NEED & USE OF DRINKING WATER
1974 → The water Act (Prevention & Control of pollution)
1981 → The air Act (Prevention & Control of pollution)
1986 → The environment protection Act
1987 → 1st National water policy by govt of india
% of water in earth = 71% = 35 x 10¹²m³, Fresh water = 2%
Sea water = 80% of oxygen contain in freshwater stream
DBU → Designated best uses
OSHO → Occupational safety and health administration
Intakes → Device installed for draining water from source
Fresh water → Alkaline (pH > 7)
Septic tank → Acidic (pH < 7)
Fire extinguisher → Type extinguishers, Foam type extinguishers, dry chemical powder extinguishers, mist type, wet chemical type, CO2 type extinguishers
Keystone species → Which if eliminated seriously affect the ecosystem
Whole some water → Not chemically pure but doesn't contain anything harmful to human health
Population response → An interdependent population of organism interacting with their physical and chemical environment
Fire hydrants are usually fitted in the water mains about 100 - 150 m Apart
Losses in water supply → Assumed as 15%
Water from springs are free from impurities
Most important source of water for public water supplies rivers
Time gap between explosion and machine process within which the ventilation system is called should clear all poison gases and dust in tunnels = 30min
Population forecasting
Methods → Arithmetic increase method, geometric increase method, method of wearing increment, decreasing rate of growth method, simple graphical method, comparative graphical method, master plan method or joining method, Logistic Curve method
Population depends on → Birth & death rates, migration
Best judged by → Geometric increase method
Arithmetic increase method
Old , Very large cities, constant rate of change of population
Pn=Po+nx̅
n = decades
Geometric increase Method/Uniform ↑es method
GOI recommended
New cities expanding with faster rate
Gives highest value of forecasted
% increases in population from decade to decade remains constant
Pn =Po(1+r/100)n→ ↑es given per decade
Pn = Po ern→ ↑es given per year
r=r /n=(r1+r2+r3)1/n
incremental ↑es method or Method of varying increment
Any city old or new
Pn=Po+nx̅+n(n+1)y̅ /2
y̅ → avg of increment increase of known decades
S-shaped/logistic/Growth curve
Population vs time
By PF verhulst
For community with limited land area for future
Water Demand (IS 1172-1963) → Per person per day
Annual average daily requirement per person per day
IS 1172-1963 → Total requirement of water
Small town or Avg domestic purpose = 135 → Drinking = 5, cooking = 5, Bathing = 55, cloth washing = 20, Utensils washing = 10, House washing = 10, Flushing of a water closet = 30
indian cities = 200 → Water supply + Drainage + Sanitation
Domestic + commercial + industrial for avg indian people or LIG = 270 lpcd & HIG = 335 lpcd
Population > 10 lac = 335 - 360 ltr
Population < 1 lac = 275 - 335 ltr
Hospital → Bed ≤ 100 = 340, Bed > 100 = 450 lpcd
Office = 45 - 90 lpcd
School/college → Day = 45, Residential = 135
Automobile vehicle = 40 lpcd
Paper mfd unit consume max water
Peak Q for domestic purposes per capita per minute
5 - 10 user = 1.80 ltr
15 users = 1.20 ltr
20 users = 1.35 ltr
Fire Demand → BNKF
Q=100P → Q = kiloliters
1.Buston's
Q=5663P → Q = litre/min, P = Thousands
2.National Board of fire underWriters
Q=4637P (1-0.01P) → P ≤ 2 lakhs, Q = litre/min, P = Thousands
3.Kuichling formula
Q=3182P → Most preferred, Q = litre/min, P = Thousands
4.Freeman's Formula:
Q=1136(P/5 + 10) → Q = litre/min, P = Thousands
Factor affecting per capita Demand
City size, Climatic conditions, Habit of people
Quality of water → ↑es demand
Developed of sewerage system → ↑es demand
Pressure in distⁿ system↑es → ↑es demand
Cost of water → ↓es demand
Normal variation
Max hourly demand for peak demand = 2.7 x Annual hourly consumption of the max day
Max hourly demand = 1.5 x max daily demand
Max daily demand(MDD) = 1.8 x Annual Average daily demand
1.5 x 1.8 = 2.7
Max weekly demand = 1.48 x Annual Average daily demand
Max monthly demand = 1.28 x Annual Average daily demand
Daily variation factor
Population < 50k = 1.5
50k - 100k = 2.5 → Medium town
Population > 100k = 3.5
Coincident Draft
CD = Max of {max daily demand + fire demand & Max hourly demand (MHD)}
Design Parameter & period
Average water demand of a small town in India is estimated on the basis of domestic use only
i. Water treatment, Service/storage reservoir (overhead or ground level), Intake, main pipe line
t = 15 yrs
MDD
ii. Distⁿ system, pipe connection to several treatment unit, water supply scheme
t = 30 yrs
MHD on max day or Coincident Draft (whichever is more)
For a town water supply scheme is commonly design for a population after three decades
iii. Sewage treatment units
T = 25 years
For Avg flow
vi. Pumps
for 2 x Annual average daily demand
WATER QUALITY
Acidity → Due to presence of carbon dioxide in water,
Carbon monoxide (CO) act as Asphyxiant
Acid fermentation → Leads to the formation of volatile fatty acids
Most important water quality parameter for domestic use of water is coliform group of organisms
Suspended impurities in water → Bacteria, algae, silt
Dissolved impurities → iron,
Colloidal impurities → Finally divided Dispersion of solid particle in water which are not visible to the naked eye and cannot be removed by ordinary filters
Benthos → Organisms attached or resting at the bottom or living in the bottom sediments In freshwater
Disappearance of pink colour of water from a well due to addition of KMnO4 indicates → Water contained organic matter
Permissible & Rejection limit
IS 10500 : 2012 → Drinking water specification
Rejection Limit → Permissible limit in absence of an alternative source → Ex. Permissible limits in Absence of alternative sources for Hardness & Chloride are 600 & 1000 ppm respectively
Aluminium and Boron have some relaxation in acceptable limit in the absence of the Alternative sources
1ppm = 1mg/L → 1g/L = 1000 ppm
inland surface water(IS 2490-1981)
Suspended solids are limited to 100 mg/L
pH = 5.5 - 9.0
A. Physical Water Quality Parameter: (T³CS.)*
i. Suspended solids :
Only surface water not underground
Dissolved solid is chemical parameters
ii. Turbidity
Measure of the amount to which light is absorbed or scattered by the suspended material in water
Turbidity is mostly due to colloidal particle, Clay + Silt particles, Suspended solid
Turbidity is indicator of presence of suspended inorganic matter
Turbidity rod → Std. Silica scale(ppm), it is a field method
Jackson's turbidity meter: in JTU for T > 25 ppm → Basis of absorption of light
Baylis turbidimeter: FTU, absorption, using blue cobalt plate.
Nephelometer → NTU → Scattering principle
1 NTU → 1 mg of formazine dissolved in 1 litre of distilled water with the test being run according to scattering principle
B & N Methods are colour matching techniques & used for domestic water supply & are more precise.
Turbidity → Running (river) > Still water (Lake)
High turbidity encourage after growth of bacteria in distribution system
iii. Colour
Due to dissolved impurities
Tintometer → Colour matching techniques → Measurement of colours
Measured on Platinum Cobalt scale
1TCU = 1 mg/L → Platinum in form of chloroplatinate ion
True colour unit (Hazen unit)
iv. Taste & Odour
Due to Dissolve gases
Osmoscope → Graduated with pO value = (0 - 5)
Very strong > strong > distinct > faint > very faint > No perceptible odour
Removed by → Aeration, Coagulation, Activated carbon → Oxidation is best method to control taste & odour
Threshold order No. → TON = (A+B)/A = diluted solⁿ/undiluted(distilled water)
Flavour threshold No. → FTN = Taste free water required/Water to dilute
Sulphur → Rotten eggs
Type of Odour characteristics → Degree of sweetness, Degree of pungency, Degree of smokiness
v. Temperature
ideal = 13°C
↑es 10°C → Biological activity is doubled
B. Chemical Properties
i. TDS: Total dissolved Solids
By evaporating sample of water
TDS (ppm) = 0.65 x EC(μMHo/cm)
Total solid = TDS + Suspended solid
Electrical conductivity of water increases with total dissolved solids
2. Alkalinity
Due to Ca++
Quantity of ions in water that will react to neutralise hydrogen ions(H+ ion) or Acid.
