74    BIOLOGICAL REMOVAL OF HYDROGEN SULFIDE
FROM BIOGAS
Jelte Lanting, Operations Manager
Anal S. Shah, Environmental Engineer
Gb-biothane, Inc.
Camden, New Jersey 08104
INTRODUCTION
Biogas from anaerobic digestion processes may contain hydrogen sulfide in concentrations up to
several percent by volume. Processes for reducing the concentration in biogas generally are based on
physico-chemical principles. In this paper experiences with a technology to biologically remove hydrogen sulfide from biogas will be described.
BACKGROUND
During anaerobic digestion hydrogen sulfide may be formed through microbial reduction of inorganic sulfur compounds or biodegradation of organic sulfur compounds. Its formation may slaw
down the digestion process. Dissolved (and undissociated) hydrogen sulfide concentrations from 50 to
200 mg/L have been reported to cause moderate to complete inhibition.1
Hydrogen sulfide has a number of unpleasant properties:
• It has a characteristic rotten egg odor which can be detected at very low concentrations.
The odor threshold reportedly is 5 parts per billion by volume (ppbv). Poisonous concentrations, however, are odorless.2
• It is toxic. The threshold limit value is 10 parts per million by volume. Concentrations
greater than 300 ppmv may be lethal.2
• It is corrosive because it dissociates to form a weak acid. It may combine with metal ions
to form insoluble sulfides. Ferrous sulfide can cause galvanic corrosion because deposits
are cathodic to base metal.3 Microbial oxidation in the presence of air and carbon dioxide
may produce strong acids, which readily attack exposed metal and concrete surfaces.4
• Its combustion product is sulfur dioxide which is a contributor to acid rain.5 In light of
the renewed emphasis on air pollution control in this country, it is likely that even small
generators will be required to limit sulfur dioxide emissions.
All of the above seem good reasons to try and limit the formation of hydrogen sulfide during
wastewater treatment. Strategies employed or proposed include the addition of iron chloride to
anaerobic sludge digesters,6 and the addition of molybdate to inhibit sulfur reducing bacteria.7 End of
pipe strategies include the application of iron sponges to remove hydrogen sulfide from biogas,6 and
the application of biogas scrubbers that catalytically oxidize hydrogen sulfide to elemental sulfur.1 A
recent development and the topic of this paper is the application of biotechnology for clean up of
biogas.
THE BIOPURIC PROCESS
The Biopuric process was developed several years ago in what was then West Germany. The
proprietary technology makes use of micro organisms that convert hydrogen sulfide into sulfur
compounds of a higher oxidation state. The bacteria in the bioreactor can function effectively in a pH
range of one to six, at mesophilic temperatures and under micro-aerophilic conditions. Some are
capable of depositing and utilizing intracellular sulfur. The bacteria thought to be responsible for the
biochemical conversions include Thiothrix, Thiobacillus and Beggiatoa species.
A flow schematic is shown in Figure 1. The Biopuric process can be considered a combination of an
absorption tower and a trickling filter. Air is injected into the biogas in a defined volume proportion
46th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Primed in U.S.A.
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