wastewater treatment environmental chemistry tip 2011

Wastewater Wastewater TreatmentTreatment

Environmental Chemistry Environmental Chemistry

TIP 2011TIP 2011

What is Wastewater What is Wastewater Treatment?Treatment?

Wastewater treatmentWastewater treatment is also is also referred to as referred to as sewage treatmentsewage treatment

Process of removing physical, chemical, Process of removing physical, chemical, and biological contaminants from and biological contaminants from wastewater and household sewagewastewater and household sewage

Goal is to separate wastewater into:Goal is to separate wastewater into: Environmentally-safe Environmentally-safe fluid wastefluid waste stream stream Solid wasteSolid waste to be disposed or reused to be disposed or reused

Wastewater SourcesWastewater Sources

Wastewater comes Wastewater comes from:from: HomesHomes

Sinks, showers, toilets, Sinks, showers, toilets, washing machines, washing machines, dishwashersdishwashers

BusinessesBusinesses Industrial facilitiesIndustrial facilities Storm runoff Storm runoff

From roads, parking From roads, parking lots, roofslots, roofs

Image: http://www.acumen.com.my/content/chemical-testing?q=node/6

What Needs to be What Needs to be Removed?Removed?

Wastewater may contain a variety of Wastewater may contain a variety of substances:substances: trash and debristrash and debris human wastehuman waste food scrapsfood scraps oils oils grease grease soaps soaps chemicals (cleaning, pesticides, industrial)chemicals (cleaning, pesticides, industrial) pharmaceuticals and personal care productspharmaceuticals and personal care products

http://www.westfield.ma.edu/personalpages/draker/edcom/final/webprojects/sp11/triparoundworld/Marine.html

What Needs to be What Needs to be Removed?Removed?

Wastewater from both domestic and Wastewater from both domestic and industrial sources may contain a variety of industrial sources may contain a variety of potentially harmful contaminants, including:potentially harmful contaminants, including: Bacteria Bacteria

E. coli (right), Giardia, Hepatatis AE. coli (right), Giardia, Hepatatis A Viruses Viruses NitratesNitrates Metals Metals

mercury, lead, cadmium, chromium, arsenicmercury, lead, cadmium, chromium, arsenic Toxic materialsToxic materials Salts Salts

http://www.anh-usa.org/the-european-e-coli-outbreak-the-real-story/

Example 1: Example 1: ConcentrationConcentration

A 4.2 mL wastewater sample was A 4.2 mL wastewater sample was tested and found to contain 7.6 ng of tested and found to contain 7.6 ng of lead (II) ions. What is the molarity lead (II) ions. What is the molarity of lead (II) ions in this solution?of lead (II) ions in this solution?

Example 1 SolutionExample 1 Solution

7.6 ng Pb7.6 ng Pb x x 1010-9 -9 g g x x 1 mol Pb1 mol Pb x x 1 1 mL solnmL soln

4.2 mL 1 ng 207.2 g Pb 4.2 mL 1 ng 207.2 g Pb 1010-3-3 L L

= 9.1 x 10= 9.1 x 10-9 -9 mol/L mol/L

= 9.1 x 10= 9.1 x 10-9-9 M Pb M Pb

Why Treat it?Why Treat it?

The environment is able to naturally The environment is able to naturally dilute and degrade water contaminants, dilute and degrade water contaminants, but only in small amountsbut only in small amounts Wastewater Wastewater

treatment treatment reduces reduces pollutants to pollutants to levels that the levels that the environment environment can safely can safely handle and handle and process process

Why Treat it?Why Treat it? Decaying solid matter left in water Decaying solid matter left in water

consumes dissolved oxygen from the waterconsumes dissolved oxygen from the water Known as Known as Biochemical Oxygen Demand Biochemical Oxygen Demand

(BOD):(BOD): the amount of dissolved oxygen needed the amount of dissolved oxygen needed by aerobic organisms to break down organic by aerobic organisms to break down organic mattermatter

Lack of oxygen can kill plants and aquatic lifeLack of oxygen can kill plants and aquatic life Excessive nutrients (nitrogen and Excessive nutrients (nitrogen and

phosphorous) can also lead to deoxygenationphosphorous) can also lead to deoxygenation Increased plant and algae growth, which Increased plant and algae growth, which

eventually die and decompose, lead to an eventually die and decompose, lead to an increased BODincreased BOD

Process of Water Process of Water TreatmentTreatment

Water which enters a water treatment Water which enters a water treatment facility undergoes a series of steps to facility undergoes a series of steps to cleanse the water using physical, cleanse the water using physical, chemical, and biological processes chemical, and biological processes

Upon exiting the water treatment Upon exiting the water treatment facility, the decontaminated water is facility, the decontaminated water is released into rivers or streams, entering released into rivers or streams, entering again into the environment again into the environment Sometimes used specifically for agriculture Sometimes used specifically for agriculture

and irrigationand irrigation Possible to purify into clean drinking water Possible to purify into clean drinking water

againagain

Steps of the Wastewater Steps of the Wastewater Treatment ProcessTreatment Process

1. Pretreatment1. Pretreatment 2. Primary 2. Primary

TreatmentTreatment 3. Secondary 3. Secondary

TreatmentTreatment 4. Tertiary 4. Tertiary

TreatmentTreatment 5. Sludge 5. Sludge

Processing Processing

Water Treatment ProcessWater Treatment Process

Image: http://www.cityofdunbarwv.com/node/22

Treatment Process Treatment Process Step 1: PretreatmentStep 1: Pretreatment

Prepares waste water for Prepares waste water for entering the treatment plantentering the treatment plant

Removal of larger debris by Removal of larger debris by screening (shown right)screening (shown right)

