Environmental Engg.

Domestic Demand

• Public use

• First national water policy 1987.

• Air prevention & control of pollution Act - 1981.

• Water prevention & control of pollution Act - 1974.

• The Environment protection Act - 1986

Demand Calculations

• Low Income Group (LIG) without flushing: $135 \text{ (domestic)} + 135 = 270 \text{ lpcd}$

• High Income Group (HIG) with full flushing: $200 \text{ (domestic)} + 135 = 335 \text{ lpcd}$

Demand Breakdown (lpcd)

Other Demand Factors

• Industrial + Commercial Demand: $70 \text{ lpcd}$

• Losses and thefts: $55 \text{ lpcd}$

For rural water supply, the total is $270 \text{ lpcd}$.

Per Capita Demand (q)

$q = \frac{\text{Total yearly water requirement of the city in litre}}{365 \times \text{Design population}}$

Demand Variations

• Max. daily demand = $1.8 \times \text{ Avg. daily demand}$

• Max. hourly demand = $1.5 \times \text{ Avg. demand hourly of Max. day}$

• Max. hourly demand or peak demand = $2.7 \times \text{ Avg. hourly demand}$

Coincident/Draft Demand:

Maximum daily demand when added to fire draft for working out total draft.

Total draft is the max of:

• max. daily demand + Fire demand

• max. hourly demand

Fire Demand Formulas

For smaller towns (P < 50,000), fire demand is not calculated.

• ** ফিরিয়েs formula:** $Q=5663\sqrt{P}$

• Freeman's formula: $Q=1136 \left(\frac{P}{5}+10\right)$

• Kuichling's formula: $Q=3182\sqrt{P}$

• Under writers formula: $Q=4637\sqrt{P}(1−0.01\sqrt{P})$

• As per manual of the ministry: Q=100\sqrt{P} \text{ liter } (P > 50000)

Where:

• $Q$ = Required quantity of water (ltr/min)

• $P$ = Population (thousands)

Factors Affecting Demand (AAPCDD)

• Size of City

• Types of sewerage System

• Climatic condition

• Types of Industry

• Quality of water (indirectly affecting demand by affecting consumption)

• Cost of water

• Types of distribution System (i.e. continuous or intermittent)

• Pressure Distribution System

Peak Factor

Water Quality Parameter

Physical

1. Colour

2. Suspended Solid

3. Taste and Odour

4. Temperature

5. Turbidity

Chemical

1. Chlorides

2. Dissolved gases

3. Hardness

4. pH value

5. Alkalinity

6. Acidity

7. Metals & other chemical substances

8. Total solid

Biological

1. Organic matter

2. Microorganism

3. Biological activity

Odour Intensity

Odour is based on $p_O$ value:

Design Life (years)

Population Forecasting Methods

• Geometric method: Gives Highest values, suitable for growing cities.

• Arithmatic Increase Method: Gives Lowest values, suitable for very old cities.

• Incremental Increase Method: Suitable for Intermittent growth cities.

Hardness of Water

Hardness of water measured in different units:

• 1 British degree = $14.25 \text{ mg/l}$

• 1 American degree = $17.12 \text{ mg/l}$

• 1 French degree = $10 \text{ mg/l}$

Water Hardness (In ppm of Calcium Carbonate)

Types of Hardness

Temporary (Carbonate)

Due to presence of carbonate and bicarbonates ($HCO<em>3$) of calcium & magnesium. e.g., $Ca(HCO</em>3)<em>2$, $Mg(HCO</em>3)_2$

Permanent/Non-carbonate

Due to the presence of sulphates, chlorides, nitrates of calcium and magnesium. e.g., $CaCl<em>2$, $CaSO</em>4$, $MgCl<em>2$, $MgSO</em>4$

Pseudo hardness is imaginary hardness caused by salt of sodium ($Na$).

