Section Four
BIOLOGICAL SYSTEMS-C. ANAEROBIC
43    HIGH pH EFFECTS IN ANAEROBIC TREATMENT
OF LIQUID INDUSTRIAL BYPRODUCTS
Erie A. Seagren, Graduate Research Assistant
University of Illinois
Urbana, Illinois 61801
Audrey D. Levine, Assistant Professor
Civil and Construction Engineering
Iowa State University
Ames, Iowa 50011-3232
Richard R. Dague, Professor
Civil and Construction Engineering
Iowa State University
Ames, Iowa 50011-3232
INTRODUCTION
The success of anaerobic digestion of industrial wastes is dependent on environmental conditions
such as pH, the absence of toxic substances, and many other factors. The majority of research on pH
in anerobic digestion has been focused on low pH effects.
For optimum operation of anaerobic reactors, the hydrogen ion concentration must be maintained
within a narrow range near pH 7.O.'5 However, limited research has been published on the effects of
high pH on the performance of anaerobic systems. Typically, industrial waste streams that have high
pH levels are otherwise ideal candidates for anaerobic treatment. For example, grain processing
wastes and egg breaking wastes may have pH levels above 10. Another case where a high pH may be
imposed on anaerobic systems is in the application of chemical coagulation to separate anaerobic
biomass in the anaerobic activated sludge process.6 A side benefit of anaerobic treatment of appropriate high pH wastes is the methane enrichment of the gas phase which occurs as pH increases.
The objective of this research was to investigate high pH effects in completely-mixed, suspended
growth, anaerobic reactors, in particular the upper pH limit that is possible while simultaneously
avoiding toxic inhibition from the alkaline earth and alkali metals (Na + , K + , Ca + +, and Mg + +) and
ammonia (NH3/NH4). In addition, the effect of high pH on the different trophic groups of the
anaerobic mixed culture was evaluated.
BACKGROUND
Optimum pH for Anaerobic Treatment
The three groups of bacteria involved in the anaerobic digestion of organic material (i.e., the
hydrolytic/fermentative bacteria, the acetogens, and the methanogens) have different optimum values for pH in pure culture. When all three groups of bacteria involved in the anaerobic process are
functioning together as an integrated system, the optimum pH range has to accomodate all of the
species which are involved. A summary of the results of several laboratory studies that investigated
the optimum pH range for anaerobic mixed cultures is presented in Table I. One point to note about
the results in Table I is that two of the studies used anaerobic filters. These findings may not be
comparable to suspended biomass anaerobic systems since, as pointed out by Speece and Parkin8
(1983), with an anaerobic filter the methanogens located in the interior of the biofilm are not subject
to the same conditions (e.g., pH) as exist in the bulk solution. Also, as pointed out by Porter7, the
cessation of methane production that Clark and Speece4 found above pH 9 could have been due to
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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