The Hydrosphere Like air, water is essential to life as we know it - - PDF document

SLIDE 1

1

Environmental Chemistry

APCH 211 Hydrosphere

The Hydrosphere

• Like air, water is essential

to life as we know it

• Aesthetic appearance of

water often an indicator

• f quality of the

environment environment

• ~ 73% of the surface is

covered by water (3x greater than land mass)

• All of Earth’s water can be

collectively termed as the hydrosphere

The Oceans

• 97% of earths water is in

the oceans

• Most elements can be

found in sea water

– E.g. Au ~ 0.000011 ppm

Element PPM Na 10,800 Cl 19,400 Mg 1,290 S 904 K 392 Ca 411 Br 67.3 Sr 8 B 4 F 1

Layers of the Ocean

• The epipelagic zone: Surface ‐ down to 200 meters ,

brightest zone (1 0f 2 with significant amount of light). Zone where most of the familiar creatures of the sea are found e.g. fish, sharks, squid, plankton, etc & find coral reefs. The name "epipelagic" roughly means "top zone of the ocean.“

• The mesopelagic zone: Extends 200 m down to

around 1,000 m. Also known as the twilight zone. The name roughly means "middle of the ocean". Less marine life than the epipelagic zone above because

• f lower light penetration. Collectively, the epipelagic

g p y, p p g and top of the mesopelagic zones are known as the photic zone, since light gets to them. Semi‐deep sea creatures such as the Swordfish and Wolf Eels live here.

• The bathypelagic zone extends: 1,000 m ‐ 4,000 m.

Very little light reaches this depth, & therefore no living plants. Deep sea animals which live here are adapted to consuming the snow of organic detritus that continually falls from above. Giant and Colossal Squid can be found here, as well as sperm whales. Most of the animals that live at these depths are black or red in color due to the lack of light.

Layers of the Ocean

• Abyssopelagic Zone:‐ The abyssal zone or the
• abyss. 4000 ‐ 6000 meters. The name comes

from a Greek word meaning "no bottom". Water temperature is near freezing, and there is no light at all. Very few creatures can be found at these crushing depths. Most of these are invertebrates such as basket stars and tiny squids. Three‐quarters of the ocean and tiny squids. Three quarters of the ocean floor lies within this zone. The deepest fish ever discovered was found in the Puerto Rico Trench at a depth of 27,460 feet (8,372 meters).

• Hadalpelagic Zone: Usually deep ocean
• trenches. 6000 meters to the bottom. The

deepest point in the ocean is located in the Mariana Trench off the coast of Japan at 35,797 feet (10,911 meters). The temperature of the water is just above freezing, and the pressure ~ 8 tons per square inch. Still find life, starfish and tube worms

Fresh Water

http://ga.water.usgs.gov/edu/waterdistribution.html

SLIDE 2

2

Note on Hydrological Cycle

• Model that summarizes

movement and residence of water in the atmosphere, lithosphere, biosphere, hydrosphere, and anthrosphere

• Reservoirs include atmosphere,
• ceans, lakes, rivers, soils,

glaciers, snowfields, and groundwater groundwater.

• Movement from reservoir to

reservoir via processes such as evaporation, condensation, precipitation, deposition, runoff, infiltration, sublimation, transpiration, melting, and groundwater flow.

• Replacement of water in some of

these reservoirs can take 100’s – 100, 000’s of years!

• Human Beings are using these

resources at far greater rates than the replenishment times

Trenberth et al. Estimates of the Global Water Budget and Its Annual Cycle Using Observational and Model Data. Journal of

• Hydrometeorology. 2007, Vol 8, 758 – 769

HEAVY FIG!

Physical Chemical Properties of Water

• Polar Molecule
• Hydrogen Bonding:

– Liquid at ambient conditions – Boiling point higher than expected – High specific heat capacity & a High heat of vaporization (regulates earths climate Oceans

+ + –

(regulates earths climate, Oceans absorb over 70% of the heat generated by atmosphere, sun, etc) – Strong cohesion and adhesive forces (lot of work to dehydrate systems, and dew formation) – Capillary action (helps trees & plants in general to grow!) – Strong surface tension

 

Temp. (°C) heat capacity ((J/g K) 4.2176 10 4.1921 20 4.1818 30 4.1784 40 4.1785 Temp. (°C) heat of vaporization (kJ/mol) 45.054 25 43.99 60 42.482 100 40.657 200 34.962 300 25.3

Physical Chemical Properties of Water

•  ice= 0.92 g/cm3
•  water= 1.0 g/cm3
• Density of H2O changes with

Temp.

• So Ice Floats!

– Lakes – Plays a role in circulation of nutrients as seasons change (& Pollutants?) g ( )

H2O(l): each molecule is hydrogen bonded to ~ 3.4

• ther molecules

H2O(s): each molecule is hydrogen bonded to ~4

• ther molecules, more open

& regular ice structure results in greater volume

• ccupied by ice & lower

density

http://www.grow.arizona.edu/water/density/temperature.shtml

Annual circulation patterns in a dimictic (circulates 2x/yr) lake. The typical dimictic lake undergoes stratification in the summer and complete overturn in the autumn and spring. During winter, surface ice prevents further mixing by the wind. Small differences in density and temperature exist, with cooler water (0° C) staying near the surface and warmer, more dense water (4° C) extending to the bottom.

Ref: circulation: annual patterns of dimictic lakes. Art. Encyclopædia Britannica Online. Web. 25 Mar. 2011. <http://www.britannica.com/EBchecked/media/36/Annual‐circulation‐patterns‐in‐a‐dimictic‐lake>.

Solvent Properties

• Large dipole moment

– Liquid water, molecules are constantly breaking and forming new H – bonds – Able to easily surround ionic or polar substances – Process in which water molecules surround a solute involves the formation of new bonds between water molecules & solute – Overall the free energy change is negative, favors formation of a hydrated species

• “Universal Solvent”
• Hydrophilic – “Water

Water Lov Loving” i.e. easily dissolve in water

• Hydrophobic – “Wate

Water Fear Fearing” i.e. ~ do not dissolve in water

Factors that determine the mechanism via which hydration occurs is still an intense area of R&D, as evidenced by a recent article in the journal Science (Cooperativity in Ion Hydration. K.J. Tielrooij, N. Garcia‐Araez, M. Bonn and H.J. Bakker, Science, 21 May 2010)

Acid Base Properties

• Amphiprotic (Brǿnsted acid or base )

– pH < 7 can be due to organic acids from decaying

• rganic matter

– (COOH)2 + H2O ↔ H3O+

(aq) + COOHCOO– (aq)

Ka = 5.6 x10‐2 Ka 5.6 x10 – pH > 7 can be due to soluble carbonate species from rocks, etc

• Auto dissociates

– 2H2O ↔ H3O+

(aq) + OH– (aq)

Kw = 1.01 x10‐14 @ 25 °C

• Neutral water has a pH = 7.0

SLIDE 3

3

Redox Chemistry in Natural Waters

• Most important oxidizing agent in

natural waters is dissolved molecular

• xygen
• [O2] in water is small

– Henry’s law ~ “The concentration of a gas in a liquid at a specific temperature is proportional to the partial pressure of the gas above the liquid”. – The equilibrium constant for the

O H e H O

2 2

2 4 4   

  Half‐reaction in Acidic Solutions   

  OH e O H O 4 4 2

2 2 Half‐reaction in Basic Solutions gas/liquid system is given by Henry’s Law Constant KH

