Mercury

Environmental Chemistry
Part 5 Typical Pollutants
5.1 Typical Pollutants in the Environment

Typical Pollutants in the
Environment
• Typical inorganic pollutants
Heavy metals: Hg, Cd, Pb, Cr, Zn, Cu, Sn, Ba;
As, etc.
Inorganic salts: cyanide、Nitrogen
salts(ammonium salts 、nitrates、 nitrites)、
sulfides、 fluoride, etc.;
Radioactive species:Natural( 3 H, 235 U, 226 Ra)、
Man-made ( 60 Co, 137 Cs)

• Typical organic pollutants PAHs
Organic halides:halogenated hydrocarbon 、
PCBs、Dioxins
Surface active agent : anionic surfactant 、
cationic surfactant 、 amphoteric surfactant 、
nonionic surfactant

Environmental Chemistry
Part 5 Typical Pollutants
5.2 Mercury (Hg)

Mercury (Hg)
1. Source and Distribution of Mercury
in the Environment
• Abundance ratio :63 rd in the Earth’s Crust,80
mg/kg; 40 th in the Ocean,0.15 mg/L
• Forms:nonvalent mercury、univalent mercury、
bivalent mercury
• Distribution:low concentration、broad
distribution;all kinds of rocks;absorption
medium;animals and plants
• Source of pollution:waste water containing
mercury、waste gas and waste residue-from
factories using or producing mercury or mercuric
compounds.

Water: industrial sewage - chlorine alkali 、
plastics、 electronics industry 、
amalgamative ore-refining industry and
fulminating mercury ;
Soil:pesticides containing mercury and sludge
manures;
Air:waste gas containing mercury and
grainnessed mercury-ore-refining、burning
of coal and oil
Air→Soil→Water
Annual produced quantity:>10,000t →
“three wastes”

2. Transport and Transformation of
Mercury in the Environment
• Properties of Mercury
II subgroup element(Cu, Zn), similar to Cu in
chemical and geochemical properties
Specificities:
1) Relatively high oxidation-reduction potential,
presents metallic state;
2) Elementary Substance Hg and its chemical
compounds are highly volatile,p300 chart 6-1
Hg>Hg 2 Cl 2 >HgCl 2 >HgS>HgO; organic
mercury>inorganic mercury; methyl mercury /
phenyl mercury>other organic mercury;

3) Hg: the only metal in the form of liquid
under normal temperature;can
dissolve many metals and form
amalgam ( 汞 齐 ) (Na, K, Au, Ag, Zn, Cu,
Sn, Pb);
4) Covalence( 共 价 性 ): Mercury
compounds>Znic compounds
The high volatility, mobility and covalence of
mercury and its compounds make easy their
transport and distribution in the environment.

Mercury in the air
• come from volatilization of mercury and its compounds
• The volatility and forms of mercury compounds are closely
related to their solubility in water, surface absorption and
atmospheric relative humidity (RH), etc. p300 chart 6-1
• Due to their high volatility, mercury compounds can be
easily released into the air through transpiration( 蒸 腾 作 用 )
of soil and plants.
• Mercury in the air are mostly absorbed onto particulate
matters( 颗 粒 物 )
• Gaseous mercury finally enter into soil and marine
sediments.

Mercury in the water
• The existing forms of mercury compounds and their
transport and transformation in the environment are
directly related to solubility in water.
1) Hg solubility at 25 o C: 60 mg/L in pure water,25 mg/L in
deoxidized water;
2) Water-soluble salts:HgCl 2 , HgSO 4 , Hg(NO 3 ) 2 , Hg(ClO 3 ) 2 ;
3) Organic mercury:
water insoluble: diethyl mercury( 乙 基 汞 ) (CH 3 CH 2 ) 2 Hg
and ethylmercuric chloride( 氯 化 乙 基 汞 )CH 3 CH 2 HgCl;
slightly soluble:mercury phenylacetate( 乙 酸 苯 基
汞 )PhHgAc;
mercury acetate( 乙 酸 汞 )HgAc 2 has the highest solubility.

4) Hg 2+ can easily form complex compounds ( 络
合 物 ) in the water,ligancy( 配 位 数 ) is
commonly 2 or 4; Hg 2
2+
are much less likely
to form complex compounds than Hg 2+ .

