World Journal of Microbiology & Biotechnology 10, 110-111
Short Communication
Removal of H2S by the purple sulphur bacterium Ectothiorhodospira
shaposhnikovii
M.B. Vainshtein,* G.I. Gogotova and N.-J. Heinritz When Ectothiorhodospira shaposhnikovii VKM B-15 25 was used for desuphurization of biogas in the laboratory and in a pilot plant, there was complete oxidation of H2S, the main product being elemental sulphur. The advantage of this culture over green bacteria is discussed. Key words: Bacterium, desulphurization, Ectothiorhodospira shaposhnikovii, sulphide, sulphur.
The removal of H2S from waste waters, industrial gases and biogases is a well-known technological problem. Techniques for gas purification include washing with methanol under high pressure and precipitation by iron filings or by iron oxide, with the formation of insoluble iron sulphide. There are also biological techniques of desulphurization by contact with aqueous solutions or with a damp carrier containing thiobacilli. The disadvantage of all these methods is their relatively high cost o r - - i f thiobacilli are u s e d - - t h e formation of sulphuric acid, accompanied by increasing corrosion. Over the past 10 years, a technology has been developed for the removal of HzS from biogas using the green bacterium Chlorobium timicola f. thiosulfatophilum ATCC 17092 (Cork 1982; Cork et aL 1983). Certain technological difficulties result from the bacterial requirement for light but an economic advantage is that elemental sulphur is obtained. This paper presents data on the use of the purple sulphur bacterium Ectofhiorhodospira shaposhnikovii VKM B-1525 for H2S oxidation in aqueous solutions.
Materials and Methods Microorganisms The type strain of Ectothiorhodospira shaposhnikovii (VKM B-1525) was used. Biomass samples for the analysis of amino acids were M.B. Vainshtein, G.I. Gogotova and N.-J. Heinritz are with the Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; fax: + 7 (095) 9233602. *Corresponding author. © 1994 Rapid Communications of Oxford Ltd
110
WorldJournalof Microbiology& Bio#echnology,VoI 10, 1994
taken in the logarithmic growth phase in the laboratory experiments.
Chemical Analyses Concentrations of sulphide were determined by a colorimetric method (Pachmayr 1960). Polythionates, thiosulphate and sulphite were determined by classical methods based on titration (Kurtenacker 1938). Elemental sulphur was separated by filtration, and its content was determined by the reduction in the filter weight after extraction with 96% (v/v) ethanol. Biomass control samples did not contain S°. SO 2 concentrations were determined by potentiometric titration with BaCl2 in acid (i.e. carbonate-free) sample. The amino acid analysis was conducted with an auto-analyser. Experimental Conditions In laboratory experiments, oxidation of H2S was studied under batch conditions and during continuous cultivation. The culture was grown at 22 to 26°C in Larsen's medium with 5 g sodium acetate/1. In all cases the light was about 0.I kIux. The concentrations of biomass were up to about I g/1 under batch conditions of growth and 5 g/1 during continuous cultivation. A mixture of N 2 and methane containing H2S was bubbled through the liquid medium. Large scale experiments were carried out at the 'Rohrtechnic' pilot plant (Delittch, Germany) (see Beck et al. 1988). The reactor volume was 5 m3. The medium consisted of tap water with additions of NH +, PO34- and acetate. Biogas, containing H2S as the only S-compound, was bubbled through the unit at the rate of 4 m3/h per m3 of liquid medium. The concentration of the bacterial cells was more than 109 ml. The liquid and gas phases were separated by the difference in their densities. The cooled and desulphurized gas was removed through a special pipe and burnt. The bacterial suspension, enriched with CO 2, was pumped into the flat solar collector (total area 10 m2). At night and in cloudy weather, the photo-collector required up to I kW of electric lighting.
Removal of H2S 500
70
4oo i
--~ 3oo ]
qs0
o
-2°
~40--~ 30
100
~ 10 A-
Sulphur
TMosulphate Polythionate
~ Sulphite
~ k ' ~ io Sull~hate
Figure 1. Sulphide oxidation by E. shaposhnikovii in the bio-reactor. Initial H2S concentrations were 350 (m, [ ] ) and 680 (17, [ ] ) mg S/I. Products are given as mg S/I ( 1 , []) and % of total ( ~ , []).