• Solubility of gases increases with

decreasing temperature ([O2] @ 0 °C = 14.7 ppm, @ 35 °C = 7.0 ppm)

– Artificial warming of rivers or lakes ~ thermal pollution e.g. near power plants ) ( 2 ) ( 2 aq g

O O 

KH = 1.3 x10‐3 mol L‐1 atm‐1

) ( 2

] [

) ( 2

g

O aq H

P O K 

In Class Exercise: Composition of O2 ~ 21%, thus PO2 ~ 0.21 atm, therefore [O2] ~ 8.7 mg/L

In Condensed Phases: ppm based on mass not moles Thus mg/L ~ ppm

Oxygen Demand

Biochemical Oxygen Demand (BOD)

• The capacity of the organic and

Chemical Oxygen Demand (COD)

• Uses dichromate ion to oxidize
• Dissolved Oxygen usually oxidizes organic matter

from biological sources

• Can convert ammonia, or ammonium to nitrate
• High values of ‘OD’ can be detrimental to aquatic
• rganisms such as fish, etc
• The capacity of the organic and

biological matter in a sample of natural water to consume oxygen via catalytic processing of microorganisms present

• r
• The amount of oxygen required by

aerobic microorganisms to decompose the organic matter in a sample of water

– Easily determined by measuring O2 before and after sealing a water sample seeded with bacteria

• Uses dichromate ion to oxidize

biological and organic matter in a natural water sample

• Indirectly measures amount of
• xygen needed to decompose all
• rganic substances (artificial and

natural)

– Since stable organics, & anything that can be oxidized are targeted – so always larger values than BOD In Class Exercise: Show that 1.0 L of water saturated with O2 can oxidize 8.2 mg of CH2O

Anaerobic Decomposition of Organic Matter

• Anaerobic (O2 free) decomposition of organic

matter by microorganisms (fermentation) can produce CH4 and CO2

– In swamps the methane bubbles up to the surface and may ignite – In some rural communities (India, China, KZN),

2 4 Matter Organic 2

O 2CH CO CH

Bacteria

 

In some rural communities (India, China, KZN), ‘digestor units’ convert bio‐organic waste to methane – Process can also occur in landfills

http://www.biogaspro.com/

In lakes the lack of oxygen creates a reducing environment at the bottom

• Insoluble Fe3+ (+e‐)  Soluble Fe2+
• Mixing does occur with seasons (see earlier slide)

N B THIS IS AN OVERALL RXN

Sulfur in Natural Waters

4 2 2 2

2 SO H O S H  

Hydrogen sulfide : Sources include, volcanoes, hot springs, swamps (anaerobic bacteria), 10 – 15% from anthropogenic sources (oil refinery, natural gas wells, paper mills, ore smelting, etc) S bi b t i d i Overall reaction showing how some anaerobic bacteria can use sulfate ion as the oxidizing agent to decompose organic matter (important in seawater , where sulfate concentration is much higher than fresh water N.B. THIS IS AN OVERALL RXN Some anaerobic bacteria can decompose various sulfur containing organic matter (amino acids, etc) and produce, amongst other things, hydrogen sulfide, CH3SH, CH3SSCH3, etc

H2S Solubility 4370 ml/litre at 0 °C; 1860 ml/litre at 40 °C

O H CO S H O CH SO

2 2 2 2 4

5 3 2 4 3 2     

 

Acid Mine Drainage

• AKA Acidic rock drainage
• “Outflow of acidic water

(pH<3.0) from abandoned coal

• r metal/ore mines”

– Typically occurs when certain geology is exposed (mining, construction etc) to water or air resulting in the oxidation of these minerals

Chemical formula Name of compound FeS2 Pyrite FeS2 Marcosite FexSx Pyrrhotite Cu2S Chalcocite CuS Covellite CuFeS2 Chalcopyrite MoS2 Molybdenite NiS Millerite PbS Galena ZnS Sphalerite FeAsS Arsenopyrite

AMD Chemistry

  

     H SO Fe O H O FeS 4 4 2 2 7 2

2 4 2 2 2 2   

   

3 2 2 2

4 2 4 4 Fe O H H O Fe

First step produces acidity

Second step is usually slow, but can be catalyzed by acidic bacteria, & consumes some of the H produced in 1

Actually [S‐S]2‐  

   H OH Fe O H Fe 12 ) ( 4 12 4

3 2 3    

     H SO Fe O H Fe FeS 16 2 15 8 14

2 4 2 2 3 2 p 3rd step the Fe3+ is soluble in high pH water initially produced; however as AMD becomes more diluted the hydroxide ppt, giving the yellowish brown color (kills!!) Fe3+ then catalyses further production of acidity, without the need for O2

SLIDE 4

4

Consequences & Some Solution to AMD

Consequences

• High acidity leads to leaching
• f various metals

– Heavy metals (Fe, Cu, Pb, Zn, Cd, Co, Cr, Ni, and Hg) Metalloids As Sb)

Solutions

• Some mines near natural

limestone deposits which can neutralize the AMD

– Metalloids, As, Sb) – Other metals & elements Al, Mn, Si, Ca, Na, K, Mg and Ba – Whatever maybe present

• Can get pH < 0!
• Discoloration of waterways,

choking & killing of aquatic

• rganisms (fish, plant,

microorganisms, etc)

• Limestone chips can be

added

• Addition of calcium oxide or

hydroxide

• Anaerobic bacteria
• Sealing the mines

The pE Scale

• Used to characterize the reducing nature of natural water
• Low pE ~ lots of electrons available thus water is very

reducing

• High pE ~ few electrons available so dominant species are
• xidizing in nature

I i d fi d l f h ff i i (

• It is defined as – log10 of the effective concentration (or

activity of) electrons in water

– Analogous to pH scale, recall you really don’t have bare protons, so don’t really have bare ‘electrons’, – Dimensionless numbers (i.e. no units)

• Along with pH it can be used to determine the dominant

species in a body of water

Example Using pE

O H e H O

2 2

2 4 4   

 

Large amounts of dissolved O2 in H2O; dominant process is reduction of O2 Scenario: Traditional leather tanning industries soak the hides in an aqueous solution

• f chromium (III). Suppose the waste water from the tannery contains 26 mg L‐1

chromium (III). As it enters a river, the dissolved oxygen can oxidize the chromium (III) to dichromate. If the water in the river is well aerated and has a pH of 7.0, what’s the dominant species?

Q pE pE

n

• log

1

 

795 . 20 0591 . 229 . 1 0591 .   

• E

pE

63 . 14 ] [ 1 log 795 . 20

4 4 1

2

  



H P pE

O

• Can use this step for any well aerated

water system, as long as you know the pH

• Assumption O2 in eqm with the water
• Assumption is no dissolved CO2

Eqn used to calculate pE

pEo need

Step 3: set up the correct expression for Step 2: Calculate pEo Step 1: Need correct half reaction

Example Using pE…Chromium step

O H Cr e H O Cr

aq aq aq 2 3 ) ( ) ( 2 ) ( 7 2

7 2 6 14

   

  

14 7 2 7 2 3 6 1

] 10 ][ [ ] [ log 504 . 22 63 . 14

  

  O Cr Cr

504 . 22 0591 . 33 . 1 0591 .   

