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Black Sea, A Hydrogen Source
Conference Paper · July 2005
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Mehmet Haklidir
Şule Kapkin
The Scientific & Technological Research Council of Turkey
Istanbul University
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Proceedings International Hydrogen Energy Congress and Exhibition IHEC 2005
Istanbul, Turkey, 13-15 July 2005
Black Sea, A Hydrogen Source
Mehmet Haklıdır*, Şule Kapkın**
*Istanbul Technical University, Mechatronics Engineering, Maslak, Istanbul, Turkey
**Istanbul University, Mechanical Engineering Department Avcilar, Istanbul, Turkey
mhaklidir@yahoo.com, skapkin@istanbul.edu.tr
ABSTRACT
Black Sea, a highly-isolated inland sea, has a transition layer, called suboxic zone that has
simultaneously low concentration of oxygen and low concentration of hydrogen-sulfide. The
suboxic zone of Black Sea is about 50 m thick and lies between the oxygenated surface layer and
the anoxic depth at about 200 m. Hydrogen-sulfide layer appears in the Black Sea, mainly because
it is highly isolated from the open ocean, when oxygen consumption due to the input of
decomposable organic matter sinking from the upper euphotic zone or added by rivers flowing into
the sea exceeds the oxygen supply to deep waters. Hydrogen-sulphide in the Black Sea, whose
source is the process of anaerobic decomposition of organic matter of sulfate-reducing bacteria, is
one of the world's most poisonous and is a possible energy source today.
If the equilibrium in this very special sea is not maintained and steps towards healing is not taken,
environmental disaster is likely to happen. The initial signs will be seen in the surface waters, and
later, when the chemical equilibrium is disturbed further, the deep sulphur and Hydrogen-sulphide
will possibly change into a flammable, explosive phase. Even if this gas does not ignite but only
mixes into air, it will present an important environmental problem. The sea life initially will not
be suitable for consumption, and later will suffer massive extinction. This situation obviously
poses a great threat for the countries in the region. The usage of Hydrogen-sulphide in Black Sea
for obtaining hydrogen and sulphur will require large amounts of sea water to be cleaned of
Hydrogen-sulphide; this will provide a two-fold benefit: a new energy source and cleansing of
Black Sea of this poisonous substance.
In this paper, the mechanics of Hydrogen-sulphide production, and the effects of the
environmental factors like rivers pouring into the Black Sea is explored, and alternative plans for
usage of Hydrogen-sulphide in the sea water is explored.
Keywords: Hydrogen, Hydrogen Sulphide, Sulfate-reducing Bacteria, Hydrogen Energy.
1. INTRODUCTION
The causes of organic matter accumulation in Black Sea are its distance from the open oceans and
the large amount of river water pouring in to the Black Sea. The organic compounds brought in by
the rivers pouring into Black Sea are decomposed by the oxygen; but since the Black Sea is remote
to oceans and it is quite closed, the decomposition by oxygen is less so that the organic matter
accumulates at the deeper regions. The Hydrogen-sulphide-rich layer is about 50 m thick and lies
at a depth of approximately 200 m.
As a very rich source of hydrogen sulfide, The Black Sea is distinctly different from the world’s
oceans with the appearance of the hydrogen sulfide at its lower boundary. In the worlds’ oceans, as
well as in the particular case of the Black Sea, specific physical and biochemical processes as well
as morphmetric characteristics determine the health of the marine environment and the cycling of
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elements influences fishery resources. Hydrogen is currently used in many different industry
processes, such as the production of plastics, fertilizers and petroleum products. Hydrogen may be
used to power steam turbines or as fuel in internal combustion engine vehicles. Perhaps the most
interesting use for hydrogen in the future is in fuel cells. As the energy source of the future, the
hydrogen lies deep in the waters of the Black Sea in the form of a very large amount of hydrogen
sulfide.
The structure of the paper is as follows: the next section is about the organic matter composition in
the Black Sea. Following this, the formation and balance of Hydrogen-sulfide is explained and its
environmental impact is stressed. Finally, a proposal is made for production of Hydrogen from
Hydrogen-sulfate to be extracted from the waters of Black Sea.
2. ORGANIC MATTER CONCENTRATIONS IN BLACK SEA
In the Black Sea, dissolved and particulate organic matter concentrations decrease with depth. In
the upper layers, they are controlled by the photosynthetic input and respiration process and by the
supply from rivers. The riverine sources carry both dissolved and suspended organic matter of
various origins.
In the Black Sea, nitrogen and phosphorus compounds are the main nutrients triggering
eutrophication, and the main reasons of ecological problems. The majority of nutrients, 53% of the
nitrogen and 66% of the phosphorus, discharged into the Black Sea come from the Danube River.
Approximately 115,000 tons of oil enters the Black Sea each year, with %48 of it coming from the
Danube. The nutrients introduced into the Danube originate from agriculture(chemical or organic
fertilizer, Irrigation…), Metropolitan and Industrial Wastes (Petroleum chemicals, Lumber, Woodpulp Industry..) and domestic sources. But the Danube is not the only pollution source. Dnieper
(Ukraine), Dniester (Moldova), Kızılırmak, Sakarya, Yeşilırmak (Turkey), flowing into the Black
Sea, are the other sources of pollutants due to the pollutioned discharges they have.
3. H2S IN BLACK SEA
Black Sea has a large anoxic zone (90% of the sea water is anaerobic in depth). Hydrogen-sulfide
layer, was discovered more than 100 years ago. High content of organic matter, with maximum
processes of bacterial sulfate reduction is the major source of this hydrogen sulphide zone.
Other important sources of hydrogen sulfide are the geological sources – fractures and mud
volcanoes, as well as the destroyed gas-hydrate deposits, which contain the solid phase of H2S.
