UEN002 – Energy and Environment

3 Credits
• 30 Marks – MST
• 50 Marks – End Sem.
• 20 Marks – Sessional (Quizzes/assignments/group presentations)
Water Pollution
 Global water distribution

Source: http://www.cawater-info.net/all_about_water/en/?p=1335
Water Cycle
Sources of water pollution

– Point – single large sources

– Non-point - a diffuse source of pollution that cannot be attributed
to a clearly identifiable, specific physical location or a defined
discharge channel.
• general runoff of sediments
• pesticide spraying
• fertilisers from farms
Major Water Pollutants and
Their Sources
Contaminants affecting water bodies
– Biodegradable organic matter
– Suspended, colloidal and dissolved solids
– Nutrients
– Pathogens
– Acidic, basic and ionic species
– Soaps and detergents
– Pesticides
– Colour and odour causing substances
– Volatile organics
– Recalcitrant and refractory organics
– Thermal / Radioactive material
Categories
– Fund pollutants
• Degradable – organic residuals that are broken down by
bacteria
• Thermal – injection of heat into water source
• Eutrophic – excessive nutrients (nitrogen, phosphorous)
leading to too much aquatic plant growth
• Persistent pollutants – inorganic/synthetic chemicals that
are only partially broken down
• Bacteria, viruses, artificial hormones – from domestic and
animal wastes
– Stock pollutants
• Minerals and inorganic/organic chemicals that cannot be
removed by natural processes (lead, cadmium, mercury,
some agrochemicals)
Effects
– Eutrophication
– Food Chain contamination
• Metals, organics, pathogens
– Loss of biodiversity and Destruction of natural resources

Monitoring of water bodies

– Physico-chemical monitoring
– Biological monitoring
Important components of monitoring
VARIABLES
 Contaminants
 Concentrations
SOURCES
 Time
PATHWAYS  Locations

 Rates of migration
 Time
 Loss and gain functions

RECEPTOR
RECEPTOR  Types
 Sensitivities
 Time
 Concentrations
Nature and Characteristics of Wastewater
Dissolved Oxygen (DO)
– Important measure of water quality

– Oxygen is marginally soluble in water & inversely proportional to

temperature
– Maximum DO at water temperature of 16 deg.C is 10 mg/L

– DO analysis measures the amount of gaseous oxygen (O2)

dissolved in an aqueous solution
– Oxygen gets into water by diffusion from the surrounding air, by
aeration (rapid movement), and as a product of photosynthesis.
– As dissolved oxygen levels in water drop below 5 mg/l, aquatic
life is put under stress.
 Water Quality
DO (ppm) at 20°C

Good 8–9

Slightly
polluted 6.7–8

Moderately
polluted 4.5–6.7

Heavily
polluted 4–4.5

Gravely
polluted Below 4
 Physico-chemical characteristics
• Aggregate organics
– Total Organic Carbon (TOC)
– Chemical Oxygen Demand (COD)
– Biochemical Oxygen Demand (BOD)
• Chemical
– Organics – Proteins, carbohydrates, lipids, surfactants,
phenols, pesticides, etc.
– Inorganics – pH, chlorides, alkalinity, nitrogen, phosphorous,
heavy metals,
– Gases - hydrogen sulphide, methane, etc.
• Physical
– Solids, temperature, colour, odour, turbidity, oil and grease,
conductivity

• Sampling – Grab, composite & flow weighted composite

 Aggregate organics

Total Organic Carbon (TOC)

• It is used to express the pollution load in terms of carbon content
• It is measured directly by using the instrument called TOC
analyzer
• Theoretical calculation can be done if the chemical formula of the
given compound is known.
 Aggregate organics

ThOD
This is the total amount of oxygen required to completely oxidize a known compound
to CO2 and H2O. It is a theoretical calculation that depends on simple stoichiometric
principles. It can only be calculated on compounds of known composition.

C6H12O6 + 6O2 = 6CO2 + 6H2O

If you have 100 mg/L of Glucose what is the ThOD in mg/L ?