• In oxidizing natural water,
mercury are mostly in the forms of
bivalent mercury (HgCl 2 , Hg(OH) 2 )
and elementary mercury (Hg 0 ) ;
• In the forms of HgCl 3- 、 HgCl 4- in
marine water with high Cl -
concentration;
• In the forms of ethiopsite ( 硫 化 汞 )
in reduced water containing sulfur
(e.g. soil seeper) ;
• In the substrate sludge of water,
inorganic mercury can be
transformed into methyl mercury
by microorganizm.

Mercury in the soil
• Over 95% of the mercury entering the soil can be
retented or fixed by soil. Clay minerals and
organic matter in the soil have strong absorption
toward mercury. Thus, mercury accumulates
easily in the surface of soil.
• Amicrobic transformation:2Hg + = Hg 2+ + Hg o
• Microbic :HgS(thiobacillus 硫 杆 菌 )→ Hg 2+ (antimercury
bacteria 抗 汞 菌 )→ Hg 0
• Methylation of mercury (See Bioconversion of
Pollutants)

Mercury in the organizm
• Inorganic mercury compounds can easily be discharged
from organizm.
• Combined with macromolecules in the organizm, mercury
can form stable organic complex compounds which are
difficult to be discharged.
e.g. cysteine( 半 胱 氨 酸 ) and albumin( 白 蛋 白 ) can form
highly stable complex compounds with mercury, even
higher is the stability constant K of complex compounds
with methyl mecury, logK=15.7, 22.0

The methylation process of
mercury inside the organizm
1) Main products: aerobic, CH 3 Hg + ; anaerobic, (CH 3 ) 2 Hg
2) CH 3 Hg+: water-soluble, taken by organizm and enter the
food-chain
(CH 3 ) 2 Hg : water-insoluble, volatile, photolytic
3) Formation speed: methyl mercury>dimethyl mercury
4) reciprocal transformation:
CH 3 Hg +
H 2 S
pH4-5
(CH 3 ) 2 Hg
6,000 times
5) peccant materiel( 致 病 性 物 质 )of minamata disease:
methyl mercury, dimethyl mercury, propyl mercury
6) Accumulation: With high fat-solubility, mercury alkyl is
more easier to be concentrated than non-alkyl mercury
and is difficult to degrade.

Methyl mercury
Inorganic mercury in waste water is absorbed by particulate
matter and settle to the bottom of the water body, then
methylated by the microbic transferase.
Methyl mercury can also combine with Cl - or OH - and
generate methyl mercuric chloride ( 氯 化 甲 基 汞 ) or methyl
mercuric hydroxide ( 氢 氧 化 甲 基 汞 )
neutral or acid conditions, methyl mercuric chloride is
dominant
pH=8, [Cl - ]

Dimethyl mercury
Under anaerobic conditions, undersaturated methyl
metals are completely methylated.
p303

• Demethylation of methyl mercury and
reduction of mercury ion
Pseudomonas( 假 单 胞 菌 属 )
Methyl mercury is degraded into methane and
mercury.

Transport and Transformation of
Mercury in Environmental Elements
• Due to high volatility, mercury and mercury
compounds entering the soil can be released
into air through the transpiration by soil and
plants and can also enter into surface or
underground water through precipitation.
• In natural water body, mercury is mainly aborbed
by the suspended particulates and finally
become water sediments.
• Environmental factors such as pH and contents
of suspended particulates affect the absorption.

• In the bottom material of a river, mercury is
• related to the transport and transformation of
organic matter, of which suspended mercury is the
main form of mercury transport. Under the effect
of microorganizm, mercury in the bottom soil can
be transformed into methyl mercury, which is
water-soluble and thus released back into water.
• Methyl mercury taken by Aquatic organizm can
accumulate inside the organizm and concentrate
along the food-chain. Fish contaminated by
mercury has an inside concentration of mercury
over 100 times higher than the outside
concentration of mercury in the water.