Due to Carbonate (CO3⁻²), Bicarbonate (HCO3⁻) & Caustic (OH⁻).
Titration → Express in terms of ppm a CaCO3
3. pH
pH = - log10[H+] → [H+] = moles/litre
by Potentiometer
Acid indicator → Methyl orange & Basic indicator → Phenolphthalein
Acidic water → Corrosion & Alkaline water → incrustation of pipe
Acidic Ratio = [H+]1/[H+]2 = Ratio of H+
pH + pOH = 14 → [H+][OH-] = 10⁻¹⁴
H⁻ⁿ → pH = n
Talyred → PH indicator that produced yellow as the final colour when added to water sample
Sodic soil → pH > 8.5
Industrial excellent discharge into inline surface water → pH = 5.5 - 9.0
4. Hardness
Due to divalent metallic ions (Calcium and magnesium)
Measured by Spectrophotometric techniques
NaCl → Softens the water
What used in boilers should be relatively soft
Groundwater is considered soft (H = 0-60 ppm)
For public water supply hard water is not used because it consume more soap
Hardness of Boiler feed water < 50 ppm
Temporary/Carbonate H
Removed by boiling or adding lime
HCO3⁻ & CO3⁻² of calcium & magnesium → Carbonate and bicarbonate of calcium and magnesium
No harm to health
Permanent/Non Carbonate H
Sulphate(SO4), Chloride & Nitrate of Calcium & magnesium
Removed by → Zeolite, lime-soda Process & Deionisation process.
Pseudo Hardness → Due to Sodium
TH = (Ca²+ mg² + Al²) x 50 → All in millieq/ltr
TH =50/20 [Ca²] + 50/12 [Mg²] + 50/9[AL³] → All in mg/Ltr
TH, A → mg/L as CaCo3
A = 50/61 [HCO3⁻] + 50/30 [CO3⁻²] + 50/17[OH⁻] → All in mg/L as Calcium carbonate (CaCO3)
CH = min of [TA & TH]
NCH = TH - CH
TH > TA → CH = TA
TH ≤ TA → CH = TH
Water from lake source is likely to be hard
Method to determine Hardness
i. Dr. Clark's method
based on that hardness producing substance reacts with soap & forms insoluble compounds before leather is produced
Hardness is expressed in degrees
ii. Hehner's method
Determine permanent hardness.
iii. Versenate or EDTA Method
By titration
indicator → EBT (Erio-chrome Black T (Wine red)) → EBT form red Colour & Titration change it to Blue
Solution → EDTA (Ethylene Diamine Tetra-acetic Acid)
5. Chloride Content
Mohr's method → Concentration of chloride ions, Using Titrant → Silver nitrate(AgNO3) and indicator → Potassium chromate (K2Cr2O7)
Normally in the form of sodium chloride
excess → Cardiac problem, Kidney disease, Brackish water
6. Nitrogen Content
indicates presence of Organic matter
a) Free Ammonia →recent pollution
b) Organic Ammonia (Albuminoid) → Quantity of Nitrogen before Decomposition has started.
c) Nitrite - Partly decomposed condition
d) Nitrate - old pollution (fully oxidised)
Kjeldahl Nitrogen Ammonia = Free + organic Ammonia
Total Kjeldahl Nitrogen = Organic + Ammoniacal Nitrogen
Blue baby Disease (Methemoglobinemia) → if Nitrate > 45ppm
Blue green Algae can fix atmospheric nitrogen
7. Fluorides
Absence or < 1 ppm → Dental cavities
Excess → Defects of bones, Dental floureness, Bones and joints stiffness
Nalgonda method → Highly adopted for fluoride removal
8. Metals
Non Toxic → Ca, K, Na, Fe, Mn, Zn
Toxic → Arsenic, Lead, Mercury, Cyanide, Cadmium, Chromium
Potassium thiocyanate is used to colour both the water sample & the standard solution for the determination of iron
Arsenic → Affects the lungs
Excess Sulphate → Laxative effect
Excess Lead → Anaemia
Sodium → Taste and odour problem
1 ,10 Phenanthroline → Indicator for measuring iron concentration in water
Iron and manganese → Removed by aeration followed by coagulation, Iron can be removed by oxidation with chlorine
9. Dissolved Gas
CH4: explosive tendency
H2S → Bad taste & Odour, Basic cause of crown corrosion
C2O: water become corrosive & gives bad taste
C. Biological Properties
Coliform/Faecal coliform count in 100 ml of drinking water = 0
Coliforms → Bacteria coli (B-Coli), Escherichia Coli (E-Coli) & Entamoeba Histolytica harmless
Characteristics of coliform → Harmless, Bacillus, Gram-negative, Ferments lactose
Coliforms → Indicates the probable presence of pathogenic bacteria
Pathogenic bacteria enter wastewaters primary from domestic waste
Autotrophic Bacteria → Bacteria which use carbon dioxide as a source of carbon
Chemoheterotrophic Bacteria → Consume organic matter as a source of carbon and energy
Aerobic bacterias → Flourish in the presence of free oxygen, Consume organic matter as their food, Oxidise organic matter in sewage
Anaerobic bacterias → Sludge digestion
Facultative Anaerobic → Can survive with or without free oxygen
Agar of gelatine → The cultural medium used in finding the total count of bacteria
Coliforms Test
i. Membrane filter techniques
Nutrient
coliform colonies is counted
ii. MPN test (Most Probable number)
By multiple tube fermentation
Nutrient used: Lactose
Presumptive test, Confirmative test, Completed test.
Green lactose bile is used in presumptive tests.
iii. Coliform index
15 test tube is used
Natural Organic matter(NOM)
NOM is Formed due to decay and leaching of organic detritus
NOM is found in particulate, colloidal and dissolved forms in all ground and surface waters, as well as in rainwater
NOM will have significant impacts on drinking water treatment processes aimed at protecting public health.
