1



# A Theoretical Environmental Impact Assessment of the Use of a Seawater Scrubber to Reduce SOx and NOx Emissions

from Ships

Dr. Brigitte Behrends and Prof. Dr. Gerd Liebezeit

Research Centre Terramare Wilhelmshaven, Germany2



### CONTENTS 1 Introduction ................................ ................................ ................................ ...... 5 1.1 Air pollution ................................ ................................ ...................... 5 1.2 Contribution of shipping to air pollution ................................ ........... 7 1.2.1.1 Legislation:

................................ ................................ ................................ ..... 8 1.3 Techniques to reduce atmospheric emissions in power plants .......... 9 1.3.1 Techniques for the removal of sulphur from petroleum 9 1.3.2 Flue Gas Desulphurisation 10 1.4 Technologies to reduce atmosph eric emissions from ships ............. 12

- the seawater scrubber ................................ ................................ ......... 12 

### The following reactions should take place: ................................ ................................ .. 13 2 NO2 

### + H 2

### O  

### HNO2 

### + HNO3 

### ................................ ................................ .................... 13 3 HNO2  

### HNO3 

### + 2 NO + H 2

### O ................................ ................................ ................... 13 2 HNO2  

### H 2

### O + N 2

### O 3 

### ................................ ................................ ................................ 13 N 2

### O 3  

### NO + NO 2 

### ................................ ................................ ................................ ....... 13 2 NO2 

### + H 2

### O  

### HNO 3 

### + HNO 2 

### ................................ ................................ .................... 13 overall: 3 HNO2  

### HNO 3 

### + 2 NO + H 2

### O ................................ ................................ .. 13 1.4.1 Composition of the effluent 14 1.5 Questions of concern ................................ ................................ ...... 14 

### 2 Element cycles ................................ ................................ ............................... 15 2.1 Sulphur ................................ ................................ ........................... 15 2.1. 1 Sulphur: an important component of the world economy Production 15 2.1.2 Sulphur emissions to the atmosphere 17 2.1.2.1 Natural emissions of sulphur

................................ ................................ .... 17 2.1.2.2 Global anthropogenic sulphur emissions

................................ ............... 17 2.1.2.3 Particulate sulphate

................................ ................................ .................... 18 2.1.3 Deposition of sulphate and sulphuric acid 18 2.2 Nitrogen cycle ................................ ................................ ................. 19 2.2.1 Emissions of nitrogen compounds to the atmosphere 19 2.2.1.1 Natural emissions of nitrogen

................................ ................................ .. 20 2.2.1.2 Anthropogenic emissions of nitrogen

................................ ..................... 20 

### 3 Composition of seawater................................ ................................ ............... 22 3.1 Marine sulphur cycle ................................ ................................ ....... 23 3.2 Marine nitrogen cycle ................................ ................................ ..... 25 3.3 The pH of seawater: the carbonate system ................................ ..... 26 

### 4 Laboratory measurements ................................ ................................ ............ 30 4.1 Impact of diluted sulphuric acid (pH 4) on seawater ...................... 30 4.2 Impact of diluted sulphuric acid (pH4) on brackish waters ............ 32 Deleted: 133

4.3 Summary of laboratory experiments ................................ .............. 34 4.4 Impact of the acidic effluent of the Kryst a llon Scrubber on the pH of the receiving water ................................ ................................ ................ 34 4.5 Estuaries ................................ ................................ ......................... 35 4.5.1 Harbour areas like the Port of Rotterdam 37 4.6 The Baltic Sea ................................ ................................ ................. 38 4.6.1 Vital inflow from the North Sea 38 4.7 Acidification of surface waters ................................ ....................... 39 4.8 Experiences with a cid disposals at sea. ................................ .......... 40 4.9 Eutrophication effects ................................ ................................ ..... 40 

### 5 Environmental impact of scrubbing waters - Synthesis ............................. 42
Figures Fig. 1: Mean composition of atmospheric nitrogen compounds (nmol m -3) in the German Bight

_______21 Fig. 2: Scheme of the microbiological cycle of sulphur and its possible influence on the atmosphere

___23 Fig. 3: Schematic seasonal variation of nutrients and phytoplankton biomass in temperate areas.

_____25 Fig. 4: Major reactions and pathways in the marine nitrogen cycle

_____________________________26 Fig. 5: Impact of sulphuric acid (pH 4) on the pH of seawater (S = 29 PSU)

______________________31 Fig. 6: Percentage of sulphuric acid (pH 4) in brackish water with resulting pH (t = 0 and t = 1 h).

___33 Fig. 7: pH ranges that support aquatic life

________________________________________________36

List of Tables Tab. 1: Comparison of estimates for global exhaust gas emissions from ships.

____________________ 8 Tab. 2: World production and consumption of sulphuric acid

________________________________ 16 Tab. 3 Important Atmospheric nitrogen oxides

___________________________________________20 Tab. 4 Average sea

- and freshwater compositions

___________________________________________23 Tab. 5: Percentage of sulphuric acid (pH 4) in brackish water with resulting pH (t = 0 and t = 1 h)

__32 Tab. 6: Contribution of nitric acid to the acidity of the effluent

_______________________________ 35 Tab. 7: Ports in the EU ranked by estimated annual emissions of NOx in 2000

___________________37 Tab. 8: discharge of sulphate and nitrate per hour

____________________________________________434



### List of used abbreviations
amu atomic mass units CCN cloud condensation nuclei DIN dissolved inorganic nitrogen (N H 4 + , NO 2 - , NO 3 - ) DMS Dimethyl sulphide DON dissolved organic nitrogen FGD Flue gas desulphurisation IMO International Maritime Organization Mam - Pec Computer model to generate predicted environmental concentrations MCR Maximum continuous rating NO x Oxid es of Nitrogen PAH polycyclic aromatic hydrocarbons PON particulate organic nitrogen PSU practical salinity units SOx Oxides of Sulphur SWS seawater scrubber VOC volatile organic compounds Formatted: Italian (Italy)5



### 1 Introduction The b urning of fossil fuels is one of the most s ignificant contributo r’s to atmospheric pollution. For several decades concern has been expressed about the major pollutants, carbon dioxide, sulphur dioxide and nitrous oxides. Carbon dioxide is considered to be largely responsible for global warming whil e the latter two gases contribute amongst others to acid rain. Additionally, NO x enhances eutrophication of terrestrial and aquatic ecosystems. A large number of emission reducing technologies have been developed for power stations (see chapter 1.3 ), but the shipping industry has made less progress in limiting emissions. This is despite the fact that recent estimates suggest that shipping is a major factor in global S and N cycles (chapter 2.1). The main objective of this report is therefore the reduction of atmospheric emissions from ships, by use of a seawater scrubber technology (flue gas desulphurisation process).



### 1.1 Air pollution Air pollutants are substances that are introduced into the atmosphere via anthropogenic activities. Air pollution occurs both in gaseous and particulate forms which, when present in excess, are harmful to human health, buildings and ecosystems. Five major impacts determine the classification of pollutants under the traditional policy field , Air Pollution :  acidification of soil and water by pollutants such as sulphur oxides and nitrogen oxides ;  eutrophication of ecosystems, especially by nitrogen compounds ;  damage to buildings sensitive to the same substances;
 formation of tropospheric ozone from so
- cal led ozone precursors, e.g. volatile organic compounds, nitrogen oxides and carbon monoxide, thus indirectly affecting human and animal health and vegetation;
 direct effects on human health and ecosystems, e.g. through high atmospheric concentrations of pa rticles and volatile organic carbon compounds (VOCs). Although some of these compounds are also produced by natural processes, the main environmental problems result from human activities, such as the burning of fossil fuels (coal, oil and natural gas ). A ir pollutants may be transported over considerable distances, affecting air quality, ecosystems, lakes and other surface waters, Eutrophication is the process whereby a body of water becomes over
- enriched with nutrients which results in overgrowth of algae and depleted oxygen levels in the water6

groundwater, soils and buildings also in areas remote from the pollution source. Public concern is focussed mainly on damage to forests and smog, although in Scandinavian countries emphasis is also placed on the acidification of lakes. The atmospheric pollution by sulphur dioxide and nitrous oxides is described in detail in chapters 2.1.2.2 and 2.2.1.2
.

Particulates Particulate air pollution originates from diverse sources. One major source of primary particle emissions is fuel combustion, including that by mobile sources such as diesel and gasoline
- powered ve hicles. The relative contributions of these different sources to the particle concentration at a given site may vary significantly. Atmospheric particles consist of organic and inorganic substances and are present in liquid or solid forms. They are subdivi ded according to diameter: coarse particles >2.5 μm, fine particles <2.5 μm. A further distinction is to classify particles as either primary or secondary, according to their origin. Particles that are emitted directly into the atmosphere are termed primary particles, whereas secondary particles form during atmospheric reactions. The primary particles contain carbon, hydrocarbons, metal oxides and other solid materials, which are primarily formed during combustion processes. Fine particles also include seco ndarily formed aerosols, smaller combustion particles and re - condensed organic and metallic compounds with low volatility. Most secondary particulate matter occurs as ammonium sulphates and nitrates formed from reactions involving sulphur dioxide , nitrogen oxides and ammonia. Shipping contributes to both, primary and secondary particles. Natural atmospheric emissions of particulates also derive from volcanic activities.
1. Primary particulates: Flue gases contain soot particles, which are produced by incomplete combustion of fossil fuels. Due to the ability of these particles to serve as condensation nuclei, soot contains polycyclic aromatic hydrocarbons (PAHs), a family of semi
- volatile organic pollutants encompassing compounds such as extremely small amounts of anthracene, and some pyrene, or benzo [ a ] pyrene. Some PAHs from combustion products have been identified as carcinogenic. Combustion
- derived PAHs are rapidly transferred from t he atmosphere to aqueous systems and accumulate in the sediment. 2. Secondary particulates Secondary particles (including sulphate and nitrate aerosols) are formed from gaseous pollutants (SO 2 , NO x, NH 3 ). Ships emit sulphur dioxide and nitrous oxides throu gh the Formatted: French (France)7

combustion of fossil fuels. The primary air pollutants sulphur dioxide and nitrogen oxides are oxidised as they are dispersed in the atmosphere, forming sulphuric acid and nitric acid respectively, which may be deposited downwind as acid rain . Secondary particles can be transported over long distances.