TrashTrash Tree limbsTree limbs

Removal of grit and gravel by Removal of grit and gravel by screening and settling screening and settling

Gravel must be removed early Gravel must be removed early as it can damage machinery as it can damage machinery and equipment in the and equipment in the treatment planttreatment plant

http://www.alard-equipment.com/wastewater/index.htm

Treatment ProcessTreatment ProcessStep 2: Primary TreatmentStep 2: Primary Treatment

In In Primary TreatmentPrimary Treatment, as much solid material , as much solid material is removed as possible by relying on gravityis removed as possible by relying on gravity

Removes most of the Removes most of the sludgesludge and and scumscum Sludge: Organic and inorganic materials Sludge: Organic and inorganic materials

which will naturally settlewhich will naturally settle removed by sedimentationremoved by sedimentation

Scum: Materials which will float (oil, grease, Scum: Materials which will float (oil, grease, soap) soap) removed by skimmingremoved by skimming

This step successfully removes 50 to 70% of This step successfully removes 50 to 70% of suspended solids and up to 65% of oil and suspended solids and up to 65% of oil and greasegrease

Colloidal and dissolved materials are not Colloidal and dissolved materials are not affected by this stepaffected by this step

Separation of Oil and Separation of Oil and GreaseGrease

Oil and grease will naturally separate from Oil and grease will naturally separate from water due to differences in water due to differences in polaritypolarity

This is also known as the This is also known as the hydrophobic effecthydrophobic effect Water is considered a polar substance, while oils Water is considered a polar substance, while oils

and grease are considered nonpolar substancesand grease are considered nonpolar substances

A polar molecule is one in A polar molecule is one in which electrons are which electrons are unevenly distributed within unevenly distributed within the molecule due to the molecule due to differing electronegativitiesdiffering electronegativities

Nonpolar molecules Nonpolar molecules generally have evenly generally have evenly distributed electrons distributed electrons andhave no areas of partial andhave no areas of partial chargescharges

http://novocreamseparators.com/blog/clean-separation/


Water molecules have regions of differing Water molecules have regions of differing electron density, making one end of the electron density, making one end of the molecule have a partially negative side, while molecule have a partially negative side, while the other is partially positivethe other is partially positive

Water molecules are attracted to one another Water molecules are attracted to one another due to attractions between these positive and due to attractions between these positive and negative regions (hydrogen bonding)negative regions (hydrogen bonding)

http://marineodyssey.co.uk/abioticoceans.htmlhttp://bioweb.wku.edu/courses/biol115/Wyatt/Bonds.htm


Oil and grease are typically long Oil and grease are typically long chains of hydrocarbons, making them chains of hydrocarbons, making them nonpolar, hydrophobic substances nonpolar, hydrophobic substances

Mixing a hydrophobic substance such Mixing a hydrophobic substance such as oil into water disturbs the as oil into water disturbs the attractions between polar water attractions between polar water moleculesmolecules

Hydrophobic substances tend to Hydrophobic substances tend to aggregate together in water in order aggregate together in water in order to minimize the surface area that to minimize the surface area that contacts the water which minimizes contacts the water which minimizes the disturbancethe disturbance

Oils and grease rise to the top of Oils and grease rise to the top of water due to a difference in density water due to a difference in density

http://en.wikibooks.org/wiki/Structural_Biochemistry/Chemical_Bonding/Hydrophobic_interaction

Primary Treatment: Primary Treatment: Physical SeparationPhysical Separation

Sewage flows through large tanks known as Sewage flows through large tanks known as primary clarifiersprimary clarifiers or or primary sedimentationprimary sedimentation tankstanks

Round or rectangular basins, 3 to 5 meters deepRound or rectangular basins, 3 to 5 meters deep Water retained here for 2 to 3 hoursWater retained here for 2 to 3 hours

Sludge will settle toward the bottom of tanks, Sludge will settle toward the bottom of tanks, while scum will rise to the top. Both are while scum will rise to the top. Both are removed and pumped to sludge treatment tanksremoved and pumped to sludge treatment tanks

Mechanical scrapers continuously drive sludge Mechanical scrapers continuously drive sludge into a well at the bottom of the tanks to be into a well at the bottom of the tanks to be removed removed

Mechanical skimmers or rakes remove oils and Mechanical skimmers or rakes remove oils and grease from the surface. grease from the surface.

May be recovered to use in May be recovered to use in saponificationsaponification

SaponificationSaponification

SaponificationSaponification is the base hydrolysis of is the base hydrolysis of fats and oils to produce glycerol and a fats and oils to produce glycerol and a crude soapcrude soap

triglyceride (fat)triglyceride (fat) glycerol glycerol

Primary Treatment: Primary Treatment: AerationAeration

Another process during primary Another process during primary treatment is treatment is aerationaeration

Water is agitated and exposed to air, Water is agitated and exposed to air, which serves two purposes:which serves two purposes:

Allows some dissolved gases to escape, Allows some dissolved gases to escape, such as foul smelling hydrogen sulfide gassuch as foul smelling hydrogen sulfide gas

Allows more oxygen to be dissolved into Allows more oxygen to be dissolved into the water. Oxygen may be bubbled into the water. Oxygen may be bubbled into water at this point. water at this point.

Increasing dissolved oxygen in water Increasing dissolved oxygen in water compensates for the increased BOD compensates for the increased BOD and helps with the sludge settling and helps with the sludge settling processprocess

Example 2: ConcentrationExample 2: Concentration

9 ppm is considered a healthy 9 ppm is considered a healthy dissolved oxygen concentration in dissolved oxygen concentration in water. What is this concentration water. What is this concentration expressed in molarity?expressed in molarity?