Water borne disease
Bacteria → Typhoid fever, Cholera, Bacillary dysentery, Tularemia
Protozoa → Amoebic dysentery
Virus → Jaundice, Poliomyelitis, infectious
Other → Gastroenteritis, Tinnitus
Other disease
Goitre → Lack of iodine
TREATMENT OF WATER
River water as property of self purification
Ground water containing Excessive iron, Dissolved CO2 & odorous gases
For construction use at a village site → the local pond water must be Sieved
Screening → Aeration → Coagulation and Flocculation(1st stage) → Sedimentation(2nd stage) → Filtration(3rd) → Disinfection/Chlorination(4th) → Softening → Defluoridation
Unit process in water treatment system → Softening, Coagulation, Adsorption
Surface water (river, canal) → coagulation, flocculation, sedimentation, filtration and disinfection
infiltration gallery → Aeration, coagulation, sedimentation and Disinfection
Lake/ Pond water → CuSo4 treatment, coagulation, sedimentation, filtration and disinfection
Tube well water → Disinfection
Iron and manganese → Aeration and sedimentation
The chemical energy content in an algae cell = 600o calories per gram of algae
Activated Carbon
Most commonly used adsorbent in water and wastewater treatment
Removes → Taste and Odours, Colour, Soluble organic Chemicals, Phenol type impurities, iron, manganese, Organic matter
As a Coagulant it accelerates the coagulation
Minimise chlorine demand
Overdose is not harmful
Screening
Area of opening should be such that→ that Vf = 0.75 - 1.0 m/s
inclined 3 - 6V : 1 H or 45° - 60° → Help in racking
Coarse & Fine Screen
IS 6280 → The screening units provided before the wet well
Microstrainer
useful for screening stored water
Plankton, Algae, other small size particle
wire mesh = 10mm size
Pre-chlorination
raw water not so turbid but high bacteria count
kills Algae, Bacteria and ↓es colour & slime formation
extremely polluted clear raw water
Algae Control
Best way is by Pre Chlorination
Remove → Alum
if org is more → Heavier dose of Copper Sulphate (2 mg/l) or Chlorine(3-5 ppm)
Aeration
Removes → Dissolved gases CO2, H2S, oil, Algae, Bad Odour, Undesirable gases, Excess iron
Generally used for Groundwater
remove Volatile liquid ex. Phenols & humic Acid
Remove or Converts iron & manganese Soluble to insoluble state → Dissolved iron is oxidised into forric hydroxide
Disadvantage of Aeration
Excessive Aeration absorb too much oxygen & water becomes Corrosive
↑es Acidity of water, Excessive aeration may result into corrosion of metal
Needs Higher Capital cost, operating cost & maintenance cost
Sometimes it creates odour & nuisance
Process of Aeration
i. Spray nozzle → Remove 90% CO2 & 99% H2O
ii. Cascade method → Cheapest method
KMnO4 is used to help Oxidation
COAGULATION
Chemical + Water → Used to enlarge size of impurities → Reduces the net electrical repulsive force at particle surface
Remove → Colloidal impurities/solids, suspended
Jar test → To choose best coagulant, Optimal time required for flocculation, To find the chlorine content of water
Coagulant perform better in alkaline water
Went Turbidity > 40 ppm
Detention period = 2 - 6 hrs
Sweep coagulation → Raw water having high turbidity and high alkalinity
Vigorous mixing is done in a chamber where coagulant is added
Types of Coagulant
i. Alum or Aluminium sulphate (AL2(SO4)3.18H2O) → Best, cheap, most commonly used for water treatment, Function Better if Raw water is alkaline with high turbidity, pH range = 6.5 - 8.5, Increases acidity of water(↓es pH), Best for removing colour, taste, odour, colloidal particles
ii. Chlorinated Copper → Chlorine:Copper = 1:12.5, Work in large pH, Singularly effective in production sludge for the activated sludge process
iii. Copperas or Ferrous sulphate →
iv. Sodium Aluminate: Costlier coagulant
v. Iron Sulphate: Colour removal
vi. Ferric chloride → Widely used for sewage treatment, If about 90% of suspended solids are to be removed by coagulation
Na3PO4 → Highest power for coagulating positive colloids
FLOCCULATION
Flocculation agent is added to remove fine suspended particles → Gently mixing the water and coagulant allowing the formation of large particle of flocc
Slow mixing & agitation process
Most efficient Floc formⁿ → ↑es V gradient & ↓es time
Clarification → Process of adding chemicals to induce aggregation & Settling/Removing of finely divided suspended matter, colloidal substance etc
The efficiency of a clear clarifier → Depends on depth of the clarifier
Optimum time of flocculation = 30 minutes → Time increase beyond this the flocs will entrap air and will float in the sedimentation tank
Temporal mean velocity gradient → G = 20S-1 - 80S-1
SEDIMENTATION
To remove suspended solids → Process related to bed material carried by flowing water
essential factor = surface loading of tank
pH value of water doesn't affect Sedimentation
Discrete settling → free settling of particles
Backwash arrangement is made only in the case of a sedimentation tank
If the temperature of a sedimentation tank is increased → Sedimentation speed will get Hastened
Velocity of flow of water = 15 - 30 cm/min ( 2.5 - 5 mm/sec)
Depth of sedimentation tank ≤ 6 m
Displacement efficiency → Represents the short circulating occurring in a sediment tank
Critical shear stress ∝ Particle size
Categories of Sedimentation
i. Plain sedimentation (Type-I)
Due to Self weight of by action of natural forces alone
Generally rectangular shape tank is used
Surface overflow rate = 12k - 18k ltr/m²/day = 500-750 ltr/m²/hr
Detention period = 6 - 8 hrs → Time taken by a particle of water to pass between entry and exit
ii. Sedimentation with coagulation (Type-II)
Surface overflow rate = 24k - 30k ltr/m²/day = 1000 - 1250 ltr/m²/hr
Detention period = 2 - 4 hrs
Clariflocculator → Coagulation cum sedimentation unit
Tank type
i. Quiescent type tank
min = 3 → 2 Operational & 1 standby
ii. Continuous flow Type
Horizontal flow → Rectangular
Vertical Flow → Circular
Rectangular tank
(BxLxH) → L < 4B
Horizontal flow time → t = L/Vf = tank length/ flow Velocity
Flow velocity → Vf = Q/BH
Surface overflow rate → Vo = Q/BL = Discharge/surface Area
Overflow rate, surface overflow rate & Surface loading (Vo) → All are Same & it is the most imp design parameter → Vo Should we such so we can achieve settling velocity
Detention period → t = Vol/Q = Volume/Flow rate
Setting Velocity → Vs = L/t
Efficiency → η = h/H = Vs/Vo=Settling velocity/ Surface overflow rate
η ∝ 1/Vo ∝ As → Efficiency does not depend upon depth of the tank
For a given discharge efficiency of sedimentation tank can be increased by increasing the surface area of tank
Setting Velocity Vs
if Re < 1 & d ≤ 1mm
Stoke's Law → Vs = (γs-γw)d²/18μ =(G-1)γwd²/18μ → Laminar flow, μ = NS/m² & V = m/s, d = particle size
Settling velocity < Surface loading
Vs → Depends upon length of tank
FILTRATION
Process of purifying water by passing it through a bed of fine granular material
Removal of suspended impurities → Remove fine flocs, colour, dissolved mineral, microorganisms, Removes bacteria and colloidal solids
Economically effective in controlling Guinea worm disease
Rapid gravity filters → Remove bacteria and colloidal solids
Process: Bio-filtration
Best filter media send → D60/D10=02
Stone/Brick ballast → filter material used in contact bad
Double filtration → 1st filter is Pressure filter
Basic filtration mechanisms → Interception, inertia, Brownian diffusion
The void spaces in the filtering material act like a tiny setting basins
Well screen recruitment → Resistance to corrosion, incrustation and deterioration, Enough structural strength to prevent collapse, minimum resistance to flow of water into the well
Rate of demand = (Area x filtration rate)/(population).
Area of filter = Total water demand /filtration rate
Li(1-ni) = Le(1-ne)
DISINFECTION
Killing harmful organisms, Pathogens causing disease → Also for Colour, Odour, Algae
pH is control during disinfection to ensure that powerful residual Hypochlorous acid (HOCl) is formed
HOCl is most destructive, it is 80% more effective than OCl⁻ ion
Sterilisation Process: all organism (Harmful & non-Harmful) are killed by a physical phenomenon
Drinking Purpose: plain disinfection is sufficient → Most ideal disinfectant used for drinking water is chlorine
Swimming pool disinfection → Chlorine, Bromine, Ultraviolet rays
Potassium permanganate is not desirable for disinfecting drinking water because it imparts pink colour
In chlorination due to rise in temperature of water → Death rate of bacteria increases
Chick’s law → Nt=Noe-kt
Methods of disinfection
Physical method → By Boiling, By UV rays(turbidity < 15 ppm)
Chemical method → Oxidising agent (O3,I2,Cl, Br2), Metal ions (Ag, Cu), Alkalies & Acids
Minor method of Disinfection → Ozone Treatment, Treatment with excess lime, Treatment with F & Br, Treatment with KMnO4
Major method of Disinfection → Chlorination
Dechlorinating agents → Sulphur dioxide gas (SO2), Activated carbon, Sodium thiosulphate(NaHSO3), Sodium sulphite (Na2SO3)
Amount of potassium permanganate required for disinfection → 1 - 2 mg/L
O3 → Necessary residual Ozone can induce cancer
Disinfection Power → Ozone > HOCL > Monochloramine > NCl3
Chlorination
Generally used for Drinking water → Controls Schistosomiasis
Chlorine demand = Applied - Residual chlorine
Dosage of Cl2 = Demand of Cl2 + Residual Cl2
Fresh Bleaching powder = 30 - 35% Chlorine
HOCL is most Destructive
η ∝ Temp
[(HOCL)/(HOCL + OCL)] = 1 / 1 + K/[H+]
K = reactⁿ rate & H+ = moles/ltr
At lower pH contact period required for chlorination is low & vice-versa
Disinfection efficiency of chlorine is reduced → By increased PH value
Efficiency of disinfection by chlorine water treatment increase → by prechlorination
If Coagulation & Flocculation are poor then chlorine Demand will increase
Test of Chlorine Residue → DiSCO → DPD, Starch iodine, Chlorotex, Orthotolidine
The amount of residual chlorine left in public water supply for safety against pathogenic bacteria = 0.05 - 0.5 ppm
Types of Chlorination
Plain Chlorination → For clean water, Treatment of water with only chlorine
Pre Chlorination → Before coagulation and filtration, Reduce tastes and odour
Post Chlorination → After all the treatments of purification of water are completed
Double Chlorination → Pre + Post combinedly
Breakpoint Chlorination → in the stage when chlorination of water should be Stopped, Addition of chlorine in and amount sufficient to react with any Ammonia and readily oxidizable organic matter
Super Chlorination → Chlorination is done beyond breakpoint, During an epidemic
Dechlorination → Removing of residual chlorine
PH values for Chloramine
Mono chloramine > 7
Dichloramine = 4- 7
Trichloramine = 1 - 3
SOFTENING
Temporary hardness is removed by simple boiling
Lime is added to remove calcium hardness
Permanent hardness removal methods
Zeolite process is costlier than lime soda process
i.Lime soda process
Huge amount of precipitate form which creates Disposal problem
↓es corrosion & ↑es Alkalinity
Lime reduces the carbonate hardness while soda reduces the non-carbonate hardness
Recarbonation → Conversation of precipitators to soluble forms in water
ii.Base exchange process (Cation exchange process)
Zeolite is a natural or synthetic Cation ex. Hydrated sodium aluminium silicate.
