4    AUTOTHERMAL THERMOPHILIC AEROBIC
WASTE TREATMENT SYSTEMS:
A STATE-OF-THE-ART REVIEW
Timothy M. LaPara, Graduate Research Assistant
James E. Alleman, Professor
Purdue University
West Lafayette, Indiana 47907-1284
ABSTRACT
Thermophilic aerobic biological treatment systems have many advantages compared to conventional techniques for high-strength wastewaters, including faster biodegradation rates, greater
overall process efficiencies, and low rates of residual biosolids production. High reactor temperatures, however, alter the physical, chemical, and biological characteristics of the treatment
process, so that the enormous knowledge-base for conventional activated sludge operations no
longer directly applies. Several of these unique operating conditions are discussed. Process kinetics are also examined, with a particular focus on the high rate of endogenous decay typically
observed with thermophilic systems.
INTRODUCTION
Microbial life at temperatures exceeding 45(C has long been a peculiar phenomenon to scientists and engineers. Recent advances in biotechnology, however, have propelled the study of thermophilic bacteria from mere curiosity to the search for potential solutions to real problems. The
most well-known beneficial use of thermophilic bacteria is the Taq polymerase isolated from
Thermus aquaticus,x used in DNA amplification during the polymerase chain reaction (PCR).
This DNA polymerase, stable at temperatures well above those of more common enzymes, allows for repeated cycles of strand separation (95°C), primer hybridization (54°C), and DNA synthesis (72°C) without supplying any additional enzyme (for a review of PCR, see Reference 2).
Along with the demonstrated utility of thermostable enzymes with PCR, engineers and scientists have searched for other uses of thermophilic microorganisms and their enzymes for the production of antibiotics, chemical feedstocks, fuels, etc.3 Advantages of thermophilic biotechnology include faster reaction rates (production) and a significantly decreased potential for process
contamination. Extending beyond the use of thermophiles for production purposes, this chapter
reviews thermophilic treatment processes for the destruction and remediation of environmental
contaminants and wastewaters. As with biotechnological applications, thermophilic treatment
processes benefit from faster reaction rates (degradation) and, in this case, a significantly improved ability to destroy pathogens.
Clearly the limiting factor preventing the widespread use of thermophilic biotechnology in environmental engineering is the cost of raising reactor temperatures. Two situations exist in which
this cost can be avoided: (1) when wastewaters are produced hot; and (2) when the wastewaters
are highly concentrated such that the heat released during contaminant biodegradation is sufficient for autothermal operation. The former condition exists at a select few industries (e.g., pulp
and paper facilities), while the latter circumstance is much more common. Indeed, in addition to
the multitude of industries which produce high-strength wastewaters, virtually every publicly-
owned treatment works (POTW) produces residual biosolids which can be readily concentrated
to allow for autothermal thermophilic aerobic digestion (ATAD).
52nd Purdue Industrial Waste Conference Proceedings, 1997, Ann Arbor Press, Chelsea. Michigan 48118. Printed in
U.S.A.
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