### 1.2 Contribution of shipping to air pollution Shipping contributes to air pollution by the burning of fossil fuel. The emission of NO x and SO x have different consequences for the atmosphere: NO x is involved in production of ground level ozone but it also reacts with tropospheric ozone thus aiding in the depletion of the ozone layer. SO 2 is oxidised to SO 3 and eventually forms sulphuric acid, which contributes to acid rain and provides cloud condensation nuclei by formation of secondary particles, thereby increasing the albedo. Owing to the reactivity of sulphur gases in the atmosphere, most anthropogenic SO 2 emissions are deposited locally; therefore shipping contributes mainly to coastal air pollution. Corbett and Fischbek (1997) give annual emissions of 3.08 * 10 6 ton N and 4
. 24 * 10 6 ton S for the global fleet accounting for 14% (N) and 16% (S) of emissions from all fuel combustion sources (Tab 1). On the other hand, only 2% of the 6,000 * 10 6 ton carbon dioxide emitted annually from fossil fuel combustion is related to the operation of ships. This implies that ship engines although highl y efficient at converting fuel into power, emit very high levels of nitrogen and sulphur gases. Various estimates for the contributions of shipping to global air pollution are presented in (Tab 1).8

Tab. 1 : Comparison of estimates for global exhaust gas emissions from ships. Source Calculation (1) Year C (2) [10 6 t] SO 2

[10 6 t] NOx

[10 6 t] Isensee, 2001 1997 101 6.4 6.0 IMO, 2000 M 1996 112 5.5 9.8 IMO, 2000 F 1996 117 5.8 10.3 Det Norske Veritas, 1999 M 1996 109 5.5 9.9 UNFCCC, 1997 ? 1994 109 7.7 - 11.5 9.3 Corbett and Fischbeck, 1997 F 1996
- 8.5 10.1 Corbett, 1999 ? 1992 123.6 8.5 10.1 Mean 1994
- 1997 114.2 6.7 9.3
(1) M = model, F = fuel based calculations (2) Calculated from CO 2 emissions
Emissions from shipping operat ions are not equally distributed over the seas. Most vessels navigate relatively near shore, following the main shipping lanes. Corbett (1999) concludes that almost 70 % of these emissions occur in a coastal zone of 400 km (216 nautical miles) width. Simil arly, Oftedal (1996) estimates that 74
- 83 % of all vessels are within 200 nautical miles (370km) of land at any time. Consequently, the impact of shipping on NO X and SO 2 levels is highest in the northern hemisphere, particularly along the west and east c oasts of the United States, in northern Europe and the North Pacific.

1.2.1.1 Legislation: As soon as the IMO regulation for the prevention of air pollution from ships (Marpol 73/78 Annex VI) came into force, emissions from ship exhausts ha d to be reduced. Annex VI contain ed provisions allowing for special "SO x Emission Control Areas" to be established with a more stringent control on sulphur emissions. In these areas, the sulphur content of fuel oil used on board ships must not exceed 1.5 % m/m. Alternatively, sh ips must fit an exhaust gas cleaning system or use any other technical9

method to limit SOx emissions. Currently the Baltic Sea, the North Sea and the Channel are designated as SO x Emission Control Areas in the Protocol. Marpol Annex VI entered into force o n the 19th May 2005.
.


### 1.3 Techniques to reduce atmospheric emissions in power plants The technology for the reduction of atmospheric pollutants should be environmentally benign. Otherwise, the problem is merely being shifted to another area. There are three po ssibilities to reduce SO 2 emissions from combustion processes: removal of sulphur or sulphur dioxide before, during or after combustion.
1.3.1 Techniques for the removal of sulphur from petroleum After World War II , production of high sulphur crude oils increas ed considerably
. As a result of increased use of high sulphur crudes and increasing awareness of environmental considerations , product specifications became more stringent
. The oil industry had to develop techniques for the removal of sulphur and t he plati num reforming process was developed. However it should be noted that platinum reforming is only suitable for white oils containing relatively low ppm levels of sulphur. The major process used today is Hydrotreating or Hydrodesulphurisation, i.e. treatment of the oil with hydrogen gas obtained e.g. during catalytic reforming. In this process sulphur compounds are reduced by conversion to hydrogen sulphide (H 2 S) in the presence of a catalyst. As only sulphur is removed, high yields of liquid end products res ult. In addition, H 2 S can be washed from the product gas stream by an amine wash. H 2 S is recovered in highly concentrated form and can then be converted to elemental sulphur via the Claus
- Process. For Hydrotreating two processes are used, the liquid phase or trickle flow and the vapour phase processes for light straight
- run and cracked fractions. In both cases the feedstock is mixed with hydrogen
- rich make
- up and recycle d gas and reacted at temperatures of 300
- 380 °C. Pressures of 10
- 20 bar for naphtha and kerosine and 30
- 50 bar for diesel are applied. Removal of sulphur from heavier oils such as marine fuel oil often requires pressures of up to 200 bar. Under these conditions, S and N compounds are converted to hydrogen sulphide and ammonia, while a p art of the aromatic compounds present will by hydrogenated. Catalysts employed are cobalt, molybdenum or nickel finely distributed on alumina extrudates. More recent developments include biological conversion of sulphur
- containing petroleum components to e lemental sulphur. Biological removal of hydrogen sulphide10

and light mercaptans from refinery streams has been commercially implemented. A biological process for removal of sulphur from diesel oils was under development for several years, but the firm has s ubsequently ceased operation. Sonocatalytic treatment (optional) with hydrogen peroxide oxidation in the presence of iron(III)complexes at low temperatures has removed sulphur from diesel oils. Several developers are engaged in advanced pilot plant studies seeking to commercialise such a process. This approach will remove dibenzothiophenes, compounds which are of particular concern to the oil industry. The effectiveness of this method for removing sulphur from heavy fuel oils has not yet been quantified, an d disposal of product sulphones must be factored into any process design.
1.3.2 Flue Gas Desulphurisation The removal of SO 2 after the combustion process is termed Flue Gas Desulphurisation (FGD). The different FGD processes can be classified by their technologi es:
Limestone/Gypsum System The limestone FGD is to date the most widely used process. In principle, a suspension of crushed limestone in water is sprayed into the flue gases. The SO 2 reacts with calcium ions to form a calcium sulphite slurry. Aeration of the slurry with compressed air oxidises calcium sulphite to calcium sulphate. After removal of the water, the calcium sulphate can be disposed of or used by the building trade. Although the reduction of SO 2 is around 90 % , the process has the disadvantage that limestone has to be stored and large quantities of gypsum waste is produced.
Spray Dry System A slurry of slaked lime is used as an alkaline sorbent. The slurry is injected into the flue gases in a fine spray. The flue gases are simultaneously cool ed by the evaporation of water. The SO 2 present reacts with the drying sorbent to form a solid reaction product, with no wastewater.

Wellman
-Lord Process In the Wellman
- Lord process, hot flue gases are passed through a pre
- scrubber where ash, hydrogen chl oride, hydrogen fluoride and SO 3 are removed. After pre
- scrubbing, the gases are then cooled and fed into an absorption tower, where the SO 2 reacts with a saturated sodium sulphite solution to form sodium bisulphite. The sodium bisulphite11

is regenerated after a drying step to sodium sulphite again. The remaining product
- the released and clean SO 2 - may then be liquefied or converted to elemental sulphur or sulphuric acid. The sorbent is regenerated during the combustion process and is continuously recycle d, but the products (sulphur compounds) have to be stored.
Seawater Scrubbing Process (SWS) Experience with the FGD by seawater scrubbing process in power plants Probably the first large sized FGD was installed at the Battersea power plant (London Power Company) in the UK in 1930. During the power station planning approval local authorities expressed concern about the impact on the local community of the emissions of large quantities of SO x from the combustion of coal. The water of the Thames was used as the major sorbent although for a short period limestone was added. This practise was soon discontinued as it was determined that it provided no additional benefit to the scrubbing system. The Battersea power station operated in this mode for more than 50 y ears. In 1972, ABB Environmental in Norway and Norsk Hydro started the development of a flue gas desulphurisation process (Flakt Hydro process) using seawater for the absorption of SO 2 from flue gases. The first seawater scrubber was introduced in 1988 at the Statoil refinery in Mongstad Norway (Tokerud, 1989). The seawater scrubbing process exploits the natural buffering capacity of seawater to absorb acidic gases instead of producing huge amounts of gypsum. After passing through a dust collector, the hot flue gas enters the scrubber. The scrubber is a packed absorption tower, where the gases flow counter
- current to seawater. During this process SO 2 is efficiently absorbed by the seawater. Air is supplied to oxidise the absorbed SO 2 to sulphuric acid and to saturate the seawater with oxygen. Before discharging the effluent into the sea, further seawater is added to bring the pH back to normal seawater values. As the Norwegian Sea is deep and well mixed, further water treatment was regarded unnecessary (Glen na and Tokerud, 1991). Several other sea water scrubbing flue gas desulphurisation systems have been installed in power plant s around the world. The sulphate ions themselves are harmless, as they are major constituents of ordinary seawater. However, the pH of the effluent may be of concern. To reduce the sulphuric acid problem, e.g. in sensitive areas, precipitation of sulphate with limestone is possible. This system is simple and inherently reliable with low capital and operational costs. It can remove u p to 99 % of SO 2 , with no disposal of waste to land. However, heavy metals and chlorides that are also present in the scrubbing water must be12

captured by use of a water treatment system, otherwise they will be released to the sea with the wash water.

Conclusion of Marine FGD technologies Each method has both advantages and limitations related to cost, removal efficiency, operational experience and waste products produced. For ships, the lack of space is an important criterion. Space is not only needed for the FGD itself, but also for chemicals (depending on the technology) and waste products. Some emission control technologies affect more than one pollutant and have different impacts on environmental effects. FGD simultaneously removes SO 2 , NO x and particul ate matter.


### 1.4 Technologies to reduce atmospheric emissions by ships

- the seawater scrubber For ships seawater scrubbing is a very suitable process, because
 no limestone has to be stored on board,
 no waste (gypsum) is produced, which has to be deposited on land,
 the seawater already contains substantial amounts of sulphate and nitrate The Krystallon Scrubber seawater scrubber removes 90
- 95 % of SO 2 and 10
- 20 % of NO x . Additionally, the SWS removes 80 % of the particulates and 10
- 20% of hydrocarbons. The use of cyclone technology ensures that the particulate material is retained on board ship and not included with effluent overboard seawater. The particulate sludge is then deposited ashore along with shipboard oily waste according to local environmental a nd safety regulations. The system needs little extra space, as the majority of the system replaces existing exhaust silencers of the exhaust system. The accompanying positive side effects are the reduction of engine noise and a reduction of the diesel smel l. As the conversion of SO 2 to SO 4 2
- and NO x to NO 3 - consumes oxygen, aeration of the effluent is necessary. The system incorporates a high degree of recirculation, thus ensuring that sulphur oxides are given adequate time and oxygen contact to be converted to SO 4 . In the following calculations complete oxidation will be assumed.