Costlier than LSP due to presence of iron & manganese
Zero hardness → By ion exchange treatment
Zeolite process: removal of calcium & magnesium cations
Most common artificial zeolite is Permutit
iii.Demineralization Process
Removes all minerals in water
Treatment of Salinity of water
Reverse osmosis and electrodialysis
Reverse osmosis
To remove dissolved solids
DISTRIBUTION SYSTEM
Water supply system means the complete Layout from the source of supply to the distribution system
Storage of water by impounding → Where Large variation in quantity of the river flow from time to time
Leakage losses are less when the water supply is intermittent → Pressure is less in intermittent Water supply
Maximum score depth for a severe band = 1.75R
Design period for water supply project = 20 - 30 years
Water losses in water supply is assumed = 15%
Cesspool → To collect foul and wastewater
Double stack system → To separate pipes for drainage of soil waste and wastewater
Hazen-Williams formula
Design of distribution system for water supply
Hazens Williams : Velocity of water supply
hf=(10.67LQ1.852)/(C1.852D4.87)
V=0.85CR0.63S0.54 → Water supply mains or Pipe flow
C = 99 - 100 → 20 year old C.I. Pipe
Methods
Gravitational system → From high level water resource
Direct Pumping → Low level resource or groundwater, Axial flow pump is used
Combined system → Elevated tank
Layouts of distⁿ system
1. Dead end/Tree system
Old town, randomly planned city, irregular grown town, Haphazard growth
Flow is unidirectional
Least number of cutoff valves
2. Grid iron/Reticular/interlaced system
Well planned city & town → Where the water mains and branches are laid in rectangles → Lateral are provided only one side of sub-main → Mains, sub mains and branches are interconnected
Cut off valves are provided at every junction
Disadvantage
Requires more length of pipelines and a greater number of cut-off valves
Its construction is costlier
3. Ring/Circular system
The supply main is laid all along the peripheral roads and sub mains branch out from the mains
4. Radial system
Very large area is divided into different zones the water is pumped into the distribution Reservoir kept in the middle of each zone
City with Roads radiating from centre
higher service head & efficient water distⁿ
water flows towards the outer periphery
Types of pipe
Life of cast iron pipes > life of wrought iron pipes
Sulphur bacteria causes the corrosion of iron and steel pipes embedded in soil
Concrete pipes → Jointed by Collar joint and Flush joint
Cast iron pipe → Pressure ≤ 7 kg/cm², Generally used in India for conveying water, Rising main, Spigot and socket joint is provided
Galvanised iron pipes → Coating of zinc, Water supply to residence or Within building
Gooseneck → A small sized bent/curved flexible pipe provided between ferrule and stop-cock, L = 75cm → To avoid stresses and strains on the joint due to temperature variation and vibrations
Ferrule → Installed in water distribution system
Minimum residual pressure at ferrule for one storey building = 7m, 2 storey = 12m, 3 storey = 17m
Working pressure of a class A pipe of increasing thickness for the same diameter = 1800 kN/m²
One pipe system → Commonly used in multistoried building
Pipe test
Air test → Underground & vertical pipe
Water test → Underground house sewer pipes
Smoke test → Rainwater pipe or Existing vertical sullage leakage
Food drainage pipes in building → smoke test
Economical dia of pumping mains
D = (.97 - 1.22)√Q, D = m & Q = m³/s
Valve closure time Max t = 2L/V.
Ht of the sink of the wash basin above floor level = 75 - 80 cm.
Pipe Size → Design Condition
D < 0.4m→ ½ full at max Q
0.4 ≤ D ≤ 0.9m →⅔ full at max Q
D > 0.9m→ ¾ full at max Q
D = 40 cm → V > 1.8 m/sec
Network Analysis
i. Hardy-cross method
Most widely used for analysing and designing the pipes of all types of complex water distribution network
Σ Pressure drop = 0 around close loop
Σ inflow = Σ outflow
Head loss = rQⁿ.
ii. Equivalent pipe method
Sluice elbow pipe fitting as least frictional resistance in equivalent pipeline in terms of diameter of the pipe
Valves
Sluice or Gate or Shut off valves → Regulate the flow of pipe and overhead reservoir
Globe valve → Regulate the flow of after through the pipeline
Air valves or Air relief valve → To prevent air accumulation, Every summit of pipeline & d/s of sluice valve
Check/Reflux/Non-returning Valve → Works Automatically and Only one direction flow → Suctⁿ pipe, Tube wells, Pump
Scour/Blow off/Drain Valve → At Dead end or low point of pipe line, Drain off all accumulated water in pipes, Remove sand, silt .etc, Drain/Empty/dewatering the pipeline
Relief/Cut Off/Safety Valve → Regulate water hammer Pressure, Operates automatically when the pressure in the pipe exceeds the set pressure
Foot valve → Prevent entry debris & backflow
Ball/ball float Valve → Maintain constant level in reservoir & tank
Butterfly Valve → Large size conduit regulate & stop the flow
Pilot Valve → Reduce high inlet pressure to lower inlet pressure
Release Valve → Remove air from the pipeline
Pressure reducing valve is actuated by the fluid pressure at downstream
SOLID WASTE MANAGEMENT
Ministry of environment, forests and Climate change → Brings about the hazardous waste management and handling rules in India, Responsible for the overall monitoring of the implementation of the solid waste management rules
Jacobs Hochheiser method → Determine N02
Non disposal of solid waste may cause the spread of typhoid
Solid waste → Cow dung = 18 - 25 %, Night soil = 11 - 15%
Field capacity → Physical characteristics of municipal solid waste → Critical importance in determining the volume of leachate in landfills
Bulk density of MSW compost → Sample dried in a hot air oven at 70°C for 24 hours
With passes of time filled up solid waste will get stabilised by decomposition
Waste management hierarchy :– Prevention → Reuse → Recycle → Disposal
Type of solid waste
Municipal Solid Waste → Refuse, Trash, garbage, Institutional waste, demolition waste, Municipal service waste, Non hazardous waste
Industrial Waste →
Hazardous Waste →
Refuse → Dry or solid waste of society
Rubbish → Non-putrescible waste (inorganic) except ash
Garbage → Putrescible(सड़ने योग्य) organic waste, 0.2 - 0.4 kg per person, City = 450 gm per head per day
Bacillary dysentery: By garbage 70k fly
Solid waste generated per day per capita → Small city = 0.1kg, Medium city = 0.3-0.4kg, Large City = 0.5kg
Sullage/Dirty water → Waste water drained out from kitchen, bathroom, wash basin & floor washing
Sludge → Generic term for solid separated from suspension in a liquid → 20 litres per person per year
DWF → Dry weather flow
Disposal of Solid waste or Refuse
Chemical transformation of solid waste → Combustion, gasification, pyrolysis
Best process of disposal of batteries is recycling
Aerobic decomposition → CO2, NH3, H2S
i. Open dumping
Oldest & not an economical method, highly unacceptable
impact →
ii. Sanitary land filling
An engineered pit, in which layers of solid waste are filled compacted and convert for final disposal
Canyon Method → Landfilling of solid waste
Area method → Used in flat areas or gently sloping land, as well as in quarries, ravines, and pits
Trench method
Clay(bentonite) is used for landfill cover material → Control of gas and leachate movement
Rat & fly breeding
Can no longer be used for disposal of solid waste in India due to leachates
Leachate → The liquid that collects at the bottom of a sanitary landfill and may pollute the groundwater
Central pollution control board → Ambient air quality at the landfill site shall meet the standard → for Industrial Area
Post closure care of landfill site shall be conducted for at least 15 years
Land filling is not used for disposal of hospital waste
Bioreactor landfills → Moisture is the main factor for controlling microbial digestion
