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Environmental Engineering – Complete Study Notes

GATE ESE / IES SSC JE State PSC RRB JE

Comprehensive chapter-wise notes on Water Supply Engineering, Waste Water Engineering, Solid Waste Management, and Air & Noise Pollution. Covers all IS codes (IS 10500, IS 2470, CPCB norms), design formulae, treatment processes, diagrams, and exam-focused tables for GATE, ESE & SSC JE.

Ch 1 · Water Demand Ch 2 · Water Conduits Ch 3 · Ground Water & Wells Ch 4 · Water Quality Ch 5 · Water Treatment Ch 6 · Sewer Design Ch 7 · Sewage Quality Ch 8 · Sewage Disposal Ch 9 · Sewage Treatment Ch 10 · Air & Noise Pollution ★ Solid Waste & Quick Revision

1Water Demand►

1.1 Sources of Water

Source Type	Examples	Quality	Suitability
Surface water	Rivers, lakes, tanks, reservoirs	Variable; turbid, may have bacteria	Large cities after treatment; cheapest to develop
Ground water	Wells, springs, infiltration galleries, tube wells	Generally better; may have hardness, iron	Rural and small towns; often requires only disinfection
Rainwater / Rooftop harvesting	Roof collection, check dams	Generally clean initially	Supplementary; arid zones
Sea water (desalination)	SWRO, MSF plants	High TDS (35,000 mg/L)	Coastal cities; expensive

1.2 Types and Per Capita Demand

Type of Use	IS 1172 Per Capita (lpcd)	Remarks
Domestic	135 lpcd (cities >1 lakh)	Drinking, cooking, bathing, flushing; 70% is indoor
Industrial	50 lpcd (allowance)	Highly variable; 45–450 kL/tonne of product
Commercial / Institutional	20 lpcd	Hotels, hospitals, offices, schools
Fire demand	As per Kuichling's formula	Not added to average; governs pipe sizing at hydrants
Losses / Thefts	15% of total	Leakage, metering error, illegal use
Total design	170–200 lpcd (urban India)	Sum of above with safety factor

1.3 Factors Affecting Water Demand

Population size: Larger cities → higher per capita demand (more commercial, industrial use)
Climate: Hot and dry → more demand; cold regions → less bathing
Living standards: Higher income → more water-using appliances
Metering: Metered supply reduces consumption by 20–25% (accounts for waste)
Pressure: Higher pressure in mains → more losses through leakages
Quality: Poor quality → less willingness to use domestically
System efficiency: Old pipes → more leakage losses

1.4 Variation in Demand — Peak Factors

Average Daily Demand (ADD) = Annual consumption / 365

Maximum Daily Demand (MDD) = 1.8 × ADD
Maximum Hourly Demand (MHD) = 1.5 × MDD = 2.7 × ADD
Minimum Hourly Demand = 0.5 × ADD

Peak factor = MHD / ADD = 2.7
(IS 1172 values; some references use 1.5–2.0 for MDD and 2.5–3.0 for MHD)

1.5 Design Period and Population Forecasting

Design period: 30 years for dams, 15–20 years for treatment plants, 10 years for distribution

Arithmetic growth: P_n = P_0 + n × r (r = average annual increment)

Geometric growth: P_n = P_0 × (1 + r/100)^n [r = % growth rate]

Incremental increase method:
Average increment = Σ(increment per decade) / no. of decades
Average incremental increase = Σ(change in increment) / (no. of decades − 1)
P_n = P_last + n/10 × avg_increment + n(n+1)/20 × avg_incr_increase

Logistic (S-curve): P = P_s / (1 + m × e^(−kn))
P_s = saturation population; used when growth is expected to stabilize

1.6 Fire Demand Formulae

Kuichling's formula: Q = 3182 × √P (Q in litres/min, P in thousands)
Freeman's formula: Q = 1136 × (P/5 + 10) / 10
IS formula: Q = 100√P (Q in m³/hr, P in thousands)

Duration of fire fighting: 4–8 hours for most cities (IS 3764)
Pressure at fire hydrant: minimum 7 m head residual

📝 GATE Tip: Per capita demand = 135 lpcd (domestic), Total design ≈ 200 lpcd. Peak factors: MDD = 1.8× ADD; MHD = 2.7× ADD. These specific numbers appear in almost every GATE environmental question on water demand.