• E

pE The chromium and oxygen are in the same water system, so they are at eqm! i e same pE!!! Step 5: Simplify the expression Step 4: Simple rule of logs re‐arrange the expression Step 3: set up the correct expression for Q, & sub’ in your known values

] [ ] [ log ] 10 [ 1 log 504 . 22 63 . 14

2 7 2 3 6 1 14 7 6 1   

   O Cr Cr ] [ ] [ log 504 . 8 63 . 14

2 7 2 3 6 1  

  O Cr Cr ] [ ] [ log 756 . 36

2 7 2 3  

  O Cr Cr ] [ ] [ 10 75 . 1

2 7 2 3 37   

 O Cr Cr x

they are at eqm! i.e. same pE!!! Finally SOLVE! This small number means the dichromate dominates! Which is very toxic, and carcinogenic

pE‐ pH Diagrams (Pourbaix Diagrams)

• These are graphical representations of the most dominant species at a particular

pE/pH combination

• Solid line = [] where both species are equally dominant
• Dashed lines (shaded area) where water actually decomposes

Figures adapted from Baird & Cahn 4th Edition. Environmental Chemistry

Acid Base Chemistry in Natural Waters

• Natural waters contain lots of CO2

– Source mostly from air, but can be from decomposition of organics – Easily forms carbonic acid – Acid easily dissociates (rxn 1 in table) – Reason rain water, etc slightly acidic

) ( 3 2 ) ( 2 ) ( 2 aq aq g

CO H O H CO  

In Class e.g. Show that the pH of CO2 saturated water is 5.6 @ 25 °C, given that the [CO2] is 365 ppm

• Oceans are a large sink for atmospheric CO2

– Sequestration of CO2 in the ocean would increase the acidity of surrounding waters – Increased acidity could be detrimental to some ocean life – Increase in atmospheric CO2 has decreased ocean pH ~ 0.1

SLIDE 5

5

CaCO3/H2O Equilibrium

  



2 3 2 ) ( 3

CO Ca CaCO

s Ksp = [Ca2+][CO32‐] Solubility ‘S’ of CaCO3 = S = [Ca2+] = [CO3

2‐]

S2 = 4.6 x10‐9 S = 6.8 x 10‐5 M

Solubility of CaCO3 = 6.8 x 10‐5 M assuming other rxns are negligible

  

   OH HCO O H CO

3 2 2 3

Dissolved carbonate acts as a base in water Overall rxn

• btained by

adding 2 equations

  

OH HCO C O H C CO

2

    OH HCO Ca O H CaCO

s 3 2 2 ) ( 3

New K = Ksp ● Kb K = 9.7 x 10‐13 Note: K = [Ca2+] [HCO3

‐] [OH‐]

Thus S = [Ca2+] = [HCO3

‐] = [OH‐]

S3 = 9.7 x 10‐13 S = 9.9 x 10‐5 M

• Took into account

role of CO3

2‐

• Most of the CO3

2‐

reacts with water

pH = 14 – pOH 14 – log[OH‐] 14 – log(9.9 x10‐5) pH = 10.0

OVERSIMPLIFIED!!!!! Didn’t account for OH/H already present Le Châtelier’s Principle Solubility decreases as [OH-] increases

Multiply all K’s

CaCO3/H2O & CO2! Equilibrium

3 2 ) ( 2 ) ( 2

CO H O H CO

l g

 

  



2 3 2 ) ( 3

CO Ca CaCO

s   

   OH HCO O H CO

3 2 2 3   



3 3 2

HCO H CO H O H OH H

2

 

  Ka(H2CO3) = 4.5 x 10‐7 KH = 3.4 x 10‐2 Ksp = 4.6 x 10‐9 Kb(CO3

2‐) = 2.1 x 10‐4

1/Kw = 1.0 x 1014

1 2 3 4 5

1 should suppress 4 5 drives 1&4 right   

  

2

2HCO Ca O H CO CaCO

Overall

all K s

   

3 ) ( 2 ) ( 2 ) ( 3

2HCO Ca O H CO CaCO

l g s rxn

• Overall CO2 from the air (acid) titrates carbonates

from rocks (base)

• Overall reaction is an approximation of whole process
• Ocean sequestration of CO2 maybe viable via this

pathway i.e. slurry of calcium carbonate with CO2 dumped in deep ocean avoids pH lowering of CO2 alone

• Water that contains CO2 more readily dissolves

carbonate rocks

• Typical pH of such waters 7 ‐ 9

Abundant Ions in Natural Waters

• Fewer dissolved salts in non –

calcareous waters

• Do get some bicarbonate ions due to

presence of other minerals (aluminosilicates)

• Saline Water – abnormally high

concentration of ions – produced from farming industry de‐icing roads from farming, industry, de icing roads in northern climes

• F‐ in water varies globally, 1 – 4 ppm

can be added to drinking water, can prevent tooth decay, too much mottles teeth

• Alkalinity value gives an idea of the

anions present that can act as a base

• Hardness index measures total

amount of Ca and Mg ions (>150 mg/L ~ hard water)

Few More Notes on Natural Acidity

• Although carbonic acid is a weak acid, it is very

effective over geologic time. Carbonic acid is largely responsible for the breakdown of rocks to soil during chemical weathering and the formation of limestone caverns and sinkholes. The lower the pH, the more p , acidic the water, and the more minerals it can dissolve.

• Sea spray, carried aloft by winds blowing across the
• cean, contributes to dissolved constituents in
• rainwater. Sea spray is the primary source of chloride

(Cl−) in rainwater and a significant amount of sodium (Na+).

Streams, Rivers, Lakes, etc…

• The composition of stream and lake

water varies from one place to another, and within a single watershed varies both seasonally and along the stream's path.

• The major source of dissolved minerals

in streams and lakes is the rocks the water moves over and through along its path from where it falls as precipitation t h it it th t h d to where it exits the watershed or enters the lake.

• As the slightly acidic water encounters

rocks, the minerals begin to dissolve and contribute their elements to the water.

• The type of rocks in the watershed

influence stream‐water composition. A stream flowing over sedimentary rocks will have a different composition than a stream flowing over igneous rocks.

Horwick Waterfalls (KZN)

Streams, Rivers, Lakes, etc…

• Also contributing to stream‐water and lake‐water

composition are reactions between the water and the biomass.

• Temperature influences the amount of dissolved gases

(e g oxygen) (e.g., oxygen).

• Stream‐water composition changes from headwaters

to outlet because the water is in contact with the rocks and sediments of the streambed for cumulatively longer times. Also, tributaries draining different geologic areas may enter the stream, and groundwater may seep into the stream.

SLIDE 6

6

Streams and Lakes…

• Seasonal variations in stream‐water composition may

reflect differing precipitation amounts and stream's flow that is contributed by groundwater.

• In the drier times of the year the proportion of

precipitates in groundwater is greater than in the wet season.

• Lake‐water composition is influenced by evaporation,

among many other factors. As water evaporates, the dissolved minerals are left behind.

• The more the evaporation, the higher the

concentration of dissolved minerals (salts) in the water

• r the salts will precipitate from the solution.

Surface & Ground water composition

• Many of the factors that influence the surface

water composition also influence groundwater composition.

• Groundwater is always in contact with rocks and

minerals and moves more slowly than surface water in centimeters per day instead of kilometers per hour. As a result, groundwater

• ften contains more dissolved minerals than

surface water (as is evident from comparing streams and groundwater in the table below).

surface & ground water…

• When water seeps below the

surface, it passes through the soil where microbial respiration processes release

• CO2. As water encounters the

CO2, the pH is lowered, and the water can dissolve more the water can dissolve more minerals.

