Environmental Engineering: Comprehensive Study Notes for Civil Engineering

Chapter 1: Quantity of Water

• Introduction to Public Health Engineering

  • Public Health Engineering: A combination of "water supply engineering" and "sanitary engineering" dealing with the general health and well-being of the population.

  • Water Supply Engineering: Focuses on providing adequate quantity and high quality of water for domestic and industrial use. It involves purification and distribution networks.

  • Key Areas of Water Supply:

  • Quality and Quantity of water.

  • Water treatment.

  • Conveyance (transportation) of water.

  • Valves, fittings, and distribution system maintenance.

  • Sanitary Engineering: A branch dedicated to the prevention of communicable diseases and the maintenance of individual and community health through sewage management.

  • Key Areas of Sanitary Engineering:

  • Collection and conveyance of sewage.

  • Sewage treatment and disposal.

  • Maintenance of sewage systems.

• Sources and Considerations for Water Supply

  • Raw Water: Water derived from natural sources that has not undergone artificial treatment.

  • Raw Water Estimation: Depends primarily on the Rate of Demand and the Population.

  • Selection Criteria for Public Water Supply:

  • Quantity: The source must provide sufficient water in all seasons.

  • Gravity Flow: Ideally, the source should be at an elevation allowing water to flow to water works under gravity.

  • Quality: Sources requiring minimal treatment are preferred.

  • Future Demand: Must meet the projected needs of the city.

  • Distribution Elevation: The location should allow water to reach buildings up to $10-15\,m$ high using gravitational force.

  • Criteria for Water Supply Schemes:

  1. Financial aspects.
  2. Population.
  3. Water Quality.
  4. Rate of Consumption.
  5. Sources available.
  6. Sanitary survey and Topography.
  7. Trends in town development.

• Components and Sources of Water

  • Water Supply Scheme Components:

  • Collection Works: Intake from source.

  • Transmission Works: Moving water to treatment/city.

  • Purification Works: Treatment plants.

  • Distribution Works: Pipe networks to consumers.

  • Surface Water Sources:

  • Lakes: Natural depressions filled with rainwater. Quality is generally good; larger/older lakes are purer. Algae growth is common.

  • Ponds: Smaller and shallower than lakes.

  • Streams: Small water bodies from hills; may go dry.

  • Rivers: Combined streams; the most important source for public supply but quality varies (highly turbid in monsoon).

  • Storage Reservoirs: Formed by dams across valleys for supply, irrigation, power, and flood control.

  • Ground Water Sources:

  • Infiltration Wells: Sunk in series in sandy river beds. Constructed of brick masonry with open joints for percolation. Water is collected in a jack well and pumped.

  • Infiltration Gallery: Horizontal tunnels in river beds at shallow depths ($3-5\,m$). Perforated pipes collect water flowing toward a sump well. Suitable for small schemes.

  • Springs: Natural outflow of groundwater where a pervious layer is between two impervious layers. Types include: Artesian, Gravity, and Surface springs.

  • Wells: Vertical shafts excavated to source groundwater. Classified as Open Wells (Shallow/Deep, Kachha/Lined) or Tube Wells (Strainer, Cavity, Slotted types).

• Water Demand and Formulas

  • Types of Demand: Domestic, Industrial, Commercial, Public use, Fire demand, and Losses.

  • Fire Demand (Empirical Formulas):

  • Kuichling’s Formula: $Q = 3182 \times \sqrt{P}$

  • National Board of Fire Underwriters: $Q = 4637 \times \sqrt{P} \times (1 - 0.01 \times \sqrt{P})$

  • Freeman’s Formula: $Q = 1136 \times (\frac{P}{5} + 10)$

  • Buston’s Formula (Buston is identified as Buston in transcript): $Q = 5663 \times \sqrt{P}$

  • Note: $Q$ is in liters/minute, $P$ is population in thousands.

  • Per Capita Demand ($q$): The annual average daily water required by one person, expressed in liters/capita/day (lpcd).