Results and Discussion The choice of E. shaposhnikovii as a biotechnological culture for the removal of H2S was prompted by at least two advantages it has over green bacteria. Firstly, purple bacteria biomass is a valuable fodder ingredient owing to its high content of carotenoids and provitamin A (Kobayashi & Kurata 1977). In media with organic substrates, large amounts of extracellular polysaccharides are also formed (Schmiechen et a]. i992) and these may find independent biotechnological use. Secondly, although both green and purple sulphur bacteria are anaerobic, E. shaposhnikovii can survive in air, which often cannot be avoided in the technology used and is capable of aerobic oxidation of H2S in the dark (Gogotova & Vainshtein 198I). Preliminary tests on the ability of E. shaposhnikovii to oxidise H2S from the gas mixture were carried out using cells grown to stationary phase and methane as the carrier gas, which was bubbled through the liquid medium. The sulphide concentration increased, as the result of the dissolution of H2S, at a rate of 16 mg S/1.h. The sulphide oxidation represented approximately half of the content of dissolved H2S. In continuous cultivation, the bacterial biomass was higher and the oxidation rate increased accordingly. After 12 h in the light, the specific rate of anaerobic oxidation was 18 to 23 mg S/h.g wet biomass. The rate of aerobic sulphide oxidation was also measured in the dark, to estimate the potential biotechnological use of the culture without artificial light. In this case, the specific rate after 12 h was 8.0 to 8.2 mg S/h.g wet biomass. Non-corrosive sulphur compounds were the main products of sulphide
oxidation by E. shaposhnikovii, and their largest bulk was constituted by elemental sulphur (Figure 1). The use of the culture for the desulphurization of biogas at the 'Rohrtechnic' pilot plant showed that HzS, at up to 30 mg S/l, was completely oxidised in solution and did not pass through the reactor with the biomass suspension. Thus, the experiments in the laboratory and in the pilot plant demonstrated that cultures of E. shaposhnikovii desulphurized biogas with no accumulation of corrosive compounds. Experimentation in a pilot plant demonstrated the potential use of the method in an industrial environment.
Acknowledgements The authors are grateful to Drs B. Kirsop and B. Tindall for their critical reading of the manuscript.
References Beck, D., Heinritz, H.-J., Wiessner, A., Ringpfeii, M., Recha, G., Passin, H., Iwanow, M., Weinstein, M., Gogotova, G. & Kondratieva, E. 1988 Verfahren zur Enffernung von Schweffelwasserstoff aus Gasen und fluessigen Medien. German Democratic Republic Patent DD 256426. Cork, D.J. 1982 Acid waste gas bioconversion--an alternative to the Claus desulphurizafion process. Developments in Industrial Micribiology 23, 379-387. Cork, D.J., Garunas, R. & Sajjad, A. 1983 Chlorobium limico]a forma thiosu]fatophilum: biocatalyst in the production of sulphur and organic carbon from a gas stream containing HzS and CO 2. Applied and Environmental Microbiology 45, 913-918. Gogotova, G.I. & Vainshtein, M.B. 1981 The oxidation of thiosulfate by purple sulphur bacterium Ectothiorhodospira shaposhnikovii in the dark. Microbiologia (USSR) 50, 96-963. Kobayashi, M. & Kurata, Sh.-I. 1977 Use of photosynthetic bacteria. In Proceedings of 2nd International Symposium, Growth of Microorganisms on C-I Compounds, pp. 207-210. Pushchino: USSR Academy of Science. Kurtenacker, A. 1938 Analytische Chemie der Sauerstoffsauren des Schwefels. Stuttgart: Enke. Pachmayr, F. 1960 Vorkommen und Bestimmung von Schwefelverbindungen in Mineralwasser. Dissertation, Universit/it M6nchen. Schmiechen, H., Wittig, H. & Martin, S. 1992 Entfemung von Schwermetallen aus Abwaessem mittels Sorption am Biopolymer des Mikroorganismus Ectothiorhodospira shaposhnikovii. BioEngineering 1, 38-41.
