A butane freezing process for dewatering sludge
Utilizing butane as the refrigerant, the direct slurry freezing process was employed to condition waste activated sludge in order to improve subsequent dewatering. Using batch and continuous flow labreactors, the process was evaluated from both a technical and economical standpoint. The sludge was placed in a closed reactor maintained at slightly less than atmospheric pressure, and liquid butane was bubbled through the sludge from a sparger at the bottom of the reactor. The boiling of the butane resulted in the formation of ice in the sludge but sufficient mixing was induced to prevent solid freezing. The sludge-ice slurry formed was removed, thawed and then dewatered using a variety of techniques. Recovery, liquification and reuse of butane vapors, and the utilization of latent heat of fusion of the sludge-ice slurry to minimize energy requirements were evaluated to permit economic analysis. Reactor design requirements were determined. Waste sludges from five separate sources were obtained. Conditioning effectiveness was evaluated by gravity settling, vacuum filtration, and sandbed dewatering techniques. Both Buckner funnel and leaf test experiments, with and without chemical addition, were used to evaluate filtration effectiveness. The results showed that the direct slurry freezing process using liquid normal butane as the refrigerant is an extremely effective method for conditioning waste activated sludge to promote settling, concentration and dewatering. Furthermore, conditioning can be accomplished without the generation of a high strength supernatant. Important variables affecting slurry freeze conditioning are (1) the length of time the sludge is exposed to slurry freezing conditions; and (2) the rate of freezing.
- Research Organization:
- Virginia Polytechnic Inst. and State Univ., Blacksburg (USA). Water Resources Research Center
- OSTI ID:
- 7308166
- Report Number(s):
- PB-262235
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
320604* -- Energy Conservation
Consumption
& Utilization-- Municipalities & Community Systems-- Municipal Waste Management-- (1980-)
ALKANES
BUTANE
DESIGN
DRYING
ECONOMICS
FREEZING
HYDROCARBONS
LIQUID WASTES
MANAGEMENT
MATERIALS RECOVERY
ORGANIC COMPOUNDS
PROCESSING
RECOVERY
SEWAGE
SEWAGE SLUDGE
WASTE DISPOSAL
WASTE MANAGEMENT
WASTE PROCESSING
WASTES