iii.Composting
Most acceptable economically and ecologically, Most hygienic → limited to special waste & selected material
Suitability → High moisture content, high organic materials, low calorific value, low inorganic materials
Bangalore method → Anaerobic method
indore method → Aerobic method, the entire process takes 04 months
Mechanical composting → Dano process, Buhler process, Tollemache process, Nusoil process
Window composting → Time required for decomposition = 2-6 months
Catalytic combustion → Used in purifying emissions from Industries like varnish, cooking and asphalt oxidation
For high rate composting → moisture content = 50 - 55% minimum
Maximum C/N = 30 → Municipal solid waste compost
Ideal Carbon to nitrogen ratio → C/N = 25 - 30
High C/N ratio → Correct by adding dehydrated mud
iv. Pulverization
Pulverised in a grinding machine to ↓es Vol
v. Incineration
Presence of air Burning in well designed furnace ex. Screen
High operation & maintenance cost
Indian Municipal solid waste is not suitable for incineration → Due to high moisture content
vi. Pyrolysis or Destructive distillation
It is an Irreversible chemical change
Thermal decomposition of waste in absence of air/oxygen → Oxidation at high temperature 540 - 1000℃
Internal heating causes organic matter to decompose physically and chemically rather than burn
Plastic, rubber, leather
Pyrolysis is an Endothermic process
Most efficient method to conserve energy in the form of oil or gas
WASTEWATER CHARACTERISTICS
Harmful Bacteria in sewage → E-Coli, Salmonella
Pathogenic bacteria enter wastewaters primarily from domestic waste
Tolerance limit for industrial effluents discharged into public sewer → T < 45℃, pH = 5.5 - 9, BOD5 = 30 - 100 ppm
Specific gravity of sewage = 1.2 - 1.4
Deoxidation is caused by Organic matter in solution
Strength of sewage is given by concentration of organic matter
Physical Characteristics
Turbidity → Normally turbid
Colours → Fresh sewage is grey , as time passes it becomes black
Temperature → Sewage > Water
Chemical Characteristics
Dissolved solid : Reverse Osmosis, trickling filter
Colloidal solid: Coagulation
Volatile Solid: Digestion → muffle furnace
Settleable Solid: Sedimentation→ imhoff tank
pH → Potentiometer
For fresh sewage → pH = 7 - 14, usually = 8
Every daily per capita contribution of suspended solids = 90 grams
Fresh sewage → Alkaline, Septic sewage → Acidic
DO → Dissolved oxygen
DO ≥ 4ppm → Survival of organisms
By winkler's method
Measured by → Titrating water with (N/40)Na2S2O3
DO in sea water = 20% Less than stream/river water
Production of oxygen due to algae photosynthesis during daytime → Highly supersaturated with dissolved oxygen in water
Excess DO → Corrosion of pipe
Odour of hydrogen sulphide is emitted from domestic waste water when dissolved oxygen is absent
DO ∝ 1/Temp
DO → Maximum at noon in stream
DO winter > DO summer
Natural unpolluted water at normal temperature → DO = 10 mg/L
DO Test
A single Rapid test to determine the pollution status of river water
Manganese ions react with Hydroxide to form a precipitate of Mn(OH)2
Oxygen present → Brown precipitate, Oxygen not present → White precipitate is formed
TOC → Total organic carbon
Detect the total organic carbon of the sample → Reflects the organic contamination
COD → Chemical oxygen demand
COD represents Strength of sewage
meas content of organic matter of waste water Both biodegradable & Non - biodegradable → Amount of oxygen consumed by sewage from an oxidising agent like potassium dichromate
Potential Dichromate taste in presence of Sulfuric acid
TOD ≥ COD ≥ BOD ≥ TOC
ideal conditions → COD/TOC = 2.66
Typical untreated domestic wastewater → BOD/COD = 0.40 - 0.80 → COD/BOD > 1
High COD/BOD ratio → Low biodegradability of the pollutant
Chemical oxygen demand test
95% organic matter is oxidised & results are available within 3 hrs.
Titrated with standard ferrous Ammonium Sulphate → To determine the unreacted amount of mercuric sulphate
Organic matter is oxidised by potassium dichromate (K2Cr2O7) in the presence of sulphuric acid (H2SO4)
Indicator → Ferroin
COD test is relatively quick process then BOD test
BOD → Biochemical oxygen demand
BOD is the amount of oxygen required for biological decomposition of dissolved organic solids under aerobic conditions for 5 days at 20 degrees celsius
For biodegradable Organic matters only
The amount of organic material remaining at any time(t) is governed by first order function
5day at 20°C is taken as Standard → Which is 68% of total/ultimate demand
Strong sewage → BOD5 = 450 - 550
BOD5 = (DOi- DOf) x DF → @20°C
BOD5 days = 0.68BODultimate=2/3 of BODultimate → @20°C
BOD520°C= BOD3 27°C , BOD5,32°C>BOD5,20°C
BOD10 days = 0.90BODultimate
KT=K201.047T-20
BOD5,T=Lo(1-e-KTt) → Lo=BODultimate
K → Increases with temperature if T > 20, Decreases with temperature if T < 20
BODultimate → Not affected by temperature
Average daily per capita contribution of BOD5 = 45 grams and BOD = 50 - 70 gm/day
Safe drinking water BOD = 0
Discharging sewage and industrial equipments into stream →BOD520°C<30 mg/L
Tolerance limit in public sewer → BOD520°C=350 mg/L
Deoxygenation: Exertion of BOD by microorganisms
If any Biodegradable organic material is present in Wastewater → BOD = 0
Effluent from secondary biological treatment of sewage → BOD = 5 - 10% of the original
BOD Removal efficiency during primary treatment under normal conditions = 30%
BOD → Industrial water > river water > tap water > bottled water
BOD Curve
Stage 1 → Carbonaceous demand
Stage 2 → Nitrogenous demand
Lt = Organic matter at present
Biomass curve :– Lag phase → Log → Growth phase → Stationary phase → Endogenous phase
Dilution Factor
DF = Vol diluted sample/Undiluted sewage sample
DF = Vs + Vw / Vs → Vs = sewage, Vw = water
if Dilution = 5% → DF = 100/5
DF > 500 → No treatment required
DF = 300-500 → plain sedimentation
DF = 150-300 → secondary treatment
DF < 150 → all treatment required
DF = 100 → Extensive treatment to bring BOD below 20 PPM and suspended solid (SS) below 30 PPM
Population Equivalent
Use to compare pollution potential sewage
Avg std domestic sewage → BOD = 80 gms per person per day
PE = Total demand of BOD of a city per day / individual BOD produced by a person per day = Total/80
Relative Stability
RS = (Available oxygen/Required oxygen)100 → Satisfying the first biochemical oxygen demand
RS = (BOD removed / Total BOD) 100
Oxygen sag
The difference between saturated dissolved oxygen content and the actual dissolved oxygen content in the stream at any point during self purification process
SEWAGE TREATMENT
Neutralization of alkaline effluent → Carbon dioxide treatment, using waste boiler flue gas, sulphuric acid treatment
Sewage treatment plant/units are normally design for 30 - 40 years
Dewater raw sludge → Filtering, Drying using flatbed, Centrifugal action
The treated sewage effluents are generally → Used for irrigation crops
Grab sample → Relatively employed for the design of wastewater treatment plants
Centrifuge → A device in which sludge is dewater by rapid rotation and automatically discharged
Aqua privy → Most economical and hygienic privy for rural areas
Deplorable aspect of conservancy → Human element is involved in collection and transportation of human waste
Water carried sewage system is better than the old convergence system
Sludge bulking → Sludge with poor setting characteristics → Can be controlled by Chlorination
Oxidation is Essential → for the biochemical treatment of sewage effluents
Nitrogen is present in wastewater sample due to the decomposition of proteins
Raw domestic sewage mostly contains Nitrogen in form of → organic-N and ammonia-N
Allowable disposable rate of application of sludge on land is determined by → Nitrogen content of sludge