9 g O9 g O22 x x 1000 g H1000 g H22OO x x 1 1 mol Omol O22

1000000g H1000000g H22O 1 L HO 1 L H22O O 32 g O32 g O22

= 3 x 10= 3 x 10-4 -4 M OM O22

Treatment Process Step 3:Treatment Process Step 3:Secondary TreatmentSecondary Treatment

Secondary treatmentSecondary treatment is designed to is designed to remove residual organic materials and remove residual organic materials and suspended solids that were not suspended solids that were not removed during primary treatmentremoved during primary treatment

Works to degrade the biological Works to degrade the biological content of the sewage that comes from content of the sewage that comes from human waste, food waste, soaps and human waste, food waste, soaps and detergent. detergent.

Removal of biodegradable dissolved Removal of biodegradable dissolved and colloidal organic matter using and colloidal organic matter using aerobic biological treatmentaerobic biological treatment and and flocculationflocculation

Secondary Treatment: Secondary Treatment: Aerobic Biological Aerobic Biological

Treatment Treatment performed in the presence of oxygen performed in the presence of oxygen

by aerobic microorganisms by aerobic microorganisms Aerobic = in presence of oxygenAerobic = in presence of oxygen

principally bacteria and protozoaprincipally bacteria and protozoa metabolize the organic matter in the metabolize the organic matter in the

wastewater, including sugars, fats, wastewater, including sugars, fats, and short-chain hydrocarbonsand short-chain hydrocarbons

Results in production of several Results in production of several inorganic products, including COinorganic products, including CO22, , NHNH33, and H, and H22O, as well as reproduction O, as well as reproduction of more microorganisms of more microorganisms

Secondary Treatment:Secondary Treatment:FlocculationFlocculation

Process in which Process in which colloids come out colloids come out of suspension to of suspension to form flakes, or flocform flakes, or floc

Differs from Differs from precipitation!precipitation!

PrecipitationPrecipitation involves particles which involves particles which are dissolved in a solutionare dissolved in a solution

FlocculationFlocculation involves particles that are involves particles that are suspended within a liquid, not dissolvedsuspended within a liquid, not dissolved

http://www.tech-faq.com/flocculation.html

Colloid Properties Colloid Properties

Colloids contain microscopic Colloids contain microscopic particles dissolved evenly particles dissolved evenly throughout a substancethroughout a substance

Particles finer than 0.1 µm in Particles finer than 0.1 µm in water remain in constant motion water remain in constant motion because they often carry an because they often carry an electrostatic charge which electrostatic charge which causes them to repel each other. causes them to repel each other.

Colloids and FlocculationColloids and Flocculation

If the electrostatic charge of colloid If the electrostatic charge of colloid particles is neutralized, the finer particles is neutralized, the finer particles start to collide and combine particles start to collide and combine together into larger groups of particlestogether into larger groups of particles Due to the influence of Van der Waals Due to the influence of Van der Waals

forces: forces: These larger and heavier particles are These larger and heavier particles are

called flocs called flocs Floc can either be filtered out of Floc can either be filtered out of

wastewater or left to settle out as wastewater or left to settle out as sludgesludge

Colloids and FlocculationColloids and Flocculation Flocculants, or flocculating agents Flocculants, or flocculating agents

are chemicals that promote are chemicals that promote flocculation by causing colloids flocculation by causing colloids and other suspended particles in and other suspended particles in liquids to combine, forming a floc. liquids to combine, forming a floc.

Many flocculants are multivalent Many flocculants are multivalent cations such as aluminum, iron, cations such as aluminum, iron, calcium, and magnesiumcalcium, and magnesium Often, colloid particles carry a Often, colloid particles carry a

negative chargenegative charge These positively charged These positively charged

flocculant molecules interact with flocculant molecules interact with negatively charged colloid negatively charged colloid particles and molecules to reduce particles and molecules to reduce the barriers to aggregation. the barriers to aggregation.

http://water.me.vccs.edu/courses/env110/lesson4.htm

Colloids and FlocculationColloids and Flocculation Many flocculating agents Many flocculating agents

under appropriate under appropriate conditions (such as pH, conditions (such as pH, temperature and salinity) temperature and salinity) will react with water to will react with water to form insoluble hydroxidesform insoluble hydroxides

These hydroxides will These hydroxides will precipitate from solution precipitate from solution and link together to form and link together to form long chains or mesheslong chains or meshes physically traps small physically traps small

particles into the larger flocparticles into the larger floc

Polymers can also be Polymers can also be used as flocculantsused as flocculants

http://www.kolonls.co.kr/eng/product/pop02_16.asp

Common FlocculantsCommon Flocculants

Chemical Flocculating Chemical Flocculating Agents:Agents:

AlumAlum Aluminum Aluminum

chlorohydratechlorohydrate Aluminum sulfateAluminum sulfate Calcium oxideCalcium oxide Calcium hydroxideCalcium hydroxide Iron (II) sulfateIron (II) sulfate Iron (III) chlorideIron (III) chloride PolyacrylamidePolyacrylamide Sodium silicateSodium silicate

Natural Products Natural Products Used as Used as Flocculants:Flocculants:

ChitosanChitosan IsinglassIsinglass Horseradish tree Horseradish tree

seedsseeds GelatinGelatin Guar GumGuar Gum Alginates (from brown Alginates (from brown

seaweed)seaweed)

Treatment Process Treatment Process Step 4: Tertiary TreatmentStep 4: Tertiary Treatment

Tertiary treatmentTertiary treatment (also known as (also known as advanced treatmentadvanced treatment) includes the remaining ) includes the remaining processes necessary to remove the following processes necessary to remove the following from wastewater: from wastewater: NitrogenNitrogen PhosphorusPhosphorus additional suspended solidsadditional suspended solids remaining organicsremaining organics heavy metalsheavy metals dissolved solidsdissolved solids

