40    CLASSIFYING INDUSTRIAL SLUDGE USING A
KNOWLEDGE-BASED EXPERT SYSTEM
Allen C. Chao, Associate Professor
William J. Rasdorf, Assistant Professor
Department of Civil Engineering
North Carolina State University
Raleigh, North Carolina 27695
William E. Paige, Environmental Engineer
North Carolina Department of Human Resources
Solid and Hazardous Waste Management Branch
Raleigh, North Carolina 27602
INTRODUCTION
Sanitary landfills have been used as the most common method for disposal of most industrial
sludge materials.1 However, since hazardous constituents may leach out of the landfill, migrate into
ground water, and cause potentially serious problems, regular sanitary landfill facilities designed for
municipal solid wastes are not allowed to accept hazardous industrial sludge. Industries in the State of
North Carolina are required by law to submit to the state information concerning the sludge they
produce. Environmental experts in the State Department of Human Resources and Community
Development then determine the sludge classification based on the information submitted. The criteria for identifying the characteristics of hazardous wastes listed in the N. C. Hazardous Waste
Management Rules & Solid Waste Management Law2 are used as bases by the North Carolina
regulatory agencies to determine whether an industrial sludge is non-hazardous and thus can be
disposed of in a municipal sanitary landfill.
To implement the regulations, human experts need to possess a detailed understanding of the
procedures for implementing these criteria and regulations. An inexperienced engineer may need an
extended period of training before he can be entrusted to successfully carry out sludge classification
activities. Even for experienced experts, inconsistent conclusions may occasionally be drawn by
different individuals due to varying interpretations of the criteria and regulations.3-4 Additionally, a
serious drawback of the current method of sludge classification is that the criteria and regulations
frequently change. Thus, a person who has not followed those changes for a period of time may
become unfamiliar with the current criteria and regulations.
A prototype knowledge-based expert system has been developed to overcome these problems while
assisting environmental experts in classifying industrial sludge. This prototype program is written in
M.l, a microcomputer-based knowledge engineering tool for building small knowledge systems. The
main objective of this program is to test the feasibility of utilizing knowledge-based expert systems to
assist an inexperienced environmental expert in classifying industrial sludge. Successful test runs of
the prototype expert system have led to a plan for developing a more versatile system using a more
powerful knowledge engineering tool running on a minicomputer.
CONSIDERATIONS AND CRITERIA IN CLASSIFYING INDUSTRIAL SLUDGE
From among the numerous items listed in the hazardous waste management criteria and solid waste
management law for identifying hazardous sludge, there are two criteria considered to be the most
pertinent for classifying industrial sludge. The first criterion is that if a sludge exhibits certain
hazardous characteristics, it is classified as hazardous. Four categories of characteristics and their test
methods have been specified: ignitability, corrosivity, reactivity and EP toxicity. In each of these
categories, the waste characteristics and their test methods are described in detail. For example, a solid
waste or sludge is considered to exhibit the characteristic of ignitability and thus is classified as
hazardous if a representative sample of the waste or sludge exhibit one of the following properties:
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