2Conduits for Transporting Water►

2.1 Pipe Flow — Manning's and Hazen-Williams Equations

Manning's equation (gravity flow):
V = (1/n) × R^(2/3) × S^(1/2)
Q = A × V = (A/n) × R^(2/3) × S^(1/2)
R = A/P (hydraulic radius); S = slope of hydraulic gradient; n = Manning's roughness

n values: CI pipe = 0.012–0.014; PVC = 0.009–0.011; concrete = 0.013–0.015

Hazen-Williams (pressurised water distribution):
V = 0.8492 × C × R^0.63 × S^0.54 (V in m/s, R in m)
Q = 0.2785 × C × D^2.63 × S^0.54
C = Hazen-Williams coefficient: CI new = 130; old CI = 100; steel = 120; PVC = 140–150

Darcy-Weisbach (head loss):
h_f = f × L × V² / (2gD)
f = friction factor (from Moody chart); typical 0.01–0.05

2.2 Pipe Materials for Water Supply

Material	Advantages	Disadvantages	Use
Cast Iron (CI)	Strong, long life, joints easy	Heavy, brittle, corrodes over time	Distribution mains; 75–600 mm dia
Ductile Iron (DI)	Strong + ductile; better than CI	Expensive	Modern distribution; replacing CI
Steel (MS)	Light, strong, any size	Corrodes; needs lining or coating	Transmission mains; large dia
PVC / CPVC	Light, corrosion-proof, cheap	Limited temperature/pressure range	Small dia distribution; house connections
HDPE	Flexible, good chemical resistance	UV degradation if exposed	Rural supply; sliplined rehabilitation
Asbestos Cement (AC)	Smooth, light, cheap	Brittle; health concerns (asbestos)	Now largely phased out
Pre-stressed Concrete	Large dia; suitable for gravity mains	Heavy; joints critical	Large transmission mains >600 mm

2.3 Distribution System Layout

Fig. 2.1 — Distribution layouts: Tree system (dead-ends; simple, unreliable) vs Ring/Grid system (interconnected; reliable; used in cities)

2.4 Hardy-Cross Method for Pipe Network Analysis

Hardy-Cross iterative method for looped networks:
Head loss in pipe: h_f = r × Q^n (r = pipe resistance; n = 1.85 for HW, 2 for DW)

Correction factor for flow in each loop:
ΔQ = −ΣhL / (n × Σ|hL/Q|)
= −Σ(rQ|Q|^(n-1)) / (n × Σr|Q|^(n-1))

Convergence criterion: ΔQ < 0.001 m³/s (or any small tolerance)

Procedure:
1. Assume flows Q in each pipe satisfying continuity at each junction
2. Compute h_f = r·Q|Q| in each pipe; assign sign by flow direction convention
3. Compute ΔQ for each loop; update flows: Q_new = Q_old + ΔQ
4. Repeat until convergence (typically 3–5 iterations)

2.5 Service Reservoir (Storage)

Storage capacity = balancing storage + fire reserve + emergency reserve

Balancing storage: 1/3 of daily demand (from demand–supply fluctuation curves)
Fire reserve: 4 hours of fire demand at hydrant
Emergency/breakdown reserve: 25% of daily demand

Elevated storage tank height:
Provides pressure head; minimum 7 m residual at consumer's tap
Tank bottom elevation = service area highest ground + 7 m + pipe friction losses

📝 GATE Tip: Hazen-Williams C: CI (new)=130, old CI=100, PVC=140–150. Hardy-Cross ΔQ = −Σh_L / (n·Σ|h_L/Q|). Balancing storage = 1/3 of daily demand. These are the three most tested facts in this chapter.

3Ground Water Development & Well Hydraulics►

3.1 Types of Aquifers

Aquifer Type	Description	Water Table	Example
Unconfined (phreatic)	Water table exposed to atmosphere; water table is upper boundary	Varies freely with seasons	Alluvial plains; dug wells
Confined (artesian)	Sandwiched between impervious layers; water under pressure	Piezometric surface > top of aquifer	Deep tube wells; artesian wells
Semi-confined (leaky)	Confining layer is semi-permeable; leakage from adjacent aquifer	Piezometric varies with leakage	Alluvial basins with clay lenses
Perched aquifer	Local impervious lens above main water table	Localised; above regional WT	Hillside springs; seasonal

3.2 Darcy's Law

Q = K × i × A
where K = hydraulic conductivity (m/day or m/s)
i = hydraulic gradient = dh/dL
A = cross-sectional area normal to flow

Validity: Laminar flow (Re = V×d_50/ν < 1–10)
Not valid for gravel/rock (high velocities, turbulent flow)

Intrinsic permeability: k_i = K × μ / (ρg) [depends on pore structure only]

3.3 Well Hydraulics — Steady State

Fig. 3.1 — Unconfined well: cone of depression; R = radius of influence; H = undisturbed head

Fig. 3.2 — Confined (artesian) well: piezometric surface above aquifer top; flow equation uses aquifer thickness b

3.4 Well Discharge Equations

UNCONFINED WELL (Dupuit-Thiem, steady state):
Q = π × K × (H² − h²) / ln(R/r_w)

Where: H = undisturbed water table height above impermeable base
h = water level in well during pumping
r_w = well radius; R = radius of influence (Sichardt: R = 3000×(H−h)×√K)
K = hydraulic conductivity (m/s or m/day)