• At higher temperatures,

minerals dissolve more readily. Deep groundwater tends to be warmer (e.g, the source of water from hot springs) thus higher mineral content.

Factors controlling groundwater composition

• (1) geologic materials groundwater
• (2) type of reactions taking place, and
• (3) contact time, or length of time

d h b i i h h groundwater has been in contact with the

• rocks. The contact time may vary from a few

days to more than 10,000 years.

Origin of Saline Groundwater

 Typically, groundwater has a total dissolved solids (TDS) content

• f

less than 250 milligrams/liter (mg/L).  Groundwater with a TDS > 100,000 mg/L is found in some cases.  Sea water has a TDS content of approximately 35,000 mg/L)

 Saline groundwater has been found in a variety of geologic environments, commonly in marine sedimentary rocks, but also in ancient metamorphic and igneous rocks.

Saline Groundwater

Saline groundwater can form in at least three ways: (1) from trapped sea water; (2) from dissolving highly soluble minerals; (3) as a result of a long contact time with rocks, and thus chemical reaction time with surrounding rocks.

SLIDE 7

7

Examples of Groundwater Cases

 Trapped Sea Water (connate water). When marine sediments are deposited, some sea water commonly remains trapped between the mineral grains. Connate water later may migrate through the rocks as groundwater.  Highly Soluble Minerals. Groundwater encountering easily dissolved minerals such as gypsum (CaSO4.2H2O)

• r halite (NaCl), will become saltier.

 Contact Time. Groundwater that follows deep paths below p p the ground may be in contact and able to react with rocks for thousands or tens of thousands of years. This groundwater will acquire a higher TDS with time.  Sea spray, carried aloft by winds blowing across the

• cean, contributes to dissolved constituents in rainwater.

Sea spray is the primary source of chloride (Cl−) in rainwater and a significant amount of sodium (Na+).

INORGANIC AND ORGANIC WATER POLLUTANTS

Filthy water cannot be washed… WEST AFRICAN PROVERB

Water Pollution

Throughout history, the quality of drinking water has been a factor in determining human welfare.

Cities downriver affected by guys upriver dumping waste… plagues, disease, etc Poor crop yields…

Conflicts

Past Conflicts – Not really, but attack/destroying the enemies water supplies has been done numerous times Modern era – Examples where attacks are fueled by accessibility to safe water (http://www.worldwater.org/conflict/timeline/)

Sources of Water Pollution (In General)

• Point source pollution: “any single identifiable source of pollution from which

pollutants are discharged, such as a pipe...” (USA – EPA)

– legal definition of "point source" in section 502(14) of the Clean Water Act. That definition states: “The term "point source" means any discernible, confined and discrete conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding

• peration, or vessel or other floating craft, from which pollutants are or may be
• discharged. This term does not include agricultural storm water discharges and

return flows from irrigated agriculture.” E l f i t i l d – Examples of point sources include:

• Discharges from industries
• Sewer outfalls
• Non‐point source pollution: ‘Pollution that does not come from any specific

source, but originates from many areas’

– Examples include:

• Excess fertilizers, herbicides and insecticides from agricultural lands and residential areas
• Oil, grease and toxic chemicals from urban runoff and energy production
• Sediment from improperly managed construction sites, crop and forest lands, and eroding

stream banks

• Salt from irrigation practices and acid drainage from abandoned mines
• Bacteria and nutrients from livestock, pet wastes and faulty septic systems
• Atmospheric deposition

Class of Pollutant Significance/Impact Trace elements Health, aquatic biota, toxicity Heavy Metals Health, aquatic biota, toxicity Organically Bound metals Metal transport Radionuclides Toxicity Inorganic pollutants Toxicity, aquatic biota Asbestos Human health Algae nutrients Eutrophication Acidity, alkalinity, salinity (in excess) Water quality, aquatic life Sewage Water quality, O2 levels Taste, odor and color Esthetics Biochemical oxygen demand Water quality, oxygen levels Trace Organic Pollutants Toxicity Pesticides Aquatic biota, wildlife Polychlorinated biphenyls Possible biological effects Chemical carcinogens Incidence of cancer Petroleum wastes Affect wildlife, esthetics Pathogens Health effects Detergents Eutrophication, wildlife, Sediments Water quality, aquatic biota, wildlife

Elemental Pollutants

Trace elements  Trace levels refer to those elements that occur at very low levels in a given system. Depending on the instrument, trace concentrations may not be

• detectable. Generally, levels in parts per million
• r less can be referred to as trace.

 Some trace elements encountered in natural waters are recognized as nutrients required for animal and plant life. Of these, many are essential at low levels but toxic at higher levels

42

SLIDE 8

8

El’ Sources Impact TWQR (mg/L) WHO (mg/L) EPA (mg/L) As Mining & Chemical Waste Toxic, carcinogenic 0 ‐ 10 0.01 0.01 Be Coal, Industrial wastes Toxic N/A N/A 0.004 B Coal, Industrial wastes, detergents Toxic N/A 0.5 0.6- 1.0 Cr Metal plating Cr(III) essential, Cr(VI) toxic 0‐ 0.05 0.05 0.1 Cu metal plating, mining, industrial waste essential trace element, toxic to plants & algae at high levels 0 ‐ 1 2 1.3 F geology, waste, additive prevents tooth decay, toxic 1.5 4 I natural brines, Industrial wastes Prevents goiter N/A N/A N/A Fe Coal (indirect), Industrial wastes, AMD microbial action corrosion essential nutrient, damages fixtures via staining 0 ‐ 0.1 0.3 0.3 AMD, microbial action, corrosion fixtures via staining Pb Coal, Industrial wastes, mining, fuel (almost gone) Toxic 0 ‐ 10 0.01 0.015 Mn Coal, Industrial wastes, AMD, microbial action Toxic 0 ‐ 0.05 0.4 0.05 Mo Natural sources, Industrial wastes Essential to plants, toxic to animals N/A 0.07 N/A Hg Coal, Industrial wastes, mining Toxic 0 ‐ 1 0.006 0.002 Se Coal, natural sources Essential at low levels, toxic at high levels 0 ‐ 20 0.01 0.05 Zn metal plating, Industrial wastes, plumbing essential element, toxic to plants at high levels 0 ‐ 3 3 - 5 5

Heavy Metals

 Heavy metals are located near the middle and the bottom of the periodic table  Main ones include/ Most studied

 Hg, Pb, Cd, Cr, As, Mn, Ni, Zn, Ag

 All are dangerous in the f f th i ti forms of their cations and most are highly toxic when bonded to small carbon chains.