(Received in revised form I8 ]une I993; accepted 21 June 1993)
WorldJournalof Microbiology& Biotechnology,Vol I0, 1994
111
Short Communication
Removal of H2S by the purple sulphur bacterium Ectothiorhodospira
shaposhnikovii
M.B. Vainshtein,* G.I. Gogotova and N.-J. Heinritz When Ectothiorhodospira shaposhnikovii VKM B-15 25 was used for desuphurization of biogas in the laboratory and in a pilot plant, there was complete oxidation of H2S, the main product being elemental sulphur. The advantage of this culture over green bacteria is discussed. Key words: Bacterium, desulphurization, Ectothiorhodospira shaposhnikovii, sulphide, sulphur.
The removal of H2S from waste waters, industrial gases and biogases is a well-known technological problem. Techniques for gas purification include washing with methanol under high pressure and precipitation by iron filings or by iron oxide, with the formation of insoluble iron sulphide. There are also biological techniques of desulphurization by contact with aqueous solutions or with a damp carrier containing thiobacilli. The disadvantage of all these methods is their relatively high cost o r - - i f thiobacilli are u s e d - - t h e formation of sulphuric acid, accompanied by increasing corrosion. Over the past 10 years, a technology has been developed for the removal of HzS from biogas using the green bacterium Chlorobium timicola f. thiosulfatophilum ATCC 17092 (Cork 1982; Cork et aL 1983). Certain technological difficulties result from the bacterial requirement for light but an economic advantage is that elemental sulphur is obtained. This paper presents data on the use of the purple sulphur bacterium Ectofhiorhodospira shaposhnikovii VKM B-1525 for H2S oxidation in aqueous solutions.
Materials and Methods Microorganisms The type strain of Ectothiorhodospira shaposhnikovii (VKM B-1525) was used. Biomass samples for the analysis of amino acids were M.B. Vainshtein, G.I. Gogotova and N.-J. Heinritz are with the Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; fax: + 7 (095) 9233602. *Corresponding author. © 1994 Rapid Communications of Oxford Ltd
110
WorldJournalof Microbiology& Bio#echnology,VoI 10, 1994
taken in the logarithmic growth phase in the laboratory experiments.
Chemical Analyses Concentrations of sulphide were determined by a colorimetric method (Pachmayr 1960). Polythionates, thiosulphate and sulphite were determined by classical methods based on titration (Kurtenacker 1938). Elemental sulphur was separated by filtration, and its content was determined by the reduction in the filter weight after extraction with 96% (v/v) ethanol. Biomass control samples did not contain S°. SO 2 concentrations were determined by potentiometric titration with BaCl2 in acid (i.e. carbonate-free) sample. The amino acid analysis was conducted with an auto-analyser. Experimental Conditions In laboratory experiments, oxidation of H2S was studied under batch conditions and during continuous cultivation. The culture was grown at 22 to 26°C in Larsen's medium with 5 g sodium acetate/1. In all cases the light was about 0.I kIux. The concentrations of biomass were up to about I g/1 under batch conditions of growth and 5 g/1 during continuous cultivation. A mixture of N 2 and methane containing H2S was bubbled through the liquid medium. Large scale experiments were carried out at the 'Rohrtechnic' pilot plant (Delittch, Germany) (see Beck et al. 1988). The reactor volume was 5 m3. The medium consisted of tap water with additions of NH +, PO34- and acetate. Biogas, containing H2S as the only S-compound, was bubbled through the unit at the rate of 4 m3/h per m3 of liquid medium. The concentration of the bacterial cells was more than 109 ml. The liquid and gas phases were separated by the difference in their densities. The cooled and desulphurized gas was removed through a special pipe and burnt. The bacterial suspension, enriched with CO 2, was pumped into the flat solar collector (total area 10 m2). At night and in cloudy weather, the photo-collector required up to I kW of electric lighting.
Removal of H2S 500
70
4oo i
--~ 3oo ]
qs0
o
-2°
~40--~ 30
100
~ 10 A-
Sulphur
TMosulphate Polythionate
~ Sulphite
~ k ' ~ io Sull~hate
Figure 1. Sulphide oxidation by E. shaposhnikovii in the bio-reactor. Initial H2S concentrations were 350 (m, [ ] ) and 680 (17, [ ] ) mg S/I. Products are given as mg S/I ( 1 , []) and % of total ( ~ , []).
