wastewater treatment

04/13/2023 Waste treatment and cleaner Technologies

Water & Wastewaters Treatment

Distribution of water on earth

• Ocean and sea - 97% • Snow and ice caps - 2% • Rivers, lakes, Ground water - 1%


Safe drinking water• Free from pathogenic organisms

• Clear

• Not saline

• Free from offensive taste or smell

• Free from compounds that may have adverse effect on human health

• Free from chemicals that cause corrosion of water supply systems


WATER QUALITY PARAMETERS

• Physical parameters • Chemical• Bacteriological


BUREAU OF INDIAN STANDARDS IS 10500 -1991

Parameters Disirable limit Permissible limit

Colour Hazen unit 5 25

Turbidity- NTU 5 10

pH 6.5 - 8.5 6.5 -8.5

Hardness (as CaCO3)mg/l 0.3 1

TDS 500 22000


BUREAU OF INDIAN STANDARDSIS 10500 -1991

Parameters Desirable limit Permissible limit

Nitrate mg/l 45 45

Chloride mg/l 250 1000

Flouride mg/l 1 1.5

Arsenic mg/l 0.05 0.05

Aluminium mg/l 0.03 0.2


Colour • May be due to the Presence of organic matter, metals(iron, manganese) or

highly colored industrial waste

• Aesthetically displeasing

• Desirable that drinking water be colourless

• Desirable limit, 5 Hazen unit

• Permissible limit 25 Hazen Unit


Taste and Odour

• Mainly due to organic substances, ,Biological activity, industrial pollution

• Taste buds in the oral cavity specially detect inorganic compounds of metals like magnesium, calcium, sodium, copper, iron and zinc

• Water should be free from objectionable taste and odour.


Turbidity• Caused by suspended matter

• High level turbidity shield and protect bacteria from the action of disinfecting agents

• Desirable limit-5 NTU should be below 1 NTU when disinfection is practiced Permissible limit-10 NTU


pH• It is the measure of hydrogen ion concentration

• Neutral water pH-7

• Acidic water has pH below 7

• Basic water has pH above 7

• Desirable limit 6.5-8.5 Beyond this limit the water will affect the mucous membrane and water supply system


Substances that change pH of water

Acidic Industries Basic industries

Sugar 5-6 Paper 8-10

Distillery 3-4 Textile 8.5-11

Electroplating unit 2.5-4 Fertilizer 6.5 - 9

Pickle 2-3 Oil Refineries 6.5- 9

Battery acids <1.0 Milk 6.7

Carbonated Beverages 2 – 4 Rain water 6.5

Lemon juice 2.3 Blood 7.5

Orange juice 4..2 Sea water 8.0

Vinegar 3 Ammonia solution 11.3

Domestic sewage 6.5-8.5 Ground water 7.5-8.5


HARDNESS• Capacity of water for reducing and destroying the lather of soap

• It is total concentration of calcium and magnesium ions

• Temporary hardness – Bicarbonates of Calcium and Magnesium

• Permanent hardness – Sulphates, chlorides and nitrates of calcium and magnesium

• 0 – 5 0 mg/ l - soft• 50 – 15 0 mg/l - moderately hard• 150 – 3 00 mg/l - hard• 300 above - very hard• Surface water is softer than ground water• Causes encrustations in water supply structures


ALKALINITY• Capacity to neutralize acid

• Presence of carbonates, bi-carbonates and hydroxide compounds of Ca, Mg, N a and K

• Alkalinity = hardness, Ca and Mg salts

• Alkalinity > hardness - presence of basic salts, N a, K along with Ca and Mg

• Alkalinity < hardness – neutral salts of Ca & Mg present


IRON• One of the earth’s most plentiful resource

• High iron causes brown or yellow staining of laundry, household fixtures

• Metallic taste, offensive odour, poor tasting coffee

• Cause iron bacteria

• Acceptable limit – 0 .3 mg / l


CHLORIDECauses• Dissolution of salt deposit• Discharge of effluents• Intrusion of sea water• Not harmful to human beings• Regarding irrigation – most troublesome anion• Acceptable limit – 250 mg/l