The very first stage decomposition of organic matter in sewage → Ammonia is formed
A well oxidised sewage contains nitrogen mainly as nitrates
Nitrate detection in sewage → Colour developed by adding phenol-di-sulphuric acid and potassium hydroxide
Dilution → To maintain the aerobic condition of sewage, the sewage is mixed with a large quantity of water
Crude sewage → Sewage that has received no purification treatment
Sewage sickness
Phenomenon by virtual which soil pores gets clogged with sewage matter, due to excessive application of sewage to land, obstructing aeration and leading to septic condition
Prevent → Rotation of crop, Pretreatment of Sewage, Shallow depth application
Treatment Methods
Sludge treatment → Stabilise the organic matter, Destroy the pathogenic bacteria, Reduce the water content
Unit Operations → Physical forces are predominant e.x. Sedimentation, screening, mixing .etc
Unit Process → Addtⁿ of chemicals, biological mass or microbial activities ex. ASP, Trickling filter, Oxidation Pond
Primary Treatment → Screening, Great chamber, Skimming tank
Secondary Treatment → Trickling filters, Contact beds, Sand filters
Screening → Grit chamber → Primary sedimentation → Aeration → Secondary sedimentation
Conventional sewage treatment → Grit chamber is placed ahead of the trickling filter
CETP → Common effluent treatment plant
Clariflocculator → Floc formation & its subsequent removal by Sedimentation
Algae-bacteria symbiosis is observed in stabilisation pond
Sewage treatment units are designed for → Average flow only
Decomposition of sewage takes place causing a pungent smell of H2S
Equalisation basin → To absorb fluctuation of flow rate, Damping the hourly variation in the sewage flow
PRIMARY TREATMENT
BOD removal efficiency under normal condition = 30%
Screening
Floating material, Large size stones and gravels
To protect Pumps & other mechanical equipment
Head loss h = 0.0729(V² - v²) = k(V² - u²)/2g
h ≥ 50% → The Cleaning is Required
Micro screening → Removal of algae from stabilisation pond effluents
Spacing of Steel bars in coarse screen = 50mm
Grit Chamber
To remove suspended inorganic grit like sand gravel & any other mineral matter with a nominal size of 0.15 - 0.20mm
Removes particles of size ≥ 0.2mm, Gs ≈ 2.65, Dt = 30 - 60 sec & Depth = 1 - 1.5m
for 0.2mm particle Settling V = 0.025 m/s
Grit chambers are usually changed after 2 weeks
Horizontal critical flow Velocity → Vc = Kc√(g(GS - 1)d) ← Critical Scour Velocity, Kc = 3 - 4.5
Proportional flow weir (Parshall flume) → To maintain constant flow velocity in the grit chamber over a certain depth range
Detritus tank → Removal of fine sand particles and grit
Skimming Tank
Removal of Soap, oil, Grease, Fat .etc
A = 0.00622q/Vr
Rate of flow q → m³/day
Settling tanks
in primary settling tanks the suspended solids are reduced to 40 - 70%
Secondary settling tanks are designed to remove bio flocculated solids
SECONDARY TREATMENT
Attached + Aerobic biological →Trickling filter & RBC → Conversion of suspended organic matter into settleable biofloc and stable inorganics
Suspended Aerobic → Activated sludge Process & Oxidation/Stabilisation pond
Suspended Anaerobic → Septic tank & UASB Reactor
Imhoff Tank → Suspended Anaerobic (Lower part) & Suspended Aerobic (Upper part)
Bulking of sludge can be controlled by chlorination
Max efficiency of BOD removal → oxidation ditch
Largest land area for a given discharge will be needed for oxidation pond
Activated sludge process
Biological process → Aerobic bacteria + Protozoa + algae
Oxidation ditch → A modified activated sludge process
Activated sludge → Contents fertilising constituents, indicates the degree of aeration, indicates high water content
Dominating micro organisms are → Aerobic heterotrophs
Rising sludge occurs due to → Denitrification in the settling tank
Bacteria are removed = 80 - 95%, BOD removal eff = 95%
BOD of secondary effluent < 30 mg/L
Indian Condition → SVI = 150 - 350, Good sludge →SVI = 50 - 100 ml/gm
Sludge vol index → SVI = (Sludge vol / Suspended solid wt)x1000
SVI use → Indicate physical state of the sludge produced, Decide recirculation ratio of sludge
F/M = QoSo/VX= BOD load / microbial mass = food added / Bacteria in system
Lower F/M ratio → Higher BOD removal
Conventional activated sludge treatment plant → The return sludge is added at entrance of the aeration tank, F/M = 0.3 - 0.4
Mixed liquor → The combination of liquid and microorganism undergoing aeration
Removal of soluble organic Chemicals is possible by the addition of activated carbon to the biological mixed liquor of an active sludge process
Recirculation → To supply seed materials to the aeration tank
Trickling filter
Biological oxidation process to remove → Dissolved and Colloidal organic matter, BOD
Surface area for growth of biofilm is provided by randomly packed solid forms
Inherent problems of Odour, Ponding and fly nuisance
η = η1 + (1 - η1) η2
Design parameters → Hydraulic loading rate(m³/m²/day), Organic loading rate (kg/m³/day), Depth
TF Sizing criteria is based on hydraulic loading
Hydraulic loading rate of high rate trickling filter including Re-circulation = 10 - 40 m³/m²/day
Distributing arms of large trickling filter units are rotated at speed of 1/3 - 1/2 RPM
Work on Aerobic Decomposition of organic matter
Hydraulic Recirculation ratio = 1 + R, R = Circulation ratio
High rate trickling filter → Hydraulic loading rate = 10 - 30 m³/m²/day
Low rate trickling filter → Recirculation factor = 1
Unit organic loading → u = W/VF
Vacuum filters → Dewatering of sludge
Sloughing → Phenomenon of losing the Slime layer
BOD removal efficiency = 85%, BOD5 = 70 - 80%
BOD after the filtration of sewage from the low rate trickling filter = 80 - 90%
Problem of ponding can be solved by Raking and chlorination
RBC → Rotating Biological contactor
UASB → Upflow anaerobic Sludge blanket
Does not require any special media to keep sludge in suspension during treatment
Oxidation/Stabilisation Pond/lagoons
Anaerobic stabilisation → Gases CO2, CH4, Nitrate
Primary settling time is not required in some case, BOD removal occurs in two stage, Aeration volume requirements are approximately 50% of those of conventional or tapered aeration plant
Design factor → Surface area, depth and shape, inlets and outlets
Area → Based on 2000 persons to one acre of pond area
Sodium nitrate → Used to stimulate the algae growth when it gets overloaded
Biological waste treatment is governed → By bacterial degradation and Algal-bacterial symbiosis → The growth of algae is useful in oxidation pond
BOD and coliform removal is up to 99%
Types → Aerobic, Anaerobic, facultative
The process of lagooning is primarily a means of disposal of sludge
Mechanically aerated lagoons → Less detention time and areas are required, because these ponds are deeper than the oxidation ponds
Oxidation ditch
Excess sludge is taken to drying digester
Sludge Digestion
↓es Vol of sludge & Render remaining solids and relatively pathogens free
Use both Aerobic & Anaerobic mechanism
pH = 6.5 - 8.0 → Alkaline condition should prevail
As a result of sludge digestion combustion gas → Marsh gas is generated → Methane(CH4)
Stages :– Acid fermentatⁿ → Acid Regression → Alkaline fermentatⁿ
Digestion step :– Hydrolysis→ Acidogenesis → methanogenesis
X(100 - P1) = Y (100- P2) → P1, P2 Moisture content corresponding to sludge quantity X and Y
i. Aerobic digestion
ii. Anaerobic digestion → Methane > CO2 formed, Acid formed, Reduces odour/flies problem, low operating cost, Total solid destroyed = 40-60%, Necessary to maintain proper pH
Moisture content reduced from 90% to 80% → 50% decrease in the volume of sludge
Sludge drying → To separate water from digested sludge or dewatering sludge
Septic tank
A Watertight chamber made of concrete, fibreglass, PVC or plastic, through which domestic waste water, sewage flows for primary treatment
