DILUTE SWINE WASTE TREATMENT IN AN ANAEROBIC FILTER
Thomas J. Brumm, Research Engineer
Agricultural Engineering Department
University of Illinois
Urbana, Illinois 61801
John C. Nye, Associate Professor
Agricultural Engineering Department
Purdue University
West Lafayette, Indiana 47907
Anaerobic digestion is a relatively recent animal waste management alternative. Although
this process has been used in industrial and municipal applications for over 50 years, its use
in farm situations has been limited to the last decade. The prospect of surplus energy (methane), in addition to waste stabilization, has prompted a number of on-farm units to be built
and studied. Many of these have been high-rate, mesophilic anaerobic digesters.
A number of problems are encountered in farm situations. On the farm, a greater emphasis is placed on energy production from an anaerobic system than in municipal treatment
systems, for example. Hence, there is a need to optimize methane output. A significant portion of the methane, however, is needed to maintain the temperature of the digester. This
decreases the net methane yield.
These digesters are generally operated by the farmers themselves, who at best have had
limited exposure to anaerobic systems. They often do not have the experience necessary to
deal with problems that arise in the operation of an anaerobic digester. Also, farmers are
limited in the amount of time they can spend operating and maintaining their digesters due
to their other activities on the farm.
In animal production systems that incorporate hydraulic removal (flushing) of animal
manures from confinement buildings, conventional anaerobic digestion becomes a marginal
alternative. The large amount of dilution water often increases the volume of waste to be
treated past the point of physical or economic feasibility.
One alternative to the high-rate mesophdic digester is the anaerobic filter. The high solids
retention time induced by the filter media and the resultant accumulation of a high concentration of active biological solids allows treatment at temperatures 10-15 C below mesophilic. These lower temperatures free much of the methane normally used to heat the reactor for external use.
The anaerobic filter is less sensitive to changes in environmental and operating conditions.
It can respond instantaneously to changes in loading rate and detention time. This characteristic is ideal for an on-farm situation, minimizing the management and time problems experienced by the farmer.
Dilute wastes, such as the effluent from a flushed swine building, are ideal for treatment
in an anaerobic filter. The low hydraulic detention times (compared to high-rate mesophilic
digesters) decrease considerably the size of reactor needed.
Anaerobic filters have been used to treat a variety of industrial and food processing
wastes, but the application to animal wastes, in particular swine waste, has been limited.
Smith and Miner [ 1 ] suggested that the anaerobic filter could be used to treat the liquid
portion of the effluent from a flushed swine unit. Smith et al. [2] used an anaerobic filter
as the second stage of a two-stage (acid and methane) anaerobic digestion system that
treated waste from a finishing swine deep pit.
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