Molecular weight of C6H12O6 = 180

= 192/180
= 1.067 g O2/g of C6H12O6
= 106 mg/l
 Aggregate organics
Chemical Oxygen Demand (COD)
– Organic matter assessed in the term of oxygen required to
completely oxidise the organic matter to CO2 and H2O and
other oxidized species
– Potassium dichromate (K2Cr2O7) is used as an oxygen source
to oxidize the organic carbon present in the sample
– Expressed in equivalent amount of oxygen
– The COD measurement is applicable to measure the pollution
load in the industrial wastewaters containing organic carbon
like: textile, paper industries, pharmaceutical etc.
Chemical Oxygen Demand (COD)
 The chemical oxygen demand (COD) of a waste is
measured in terms of the amount of potassium
dichromate (K2Cr2O7) reduced by the sample during
2 hr at 150°C

 COD test is faster than BOD analysis: used for quick

assessment of wastewater strength and treatment
performance

 It does not distinguish between biodegradable and

non-biodegradable organic matter. As a result
COD's are always higher than BOD's.
 Aggregate organics
Biochemical Oxygen Demand (BOD)
– BOD is not a measure of any specific pollutant
– A measure of amount of oxygen required by microorganisms
engaged in stabilizing decomposable organic matter
– Important factors of variations
• Temperature; Time; Light
– BOD measurements – BOD5 & BOD3
– BOD5 – BOD test carried out in dark at 20 deg.C for 5 days
– Why 5 day BOD ?
• Oxidation of biochemical oxygen demanding substances is
an exponential decay curve
• Decay constant is usually that most of these substances are
oxidized (85%) in the first 5 days
Biochemical Oxygen Demand (BOD)
Briefly, the BOD test employs a bacterial seed to catalyze the oxidation of 300 mL of
full-strength or diluted wastewater. The strength of the un-diluted wastewater is then
determined from the dilution factor and the difference between the initial D.O. and
the final D.O.
BODt  DOi  DO f

BODt = (DOi – DOf) *D

Where BOD
BODt = biochemical oxygen demand at t days, [mg/L] Bottle
DOi = initial dissolved oxygen in the sample bottle,
[mg/L]
DOf = final dissolved oxygen in the sample bottle,
[mg/L]D = V /V
b s
D V = sample Factor
= Dilution bottle volume, usually 300 mL
b
Vs = sample volume, [mL]
20
Method for the measuring of BOD

BODt = UBOD (1-e-kt)

BODt = BOD after t days (mg/l)

UBOD = Ultimate BOD (mg/l)
k = BOD rate constant at particular temperature (day-1)
t = Time in days
 Aggregate organics

BOD and COD relationship

– COD values are higher than BOD values in nearly all cases,
because COD includes both degradable and non-biodegradable
substances whereas BOD contains only bio-degrabable

– Greater BOD to COD ratio – higher the efficiency of organic

treatment by biological methods
Problem 1

Determine the 5‐day BOD for a 15 ml sample that is diluted

with dilution water to a total volume of 300 ml when the initial
DO concentration is 8 mg/l and after 5 days, has been
reduced to 2 mg/l.

BOD5 = (initial DO – Final DO) * dilution factor

BOD5 = (8 – 2) * (300/15)

BOD5 = 120 mg/l

Problem 2

A sample of wastewater has an ultimate BOD of 280mg/L and a 5‐

day BOD of 240mg/L. Calculate 10‐day BOD of this sample.

BODt = UBOD (1-e-kt)

BOD5 = UBOD (1-e-k (5))

240 = 280 (1-e-k (5))
k = 0.39 day-1
BOD10 = 280 (1-e-0.39 (10))

BOD10 = 274 mg/l

 Physical Parameters

Solids
Total Solids Residue remaining after wastewater sample has been
(TS) evaporated and dried at a specific temperature (103 –
105 deg. C)
Total Volatile Burn off solids when TS is ignited to 500 deg.C
solids (TVS)