Anaerobic method of onsite sewage treatment → Both Sedimentation + Digestion process → Settling + Digestion tank
Ideal for a small Colony, Rural area → Design as ordinary settling tank
Gases → CO2, H2, S, CH4
Decomposition of organic Bacteria is done by anaerobic bacteria
Rate of accumulation of sludge = 30 ltr/person/year
Sludge should be removed in 1 - 3 years
Desirable self cleaning velocity = 0.5 m/sec
Brick wall in cement > 20 cm
Capacity = 0.1 m³ per user → 25 users = 2.5m³
Detention time = 12-36 hrs, L/B = 2 - 3, Connecting pipe ≥ 50mm
Soak/Seepage Pit → Circular covered pit through which the effluent is allowed to be soaked into the surrounding soil
Soak pit dia ≥ 3.0 - 5 feet
Imhoff Tank
Both Sedimentation + Digestion process of sludge takes place simultaneously
Settleable solids
Upper compartment → Aerobic
Lower compartment → Anaerobic
SEWERAGE SYSTEM
Sewerage → The process of collecting, treating and disposing of the sewage
Clamshell → Removing material from cofferdam, sewer manholes and well Foundation
Concrete sewer corrosion → Due to septic condⁿ & Anaerobic decomposition of sewage (Hydrogen sulphide)
Well oxidised sewage content sulphur largely in the form of sulphate
Maximum scour depth at a severe band = 1.75D
Storm sewage → Quantity of liquid waste which flows in sewers during the period of rainfall
Flushing tank → Located at sewer line with steep gradient
Axial flow screw pumps are mostly used in sewage pumping area
Nomograms → For ease in the design of sewers
During sewer cleaning the worker are exposed to hazards primarily due to presence of Methane
important factor for design of wastewater disposal → record of population and its change, water consumption rate and sewage flow, hydrological data
Properties
Sewer → The underground pipeline to dispose waste water produced by public
Gases in sewer → H2S, CO2, CH4
Sewage → 99.90% water + 0.1% Solids → Any wastewater of domestic or industrial origin
Max sewage flow → Q = q[(4+√P)/(15 + √P)] → P = population, q = avg sewage flow
Capacity of sewage pipe Q ∝ √S, S = bad Slope.
Supply reaches to sewer = 70-80% water
Sewer Dia = 100mm(L ≤ 6m) & = 150mm(L > 6m)
Minimum diameter for public sewer in hilly areas where steep slopes are prevalent = 100 mm
Velocity running full = V runing half
The minimum velocity at initial peak flow and ultimate peak flow in sewer ≥ 0.6m/s and 0.8m/s
Sewer must be off adequate size to avoid overflow
Flowing under Gravity 1/2 to 3/4th full
Sewerage system is usually designed for 25 years
Laying of sewers is usually done with the help of Sight rails and boning rods
Laid at least 2m - 3m deep to collect water from basements
Sewer should not be design to run full → To facilitate ventilation of sewer
Sewer are generally laid starting from their out fall point
Flow velocity in sewers does not depend on its length
Peak infiltration flow curves → Curve A = old sewers
Sewer pipes
Properties→ Heavy wt, highly impervious, High resistance to sulphide corrosion, High compressive strength
Test → Water test, mirror test, ball test
Sewer pipes have to be designed and checked for both maximum and minimum flow
Sewer pipes are made of stoneware → In stoneware pipe glazing is made for waterproofing
Lead sewer → Resists sulphide corrosion
Best sewer material to resist hydrogen sulphide corrosion → Glazed stoneware
Corrosion in concrete sewer is caused by H2S → Crown corrosion in sewer caused by sulphate
Types of sewer
Circular shaped sewer → Mostly used for all type of sewer, most commonly used under culvert
Oval/Egg-Shaped sewer → For combined & provide self cleansing velocity at low Q, Suitable for Varying Discharge
New-Egg-Shaped sewer → Overall depth = 1.625D
V-shaped with Circular → Best sewer section for dry weather flow
Common sewer → Shared more than one house
House sewer → Pipe carrying water waste from a building to the immediate point of its disposal
Branch → From the first element of a wastewater collection system or from one or more building to main or Trunk sewer
Lateral sewer → Receives Q of a number of house sewers
Main sewer → From one or more lateral sewers to trunk sewers or intercepting sewers
Trunk sewer → They are large in size, Discharge from two or more main sewers to waste water treatment plant or to intercept sewer
Outfall sewer → Collects sewage from the collecting systems and transport the sewage to the point of treatment or final discharge or to disposal plant
Interceptor sewer → From number of transverse sewers or outlets
Corrosion of concrete sewer occurs due to anaerobic decomposition of sewage solid
Combined sewerage system
Sanitary/domestic sewage + Surface(Strom) water → Dry weather flow + Rain water
Egg shaped Sewer are Preferred → Best shape of sewer considering the hydraulic properties
Cost of Construction & Pumping is high
More suitable for narrow streets
Less intensity of rainfall → Rainfall is distributed throughout the year such that it is ≤ 10 x DWF
Storm/Surface sewer
Time of concentration is relevant to determine the rainfall intensity
Sanitary sewer
Expected to run full
Self cleaning
Self cleansing velocity is velocity at which no accumulation remains in the drain → Achieved by providing adequate discharge, gradient through sewer lines → Neither sitting nor scouring occur at the bottom
Sewer is usually designed to attain self cleansing velocity at the minimum hourly flow rate
Vs = √[8KgD(G-1) / f]
Vs ∝ D(particle size)
All Sewer in india → Vs = 1.0 - 1.2 m/s
Self cleaning velocity recommended for Indian conditions = 0.75 m/s
Non scouring velocity for cement concrete sewer = 2.5 - 3.0 m/s
Self cleansing velocity should be maintained at least once in a Day = 0.45m/s
The minimum velocity of flow in a sewer should be ideally equal to self cleansing velocity
Gradient required to generate self cleansing velocity → Sewer dia = 150 mm → 1 in 100, 225 mm → 1 in 180, 300 mm → 1 in 220
Aerodynamic diameter is the diameter of a sphere of unit density(1g/cc) that has the same terminal setting velocity
Note
1. max hourly Q = 3 x Avg daily Q
2. max daily Q = 2 x avg daily Q
3. min hourly Q = ⅓ of avg daily Q
Sewers must be checked for minimum velocities at their minimum hourly flows i.e. is ⅓ of Qavg.
The velocity of exit waste gases should be a min of 5/2 of wind speed to prevent downdraught
Joints
Mechanical joint → Used in metallic sewer
TRAP
Used to prevent entry of foul gases in the house
Their are 03 kinds of trap → P, Q & S trap
indian Type → 450, 300, 500mm
P-Trap used for an Indian Water closet
Height of the Sink of the Wash basin above floor level is kept 75 cm - 80 cm.
Gully trap → Collect wash water from floors, washbasins, kitchens and bathrooms → At the junction of unfoul Roof or room drain and a foul bath or kitchen drain
Anti-Siphonage Pipe → Connected to top of P-trap W.C. → To preserve the water seal of straps → Siphonage action occurs due to sewage discharge from the upper floor
Sewer trap → Provided at the last manhole connection of building drainage line to corporation main drainage line
intercepting traps → Provided to disconnect the house drain from the street sewer → At junction of a house and a municipal sewer
Floor or Nahani trap → Wastewater from floors of bath & kitchen.
Waste water pipe → Q from sanitary fittings like kitchens, wash basin, bathrooms etc. → But not human excreta
Vent Pipe → For ventilation purpose, exit foul gas in Atm.
Soil Pipe → Human excreta from water closet to septic tank
Two pipe system in building → One soil pipe + one waste pipe + two vent pipe
Water Seals → Provided to prevent foul gases
Cowl → Ventilating pipe, Provided on the top of soil pipe to prevent birds from entering and nesting in it
Sewer Appurtenances
Manholes, Drop Manholes, Lamp holes, Clean outs, Catch basins, Flushing Tanks.