The Krystallon Scrubber works by bringing water in contact with hot exhaust gas. The exhaust gas is channelled through a concentric duct into a shallow water tank. Within13

the water, there are a set of mixing baffles which break up large gas flow into smaller bubbles, forcing the gas to come in contact with water, and thereby encouraging transfer of species from gas to water. The SO x in exhaust gas is relatively soluble in seawater, so this transfer happens to a very high degree. Larger particles (greater than 2.5 micron) are predominantly captured in the water. Fine particles (smaller than 2.5 micron) may pass through without capture. Since the recirculated water is maintaine d at a pH of 2.0
- 4.0, this makes a very good medium for scrubbing of NO x ( eg Scheme 1). Measurements have shown up to 20 % removal of NO x , and this is enhanced due to the acidity of scrubbing liquor. The following reactions should take place: 

### 2 NO + O 2 

###  2 NO 2 

### + 27.28 kcal As this is an exothermic reaction the equilibrium is shifted to the left of the equation with increasing temperature. Accordingly, there is no reaction of NO with oxygen at temperatures >650 °C. 2 NO 2 + H 2 O  HNO 2 + HNO 3 3 HNO 2  HNO 3 + 2 NO + H 2 O 2 NO + O 2  2 NO 2 overall: 4 NO 2 + 2 H 2 O + O 2  4 HNO 3 The following reaction also takes place at higher temperatures:

2 HNO 2  H 2 O + N 2O 3 N 2O 3  NO + NO 2 2 NO 2 + H 2O  HNO 3 + HNO 2 overall: 3 HNO 2  HNO 3 + 2 NO + H 2 O The final product in any case will be nitric acid. Water that is removed from the scrubber is pumped through a set of large cyclones. These cyclones are designed to separate some of the heavy particles, as well as light particles in a two
- stage system. Underflow from the main cyclones is concentrated again, and the underflow is fed to a settling tank for collection of soot and oil. Under normal operating conditions this system can be run with no ongoing maintenance (such as filter backwash or media recharge), and the resulting cleaned recirculated water is maintained at extremely low concentrations of hydrocarbons, making it safe for discharge to sea.14

1.4.1 Composition of the effluen t While NO x production depends on the engine design and engine operating conditions, SO 2 production depends on the sulphur content of the fuel. During seawater scrubbing the SO 2 is finally converted to sulphuric acid and NO x to nitric acid. 95 % of the SO 2 is eliminated by this technique and ca. 20 % of NO x . The salts in the effluent are SO 4 2
- , SO 3 2
- , NO 3 - and NO 2 - . The seawater scrubber is fed with natural seawater, which is then added to the seawater cooling system. The dilution is typically between 5:1 and 10:1. The mixture of cooling water and buffering water is then discharged to the sea. The pH of the effluent mixture ranges from 4.8 to 6.4 depending upon dilution rate which is a function of engine operating conditions. The intention of this work is to analyse the impact of the produced ions and the low pH on marine life.


### 1.5 Questions of concern
 Is air pollution simply converted to seawater pollution by discharging the scrubbing water directly into the surrounding waters?
 Are there differences in the effects on fully marine and brackish waters? Is there any breakpoint for salinity, at which the scrubbing water should not be discharged anymore?
 Can the produced sulphuric and nitric acids be buffered in semi
- enclosed systems and brackish waters?
 Does the ad dition of nitrate from nitric acid lead to higher primary production of biomass, i.e. to eutrophication?
 Is there any oxygen deficiency in the surrounding seawater by discharging sulphuric acid?
 What are the impacts of scrubber effluent on harbour waters c ompared to power stations effluents
 What is the worst
- case scenario?
To answer these questions, background information on global sulphur and nitrogen cycles and seawater chemistry is provided in the following section and then the effects of acid discharge are discussed.15



### 2 Element cycles

2.1 Sulphur The element sulphur occurs as crystals, granular aggregates, massive layers and powdery crusts in three different forms: amorphous, rhombic and monocline crystals. It forms as a product of volcanic activity, around volcanic craters and hot springs, but also by weathering of sulphide minerals and bacterial reduction of dissolved sulphate. Sulphur melts easily and burns producing sulphur dioxide gas. Sulphur is an essential nutrient for plants. It is also a major elem ent of seawater and marine sediments. In nature sulphur compounds may cycle through a series of oxidation states (
- 2, 0, +2, +4, +6). Therefore, sulphur compounds may act as both electron acceptors and electron donors. Bacteria of a wide range of genera ga in metabolic energy from either oxidising or reducing sulphur compounds. Major forms of sulphur include sulphate and sulphide minerals, dissolved sulphate (SO 4 2
– ), dissolved sulphide (HS – ), and hydrogen sulphide gas (H 2 S). Organic sulphur is a component of organic compounds such as humic substances, kerogen and proteins. Sulphur in fossil fuels (mercaptans, thiophenes, mono
- and polycyclic sulphur compounds) originates from these latter sources (e.g. Guadelupe et al., 1991; Thompson, 1994; Saiz
Jiminez, 199 5; Sinninghe
- Damsté et al., 1998).
2.1.1 Sulphur: an important component of the world economy Production Elemental sulphur for industrial purposes is produced by oxidation of hydrogen sulphide gas or reduction of sulphur dioxide and organic sulphur. These compou nds are constituents of natural gas and oil, from which they are also recovered. Of all sulphur sources, natural sulphur from open pit mining accounts for less than 1 %, nevertheless representing 3 * 10 6 t/yr world
- wide. Most of the sulphur is recovered from natural gas and oil (CIEC, 1999). For the exploitation of deep sulphur layers the Frasch process is the most important technique: Sulphur is melted with heated water under pressure and the liquefied sulphur is then pumped to the surface with compressed air (Hollemann and Wiberg, 1985). Uses of sulphur Sulphur is an essential nutrient for the growing plant. It is present in fertilisers, usually in the sulphate form that plants can use. For example, superphosphate contains about 11 % S , while ammonium sul phate, usually regarded as a nitrogenous fertiliser, contains 24 % S which is more than its nitrogen content. However, about 90 % of industrial sulphur is used in the manufacture of sulphuric acid, the most16

important sulphur compound. More sulphuric acid i s produced than any other chemical in the world. In Western Europe in 1997 over 19 * 10 6 tonnes were produced, the total production world
- wide being estimated at around 150 * 10 6 tonnes (Smith et al., 2001). It is said that the economic prosperity of a cou ntry can be assessed by its consumption of sulphuric acid. Sulphuric acid was manufactured by the lead
- chamber process until the mid
- 1930s. This process has now been replaced by the contact process, involving the catalytic oxidation of sulphur dioxide.

Tab. 2 : World production and consumption of sulphuric acid 1992 1993 1994 1995 1996 1997

10 6 tonnes H 2 SO 4 P roduction 145.7 132.5 137.9 148.9 151.3 155.6 Consumption 147.1 132.8 138.8 150.1 153.3 157.5 (EFMA, 2000) Demand for sul phuric acid The largest single sulphuric acid consumer by far is the fertiliser industry. Sulphuric acid is used with phosphate rock in the manufacture of phosphate fertilisers while smaller amounts are used in the production of ammonium and potassium sulp hate. Substantial quantities are also used as an acidic dehydrating agent in organic chemical and petro
- chemical processes, as well as in oil refining. In the metal processing industry, sulphuric acid is used for pickling and descaling steel; for the extra ction of copper, uranium and vanadium from ores, in the purification of non
- ferrous metals and plating. In the inorganic chemical industry, it is used most notably in the production of titanium dioxide. Further applications of sulphuric acid are wood pulpi ng processes for paper production, some textile and fibres processes, leather tanning, the use as electrolyte in car batteries and production of detergents and pharmaceuticals. Other end uses for sulphuric acid include effluent/water treatment, production of plasticisers, dyestuffs, explosives, silicate for toothpaste, adhesives, rubbers, edible oils or lubricants and the manufacture of food acids such as citric acid and lactic acid. Waste streams containing sulphate are generated by many industries, inclu ding mining, metallurgical, pulp , paper and petrochemical industries. By discharging these sulphate containing wastes to the rivers, all sulphate finally ends up in the sea.17

2.1.2 Sulphur emissions to the atmosphere No gaseous sulphur compound is a permanent or long
- lived constituent of the atmosphere. The short residence time for sulphurous gases is a consequence of rapid oxidation: Sulphur and its gaseous compounds hydrogen sulphide (H 2 S) and sulphur dioxide (SO 2 ) are oxidised to sulphur trioxide (SO 3 ), which d issolves in water droplets of the clouds to form sulphuric acid (H 2 SO 4 ). This process is responsible for acid rain. However a significant concentration is neutralised by gaseous ammonia in the atmosphere to form the corresponding ammonium salts e.g. ammoni um sulphate (this is a secondary particulate). 2.1.2.1 Natural emissions of sulphur Natural emissions of sulphur into the atmosphere from biogenic sources and from volcanoes are estimated to be around 60 * 10 6 S yr- 1 (2 * 10 12 mol S yr- 1 ). These values range from 46 to 124 * 10 6 S yr- 1 (Whelpdale, 1992). In addition, sea spray contributes by the release of sulphate , to a large amount of sulphur emissions. This estimate is very imprecise with 35 to 315 * 10 6 S yr- 1 , of which around 90 % cycles back into the oceans. Finally, the biogenic production in the open sea contributes to almost half (46 %) of all natural sulphur emissions to the atmosphere (Whelpdale, 1992). Dimethyl sulphide (DMS), the main volatile sulphur species emitted by marine phytoplankton in the ocea ns, plays a major role in the atmospheric sulphur cycle (Lovelock et al., 1972; Nguyen et al., 1984; Andreae and Raemdonck, 1983, Bates and Cline, 1985) In short, DMS released by marine phytoplankton enters the troposphere and is oxidised there to sulphate particles, which then act as cloud condensation nuclei (CCN) for marine clouds (Charlson et al., 1987). Both the nature of the DMS oxidation mechanism as well as the quantification of the extent to which the oxidation product H 2 SO 4 contribute to new CCN is largely unknown. Further, DMS has an indirect impact on the acidity of rainwater. The atmospheric DMS concentration varies seasonally, dependent on phytoplankton blooms. The DMS production in the Southern Indian Ocean has been reported to be by a factor of 20 or higher in the summer compared to the winter (Sciare et al., 2000). 2.1.2.2 Global anthropogenic sulphur emissions The emission of sulphur compounds into the environment is undesirable because of their acidifying characteristics. The global anthropogeni c sulphur emissions have been estimated to be in a range from 60 to 110 * 10 6 t S yr- 1 (2
– 3 x 10 12 mol yr- 1 ) for the18

years 1976 to 1985 (Moller, 1984; Hameed and Dignon, 1988). The combustion of fossil fuels accounts for 80 to 85% of the total. 2.1.2.3 Particul ate sulphate Sulphate compounds are emitted as primary ( directly released ) and secondary particles. The sources of primary sulphate particles include open pit mines, dry lakebeds, and desert soils. Other sources of primary sulphate particles are various fu el combustion processes from both stationary and mobile sources. Secondary sulphate particles are produced in the atmosphere when oxides of sulphur (SO x) are transformed into particles via physical and chemical processes. The main source of SO x is station ary and mobile fuel combustion. The types of sources that emit SO 2 are generally located in urban areas. Secondary sulphate particles formed from SO 2 emissions can be transported over long distances. These transported sulphate particles can comprise a sign ificant portion of the ambient sulphate in some rural areas.
2.1.3 Deposition of sulphate and sulphuric acid Gases in the atmosphere can reach the earth’s surface by wet and dry deposition processes. For wet deposition , precipitation is the delivery mechanism to the surface. The gases can dissolve in clouds and rain drops or adsorb to frozen precipitation elements. Sulphate particles represent good condensation nuclei and may be scavenged by the clouds. Those deposition processes, which do not involve precipitat ion, are collectively termed dry deposition. Sulphate can be chemically bound or adsorbed to small particles, which then reach the surface by gravitational settling (Whelpdale, 1992). The direct adsorption of SO 2 to particles is still poorly understood. S econdary particles formed through chemical reactions are typically much smaller (<2.5 μm diameter) than particles derived from physical processes (>2.5 μm diameter). The smallest particles in the atmosphere are the result of high temperature combustion and gas to aerosol conversions. Depending on the relative humidity and the presence of other atmospheric gases like ammonia, the sulphuric acid formed will be removed directly in precipitation, or neutralised and converted to ammonium sulphate. The atmospher ic conversion of sulphur dioxide via sulphuric acid to ammonium sulphate (Scheme 1) is an example of a gas to aerosol conversion process.19 

