MOLASSES PROMOTED BIOLOGICAL SULFUR RECOVERY
FROM HIGH SULFATE WASTES
Alon Lebel, Graduate Student
Henrique C. G. do Nascimento, Research Assistant
Teh Fu Yen, Professor
Department of Civil Engineering
University of Southern California
Los Angeles, California 90089
INTRODUCTION
Oil shale represent one of the largest undeveloped natural energy resources in the United States.
The recoverable energy estimated in the Green River formation alone is equivalent to 600 billion
barrels, nearly twice the amount of the petroleum deposits in the Middle East [1].
The organic compound of the greatest potential, kerogen, is trapped in a mineral matrix of dolomite (magnesium-calcium carbonate) and quartz. It has been shown that up to 40% of the mineral
matrix can be dissolved through the action of sulfuric acid, a byproduct of Thiobacillus species [2,3].
However, in order to commercialize such a concept, inexpensive sulfur in high quantities should
be supplied to allow acid production by the Thiobacillus organisms. The utilization of the natural
sulfur cycle was thought as an advantage. The sulfate slurry produced in this process can be reduced
anaerobically by dissimilatory sulfate reducing bacteria (SRB) to hydrogen sulfide (H2S) and further
oxidized to elemental sulfur which then can be served as nutrient for the Thiobacillus species [4]. A
sulfur recovery process suggested by Laseter is presented in Figure 1.
The oxidation of sulfide to elemental sulfur, a well established process can be carried out by either
biological [5,6] or chemical [7] means. Therefore, the research work concentrated on the first stage
of the proposed process, the sulfate reduction via sulfate reducing organisms.
Although basic knowledge has been available for decades, such a process has not yet been successfully applied. A major reason is probably the unavailability of a commercially attractive carbon
source. The use of an advanced ion chromatography system allowed a thorough investigation of the
optimal nutrition requirement in the sulfate reduction system in a new approach [8]. It introduced
the ability to simultaneously analyze organic acid and inorganic anions in less than 25 minutes and,
thus, allowed a detailed study of the metabolic behavior of the SRB.
The work presented in this paper discusses the alternative carbon sources to SRB and studies one
of the most attractive sources, molasses, and its applicability to the process.
Purge Cos Mokeup
Growth  Stimulators"
Hydrocarbon   Substrate
Gypsum Surry
Purge Gas Recycle
Pressure Controller —
Purge Gas and H2S
Liquid
Phase
Fermentor  Tank
Extraction
Technology
Useful Organic
Products
Figure 1. Sulfur Recovery Process Suggested
by Laseter.
Sulfur
Recovery Plont
To Sewoge Plont
891