H2 S REMOVAL BY PURPLE SULFUR BACTERIA
IN SWINE WASTE LAGOONS
Theo J. M. van Lotringen, Graduate Assistant
John B. Gerrish, Assistant Professor
Agricultural Engineering Department
Michigan State University
East Lansing, Michigan 48824
INTRODUCTION
Odor production is considered as a major disadvantage for the operation of anaerobic
lagoons.   Several authors [1-5]  report on the occurrence of purple sulfur bacteria in anaerobic lagoons and associate them with reduced odor levels.   Often, however, the
presence of the purple sulfur bacteria is of a transient nature, because of changing load
ing rates or a cold winter season.
The purple sulfur bacteria, belonging to the family Chromatiaceae are known to
oxidize reduced sulfur compounds in the presence of light and under anaerobic conditions.   Simple organic compounds, like volatile fatty acids and carbon dioxide, can
serve as their source of carbon.   The simple organic compounds are used preferentially.
In contrast to the flow of carbon from fermentative organisms (also called acid-
formers) to methanogenic organisms, the flow of sulfur in an anaerobic environment
is more of a cyclic nature as a result of the interaction between purple sulfur bacteria
and desulfurizing bacteria.   This interaction also causes an enhanced growth of both
types of organisms in mixed culture [6].
There are already several successful models for the non-cyclic methane digestion
process [7-10]  but there are no models which describe the cyclic sulfur metabolism.
This paper summarizes the development of a model for the latter process; a more detailed description is to be found in the doctoral dissertation of the senior author [11].
MODEL
In order to obtain a better understanding of lagoon performance, a model is developed which emphasizes lagoon odor production.   The basis for this model is the sulfur
cycle, which is schematically presented in Figure 1.   The major sources of sulfide are:
-decomposition of feces in the bottom sediments
-conversion of sulfate (partially introduced into the lagoon with the urine) to sulfide
by the desulfurizing bacteria
-reduction of elemental sulfur by purple sulfur bacteria in the dark
In this model, the odorous air pollutant, hydrogen sulfide, leaves the lagoon along two
different pathways:   via the surface and via the gas bubbles.   The presence of purple
sulfur bacteria (PSB) effects a removal of sulfur as non-odorous intracellular elemental
sulfur when lagoon liquid is pumped to the field.
Regarding the photosynthetic metabolism of the purple sulfur bacteria, an anaerobic
lagoon can be considered as consisting of three regions (Figure 2):
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