 Most of the metals have a strong affinity for sulfhydral bonds (-SH) in enzymes.  Enzymes control the speed of various critical metabolic reactions in the human body  Once bonded by a heavy metal, the enzyme no longer functions properly, resulting in adverse health effects

Toxicity of heavy Metals Continued…

Chelation Therapy

• Administration of a compound

that binds to the metal more strongly than the enzyme

• This metal‐compound is then

solubilized & excreted from the body

• Pb & Hg can be treated using

Toxicity

• Depends on speciation of the

metal ion

• Can cause sickness & death
• Can pass through the blood

brain barrier

• Can pass through the placental

barrier Pb & Hg can be treated using British Anti‐Lewisite (BAL)

• Other options for heavy metal

therapy are the calcium salt of ethylenediamineteraacetic acid (EDTA) barrier

• Hg & Pb attached to alkyl

groups are soluble in animal tissue

• [Hg ] can increase

progressively along the food chain

Hg – Sources & Use

REF: E.G. Pacyna et al. Atmospheric Environment, Volume 44, Issue 20, June 2010, Pages 2487-2499,

Hg – Aquatic Cycle

http://sofia.usgs.gov/geer/2000/posters/merc_cycle/

Hg2+

Inorganic Forms

• Hg2+

– Hg vapor & to a lesser extent salts of Hg, attacks nervous system, but mainly affects kidney & liver – Most Hg in the environment is inorganic Hg2+ – Levels can be 10x > preindustrial levels – Most attaches to suspended particles so deposits in sediments

Organic Forms

• Dimethylmercury (Hg(CH3)2)

– Formed under anaerobic conditions by microorganisms in the sediments of lakes & rivers – Highly volatile liquid

• CH3HgCl & CH3HgOH collectively

called methylmercury

– Also formed in similar conditions

particles, so deposits in sediments – HgS (cinnabar) insoluble in water – HgO used in batteries

• Hg2

2+ not very toxic, cause

combines with chloride (in stomach) to form an insoluble salt Also formed in similar conditions to dimethylmercury, however favored in acidic to neutral water – Is photodegraded – More potent toxin than inorganic Hg salts – Bioaccumalates & biomagnifies – Most lethal form of Hg, followed by Hg vapor – Note once in various cells, this can then be converted to lethal +2 form (i.e. bypass mechanism)

• Most methyl mercury in humans comes from

fish

• It binds to proteins in fish, so all over the fish
• Ratio of methyl mercury in water: fish muscle ~

1: 1000000

• Pregnant Women not allowed to eat various

fish (tuna, salmon, etc)

SLIDE 9

9

Lead

• Low m.p. (327 C)

– Easily separated from it

• res

– Historically known since ancient times (extensively used by ancient Greeks and Romans over 2000 years ago)

• Water pipes, water ducts,

cooking utensils, building

• Elemental Lead

– From bullets/ammunition used by hunters esp of water fowl – Has been banned in several countries

• Pb2+

– PbS main lead ore galena, very insoluble Pb metal stable in lead acid

cooking utensils, building supports

• Modern uses of Pb

– Roofing & flashing – Soundproofing – Electronics as solder (alloy

• f Sn & Pb)

– Lead batteries (cars, etc) – Pb metal stable in lead acid batteries, but unstable in the solder that used to be used to seal tin cans 2Pb(s) + O2 + 4H+  2Pb2+

(aq) + 2H2O

– Insoluble lead salts are actually soluble in acidic waters – Old water pipes, & solder of Cu pipes can be a source in drinking water, which can be reduced by

• Calcerous waters ‐ formation of

PbCO3(s)

• Addition of phosphate to form

insoluble lead phosphates

Pb Salts from glazes & Pigments

PbO

• Yellow solid used since ancient Egyptian times to glaze pottery
• Hazard if not applied properly ‐ any acidic food or liquid (hr‐d)

PbO(s) + 2H+

(aq)  Pb2+ (aq) + H2O

• Been replaced by lead silicate

Bright red , red lead (Pb3O4)

• Used in corrosion resistant

paint for iron & steel Lead acetate used in formulas to color grey hair (Pb2+binds to SH in hair)

Lead Dust

• From soil containing particles of

Lead

Lead Chromate (PbCrO4)

• Yellow paint used on roads, (&

school buses in N. America) hair) White lead (Pb3(CO3)2(OH)2

• Was used in white paint
• Still used in outdoor paints (may

contaminate soils)

• Been replaced by TiO2

Lead

• Pb comes from various sources

including paints flakes, ceramics, plastics, gasoline, recycling plants, hair products, pesticides (with Pb(AsO4)

Pb4+

• Lead Acid Batteries

– Occurs as PbO2 – Most are recycled for Pb, such recycling centres can be ‘hot spots’

• Tetravalent Organic Lead

– Most Pb(IV) compounds are covalent – Petrol (Gasoline) additives Pb(CH3)4 & Pb(C2H5)4

• Very volatile, not water soluble, easily

absorbed through the skin, liver t th i t t i (PbR +) converts them into neurotoxins (PbR3+)

• Additives (ethylene dibromide, ethylene

dichloride) in petrol prevent Pb depositing as metal in the engine – thus released as Pb halides

• PbBrCl, PbBr2, PbCl2  all converted to

PbO under UV

• In RSA LRP was introduced in 1996,

and lead completely phased out by 2006 (Source: http://www.naamsa.co.za/unleaded/f aq.htm) – UNEP program had a goal for 2008 for rest of Sub – Saharan Africa

http://www.unep.org/transport/ pcfv/corecampaigns/campaigns. asp#lead

Maximum Contaminant Level (MCL)—The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment water technology and taking cost into consideration. MCLs are enforceable standards. Treatment Technique (TT)—A required process intended to reduce the level of a contaminant in drinking water. Adapted from EPA ( National Primary Drinking Water Regulations)

Basics on Toxicology

• Toxicology: Study of the harmful effects

foreign substances have on living

• rganisms

– Synthetic or natural!

• A toxic substance is an element,

compound or micro‐organism that, upon exposure, creates harmful effect

• n a living organism.
• Toxicity applies to plants, animals and

micro‐organisms, but the degree to g , g which any life‐form is affected by a toxic agent depends on the species and

• ther environmental factors.
• Serious cases of toxicity can lead to

death of the organism either suddenly (acute toxicity) or extended exposure (chronic toxicity).

• Toxicity is different from carcinogenicity

(cancer‐generating effects) but both can lead to extremely serious consequences.

Additional Resources: http://www.toxicology.org/index.asp http://www.eoearth.org/article/Toxicology

SLIDE 10

10

Concepts & Terminology

• A toxic substance (or agents) may be chemical (for example, cyanide), physical (for

example, radiation), and biological (for example, snake venom).

• Organisms that invade and multiply within the organism & produce their effects by

biological activity are not classified as toxic agents. E.g. A virus that damages cell membranes resulting in cell death.

– If the invading organisms excretes chemicals which is the basis for toxicity, the excreted substances are known as biological toxins. These organisms, in this case, are referred to as toxic organisms. E.g. tetanus. Tetanus is caused by a bacterium, Clostridium tetani. The bacteria C. tetani does not cause disease by invading & destroying cells, but the toxin it releases is a neurotoxin

• A toxic substance may be a discrete toxic chemical or a mixture of toxic chemicals. For

example, lead chromate, asbestos, and gasoline are all toxic substances.

– Lead chromate is a discrete toxic chemical. – Asbestos is a toxic material that consists of various fibers and minerals. – Gasoline is a toxic substance, rather than a toxic chemical, that contains a mixture of many chemicals.

• Toxic substances may be organic or inorganic in composition
• Toxic substances may be systemic toxicants or organ toxicants.

– A systemic toxicant is one that affects the entire body or many organs rather than a specific site. For example, potassium cyanide is a systemic toxicant in that it affects virtually every cell and organ in the body by interfering with cells' ability to utilize oxygen.

• Toxicants may also affect only specific tissues or organs while not producing damage to

the body as a whole. These specific sites are known as the target organs or target tissues.

– Benzene is a specific organ toxin in that it is primarily toxic to the blood‐forming tissues. – Lead is also a specific organ toxin; however, it has three target organs: the (central nervous system, the kidney, and the hematopoietic system).