CONFINED WELL (Thiem, steady state):
Q = 2π × K × b × (H − h) / ln(R/r_w)
= 2π × T × (H − h) / ln(R/r_w)
T = transmissivity = K × b (m²/day)

Between two observation wells at r₁ and r₂ (confined):
Q = 2π × T × (h₂ − h₁) / ln(r₂/r₁)

3.5 Transient Well Flow — Theis Method

Theis equation (unsteady confined well):
s = Q / (4πT) × W(u) [s = drawdown = H − h]
u = r² × S / (4Tt)

W(u) = well function = −Ei(−u) = −0.5772 − ln(u) + u − u²/2! + u³/3! ...
S = storage coefficient (dimensionless)
t = time since pumping started

For small u (u < 0.05) — Cooper-Jacob approximation:
s = Q / (4πT) × [−0.5772 − ln(u)]
= 2.303Q / (4πT) × log(2.25Tt / r²S)

3.6 Types of Wells

Well Type	Depth	Dia	Method	Yield
Open / Dug well	10–20 m	1–6 m	Manual/mechanical excavation	Low; 50–500 L/hr
Tube well (deep)	60–300 m	100–450 mm	Rotary/cable tool drilling	High; 100–3000 m³/day
Infiltration gallery	5–10 m	—	Horizontal perforated pipe near riverbank	Medium; induced recharge
Spring collection	At surface	—	Gravity collection of natural spring	Variable; gravity-fed
Collector (Ranney) well	15–30 m	Large caisson	Radial horizontal laterals	Very high; 1000–50,000 m³/day

📝 GATE Tip: Unconfined: Q = πK(H²−h²)/ln(R/r_w). Confined: Q = 2πKb(H−h)/ln(R/r_w). Transmissivity T = Kb (m²/day). Radius of influence R = 3000(H−h)√K (Sichardt). These equations appear every year.

4Quality Control of Water Supplies►

4.1 Physical Characteristics

Parameter	Unit	Permissible (IS 10500)	Desirable	Test Method
Turbidity	NTU	5 NTU	<1 NTU	Nephelometer; Jackson turbidimeter
Colour	Hazen units	15 HU	5 HU	Visual comparison; spectrophotometer
Taste & Odour	TON (threshold)	Unobjectionable	—	Dilution-to-threshold method
Temperature	°C	10–25°C (max 45°C)	10–20°C	Thermometer
Total Dissolved Solids (TDS)	mg/L	500 mg/L	—	Gravimetric (105°C evaporation)

4.2 Chemical Characteristics

Parameter	Permissible Limit (IS 10500:2012)	Health Effect if Exceeded
pH	6.5 – 8.5	Corrosion (<6.5); scaling (>8.5)
Total Hardness	300 mg/L (max 600)	Scale in pipes/boilers; soap wastage; not harmful directly
Fluoride	1.0 mg/L (max 1.5)	Dental fluorosis >1.5; skeletal fluorosis >3–6
Nitrate (as NO₃)	45 mg/L	Methaemoglobinaemia (blue baby syndrome) in infants
Arsenic	0.01 mg/L	Skin cancer, arsenicosis (chronic); WHO 0.01 mg/L
Iron	0.3 mg/L	Staining, taste; no direct health effect at low levels
Chloride	250 mg/L (max 1000)	Salty taste; corrosion of pipes
Chlorine (residual)	0.2 mg/L (min)	Below → bacterial growth; above 0.5 → taste/odour
Sulphate	200 mg/L (max 400)	Laxative effect; concrete attack
Lead	0.01 mg/L	Neurotoxin; cumulative; children most vulnerable

4.3 Biological Characteristics

Coliform organisms — indicator bacteria (Escherichia coli as index):
IS 10500: No coliform in 100 mL of treated water (MPN = 0)
Source water (untreated): MPN ≤ 10/100 mL permissible for surface source

MPN (Most Probable Number): statistical method using multiple dilution tube test
MPN index gives probable number of coliforms per 100 mL from positive/negative results

Membrane Filter (MF) technique: filter 100 mL; incubate on selective media 37°C for 24 hr;
count colonies → coliform count per 100 mL

Bacteria: Total Plate Count (TPC) at 37°C: < 100 colonies/mL for treated water

4.4 Hardness of Water

Temporary hardness (carbonate): Ca(HCO₃)₂, Mg(HCO₃)₂ → removed by boiling
Permanent hardness (non-carbonate): CaSO₄, MgSO₄, CaCl₂ → NOT removed by boiling
Total hardness = temporary + permanent

Expressed as mg/L of CaCO₃ equivalent:
Hardness (as CaCO₃) = ion concentration (mg/L) × (50 / eq. weight of ion)
Ca²⁺: eq. wt = 20; Mg²⁺: eq. wt = 12; HCO₃⁻: eq. wt = 61

