42    CO-IMMOBILIZATION OF NITRIFYING BACTERIA AND
CLINOPTILOLITE FOR ENHANCED CONTROL OF
NITRIFICATION
Kurt T. Preston, Environmental Engineer
U.S.Army Corps of Engineers
Waterways Experiment Station
Vicksburg, Mississippi 29180
James E. Alleman, Professor
School of Civil Engineering
Purdue University
West Lafayette, Indiana 47907
INTRODUCTION
This research examines the co-immobilization of nitrifying bacteria with clinoptilolite in a barium
alginate matrix as a method to enhance the control of the nitrification process in wastewater treatment
operations.
Current Systems
Biological nitrification in wastewater treatment remains a technical challenge.1 Currently, there are
two basic systems for biological treatment with ammonia removal, fixed film and flocculation. As
methods of biomass retention, these systems are considered passive immobilization techniques
because nitrifying bacteria native to the wastewater influent are encouraged to remain in the reactor to
degrade ammonia, the target substrate. In fixed film systems, surface area is maximized to encourage
colonization and retention within the reactor. By contrast, flocculating systems use hydraulic methods
to separate the bacterial colonies from the bulk solution in quiescent settling tanks. A portion of the
underflow of the settling tank is then returned to the reactor. In both fixed film and flocculating
systems, ammonia is oxidized to nitrate by nitrifying biomass. The biomass is retained in the reactor
only by methods associated with the inherent reactor design. In other words, no physical, chemical or
biological enhancement methods are used apart from the reactor to retain the biomass.
Unfortunately, nitrifying bacteria are not especially adept competitors in fixed film and flocculating systems. They are slow growing, inhibited by a wide range of compounds, and greatly affected by
temperature.2"5 As a result, wastewater treatment operations find nitrification difficult in the face of
heterotrophic competition, unknown inhibition, and seasonal low temperatures. In the future, the
limits of passive immobilization for nitrification will become more apparent as discharge limits
become increasingly stringent.
Immobilized Systems
The retention of specific enzymes, bacteria, or bacterial communities by physical or chemical
means, not directly associated with the wastewater treatment process, defines active microbial immobilization.6 With active immobilization systems, specific microbial communities are secured into or
onto a specific matrix for wastewater treatment purposes. Although a new concept in wastewater
treatment, active immobilization has been applied in the biochemical and pharmaceutical industry for
some time. The chief advantages to active microbial immobilization are retention of biomass, manipulation of growth rate independent of washout, capability for high cell concentration, ease of reactor
start-up, and possible protection from inhibitory compounds.7
The literature reports some attempts at active immobilization techniques for ammonia removal in
wastewater. Two groups have worked in this area, one in Holland at the University of Wageningen8
and one in Japan under the auspices of Hitachi Plant Engineering and Construction Co. Ltd.9 Both
groups use activated sludge selectively enriched for nitrification prior to immobilization as the bacte-
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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