• A toxicant may affect a specific type of tissue (for example, connective tissue) that is

present in several organs. The toxic site is then referred to as the target tissue.

Detrimental to Human Health…

Mutagens:

• Substances that cause

mutations in DNA, most of which are harmful & can produce inheritable traits if they occur in the DNA of they occur in the DNA of sperm & eggs Carcinogens:

• Substances that cause cancer

Teratogens:

• Substances in the mother

that cause birth defects in the fetus

Examples of carcinogens

• Benzene
• Benzaldehyde,
• Benzyl acetate
• Methylene chloride
• Formaldehyde

Note:

• Some of these various

carcinogens maybe found in various consumer products

S d d t

Formaldehyde

• Isopropyl Alcohol
• Cadmium
• Nickel
• Mercury
• Etc……….

– Soaps, deodorants, shampoo’s, make –up products – Foods (especially processed foods) – Household cleaners, DIY products (paints, resins, tiles, carpets, etc)

Reference: Report on Carcinogens, Eleventh Edition; U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program

Measuring Toxicity of a Pollutant

• Measuring toxicity is a

complex process but a fundamental experiment is one in which an

• rganism is exposed to

controlled amounts of the potential toxic agent

Dose = Controlled variable, e.g amount of toxic

• agent. Usually expressed as mass of chemical (mg)

per unit test animals body weight (kg), mg/kg

• Necessary because toxicity of a substance

decreases as the size of the individual increases (children take smaller amounts of medicine!!)

• Maybe transferrable to humans on such a scale
• Response = measured variable e.g death

p g under carefully defined conditions.

• After controlled exposure,

the influence on the

• rganism is measured in

some appropriate way.

• In the toxicity measuring

experiments;

Dose – Response Curves

Dose – Response Relationships

• People respond differently to toxins, what may kill

you, may irritate someone else…

• Thus have dose response curves to illustrate this

phenomena

– X‐axis has dose, and y‐ axis has effect (e.g. death) – Usually use a log – scale on the x‐axis, so as to clearly see low end of the dose scale (usually important for policy)

• LD50 – “The dose that proves to be lethal to 50% of

the population of test animals/subjects”

– Smaller the value, more lethal the chemical!

• LOD50 – Similar concept, except looking at oral

d i i t ti f th h i l (LOD l th l l

“All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy”… Paracelsus

administration of the chemical (LOD = lethal oral dose)

• Threshold – The dose at which no animal was

affected

• NOEL – No Observable effects level (slightly below

threshold)

• LC50 – lethal concentration that kills 50% of a

specified organism, within a fixed exposure period. Refers to [] in air or aqueous solution(mg/L). NOTE!

• What maybe true for the test animal, may not be true

for humans!

– For Rats, DDT LOD50 = 110 mg/kg, but humans have survived 10 mg/kg, but no evidence they can survive 110 mg/kg

Risk Assessment

• E.g.

An average person drinks 2.0L/day, and has an average body weight of 70 kg. If the ADI for a pollutant is 0.0020mg/kg/day, what is the maximum allowable concentration of the chemical in water? Find how much the person would consume per day:

0.0020 mg/kg/day x70 kg = 0.14mg/day

• Quantitative tool used to assess

– Likely types of toxicity expected for a human population – Probability of each effect occurring within the population – May determine permissible exposure limits

• Information Needed

– Hazard evaluation (types of toxicity) – Dose – response data 0.0020 mg/kg/day x70 kg 0.14mg/day

Then determine the concentration 0.14mg/2.0 L = 0.07 mg/L Ans = 0.07 ppm

• This is basically how regulations

for certain chemicals in drinking water can be determined

– Estimation of potential human exposure

• For Chronic exposures

– NOEL expressed as mg/kg/day – A safety factor of 100 is usually used for most sensitive members of a population (infants & children) i.e. NOEL/100 – NOEL/100 = maximum acceptable daily intake (ADI), U.S. EPA uses toxicity reference dose (RfD)

• Often, regulations to control risk do

not take into account cost ‐ benefits

SLIDE 11

11

Organic Pollutants

• There are hundreds (if not thousands) of synthetic organic

chemicals, derived from petroleum or natural gas, that have widespread use and far reaching environmental consequences

– Pesticides: chemicals that kill or control unwanted organisms (rats, insects, weeds, birds, fungus, bacteria, molds, termites, fish, mosquito’s, etc) – Hazardous By – Products: Organic chemicals that are a result of some kind of anthropogenic or environmental process – Persistent organic pollutants (POPs): Organic compounds that are resistant to environmental degradation (chemical biological or resistant to environmental degradation (chemical, biological, or photolytic)

• Note: There are several other kinds of organic compounds that

cause serious environmental problems, but do not necessarily fall into a single class

Useful Terms

• Bioconcentration: uptake of a chemical from the media to concentrations in the organism's

tissues that are greater than in surrounding environment (e.g. chemical from water a fish lives in, accumulating in its gills)

• Biomagnification: the tendency of some chemicals to become increasingly concentrated at

successively higher trophic levels of a food chain or food web (e.g. small fish eats plankton, big fish eats the small fish, you eat the big fish!)

Pesticides… DDT

• DDT – para‐

dichlorodiphenyltrichloroethane

– First synthesized in 1873 – 1943 (Paul Muller) discovers its insecticidal properties – Widely overused 1950s & 1960s

• Affected reproduction of birds (soft egg shells),

and killed some fish

• Can stay in the environment for weeks –

years (in Canada half life from soils ~ 200 years)

• Has been found everywhere, from

deserts to ocean depths (& at the poles!)

• Banned in most ‘western’ Nations

– Bald eagle in U.S.A removed from endangered list (also Arctic peregrine Falcons) since DDT ban, & levels dropped

• Used extensively in parts of RSA

– Banned in 1974 for agricultural use – Malaria control stopped in 1996 – Started again in 2000 (KZN) – This successful use of DDT has refueled an interest in using it to control Malaria – Endocrine disruptor? DDE – dichlorodiphenyldichloroethene

• Metabolic by – product of DDT
• Very fat soluble, & almost non ‐ biodegradable

Dioxins

• This is a general term given to any

molecule with the ‘dioxin’ moiety i.e. a 6 member ring with 2C replaced with O.

• Dioxins are mainly by products of

industrial processes but can also result from natural processes, such as volcanic eruptions and forest fires.

– manufacturing processes that can produce dioxins include smelting, chlorine bleaching

• f paper pulp, manufacturing of some

herbicides and pesticides, and uncontrolled waste incinerators (solid waste and hospital waste incinerators (solid waste and hospital waste)

• Short‐term exposure

– At high levels, may result in skin lesions, such as chloracne and patchy darkening of the skin, and altered liver function.

• Long‐term exposure

– Impairment of the immune system, the developing nervous system, the endocrine system and reproductive functions. – WHO has classified dioxins as "known human carcinogen”. 1, 4 dioxin or: Tetrachlorodibenzo‐p‐dioxin

Some Other Organic Pollutants (The Stockholm Convention

• n Persistent Organic Pollutants (POPs))

The first 12 compounds covered under the Convention are Aldrin, Chlordane, DDT, The Stockholm Convention on Persistent Organic Pollutants (POPs) is a global treaty to protect human health and the environment from highly dangerous, long‐lasting chemicals by restricting and ultimately eliminating their production, use, trade, release and storage. Ref: http://chm.pops.int/Home/tabid/36/language/en‐US/Default.aspx Dieldrin, Endrin, Heptachlor, Hexachlorobenzene, Mirex, Polychlorinated Biphenyls, Polychlorinated dibenzo‐p‐dioxins, Polychlorinated dibenzofurans, and Toxaphene. The 9 new POPs added to the Convention are Alpha hexachlorocyclohexane, Beta hexachlorocyclohexane, Chlordecone, Commercial octabromodiphenyl ether (hexabromodiphenyl ether and heptabromodiphenyl ether), Commercial pentabromodiphenyl ether (tetrabromodiphenyl ether and pentabromodiphenyl ether), Hexabromobiphenyl, Lindane, Pentachlorobenzene, Perfluorooctane sulfonic acid (PFOS), its salts and perfluorooctane sulfonyl fluoride (PFOS‐F).

