastic
characteristics. In short, thickened sludge does not act like general
comparable pseudo-plastic
fluids.
01.26.13