. Hazards of Mercury Pollution
• Mercury’s damage to human health depends on the chemical
state, environmental conditions of mercury and the ways of
entering the human bodies.
• Mercury vapor is highly diffusible and fat-soluble. It gets
through the respiratory tract and is carried through the whole
body by blood circulation. A large inhalation of mercury vapor
can cause acute toxication such as hepatitis( 肝
炎 ),hepatonephritis( 肾 炎 ),hematuria( 尿 血 ) and uraemia( 尿
毒 ),etc.
• The toxicity effect of organic mercury inside the human body is
related to the organic radicals. Short-chained derivatives of
mercury alkyl are more toxicant than aryl mercury( 芳 基 汞 ) and
methoxyl-ethide mercury compounds( 甲 氧 基 乙 基 汞 化 合 物 ).

Hazards
• Inhibiting a series of SH enzymes, thus damaging
the basic functions and metabolism of cells as well
as the detoxificating function of liver, destroying the
cellular ionic equilibrium by changing the
membrane permeability, preventing the nutrition
from entering the cells and causing the ions to
diffuse from inside the cells, finally bringing death
to the cells.
• Chronic intoxication of mercury includes
neuropathic
symptoms such as headache, faintness, limp
numbness, aches, muscle quivering and ataxia, etc.

. Prevention of Mercury pollution
• Improve traditional techniques, adopt substitute
materials and reduce the use of mercury.
• Sealed storage; prevent leaking when using; in case of
dropping, cover with sulfur powder.
• Treatment of waste water containing mercury
Settling method :add sulfide to form HgS, through
settlement and centrifugation.
Ion-exchange method:pump in chlorine gas to transform
elementary mercury into ionic mercury, then add chloride to
change it into anionic complex compounds, and then
remove it using anion exchange resin. Sometimes using
cation exchange resin to treat waste water with a low
concentration of Cl-.

Coagulation method:using alum, iron salts and limes,
etc. as the coagulant
Absorption method:Using active carbon or other
natural macromolecular compounds with strong chelating
power.
Reduction method:ionic mercury is reduced to
elemetary mercury and then filter the waste water.
reducing agent: Al, Zn, SnCl2 etc.
Ion-exchange method/ Coagulation method using iron
salts or aluminum salts/ Absorption method using active
carbon can reduced the concentration of dissolved
mercury in the water to lower than 0.01 mg/L;
The combination of Settling method using sulfide and
Coagulation method can reduce the concentration of
dissolved mercury to 0.02 mg/L;Reduction method is
used when the concentration of mercury in the waste
water is very low.

Environmental Chemistry
Part 5 Typical Pollutants
5.3 Polychlorinated Biphenyls (PCBs)

polychlorinated biphenyls
(PCBs)
• Structure and characteristics of PCBs
209 isomers ( 异 构 体 )
Commonly 3~6 hydrion is substituted by chlorine ion, the
content of Cl is as much as 42%~54%
PCBs with less Cl content is usually in the liquid state. The
more Cl content, the higher the viscosity. As for the external
appearance, it varies from transparent liquid to white
crystallines.

asic characteristics of PCBs
1) Highly stable both chemically and physically; resistant to
heat, acid, alkali, corrosion and oxidation; non-corrosive to
metals.
2) Difficult to dissovle or insoluble, soluble to oil or organic
dissolvant (particularly chloride with high Cl content), also
inter-soluble with plastics.
3) Incombustible except monochloro and dichlor substitutes.
4) Fine adhesive and extensive propeties.
5) Low vapor pressure and volatility (particularly chloride with
high Cl content)
6) High specific inductive capacity (SIC), fine insulativity and
electrochemical properties.

The uses of PCBs
• As the insulative fluid in the transformers and capacitors;
• As the medium in the heat-exchange systems and hydrolic
systems;
• As the additives in the production of lubricant, cutting oil,
pesticide, paint, manifold paper, mastic and encapsulant,
etc;
• As the plasticiser in the production of plastics.
Commercial production of PCBs began in 1930 and
were gradually banned after 1977. PCBs is listed
among the organic pollutants in priority control in
many countries.