  • $q = \frac{\text{Total annual quantity (liters)}}{P \times 365}$

• Fluctuation and Forecasting

  • Fluctuations in Demand:

  • Maximum Seasonal: $130\% \times \text{avg daily} = 1.3q$

  • Maximum Monthly: $140\% \times \text{avg daily} = 1.4q$

  • Maximum Daily: $180\% \times \text{avg daily} = 1.8q$

  • Maximum Hourly: $150\% \times \text{avg daily} = 1.5q$

  • Total Demand (Coincident Demand): The greater of [Max Daily + Fire Demand] or [Max Hourly Demand].

  • Population Forecasting Methods:

  1. Arithmetic Increase Method: Assumes constant rate of increase. $P_n = P + n \times i$ (Suitable for old, large cities).
  2. Geometric Increase Method: Assumes constant percentage increase. $P_n = P \times (1 + \frac{r}{100})^n$ (Suitable for young, growing cities).
  3. Incremental Increase Method: Combination of arithmetic and geometric increase. $P_n = P + n \times i + \frac{n \times (n+1)}{2} \times r_1$.
  4. Decreasing Rate of Growth: Used when a city is nearing saturation.
  5. Simple/Comparative Graphical Methods: Plotting data against time/similar cities.
  6. Zoning/Master Plan Method: Based on planned density (e.g., 5 persons/plot).
  7. Logistic Curve Method: S-shaped curve representing early growth, transition, and saturation ($P_s$).

Chapter 2: Quality of Water

• Impurities in Water

  • Suspended Impurities: Large solid particles ($10^{-1}$ to $10^{-3}\,mm$). Includes clay, silt, algae, and organic matter. Measured via turbidity.
  • Dissolved Impurities: Smaller than $10^{-6}\,mm$. Includes organic compounds, inorganic salts, and gases. Measured by weighing residue after evaporation.
  • Colloidal Impurities: ($10^{-2}$ to $10^{-6}\,m$). Finely divided particles that are electrically charged and do not settle. Associated with color and bacteria.

• Physical Parameters

  • Turbidity: Measure of dirtiness/resistance to light passage.

  • Units: $ppm$ ($mg/l$) or NTU (Nephelometric Turbidity Unit).

  • Limit: Permissible limit for public supply is $5\,NTU$ (per IS: 10500-2012).

  • Measurement Devices:

    • Turbidity Rod: Field method using a platinum needle.
    • Jackson’s Turbidimeter: Laboratory method for values above $25\,ppm$; based on light absorption.
    • Baylis Turbidimeter: Based on color matching; measures low turbidity.
    • Nephelometer: Modern method based on scattering principle at right angles ($90^\circ$) to incident light.

  • Colour: Due to organic matter or metals like iron/manganese.

  • Scale: Measured against Platinum-Cobalt Scale using a Tintometer.

  • Unit: $1\,TCU\,\text{(True Colour Unit)} = 1\,mg\,\text{of Platinum in } 1\,dm^3\,\text{of water}$.

  • Limit: Should not exceed $20$; preferably less than $10$.

  • Odour and Taste: Measured by Threshold Odour Number (TON).

  • $TON = \frac{A + B}{A}$ where $A$ is sample volume and $B$ is distilled water.

  • Limit: TON should not exceed $3$ at $20^\circ C$.

  • Temperature: Ideal range for domestic use is $10^\circ C$ to $20^\circ C$. Density is maximum at $4^\circ C$.

• Chemical Parameters

  • Total Dissolved Solids (TDS): Preferred limit is less than $500\,ppm$.

  • pH Value: Negative logarithm of Hydrogen ion ($H^+$) concentration.

  • $pH = -\log_{10}(H^+)$. Neutral water ($pH = 7$) has $10^{-7}\,\text{moles/litre}$.

  • Limits: Potable water range is $6.5$ to $8.5$.

  • Indicators: Methyl Orange ($pH < 4.5\,\text{is Red, } > 4.5\,\text{is Yellow}$) and Phenolphthalein ($pH < 8.3\,\text{is Colorless, } > 8.3\,\text{is Pink}$).

  • Alkalinity: Ability to neutralize acids. Caused by Hydroxides ($OH^-$), Carbonates ($CO_3^{2-}$), and Bicarbonates ($HCO_3^-$). Measured as $mg/l\,\text{as } CaCO_3$.

