Treatability vs. Oxidizability of
Industrial Wastes, and the
Formulation of Process Design Criteria
A. W. BUSCH, Assistant Professor
Department of Civil Engineering
Rice University
Houston, Texas
The intent of this paper is to focus attention on the basic philosophy of
engineering design in the aerobic bio-oxidation of industrial wastes containing soluble organics. The point at issue is the possible discrepancy between
basic susceptibility to degradation and the economic and practicable feasibility of biological treatment. In short, amenability to bio-oxidation, particularly if determined solely in batch operation, does not indicate treatability,
per se. This is not to deny that some system can theoretically be provided for
the treatment of any wastewhich can be degraded biologically. However, engineering design must take cognizance of all factors, of which space requirements are among the most pertinent, ranking perhaps second to the ubiquitous
monetary considerations.
The writer readily admits to an emphasis on semantics but feels strongly
that an engineer's assessment of treatability must be inclusive of design criteria for a treatment process which can then be evaluated for economic and
practicable feasibility prior to the statement of a final engineering recommendation. There follows a presentation of a procedure for the establishment
of design criteria for completely-mixed bio-oxidation systems encompassing
integral clarification and continuous solids recirculation with positive control
of mixed-liquor suspended solids.
Recently, Symons, et al (1) proposed a procedure for determining bio-
logical treatability of industrial wastes. These workers clearly state that their
procedure is only for treatability and not for the establishment of design criteria; however, their justification for this is that "suitable design factors have
already been established and can be applied once the extent of biological degradation for a particular waste is determined." It is this statement with
which the writer disagrees. The writer maintains that design criteria, other
than effluent requirements, are both dependent on, and a characteristic of,
the particular waste in question. With effluent requirements as a starting
point, criteria for the design of a process capable of meeting these requirements can be delineated with little, if any, more effort than is required for
the degradability determination proposed by Symons, et al (1). Another recent publication, by Stack and Conway (2), presented a laboratory technique
for obtaining design data for completely-mixed activated sludge systems.
These workers used a continuously-fed oxy-utilometer. Unfortunately, neither
Stack and Conway (2) or Symons, et al (1) discussed the importance of the
hydraulic regime, characterized conveniently by surface loading or overflow-
rate, in the selection of micro-organisms which will be characteristic representatives of the population to be expected under prototype conditions. Furthermore, neither paper brought out the significance of the organic loading on
effluent quality. This relationship was first established by Garrett and Sawyer
(3) in 1952 ana will be discussed further subsequently.
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