Langelier Saturation Index (LSI): Indicates corrosiveness or scaling tendency
LSI = pH_actual − pH_s
LSI > 0 → scaling tendency; LSI < 0 → corrosive; LSI = 0 → stable

4.5 Chlorine Demand and Breakpoint Chlorination

Chlorine demand = chlorine added − residual chlorine

Breakpoint chlorination:
Phase 1 (0 to ~1.5× NH₃): chloramines form; residual rises slowly
Phase 2 (dip — breakpoint): chloramines destroyed; chlorine demand high; residual drops
Phase 3 (beyond breakpoint): free residual chlorine increases linearly with dose

Breakpoint dose ≈ 7.6 × (NH₃-N concentration)
Beyond breakpoint: 0.2 mg/L free residual Cl₂ must remain at consumer tap

Superchlorination: adding very high doses; followed by dechlorination with SO₂ or activated C

⭐ IS 10500:2012 Key Limits: Turbidity ≤ 5 NTU; TDS ≤ 500 mg/L; Hardness ≤ 300 mg/L; pH 6.5–8.5; Fluoride ≤ 1.0 mg/L; Nitrate ≤ 45 mg/L; Arsenic ≤ 0.01 mg/L; Coliforms = 0 per 100 mL (treated water). Memorise these for GATE.

5Water Treatment & Distribution System►

5.1 Flow Chart of Water Treatment Plant

Fig. 5.1 — Water treatment plant flow sequence: Screening → Aeration → Coagulation/Flocculation → Sedimentation → Filtration → Disinfection → Distribution

5.2 Aeration

Removes dissolved gases (CO₂, H₂S, volatile organics), oxidises Fe²⁺ and Mn²⁺ (to Fe³⁺ and MnO₂ for removal in subsequent sedimentation), and reduces taste and odour.

Spray aerator: Nozzles spray water into air; simple; effective for taste/odour
Cascade aerator: Water flows over stepped weirs; increases DO; removes CO₂
Diffused air aerator: Air bubbled through water; used in activated sludge process also
Packed tower aerator: Counter-current air flow; most efficient for VOC removal

5.3 Coagulation and Flocculation

Purpose: Destabilise colloidal particles (–ve charged; 1–1000 nm) by adding coagulant

Common coagulants:
Alum: Al₂(SO₄)₃·18H₂O → Al(OH)₃ (gelatinous floc) + H₂SO₄
Optimal pH for alum: 6.5–7.5 (Al(OH)₃ least soluble)

Ferric sulphate: Fe₂(SO₄)₃ → Fe(OH)₃; better at low pH and low temp than alum
Ferric chloride: FeCl₃; fast settling; pH range 5–9
Lime (CaO): raises pH; precipitates Mg(OH)₂; removes hardness

Jar test: laboratory determination of optimum coagulant dose and pH

Flocculation: gentle agitation to aggregate micro-flocs into settle-able macro-flocs
G×t product (Camp number): 10⁴–10⁵ for flocculation (G = velocity gradient, t = detention time)
G = √(P / μV); P = power input, μ = dynamic viscosity, V = volume of tank

5.4 Sedimentation Tanks

Overflow rate (surface loading rate): q_s = Q / A_s
Particle removal: all particles with v_s > q_s are removed; fraction q_s/v_s for smaller particles

For plain sedimentation (no coagulation): q_s = 12,000–18,000 L/m²/day
For coagulation-sedimentation: q_s = 30,000–40,000 L/m²/day (heavier floc)

Horizontal velocity: v_h = Q / (W × D)
Detention time: t = V/Q = L×W×D/Q (typically 2–4 hours)

Weir loading: Q / (total weir length) ≤ 300 m³/m/day (prevents resuspension at outlet)

Stokes' law settling velocity:
v_s = g(ρ_s − ρ_w)d² / (18μ)
ρ_s = particle density, d = particle dia, μ = dynamic viscosity

5.5 Filtration

Parameter	Slow Sand Filter (SSF)	Rapid Sand Filter (RSF)
Filtration rate	0.1–0.4 m/hr (0.1–0.2 usual)	4–12 m/hr (5 m/hr typical)
Media	Sand (0.15–0.35 mm, UC<2)	Sand (0.45–0.70 mm) on gravel
Schmutzdecke (biofilm)	Critical; biological action; vital	Not present; purely physical
Turbidity of influent	≤5 NTU (needs pre-treatment if higher)	Can handle higher (after coagulation)
Backwash	Scraping and washing; 1–2 months	Backwashing every 24–72 hrs (upward flow)
Area needed	Very large (low rate)	Much smaller
Cost	Low operating; high land cost	High capital (coagulation needed); lower land
Coliform removal	98–99%	Lower; relies on disinfection