Final treatment stage before water is Final treatment stage before water is released into rivers, lakes, or groundwaterreleased into rivers, lakes, or groundwater

Example 3: Dilution and Example 3: Dilution and ConcentrationConcentration

Nitrogen is usually present in Nitrogen is usually present in wastewater as ammonia. 3.5 million L wastewater as ammonia. 3.5 million L of wastewater entering a treatment of wastewater entering a treatment plant have an initial ammonia plant have an initial ammonia concentration of 0.75 mM. By the time concentration of 0.75 mM. By the time the wastewater reaches the tertiary the wastewater reaches the tertiary treatment phase, the volume has been treatment phase, the volume has been reduced to 2.9 million L. What is the reduced to 2.9 million L. What is the concentration of ammonia at this point? concentration of ammonia at this point?


(M(M11)(V)(V11) = (M) = (M22)(V)(V22))

(0.75 mM NH(0.75 mM NH33)(3.5 million L)=(M)(3.5 million L)=(M22))(2.9 million L)(2.9 million L)

MM22 = 0.91 mM = 0.91 mM

Tertiary TreatmentTertiary Treatment

Depending on the types of Depending on the types of contamination and the desired end use, contamination and the desired end use, one or more processes may be used in one or more processes may be used in tertiary treatment:tertiary treatment: Sand filtrationSand filtration Nutrient removal (nitrogen and Nutrient removal (nitrogen and

phosphorous)phosphorous) Odor removalOdor removal Disinfection (via chlorination, ozone, or UV Disinfection (via chlorination, ozone, or UV

radiation)radiation)

Tertiary TreatmentTertiary Treatment Sand filtrationSand filtration

Removes any remaining suspended Removes any remaining suspended solids not removed by sedimentation solids not removed by sedimentation and flocculationand flocculation

May be combined with filtering over May be combined with filtering over activated carbon to remove toxins and activated carbon to remove toxins and odorsodors

http://water.me.vccs.edu/concepts/filters.html

Tertiary TreatmentTertiary Treatment Nutrient RemovalNutrient Removal

Excessive release of nitrogen and Excessive release of nitrogen and phosphorous leads to a condition known phosphorous leads to a condition known as as eutrophicationeutrophication (presence of excessive (presence of excessive nutrients)nutrients) Eutrophication Eutrophication

encourages encourages excessive algae excessive algae and weed growthand weed growth

Leads to Leads to deoxygenation deoxygenation of water of water

Some algae can Some algae can release toxins release toxins into waterinto water http://05lovesgeography.blogspot.com/2011/02/eutrophication.html

Tertiary TreatmentTertiary Treatment Nutrient removal may be accomplished Nutrient removal may be accomplished

through biological processes by passing through biological processes by passing wastewater through 5 different chambers:wastewater through 5 different chambers:

1.1. Anaerobic fermentation zone Anaerobic fermentation zone very low dissolved oxygen levels and the very low dissolved oxygen levels and the absence of nitratesabsence of nitrates

2.2. Anoxic zone Anoxic zone low dissolved oxygen levels but nitrates low dissolved oxygen levels but nitrates presentpresent

3.3. Aerobic zone Aerobic zone 4.4. Secondary anoxic zoneSecondary anoxic zone5.5. Final aeration zone Final aeration zone

Biological Nutrient Biological Nutrient Removal ZonesRemoval Zones

http://www.wedotanks.com/anaerobic-aerobic-wastewater-treatment-plant.asp

Nutrient Removal: Nutrient Removal: NitrogenNitrogen

The majority of nitrogen in wastewater is The majority of nitrogen in wastewater is in the form of ammonia, NHin the form of ammonia, NH33

Nitrogen removal takes place in two Nitrogen removal takes place in two parts:parts: Nitrification: oxidation of ammonia to Nitrification: oxidation of ammonia to

nitratenitrate Denitirication: reduction of nitrate to Denitirication: reduction of nitrate to

nitrogen gasnitrogen gas Nitrogen gas is then released into the Nitrogen gas is then released into the

atmosphereatmosphere


NitrificationNitrification Nitrification occurs in the 3Nitrification occurs in the 3rdrd zone (aerobic zone (aerobic

zone) zone) Two step processTwo step process

Each step carried out by a unique bacteriaEach step carried out by a unique bacteria Step 1: oxidation of ammonia to nitrite (NOStep 1: oxidation of ammonia to nitrite (NO22 --

11))

NHNH33 NO NO22 -1-1

Step 2: oxidation of nitrite to nitrate (NOStep 2: oxidation of nitrite to nitrate (NO3 3 -1-1 ) )

NONO2 2 -1-1 NO NO3 3

-1-1


DenitrificationDenitrification After nitirification in the 3After nitirification in the 3rdrd zone, zone,

wastewater rich in nitrates is recycled wastewater rich in nitrates is recycled back to the 2back to the 2ndnd zone (first anoxic zone) zone (first anoxic zone)

The recycled nitrates, in the absence of The recycled nitrates, in the absence of dissolved oxygen, are reduced by bacteria dissolved oxygen, are reduced by bacteria to nitrogen gasto nitrogen gas

NONO3 3 -1-1 N N22

Incoming organic carbon compounds present Incoming organic carbon compounds present in this zone act as hydrogen donors in this zone act as hydrogen donors


DenitrificationDenitrification In zone 4, the second anoxic zone, In zone 4, the second anoxic zone,

any nitrates not reduced in zone 2 any nitrates not reduced in zone 2 are reduced by the respiration of are reduced by the respiration of bacteria presentbacteria present