NITRATE

Increasing level of nitrate is due to

• Agricultural fertilizers, manure, animal dung, nitrogenous material ,sewage pollution(blue baby diseases to infants)

• Maximum permissible limit 45 mg / l


FLOURIDE• Occurs naturally

• Long term consumption above permissible level can cause – dental flurosis (molting of teeth) and Skeletal flurosis

• Acceptable limit – 1 mg / l

• Maximum permissible limit – 1.5 mg / l

• Remedy – 1) Deflouridation 2) Mixing Fluoride free water 3) Intake of vitamin C, D, calcium, antioxidants


FLOURID E CAUSES

Three types of flurosis1. Dental flurosis2. Skeletal flurosis3. Non-skeletal flurosis


A R S E N I C

• Occur in ground water from arseniferous belt

• Industrial waste, agricultural insecticide

• High arsenic causes 1) various type of dermatological lesions, muscular weakness, paralysis of lower limbs, can also cause skin and lung cancer

• Acceptable limit – 0.05 mg / l


Heavy Metals• Present as mineral in soil and rocks of earth• Human activities Battery – Lead & Nickel Textile - Copper Photography – Silver Steel production – Iron


Pesticides• Cancer• Birth defects• Blood disorder• Nervous disorder• Genetic damage


Common problems Visible effects Reasons

Iron taste, change in colour after exposure to atmosphere, change in colour of cloths, utensils Oily appeal- rance on top of water body Iron

Soap not lathering hardness

Brownish black streaks on teeth Fluoride

Growth of Algae Nitrate, phosphate

Fish kills Low pH less DO

water turns black, smell Waste water

Acidic taste Low pH

Alkaline taste High pH

Boiled Rice hard and yellow High Alkalinity

White deposits on boiling Hardness


Good 8 –9

Water Quality DO (ppm) at 20°C

Slightly polluted 6. 7 – 8

Moderately polluted 4.5 – 6. 7

Heavily polluted 4 – 4.5

Gravely polluted Below 4


• Dilution• Biodegradation of wastes by bacteria

takes time • Oxygen sag curve


Major Water Pollutants Have Harmful Effects

• Infectious disease organisms: contaminated drinking water• The World Health Organization ( WHO)

– 3 Million people die every year, mostly under the age of 5


IMPORTANT WASTEWATER CONTAMINANTS

Contaminant Source Environmental significance

Suspended solids Domestic use, industrial wastes, erosion by infiltration/inflow

Cause sludge deposits and anaerobic conditions in aquatic environment

Biodegradable organics Domestic and industrial waste Cause biological degradation, which may use up oxygen in receiving water and result in undesirable conditions

Pathogens Domestic waste Transmit communicable diseases

Nutrients Domestic and industrial waste May cause eutrophication

Refractory organics Industrial waste May cause taste and odor problems, may be toxic or carcinogenic

Heavy metals Industrial waste, mining, etc. Are toxic, may interfere with effluent reuse

Dissolved inorganic solids Increases above level in water supply by domestic and/or industrial use

May interfere with effluent reuse


Unit operations, unit processes, and systems for wastewater treatment

Contaminant Unit operation, unit process, or treatment system

Suspended solids Sedimentation Screening and comminution Filtration variations FlotationChemical-polymer addition Coagulation sedimentation Land treatment systems

Biodegradable organics Activated-sludge variations Fixed-film: trickling filters Fixed-film: rotating biological contactors Lagoon and oxidation pond variations Intermittent sand filtration Land treatment systems Physical-chemical systems

Pathogens ChlorinationHypochlorinationOzonationLand treatment systems


Nutrients: Nitrogen Suspended-growth nitrification and denitrification variationsFixed-film nitrification and denitrification variationsAmmonia strippingIon exchangeBreakpoint chlorinationLand treatment systems