Transport and transfomation of
PCBs in the environment
• Since the production of PCBs, it is estimated that over half of
the related products have entered the gabbage dumps. The
combustion of such kinds of gabbage release PCBs to the
atmosphere.
• For the difference in climatic, biological, hydrographical and
geological factors, etc. , the PCBs in the environment
undergo a series of transport and transformation. PCBs are
finally stored up mainly in soil, rivers and the bottom soil
along the water bodies.
• PCBs is water-insoluble and have high octanol-water
partition coefficient, thus are more easily distributed among
settled organic matters and soluble organic matters.

Transport and transfomation of
PCBs in the atmosphere
• PCBs enter into the atmosphere during the process of
using and disposing.
• The depletion of different PCBs depends on their
environmental, phycial and chemical properties.
• There are two main ways of depletion of PCBs in the
atmosphere: direct photodecomposition; reaction with
radicals like OH and NO 3 and also ozone.
The radical OH has the most influence. The half-life of
the reactions with PCBs activated by OH is 2~34 days; with
every one more Cl ion in the PCBs molecule, the reactivity is
reduced in half.

The atmosphere is purified of PCBs through
rainwater flush and dry or wet precipitation, the
process of which transports the pollutants from
atmosphere to water or soil.
Hydrophobic organic matters in the atmosphere
are mainly in gaseous state or absorpt state. PCBs in
the gaseous state and PCBs absorpt by particulate
matters can reach the earth’s surface through dry or
wet precipitation such as gas phase absorption,
gravitational settling and eddy diffusion, etc.

he transport of PCBs in soil
• PCBs continuously enter into soil in different ways.
• Precipitaion of particulate matters is the main resource of
PCBs in soil, while they are also partly from the sludge manure,
leakage from the landfill and the prepartion of pesticides, etc.
It is reported that the content of PCBs in the soil are in
most cases over 10 times higher than that in the air above.
• Except temperature, some other environmental factors such as
clay content and the level of choloridization of PCBs also have
some effect on the volatilization of PCBs in the soil.
Biodegradation and invertible absorption contribute little to
the depletion of PCBs.
• Only the process of volatilization is most likely to cause the
depletion of PCBs, especially those having more Cl content.

The transport of PCBs in water
• PCBs enter into water (rivers, lakes and coastal water
bodies) mainly through the process of atmospheric
precipitation and the discharge of industial sewage,
etc.
• PCBs in water is low in amount is low due to their
high volatility and low solubility in water.
• PCBs are absorpt easily by particulate matters so that
PCBs in water are mostly contained on the surface of
suspended particulate matters and finally settle to the
bottom soil. Thus, PCBs in the substrate sludge is 1 to
2 times higher in amount than that in the water around.

PCBs in the substrate sludge can not easily be
transported or distributed, which makes them stay in the soil
for a long time. Also due to their high fat-solubility, PCBs are
easily accumulated and concentrated in the organism.
Hydrolic systems including substrate sludge and soil, etc.
act as a very important deposition utensil to PCBs and other
hydrophobic organic compounds. With the disappearing of
primary pollution sources, they are likely to become the
secondary pollution sources and release PCBs to the
environment.
The settled PCBs in the environment will continuously
disperse to the oceans and cause the decreasing biotic
population and aggravate the damage to the biological
environment.

The transformation ways of PCBs
in the environment
• PCBs become persistent organic pollutants in the envrinment
(POPs) due to its chemical inertia.
• Main transformation ways of PCBs include photochemical
decomposition and biotransformation.
• Photochemical decomposition :p314 The agitation of ultra
violet can cause the breaking of C-Cl bond and produces aryl
radicals and chlorine radicals.
• Biodegradation:PCBs can be degraded by pseudomonads( 假 单
胞 菌 ), etc. The less Cl content, the more easy the biodegradtion.
• Transformation in internal animals:except accumulation, PCBs
can also undergo transformation through metabolism, the
speed of which is reduced with more chlorine ions in the
molecule.

Hazards of PCBs
• Affect the growth of aquatic plants;
at 0.1-1 mg/L, reduce photosynthesis;
at 10-100 mg/L, inhibit the growth of aquatic plants.
• Most species of fish are senstitive to PCBs during all stages
of their growth. 。
• The absorbtion of PCBs by birds can cause the expansion
and damage of liver and kidney, internal bleeding, collapse
of lien and thickened eggshell, etc.
• PCBs can induce a series of symptons to mammals such as
adenoma and cancer.
• PCBs can cause skin ulcers, acnes, hydatoncus, liver
damage and the increase of leukocytes, etc. Except causing
cancers, PCBs can also be spread to infants and cause
monstrosity.