### Scheme 1 H 2

### SO 4 

### (g)  H + 

### + HSO 4- 

### HSO 4- 

###  H + 

### + SO 4 2- 

### NH 3 

### (g) + H 2

### O (g)  NH 4 + 

### + -

### OH 2 NH 4 + 

### (g) + SO 4 2- 

### (g)  (NH 4 

### ) 2

### SO 4(aq)
Thus, particles form through complex gas phase, heterogeneous and liquid phase reactions.



### 2.2 Nitrogen cycle Elemental nitrogen (N 2 ) is gaseous and the major constituent of air (78.09 % Vol.). By this, 99 % of all nitrogen on earth occurs in the air. C hemically bound nitrogen can be found as nitrate, and organic bound nitrogen in e.g. proteins or nucleic acids. Pure nitrogen can be simply produced by fractionation of liquid air (Linde Process). By its ability to have oxidation states ranging from
– 3 up to +6, numerous combinations with other elements are possible. The most important reaction partners are hydrogen (reduced form) and oxygen (oxidised forms). Nitrogen compounds, especially ammonia , are of great importance for the world economy for use, amo ng others , as fertiliser (Hollemann and Wiberg, 1985). Nitrogen is also an essential nutrient for life, but only a few plants are able to use elemental nitrogen as source. A variety of different bacteria are able to oxidise or reduce nitrogen compounds to gain energy.

2.2.1 Emissions of nitrogen compounds to the atmosphere Nitrogen dioxide (NO 2 ) is a reddish brown, highly reactive gas that is formed in the air through the oxidation of nitric oxide (NO). Nitrogen oxides (NO x), the term used to describe the sum of NO, NO 2 and other oxides of nitrogen, play a major role in the formation of ozone. The major sources of man
- made NO x emissions are high
temperature combustion processes, such as those occurring in automobiles and power plants.20

Nitrogen oxides also contribute to the formation of acid rain and to a wide range of other environmental effects, including: potential changes in the composition and competition of some species of vegetation in wetland and terrestrial systems, visibility impairment, acidification of freshwater bodies, eutrophication of estuarine and coastal waters, and increases in levels of toxins harmful to fish and other aquatic life. The consequence of eutrophication is an explosive algae growth leading to a depletion of oxygen in the water. 2.2.1.1 Natural emissions of nitrogen Atmospheric reactions of nitrogen are much more complex than the atmospheric reactions of sulphur. Ammonia (NH 3 ) is the most reduced form of nitrogen, and is released in small quantities from anaerobic degradation of organic matt er containing nitrogen. The major contribution to natural emissions is from agriculture. Similar to hydrogen sulphide, ammonia reacts with the hydroxyl radical to form oxidised nitrogen species. Nitrogen oxides are released to the atmosphere from both natu ral and anthropogenic sources. The two most common nitrogen gases released to the atmosphere from biological processes are nitrous oxide (N 2 O) and nitrogen dioxide (NO 2 ). 2.2.1.2 Anthropogenic emissions of nitrogen Combustion processes release mostly nitrogen oxi de (NO) and nitrogen dioxide (NO 2 ). The exact composition of nitrogen oxides emitted from combustion processes varies with the temperature of the combustion process, therefore the nitrogen oxides from combustion are often referred to as NO x to indicate the uncertainty in chemical composition. Like sulphur, the modern global nitrogen cycle is very different from the "Pre
industrial" nitrogen cycle. The difference is the large amount of nitrogen added to the atmosphere through combustion processes. The exces s atmospheric nitrogen oxides contribute to acid rain in the same way that excess sulphur oxides do. Tab. 3 lists the important atmospheric nitrogen oxides and their oxidation states. Tab. 3 Important Atmospheric nitrogen oxides
N itrogen oxide Oxidation state N 2 O +1 NO +2 NO 2 +4 HNO 3 , N 2 O 5 +5 Deleted: Tab. 321

Atmospheric nitrogen compounds are transported over long distances (Schulz et al. 1998). During transport they undergo specific physical
- chemical changes ( Fig. 1 ). NO x- compounds are typical anthropogenic precursors of oxidised nutrients like nitrate. The extremely complicated reactions within the atmosphere are described in detail by Holland (1978). For example, a dramatic change in the co mposition of sea - salt aerosols in coastal area s has been observed by Schulz et al. (1998). This change is caused by the reaction of sodium chloride with (anthropogenic) nitric acid. The chloride of the sea
- salt is exchanged by nitrate and hydrochloric acid is formed: NaCl + HNO 3  NaNO 3 + HCl By this reaction up to 55 % of the original sodium chloride in aerosols may be replaced by sodium nitrate. These extremely hygroscopic aerosols are easily deposited because of their high mass. Sodium chloride contai ning particles, originating from sea spray, are highly enriched in the coastal atmosphere. Contents of up to several 10 mg Cl -/m3 have been determined which rapidly decrease landwards. Thus, the reaction outlined above will take place preferentially in coa stal areas and hence a remarkable amount of nitrogen deposition occurs in the coastal area. Although higher NO x emissions may occur in regions remote from the coast the chloride exchange reaction does not play a major role in NO x removal here due to the lo w level of atmospheric NaCl. Schulz et al. (1998) regard this reaction as one of the most important sinks for oxidised nitrogen compounds in the coastal marine atmosphere. Deleted: Fig. 122 NH 4+ (177.7)

NH 3 (53.5) NO 3- >1 μm (50.9)

NO 2 (187.3)

NO 3- <1 μm (25.7) PAN, HNO 2 , N 2O 5 (1.8) HNO 3 (28.5)

NO (13.3)

Fig. 1 : Mean composition of atmospheric nitrogen compounds (nmol m -3 ) in the German Bight (Schulz et al., 1998), PAN: peroxyacetylnitrate.



### 3 Composition of seawater Seawater is a steady
- state system. It is a solution of salts of nearly constant composition, dissolved in variable amounts of water. There are well over 70 elements to be found in seawater but only 11 make up >99 % of the dissolved salts; all occurring as ions, i.e. electrically charged atoms or groups of atoms. These major ions behave conservatively . This means that they have constant ratios (Tab. 4 ), both to one another and to the salinity in almost all ocean waters , and that they do not participate in (mostly biological) reactions to such a degree as to experience a noticeable change in concentration. This property of seawater allows the calculation of concentrations of conservative constituents from salinity data. Deleted: Tab. 423

Tab. 4 Average sea - and freshwater compositions
F reshwater (river) Seawater mg/L weight % mg/L % Sodium Na+ 7 5.83 10800 30.72 Potassium K+ 2 1.67 400 1.14 M agnesium Mg 2+ 4 3.33 1300 3.70 Calcium Ca2+ 15 12.50 410 1.17 C hloride Cl 8 6.67 19400 55.19 B icarbonate HCO 3- 58 48.33 140 0.40 S ulphate SO42
- 12 10.00 2700 7.68 S ilica SiO2 14 11.67 2 0.01 (intern et site) As well as major elements, there are many trace elements in seawater
- e.g., manganese (Mn), lead (Pb), gold (Au), iron (Fe) and iodine (I). Most of these occur in parts per million (ppm) or parts per billion (ppb) concentrations. In contrast to t he major elements, the relative abundance of trace elements are variable. Although freshwaters display high variability in their composition the most abundant ions in river water are bicarbonate and calcium (Tab. 4). Compared to seawater, the abundance of bicarbonate is only 2.6 times less. Bicarbonate plays an important role in pH buffering (chapter 3.3 ).

Non -conservative substances dissolved in seawater are, among others, some gases (e.g. oxygen and carbon dioxide) and inorga nic nutrients. These are essential for the growth of plants, including algae. Major nutrients include nitrate, phosphate, and silicate (the latter required only by silicate depositing organisms). Nutrients are usually depleted in surface waters, where plan ts grow, and are found in higher concentrations in deeper waters, where the plant and animal remains that sink from surface waters decay.


### 3.1 Marine sulphur cycle The large amount of sulphate in seawater (2.65 g L - 1 ) derives from volcanic activities and degass ing at the seafloor. Further, sulphates reach the oceans via river flows, but the concentration in seawater remains constant at around 2.65 g L - 1 . A small part of24

the total sulphate load in rivers comes from the natural weathering of pyrite and gypsum. In addition, the water cycle carries recycled sulphate of marine origin. However, most of the riverine sulphate derives from human activities, e.g. mining, erosion and air pollution. Current fluxes are double those in pre
- industrial times. Sulphate is conservative in oxic oceans but not in anoxic basins or within sediments. Sulphate is used by sulphate reducing bacteria to form HS or H 2 S. Bacteria carry out various transformations of sulphur ( Fi g. 2 ).

Fig. 2 : Scheme of the microbiological cycle of sulphur and its possible influence on

the atmosphere

1. Sulphate reduction in anaerobic environments (CH 2 O represents organic matter such as carbohydrates): 2 CH 2 O + 2 H + + SO 4 2
-  H 2 S + 2 CO 2 + 2 H 2O This reaction is analogous to aerobic respiration but with SO 4 2
- rather than oxygen acting as the terminal electron acceptor in the oxidation reaction. The H 2 S produced may precipitate as authigenic minerals such as greigite, mackinawite and pyrite or may be used in one of the following reactions:

2. Sulphur
-based (anaerobic) photosynthesis : 2 H 2 S + CO 2  CH 2 O + 2 S + H 2 O Deleted: Fig. 225

This reaction is probably the earliest form of photosynthesis using H 2 S rather than H 2 O as the hydrogen donor in the re duction of CO 2 . Today it is employed by green and purple sulphur
- bacteria. 3. Chemoautotrophy under oxic conditions: 4 H 2 S + CO 2 + O 2  CH 2 O + 4 S + 3 H 2 O This reaction is performed by species of Thiobacilli in environments with free elemental sulphur or with H 2 S, for example near deep
- sea hydrothermal vents.


### 3.2 Marine nitrogen cycle In contrast to sulphate, nitrate is strongly linked to primary production in the sea. The general seasonal development of nutrient concentrations in seawater is characterised by a decrease during springtime ( Fig. 3 ) when phytoplankton blooms, transforming inorganic nitrate into organic nitrogen compounds such as proteins or nucleic acids. In summer the nutrients reach a minimum , leading sometimes to a lim itation of certain nutrients. Remineralisation processes in the sediment may support a second phytoplankton bloom in late summer. In autumn, nutrients increase because of low primary production to maximum concentrations in winter.