Phosphorous Metal-salt addition Lime coagulation; sedimentation Biological-chemical phosphorus removal Land treatment systems

Refractory Organics Carbon adsorption Tertiary Ozonation Land treatment system

Heavy Metals Chemical precipitationIon exchangeLand treatment systems

Dissolved inorganic solids Ion exchange Reverse osmosis Electrodialysis


MicroorganismsClassification: Heterotrophic- obtain energy from

oxidation of organic matter (organic Carbon)

Autotrophic- obtain energy from oxidation of inorganic matter

(CO2, NH4, H+ )

Phototrophic- obtain energy from sunlight


Biochemical Pathways

oxidation of organic molecules inside the

cell can occur aerobic or anaerobic manner

generalized pathways for aerobic & anaerobic fermentation


aerobic pathways contains- EMP(Embden–Meyerhof–Parnas) pathways, TCA(tricarboxylic acid cycle) cycle, respiration

anaerobic pathways contains- EMP pathways

released energy stored as ATP molecules

excess food is stored as Glycogen

C6H12O6 + 6O2 +38 ADP + 38 Pi 6 CO2 +38 ATP + 44 H2O

Biochemical Pathways


Embden-Meyerhof-Parnas pathway (EMP pathway), which was first discovered by Gustav Embden, Otto Meyerhof and Jakub Karol Parnas.


http://en.wikipedia.org/wiki/Gustav_Embden

http://en.wikipedia.org/wiki/Otto_Meyerhof

http://en.wikipedia.org/wiki/Jakub_Karol_Parnas

Tricarboxylic acid cycle (TCA cycle), the Krebs cycle, or the Szent-Gyorgyi–Krebs cycle


Biological growth

- exponential growth (batch)

- Monod kinetics

- Haldane kinetics

under toxic conditions


exponential growth

Biological growth...

dt

dX = X

Log

No

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Time

Lag

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Log

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Monod kinetics

Biological growth...

Substrate Concentration (S)

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( µ

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ks

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Treatment stages - Secondary treatment

• Degrade biological content (dissolved organic matter) of the sewage– Ex: human waste, food waste, soaps, detergent

• Added bacteria and protozoa into sewage• 3 different approaches

– Fixed film system– Suspended film system– Lagoon system


Biological Carbonaceous Removal

aerobic- oxidation

bacteria CHONS + O2 + Nutrients CO2 + NH3 + C5H7NO2 + other end

products(organic matter) (new bacterial cells)

- endogenous respiration

bacteriaC5H7NO2 + 5O2 5CO2 + 2H2O + NH3 + energy (cells)


Biological Carbonaceous Removal

anaerobic

Schematic of the Anaerobic Process

Hydrolysis

Acidogenesis

Methenogenesis

Complex Organics

Intermediates Propionate

H 2Acetate

CH 4

20% 5%

60% 15%

35% 10% 13%17%

15%

72% 28%

100%


Biological treatment– Trickling bed filter– Activated sludge


• Fixed Film Systems– grow microorganisms on substrates such as rocks,

sand or plastic – wastewater is spread over the substrate– Ex: Trickling filters, rotating biological contactors


Trickling filters bed• Spread wastewater over microorganism

• made of coke (carbonized coal), limestone chips or specially fabricated plastic media

• Optimize their thickness by insect or worm grazing


Advantages

• Simple, reliable, biological process.• Suitable in areas where large tracts of land are

not available for land intensive treatment systems.

• May qualify for equivalent secondary discharge standards.

• Effective in treating high concentrations of organics depending on the type of medium used.

• Appropriate for small- to medium-sized communities.

• Rapidly reduce soluble BOD5 in applied wastewater.

• Efficient nitrification units.• Durable process elements.• Low power requirements.• Moderate level of skill and technical expertise

needed to manage and operate the system.

Disadvantages

• Additional treatment may be needed to meet more stringent discharge standards.