Degradation of PCBs
• Substrate sludge contains more PCBs with less Cl
content while upper sludge contains more PCBs with
more Cl content, because in the upper strata active soft
soil, PCBs with less Cl content are easily degraded by
microorganizm while PCBs with more Cl content are
relatively stable.
• Water solubility is also a factor. PCBs with higher solubility
are easily biodegraded.
• There is a marked concentration of PCBs when it comes
to biodegradation, which is the lowest required
concentration of PCBs for them to be biodegraded.

Treatment of PCBs
• Mainly include sealing and storage, hightemperature
treatment, chemical treament and
biodegradation, etc.
• Combustion at high temperature is a developed
treatment way for PCBs which will be degraded
completely in 2 seconds at 1200 o C but needs to
prevent the production of dioxins, a significant
canceroge.
• Sealing and storage is a temporary way of
treatment and can’t solve the problem of PCBs
pollution fundamentally.

1) Sealing and storage
• To seal and store the disposed transformer oil
containing PCBs in certain stockhouses or
bury them deeply in concrete pools or store
them in remote caves, waiting for further
treatment.
• However, it would bring risks to the
environment due to the possible leakage of
PCBs from the rusty crust to the surounding
area.

2) High-temperature treatment
• It’s the most common way for treatment of PCBs at
present.
• Simple combustion: By adding a large amount of
fuel and dissolvant, the temperature is raised to up
to 1200 o C-1600 o C in several seconds so that the
disposed transformer oil containing PCBs can
combust and transform into other compounds.
disadvantages: the production of dioxins, benzfuran
and other secondary pollutants.

Fusion medium method( 熔 融 介 质 法 ):using some
inorganic medium such as metals and inorganic
salts, etc. instead of air as the medium for heat
transfer and reaction during the process of
combustion.
This method would not produce dioxins and other
related pollutants and doesn’t have strict
requirements for the samples, but high expense is
needed in the treatment of waste gas and residue.
Plasma method: a technology using plasma as the
heat source, high cost.

3) Chemical removal method
• Under certain conditions, reaction between the
added reagents and PCBs would remove chlorine
from PCBs and produce diphenyl compounds or
other intoxicant or slightly toxicant matters.
• Advantages: complete treatment of waste; simple
equipment that can be easily carried by car after
simple design; applicable to the treatment of
centralized and concentrated PCBs waste, while
also applicable to scattered waste with a low
concentration of PCBs.
• Mainly include:metal reduction method,
hydrogenation method, vulcanization method and
oxidization and chlorinization method, etc.

4) Biodegradation
• A potential method only applicable to waste with
a low concentration of PCBs and slow reaction.
• A combination of primary UV treatment and
secondary microorganizm treamtment is also
practical for the degradation treatment of PCBs.
A thorough and environment-friendly way
for PCBs degradation is badly needed to
solve this tough global problem.

Environmental Chemistry
Part 5 Typical Pollutants
5.4 Surface Active Agent

surface active agent
• Definition: under a low concentration, surface
active agent can fix on to the surfaces of two
phases of a system, through changing the interface
properties, significantly reducing the surface
tension and altering the interface state, thus
causing wetting and dewetting, emulsification and
deemulsification, bubbling and debubbling and
producing solubilizing matter under relatively high
concentration.

Principles
• Surface active agent’s ability to fix on to the interface and
change its properties is due to its amphiphilicity( 两 亲 性 ).
• Molecular structure nonpolar lipophilic group and polar
hydrophilic group;
• Lipophilic group: hydrocarbon chain, polyoxyalkylene chain( 聚
氧 丙 烯 链 ) , fluorocarbon chain( 碳 氟 链 ), silane chain( 硅 烷 链 ),
etc.
• Hydrophilic group: -COOM, -SO 3 M, -CH 2 -CH 2 -O-( 聚 氧 乙 烯 链 )
• Not all molecules with amphiphilic structure are surface active
agents, like sodium formate with a short lipophilic group, thus
it’s not lipophilic enough to become surface active.