RSF Design (IS 4090):
Filtration rate: 5 m/hr (range 4–6 m/hr)
Sand depth: 600–900 mm (effective size 0.45–0.70 mm, uniformity coefficient <1.7)
Gravel support: 450–600 mm (graduated; 5 mm to 50 mm from top to bottom)
Backwash rate: 12–15 m/hr; duration 5–10 minutes
Expansion during backwash: 25–50% of sand bed depth

5.6 Disinfection

Chlorination (most common): Cl₂ gas; NaOCl solution; Ca(OCl)₂ (bleaching powder)
Hypochlorite of lime (bleaching powder): 25–35% available chlorine

Chick's law (disinfection kinetics): dN/dt = −k × N
N = N₀ × e^(−kt) [N = surviving organisms, k = rate constant, t = contact time]

CT concept: C × t = constant for a given log inactivation
C = disinfectant concentration (mg/L), t = contact time (min)

Free residual Cl₂ at tap: minimum 0.2 mg/L (IS 10500)
Ct value for 99% removal of Giardia cysts: ~80–100 mg·min/L for free Cl₂ at 10°C

Ozonation: powerful oxidant; no residual; used in advanced treatment
UV disinfection: effective; no chemicals; no residual (must be combined with Cl₂)
Chloramine (Cl₂ + NH₃): slower acting but more stable residual; less THM formation

📝 GATE/ESE Tip: SSF rate = 0.1–0.4 m/hr; RSF = 4–12 m/hr. Alum optimal pH = 6.5–7.5. Overflow rate for plain sedimentation = 12,000–18,000 L/m²/day; after coagulation = 30,000–40,000. Chick's law: first-order die-off. These are classic question areas.

6Design of Sewer►

6.1 Sewerage Systems — Types

System	Description	Advantage	Use
Separate system	Two separate pipes: one for sewage, one for storm water	Smaller sewage treatment plant; no dilution	New planned developments; most modern systems
Combined system	Single pipe carries both sewage and storm water	Lower initial cost; single network	Old cities; can cause overflow in heavy rain
Partially separate	Some storm water (from roofs) enters sewer	Compromise; reduces surcharge	Older cities modifying to separate

6.2 Quantity of Sewage

Dry Weather Flow (DWF): sewage from domestic/industrial use (no rain)
DWF ≈ 80% of water supply (return flow fraction = 0.7–0.8)

Peak flow factor: DWF × 3 (for small sewers); DWF × 2 (for large interceptors)
Minimum flow: 1/3 × DWF (for self-cleansing velocity check)

Estimation:
Q_sewage = (80/100) × Q_water_supply
Q_water = 200 lpcd × population
Q_sewage = 160 lpcd × population (dry weather average)

Storm water (rational method):
Q_storm = C × I × A / 360 (Q in m³/s, I in mm/hr, A in hectares)
C = runoff coefficient (0.1 for parks, 0.9 for paved areas)

6.3 Sewer Hydraulics — Design

Manning's equation for sewer pipe:
V = (1/n) × R^(2/3) × S^(1/2)
Q = (A/n) × R^(2/3) × S^(1/2)

n = 0.013 (RCC sewer); 0.011 (glazed stoneware); 0.009 (PVC)

Self-cleansing velocity: minimum V to prevent sedimentation
V_min = 0.6–0.9 m/s (at full flow or 2/3 full); IS recommends 0.75 m/s at design flow
V_max = 3.0 m/s (to prevent erosion/abrasion of sewer lining)

For circular pipe RUNNING FULL:
R = D/4 A = πD²/4
V_full = (1/n)(D/4)^(2/3) × S^(1/2)
Q_full = (π/4)D² × V_full

Maximum discharge in circular pipe: at 0.94 D depth (not full!)
Maximum velocity in circular pipe: at 0.81 D depth

6.4 Hydraulic Elements — Circular Pipe

Fig. 6.1 — Hydraulic elements of circular pipe: Q_max occurs at 94% full depth (Q = 1.08 Q_full); V_max at 81% depth. Design so that peak flow ≤ Q_max.

6.5 Sewer Appurtenances

Appurtenance	Purpose	Spacing / Size
Manhole	Access for inspection, cleaning, rodding	Every 30–50 m on straight; at every change of direction, dia, gradient; junction
Drop connection	House drain enters sewer at much higher elevation	When incoming pipe invert is >0.6 m above sewer invert
Flushing tank	Periodic flushing of flat-gradient small sewers	Self-priming; at dead ends; automatic
Catch basin	Trap grit and floating material from storm drains	At road inlets; prevents grit entering sewer
Inverted siphon	Carries sewage under an obstruction (road, river) under pressure	Velocity ≥ 1.0 m/s to prevent deposition; minimum 2 barrels
Ventilation shaft	Releases sewer gases; prevents septic conditions	At every 150–300 m; at siphon ends

📝 GATE Tip: Self-cleansing velocity = 0.75 m/s (IS). Max velocity = 3.0 m/s (erosion limit). Q_max for circular pipe = 1.08 × Q_full at d/D = 0.94. Manhole spacing: 30–50 m on straight runs. Inverted siphon velocity ≥ 1.0 m/s. These are core design facts.