In zone 5, the re-aeration zone, In zone 5, the re-aeration zone, oxygen levels are increased to stop oxygen levels are increased to stop the denitirication processthe denitirication process Stopping denitirification prevents Stopping denitirification prevents

problems with settlingproblems with settling

Example 4: Redox Example 4: Redox ReactionsReactions

Redox Reactions: Balance the three Redox Reactions: Balance the three redox half reactions associated with redox half reactions associated with nitrogen removal:nitrogen removal: Nitrification Step 1Nitrification Step 1 Nitrification Step 2Nitrification Step 2 DenitrificationDenitrification

Example 4 SolutionExample 4 SolutionNitrification Step 1Nitrification Step 1

NHNH33 NO NO22-1-1

NHNH33 + 2H + 2H22O O NO NO22-1-1 + 7 H + 7 H++

NHNH33 + 2H + 2H22O O NO NO22-1-1 + 7 H + 7 H++ + 6 e- + 6 e-

Nitrification Step 2Nitrification Step 2

NONO22-1-1 NO NO33

-1-1

NONO22-1-1 + H + H22OO NO NO33

-1-1 + 2 H + 2 H++

NONO22-1-1 + H + H22OO NO NO33

-1-1 +2H +2H++ + 2e- + 2e-Denitrification Denitrification

NONO33-1-1 N N22

2 NO2 NO33-1-1 N N22

2 NO2 NO33-1-1 + 12 H + 12 H++ N N22 + 6H + 6H22OO

2 NO2 NO33-1-1 + 12H + 12H++ + 11e- + 11e- N N22 + 6H + 6H22OO

Nutrient Removal: Nutrient Removal: PhosphorousPhosphorous

Phosphorous may occur as organic or Phosphorous may occur as organic or inorganic formsinorganic forms Of the 5 to 20 mg/L total phosphorous content Of the 5 to 20 mg/L total phosphorous content

in wastewater, 1 to 5 mg/L is organicin wastewater, 1 to 5 mg/L is organic Phosphorous is typically present in the form Phosphorous is typically present in the form

of phosphatesof phosphates Typical forms include:Typical forms include:

Orthophosphates: easily used in biological Orthophosphates: easily used in biological metabolismmetabolism

Polyphosphates: contain two or more Polyphosphates: contain two or more phosphorous atoms in a complex molecule. phosphorous atoms in a complex molecule. Can slowly undergo hydrolysis to Can slowly undergo hydrolysis to orthophosphatesorthophosphates

Phosphorous may be removed biologically Phosphorous may be removed biologically or chemicallyor chemically


Biological Removal:Biological Removal: Biological phosphorous removal takes place in Biological phosphorous removal takes place in

Zones 1 and 2 of the five zone system mentioned Zones 1 and 2 of the five zone system mentioned earlierearlier

In Zones 1 and 2, the anaerobic fermentation zone In Zones 1 and 2, the anaerobic fermentation zone and first anoxic zone, bacteria are stressed by the and first anoxic zone, bacteria are stressed by the low oxygen conditions and release phosphorous to low oxygen conditions and release phosphorous to maintain cell equilibriummaintain cell equilibrium

When these bacteria reach later zones with higher When these bacteria reach later zones with higher oxygen supplies, they rapidly accumulate oxygen supplies, they rapidly accumulate phosphorous in excess of what they normally wouldphosphorous in excess of what they normally would

Removed along with sludgeRemoved along with sludge


Chemical RemovalChemical Removal Phosphorous can be precipitated out of the Phosphorous can be precipitated out of the

wastewater mixture using salts of iron, wastewater mixture using salts of iron, aluminum, or calciumaluminum, or calcium

Some of this is accomplished during flocculationSome of this is accomplished during flocculation Produces more sludge due to precipitate Produces more sludge due to precipitate

formationformation More expensive than biological removal (added More expensive than biological removal (added

cost of chemicals)cost of chemicals) Usually more reliable and more effective than Usually more reliable and more effective than

biological removalbiological removal

Chemical Removal of Chemical Removal of PhosphorousPhosphorous

Using CalciumUsing Calcium Usually added in the form of lime, Ca(OH)Usually added in the form of lime, Ca(OH)22.. Reacts with the natural alkalinity in the Reacts with the natural alkalinity in the

wastewater to produce calcium carbonatewastewater to produce calcium carbonateCa(HCOCa(HCO33))22 + Ca(OH) + Ca(OH)22 2CaCO 2CaCO33 + 2H + 2H22OO

As the pH value of the wastewater increases As the pH value of the wastewater increases past 10, excess calcium ions will then react with past 10, excess calcium ions will then react with the phosphate, to precipitate in hydroxylapatite:the phosphate, to precipitate in hydroxylapatite:10 Ca10 Ca2+2+ + 6 PO + 6 PO44

3-3- + 2 OH + 2 OH-- ↔ Ca ↔ Ca1010(PO(PO44)*6(OH))*6(OH)22 (s)(s) Amount of lime required depends on pH of water Amount of lime required depends on pH of water

rather than amount of phosphate presentrather than amount of phosphate present Neutralization may be required to lower the pH Neutralization may be required to lower the pH

before further treatment or disposal, typically by before further treatment or disposal, typically by recarbonation with carbon dioxiderecarbonation with carbon dioxide

Example 5: Acids, Bases, Example 5: Acids, Bases, and pHand pH

The pH of domestic wastewater is The pH of domestic wastewater is about 7.2. about 7.2. What are the concentrations of What are the concentrations of

hydronium and hydroxide ions in water hydronium and hydroxide ions in water at this point?at this point?

Lime is only effective in removing Lime is only effective in removing phosphorous at a pH higher than 10. phosphorous at a pH higher than 10. What is the pH of 9800 L of water What is the pH of 9800 L of water treated with 50 g Ca(OH)treated with 50 g Ca(OH)22??


