Chemical Conditioning of Biological
Sludges for Vacuum Filtration
MARK W. TENNEY, Associate Professor
WAYNE F. ECHELBERGER, JR., Associate Professor
JOHN J. COFFEY, Graduate Student
TIMOTHY J. MC ALOON, Graduate Student
Department of Civil Engineering
University of Notre Dame
Notre Dame, Indiana
INTRODUCTION
During the treatment of wastewaters numerous separation processes are employed with or without prior treatment in order to remove dissolved or suspended
impurities. The residue resulting from these various separation processes is loosely
termed sludge and may be physically inert, chemical, or biological in nature. Primary
treatment of domestic wastewater, for example, yields a sludge resulting from the
removal of settleable suspended material which averages approximately 65 per cent
organic material; secondary treatment yields a sludge which is principally biological
(approaching 90 per cent organic material) resulting from microbial synthesis during
the metabolism of dissolved organic impurities; and tertiary treatment can yield
either a chemical or biological sludge depending on the tertiary treatment scheme
selected.
In order to achieve complete treatment, within the scope of the treatment
process, consideration must be given to the subsequent treatment and ultimate disposal of these sludges. The quantities of sludge produced from wastewater treatment
processes are extremely large. McCarty (1), for example, has estimated that the
sludge production from secondary treatment of domestic wastewater alone will reach
approximately 120 mgd by 1970. With the emphasis that our now approved state
water quality standards place on improved and advanced secondary and tertiary
treatment, the amount of sludge collected as a result of wastewater treatment can be
expected to increase substantially in future years.
Numerous individual processes and associated combinations exist for the treatment of sludges, such as: anaerobic digestion, wet burning, Zimpro, centrifugation,
vacuum filtration, dry burning, etc. Some of these processes are subject to severe
limitations, however, particularly if one considers the potential re-pollution
capability from inorganic fertilizing elements (e.g., nitrogen and phosphorus) or organic constituents, both of which can be released during certain of the above cited
treatment processes. Anaerobic digestion, for example, although effective for the
destruction and stabilization of the organic fraction of biological sludges, releases
appreciable concentrations of fertilizing elements to the supernatant liquid, thus
requiring additional treatment of the supernatant liquid prior to its discharge.
One process which appears to exhibit significant potential for present and
future   sludge   treatment   applications  is   that  of sludge  dewatering by vacuum
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