Classification and properties
of surface active agent
• Ways of classification: according to the use,
properties and chemical structure;
• Surface active agents are internationally
classified according to the type of the
dissociated surface active ions in water, as the
following:
1. anionic surfactant
2. cationic surfactant
3. amphoteric surfactant
4. nonionic surfactant

1. Anionic surfactant
• The hydrophilic group linking with hydrophobic group is an
anion when anionic surfactant dissovles in water.
• carboxylate:eg. soap RCOONa
• xanthagenate :eg. sodium alkyl benzene sulfonate( 烷 基 苯
磺 酸 钠 )
• sulfuric acid ester salts( 硫 酸 酯 盐 ):eg. sodium lauryl
sulfate( 硫 酸 月 桂 酯 钠 ) C 12 H 25 OSO 3 Na
• organic phosphate salts( 磷 酸 酯 盐 ):eg. sodium alkyl
phosphate( 烷 基 磷 酸 钠 )

2. Cationic surfactant
• The hydrophilic group linking with hydrophobic
group is a cation when cationic surfactant
dissovles in water. ;
• Mainly include the derivatives of orgainic amine( 有
机 胺 ), commonly quarternary ammonium salt( 季 胺
盐 ) like hexadecyl trimethyl
ammonium bromide
( 十 六 烷 基 三 甲 基 溴 化 铵 )
• Aqueous solution of ationic surfactant is highly
disinfectant and thus broadly used as fungicide.

3. Amphoteric surfactant
• It’s the surface active agent composed of both
anionic and cationic ions, the molecular structure of
which is similar to amino acid and the properties of
which in aqueous solution varies with pH.
• Under alkaline condition it presents
anionic properties;
• At isoelectric point it presents nonionic properties;
• Under acid condition it presents cationic properties;
• Can form internal salts inside the molecule;
• Low toxicity, easy biodegradation, fine effects of
rinsing, emusifying, anti-corrosive, disinfectant and
antistatic, etc.;
• High cost, low dosage, potential and promising

4. Nonionic surfactant
• Nonionic surfactant doesn’t disassociate as ions in
aqueous solution but appears in the forms of
molecule or micelle.
• lipophilic group: commonly hydrocarbon chain or
polyoxyalkylene chain( 聚 氧 丙 烯 链 ) ;
• Hydrophilic group: etheriality( 醚 基 ) and hydroxy( 羟
基 )
• Nonionic surfactants are stable in netrality, acid,
slight alkaline conditions and hard water.
• Broadly used in textile, dye printing, metal purging,
food production and pesticide emulsification and
some other industries.

The properties of surface active agent depends
on their chemical structure, related to the
following factors: hydrophilicity, the relative
position of hydrophilic groups, the size of
molecules and the hydrophobic groups
1) hydrophilicity (HLB) is the equilibrium ratio of
the surface active agent’s hydrophilicity and
lipophilicity:
HLB=hydrophilicity of hydrophilic groups
/hyrophobicity of hydrophobic groups
Surface active agent’s HLB value is related to the
HLB value of each of its radicals, the computing
of which is :
HLB=7+Σ(HLB of hydrophilic groups)-Σ(HLB of
hydrophobic groups)

2) the relative position of hydrophilic
groups
• A molecule has stronger wettability when its
hydrophilic groups are located in the middle rather
than at the end of the chain, like the following
molecule, a famous penetrant:
• A molecule has better dirt removing power when its
hydrophilic groups are located at the end rather
than in the middle of the chain, e.g.:
• C 16 H 33 OCOCH 2 CH(SO 3 Na)COOH has better dirt
removing power

3) the size of molecules
• Small-sized surface active agents have better
wettability and permeability;
• Large-sized agents have better ablution ( 洗 涤
作 用 ) and dispersant effect ( 分 散 作 用 ).
e.g. the order of the ablution effectiveness of
alkyl sodium sulfate surface active agent is as
follows:
C 16 H 33 SO 4 Na> C 14 H 29 SO 4 Na> C 12 H 25 SO 4 Na
• Concerning wettability, it appears the
opposite.

