Anaerobic digestion of dairy cattle manure autoheated by aerobic pretreatment
A novel way to heat anaerobic digesters was investigated. Dairy cattle manure was autoheated by an aerobic pretreatment process and then fed to the anaerobic digester. Important physical properties of the dairy cattle manure were determined. These included bulk density, specific heat, thermal conductivity and the rheological properties; consistency coefficient, behavior index and apparent viscosity. These parameters were used to calculate the overall heat transfer coefficients, and to estimate the heat losses from the aerobic reactor to the outside environment. The total energy balance of the aerobic treatment system was then established. An optimization study of the main parameters influencing the autoheating process showed that the total solids, the air flow rate and the stirring speed for operation of the aerobic pretreatment should be approximately 7%, 70 L/H and 1,400 rpm respectively. Temperatures as high as 65C were reached in 40 hours of aerobic treatment. At the above recommended levels of total solids, the air flow rate and the stirring speed, there was little difference in the energy requirements for heating the influent by aeration and heating the influent by a conventional heating system. In addition to the temperature increase, the aerobic pretreatment assisted in balancing the anaerobic digestion process and increased the methanogenesis of the dairy cattle manure. Despite the 8% decomposition of organic matter that occurred during the aerobic pretreatment process, methane production of the digester started with the aerobically heated manure was significantly higher (at least 20% higher) than of the digester started with conventionally heated manure. The aerobic system successfully autoheated the dairy cattle manure with an energy cost equal to that of conventionally heated influent.
- Research Organization:
- Minnesota Univ., Minneapolis, MN (United States)
- OSTI ID:
- 5581811
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
MANURES
ANAEROBIC DIGESTION
METHANE
YIELDS
BIOREACTORS
CATTLE
HEAT TRANSFER
AGRICULTURAL WASTES
ALKANES
ANIMALS
BIOCONVERSION
DIGESTION
DOMESTIC ANIMALS
ENERGY TRANSFER
HYDROCARBONS
MAMMALS
MANAGEMENT
ORGANIC COMPOUNDS
ORGANIC WASTES
PROCESSING
RUMINANTS
VERTEBRATES
WASTE MANAGEMENT
WASTE PROCESSING
WASTES
090900* - Biomass Fuels- Processing- (1990-)