5    REMEDIATION OF TOXICITY CHARACTERISTICS SLUDGES
Fred Closmann, Project Engineer
Don Sherman, Senior Project Manager
Remediation Technologies
Austin, Texas 78705
INTRODUCTION
The Hazardous and Solid Waste Amendments (HSWA) to the Resource Conservation and Recovery Act (RCRA) were passed by Congress in 1984, reflecting a significant change in direction in
national policy concerning waste management and disposal practices.1 One group of wastes which
became regulated as hazardous were those that failed to meet the Toxicity Characteristics Leaching
Procedure (TCLP) which went into effect on September 25, 1990.
The TCLP rule (Federal Register, 1986) established a new regulatory value for benzene of 0.5 ppm,
when tested by the specified procedure. This newly established limit affected a number of operators in
the hazardous waste management industry. In particular, a Gulf Coast chemical products facility
operating a wastewater treatment system was in danger of being out of compliance with the TCLP
regulation if they were unable to reduce their wastewater impoundment TCLP benzene level by the
promulgated deadline.
LIQUID/SOLIDS TREATMENT (LST)
Bioremediation has gained wide acceptance throughout the hazardous waste management industry
as an effective treatment technology. In particular, land treatment has been the principal bioremediation method for contaminated solids.2 The HSWA restrictions are primarily concerned with off-site
migration of contaminants, limiting the application of bioremediation to technologies other than land
treatment. Additionally, land treatment is a relatively slow process, favoring LST where engineering
controls allow for greater degradation rates.
LST involves the aerobic degradation of soluble organics in an aqueous slurry suspension. The
process is similar to activated sludge treatment. The primary difference between the two technologies
is that LST is conducted at high solids loading relative to conventional activated sludge. Mixing
equipment is generally required in LST to maintain solids in suspension, whereas aeration alone is
generally sufficient in conventional activated sludge systems.
LST's effectiveness at treating organic contaminants in waste slurries stems from the high degree of
control the remediation engineer has on the process allowing for optimization of process variables.
Important variables which can be controlled and optimized include:
• system temperature and pH,
• mixing energy to effect sufficient mass transfer,
• aeration energy to provide sufficient dissolved oxygen (DO),
• ratio of microorganisms to substrate (organics),
• availability of required nutrients, and
• amount of volatile emissions.
Mixed liquor pH can be controlled through the addition of aqueous form acid or caustic. Nutrients,
specifically nitrogen and phosphorus, can be elevated through the addition of aqueous form fertilizer.
Nitrogen is added as urea or ammonium nitrate and phosphorus is added as phosphoric acid (75% by
volume). A combination of mixers and aerators provide the energy required for sufficient mass
transfer and turbulent mixing of substrate, microorganisms, and dissolved oxygen. Volatile emissions
are also controlled by the type and extent of mixer/aerator operation.
Through extensive experience on a number of LST systems, ReTeC has found the following LST
process conditions to be optimal:
46th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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