Part 1:Part 1:[H[H33OO++] = 10 ] = 10 -pH -pH

= 10 = 10 -7.2-7.2 = 6.3 x 10= 6.3 x 10-8-8 M M

[H[H33OO++] [OH-] = 1 x 10] [OH-] = 1 x 10-14-14

[OH-] = [OH-] = 1 x 101 x 10-14-14

6.3 x 106.3 x 10-8-8

= 1.6 x 10= 1.6 x 10-7-7MM

Part 2:Part 2:50.0 g50.0 g x x 1 mol Ca(OH)1 mol Ca(OH)22 x x 2 mol 2 mol

OHOH9800 L 74.1 g 1 mol 9800 L 74.1 g 1 mol

Ca(OH)Ca(OH)22

= 1.38 x 10 = 1.38 x 10 -4 -4 M OH-M OH-

[H[H33OO++] = ] = 1 x 101 x 10-14-14

1.38 x 10 1.38 x 10 -4 -4

= 7.25 x 10 = 7.25 x 10 -11-11 M H M H33OO++] ]

pH = -log[HpH = -log[H33OO++] ] = -log (7.25 x 10 = -log (7.25 x 10 -11-11 M) M)= 10.1= 10.1

Chemical Removal of Chemical Removal of PhosphorousPhosphorous

Using AluminumUsing Aluminum Typically use alum or hydrated Typically use alum or hydrated

aluminum sulfate to precipitate aluminum sulfate to precipitate aluminum phosphates (AlPOaluminum phosphates (AlPO44). ).

AlAl3+3+ + H + HnnPOPO443-n3-n ↔ AlPO ↔ AlPO44 + nH + nH++

Reaction affected by pH, equilibrium of Reaction affected by pH, equilibrium of competing reactions, and presence of competing reactions, and presence of trace elements in wastewatertrace elements in wastewater

Aluminum may adversely affect some of Aluminum may adversely affect some of the bacteria used in sludge and the bacteria used in sludge and digestion and should be used carefullydigestion and should be used carefully

Chemical Removal of Chemical Removal of PhosphorousPhosphorousUsing IronUsing Iron

Iron (III) chloride or sulfate or iron Iron (III) chloride or sulfate or iron (II) sulfate can be used to form iron (II) sulfate can be used to form iron phosphate precipitatesphosphate precipitates

FeFe3+3+ + H + HnnPOPO44 3-n3-n ↔ FePO ↔ FePO44 + + nHnH++

Lime is usually added to raise the Lime is usually added to raise the pH to enhance the reactionpH to enhance the reaction

Example 6: Solubility and Example 6: Solubility and Net IonicNet Ionic

Write the full balanced equation Write the full balanced equation (including states) and the net ionic (including states) and the net ionic equation for the reaction of iron (III) equation for the reaction of iron (III) sulfate with sodium phosphate.sulfate with sodium phosphate.


Balanced Reaction:Balanced Reaction:FeFe22(SO(SO44))33(aq)(aq) + 2Na + 2Na33POPO44(aq)(aq) 2FePO 2FePO44(s)(s) + +

3Na3Na22SOSO44(aq)(aq)

Net: Net:

FeFe3+3+(aq)(aq) + PO + PO44

3-3-(aq)(aq) FePO FePO44 (s)(s)

Tertiary Treatment: Tertiary Treatment: DisinfectionDisinfection

Disinfection of wastewater reduces the Disinfection of wastewater reduces the number of microorganisms in water that number of microorganisms in water that may lead to disease before discharging may lead to disease before discharging back into the environmentback into the environment

Usually the very last step before Usually the very last step before dischargedischarge

Effectiveness depends upon conditions of Effectiveness depends upon conditions of treated water at this point, including treated water at this point, including cloudiness and pHcloudiness and pH

Three major strategies: chlorination, Three major strategies: chlorination, ozone, and UV radiationozone, and UV radiation

http://www.purewater2000.com/Ultraviolet.html

Disinfection: Disinfection: ChlorinationChlorination

Most commonly used Most commonly used form of disinfection form of disinfection due to low cost and due to low cost and high effectivenesshigh effectiveness

The exact mechanism The exact mechanism by which chlorine by which chlorine disinfects is not fully disinfects is not fully understood. It likely understood. It likely involves oxidative involves oxidative damage to microbial damage to microbial cell membranes and cell membranes and vital protein systemsvital protein systems

Chlorination also helps Chlorination also helps to reduce any odors in to reduce any odors in the waterthe water

Drawbacks: Drawbacks: may create chlorinated may create chlorinated

organic compounds that may organic compounds that may be carcinogenicbe carcinogenic

Residual chlorine is toxic to Residual chlorine is toxic to aquatic life aquatic life

May be necessary to May be necessary to dechlorinate water before dechlorinate water before releaserelease

http://chlorination.us/chlorination/chlorination/

Disinfection: Disinfection: ChlorinationChlorination

When chlorine (ClWhen chlorine (Cl22) is injected into water, it ) is injected into water, it forms hypochlorous acid and hydrochloric acid forms hypochlorous acid and hydrochloric acid in a pH dependent equilibriumin a pH dependent equilibrium

ClCl22 + H + H22O → HOCl + HClO → HOCl + HCl Depending on the pH, the hypochlorous acid Depending on the pH, the hypochlorous acid

will partly dissociate to hydrogen and will partly dissociate to hydrogen and hypochlorite ions:hypochlorite ions:

HClO → HHClO → H++ + ClO + ClO--

In acidic solution, the major species are ClIn acidic solution, the major species are Cl22 and HOCl while in basic solution only ClOand HOCl while in basic solution only ClO-- is is present. present.

