Premium
Improved dewatering by freeze–thawing of predewatered sludge cakes
Author(s) -
Saveyn H.,
Curvers D.,
Jacobsen R.,
Van der Meeren P.
Publication year - 2009
Publication title -
asia‐pacific journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.348
H-Index - 35
eISSN - 1932-2143
pISSN - 1932-2135
DOI - 10.1002/apj.409
Subject(s) - dewatering , raw material , waste management , pulp and paper industry , environmental science , liquid nitrogen , chemistry , engineering , geotechnical engineering , organic chemistry
Biological sludge dewatering is known to be a troublesome operation due to the nature of the raw material. Dry matter contents of more than 30% are seldom obtained, leaving a final product containing more than two thirds of water. Many approaches have been used to improve the dewatering step by influencing the conditioning or dewatering process. One of the physical conditioning methods used is freeze–thawing, in which the physical structure of the sludge is destroyed. Most studies so far have been focusing on freeze–thawing of sludge at low solids concentrations, making it an inefficient process with regard to energy and cost. This study focuses on the freeze–thawing of predewatered sludges for subsequent mechanical dewatering in order to reduce the final sludge volume and hence disposal costs. Predewatered sludge with a dry matter content of 25–30% was frozen for different times periods (1–96 h) and at different temperature gradients (slow to fast freezing) using a variety techniques (submersion in glycol, commercial freezer and liquid nitrogen). The results from this study indicated that thawing followed by a second mechanical dewatering resulted in dry matter contents of up to 50%. Slow freezing times and long storage times yielded the best dewaterability results. An economical assessment of the process showed that a depreciation time of 2 years already delivers a profitable process. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.