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Cheatsheet: Environmental Engineering
1. Water Quality Parameters
1.1 Physical Parameters
- Colour: Measured in Hazen units (Pt-Co scale)
- Turbidity: Measured in NTU (Nephelometric Turbidity Units) or JTU (Jackson Turbidity Units)
- Temperature: Affects viscosity, dissolved oxygen (DO), reaction rates, and biological activity
- Odour: Threshold Odour Number (TON) indicates minimum dilution required
- Total Dissolved Solids (TDS): Desirable limit < 500 mg/L, Maximum permissible < 2000 mg/L
- Total Suspended Solids (TSS): Matter that can be filtered
1.2 Chemical Parameters
- pH: pH = -log[H⁺]; Drinking water range: 6.5-8.5
- Alkalinity: Capacity to neutralize acids; OH⁻, CO₃²⁻, HCO₃⁻ (expressed as mg/L CaCO₃)
- Acidity: Capacity to neutralize bases; CO₂, H₂CO₃, mineral acids
- Hardness:Ca²⁺ and Mg²⁺ salts (as CaCO₃)
- Soft water: < 50 mg/L
- Moderately hard: 50-150 mg/L
- Hard: 150-300 mg/L
- Very hard: > 300 mg/L
- Chlorides: Indicator of sewage contamination; Desirable limit < 250 mg/L
- Fluoride:
- < 1.0 mg/L causes dental caries
- > 1.5 mg/L causes dental and skeletal fluorosis
- Optimum range: 0.6-1.2 mg/L
- Iron: Max permissible limit = 0.3 mg/L
- Nitrate: Max permissible limit = 45 mg/L (as NO₃)
- Dissolved Oxygen (DO): Essential for aquatic life; > 4-5 mg/L required
1.3 Biological Parameters
- BOD₅:Biochemical Oxygen Demand in 5 days at 20°C
- Formula: BOD₅ = (D₁ - D₂) × Dilution Factor
- BODₜ = BODᵤ(1 - 10⁻ᵏᵗ) or BODₜ = BODᵤ(1 - e⁻ᵏᵗ)
- k = BOD rate constant (base 10 or e)
- COD:Chemical Oxygen Demand; oxygen equivalent of chemical oxidation
- COD ≥ BOD (always)
- COD/BOD ratio indicates biodegradability
- TOC: Total Organic Carbon
- MPN: Most Probable Number (coliform count)
2. Water Treatment Processes
2.1 Screening
- Removes large floating and suspended solids
- Types:
- Coarse screens: 50-100 mm opening
- Medium screens: 10-50 mm opening
- Fine screens: < 10 mm opening
- Microstrainers: 20-60 microns
2.2 Aeration
- Increases DO content
- Removes dissolved gases (CO₂, H₂S, CH₄)
- Removes volatile organic compounds
- Oxidizes iron and manganese
2.3 Coagulation and Flocculation
- Common coagulants:
- Alum [Al₂(SO₄)₃·18H₂O] - Optimum pH: 5.5-7.5
- Ferric Chloride (FeCl₃) - Optimum pH: 4.5-6.5
- Ferrous Sulfate (FeSO₄) - Optimum pH: 8.5-9.5
- Coagulation: Rapid mixing, 30-60 seconds, Velocity gradient 700-1000 s⁻¹
- Flocculation: Slow mixing, 20-40 minutes, Velocity gradient 20-70 s⁻¹
- Coagulant aids: Activated silica, polyelectrolytes
2.4 Sedimentation
- Surface Overflow Rate (SOR): Q/A (m³/m²/day or m/hr)
- Particle removal efficiency independent of depth (Ideal settling)
- Detention time: 2-6 hours for horizontal flow tanks
- Weir loading rate: 100-500 m³/day/m
- Types: Rectangular, Circular (radial flow)
- Stokes' Law: v = (g/18μ) × (ρₛ - ρ) × d²
2.5 Filtration
| Parameter | Slow Sand Filter | Rapid Sand Filter |
|---|---|---|
| Filtration Rate | 0.1-0.3 m³/m²/hr (100-200 L/m²/hr) | 5-15 m³/m²/hr (5000-7500 L/m²/hr) |
| Sand Size (Effective) | 0.2-0.4 mm | 0.45-0.7 mm |
| Depth of Sand Bed | 0.9-1.2 m | 0.6-0.9 m |
| Uniformity Coefficient | 2-3 | < 1.7 |
| Cleaning Method | Scraping top layer | Backwashing |
| Cleaning Frequency | 1-3 months | 24-48 hours |
| Schmutzdecke | Present (biological layer) | Absent |
| Pre-treatment | Not required | Coagulation required |
2.6 Disinfection
- Chlorination:
- Dose = Demand + Residual