### NUTRIENTS PLANKTON BIOMAS

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 

### low pH high pH

Fig. 3 : Schematic seasonal variation of nutrients and phytoplankton biomass in

temperate areas. Deleted: Fig. 326

Deposition of organic material (plankton and detritus) into surface sediments supports benthic mineralisation. Mineralisation of organic nitrogen compounds occurs in several enzymatic steps (proteins
- peptides
- amino acids). Finally ammonia is liberated from amino acids by deamination. Degradation of organic material by heterotrophs leads to dissolved inorganic nitrogen (DIN) again (Schlegel, 1981). Ammonia production is highest under anoxic conditions ( Fig. 4 ). The concentration of ammonia in the porewater is governed by production, adsorption to particles, diffusion and reaction processes. Fig. 4 : Major reactions and pathways in the marine nitrogen cycle (Lohse, 1996)

DIN = dissolved inorganic nitrogen (NH4+, NO2
-, NO3
-), DON = dissolved organic nitrogen, PON = particulate organic nitrogen. In the presence of oxygen, ammo nia is oxidised in two steps via nitrite to nitrate. This process is called nitrification and is performed by the bacteria species Nitrosomonas spp. and Nitrobacter spp. These are restricted to the upper oxic part of the sediment column. Nitrate is the end product of nitrification and can diffuse into the overlying water column or deeper into the sediment where it undergoes further reactions. During denitrification nitrogen and dinitrogen oxide are released to the atmosphere, the latter contributing to the greenhouse gases. During summer months when input of organic material is high and hence high remineralisation rates prevail , oxygen deficiency can impede nitrification. Under these conditions ammonification becomes the dominant process. All these processes are seasonal dependent and are in exchange with the atmosphere. Quantification is difficult. The marine system also receives anthropogenic nitrogen via the rivers and the atmosphere.


### 3.3 The pH of seawater: the carbonate system The pH of surface seawater usu ally ranges from 8.1 to 8.9 and is therefore slightly alkaline
. This is largely due to the presence of carbonate (and other weak acid) species in natural waters. These are needed to balance the excess positive charge of the major cations. There is a balanc e between carbonate , and dissolved and atmospheric carbon dioxide. When carbon dioxide dissolves in water, carbonic acid is formed and thus the pH becomes lower due to increased acidity. Dissolved inorganic carbon (CO 2 * , HCO 3 - + CO 3 2
- ) varies by ~20 % due to vertical transport in the water column and remineralisation of both CaCO 3 and organic matter. Natural changes of seawater pH are related to primary production, which converts inorganic (carbon?) to organic carbon, and then degradation of the produced ma terial Formatted: English (U.K.) Deleted: Fig. 427

( Fig. 3 ). Photosynthetic activity increases the pH while the opposite, organic matter remineralisation, leads to a decrease in pH values. The ability to neutralise acids and bases to a certain extent is termed the buffer capacity or alkalinity of seawater. Total alkalinity is found by measuring the amount of acid (e.g. sulphuric acid) needed to bring a sample of seawater to a pH of 4.2. At this pH, all the alkaline compounds in the sample are "used up"
. The result is reported as milligrams per litre of calcium carbonate (mg L - 1 CaCO 3 ). The amount of bicarbonate and other weak bases in seawater buffers the system, thus keeping the pH within a narrow range. Dissolved CO 2 and carbonates belong to the buffer system and are all rel ated by the following four equations:

1. CO 2 + H 2 0 < ------ > (CO 2 ) aq 2. (CO 2 ) aq + H 2 0 < ------ > H 2 CO 3 (carbonic acid) 3. H 2 CO 3 < ------ > H + + HCO 3 - (bicarbonate) 4. HCO 3 - < ------ > H + + CO 3 2
- (carbonate)
(CO 2 ) aq and H 2 CO 3 are difficu lt to measure and are usually given as CO 2 * . The solubility of CO 2 in water is 1.7 g L - 1 (0
. 04 mol L- 1 ) and is governed by Henry’s Law, assuming ideal gas behaviour: S CO2 = [CO 2 ] = K H * p CO2 i.e. the solubility (S) of a gas is proportional to its partial p ressure (pA ). Henry's law is derived from K D = [CO 2(aq) ]/[CO 2(gas) ] [CO 2(gas) ] = pCO2/RT {Dalton's law of partial pressure} [CO 2(aq) ] = ( K D/RT) pCO2 = K H * p CO2 { K

H [mol L- 1 atm - 1 ]} As the carbonate system encompasses polyprotic acids, it is able to buffe r against changes in pH caused by addition of either acid or base: H + + HCO 3 - < ------ > H 2CO 3 H + + CO 3 2
- < ------ > HCO 3 - OH - + HCO 3 - < ------ > H 2 O + CO 3 2
- OH - + H 2 CO 3 < ------ > H 2 O + HCO 3 - Deleted: Fig. 328

As calcium carbonate (solid) reacts with water in presence of free hydrogen ions, the solid calcium carbonate dissolves forming free Ca +2 ions and free bicarbonate ions, hence consuming free hydrogen ions, decreasing hydrogen ion activity, and by definition increasing pH (becoming more basic). i.e. calcium carbonate acts to n eutralise or buffer the solution by consuming hydrogen ions. Both carbonic acid and bicarbonate are weak acids with pK values of pK 1 = 6.5, pK 2 = 10.4. When pure water is equilibrated with CO 2 the system is defined by two independent variables (in addition to total pressure), e.g. temperature and p CO2 . If, besides temperature, one other variable such as pCO 2 , [CO 2 *] of [H + ] is known, then all components can be calculated from the equilibrium concentrations, using Henry's law, the acidity constants and the p roton condition or charge balance. The pH of a pure aqueous CO 2 solution is defined by the charge balance: [H + ] = [HCO 3 - ] + 2 [CO 3 2
- ] + [OH - ] If the system is kept in equilibrium with constant p CO2 , the pH can be varied only by the addition of a base , C B o r an acid , CA . Electroneutrality must be observed for such an addition. As B is equivalent to the concentration of a monovalent cation (e.g. [Na + ] from NaOH) and A is equivalent to the concentration of a monovalent anion (e.g. [Cl - ] from HCl). C B + [H + ] = [HCO 3 - ] + 2 [CO 3 2
- ] + [OH - ] + CA C B - CA = CT (        [OH
- ]
- [H+] where, CT = total CO 2 concentration ;  is the Bunsen coefficient (  0 = K H * 22.414 [atm 1 ] ; and (C B - CA ) is the acid neutralising capacity of the solution with respect to the pure sol ution of CO 2 . This difference is defined as the alkalinity, [Alk].

] [H ] [OH ) 2 β ( β C C [Alk] 2 1 A B 


 
    0 2

β p K CO H This model has three independent variables in addition to total pressure. It is therefore sufficient to give T, p CO2 , and alkalinity to define the system. The pH is given by [Alk] and p CO2 . There are other bases apart from those present in the carbonate system which contribute to the total alkalinity of seawater . These are B(OH) 4 - , HPO 4 2
- and PO 4 3
- and, under specific environmental conditions, hydrogen sulphide HS - . If this is included then C B + [H + ] = [HCO 3 - ] + 2 [CO 3 2
- ] + [B(OH) 4 - ] +[OH - ] + CA29

C B - CA = CT (        BT B  [OH - ]
- [H + ] with BT = [H 3 BO 3 ] + [B(OH) 4 - ] and  B = [B(OH) 4 - ] BT and ] [H ] [OH β B ) 2 β ( β β p K C C [Alk]

- B T 2 1 CO H A B 


  
    0 2 In the system containing only carbonate specie s, alkalinity is commonly referred to as titration or carbonate alkalinity (CA). Incorporating other bases alkalinity is then referred to as total alkalinity (TA). CA and TA differ by about 100 μequivalents L - 1 only. Total alkalinity of seawater averages 1 16 mg L- 1 and is greater than fresh water, which varies significantly, depending on the drainage area. TA can have a total alkalinity of 30 to 90 mg L - 1 . Brackish waters like in estuaries, where river water is mixed with seawater, have TA varying between t hese values. The pH values after addition of acid or base can be calculated using the above equation(s) taking into account ionic strength effects on the constants. Corrected values are tabulated. The neutralisation of sulphuric acid in seawater occurs in two steps: 1. H 2 SO 4 + H 2 O  HSO 4 - + H 3 O + pKa (H 2 SO 4 ) =
- 3 2. HSO 4 - + H 2 O  SO 4 2
- + H 3 O + pKa (HSO 4 - ) =1.92 Both sulphuric acid and hydrogen sulphate have low pK a values (
- 3 and 1.92, respectively), and are hence strong acids which dissociate completely. Therefore all the protons of sulphuric acid contribute to the pH
- shift. The carbonate system will buffer the additional protons by releas ing CO 2 in order to keep the pH constant. One molecule of sulphuric acid will therefore produce 2 molecules of CO 2 . The equations 1
- 3 of the carbonate system (see above page 27 ) will shift from the right to the left sides, finally releasing the dissolved CO 2 to the atmosphere.30



### 4 Laboratory measurements A model of Abdulsattar et al. (1977) allows the prediction of the pH of effluent from seawater scrubbers, but leads to an overestimation of acidity (Baalina, et al., 1997). The reason is that the oxidation of SO 2 to SO 4 2
- is not taken into account nor is the impact that the temperature of the seawater has on pH (Hunter, 1998). The calculations in the previous chapter are based on an ideal seawater composition and do not take into account other seawater constituents (e.g. organic acids like amino or humic acids). As the above described equations are simplified , and some da ta is difficult to obtain or absent, laboratory measurements were carried out at Terramare to quantify the ability of seawater to buffer sulphuric acid solutions.



### 4.1 Impact of diluted sulphuric acid (pH 4) on seawater To mimic the conditions of the seawater scrubber effluent, concentrated sulphuric acid (98 %) was diluted with seawater to a pH of 4 (assumed worst case for scrubber effluent, Ref 1.4.1). The amount of sulphuric acid in 1 L was 1
. 25 g H 2 SO 4 . Assuming that this effluent would be discharged directl y to the sea, this solution was added in small portions to natural seawater (salinity = 29 PSU), taken at the Nassau Bridge in Wilhelmshaven, Germany in October 2002. The concentration of the sulphuric acid was recalculated because of the changing end
- volu me. The pH shift caused by the addition of sulphuric acid was measured directly ( Fig. 5 ). Formatted: English (U.S.), Check spelling and grammar Deleted: Fig. 531 

### 0 100 200 300 400 500 600

7.4 7.5 7.6 7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 8.5 pHconcentrationofsulphuricacidinseawater[mg/L] raw data

Y = (A+X)/(B+C*Xexp2)

Fig. 5: Impact of sulphuric acid (pH 4) on the pH of seawater (S = 29 PSU)

corresponds to regression line. The addition of 2.48 mmol (68 mg) sulphuric acid to 1 L seawater caused a pH shift of pH 0.1 units only. This amount of sulphuric acid corresponds with a mixture of 1:10 (v:v, sulphuric acid in seawater pH 4 : natural seawater). Even a mixture of 1:5 (5.08 mmol L - 1 ) only caused a pH shift of 0.23. The scrubber effluent is diluted with natural seawater ten times. Thus, the requirements of US
- EPA (1976) that changes in pH shall not exceed 0.2 units for marine waters are fulfilled. The regression l ine in Fig. 5 was calculated using the Lab
- Fitting software. The equation for the regression line is: Y = (A+X)/(B+C*X 2 ); R2 = 0.999 A =
-8.43463908 B =
-0.00536647 C = 0.00006588 Deleted: Fig. 532



### 4.2 Impact of diluted sulphuric acid (pH4) on b rackish waters In a second experiment, the same test was carried out with brackish water (Ems
- Jade Kanal, Wilhelmshaven, Salinity = 14 PSU). Different ratios of the original and the acidified brackish water (pH 4) were mixed. The pH was measured directly a fter mixing, and after stirring the solutions for 1 hour again. Within this time, the carbonate system was able to buffer the pH by release of CO 2 to the atmosphere, while the pH increased again (Tab. 5 , Fig. 6 ).