• Possible accumulation of excess biomass that cannot retain an aerobic condition and can impair TF performance (maximum biomass thickness is controlled by hydraulic dosage rate, type of media, type of organic matter, temperature and nature of the biological growth).

• Requires regular operator attention.• Incidence of clogging is relatively high.• Requires low loadings depending on the

medium.• Flexibility and control are limited in comparison

with activated-sludge processes.• Vector and odor problems.• Snail problems.


• Suspended Film Systems– stir and suspend microorganisms in wastewater

– settled out as a sludge

– pumped back into the incoming wastewater

– Ex: Activated sludge, extended aeration


Activated sludge

• mixed community of microorganisms

• Both aerobic and anaerobic bacteria may exist

• Biological floc is formed


physical components of activated sludge process

• Aeration tank – oxygen is introduced into the system

• Aeration source– ensure that adequate oxygen is fed into the tank– provided pure oxygen or compressed air

• Secondary clarifiers – activated-sludge solids separate from the surrounding wastewater

• Activated sludge outflow line– Pump activated sludge back to the aeration tank

• Effluent outflow line– discharged effluent into bay or tertiary treatment plant


• Lagoon Systems– hold the waste-water for several months – natural degradation of sewage


Treatment stages – Tertiary treatment

• remove disease-causing organisms from wastewater • 3 different disinfection process

– Chlorination– UV light radiation– Ozonation


What can effluent use for?

• discharged into a stream, river, bay, lagoon or wetland • used for the irrigation of a golf course, green way or park

• If it’s sufficiently clean, it can be used for groundwater recharge


Advanced Treatment

• Nitrogen removal– Ammonia (NH3) → nitrite (NO2

-)→ nitrate (NO3-)

• Phosphorous removal– Precipitation with iron or aluminums salt

• Lead to eutrophication

• May cause algae bloom


Sludge treatment

• Primary sludge usually have strong odors• Secondary sludge have high

concentration of microorganism• Goals of treatments are:

– Reduce odors– Remove water reduce volume– Decompose organic matter


3 different sludge treatments

• Aerobic digestion• Anaerobic digestion• composting


Aerobic digestion

• Bacterial process• Need oxygen• Consume organic matter• Convert into carbon dioxide (CO2)

Anaerobic digestion

• Bacterial process• Do not require oxygen• Consume organic matter• Produce biogas, which can be used in generators for

electricity


Composting • aerobic process

• requires the correct mix of carbon, nitrogen, oxygen and water with sludge

• Generate large amount of heat


Sludge disposal

• Superheat sludge and convert into small granules that are rich in nitrogen– Sell it to local farmer as fertilizer

• Spread sludge cake on the field• Save landfill space


Water Quality Parameters and DefinitionsTemperature it affects the amount of dissolved oxygen

Temperature also affects the rate of photosynthesis of plants, the metabolic rate of aquatic animals, rates of development, timing and success of reproduction, mobility, migration patterns and the sensitivity of organisms to toxins, parasites and disease. Life cycles of aquatic organisms are often related to changes in temperature.

Salinity Salinity is a measure of the dissolved salts in the waterpH pH is a measure of the acidity or alkalinity of water.Turbidity a measure of the water’s murkiness. Turbidity is measured in

Nephelometric Turbidity Units (NTU’s).Dissolved oxygen (do) The amount of oxygen in waterConductivity Conductivity indicates the presence of ions within the waterColour (Hazen) Colour is vital as most water users, be it domestic or industrial,

usually prefer colourless waterTotal Suspended Solids, TSS Total Dissolved Solids, TDS The total dissolved solids (TDS) in water consist of inorganic salts

and dissolved materials. Biochemical Oxygen Demand, BOD BOD is a measure of organic pollution to both waste and surface

water Chemical Oxygen Demand, COD

Ammoniacal Nitrogen Potassium Microbiological Total Coliform Count

Faecal Coliform Count Pesticides Chlorinated, Glyphosphate, Paraquat ,Methamidaphos


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