7Quality & Characteristics of Sewage►

7.1 Composition of Domestic Sewage

Sewage is approximately 99.9% water and 0.1% solids (dissolved, suspended, colloidal). The solids include organic matter, inorganic salts, and microorganisms.

Parameter	Typical Range	Significance
BOD₅ (5-day BOD at 20°C)	150–300 mg/L	Organic pollution indicator; O₂ demand for biodegradation
COD (Chemical Oxygen Demand)	250–600 mg/L	Total oxidisable matter (biodegradable + non-biodeg.); COD > BOD always
Suspended Solids (SS)	100–350 mg/L	Settles; causes sludge; reduces clarity
Dissolved Oxygen (DO)	0–1 mg/L (septic)	Low/zero DO → anaerobic decomposition; H₂S odour
pH	6.5–8.0 (fresh); acidic when septic	Controls biological treatment
Nitrogen (total)	20–85 mg/L as N	Nutrient; causes eutrophication; TKN + NO₃-N
Phosphorus	4–15 mg/L as P	Nutrient for algae; eutrophication
Coliforms (MPN)	10⁶–10⁹/100 mL	Pathogen indicator; faecal contamination

7.2 BOD — Biochemical Oxygen Demand

First-order BOD kinetics:
BOD_t = L₀ × (1 − e^(−k_d × t))
where L₀ = ultimate BOD (BOD_u), k_d = deoxygenation rate constant (day⁻¹), t = time (days)

Temperature correction:
k_d(T) = k_d(20°C) × θ^(T−20) θ = 1.047 (Streeter-Phelps)

Typical values:
k_d at 20°C ≈ 0.1–0.15 day⁻¹ (base-10), 0.23 day⁻¹ (base-e) for domestic sewage
BOD₅/BOD_u ≈ 0.65–0.75 (i.e., 5-day BOD is 65–75% of ultimate)
COD/BOD₅ ratio ≈ 1.5–2.5 for domestic sewage; > 2.5 suggests non-biodegradable waste

7.3 Dissolved Oxygen and Streeter-Phelps Equation

Oxygen sag curve (river below sewage discharge):
D_t = k_d × L₀ / (k_r − k_d) × (e^(−k_d × t) − e^(−k_r × t)) + D₀ × e^(−k_r × t)

D_t = dissolved oxygen deficit at time t (= DO_sat − DO_actual)
D₀ = initial deficit; k_r = re-aeration rate constant (day⁻¹); k_d = deoxygenation constant
L₀ = initial BOD of mixed stream

Critical point (minimum DO = maximum deficit):
t_c = 1/(k_r − k_d) × ln[(k_r/k_d) × (1 − D₀(k_r − k_d)/(k_d × L₀))]
D_c = (k_d/k_r) × L₀ × e^(−k_d × t_c)

DO_sat at 20°C = 9.08 mg/L; at 25°C = 8.26 mg/L (decreases with temperature)

Fig. 7.1 — Streeter-Phelps DO Sag Curve: DO drops to minimum (D_c) at critical point; recovers downstream as re-aeration exceeds de-oxygenation

7.4 Sludge Volume Index (SVI)

SVI = Volume of settled sludge (mL/L after 30 min) / MLSS (mg/L) × 1000

Good settling sludge: SVI = 80–120 mL/g
Bulking sludge: SVI > 200 mL/g (filamentous bacteria; poor settleability)

Sludge Density Index (SDI) = 100/SVI
Food to Microorganism ratio (F/M):
F/M = BOD input / (MLVSS × aeration volume) [day⁻¹]
Extended aeration: F/M = 0.05–0.15; Conventional: F/M = 0.2–0.4

8Disposing of the Sewage Effluents►

8.1 Land Disposal Methods

Method	Description	BOD Removal	Best for
Irrigation (Land treatment)	Sewage applied to agricultural land; plants uptake nutrients	85–95%	Nutrient-rich effluent; agriculture
Rapid infiltration	High rate loading in basins; percolates through soil	90–99%	Recharge of groundwater
Overland flow	Sheet flow over grass terraces; collected in drain	80–90%	Slow-draining soils
Subsurface application	Tile drains or absorption trenches	90–99%	Small installations; septic tanks

8.2 Dilution and Self-Purification in Rivers

Dilution factor: D = (Q_river + Q_sewage) / Q_sewage

Conditions for safe dilution in rivers (IS 2306):
For pathogenic safety: minimum dilution of 1:20 (1 part sewage : 20 parts river)
For DO maintenance: outfall must not reduce river DO below 4 mg/L