Very small concentrations of ClOVery small concentrations of ClO22--, ClO, ClO33

--, ClO, ClO44--

are also foundare also found

Disinfection: UV Disinfection: UV RadiationRadiation

Ultraviolet radiation damages the genetic structure of Ultraviolet radiation damages the genetic structure of bacteria and viruses which makes them incapable of bacteria and viruses which makes them incapable of reproductionreproduction

Since no chemicals are used, UV disinfection poses no Since no chemicals are used, UV disinfection poses no risk to organisms which will later encounter the risk to organisms which will later encounter the treated watertreated water Requires highly treated Requires highly treated

water with little water with little cloudiness. Suspended cloudiness. Suspended solids in the water may solids in the water may block out the UV raysblock out the UV rays

Maintaining UV lamps Maintaining UV lamps can be costlycan be costly

http://www.blog.waterfilters.net/uv-technology-explained/1207

Disinfection: OzoneDisinfection: Ozone

Ozone (OOzone (O33) is generated by passing ) is generated by passing oxygen gas (Ooxygen gas (O22) through a high voltage ) through a high voltage potential. Voltage breaks Opotential. Voltage breaks O22 into into oxygen atoms which will recombine as oxygen atoms which will recombine as OO33 gas gas

OO22 + electricity + electricity O O33

Ozone is very unstable. Generated as Ozone is very unstable. Generated as needed rather than storedneeded rather than stored

Produces fewer by-products than Produces fewer by-products than chlorination, but much more costlychlorination, but much more costly

Example 7: Reaction Example 7: Reaction StoichiometryStoichiometry

Write the balanced equation for the Write the balanced equation for the synthesis of ozone from oxygensynthesis of ozone from oxygen

If 56.8 g of ozone must be If 56.8 g of ozone must be synthesized, how many moles of synthesized, how many moles of oxygen gas are required?oxygen gas are required?


3 O3 O22 2 O 2 O33

56.8 g O56.8 g O33 x x 1 mol O1 mol O33 x x 3 mol O3 mol O22

48 g O48 g O33 2 mol O 2 mol O33

= 1.78 mol O2= 1.78 mol O2

Disinfection: OzoneDisinfection: Ozone

Ozone is very effective in destroying Ozone is very effective in destroying viruses and bacteria and may act by viruses and bacteria and may act by several mechanisms:several mechanisms: Direct oxidation and destruction of the cell Direct oxidation and destruction of the cell

wall with leakage of cellular components wall with leakage of cellular components Reactions with radical by-products of ozone Reactions with radical by-products of ozone

decompositiondecomposition Damage to the constituents of the nucleic Damage to the constituents of the nucleic

acids (purines and pyrimidines)acids (purines and pyrimidines) Breakage of carbon-nitrogen bonds leading to Breakage of carbon-nitrogen bonds leading to

depolymerizationdepolymerization

Tertiary Treatment: Odor Tertiary Treatment: Odor RemovalRemoval

Odor in waste water typically form as a Odor in waste water typically form as a result of anaerobic conditionsresult of anaerobic conditions

Most common odor is hydrogen sulfide Most common odor is hydrogen sulfide gasgas

Odor is eliminated along the way by Odor is eliminated along the way by aeration, chlorination, biological aeration, chlorination, biological degradation, and circulation of fluidsdegradation, and circulation of fluids

Other methods to eliminate hydrogen Other methods to eliminate hydrogen sulfide are by adding iron salts, hydrogen sulfide are by adding iron salts, hydrogen peroxide, or calcium nitrateperoxide, or calcium nitrate

Treatment Process Treatment Process Step 5: Sludge TreatmentStep 5: Sludge Treatment

Sludge consists of all the Sludge consists of all the solidsolid material removed material removed from wastewater during the water treatment from wastewater during the water treatment processprocess

While the water in treatment is ready for release While the water in treatment is ready for release into streams and groundwater, sludge requires into streams and groundwater, sludge requires further treatment before it can be disposed or further treatment before it can be disposed or usedused Must reduce the amount of organic matterMust reduce the amount of organic matter Must reduce the number of disease causing microbes Must reduce the number of disease causing microbes Remove as much remaining liquid as possible Remove as much remaining liquid as possible

Sludge treatment options include:Sludge treatment options include: Aerobic digestionAerobic digestion Anearobic digestionAnearobic digestion CompostingComposting IncinerationIncineration

Sludge TreatmentSludge Treatment Sludge is most often processed by Sludge is most often processed by biological biological

anaerobic digestionanaerobic digestion Bacteria metabolize the organic material in Bacteria metabolize the organic material in

the sludgethe sludge Occurs over a period of 10 to 60 days, depending Occurs over a period of 10 to 60 days, depending

on the capabilities of the digesting tankson the capabilities of the digesting tanks Reduces the volume of sludge that requires Reduces the volume of sludge that requires

disposaldisposal Makes the sludge more stable Makes the sludge more stable Improves the dewatering characteristics of the Improves the dewatering characteristics of the

sludgesludge Shorter retention time and smaller tanks Shorter retention time and smaller tanks

requiredrequired Requires higher temperatures, resulting in a Requires higher temperatures, resulting in a

higher energy costhigher energy cost

Sludge TreatmentSludge Treatment One byproduct of One byproduct of

anaerobic sludge anaerobic sludge digestion is the digestion is the production of production of biogasbiogas

Biogas contains about Biogas contains about 60 to 65% methane 60 to 65% methane (CH(CH44) and can be ) and can be recovered as an recovered as an energy source. energy source.

