THE FEASIBILITY OF USING NITRIFYING BACTERIA
TO ASSIST THE REGENERATION OF CLINOPTILOLITE
M. J. Semmens, Assistant Professor
Department of Civil Engineering
University of Illinois
Urbana, Illinois 61801
INTRODUCTION
Studies have been made, and are continuing, to identify the feasibility of employing
nitrifying bacteria to assist in the regeneration of spent clinoptilolite.   This paper provides
a summary of the major findings in the research already completed, and the process costs
for biological regeneration are estimated and compared with the costs of chemical
regeneration processes.
RESULTS OF STUDIES COMPLETED
In early studies [1,2] of the biological regeneration process, batch tests were conducted
to identify the mechanism of regeneration and the factors influencing the rate of regeneration.   These studies clearly demonstrated that rapid and complete regeneration of
clinoptilolite could be achieved, and identified the mechanism as being ion exchange
followed by nitrification of the liberated ammonium ions.
The mechanism of regeneration may be summarized as follows: the first step is ion
exchange, and as soon as the ammonium-saturated zeolite is placed in solution, a small
amount of ammonium is displaced, according to Equation 1.
Z.NH4+ + Na+ ■+ Z.Na+ + NH4+ (1)
The amount of ammonium displaced depends upon the amount of ammonium on the
zeolite and the concentration of salt in solution.   Even if only a small concentration of
salt is present, when there is an appreciable amount of ammonium on the clinoptilolite a
concentration of free ammonium ions will be found.
As the ammonium ions are liberated they are oxidized by the nitrifying bacteria.   The
reaction stoichiometry is represented by Equations 2-4.
Nitrite Production (Nitrosomonas)
NH4++y0j -»N02  + 2H+ + H20 (2)
Nitrate Production (Nitrobacter)
N02" + 2H+ + i 02 -* N03- + H20 (3)
Overall Nitrification
NH4+ + 202 -* N03" + 2H+ + 2H20 (4)
The hydrogen ions produced during the nitrification process are neutralized by the addition of sodium carbonate.   Equation 4 may be rewritten to include the concurrent
neutralization of hydrogen ions, and the overall equation is presented in Equation 5.
NH4+ + 202 + Na2C03 ■+ N03" + 2Na+ + 2H20 + C02 (5)
Combining Equations 1 and 5, we obtain Equation 6, which describes the overall
regeneration process.
733