PURIFICATION OF WATER

“Water has become a highly precious resource. There are some places where a barrel

• f water costs more than a barrel of oil.”

Lloyd Axworthy, Foreign Minister of Canada (1999 ‐ News Conference)

Raw Water

• Raw water can refer to water drawn from surface (river, lake, pond, etc) or

groundwater

– Quality & pollutants will vary due to location, thus treatment processes will vary – The various processes may be arranged in a "treatment train" (a series of processes applied in sequence). Most commonly used processes include filtration, flocculation and sedimentation, and disinfection for surface water. Additional steps may include ion exchange and adsorption.

• Common Treatment steps include:

– Aeration: Simple bubbling of air through water to remove dissolved gases (H2S,

• rganosulfur compounds), and may oxidise some organics. Also any Fe2+

converted (Fe2+ + 3OH‐  Fe(OH) ) converted (Fe + 3OH  Fe(OH)3(s)) – Activated Carbon: Activated charcoal, made by heating biomass in low/zero

• xygen atmosphere @ 600C, then heating in CO2 or steam. Porous substance has

a high surface area (1400 m2/g) for physical adsorption processes. Relatively expensive, so limited use, but used in household tap filters – Removal of Mg & Ca: Ca can be removed by ppt with phosphate, or more commonly by adding sodium carbonate, or raising the pH (if enough HCO3‐). OH‐ + HCO3‐  CO32‐ + H2O Ca2+ + CO32‐ ↔ CaCO3(s) Mg usually removed by adjusting the pH (alkaline) – Disinfection: various methods available, choice depends on water quality, and economics, include chemical, physical, or combination of both

SLIDE 12

12

Treating Raw Water

• Filtration: Typical raw water can contain various

suspended particles either from erosion of soil or rock, mining, agriculture, etc.

– Can be removed using sand bed filter (can remove particles down to 10 m). C i l filt t i i & – Can use special filters to remove some microorganisms, & some chemicals

• Coagulation (& flocculation): Colloidal particles

captured by the ppt of added iron (III) sulfate or aluminum sulfate

– Colloids are charged suspended particles in water with diameters between 0.001 – 0.1 m. Originate from geology, decomposing plant and animal matter.

Coagulants in Action!

neutralize the negative charge on the surfaces of the particles (suspended solids) present in the water, thereby eliminating the repulsive forces between the particles and enabling them to aggregate

) ( 2 ) ( 4 ) ( 3 ) ( 3 2 ) ( 2 ) ( 4 3 ) (

3 ) ( 3

g s s aq aq aq aq

CO CaSO OH Al HCO Ca SO Al      

   

Notes on Desalination

Thermal Desalination

• Boil salty/brackish water
• Flash evaporate the liquid
• Saline residue left behind

Reverse Osmosis

• Energy intensive process as well
• High pressures force saline water

through a semi – permeable membrane

• Portable domestic units use ~ 2 atm
• π = cRT
• E = p∙V / 36

tial Scheme for Raw reatment Summary of Potent Water Tr

Treatment of Wastewater and Sewage

• Once water has been used it becomes

wastewater.

• Wastewater is recovered from domestic or

industrial sources.

– Rainwater (snow, wet ppt, etc) collected in separate t t d di tl di h d i t storm sewer system, and directly discharged into natural waters

• If the water is to be returned back to the natural

environment, then it has to meet certain requirements.

• Generally wastewater should not contain

UNACCEPTABLE levels of toxic chemicals or

• rganisms.

The guidelines for water

 The guidelines for water to be used for irrigation are different from those for drinking water. In

• rder

to meet the guidelines, a variety

• f

treatment procedures have been developed.  Treatment may include physical, chemical and biological processes operating sequentially or simultaneously.  Example of specific requirement include: BOD (15mg/L), SS (15mg/L) and Total phosphorous (1 mg/L); etc.

SLIDE 13

13

Primary Treatment Stage

• Water passes across large screens or other types of

mechanical separators to remove physical objects (trash…use your imagination)

• Water then passes through special system of

lagoons/basins/channels that decrease the waters g / / velocity, and results in the settling of heavy inorganic matter, & flotation of ‘liquid grease’

– The liquid grease includes fats, oils, waxes, and soaps – Layer is skimmed off

• 30% of BOD removed by this primary process

– BOD still several hundred ppm – BOD mainly due to organic colloidal materials

Secondary treatment

• The secondary processes are mainly biological

where conditions are adjusted so that aerobic microorganisms are able to thrive.

• A widely used method of secondary

treatment is known as the activated sludge process (ASP).

– In general water goes to a special tank where it is aerated & mixed with various microorganisms – After a period of time, water is passed into p , p separate clarifiers to allow the microorganisms to settle – The settled microorganisms are recycled back into the original aeration tank, and the clarified water sent to the final stage

• BOD in this process can be reduced to 100

ppm or less

• Some nitrification occurs during this stage,

where organic nitrogen is converted to nitrate ion and CO2.

Tertiary (Advanced or Chemical) treatment

• Tertiary treatment includes a variety of advanced processes to

remove specific contaminants before final disinfection of the water.

– In some cases can be pure enough for drinking water, or discharged into rivers which maybe a source for drinking water downstream – Common in Europe, Some parts of North America where population density is high, and fresh water availability is low

• Tertiary processes include
• Tertiary processes include

– Further reduction of BOD via coagulation using alum (see earlier slide) – Adsorption, organics & some heavy metals, onto granular activated charcoal (GAC) – Phosphate removal – Heavy metal removal using sulfide ions (ppt of insoluble hydroxides or sulfides) – Fe removal using aeration – Removal of excess inorganic ions

Removal of Nitrogen & Phosphorous

Nitrogen Compounds

• Ammonia can be removed by

adding lime to raise the pH, followed by aeration to force it

• ut as a gas

Phosphorous Compounds

• Can be ppt using calcium

hydroxide, (Ca3(PO4)2 &/or Ca5(PO4)3OH), ferric chloride,

• r alum
• Biological action using an

Enhanced Biological Phosphorus Removal process

– 2 step processes; anaerobic conditions force the bacteria to Sources:

• Agriculture, industry,

NOx

• ut as a gas
• Ion exchange using resins
• Nitrifying bacteria can oxidize

all organic nitrogen and ammonia to nitrate, which is then denitrified using anaerobic bacteria & some

• rganic (methanol) as an
• xidant:

conditions force the bacteria to produce volatile fatty acids, & 2nd aerobic process forces bacteria to use phosphorus – The sludge has a high phosphorous content & can be sold as fertilizer

O 13H 3N 5CO 6H 6NO OH 5CH

2 2 2 bacteria 3 3

       

  Sources:

• Polyphosphates from detergents
• Large extent been banned globally

Consequences of Excess N & P

Eutrophication:

• “The process by which a body of

water acquires a high concentration of nutrients, especially phosphates and

• nitrates. These typically promote

excessive growth of algae. As the l d d d h h algae die and decompose, high levels of organic matter and the decomposing organisms deplete the water of available oxygen, causing the death of other

• rganisms, such as fish.