Alkalinity

It is due to the presence of:

• Major source: $HCO<em>3$, $CO</em>3$ and $OH$

• Minor source: $HS$, $HSiO_3$, $HPO$

Hydrogen-ion concentration (pH value)

$pH = -\log[H^+]$
$pH + pOH = 14$
$pOH = -\log[OH^-]$
$[H^+] \cdot [OH^-] = 10^{-14}$

• [H+] ↑-pH ↓ Acidic

• [OH-] ↑-pH↑ Alkaline

Two types of colour indicator technique is used:

1. Methyl Orange (Acidic indicator): Initial colour is red and final is yellow at pH value 2.8 to 4.4.

2. Phenolphthalein (Basic indicator): It is initially colorless and final colour is pink at pH value is 8.6 to 10.3

Water Quality Standards (As per IS: 10500: 2012)

Values are given as AL (Acceptable Limit) and CFR (Cause for Rejection) in mg/l unless otherwise specified.

Tests and Instruments

Water Treatment Steps:

Screening → Pre-Sedimentation → Aeration → Coagulation & Flocculation → Post Sedimentation → Filtration → Disinfection → Water softening Distribution.

Treatment Methods for Various Impurities

Types of Coagulants

Alum [$Al<em>2(SO</em>4)<em>3 \cdot 18H</em>2O$]

Produces effective floc in water when the pH range is 6.5 to 8.5.

Ferrous Sulphate ($FeSO<em>4 \cdot 7H</em>2O$)

Works in pH range > 8.5. Hence, it is always used with lime.

Chlorine + Copperas [$Fe<em>2(SO</em>4)<em>3$ chlorinated copperas & $FeCl</em>3$]

pH range 3.5-6.5 or > 8.5

Sodium Aluminate ($Na<em>2Al</em>2O_4$)

Normal dose = 10 - 30 mg/l. Working pH range - 6.5-8.5

Design Criteria of Sedimentation Tank

Over flow rate or surface loading:

• Plain sedimentation - 500 - 750 Ltr./hr/m²

• Sedimentation with coagulation = 1000 - 1250 Ltr./hr/m²

Depth - 3 to 4.5m (< 1.8m and > 6.0m)

Slow Sand Filter

Rapid Sand Filter

Where, Q = Plant capacity in MLD.

Pressure Filters

• It is less efficient than the rapid gravity filters in removing bacteria and turbidities.

• It may be horizontal or vertical type and used for the treatment of industrial or swimming water.

Types of Chlorination

Plain chlorination

Done if water is only chlorinated and turbidity<10 NTU. Dose-0.5 mg/ltr.

Pre-chlorination

Chlorine is added before Sedimentation, filtration, coagulation etc. Normal dose- 5-10 ppm.

Post-Chlorination

Chlorine added after the filtration process. Contact period- 20 minute, Residual chlorine-0.10-0.20 ppm

Double chlorination

Chlorination is done at two different points during the water treatment process

Break point chlorination

It is the difference of applied chlorine & residual chlorine beyond breakpoint, Residual chlorine at this stage = 0

Super chlorination

Application of chlorine beyond the stage of break point. residual chlorine - 0.2 to 0.3 ppm

Effectiveness of Chlorination Compounds

HOCl > ClO2 > Cl2 > \text{Chloramines}

Reactions:

• NH3 + Cl2 \rightarrow HCl + NH_2Cl \text{ (Monochloromines) } pH > 7.5

• NHCl2 + Cl2 \rightarrow HCl + NHCl_2 \text{ (Di-chloromines) } pH < 7

• NHCl2 + Cl2 \rightarrow HCl + NCl_3 \text{ (Nitrogen trichloromines) } pH < 4.4

Dechlorination Chemical compounds

a. Sodium thiosulphate ($Na<em>2S</em>2O<em>3$) b. Sodium bisulphate ($Na</em>2H SO<em>4$) c. Sodium meta sulphate ($Na</em>2 S<em>2 O</em>5$)
d. Sulphur dioxide ($SO<em>2$) (Gas/liquid form) e. Sodium sulphite ($Na</em>2SO<em>3$) f. Potassium permagnate ($KMnO</em>4$)
g. Activated carbon

Chlorine Residue Testing

i. Orthotolidene Test ii. Chlorotex Test iii. Starch Iodide Test iv. Colour matching method v. DPD (Diethyl Phenylene diamine) test

Fluorine Removal Methods

Activated Alumina

Excellent medium to remove excess fluorine along with NaOH solution.