Self-purification processes:
1. Dilution: physical mixing reduces concentration
2. Sedimentation: settleable solids deposit
3. Oxidation: aerobic bacteria oxidise organic matter
4. Sunlight: UV kills pathogens (photo-oxidation)
5. Re-aeration: atmospheric O₂ dissolves into water

8.3 Septic Tank Design

Septic tank: two-stage (anaerobic + clarification) underground tank for individual dwellings

Minimum capacity (IS 2470):
For 1–5 users: 1000 litres
For each additional user beyond 5: add 180 litres

Liquid detention time: 24 hours minimum
L:B:D ratio = 2:1:1 to 4:1:1 (L = length, B = width, D = depth ≥ 1.0 m)

Followed by: soak pit or absorption trench (subsurface percolation)
Soak pit dia: 900–2400 mm; depth 1.5–4 m; percolation test required

Sludge: requires desludging every 1–3 years

8.4 Wastewater Irrigation Standards (IS 11624)

Treated wastewater for unrestricted irrigation: BOD ≤ 10 mg/L; SS ≤ 20 mg/L; Coliforms ≤ 1000/100 mL
Restricted irrigation (non-food crops): BOD ≤ 30 mg/L; Coliforms ≤ 10⁵/100 mL
Treated effluent standards for discharge to land (CPCB): BOD ≤ 30 mg/L; SS ≤ 100 mg/L
Discharge to inland surface water (CPCB): BOD ≤ 30 mg/L; SS ≤ 100 mg/L; pH 5.5–9; NH₃-N ≤ 50 mg/L

9Treatment of Sewage (Waste Water Treatment)►

9.1 Levels of Sewage Treatment

Level	Processes	BOD Removal	SS Removal
Preliminary	Screening, grit removal, comminution	5–10%	5–10%
Primary	Plain sedimentation; skimming of floatables	25–40%	50–70%
Secondary (biological)	Activated sludge; trickling filter; waste stabilisation pond	80–95%	80–95%
Tertiary (advanced)	Nutrient removal (N, P); MF/UF; RO; disinfection	>95%	>95%

9.2 Activated Sludge Process (ASP)

Fig. 9.1 — Activated Sludge Process: raw sewage → Primary clarifier → Aeration tank (biomass + air) → Secondary clarifier → treated effluent; return activated sludge (RAS) maintains MLSS in aeration tank

Key ASP design parameters:
MLSS (Mixed Liquor Suspended Solids): 2000–4000 mg/L (conventional)
MLVSS = 0.7–0.8 × MLSS (volatile fraction = active biomass)
Sludge Retention Time (SRT / θ_c): 5–15 days (conventional); 20–30 days (extended aeration)
HRT (Hydraulic Retention Time): 4–8 hours (conventional aeration tank)
F/M ratio = BOD_in / (MLVSS × HRT): 0.2–0.5 kg BOD/kg MLVSS/day

BOD removal: 85–95%
Sludge production: 0.5–0.8 kg VSS / kg BOD removed
Air requirement: 7–20 m³ air per m³ sewage (diffused aeration)

9.3 Trickling Filter (Biological Filter)

Media: crushed stone, plastic (random pack, structured); dia 25–100 mm
Depth: 1.5–3 m (conventional); up to 6 m (tower filter)
Hydraulic loading: 1–4 m³/m²/day (low rate); 4–40 m³/m²/day (high rate)
BOD loading: <0.08 kg/m³/day (low); 0.24–0.48 kg/m³/day (high rate)

NRC formula for BOD removal (low rate trickling filter):
E = 1 / [1 + 0.4432 × √(BOD / (V × F))]
E = BOD removal fraction; V = volume (10³ m³); F = recirculation factor
F = (1 + R) / (1 + R/10)² (R = recirculation ratio)

Types: Low-rate (stone media, 0.6–1.2 m/day HR); High-rate; Tower filter; Plastic media

9.4 Waste Stabilisation Ponds (WSP)

Pond Type	DO	Depth	HRT	BOD Loading	Removal
Anaerobic pond	Zero	2–5 m	5–30 days	100–300 g/m²/day	50–70% BOD
Facultative pond	Aerobic top; anaerobic bottom	1–2 m	5–30 days	100–350 kg/ha/day	70–90% BOD
Maturation pond	Aerobic throughout	0.5–1.5 m	5–10 days	Low	Pathogen removal (log reduction)

9.5 Sludge Treatment and Management

Sludge thickening → Digestion → Dewatering → Disposal/Reuse

Anaerobic Digestion:
- Stage 1: Hydrolysis + Acidogenesis (acidogenic bacteria produce VFAs)
- Stage 2: Methanogenesis (methanogens convert VFAs to CH₄ + CO₂)
- Biogas: 60–70% CH₄, 30–40% CO₂; energy value ~22 MJ/m³
- Gas production: 0.5–1.0 m³ per kg VS destroyed
- Optimal temperature: 35°C (mesophilic); 55°C (thermophilic)
- SRT for mesophilic digestion: 20–30 days
- VS destruction: 50–60%