4) hydrophobic groups
• The order of lipophilicity of surface acitve
agents with different hydrophobic groups is as
follows:
Fatty alkane 脂 肪 族 烷 烃 >cyclane
环 烷 烃 >fatty alkene 脂 肪 族 烯 烃 >fatty aromatic
hydrocarbon 脂 肪 族 芳 烃 > aromatic hydrocarbon
芳 香 烃 >hydrocarbon with weak hydrophilic
groups 带 弱 亲 水 基 团 的 烃

source and pollution of surface
1. source:
active agent
• 1960s, already largely used in detergent industry
• 1999, global annual use reached 9.3 million t
• 2000, global annual use reached 10.8 million t
• 2005, global annual use reached 12.5 million t
• A large portion of used surface active agent enters
waste water.
• The problem of the degradation of surface active
agent requires attention from environmentalists.

2. hazards
1) Surface active agent is a source material for producing
detergents. As organic matter, synthetic detergents can be
bio-degraded, consuming the dissolved oxygen in the water.
Permernant bubbles appear when the concentration of
surface active agent reaches .
Anionic surfactant produces bubbles in water more
easily than other surfactants.e.g. in 1963,a 0.6 m-thick
sheet of bubbles appeared on the surface of Ohio river
of America, due to the pollution of detergents;
The speed and level of reoxygenation in bubble-covering
river will be largerly reduced. e.g. the pollution of
detergents in Thames river of Britain caused water
deoxidation and people could even smell hydrogen
disulfide along the river.

2) The large amount of phosphates such as trimeric
sodium phosphate ( 三 聚 磷 酸 钠 Na 5 P 3 O 10 )
contained in detergents can cause eutrophy( 富 营
养 化 ) to the water bodies. It’s estimated in Britain
and U.S. and other other countries that 30%~75%
phosphorus in the urban sewage comes from
detergents. Also due to the large amount of
discharged waste water, it would constitute
hazards to aquatic plants and fish.
3) Surface active agents can accelerate the
emulsification and dispersion of petrol, PCBs and
other indissolvable organic matters in water, thus
raising the difficulty of waste water treatment.

4) The sterilization of high-concentrationed cationic
sufactant can make demages to the aquactic
microorganizm communities.
5) The strong dissolving capacity of detergents
toward unctuous matters can damage the
gustatory organ of fish, thus depriving them the
ability to avoid toxicant matters and look for food.
It’s reported that fish can not survive in water
with detergents at a concentration of over
10mg/L.

he degradation of surface active
agent
• It means under the environmental factors,
the molecular structure of surface active
agents is changeg, from environmentharmful
matters to environment-friendly
molecules such as CO 2 , NH 3 and H 2 O.
• Mainly include bio-degradation and
photodecomposition.

1. Bio-degradation of surface
active agent
• priciples:the depletion of surface active agent
entering the water environment depends mainly on
degradation by microorganizm, the principle of which
includes the oxidation of methyl on the methyl-chain
(ω-oxidation), β -oxidation, the oxidation of aromatic
ring and 脱 磺 化 。
1) Methyl oxidation means the oxidation of the methyl at
the end of the hydrophobic groups of surface active
radical and then the respective production of of
formyls ( 醛 基 ) and carboxyls ( 羧 基 ).

2) β -oxidation
• Carboxylic acid in the surface active agent
molecue is oxidized under the effect of A
coenzyme ( 辅 酶 A) and the second carbon
bond breaks.
3) The process of desulfonation
The process of desulfonation happens in the
alkyl chain oxidation of both branched-chain
and linear alkylbezene sulfonates.

4) Oxidation of aromatic
compounds
• The ring-opening process of phenol ( 苯 酚 ) and
salicylic acid ( 水 杨 酸 ) and other compounds includes
the primary production of pyrocatechol ( 邻 苯 二 羟 基 ),
the secondary split of two hydroxyls ( 羟 基 ), and then
the production of dicarboxylic acid ( 二 羧 酸 ) and the
final disappearing.