- Chlorine demand = Applied dose - Residual chlorine
- Free residual: 0.2-0.5 mg/L (minimum 30 min contact)
- Combined residual: 1.0-2.0 mg/L
- Break-point chlorination: destroys chloramines
- Other methods:
- Ozonation: Powerful oxidant, no residual
- UV radiation: 254 nm wavelength, no chemical addition
- Chlorine dioxide: No THM formation
2.7 Water Softening
- Lime-Soda Process:
- Removes temporary and permanent hardness
- Lime for temporary hardness; Soda ash for permanent hardness
- Ion Exchange:
- Zeolite process: Na-zeolite exchanges Na⁺ for Ca²⁺, Mg²⁺
- Regeneration with NaCl solution
3. Wastewater Characteristics and Treatment
3.1 Wastewater Characteristics
- Domestic sewage:
- BOD₅: 200-400 mg/L (typical 300 mg/L)
- COD: 400-800 mg/L
- BOD/COD ratio: 0.4-0.6 (typical 0.5)
- TSS: 200-400 mg/L
- Per capita sewage flow: 100-200 LPCD
- Industrial wastewater: Characteristics vary widely
3.2 Preliminary Treatment
- Screens: Remove large floating objects
- Grit chambers:Remove heavy inorganic particles
- Detention time: 30-60 seconds
- Horizontal velocity: 0.15-0.4 m/s
- Skimming tanks: Remove oil and grease
3.3 Primary Treatment
- Physical/mechanical process
- Primary sedimentation:
- Detention time: 1.5-2.5 hours
- Surface overflow rate: 30-50 m³/m²/day
- Removes 50-70% TSS and 25-40% BOD
- Imhoff Tank: Combined settling and digestion
3.4 Secondary Treatment (Biological)
3.4.1 Activated Sludge Process (ASP)
- Principle: Aerobic decomposition by microorganisms
- Components: Aeration tank, Secondary clarifier, Return sludge system
- Key parameters:
- F/M ratio (Food to Microorganism): 0.2-0.6 kg BOD/kg MLSS/day
- MLSS (Mixed Liquor Suspended Solids): 2000-5000 mg/L
- MLVSS/MLSS: 0.7-0.8
- SVI (Sludge Volume Index): 80-150 mL/g
- Aeration period: 4-8 hours
- BOD removal: 85-95%
- Return sludge ratio: 25-75%
- Sludge age (θc): 5-15 days for conventional ASP
- Variations: Extended aeration, Contact stabilization, Step aeration
3.4.2 Trickling Filter
- Fixed film biological treatment
- Media: Crushed stone, plastic media
- Organic loading rate: 0.1-0.4 kg BOD/m³/day
- Hydraulic loading rate: 1-4 m³/m²/day
- BOD removal: 80-90%
- Recirculation ratio: 0.5-3.0
3.4.3 Oxidation Pond/Stabilization Pond
- Natural treatment system
- Organic loading: 100-400 kg BOD/ha/day
- Detention time: 20-30 days
- Depth: 1-2 m
- Types: Aerobic, Facultative, Anaerobic
3.4.4 Rotating Biological Contactor (RBC)
- Attached growth process
- Discs rotate through wastewater and air
- Hydraulic loading: 0.03-0.16 m³/m²/day
3.5 Tertiary Treatment
- Purpose: Advanced treatment for specific pollutant removal
- Nutrient removal (N, P)
- Filtration (sand filters, membrane filtration)
- Activated carbon adsorption
- Ion exchange
4. Sludge Treatment and Disposal
4.1 Sludge Characteristics
- Primary sludge: 95-97% moisture, organic content 60-80%
- Activated sludge: 98-99% moisture, organic content 75-90%
- Digested sludge: 90-95% moisture after dewatering
4.2 Sludge Thickening
- Gravity thickening: 4-6% solids concentration
- Flotation thickening: For activated sludge
- Centrifugation: 5-10% solids
4.3 Sludge Digestion
4.3.1 Anaerobic Digestion
- Temperature: Mesophilic (30-35°C) or Thermophilic (50-55°C)
- Detention time: 15-30 days
- Volatile solids reduction: 50-60%
- Biogas composition:
- Methane (CH₄): 60-70%
- Carbon dioxide (CO₂): 30-40%
- Other gases: H₂S, N₂ (traces)
- Gas production: 0.6-1.0 m³/kg VS destroyed
4.3.2 Aerobic Digestion
- Used for small plants