Tab. 5: Percentage of sulphuric acid (pH 4) in brackish water with resulting pH (t = 0

and t = 1 h) Percent sulphuric acid in brackish water (pH

4) [%] Percent natural

brackish water [%] pH

measured immediately pH

measured af ter 1 hour  pH between

t = 0 and t = 1 h 0 100 7.60 7.63 10 90 6.63 7.50 0.87 20 80 6.52 7.35 0.83 30 70 6.45 7.02 0.57 40 60 6.31 7.01 0.70 50 50 6.08 6.88 0.80 60 40 5.85 6.47 0.62 70 30 5.63 6.15 0.52 80 20 5.38 5.65 0.27 90 10 4.54 4.95 0 .41 100 0 4.03 4.07 Deleted: Tab. 5 Deleted: Fig
. 633 

### 0 10 20 30 40 50 60 70 80 90 100

3 4 5 6 7 8 pHpercentageacidifiedbrackishwater pH immediately measured

pH after 1 h stirring

Fig. 6 : Percentage of sulphuric acid (pH 4) in brackish water with resulting pH (t = 0

and t = 1 h).

The test with the brackish water (S = 14 PSU) showed that the same dilution factor of 1:10 caused an imme diate shift of about 1 pH
- unit. After one hour the pH returned to almost its original value ( pH = 0.1). These preliminary experiments show that the addition of sulphuric acid in seawater to pure seawater is not only dependent on the amount of sulphuric ac id, but also on time. The carbonate system reacts in two steps: first the production of dissolved (CO 2(aq) ), second the release of gaseous carbon dioxide (CO 2 (g) ) from the system, to keep the pH almost constant.34



### 4.3 Summary of laboratory experiments The experiments with the hypothetical effluent of the seawater scrubber ( SWS ) (pH 4) showed that even with a dilution factor of only 10, the discharge would not change the pH of the receiving seawater more than 0.2 standard units. Brackish water reacted wi th a spontaneous pH shift around 1 standard unit , but within one hour it had almost returned to the original pH (pH shift 0.1). These measurements were carried out in closed systems, where only gas
- exchange was allowed. However the results for any experim ents conducted to demonstrate the impact of releasing a sulphuric acid discharge from a (moving) ship into the sea, must take into account realistic conditions. For example , the extent to which the effluent mixes with the seawater is dependant on the speed of the water at the time of discharge ( a parameter which varies with ship speed), and the tidal currents which vary hourly
. In estuaries, the exchange rate with the open sea and the inflow of freshwater are important factors.



### 4.4 Impact of the acidic effluen t of the Krysta llon Scrubber on the pH of the receiving water In chapter 1.4.1 the theoretical composition of the effluent is described. The lowest pH would be 4.8. The experiments were carried out with acidified seawater pH 4, representing an assumed worst case. Next to sulphuric acid, nitric acid contributes to the acidity of the effluent, but to a lesser extent. 1. NO x reduction is around 20 %, compared to 95 % SO 2 reduction 2. Nitric acid delivers only one hydrogen ion per m ol, whereas sulphuric acid delivers two hydrogen ions. Based on data for different scenarios (ship in service and ship in harbour) and sulphur contents of the fuel, the composition of the resulting effluent was calculated (Ta b. 6 )
. Noticeable is the changing amount of cooling water, which is finally discharged. This variable has a significant impact on the concentrations. The maximum relative contribution of nitrate to the acidity is calculated to be 9.66 %, but this is of minor im portance regarding the pH of the discharged effluent and its impact on the environment. The proportion of nitric acid is relevant, as it delivers nitrate to the marine system. Deleted: Tab. 635

The calculations are based on data obtained on the Krystallon Scrubber . The SO 2 adsorbing , recirculation water is diluted with cooling water (seawater) and discharged at a pH level between 4.5 and 5.5. The laboratory experiments showed that a dilution of the effluent with seawater of 1:10 causes a pH
- shift less than 0.2 pH units. Tab. 6 : Contribution of nitric acid to the acidity of the effluent
At Sea 1 I n H arbour 2 Sulphur content in fuel % 3.50 1.50 0.50 3.50 1.50 0.50 Specific NO x emissions 3 g/kWh 20 20 20 20 20 20 SO 2 removed % 95 95 95 95 95 95 NO x re moved % 20 20 20 20 20 20 D ischarged cooling water t/h 30 30 50 70 70 70 SO 2 in cooling water mg/L 412 177 59 47 20 6.7 H 2 SO 4 mg/L 631 270 90 72 31 10 mmol/L 6.44 2.76 0.92 0.74 0.32 0.11 H ydrogen ions delivered by H 2 SO 4 mmol/L 12.88 5.52 1.84 1.47 0 .63 0.21 NO in cooling water4 mg/L 20.4 20.4 8.14 2.3 2.3 0.9 mmol/L 77.1 77.1 77.1 10.5 10.5 10.5 NO 2 in cooling water4 mg/L 33.04 33.04 33.04 4.48 4.48 4.48 mmol/L 0.72 0.72 0.72 0.10 0.10 0.10 HNO 3 equivalent to hydrogen ions mmol/L 3.29 3.29 3.2 9 0.45 0.45 0.45 S um of hydrogen ions mmol/L 16.16 8.80 5.13 1.92 1.08 0.66 Contribution of NO 2 to acidity % 20.34 37.34 64.13 23.27 41.44 67.98 1 ) four main engines and two generators running 85 % MCR 2 ) two Generators running 95 % MCR 3 ) Marpol Annex VI limits emissions of NO x to between 10
– 17 g NO x/kWh, (worst case assumed as 20 g NOx/kWh) 4 ) based on the assumption that 70 % of total nitrogen is converted to NO and 30 % is converted to NO 2 . 

### 4.5 Estuaries Salinity and pH in the estuarine ecosystem In e stuaries a salinity gradient is caused by the permanent freshwater input by the rivers into marine waters. The most important estuarine characteristic is that nowhere is variation in salinity more pronounced. As seawater mixes with river water, the conservative seawater components will co
- vary directly in concentration with salinity. Any component that is added during mixing will increase in concentration versus a36

conservative mixing line. A component that is lost during mixing (e.g. precipitation of some m etals as hydroxides with decreasing pH) will decrease in concentration versus a conservative mixing line. Such non
- conservative behaviour will only be evident when the addition or loss processes are relatively rapid versus water mixing in the estuary. Oth er factors causing horizontal, vertical and seasonal variability of salinity in estuaries are:

 amount of freshwater input,

 evaporation,

 water density (vertical variability),

 tides and

 the Coriolis effect Human activities that cause significant, short
- term fluctuations in pH or long
- term acidification of a water body are exceedingly harmful. For instance, algal blooms that are often initiated by an overload of nutrients in the rivers can cause pH to fluctuate dramatically over a period of a few hours. Chang es in pH can put great strain on local organisms. The pH of an estuary can vary from 7.0 to 7.5 in the fresher, low salinity sections , to between 8.0 and 8.6 in the more marine parts. The slightly alkaline pH of seawater is due to the natural buffering fro m carbonate and bicarbonate dissolved in the water (chapter 3.3 ). The pH of water is critical to the survival of most aquatic plants and animals. Many species have trouble surviving if pH levels drop below 5.0 or rise above 9.0 ( Fig. 7 ). Fig. 7: pH ranges that support aquatic life (source: see Internet
-sites)

most acid neutral most basic 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Bacteria Plants (algae,rooted, etc) Carp, suckers,catfish, some insects Bass,bluegill,crappie Snails, Clams, mussels Largest variety of animals (Trout, mayflynymphs,stoneflynymphys, caddishfly larvae) pH ranges that support aquatic life. Changes in pH can alter other aspects of the water's chemistry, usually to the detriment of native species. Even small shifts in the water's pH can affect the solubility of some metals such as iron and copper. Such changes can influence aquatic life Formatted: English (U.S.) Deleted: 3.3 Deleted: Fig. 737

indirectly. If the pH levels are lowered, toxic metals in the estuary's sediment can be re - dissolved in the water column. This can have impacts on many aquatic species.
4.5.1 Harbour areas like the Port of Rotterdam The port of Rotterdam is a very complex area, with vital inflow from the North Sea and several rivers and canals. The complex geometry and hydrography of the port of Rotterdam was approached in the Mam
- Pec model (in CEPE report, 1999) with two different scenarios. In the first scenario the geometry of the Rotterdam port area was conceptualised as a rectangular area (2 x 20 km; 40 00 ha; depth 20 m), with a 5 km wide open front to the river in order to mimic a harbour segment with an average water exchange of 32 % per tidal period. A second scenario, with a 10 km wide open front to the river was chosen to represent harbour segments with a water exchange of 65 % per tidal period. The hydrodynamic exchange in the Mam
- Pec model is derived from the following parameters: density differences (between marine and freshwater), tidal period and height, river flux and the dimensions of the rectangular port area. Shipping: The Port Statistics from 2001 for the Port of Rotterdam show that the number of ship arrivals of seagoing vessels is around 30 000/a nnum in recent years and 133 000 arrivals of inland vessels per year. Movements of seagoing ves sels are on average 82 000/a. Within the EU the port of Rotterdam has the maximum NO x, SO 2 and CO 2 emissions. Tab. 7: Ports in the EU ranked by estimated annual emissions of NOx in 2000 Rank Port Name Country NOx [kT] SO 2 [kT ] CO 2 [kT] 1 Rotterdam NLD 3.8 3.7 219.9 2 Antwerp BEL 2.2 2.2 134.0 3 Milford Haven GBR 2.0 2.2 130.4 4 Hamburg DEU 2.0 1.9 115.5 5 Augusta ITA 1.8 2.0 121.4 6 Agioi Theodoroi GRC 1.7 1.8 107.0 7 Piraeus GRC 1.6 1.6 93.9 8 Eleusis GRC 1.5 1.6 95.1 9 Gothenburg SWE 1.5 1.5 91.1 10 Immingham GBR 1.3 1.4 82.0 reported by Entec, 2002. A rough calculation using data from Tab. 7 indicates that on an annual basis total SO 2 discharge into Rotterdam port waters will contribute about 2 x 10 - 4 mol H +/L ass uming38

that all SO 2 will be transferred to the aqueous phase. Using data from Table 6 and assuming the presence of 100 vessels in the port area, the H + concentrations will increase by 5.7, 9.4 and to 16.7 x 10 - 6 mol H +/L h for 0.5 %, 1.5 % and 3.5 % sulphur fuel. This corresponds to 0.5
– 2 pH units. This calculation does not take into account the buffer capacity of seawater, the exchange of CO 2 with the atmosphere, nor the tidal exchange with the open sea. Preliminary experimental data presented above (chapter 3.4) suggest that the re
- equilibrium is rapid although effects of continuous addition of acid need to be investigated in detail.