1. Manholes
Means of access for inspection + Cleaning of sewer lines + Removal of part of sewer + Providing air for oxidation
Dia of opening ≥ 50 cm
Candle is lowered → To check presence of oxygen
Manhole covers are made circular to prevent falling of the cover into the manhole
Should be provided at → Every change of Gradient, alignment, diameter & direction, head of all sewer & branch, every bend, every junction, every 30m intervals
Max spacing of manhole in sewers up to dia ≤ 0.3m → 45 m, ≤ 0.6m → 75m, ≤ 5m → 250mm, > 5m → 300 mm
Component of Manholes
Access shaft →
Working chamber → Rectangular chamber size = 1.2 x 1.5 m, Circular chamber dia = 1.2m, ht ≥ 1.8m
Types
i) Drop manhole → Sloping ground, with drop > 0.6m required to control the Gradient, To connect high level branch with low level branch sewer, Change in elevation of Ground level, Hilly township
ii. junctⁿ manhole,
iii. Flushing manhole → Located at the head of the sewer
iv. Straight-Through manhole
2.Lamp Holes:
for Lowering a lamp inside
3. Catch Basin:
carrying Drainage Q
4.inverted Syphon
Inverted syphons are provided for taking sewer line below Road/Canal/Railway line
5. inlets :
Not provided in every sewer, storm water inlets have vertical openings
DISPOSAL OF WASTE WATER
Self purification of natural stream → Due to dilution, turbulence of water, oxidation-reduction, Sedimentation
Higher temperature, Sunlight, Satisfying oxygen demand → increases the self purification of stream
Hazen and camp → First develop the commonly used mathematical model relating the BOD exertion and Recreation to DO deficit in a stream
Rate of deoxygenation → LD= -KLOe-kt
Zone of Pollution In River System
Zones formed in a polluted river under the self purification process
Sag in curve → DO is a function of the rate of both addition and depletion of oxygen from the stream, Maximum DO deficit
1. Z of Degradation
Algae die but fish survived
DO falls to 40% of saturation
2.Zone of Active Decomposition
Heavy pollution & gases
DO even fall to Zero
3.Recovery
DO rises above 40%
4.Clear water
DO rise to saturation
Pathogens may remain
AIR POLLUTION
RSPM → Respirable suspended particulate matter
The Air Act 1981 → Prevention & Control of Pollution
Due to incomplete combustion of fuels from petrol engine → Carbon monoxide
Fabric filters → Air cleaning device which removes smallest particles
Mixing ratio = No. density of gas/No. density of all gases in dry air
Aerosols → Finely divided liquid droplets or solid particle capable of remaining suspended in air
The intensity of air pollution is found to be highest during winter
During temperature inversion in atmosphere air pollutants tends to accumulate below inversion layer
Primary Air pollutants (SCN)
1. Organic compounds
2. Oxides of Sulphur
3. Oxides of Carbon, CO, CO2
4. Halogen compound
5. Oxides of Nitrogen
6. Radioactive compound
7. Particulate matter & Suspended Particulate matter
8. Hydrocarbon
Secondary pollutants
Ozone (O3)
Formaldehyde
PAN ( peroxyacetyl nitrate), PBN, PPN
Sulphuric Acid (H2So4)
Smog = Smoke + Fog
Photochemical smog = NO + Hydrocarbon/oxidant + Sunlight → PAN
Nitrogen oxide is the major pollutant present in photochemical smog.
Natural Contamination of Air → Pollen Grains
Source
Photochemical reaction → O3 and PAN
Air pollutants which are monitored for petrol driven vehicles → NOx, PM
Thermal power plants mostly produce SO2
Major source of carbon monoxide pollution is automobiles
Effect
SO2 and → Affect functioning of the respiratory system
CO → oxygen carrying capacity of blood respect, impacts hearth, Combines with haemoglobin in blood
Sulphur dioxide (SO2) is harmful for plants
Automobile exhaust:
carbon monoxide, nitrogen oxides, hydrocarbon, sulphur dioxide, lead, particulate dust.
Acid rain
Sulphur oxides (SOx) & nitrogen oxides (NOx) interact with vapour & sunlight & are converted into strong Acids H2SO4, HNO3.
pH < 5 (4.5)
Global warming
Temp ↑es
Greenhouse gases → CO2(57%) , CFC(25%), CH4 (12%), Nitrous oxide N2O(6%) & fluorinated gases.
Ozone(O3) layer Depletion
Due to HCFC, methyl bromide , CFC or freons, Halons, HCL, Carbon tetrachloride, methyl chloroform.
Vienna convention (1985), Montreal protocol (1987)
Ozone occur in Troposphere
Protect us from UV rays
Effect → Skin cancer, Irritation of the eyes
Air Pollution Controlling Devices
1. Forced field settlers
i. Gravitational settling chamber
Large size particle D > 50μm
Removes Abrasive Particles from Gas Streams
ii. Cyclonic or Centrifugal separator
To remove → SPM
D > 10 μm (10 - 100μm)
Centrifugal force generated by the spinning gas, the solid particles are thrown to the wall of cyclone
iii. Electrostatic Precipitators (ESP)
D < 1μm
Most efficient = 95-99%
Uses electrical forces, Particles are removed by rapping & collected in a hopper.
Used in: thermal power plant, mining, industries
2. Cotton bag house filter
all sizes
Dispersion of air pollutants in Atmosphere
Lapse Rate → ↓es Temp as ↑es Altitude
1. ELR = 6.5°C/Km ← environment/Ambient lapse rate
change in temp with ht in environment
2. ALR = 9.8°C/Km ← Dry adiabatic lapse rate
Super adiabatic lapse rate: ELR > ALR → Unstable EVS
Neutral : ELR = ALR
Sub-adiabatic: ALR > ELR, Stable EVS.
Negative lapse rate & inversion: ↑es Temp as ↑es Altitude.
Plume Behaviour:
Path taken by Continuous Discharge of gaseous effluent from stack/chimney
1. Looping plume: occurs in super adiabatic lapse rate (SALR), eddies are generated
2. Neutral plume: ELR = ALR, Upward vertical rise.
3. Fanning plume: under extreme inversion conditions, Plume farms out in horizontal directⁿ
4.Coning plume: Cloudy day or night & Strong wind velocity (V ≥ 32 km/hr)
5.Lofting plume: most favourable plume type
6. Fumigation plume: Bad case of atmosphere dispersion, Bhopal Gas tragedy
7. Trapping plume: neither go up nor down,
Chimney
Only two main forces are considered on the chimney one due to pressure and other due to self weight of the chimney
For stress calculations or analysis of forces on a chimney , the wind pressure is assumed to act on the Projected area of the chimney
Direct stresses → due to self weight of the chimney
Bending stress → due to Wind pressure on the chimney
Stack/Chimney ht Design
i. Emitting SO2
H = 14 Q^⅓ ,
H = m & Q = kg/hr SO2 emission
ii. Emitting particulate matter
h = 74 Q ^0.27
h = m & Q = tonnes/hr
NOISE POLLUTION
Units of Noise Pollution
Decibels (dB)
Watt/m^2
Bels
Pascal
For easy calculation
Log10(0) = 0
1,2,....9 = b/w 0 - 1
Log10(10) = 1
11, 12,...99 = b/w 1 - 2
Log10(100) = 2
Sound Pressure level
Lp = 20 x log10(Prms/20 μPa) =10 x log10(Prms/20 μPa)^2.
20 μPa = 20 micro Pascal = 20 x 10^-6 Pascal.
Two Source L1 & L2 ( L1 > L2)
Diff L1 - L2 & Resultant
0 - 1 → L1 + 3
1 - 3 → L1 + 2
4 - 8 → L1 + 1
≥ 9 → L1
Source of equal noise level
2 → increase by 3dB
3 → ↑es by 4.7
4 → ↑es by 6
5 → ↑es by 6.99
Domestic noise → operation of radio, television, record players, etc.
Permissible noise level standards(dB)
Banks/offices = 50-60 db
Noise reduction due to the construction of Barrier wall
Noise reduction(dB) = 10log10(20H^2 /λR)
R = Distance b/w source and wall
H = Height of barrier wall
λ = Wavelength of sound
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