- Detention time: 12-20 days
- Oxygen requirement: 2.3 kg O₂/kg VS destroyed
4.4 Sludge Dewatering
- Sludge drying beds:
- Solids loading: 100-200 kg/m²/year
- Final moisture: 70-80%
- Drying period: 2-4 weeks
- Mechanical dewatering:
- Filter press: 30-40% solids
- Belt filter press: 15-25% solids
- Centrifuge: 20-30% solids
4.5 Sludge Disposal
- Land application: Agricultural use as fertilizer
- Incineration: Temperature > 800°C
- Landfilling: In sanitary landfills
- Ocean disposal: Generally prohibited now
5. Air Pollution and Control
5.1 Air Pollutants
5.1.1 Primary Pollutants
- CO (Carbon Monoxide): From incomplete combustion
- SO₂ (Sulfur Dioxide): From burning fossil fuels
- NOₓ (Nitrogen Oxides): NO and NO₂ from high temperature combustion
- Particulate Matter:
- PM₁₀: Diameter < 10 μm (inhalable)
- PM₂.₅: Diameter < 2.5 μm (respirable)
- VOCs: Volatile Organic Compounds
- Pb (Lead): From leaded gasoline
5.1.2 Secondary Pollutants
- O₃ (Ozone): Photochemical reaction of NOₓ and VOCs
- PAN (Peroxyacetyl Nitrate): Component of photochemical smog
- H₂SO₄: Acid rain from SO₂
- HNO₃: Acid rain from NOₓ
5.2 Air Quality Standards (India - NAAQS)
| Pollutant | Time Weighted Average | Industrial Area | Residential Area |
|---|---|---|---|
| SO₂ | Annual / 24-hr | 80 / 80 μg/m³ | 50 / 80 μg/m³ |
| NO₂ | Annual / 24-hr | 80 / 80 μg/m³ | 40 / 80 μg/m³ |
| PM₁₀ | Annual / 24-hr | 120 / 150 μg/m³ | 60 / 100 μg/m³ |
| PM₂.₅ | Annual / 24-hr | 60 / 100 μg/m³ | 40 / 60 μg/m³ |
5.3 Control Devices for Particulate Matter
| Device | Effective For | Efficiency | Particle Size |
|---|---|---|---|
| Gravity Settling Chamber | Large particles | < 50% | > 50 μm |
| Cyclone Separator | Medium particles | 50-90% | > 10 μm |
| Bag Filter (Fabric Filter) | Fine particles | > 99% | > 0.5 μm |
| Electrostatic Precipitator (ESP) | Very fine particles | > 99% | > 0.01 μm |
| Wet Scrubber | Fine particles + gases | 80-95% | > 1 μm |
5.4 Control of Gaseous Pollutants
- Absorption: Scrubbers (wet absorption)
- Adsorption: Activated carbon beds
- Combustion: Thermal oxidation, catalytic converters
- Condensation: For VOCs
5.5 Atmospheric Dispersion
- Gaussian Plume Model: C = (Q/πσᵧσᵤu) × exp[-(y²/2σᵧ²)] × exp[-(z-H)²/2σᵤ²]
- Effective stack height: H = h + Δh (h = physical height, Δh = plume rise)
- Lapse rate:Temperature change with altitude
- Environmental lapse rate: ~6.5°C/km
- Adiabatic lapse rate: ~10°C/km (dry)
6. Solid Waste Management
6.1 Municipal Solid Waste Composition (India)
- Biodegradable organics: 40-60%
- Paper: 5-10%
- Plastics: 5-15%
- Metals: 1-2%
- Glass: 1-2%
- Inert material: 30-50%
6.2 Solid Waste Generation
- Per capita generation: 0.2-0.6 kg/day (varies with city size)
- Density: 300-500 kg/m³ (uncompacted)
- Moisture content: 40-60%
6.3 Collection and Transportation
- Collection efficiency: Should be > 85%
- Transfer station: When haul distance > 15-20 km
- Compaction ratio: 2:1 to 4:1
6.4 Treatment and Disposal Methods
6.4.1 Composting
- Aerobic decomposition of organic matter
- C/N ratio: Initial 25-35, Final < 20
- Temperature: Mesophilic (35-40°C) or Thermophilic (55-65°C)
- Time: 3-4 weeks for windrow composting
- Volume reduction: 40-50%
- Types: Windrow, Vermicomposting, In-vessel
6.4.2 Incineration
- Combustion at high temperature (800-1000°C)
- Volume reduction: 70-90%
- Weight reduction: 60-80%
- Energy recovery: 2000-3500 kJ/kg
- Minimum calorific value required: 5000 kJ/kg
- Moisture content should be < 50% for efficient burning