The effect of the structure of
surface active agent on bio-degradation
1) Cationic surfactant
The bio-degradation of cationic surfactant requires
aerobic conditions. The order of the ability of being biodegraded
of three types of alkylbenzene sulfonates (ABS)
with different structures of hydrophobic groups is as follows:
Linear ABS (LAS)>ABS substituted by a branch-chain at the
end of the group>trimethy ABS
As for those cationic surfactants difficult being degraded, we
can prepare them together with other types of surface active
agents in order to raise its bio-degradation. e.g. trimethyl
dodecyl ammonium chloride ( 三 甲 基 十 二 烷 基 氯 化 铵 )
couldnot be degraded even in 27h while it can be easily
degraded once being mixed with LAS at the radio of 1:1.

2) Anionic surfactant
• Anionic surfactants such as LAS and AES ( 脂 肪 醇 醚 硫
酸 盐 ) constitute a large portion of surface active agents
contained in detergents.
• LAS degrades the most quickly in all the detergents,
which can be hydrolysed by sulfatase to sulfates and
some related fatty alchohol ( 脂 肪 醇 ) and finally further
oxidized to CO2 和 H2O.
• As for LAS, the degradation speed grows with the
farther distance between the sulfo ( 磺 基 ) and the end of
the methyl chian and it degrades the most quickly with
the number of carbon atoms of the methyl between
6~12. The effect of branch-chain is similar to that of
nonionic surfactants.

3) nonionic surfactants
• Easiness for degradation:
linear molecule>normal branch-chain
molecule
molecule with alkyl>molecule with phenyl
Linear carbinol and disubstituted carbinol
oxyethyl compounds can be effectively
degraded by microorganizm in the activated
sludge.

The relationship between molecular
structure and the bio-degradation of
surface active agent
• The biological degradability of surface active agent depends
mainly on the hydrophobic groups. With the linearity ( 线 性 程
度 ) of hydrophobic groups, the degradability of the
quaternary carbon atom at the end of the chain is
significantly reduced with more hydrophobic groups;
• The properties of the hydrophilic groups also have some
influence on the biological degradability. e.g. LPAS( 直 链 伯 烷
基 硫 酸 盐 ) has higher primary bio-degradation speed than
other anions; short-EO-chain polyoxyethylene ( 聚 氧 乙 烯 )
nonionic surfactants are bio-degraded more easily.
• The increase of the distance between between the sulfo ( 磺
基 ) and the end of the hydrophobic groups can raise the
primary bio-degradability of methyl benzene sulfonates
(distance principle).

2. Photodiscomposition of
surface active agent
• Photocatalysic degradation and oxidation are technologies
developed in the recent 30 years.
• Advantages: low cost, mild reaction conditions, no
secondary pollution.
• Reaction speed:
anionic>cationic
aromatic ring part>methyl part
• The degradation speed constant K is only related to the
light source, catalysic activity and the reaction medium
rather than the surface active structure. 。

3 steps for the photocatalysic
degradation reaction ot the surface
active agent on the surface of TiO2:
1) Absorption of surface active agent on the
surface of TiO 2 ;
2) Absorption of UV by TiO 2 and the formation of
electron/hole pair ( 电 子 / 空 穴 对 ) (e - /h + ), and the
further reaction between this pair and the
aromatic ring (Ar) of the surface active agent
and the production of aromatic cations (Ar + );
3) The ring-opening process of Ar + , and successive
oxidation to the fnial production of CO 2.

3. Prospect for the surface
active agent technology
• The fixation of mixed bacteria using the technology of
cellular fixation technoloy ( 固 定 化 细 胞 技 术 ) can enable
several reuse of the reaction system and also reduce the
cost and increase efficiency.
• The foundation of engineering bacteria, produced with
microorganizm in alternate or symbiotic relationship by the
combination of cell fusion technology and gene
engineering technology, can give the engineering bacteria
both the fuction of mixed culture and the advantages of
simple required nutrition, stable metabolism and easy
control, making it the major research direction for the future.

One of the key points in the research of photocatalytic
degradation is to choose the suitable carriers and
develop nanometered TiO 2 , use photoactive matter in
the preparation of photocatalyst agent to produce highefficient
catalyst agent for photocatalyst degradation,
further improve the modification and fixation technology
of catalyst agent and increase the quantum efficiency of
catalyst agent.
The application of optimized combination of biodegradation
and photocatalyst degradation in treating
surface active agent will be more effective.