  • Hardness: Soap-destroying property.

  • Temporary (Carbonate) Hardness: Due to bicarbonates of Ca and Mg. Removed by boiling or lime.

  • Permanent (Non-Carbonate) Hardness: Due to sulfates, chlorides, and nitrates. Removed by Zeolite or Soda-Lime process.

  • Calculation: Total Hardness ($T.H.$) = $\text{Ca}^{2+}\,(\text{mg/l}) \times \frac{50}{20} + \text{Mg}^{2+}\,(\text{mg/l}) \times \frac{50}{12}$.

  • Classification: Soft ($< 50$), Moderate ($50-150$), Hard ($150-300$), Very Hard ($> 300$).

  • Fluorides: Lack ($< 1.0\,mg/l$) causes cavities; excess ($> 1.5\,mg/l$) causes Fluorosis/mottling of teeth.

  • Chloride: Limit is $250\,mg/l$. Excess causes salty taste.

  • Oxygen Demand: BOD (Biochemical Oxygen Demand) is the amount of oxygen consumed during microbial utilization of organics. COD is chemical demand.

• Biological Parameters

  • Pathogens: Organisms causing disease (Bacteria, Viruses, Protozoa, Helminths).
  • Coliform Group (B-Coli): Includes E-Coli. Their presence indicates sewage contamination.
  • Detection: MPN (Most Probable Number) test using Presumptive, Confirmed, and Completed tests.
  • Water-borne Diseases:
  • Bacterial: Typhoid, Cholera, Dysentery.
  • Viral: Hepatitis, Jaundice, Polio.
  • Protozoal: Amebic dysentery, Giardiasis.
  • Helminthic: Schistosomiasis, Dracontiasis.

Chapter 3: Water Treatment Processes

• Layout and Objectives

  • Objectives: Removal of germs, unpleasant taste/odour, dissolved gases, murkiness, and corrosive properties.
  • Standard Sequence:
  1. Screening (Floating matter).
  2. Plain Sedimentation (Large suspended solids).
  3. Aeration (Odours, gases, Fe/Mn removal).
  4. Sedimentation with Coagulation (Fine suspended matter).
  5. Filtration (Colloidal matter).
  6. Softening (Hardness).
  7. Disinfection (Pathogens).

• Primary Treatment Steps

  • Screening:

  • Coarse Screens (Trash Racks): Bars spaced $3-10\,cm$ c/c. Velocity $0.8$ to $1\,m/sec$. Inclined at $45^\circ-60^\circ$.

  • Fine Screens: Openings $< 1\,cm$. Often avoided as they clog easily; sedimentation is preferred.

  • Plain Sedimentation: Removal of discrete particles by gravity.

  • Newton’s Law: $V_s = \sqrt{\frac{4}{3} \times \frac{g \times d \times (G-1)}{C_D}}$.

  • Stoke’s Law (for $d < 0.1\,mm$): $V_s = \frac{g}{18} \times (G-1) \times \frac{d^2}{\nu}$.

  • Design Parameters: Detention period ($T$) is $4-8\,hours$. Velocity of flow ($V_d$) is $0.3\,m/min$. Surface Overflow Rate (S.O.R.) is $500-750\,lit/hr/m^2$.

  • Aeration: Methods include Cascade, Inclined Apron, Slat Tray, Gravel Bed/Trickling Bed, Spray Aerators, and Air Diffusion.

• Coagulation and Flocculation

  • Coagulants:

  • Alum: $Al_2(SO_4)_3 \cdot 18H_2O$. Dose: $5-25\,mg/l$. Effective at $pH\,6.5-8.5$. Forms Alum hydroxide ($Al(OH)_3$) floc.

  • Copperas (Ferrous Sulphate): Used with Lime ($CaO$). Effective at $pH > 8.5$.

  • Chlorinated Copperas: Combination of ferric sulphate and ferric chloride.

  • Sodium Aluminate ($Na_2Al_2O_4$): Removes both temporary and permanent hardness; used for boiler feed water.