6.4.3 Sanitary Landfill
- Engineered method of waste disposal
- Components: Bottom liner, Leachate collection, Gas collection, Daily cover
- Cell height: 2.5-3.0 m
- Daily cover: 15-30 cm soil
- Final cover: 60-90 cm
- Compacted density: 500-800 kg/m³
- Leachate generation: Managed by collection and treatment
- Landfill gas: 50-60% CH₄, 40-50% CO₂
6.5 Hazardous Waste Management
- Characteristics: Ignitability, Corrosivity, Reactivity, Toxicity (ICRT)
- Treatment: Incineration, Stabilization/Solidification, Chemical treatment
- Disposal: Secure landfills with double liner system
7. Noise Pollution
7.1 Noise Measurement and Units
- Sound Pressure Level:L = 10 log₁₀(I/I₀) = 20 log₁₀(P/P₀)
- I₀ = 10⁻¹² W/m² (reference intensity)
- P₀ = 2 × 10⁻⁵ N/m² (reference pressure)
- Addition of sound levels: L = 10 log₁₀(10^(L₁/10) + 10^(L₂/10))
- A-weighted scale (dBA): Adjusted for human ear sensitivity
7.2 Permissible Noise Limits (India)
| Area Category | Daytime (6 AM-10 PM) | Night time (10 PM-6 AM) |
|---|---|---|
| Industrial | 75 dB(A) | 70 dB(A) |
| Commercial | 65 dB(A) | 55 dB(A) |
| Residential | 55 dB(A) | 45 dB(A) |
| Silence Zone | 50 dB(A) | 40 dB(A) |
7.3 Noise Control Measures
- At source: Equipment modification, maintenance
- In transmission path: Barriers, enclosures, distance, vegetation
- At receiver: Ear protection devices, building insulation
- Noise barrier attenuation: 5-20 dB reduction possible
8. Environmental Impact Assessment (EIA)
8.1 Purpose of EIA
- Identify potential environmental impacts
- Suggest mitigation measures
- Involve public participation
- Aid decision-making process
8.2 Steps in EIA Process
- Screening: Determine if EIA is required
- Scoping: Identify key issues and impacts to be assessed
- Baseline study: Environmental conditions before project
- Impact prediction: Assess magnitude and significance
- Impact assessment: Evaluate environmental consequences
- Mitigation measures: Propose measures to reduce impacts
- Public hearing: Stakeholder consultation
- EIA report preparation: Document findings
- Review and decision: Expert appraisal committee review
- Monitoring: Post-project environmental monitoring
8.3 Environmental Clearance Categories (India)
- Category A: National level appraisal (large projects)
- Category B:State level appraisal (smaller projects)
- B1: Requires EIA
- B2: Does not require EIA
9. Key Environmental Regulations (India)
9.1 Major Acts and Rules
- Water (Prevention and Control of Pollution) Act, 1974
- Established Central and State Pollution Control Boards
- Standards for effluent discharge
- Air (Prevention and Control of Pollution) Act, 1981
- Control of air pollution
- Standards for emission from industries and vehicles
- Environment (Protection) Act, 1986
- Umbrella legislation after Bhopal gas tragedy
- Powers to central government for environmental protection
- Solid Waste Management Rules, 2016
- Segregation at source
- Extended Producer Responsibility
- Hazardous Waste Management Rules, 2016
- E-Waste Management Rules, 2016
- Plastic Waste Management Rules, 2016
- Bio-Medical Waste Management Rules, 2016
- Construction and Demolition Waste Management Rules, 2016
- Noise Pollution (Regulation and Control) Rules, 2000
- EIA Notification, 2006 (amended 2020)
9.2 Important Standards
- IS 10500:2012 - Drinking Water Specifications
- General Standards for Discharge of Environmental Pollutants
- Into inland surface waters
- On land for irrigation
