33    PRINCIPLES OF ORGANISM SELECTION FOR THE
DEGRADATION OF GLYPHOSATE
IN A SEQUENCING BATCH REACTOR
D. V. S. Murthy, Doctoral Student
Robert L. Irvine, Professor and Director
Center for Bioengineering and Pollution Control
University of Notre Dame
Notre Dame, Indiana 46556
Lawrence E. Hallas, Sr. Research Specialist
Monsanto Agriculture Company
St. Louis, Missouri  63141
INTRODUCTION
Glyphosate (N-phosphono-methyl glycine) is the active ingredient of the herbicide Roundup™
manufactured by Monsanto Agriculture Company. U.S. EPA pesticide effluent guidelines require
glyphosate removal from waste streams before they are discharged. In this work, bench scale Sequencing Batch Reactors (SBRs) were used to study the biodegradation of glyphosate in wastes generated at
Monsanto's manufacturing facilities. Studies done show that glyphosate degrading activity (GDA) is
related to the presence of other microbial groups including nitrifiers, dentrifiers and ammonifiers.
Thus, selection of the right organism consortium is central for optimizing GDA. At a kinetic level,
reactions competing with and inhibiting glyphosate removal have to be suppressed by suitable manipulation of reactor operation and process conditions. Examples of the concepts discussed above, and
the results obtained are presented in this paper.
MATERIALS AND METHODS
Details of the laboratory scale SBRs used in this study, and the development of the operating
strategies for GDA, have been described in detail elsewhere.1 A brief description of the experimental
set up and the process variables is presented here. The SBR is a periodic process with each reactor in
the system going through five discrete periods in time as shown in Figure 1. The waste stream is
introduced into the reactor containing the biomass during FILL, with or without aeration. Reactions
for substrate removal initiated during FILL are completed during REACT. Clarification occurs in the
same vessel during SETTLE, and the treated effluent is withdrawn during DRAW. The IDLE phase
completes the cycle till the reactor is ready to receive the wastewater again. Further details of SBR
systems and their operation can be found in the literature.2-4 The laboratory SBRs used in this study
(called SBRs A and B) were 3L reactors with a FILL volume of 1.5L, and were operated according to
the cycles shown in Table I. Mixed liquor wasted out of these reactors was used in special batch studies
described in a later section.
Feed to the reactors consisted of waste from an industrial field site, with glyphosate as the target
compound of degradation. Structures of glyphosate and other related compounds in the feed are
given in Table II. The main product of glyphosate degradation in these mixed culture, mixed substrate
systems is aminomethylphosphonic acid (AMPA), which has little herbicidal activity.5 Microorganisms which cleave the C-P bond of glyphosate to yield other products have also been isolated.6-7
Glyphosate degradation by these microorganisms, however, only occurs in the absence of inorganic
phosphate. Since glyphosate containing wastes contain substantial amounts of phosphate, these
organisms are not important for the wastestreams described herein. Besides the compounds listed in
Table II, the reactor feed contained a number of other organics, including soft carbon sources like
formate and acetate. The concentrated feed from the industrial field site, was identified as the
centrifuge spent wash (CSW), and this was suitably diluted to yield the required glyphosate concentration in the feed. The following analyses were conducted according to procedures outlined below:
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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