  • Mixing Devices: Mixing basins with baffle walls, flash mixers ($G$-value gradient formula: $G = \sqrt{\frac{P}{\mu \times V}}$), narrow channels with flumes, or centrifugal pumps.

• Filtration

  • Slow Sand Filters: Introduced in 1829. Effective size ($D_{10}$) = $0.2-0.35\,mm$. Rate of filtration is slow ($100-200\,lit/hr/m^2$). Bacterial removal is high ($98-99\%$), but requires large land area.
  • Rapid Sand Filters: Use larger sand ($0.35-0.55\,mm$). Rate of filtration is $3000-6000\,lit/hr/m^2$. Periodically cleaned by Backwashing.
  • Troubles in Filters: Air Binding (due to negative head), Mud Balls (poor washing), and Cracking of filter bed.

• Disinfection and Softening

  • Disinfection Methods: Boiling, Excess Lime, Ozone ($O_3$), Ultraviolet (UV) rays ($1000-4000\,mm$ wavelength), and Chlorination.
  • Forms of Chlorine: Liquid, Gaseous, Bleaching powder, Chloramines, and Chlorine Dioxide.
  • Break-Point Chlorination: The point where the chlorine demand is satisfied and free residual chlorine begins to appear.
  • Softening:
  • Lime-Soda Process: $Lime + Soda\,Ash$; removes both types of hardness.
  • Zeolite (Ion-Exchange) Process: Uses natural or artificial zeolite to replace Ca/Mg with Na. Regenerated using Brine ($10\%\,NaCl$).

Chapter 4 & 5: Collection and Conveyance of Water

• Intake Structures

  • Location Factors: Near treatment plant, protected from pollution/currents, upstream of sewage outfalls, approachable foundations.
  • Types of Intakes:
  • Submerged: Entirely underwater.
  • Exposed: Tower-like structure near bank.
  • Wet/Dry: Whether the tower contains water or just gates/valves.
  • Canal Intake: Simple masonry chambers with screens and bell-mouth entries.

• Water Conveyance Systems

  • Free Flow: Canals, flumes, grade aqueducts, and tunnels.

  • Pressure Systems: Pressure mains, inverted siphons.

  • Pipe Materials:

  • Cast Iron (CI): Long life ($100\,years$), corrosion-resistant, but brittle.

  • Steel: High tensile strength, lightweight, but susceptible to corrosion and external loads.

  • RCC/PSC: Durable, maintenance-free, but heavy and difficult to repair.

  • Asbestos Cement (AC): Smooth, flexible, but weak under impact.

  • Plastic (PVC/HDPE): Corrosion-free, lightweight, but sensitive to heat.

  • Joints & Valves:

  • Joints: Spigot & Socket (Lead joint), Flanged (rigid), Mechanical, Flexible (Universal), Expansion.

  • Appurtenances: Sluice/Gate (regulate flow), Air Relief (summit points), Reflux/Check (one-way flow), Scour/Blow-off (lowest points for cleaning).

Chapter 6: Distribution System

• Distribution Methods and Layouts

  • Gravity System: Most reliable and economical; source at height.

  • Pumping System: Direct pumping into mains.

  • Dual System: Combined gravity and pumping using elevated reservoirs.

  • Layout Networks:

  1. Dead End (Tree) System: Suitable for old irregular cities; easy to design but has stagnant water issues.
  2. Grid Iron (Interlaced) System: No dead ends; water flows in all loops; expensive but reduces head loss.
  3. Ring System: Main pipes form a closed loop around an area.
  4. Radial System: Area divided into zones with central elevated reservoirs; quick service.

• Systems of Supply

  • Continuous: Water available $24\,hours$; hygienic but results in wastage.
  • Intermittent: Water available at fixed hours; common in India; requires domestic storage and risk of pollution during non-supply hours.

Chapter 7 & 8: Wastewater Management

• Definitions and Decomposition

  • Sullage: Wastewater from kitchens and baths; no fecal matter.
  • Sewage: Liquid waste containing human and industrial excreta ($99.9\%\,water, 0.1\%\,solids$).
  • Aerobic Decomposition: Oxidation by bacteria in the presence of oxygen. End products: $CO_2, NO_3, SO_4$.
  • Anaerobic Decomposition: Putrefaction in the absence of oxygen. End products: $CH_4, H_2S, NH_3$.

