Call number:
ZSP-201-88/20
In:
CRREL Report, 88-20
Description / Table of Contents:
This study develops design criteria for a new sludge dewatering unit operation called a sludge freezing bed. This bed uses natural freeze-thaw to condition the sludge. The total depth of sludge that can be frozen, thawed and dewatered by this process in a year is the main criterion needed for design. Laboratory tests assessed the dewaterability of freeze-thaw conditioned water treatment plant sludge and both anaerobically and aerobically digested wastewater sludges at various depths. Mathematical models for predicting the design depth were developed; values for the input parameters to the models were obtained from the literature or from laboratory and pilot-scale experiments. The dewaterability tests indicated that the depth of sludge that can be applied is not limited by drainability. Up to 2.0 m of each sludge drained in minutes after freeze-thaw conditioning. Except for the aerobically digested sludge, the solids content after drainage is high enough to permit mechanical removal. The physical and thermal characteristics of frozen sludge were found to be equivalent to those of ice. An analysis of the freezing and thawing models reveals that the design of a freezing bed will depend on the duration and intensity of the freezing and thawing seasons.
Type of Medium:
Series available for loan
Pages:
v, 58 Seiten
,
Illustrationen
Series Statement:
CRREL Report 88-20
URL:
https://apps.dtic.mil/dtic/tr/fulltext/u2/a205955.pdf
URL:
https://hdl.handle.net/11681/9061
Language:
English
Note:
CONTENTS
Abstract
Preface
Nomenclature
Introduction
Background
Purpose
Scope
Literature review
Fundamentals of freeze separation
Applications of freeze separation technology
Conclusions
Concept development
Background
Site visits
Final concept
Dewaterability studies
Sludge characteristics
Specific resistance and capillary suction time
Filtrate quality
Drainage tests
Drying tests
Development of design models
Basic energy balance relationship
Development of freezing model
Development of thawing model
Other models
Evaluation of sludge input parameters
Frozen sludge density, ϱf
Layer thickness, ϵ
Settled solids fraction, θ
Thermal conductivities, Kfs, Kss
Latent heat of fusion, L
Absorptance, α
Freezing point, Tf
Summary
Evaluation of climatic input parameters
Ambient air temperatures, Taf, Tat
Insolation, I
Convection coefficient, hc
Use of models for design
Freezing design depth
Thawing design depth
Validation
Example
Conclusions anid recommendations
Literature cited
Appendix A: Sludge freezing at the Salem, New Hampshire, Wastewater Treatment Plant
Location:
AWI Archive
Branch Library:
AWI Library
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