Total Fixed Left out solids after ignition of TS

solids (TFS)
Total Portion of TS retained in filter of 2mm and measured
suspended after drying the filter paper at 105 deg.C
solids (TSS)
Total Solids that passed through 2mm which comprises of
dissolved colloidal and dissolved solids
solids (TDS)
 Physical Parameters

Solids
Volatile suspended Burn off solids when TSS is ignited to 500 deg.C
solids (VSS)
Fixed suspended Residue after TSS ignition
solids (FSS)

Total volatile Solids that burn off when TDS is ignited to 500
dissolved solids deg.C
(TVDS)
Fixed dissolved The residue of the TVDS
solids (FDS)

Settlable solids Suspended solids that settle over time

 Physical Parameters

Turbidity

• Measure of light transmitting properties of water

• Measurement is based on comparison of intensity of light
scattered by sample vs that of standard (formazin solution)
• Analytical Techniques – Nephelometry
• Units – Nephelometric Turbidity Units (NTU)
 Physical Parameters

Colour
• Measured by Spectrophotometer
• Units – Platinum Cobalt Units (PTU)
Temperature
• An important parameter as it affects the chemical and
biochemical reactions and the rates of these reactions
Electrical Conductivity
• A measure of the ability of solution to conduct electric current
• EC is surrogate measure of TDS [TDS mg/L = EC x 0.55 to
0.70]
• Units - MilliSiemens/ meter
 Physico-chemical characteristics
• Aggregate organics
• Physical
• Chemical
– Alkalinity
– Nitrogen
– Phosphorous
– Sulphur
– Metallic constituents
 Physico-chemical characteristics
Alkalinity
– Hydroxides, carbonates and bicarbonates
– Common – Ca & Mg bicarbonates
– Importance – Biological treatment
Nitrogen
– Importance – Nutrient
– Forms – NH3, NH4+, NO2- and NO3- & Org. N
– Measurements – Amm. N., Inorg. N., Kjeldahl N., Org. N
 Physico-chemical characteristics

Phosphorous
– Aqueous forms – Orthophosphates, polyphosphate &
organic phosphates
– Importance as nutrient
Sulphur
– Aqueous form – sulphate
– Reduced to sulphide and further to hydrogen sulfide
– Formation of sulphuric acid and pipe corrosion
Metallic constituents
– Priority pollutants – Cd, Cr, Cu, Fe, Pb, Mn, Hg, Ni & Zn
– Micronutrients / Toxicants
– Measurable forms – dissolved, suspended, acid extractable
Wastewater Treatment

• Primary – Removes Solids

– Physical Operations – Screening , Sedimentation

• Secondary – Removes Organics

– Biological and Chemical Operations

• Tertiary – Removes Nutrients

– Biological and Chemical Operations
Typical Unit Operations of a Wastewater treatment
plant
Primary and Secondary Sewage Treatment
(using Suspended Growth process)
Activated Sludge Process
Primary and Secondary Sewage Treatment
(using Attached Growth process)
Trickling Filter
Screen
• First unit operation
• Objective
– Removal of coarse and fine objects, which may get entangled
in mechanical equipment e.g., grit chambers, sedimentation
tanks, etc.
– protection of pump impellers.
– Used to remove Rocks, leaves, paper, plastic rags and other
materials
• Coarse Screens: provide a bar screen with relatively large
openings of 25 mm.
• Medium Screens: Clear openings of 12 mm.
• Fine Screens: Clear openings of 5 mm
Grit removal
• Grit removal is necessary to protect the moving
mechanical equipment and pump elements
• Removal of grit also reduces the frequency of cleaning of
digesters and settling tanks.
• The specific gravity of the grit is usually 2.4 to 2.65
Grit chambers are of three major types as follows:
i) Vortex Type Units
ii) Aerated Grit Chambers
iii) Square shaped chambers with entry and exit on opposite
sides
Primary clarification/sedimentation
• Separate the suspended solids, which can settle by gravity
• It used to remove Organic, residual inorganic solids and
Chemical flocs produced during chemical coagulation and
flocculation
• The velocity of the flow can be reduced by increasing the
length of travel and by detaining the particles for longer time
in the sedimentation tank
• The size of the particles can be altered by adding some
chemicals
• In plain sedimentation tank 60-65% of suspended solids and
30-35% of the BOD removal can be achieved
Sludge removal – circular clarifier
• Scraper
Fundamentals of biological treatment
• Objectives
– To coagulate and remove non-settlable colloidal solids
– To stabilize organic matter/substances
– To remove trace toxic organics
– To remove nutrients
– To reduce inorganic concentration