• Parameters and Testing

  • Dissolved Oxygen (DO): Essential for aquatic life; minimum required is $4\,ppm$.
  • BOD: Oxygen needed for microbial stabilization of organic matter (standard is 5-day at $20^\circ C$).
  • COD: Oxygen needed for chemical oxidation; higher than BOD.
  • Population Equivalent (PE): $PE = \frac{\text{Total 5-day BOD from industry (kg/day)}}{0.08\,kg/day}$.
  • Relative Stability ($S_R$): $S_R = 100 \times [1 - 0.794^{t_{20}}]$.

• Collection and Sewerage

  • Systems:

  • Separate: One pipe for sewage, one for storm water.

  • Combined: One single pipe for both.

  • Partially Separate: Domestic and early rain washing in one pipe; heavy rain diverted.

  • Sewers: Lateral (house), Branch/Submain, Main/Trunk, Outfall (final length), Relief, and Intercepting sewers.

  • Materials: Salt-glazed stoneware (best for small sewers), RCC (heavy loads), CI (pressure).

Chapter 9 & 10: Sewer Construction and Treatment

• Laying and Testing of Sewers

  • Steps: Setting out (Manholes), Alignment (Sight rails & Boning rods), Excavation, Laying, Testing, and Backfilling.
  • Testing Methods:
  • Straightness: Mirror and lamp.
  • Water Test: Plugging lower end; $1.5\,m$ water head applied; loss checked after $30\,min$.
  • Smoke/Air Test: For buildings or large diameter pipes.

• Sewer Appurtenances

  • Manholes: Inspection chambers classification: Shallow ($0.7-0.9\,m$), Normal ($1.5\,m$), Deep ($> 1.5\,m$).
  • Drop Manholes: Used when a branch comes at a level higher than $0.6\,m$ above the main sewer.
  • Inverted Siphons: Pipes running under pressure beneath obstructions like rivers.
  • Storm Regulators: Leaping weirs, Siphon spillways.

• Sewage Treatment Plant (STP) Units

  • Preliminary: Screens, Grit Chambers (Detritus tanks), Skimming tanks (Air blowing removes grease).
  • Primary: Sedimentation with or without chemicals.
  • Secondary:
  • Attached Growth: Trickling Filters (Bio-film/Slime), Contact Beds.
  • Suspended Growth: Activated Sludge Process (ASP), Aerated Lagoons.
  • Trickling Filters: Conventional (LRTF) and High-Rate (HRTF). HRTF utilizes Recirculation to increase efficiency.

Chapter 11 & 12: Disposal and House Drainage

• Disposal Methods

  • Dilution: Discharging into rivers, lakes, or the sea. Depends on the Dilution Factor.
  • Self-Purification: Natural forces include dilution, sedimentation, oxidation, and sunlight.
  • Zones of Pollution: Degradation, Active Decomposition, Recovery, Clear Water.
  • DO Sag Curve: Resultant of De-oxygenation and Re-oxygenation rates.
  • Land Treatment: Broad Irrigation (Effluent irrigation) or Sewage Farming. Risk of Sewage Sickness (soil clogging) if land is not aerated or rested.

• House Drainage Principles

  • Traps: P-Trap, S-Trap, Q-Trap.

  • Floor/Nahni Trap: Collects bath/kitchen waste.

  • Gully Trap: Disconnects sullage from main system.

  • Intercepting Trap: Prevents sewer gases from public main entering house pipes.

  • Pipes:

  • Soil Pipe: Human excreta ($100\,mm$).

  • Waste Pipe: Non-fecal waste ($30-75\,mm$).

  • Anti-siphonage Pipe: Preserves trap water seal ($40-50\,mm$).

  • Plumbing Systems:

  1. Single Stack: One pipe for all waste/foul matter; no vent.
  2. One Pipe: Single main pipe but each trap is ventilated.
  3. Two Pipe: Separate soil and waste pipes; all traps ventilated.
  • Testing Drains: Air test, Coloured water, Hydraulic, Smell, and Smoke tests.