### 4.6 The Baltic Sea The Baltic Sea is a relatively shallow inland sea surrounded by the countries of North
eastern Europe and Scandinavia. Its total area is about 377,400 km 2 , and its volume about 21,000 km 3 . The catchment area extends over an area about four times as large as the sea itself. The mean depth is 55 m, while the maximum depth is 459 m in the Landsort Deep. The Baltic also receives surface water drainage from five other countries: Belarus, Czech Republic, Slovak Republic, Norway, and Ukraine. The Baltic Sea is connected to the North Sea through narrow and shallow sounds between Denmark and Sweden. The outlet consists of a series of basins separated by shallow sills, which obstruct efficient water exchange. Consequently, it takes 25
- 35 years for all the water from the Baltic Sea to be replenished by water from the North Sea and beyond. Salinity in the Baltic varies fro m fully marine at the Skagerrak/Kattegatt boundary to almost fresh water conditions in the Bothnian Gulf. Due to the high riverine input of fresh water, a pronounced year
- round stratification of the water column, especially in the Baltic Proper, can be obs erved. This results in a reduced mixing of surface with bottom waters. Ice coverage occurs regularly in the northern parts. More than 500 million tonnes of cargo are transported across the Baltic Sea each year, along many busy shipping lanes. More than 50 passenger ferries also ply routes between Baltic ports.
4.6.1 Vital inflow from the North Sea The inflow of water from the North Sea is the main source of oxygen for the deep waters of the Baltic Proper, and is very significant for nutrient cycles throughout t he Baltic Sea. A stagnation period of more than sixteen years ended in January 1993 when masses of high
- salinity water entered the Baltic, and for the first time since 1977, the Baltic Sea was free of hydrogen sulphide. Unfortunately, the effects of this39

water exchange did not last, and within a couple of years the depths of the Eastern Gotland Basin were again becoming anoxic. In 1996 hydrogen sulphide was once more recorded in the depths of the Bornholm and Eastern Gotland Basins. Contaminants and nutrien ts enter the Baltic Sea in rivers, in runoff from coastal areas, through exchange of water with the North Sea, through atmospheric deposition, and due to human activities at sea. A complete water renewal takes about 25
- 35 years, so persistent pollutants ca n remain in the Baltic for a long time.



### 4.7 Acidification of surface waters The deposition of atmospheric acids is not a recent phenomenon, but the extent of the consequences is still unclear. Acidification of soils and surface waters is to some extent a nat ural process but has accelerated in recent decades. The main causes of acidification are acid rain and the use of certain fertilisers in agriculture, which reach the oceans by surface water runoff and rivers. A drop in the pH of soil to 5.5 for example , ca uses a decline in agricultural harvests as certain micronutrients become less available and microbial turnover of nitrogen and carbon are impaired. The acidity of a water body is dependent on the amount of acid deposited, the amount of acid already presen t in the water body, and the ability of the water body to absorb and neutralise acid (buffer capacity). Seawater has a tremendous ability to neutralise acids, so significant acidification does not occur in coastal waters and most estuaries. Some freshwater bodies, however, may be very sensitive to atmospheric inputs of acidic compounds (US EPA, 1976). The overall effects of seawater acidification on marine ecosystems are not yet clear. For example , the potentially harmful effects of changing environmental C O 2 concentrations on energy metabolism and growth of marine invertebrates and fish still have to be studied in detail. Acidification affects ecosystems in many ways. Aquatic organisms in acidified waters often suffer from calcium deficiencies which can wea ken bones and exoskeletons and can cause eggs to be weak or brittle. It also affects the permeability of fish membranes and, particularly, the ability of gills to take up oxygen from the ambient water. Additionally, increasing the amount of acid in a water body can change the mobility of certain trace metals like aluminium, cadmium, manganese, iron, arsenic, and mercury. Species that are sensitive to these metals, particularly fish, can suffer as a result. The effects of acidification on aluminium mobility has received the most attention because this metal is toxic to fish. The effects of increasing levels of cadmium and mercury, which are atmospheric pollutants of concern for water quality, are also becoming known.40



### 4.8 Experiences with acid disposals at sea. The waste of titanium dioxide production contains heavy metals and sulphuric acid (around 12 %; Rat von Sachverständigen, 1981; Carlson, 1986). Beginning in 1969 this waste was dumped into the sea about 12 nautical miles north of Heligoland in the central G erman Bight with increasing amounts. This disposal was stopped in 1989, because the heavy metal content of the acid caused dramatic changes in the ecosystem. At that time 750 000 t of sulphuric acid (12 %) were dumped into the sea per year. The pH of the w ater in the disposal area changed only slightly, due to the buffer capacity of the receiving seawater (Dethlefsen, 1990). Data provided by Weichart (1975) indicate s that pH changes resulting from titanium dioxide waste dumping were within the range of natu rally occurring pH values. Even in the core of the propeller wake of the dumping vessel in 5
- 10 m water depth the pH after one hour was 7.77, increasing to 8.04 after 4.7 h. With the exception of fresh propeller wake no indications of long term pH change s were found.


### 4.9 Eutrophication effects Any inorganic nitrogen and phosphorus compound added to natural waters will promote primary productivity. Enhanced production of biomass can lead to eutrophication effects under certain circumstances. In marine systems phytoplankton biomass is usually produced in
- within limits
- fixed relations of carbon : nitrogen: phosphorus, the so
- called Redfield ratio of 106 : 16 :1. Thus, any mole P added will result in the fixation of 106 moles carbon and 16 moles nitrogen. In ca ses where only nitrogen is added as in scrubber effluents the extent to which additional biomass is produced will depend not only on the actual amount added but also on the phosphorus available for primary production. In open ocean situations P is generall y regarded as the limiting nutrient. Here, additional N will not have any effects on planktonic biomass production. In near- shore or harbour situations, where P is available ( e.g. from riverine inputs, runoff from agriculture or direct input of domestic se wage ) , addition of inorganic nitrogen may lead to enhanced primary production. On the other hand, addition of nitrogen may also have beneficial effects as it counteracts the development of cyanobacteria blooms which may occur in the absence of inorganic ni trogen when there is still sufficient phosphorus in the euphotic zone. Certain cyanobacteria are able to use molecular nitrogen instead of nitrate or ammonia. This is often the case in the Baltic Sea where such blooms occur regularly.41

Here, phosphate is st ill present in measurable quantities even after the phytoplankton spring bloom has reduced nitrate levels to below the detection limit (Wasmund et al. 2001). Based on the assumption that there will be ample phosphate an input of 3.29 or 0.45 mmoles NO 3 -/L, respectively, (Tab. 4) will result in an additional biomass production of 43.6 or 6 mg/L assuming , that carbon accounts for 50 % of the produced biomass. This figure, however, does not include further dilution of the scrubber input by turbulent mixing alo ng the ship's path. Primary production, at least in temperate and polar regions, is strongly connected to the seasonality of insolation. This results in high productivity in spring when there are sufficient inorganic nutrients available and lower productiv ity in summer and early autumn when nutrients are production limiting. Thus, relative contributions of additional nitrogen
- containing nutrients will be low in spring but higher in summer. Furthermore, inter
- annual variability will also have an effect on th e relative contribution of any additional nitrogen added. In coastal areas and harbours neither P nor N are usually production limiting factors. Here, it is rather the av a ilability of light which prevents usage of inorganic nutrients by primary producers ( e.g. Colijn and Cadée 2003).42



### 5 Environmental impact of scrubbing waters - Synthesis Catalysts are used d uring the removal of sulphur i n the production of low S fuels in refineries. These contain transition metals (molybdenum, cobalt, nickel, zi nc, copper) which need to be replaced at more or less regular intervals. Only part of these metals can be recycled, the remainder, especially fine material released into the gas stream, has to be safely deposited. In addition , the amine used to remove the hydrogen sulphide produced during Hydrotreating , can also be recycled or needs to be safely deposited. The costs and environmental impacts incurred from either recycling or deposition cannot be specified on a global scale. Van Oudenhoven et al. (1993) repo rt that in 1993 , 89 refineries in Europe produced a total of 6,368 tons of spent desulphurisation catalyst . Thus, processes that are cheaper or more environmentally benign are attractive alternatives. One of these is the removal of combustion gases. Of t he processes listed above Flue Gas Desulphurisation with Seawater Scrubbing (FGD
- SWS) appears to be the most attractive option for the operation of seagoing vessels. Both laboratory experiments and field evidence indicate that acidic waste streams from FGD
- SWS introduced in full strength seawater leads to observable effects on ambient pH only for extremely short periods of time. From the dumping of much higher concentrated sulphuric acid in the North Sea it is known that the area affected is restricted to a few hundred meters behind the dumping vessel. Preliminary laboratory experiments with seawater indicate that at a 1:10 dilution the observable pH change did not exceed 0.1 pH units. For brackish waters a time lag of about one hour was observed. These valu es coincide with EPA requirements. Considering that in this case a 12 % acid (=2.634 mol H +/L) was dumped , then it can be expected that the maximum of about 6 mmol H +/L produced during waste discharge from FGD
- SWS , will affect neither the pH values nor the sulphate contents of the receiving waters to a noticeable degree. This is not only due to the low concentrations of sulphate in the waste stream. Turbulent mixing caus ed by s hip movements and screw rotation will provide further dilution. N atural mixing processes will also contribute to this. It should, however, be noted that the conclusion given above holds for fully marine salinities only. In waters such as the Baltic with generally lower salt contents and slightly different ionic composition, especially in the northern parts, the 1:10 dilution may not be sufficient. Also, during harbour times when there will be no ship movements and only limited water moveme nt this dilution factor may be too low.43

Detailed analysis of this case remains to be done. The othe r factors worth considering are the total mass of sulphur emitted in harbour versus at sea. Vessels do not burn as much fuel in port as they do at sea due to the lower demand for propulsion. A typical ferry may have 27 MW of installed power available at se a, while only 3 MW of this would be available in harbour. The amount of sulphur discharge is proportional to this power use, thus even in brackish harbours, the sulphur dilution ratio may be sufficient. In the case of nitrate , ope n sea discharge from FGD
- S WS is again due to the high dilution rate, not likely to cause any eutrophying effects. In ports, however, the high concentrations in the discharge stream together with restricted water exchange may lead to nitrate values high enough to cause unwanted effe cts such as exceptional phytoplankton blooms. Just as sulphur emission is linked to total engine output, so is the nitrogen emission rates. Vessels that are moving slowly, or anchored in harbour with only generators running will be producing much lower lev els of nitrates than under full speed at sea. The effect of 2
- 4 MW of engine power per ship in harbour may be insignificant in terms of nitrate amounts. Even when main engines are started, it is difficult to conceive of how massive amounts of fuel can be burned for propulsive motors in a small harbour. The use of propulsion engines is to get out of harbour and manoeuvre, so these sources are not continuous. Tab. 8 : discharge of sulphate and nitrate per hour Sulphate Nitrate Sulphur in fuel % 3.5 1.5 0.5 NOx emission 3,4 g/kwh 20 3MW 1,2 3MW 1,2 SO 2 kg/h 37.8 16.2 5.4 NOx kg/h 57 Reduction % 95 95 95 Reduction % 20 Discharged SO4 2
- kg/h 56.7 24.3 8.1 Discharged NO 3 - kg/h 20 27MW 2 27MW 2 SO 2 kg/h 323 138 46 NOx kg/h 432 Reduction % 95 95 95 Reduction % 20 Discharged SO4 2
- Kg/h 485 207 69 Discharged NO 3 - kg/h 153