3.1 Sulfate-Reducing Bacteria
The bacteria utilize, firstly, the free dissolved oxygen in order to decompose the sinking organic
matter. When the dissolved oxygen concentration is below 2-4 mg/L, combined forms of oxygen
are used as electron sinks by the bacteria to oxidate. The first group of compounds that supply the
combined oxygen are nitrates (NO3-) and nitrites (NO2). Metal oxides, sulfates (SO4-), carbon
dioxide (CO2) and even water itself are used by bacteria as electron sinks in parallel to the
decrease in redox potential of the water mass.
Sulfate-reducing bacteria, one of the oldest known life forms on the planet, are the anaerobic
bacteria that utilize sulfate as an oxygen source. The reduction of the sulfate is accomplished by
sulfate - reducing bacteria;
2 CH2O + (SO4)-2 —> 2 (HCO3)- + H2S
2
(1)
Haklidir and Kapkin
Figure 1: Electron micrograph of Sulfate-Reducing Bacteria
Sulfate reducing bacteria thrive and dominate the bacterial population, when the free oxygen
concentration decreases below 1 mg/L.
The most abundant bacterial population in the Black Sea belongs to the Sulfate - reducing bacteria
Desulfosarcina/Desulfococcus group. When oxygen consumption due to the input of
decomposable organic matter sinking from the upper euphotic zone or added by rivers flowing into
the sea exceeds the oxygen supply to deep waters, these bacteria thrive their population and utilize
sulfate as an oxygen source. As a result, The concentration of H2S increases, reaching to 8-10 mg/l
to depths of 1,500 m.
3.2 The Geological Sources
Fractures and mud volcanoes, as well as the destroyed gas-hydrate deposits, which contain the
solid phase of H2S are the major geological sources. Other sources are deep cracks in the sea
ground and hydrothermal waters.
3.3 Hydrogen Sulphide Concentration
The Hydrogen-sulphide concentration increases regularly from the anoxic interface (at 1000 m
depth) to the seafloor. Near the seafloor, 2000 m depth, it attains maximum values of about
400μM. Hydrogen Sulphide and Dissolved oxygen concentrations are shown in Figure 2.
Figure 2: Hydrogen Sulphide and Dissolved oxygen concentrations in the Black Sea obtained
by using the data from March – April 1995 cruise of R/V Bilim.
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4. ENVIRONMENTAL IMPACT OF H2S IN THE BLACK SEA
The lower range of oxygen must be 14.5-14.8 (1000 lt = 1014,5 kg) in the sea for fish to survive.
For this reason, there is no life at depths more than 60 m in Black Sea. Meanwhile, Hydrogen sulphide is one of the world's most poisonous substances and it is the reason for the observed
decrease of life in Black Sea ( for example; 3000 dolphines dies every year ). A full breath of H2S
is usually enough to kill a human being. Hydrogen - sulphide is a colourless gas with a rotten egg
odour which destroys the sense of smell rapidly and it is impossible to tell whether one is inhaling
more.
Environmental disaster is likely to occur in Black Sea due to Hydrogen-sulfide accumulation. The
levels of Hydrogen-sulfide may reach to high enough levels in deep waters to produce the
inflammable, explosive phases so that fire hazard may become a real problem. Even if this does
not happen, the Hydrogen-sulfide could begin to mix into the atmosphere and pollute the air. Also
the fish may become unsuitable for consumption and at later stages may suffer massive extinction.
5. PRODUCTION OF HYDROGEN FROM H2S
Hydrogen could be produced from H2S by using various different decompostion methods. Mainly,
these are the plasma, electrochemical, photochemical and thermal methods.
The plasma process uses microwave plasma chemistry to dissociate H2S into H2 and S.
Backreaction of the products to H2S is minimized by in situ cyclonic separation and a rapid quench
of the products. Furthermore, experiments with water and carbon dioxide concentrations typical of
acid-gas streams from refinery operations and natural gas production have demonstrated that these
components are compatible with the proposed process. A preliminary economic evaluation
indicates that the plasma-chemical process will be substantially cheaper to operate than the
conventional sulfur recovery technology and that the sulfur emissions will also be lower.
Photochemical reactions use photocatalysts that absorb ultra-violet light from the solar spectrum to
power chemical reaction. But this method is not effective since using UV light is very expensive to
produce Hydrogen from H2S.
Most of the hydrogen sulfide produced in the catalytic hydrodesulphurization of fossil fuels is
processed in a Clauss process, producing sulfur and low-valued steam but doesn't produce any
hydrogen. But for a long time, it has been known that H2S can be converted to H2 and elemental
sulfur by thermal decomposition of H2S at high temperatures (900-1100 K). H2S can be
catalytically decomposed to hydrogen and sulfur and the catalyst preparation, operating
conditions, catalyst type have a significant effect on the amount of hydrogen produced and on the
economics of the process. The stoichiometric equation of the thermal decomposition reaction is
2H2S
2H2 + S2
ΔH = 50 kcal/mol (Activation energy)
(2)
6. CONCLUSION
Natural accumulation of organic matter and Hydrogen-sulfide poses a great environmental threat
for the Black Sea. If preventive measures are not taken, the sea life will be impossible in the
future. We propose that the Hydrogen-sulfide in the Black Sea could be used as a source of
Hydrogen by separating Hydrogen-sulfide via any of the available methods after it has been
extracted from the sea water. Studies on the economics of the overal system and methods of
extracting Hydrogen-sulfide from sea water are under way.
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7. ACKNOWLEDGEMENT
Thanks to Dr. T. N. Veziroglu and Dr. E. Uzal for their encouragement and support throughout
this study.
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