Activated carbons

Based on adsorption technique.

Nalgonda method

Aluminium salts responsible for removal of fluoride from ground water. Simple solution for removing fluoride from drinking water.

Reverse Osmosis (R.O.) process (hyper filtration)

Efficiency = 85-92%.

Desalination

Process of removing salts or other minerals and contaminants from sea water, blackish water and waste water.

Methods:

(i) Freezing of water (ii) Evaporation (iii) Reverse Osmosis (iv) Electrodyalysis

Other Treatments

• Copper sulphate is used to removal of algae from water.

• Activated carbon is used to control taste and odour and to remove fluoride from water.

Pipe Joints

Layout of Water Distribution

Types of Valves

Sewage Types

Fresh sewage

• Lighter in colour

Old Sewage (Septic sewage)

• Darker in colour
  -Less smelling in nature

Domestic sewage

Sewage comes out from the flush system of residential buildings.

Industrial

sewage/trade effluent

The water used for keeping the machines cool and cleaning also comes out as waste water.

Storm water

When rain water starts to fall on the ground it is called storm.

Sanitary Sewage

Combined sewage obtained from urinals, water closets and business establishments is called sanitary sewage.

Characteristics of Sewage

Dissolved Oxygen (DO)

• Added by partial atmospheric pressure in water.

• Saturation oxygen: Maximum dissolved $O_2$ at any temperature.

• At 20°C, maximum DO is 9-2 mg/l.

• DO is measured by Winkler's Test.

• Oxygen consumed during Decomposition of OM is known as oxygen deficiency.

• Max DO present any streams at NOON.

• Solubility of dissolved oxygen in sewage is 95% that of distilled water.

Sewerage System Capacity

• Separate system: Rainfall +2 times of DWF

• Combined system: Rainfall + 3-6 times of DWF

Minimum Sewer Size

Sanitary Pipe Sizes

Minimum Sewer Velocity

Manhole Placement

• Starting point

• Junction of pipeline

• Change of direction

• Change of diameter

• Change of gradient

• Crossing of roads

• 30 m to 300 m in straight length of the sewers.

Types of Traps

Drop Manhole

Provided when two sewers flowing at different levels have a vertical gap of more than 60 cm.

Sanitary System Pipes

Water Proofness Testing

i. Air test ii. Smoke test iii. Colored water test iv. Hydraulic Test v. Smell Test

Notes:

• $HNO<em>3$, $H</em>2CO<em>3$, $H</em>2SO_4$ present in acidic rain.

Formula:
$\frac{BOD<em>5}{BOD</em>{ult}} = 68 \%$

$\frac{BOD}{BOD_{ult}} = 90 \%$

• B.O.D. bottle size: 300 ml.

• B.O.D of municipal sewage 100-500 mg/l.

Sewage Treatment Units

Detention Time of Various Units

Grit chamber, removes inorganic grit, S.G 2.65 whose eff. size of particles > 0.2 mm.

• Detention period - 40 - 60 sec.

• Flow velocity- 0.15-0.30 m/sec.
  Depth 1-1.8 m.

Detritus Tank removes grit and fine sand particle whose effective size ≤ 0.2 mm.

• Detention period- 3-4 min.

• Flow velocity- 0.9 m/sec.

Skimming Tank / Grease Trap separates grease, oil from sewage. Detention period: 3 - 5 min

Sludge Index

$S.V.I.= \frac{\text{Settled volume of sludge}}{MLSS (gm//)} \times 1000$

$S.V.I.= \frac{V<em>{ob}}{X</em>{ob}} \times 1000 \text{ ml/gm}$

Treatment Methods

Trickling Filter

• Low sludge volume index.

• Works by aerobic bacteria.

• Unit- kg/hectare-meter/day.

It is divided in two part: (i) Upper chamber- Working condition is aerobic; (ii) Lower chamber- Working condition is anaerobic.

Effluent: Partially clean liquid, over the sludge and comes out of the flowing tank.

Septic Tank

Oxidation Pond

Oxidation Ditch

• Modified form of activated sludge process.

• Very high efficiency.

• Excess sludge is taken to drying beds.
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