- Into public sewers
- Into marine/coastal areas
10. Additional Important Topics
10.1 Climate Change
- Greenhouse gases: CO₂, CH₄, N₂O, CFCs, O₃
- Global Warming Potential (GWP):
- CO₂ = 1 (reference)
- CH₄ = 25 (over 100 years)
- N₂O = 298
- Kyoto Protocol: Emission reduction targets
- Paris Agreement: Limit global temperature rise < 2°C
10.2 Sustainable Development
- Meeting present needs without compromising future generations
- Sustainable Development Goals (SDGs): 17 goals by UN
- Goal 6: Clean water and sanitation
- Goal 7: Affordable and clean energy
- Goal 11: Sustainable cities and communities
- Goal 13: Climate action
10.3 Water Pollution Indicators
- Coliform bacteria: Indicator of fecal contamination
- E. coli: Specific indicator of recent fecal pollution
- MPN Index: Most Probable Number per 100 mL
- Drinking water: E. coli should be absent in 100 mL
The document Cheatsheet: Environmental Engineering is a part of the Civil Engineering (CE) Course Civil Engineering SSC JE (Technical).
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FAQs on Cheatsheet: Environmental Engineering
| 1. What are the key parameters used to assess water quality? |  |
Ans. The key parameters used to assess water quality include pH, turbidity, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), and the presence of pathogens and heavy metals. These parameters help in determining the suitability of water for various uses, including drinking, irrigation, and industrial processes.
| 2. What processes are commonly employed in water treatment? | |
Ans. Common processes employed in water treatment include coagulation and flocculation, sedimentation, filtration, and disinfection. Coagulation involves the addition of chemicals to facilitate the aggregation of suspended particles, while sedimentation allows these aggregates to settle. Filtration removes remaining particles, and disinfection typically uses chlorine or ultraviolet light to eliminate pathogens.
| 3. How is wastewater characterised and treated? | |
Ans. Wastewater is characterised by its physical, chemical, and biological properties, including parameters such as BOD, COD, solids concentration, and nutrient levels. Treatment methods include primary treatment (physical processes), secondary treatment (biological processes), and tertiary treatment (advanced processes for nutrient removal and disinfection) to make the water suitable for discharge or reuse.
| 4. What are the key methods for sludge treatment and disposal? | |
Ans. Key methods for sludge treatment include anaerobic digestion, aerobic digestion, and mechanical dewatering. Anaerobic digestion reduces the volume of sludge and produces biogas, while aerobic digestion stabilises the sludge through microbial activity. Disposal options include landfilling, incineration, or land application, depending on regulations and environmental considerations.
| 5. What are the main regulatory frameworks governing environmental impact assessment in India? | |
Ans. The main regulatory frameworks governing environmental impact assessment (EIA) in India include the Environment (Protection) Act, 1986, and the EIA Notification, 2006. These regulations mandate that projects likely to have significant environmental impacts undergo an EIA process, which includes public consultation, assessment of potential impacts, and formulation of management plans to mitigate adverse effects.
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