1) In harbour situation with two generators running (3 MW) 2) Fuel consumption 180 kg/kWh 3) For 20 g NOx

/kWh 4) Assuming an NOx composition of 70 % NO, 30 % NO244

Nevertheless, as experimental evidence is lacking, it appears necessary to conduct a series of laboratory and field experiments to elucidate the actual changes in pH and sulphate as well as nitrate concentrations , under a variety of conditions. Similarly, it might be useful to adopt models developed for port sediment and water exchange , to include pH and sulphate concentration
. Comparing these results with the harmful effects of the SO 2 and NO x emissions of ships, the use of the SWS seems to be a shortcut: most of the produced sulphate and nitrate will reach the oceans by surface run
- off via the rivers. On land however, the acidification of soils, lakes and rivers causes considerably higher damage. The change of atmospheric aerosol composition by NO x emissions, which has been observed in the German Bight for example , should also be taken into account. Other positive side
- effects of the SWS are 80 % removal of particulates and noise reduction.45

References Andreae, M. O. and Raemdonck, H. (1983). Dimethylsulfide in the surface ocean and the marine atmosphere: a global view. Science, 221,744
- 7. Andreae, M.O. and Jaeschke, W.A., 1992 Exchange of Sulphur between Biosphere and Atmosphere over Temperate and Tropical Regions. In: Sulphur Cycli ng on the Continents
- Wetlands, Terrestrial Ecosystems, and Associated Water Bodies. (Howarth, R.W., Stewart, J.W.B. & Ivanov, M.V. Chapter 3, Scope 48. Bates, T. S., Cline, J. D., Gammon, R. H. and Kelly
- Hansen, S. R., 1987. Regional and seasonal variati ons in the flux of oceanic dimethylsulfide to the atmosphere. J. Geophys. Res., 92, 2930
- 2938. Capaldo, K., Corbett, J.J., Kasibhatla, Fischbek, P. and Pandis, S.N. 1999. Effects of ship emissions on sulphur cycling and radiative climate forcing over the o cean. Nature 400: 743
- 746. Carlson, H. 1986. Quality Status of the North Sea. Dt. hydrogr. Z. Erg.
- H. B 16: 1
- 424. CEPE (European Council of Paint, Printing Ink and Artists’ Colours Industry), 1999. Utilisation of more ‘environmentally friendly’ antifoulin g products, EC project No. 96/559/3040/DEB/E2, Phase 1
– Final report. Charlson, R.J., Lovelock, J.E., Andrea, M.O. and Warren, S.G. 1987. Ocea nic phytoplankton, atmospheric s ulphur, cloud albedo and climate. Nature 326: 655
- 661. CIEC The Essential Chemical Industry, 1999. Chemical Industry Information Centre, University of York, 4th ed. Colijn, F. and G.C. Cadée 2003. Is phytoplankton growth in the Wadden Sea light or nitrogen limited? J. Sea Res. 49: 83
- 93. Corbett, J.J. and Fischbek, P.S. 1997. Emission s from ships. Science 278: 823
- 824. Corbett. J.J., Fischbeck P.S., and Pandis S.N. 1999. Global nitrogen and sulfur emissions inventories for oceangoing ships. J. Geoph. Res. 104: 3457
– 3470. Det Norske Veritas 1999. Reference values for ship pollution. Technical report No. 99
- 2034, 59p. Dethlefsen, V., 1990. Ende der Verklappung von Abfällen aus der Titandioxidproduktion in der Nordsee. SDN EFMA European Fertilizer Manufactures Association, 2000. Best Available Techniques for Pollution Prevention and Cont rol in the European Sulphuric Acid and Fertilizer Industries. Booklet No. 3. Brussels, Belgium. 68 p. Entec, 2002. Quantification of emissions from ships associated with ship movements between ports in the European Community. Final Report, July 2002. Glen na, K. and Tokerud, A., 1991. Unique FGD process uses sea water as absorbent. Desulphurization of flue gases without chemicals in a Norwegian oil refinery. ABB review 4: 9
- 12. Hameed, S. and Dignon, J. (1988). Changes in the geographical distributions of g lobal emissions of NO x and SO x from fossil
-fuel combustion between 1966 and 1980. Atmospheric Environment, 22, 441
- 449. Holland, H.D. 1978. The Chemistry of the Atmosphere and Oceans. John Wiley & Sons, New York, pp. 351. Hollemann, A.F. and Wiberg E., 198 5. Lehrbuch der Anorganischen Chemie. 91.
- 100. ed., Walter de Gruyter, Berlin.46

Hunter, K.A,. 1998. The temperature dependence of pH in surface seawater. Deep Sea Res. Pt. I 45: 1919
- 1930. IMO
– International maritime organization, 2000. Study of Greenhouse Gas Emissions from Ships. Final report. Issue no. 2
- 31 March 2000 Isensee, J. (1997): Energieverbrauch und Luftverschmutzung
- ein Vergleich zwischen Schiffen und anderen Transportfahrzeugen. Institute of Ship Construction, University Hamburg Isensee, J . 2001. Reduction of CO 2 and other gaseous emissions from shipping by switching from residual fuel to sulphur free diesel. Proposal to the German members of MEPC. Leendert R. and Kwint J. 1997. The origin of DMS(P)cies. Proefschrift Rijksuniversiteit Groni ngen. Lohse, L. 1996. Sediment
- water exchange of nitrogen compounds and oxygen in the North Sea. Dissertation, Rijksuniversiteit Groningen, pp. 86. Lovelock, J. E., Maggs, R. J. and Rasmussen, R. A., 1972. Atmospheric dimethylsulphide and the natural sulphu r cycle. Nature, 237, 452
- 3. Moller, D. (1984). Estimation of the global man
- made sulphur emission. Atmos. Environ., 18, 19
- 27. Nguyen, B. C., Bergeret, C. and Lambert, G., 1984. Exchange rates of dimethyl sulfide between ocean and atmosphere. In: Brunsaert, W. and Jirka, G. H. (Eds). Gas Transfer at Water Surfaces. Reidel, Dordrecht, pp. 539
- 45. Nyman, G.B.G. and Tokerud, A., 1991. Seaw ater scrubbing removes SO 2 from refinery flue gases. Oil & Gas Journal, July 1, 1991. Rat von Sachverständigen für Umweltfragen 1981. Umweltprobleme der Nordsee. Deutscher Bundestag Drucksache 9/692 1
- 503. Schlesinger, W.H. 1997. Biogeochemistry: an analysis of global change. Chapter 13.m Academic Press, California. Schulz, M., van Beusekom, J., Bigalke, K., Brockmann, U., Da nnecker, W., Gerwig, H., Grassl, H., Lenz, C.
- J., Michaelsen, K., Niemeier, U., Nitz, T., Plate, E., Pohlmann, T., Raabe, T., Rebers, A., Reinhardt, V., Schatzmann, M., Schlünzen, K.H., Schmidt
- Nia, R., Stahlschmidt, T., Stienhoff, G. & von Salzen, K. 1998
. The atmospheric impact on fluxes of matter and energy in the German Bight. KUSTOS/TRANSWATT Abschlußbericht 1: 97
- 130. Sciare, J., Mihalopoulos, N. and Dentener, F.J., 2000. Interannual variability of atmospheric dimethylsulfide in the southern Indian Ocean. Journal of Geophysical Research 105: 26,369
- 26,377. Sinninghe
- Damsté, J.S., Kohnen, M.E.L. and Horsfield, B., 1998. Origin of low
molecular
- weight alkylthiophenes in pyrolysates of sulphur
- rich kerogens as revealed by micro
- scale sealed vessel pyrolysis. Organic Geochemistry 29: 1891
- 1903. Smith, S. J., H. Pitcher and T. M. L. Wigley 2001. Global and regional anthropogenic sulphur dioxide emissions. Global Planet. Change 29 : 99
- 119. Smolyakov, B.S., Belevantsev, V.I., Zhigula, M.V., and Ryzhikh , A. P. , 2000. Effect of transformation of the copper and lead species on their behaviour in real fresh water ecosystems. Environ. Sci. & Poll. Res. Abstracts of 17 th FECS Conference 2000. Tokerud, A. 1989. Seawater used as SO 2 removal agent. Modern Power System , June 1989, 9 (6): 21
- 25.47

United Nations Framework Convention on Climate Change (UNFCCC), Special issues in carbon/energy taxation: Marine bunker charges, Working paper 11, 1997. (http://www.oecd.org/env/docs/cc/gd9777.pdf) US EPA, 1976. Quality criteria for water. U.S. Environmental Protection Agency, Washington DC, Report No. EPA
- 44019
- 76
- 023, July 1975, 501. Van Oudenhoven, J.A.C.M., Cooper, G.R., Cricchi, G., Gineste, J., Pötzl, R. and Martin, D.E. 1995. Oil refinery waste, disposal methods and costs 1 993 survey. CONCAWE Report 1/95: 1
- 39. Wasmund, N., Andrushaitis, A. , Lysiak
- Pastuszak, E., Müller
- Karulis, B., Nausch, G., Neumann, T., Ojaveer, H., Olenina, I., Postel, L., and Witek, Z. 2001. Trophic status of the south
- eastern Baltic Sea: a compariso n of coastal and open areas. Estuar. Coast. Shelf Sci. 53: 849
- 864. Weichart, G. 1975. Untersuchungen über den pH
- Wert im Wasser der Deutschen Bucht im Zusammenhang mit dem Einbringen von Abwässern aus der Titandioxidproduktion. Dt. Hydrogr. Zt. 28: 2443
- 2 52. Whelpdale, D.M. 1992. An overview of the atmospheric sulphur cycle. In: Sulphur Cycling on the Continents
- Wetlands, Terrestrial Ecosystems, and Associated Water Bodies. (Howarth, R.W., Stewart, J.W.B. & Ivanov, M.V. Chapter 2, Scope 48. Zidouri, H., 2000. Desalination in Morocco and presentation of design and operation of the Laayoune Seawater Reverse Osmosis Plant. Proceedings of the Conference on Membranes in Drinking and Industrial Water Production, Volume 1, pages 293
– 301.

Internet sites Advances in power technology, issue 4: http://www.powertech.co.uk/downloads/R&D/fgdSeaWater.pdf US
- EPA What are the Major Effects of Common Atmospheric Pollutants on Water Quality, Ecosystems, and Human Health? http://www.epa.gov/owow/oceans/airdep/air3.html pH ranges that support aquatic life. http://www.bpa.gov/corporate/kr/ed/kidsinthecreek/materials/waterquality/graph. htm Oceanography
- Salt balance, residence times, element addition and removal. http://www.ncl.ac.uk/