Eutrophication is a natural, slow‐ aging process for a water body, but human activity greatly speeds up the process.”

Toxic algal bloom at intake to Hartbeespoort Dam treatment works National Monitoring Program (Run by DWAF): http://www.dwaf.gov.za/iwqs/eutrophication/NEMP/default.asp

SLIDE 14

14

Filtration

Gravity Filtration

• After coagulation or ppt step,

water can contain sediments that wont settle, thus passed through a filtration bed

• Force of gravity pulls water

through

• Solids get stuck in various

pores

Membrane Filtration

• Have various types with pores

ranging from 0.002 m – 10m

• Use pressure gradient to pass

water across the barrier

• Generally must pre‐treat water

before use

• Nanofiltration membranes can

disinfect water, and desalinate!

Disinfection By Chlorination

• Reduces the population of various microorganisms to a level safe enough

for discharge

• When added to water

– Reacts with whatever it can – After which it reacts with other substances to produce a residual kill effect (not as effective as chlorine) – Typically, need a total of 1.0 mg/L of chlorine (residual chlorine) for 30 minutes for effective disinfection

• First, chlorine reacts with water to produce hypochlorous acid (HOCl) as

follows:

Cl2(g) + 2H2O(l) ↔ HOCl(aq) + H3O+(aq) + Cl‐(aq) – At moderate pH eqm lies to the right – Very little molecular chlorine in solution – At high pH HOCl ionizes to give OCl‐, which is less effective (lower ability to penetrate cell walls of bacteria) – If necessary pH increased by adding lime (CaO)

• Can use Sodium hypochlorite (NaOCl aka Bleach! Contains upto 12%

chlorine), or calcium hypochlorite (Ca(OCl)2, typically used with swimming pools)

Chlorine Kills…!

Formation of Chloramines (weaker disinfectant)

• NH3 + HOCl → NH2Cl+ H2O
• NH2Cl + HOCl → NHCl2+ H2O
• NHCl2+ HOCl → NCl3+ H2O
• Killing with chlorine involves

quite complicated chemistry.

• The free available chlorine for

disinfection is both the HOCl and OCl‐ together.

• Chlorine, being a very reactive

l t ill idi i element, will oxidize organic and inorganic matter alike when added to water.

– Damage to the cell wall – Alteration of cell permeability – Alteration of the colloidal nature of the protoplasm – Inhibition of enzyme activity

Chlorination Pros & Cons

Disadvantages

• HOCl is an oxidizing agent &

chlorinating agent!

• Can form halogenated organic

compounds

l ( b

Advantages

• Reduces/eliminated water

borne diseases

– Typhoid & cholera almost eradicated in developed world – CH2Cl‐CN (60 ppb: U.S.A EPA reg’) – CHCl2‐COOH ~ more carcinogenic than chloroform – Chlorinated phenols (odiferous & toxic) – Trihalomethanes (e.g. CHCl3), limited at 80 ppb (USA & EU)

• All dependant on the amount
• f organic content in the water
• Residual chlorine protects the

water from subsequent contamination from bacteria

– Often in form of chloramines – Ammonia sometimes added deliberately to produce chloramines (less THM production, longer lifetime than HOCl)

Disinfection by O3 or ClO2

O3

• O3 generated on‐site because of

it short lifetime

• ~20, 000 V discharge in dry air

 O3

• 10 min contact time needed

between the ozone heavy air

ClO2

• Explosive compound, thus

generated onsite (1 e.g.)

– 5NaClO2 + 4HCl  4ClO2 + 5NaCl + 2H2O

• Oxidizes organic molecules

between the ozone heavy air and water

• Produces various radicals in

water (OH, OOH, etc)

• NO RESIDUAL PROTECTION
• Produces bromate ions

(carcinogenic?)

– Can react with organics to produce organobromines – Main one so far is CHBr2CN

• Oxidizes organic molecules
• Does not chlorinate

– Less toxic organic byproducts produced

• Residual chlorite and chlorate

ions are potentially toxic

UV Disinfection

•  ~ 254 nm
• Water passes over the UV lamps

– Short contact time (~ 10 seconds) – Rule of thumb need 75 mm penetration depth

• UV disrupts the DNA of

microorganisms preventing their li ti replication

– UV‐C results in formation of new covalent bonds between thymine units on the same strand of DNA – UV can destroy some organics

• Ineffective in slightly colloidal, Fe
• r humic laden waters

– Suspended particles can absorb or scatter UV, or harbor bacteria – Humic or Fe absorb UV

SLIDE 15

15

Final Product After Treatment of Wastewater

• There are two products resulting from

wastewater treatment namely: 1) Treated Water‐suitable for discharge. 2) S lid l d 2) Solid sludge

Sludge

• Sludge is in form of slurry consisting of deactivated

microbiological material, undigested residual organic matter and inorganic solids from the original wastewater as well as from coagulants.

• When removed from clarifier, the solids content is only

0.1% or less, the rest being water.

• Sludge can be digested in an anaerobic environment

Sludge can be digested in an anaerobic environment (biogas!) 2 {CH2O} → CH4(g) + CO2(g)

• The remaining sludge after this can be incinerated, dumped

(landfill or ocean), or depending on the quality sold/spread as a low grade fertilizer aka biosolid

– Quality issues can arise if unusual amounts of heavy metals are being processed through the plant

Possible Process Flow for Biosolid production

Water Quality Guidelines

• DRINKING WATER
• Criteria for end use of treated water depend on whether water is used for

(i) domestic/ drinking purposes; (ii) Irrigation; (iii) Industrial purposes e.g cleaning equipment, building or other structure.

• For drinking water, stringent requirements are necessary for water quality.
• Water quality requirements include: toxicity, colour, odour and taste.
• There are several guidelines available, most, if not all, are guided by

legislation in the respective polity legislation in the respective polity

– RSA (http://www.dwaf.gov.za/Dir_WQM/docsFrame.htm)

• Domestic use
• Recreational use
• Industrial use
• Irrigation
• Livestock watering
• Aquaculture

– USA (http://water.epa.gov/scitech/swguidance/standards/criteria/index.cfm) – WHO (http://www.who.int/water_sanitation_health/dwq/gdwq3rev/en/)

• Note the WHO guidelines are more of a resource to aide various nations develop the

appropriate framework to regulate drinking water standards

The South African Water Quality Guidelines for Domestic Water Use

Scope:

• a user needs specification of the quality
• f water required for different domestic
• uses. The document is intended to

provide the information required to make judgements as to the fitness of water to be used for domestic purposes, primarily for human consumption but also for bathing and other household uses.

• The guidelines are applicable to any

water that is used for domestic purposes, Field guide summarizes TWQR for various end uses; Below is values for Cd (mg/L) water that is used for domestic purposes, irrespective of its source (municipal supply, borehole, river, etc.) or whether

• r not it has been treated.
• The guidelines do not address:

– Water which is sold as a beverage in bottles; – Water in swimming pools.

Purpose

• used by the Department of Water Affairs

and Forestry as its primary source of information and decision‐support to judge the fitness of water for use and for

• ther water quality management

purposes.