Results and Discussion The choice of E. shaposhnikovii as a biotechnological culture for the removal of H2S was prompted by at least two advantages it has over green bacteria. Firstly, purple bacteria biomass is a valuable fodder ingredient owing to its high content of carotenoids and provitamin A (Kobayashi & Kurata 1977). In media with organic substrates, large amounts of extracellular polysaccharides are also formed (Schmiechen et a]. i992) and these may find independent biotechnological use. Secondly, although both green and purple sulphur bacteria are anaerobic, E. shaposhnikovii can survive in air, which often cannot be avoided in the technology used and is capable of aerobic oxidation of H2S in the dark (Gogotova & Vainshtein 198I). Preliminary tests on the ability of E. shaposhnikovii to oxidise H2S from the gas mixture were carried out using cells grown to stationary phase and methane as the carrier gas, which was bubbled through the liquid medium. The sulphide concentration increased, as the result of the dissolution of H2S, at a rate of 16 mg S/1.h. The sulphide oxidation represented approximately half of the content of dissolved H2S. In continuous cultivation, the bacterial biomass was higher and the oxidation rate increased accordingly. After 12 h in the light, the specific rate of anaerobic oxidation was 18 to 23 mg S/h.g wet biomass. The rate of aerobic sulphide oxidation was also measured in the dark, to estimate the potential biotechnological use of the culture without artificial light. In this case, the specific rate after 12 h was 8.0 to 8.2 mg S/h.g wet biomass. Non-corrosive sulphur compounds were the main products of sulphide
oxidation by E. shaposhnikovii, and their largest bulk was constituted by elemental sulphur (Figure 1). The use of the culture for the desulphurization of biogas at the 'Rohrtechnic' pilot plant showed that HzS, at up to 30 mg S/l, was completely oxidised in solution and did not pass through the reactor with the biomass suspension. Thus, the experiments in the laboratory and in the pilot plant demonstrated that cultures of E. shaposhnikovii desulphurized biogas with no accumulation of corrosive compounds. Experimentation in a pilot plant demonstrated the potential use of the method in an industrial environment.
Acknowledgements The authors are grateful to Drs B. Kirsop and B. Tindall for their critical reading of the manuscript.
References Beck, D., Heinritz, H.-J., Wiessner, A., Ringpfeii, M., Recha, G., Passin, H., Iwanow, M., Weinstein, M., Gogotova, G. & Kondratieva, E. 1988 Verfahren zur Enffernung von Schweffelwasserstoff aus Gasen und fluessigen Medien. German Democratic Republic Patent DD 256426. Cork, D.J. 1982 Acid waste gas bioconversion--an alternative to the Claus desulphurizafion process. Developments in Industrial Micribiology 23, 379-387. Cork, D.J., Garunas, R. & Sajjad, A. 1983 Chlorobium limico]a forma thiosu]fatophilum: biocatalyst in the production of sulphur and organic carbon from a gas stream containing HzS and CO 2. Applied and Environmental Microbiology 45, 913-918. Gogotova, G.I. & Vainshtein, M.B. 1981 The oxidation of thiosulfate by purple sulphur bacterium Ectothiorhodospira shaposhnikovii in the dark. Microbiologia (USSR) 50, 96-963. Kobayashi, M. & Kurata, Sh.-I. 1977 Use of photosynthetic bacteria. In Proceedings of 2nd International Symposium, Growth of Microorganisms on C-I Compounds, pp. 207-210. Pushchino: USSR Academy of Science. Kurtenacker, A. 1938 Analytische Chemie der Sauerstoffsauren des Schwefels. Stuttgart: Enke. Pachmayr, F. 1960 Vorkommen und Bestimmung von Schwefelverbindungen in Mineralwasser. Dissertation, Universit/it M6nchen. Schmiechen, H., Wittig, H. & Martin, S. 1992 Entfemung von Schwermetallen aus Abwaessem mittels Sorption am Biopolymer des Mikroorganismus Ectothiorhodospira shaposhnikovii. BioEngineering 1, 38-41.
(Received in revised form I8 ]une I993; accepted 21 June 1993)
WorldJournalof Microbiology& Biotechnology,Vol I0, 1994
111