Methane is a Methane is a combustible, combustible, renewable fuelrenewable fuel

CHCH44 + O + O22 CO CO22 + H + H22OOhttp://home.comcast.net/~hollywastewater/Process.htm

Sludge TreatmentSludge Treatment

In small sewage treatment plants, In small sewage treatment plants, sludge is processed using aerobic sludge is processed using aerobic digestiondigestion

Under aerobic conditions, bacteria Under aerobic conditions, bacteria will consume organic material and will consume organic material and convert it into carbon dioxideconvert it into carbon dioxide

Energy cost associated with adding Energy cost associated with adding oxygen to process and blowers to oxygen to process and blowers to remove COremove CO22

Sludge TreatmentSludge Treatment

Composting of sludge is similar to aerobic Composting of sludge is similar to aerobic digestion, except other organic materials digestion, except other organic materials such as sawdust are mixed in with the such as sawdust are mixed in with the sludgesludge

Incineration is the least used method of Incineration is the least used method of sludge treatment. sludge treatment. Sludge burns poorly due to low calorific value, Sludge burns poorly due to low calorific value,

so extra fuels must be addedso extra fuels must be added Worries of emissions associated with sludgeWorries of emissions associated with sludge High energy cost to vaporize residual water High energy cost to vaporize residual water

present in sludgepresent in sludge

Sludge TreatmentSludge Treatment Sludge that does not Sludge that does not

originate from highly originate from highly industrialized areas and is industrialized areas and is for the most part free of for the most part free of toxic chemicals can be toxic chemicals can be used as fertilizerused as fertilizer

Water is removed Water is removed from sludge by from sludge by centrifugation centrifugation and addition of and addition of chemicals that chemicals that aid in polymer aid in polymer formationformation

Dried sludge can Dried sludge can be converted into be converted into fertilizer pellets fertilizer pellets which are usually which are usually rich in rich in phosphorousphosphorous

http://www.thewatertreatmentplant.com/sludge-treatment-equipment.html

Water TreatmentWater Treatment

View the entire process in actiView the entire process in actionon

http://photosmynthesis.wordpress.com/2010/09/16/wetland-services/water-treatment-plant/

SourcesSources Severn Trent Water. “The Water Treatment Process” Online. 9 July 2011. Severn Trent Water. “The Water Treatment Process” Online. 9 July 2011. http://www.youtube.com/watch?v=9z14l51ISwghttp://www.youtube.com/watch?v=9z14l51ISwg United States Geological Survey. “Wastewater Treatment: Water Use” Online. 9 United States Geological Survey. “Wastewater Treatment: Water Use” Online. 9

July 2011. July 2011. http://http://ga.water.usgs.gov/edu/wuww.htmlga.water.usgs.gov/edu/wuww.html South Carolina Office of Regulatory Staff. “Overview of Basic Wastewater Treatment South Carolina Office of Regulatory Staff. “Overview of Basic Wastewater Treatment

Process” Online. 9 July 2011. Process” Online. 9 July 2011. http://http://www.regulatorystaff.sc.gov/orscontent.asp?pageidwww.regulatorystaff.sc.gov/orscontent.asp?pageid=654=654

Author Unknown. “Sewage Treatment” Online. 8 July 2011. Author Unknown. “Sewage Treatment” Online. 8 July 2011. http://http://en.wikipedia.org/wiki/Sewage_treatmenten.wikipedia.org/wiki/Sewage_treatment

United States Geological Survey. “A visit to a wastewater-treatment plant: Primary United States Geological Survey. “A visit to a wastewater-treatment plant: Primary treatment of wastewater” Online. 9 July 2011 treatment of wastewater” Online. 9 July 2011 http://http://ga.water.usgs.gov/edu/wwvisit.htmlga.water.usgs.gov/edu/wwvisit.html

Natural Resources Management and Environment Department. “Water Treatment” Natural Resources Management and Environment Department. “Water Treatment” Online. 10 July 2011. Online. 10 July 2011. http://www.fao.org/docrep/t0551e/t0551e05.htmhttp://www.fao.org/docrep/t0551e/t0551e05.htm

Environmental Protection Agency. “Water Treatment Process” Online. 8 July 2011. Environmental Protection Agency. “Water Treatment Process” Online. 8 July 2011. http://water.epa.gov/learn/kids/drinkingwater/watertreatmentplant_index.cfmhttp://water.epa.gov/learn/kids/drinkingwater/watertreatmentplant_index.cfm

Environmental Protection Agency. Wastewater Technology Fact Sheet: Ozone Environmental Protection Agency. Wastewater Technology Fact Sheet: Ozone Disinfection. (1999) Online. 11 July 2011 Disinfection. (1999) Online. 11 July 2011 http://water.epa.gov/scitech/wastetech/upload/2002_06_28_mtb_ozon.pdfhttp://water.epa.gov/scitech/wastetech/upload/2002_06_28_mtb_ozon.pdf

Author Unknown. “Chlorination” Online 11 July 2011. Author Unknown. “Chlorination” Online 11 July 2011. http://water.me.vccs.edu/courses/ENV149/chlorinationb.htmhttp://water.me.vccs.edu/courses/ENV149/chlorinationb.htm

Lenntech Water Treatment Solutions. “Phosphorous removal from wastewater”. Lenntech Water Treatment Solutions. “Phosphorous removal from wastewater”. Online 10 July 2011. Online 10 July 2011. http://www.lenntech.com/phosphorous-removal.htm#ixzz1RpIsY55Ohttp://www.lenntech.com/phosphorous-removal.htm#ixzz1RpIsY55O

Author Unknown. “Flocculation” Online 9 July 2011. Author Unknown. “Flocculation” Online 9 July 2011. http://http://en.wikipedia.org/wiki/Flocculationen.wikipedia.org/wiki/Flocculation

wastewater treatment environmental chemistry tip 2011

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