• All these carried out by microbes

– Based on form of carbon required
Autotrophs (photo-auto/chemo-auto) &
Heterotrophs (photohetero/chemohetero)
– Based on energy source
Phototrophs & Chemotrophs (chemo-organo/chemo-auto)
Fundamentals of biological treatment
• Most of the enzymatic reactions involve redox reactions i.e.,
addition/removal of oxygen/hydrogen
• The electron acceptor is based on surrounding medium and
cellular characteristics
– In anaerobic reactions – an oxidized compound is electron
acceptor
– In aerobic reactions – oxygen is acceptor
• Environmental factors influence microbial growth
– Temperature
 Psychrophilic – (-10 to 30 deg.C) opt. 12–18 0C
 Mesophilic – (20 to 50 deg.C) opt. 25-40 0C
 Thermophilic – (35 to 75 deg.C) opt. 55-65 0C
 Facultative
Activated sludge processes (ASPs)
• ASP is an aerobic, continuous flow, treatment system that uses sludge with
active populations of microorganisms to breakdown organic matter in
wastewater
• Activated sludge is a flocculated mass of microbes
• The organic load (generally coming from primary treatment operations such
as settling, screening or flotation) enters the reactor where the active
microbial population (activated sludge) is present.
• The reactor is continuously aerated.
• The mixture then passes to a secondary settling tank where the cells are
settled.
• The cells are recycled in order to maintain sufficient biomass to degrade
the organic load as quickly as possible
 Trickling filters
• A trickling filter (TF) is a aerobic attached growth type wastewater
treatment system that biodegrades organic matter and can also be
used to achieve nitrification.

• The wastewater trickles through a circular bed of coarse stones or

plastic material. A rotating distributor (a rotating pipe with several
holes across it) evenly distributes the wastewater from above the
bed.

• The microorganisms in the wastewater attach themselves to the

bed (also known as the filter media), which is covered with
bacteria.

• The bacteria break down the organic waste and remove pollutants
from the wastewater.
Trickling filters

   
Anaerobic fluidized bed process

• A combination of suspended growth and attached growth

process
• Anaerobic microbes grow on the surface of the medium,
expanding the apparent volume of the medium; hence this
reactor is also designated an "expanded bed reactor"
Disinfection

• Partial destruction of disease causing (pathogenic) organisms

• Characteristics of an ideal disinfectant
• Availability
• Deodourizing ability
• Homogeneity
• Extraneous material interaction
• Non-corrosive and non-staining
• Toxic to microbes
• Penetration
• Solubility and stability
Disinfection methods

Chemical Physical Mechanical Radiation

Halogens (Cl) Heating Chemical Gamma rad.&

Ozone Solar precipitators Cobalt-60 rad.
Phenolics insolation and biofilters
Alcohols
Metals
Detergents,
etc.
Disinfectant action
• Damage to cell wall and disturbance in cell permeability –
phenolics and detergents
• Damage to protoplasm and cell molecules – Radiation
• Molecular alterations and Inhibition of enzyme activity – Chlorine
and other halogens
• Factors that influence action
• Contact time
• Concentration (chemical)
• Intensity/nature (physical)
• Temperature
• Organisms
• Nature of w/w
Reference books
• Environmental Engineering (vol II); Sewage disposal and air pollution
engineering. Santosh Kumar Garg. Khanna Publications

• Environmental Engineering by Howard S. Peavy, Donald R. Rowe and

Deorge Techobanoglous. McGraw Hill Education (India) Private Limited.

• Introduction to Environmental Engineering and Science by Gilbert M.

Masters and Wendell P. Ela. Pearson India Education Service Pvt. Ltd