Dewatering methods:
Sludge drying beds: area = (V_sludge) / (4–8 months cycles/year)
Centrifuge; Belt filter press; Filter press

Sludge disposal: agricultural land application (biosolids); landfill; incineration

9.6 Industrial Effluent Treatment (ETP)

Typical ETP sequence for industrial wastewater:
1. Screening / Bar rack (large solids)
2. Equalization tank (flow and load balancing; 6–24 hr HRT)
3. Neutralization (pH adjustment to 6–9)
4. Coagulation-flocculation (chemical precipitation of heavy metals)
5. Primary clarifier
6. Biological treatment (ASP or MBBR or SBR)
7. Secondary clarifier
8. Tertiary treatment (sand filter, activated carbon adsorption, UV/ozone)
9. Sludge treatment + disposal

Zero Liquid Discharge (ZLD): mandatory for textile, distillery, paper industries in India (CPCB/MoEF norms)
Effluent Treatment Plant (ETP) mandatory for industries discharging to surface water per Environment Protection Act 1986

📝 GATE Tip: ASP: MLSS = 2000–4000 mg/L; SRT = 5–15 days; HRT = 4–8 hours. SSF filtration rate = 0.1–0.4 m/hr; RSF = 4–12 m/hr. Biogas from anaerobic digestion: 60–70% CH₄. SVI = volume of sludge (mL/L) × 1000 / MLSS. These are perennial GATE questions.

10Air & Sound (Noise) Pollution►

10.1 Composition of Clean Air

Component	% by Volume	Role
Nitrogen (N₂)	78.09%	Inert; diluent
Oxygen (O₂)	20.95%	Supports combustion and respiration
Argon (Ar)	0.93%	Inert
Carbon Dioxide (CO₂)	0.04% (415 ppm 2024)	Greenhouse gas; increasing
Water vapour (H₂O)	0–4% (variable)	Weather, humidity
Trace gases	<0.002%	CH₄, N₂O, O₃, SO₂ etc.

10.2 Major Air Pollutants and Sources

Pollutant	Primary Source	Health Effect	NAAQS Limit (24-hr)
Particulate Matter (PM₁₀)	Dust, construction, vehicles, industries	Respiratory disease; PM₂.₅ reaches alveoli	100 µg/m³ (PM₁₀); 60 µg/m³ (PM₂.₅)
SO₂	Combustion of S-containing coal; power plants; refineries	Acid rain (H₂SO₄); respiratory irritant	80 µg/m³ (24-hr annual 50)
NO₂ / NOx	High-temperature combustion; vehicles	Smog; acid rain (HNO₃); lung damage	80 µg/m³
CO	Incomplete combustion; vehicles	Binds haemoglobin (COHb); asphyxiation	2 mg/m³ (8-hr)
Ozone (O₃)	Photochemical reaction (NOx + VOC + sunlight)	Lung irritant; eye irritation; crop damage	100 µg/m³ (8-hr)
Lead (Pb)	Leaded fuel (now banned); battery industry; smelters	Neurotoxin; cognitive impairment	0.5 µg/m³ (24-hr)
VOCs / Hydrocarbons	Vehicles; evaporation; industrial solvents	Precursor to photochemical smog	—
CO₂ / CH₄	Fossil fuels; agriculture; waste	Greenhouse effect; climate change	No NAAQS (GHG)

10.3 Effects of Air Pollution

Health: Respiratory diseases (asthma, COPD, lung cancer), cardiovascular disease, neurological damage (lead, Hg)
Vegetation: Leaf burn (SO₂, O₃, HF); stunted growth; reduced yield
Visibility: Smog, haze, reduced visibility (PM, aerosols)
Materials: Corrosion of metals (SO₂); building stone damage (acid rain dissolves CaCO₃)
Climate: Greenhouse effect (CO₂, CH₄, N₂O, CFCs); ozone depletion (CFCs); acid rain (SO₂, NOx)

10.4 Air Pollution Control Devices

Device	Mechanism	Particle Size Removed	Efficiency
Gravity settling chamber	Gravitational settling; large particles fall out	>100 µm	50–70%
Cyclone separator	Centrifugal force; particles thrown to wall; slide down	5–200 µm	70–90%
Electrostatic Precipitator (ESP)	Corona discharge charges particles; collected on +ve plates	0.5–10 µm; even sub-µm	95–99.5%
Fabric filter (Baghouse)	Filtration through woven/felted bags	>0.5 µm	95–99%
Wet scrubber (Venturi)	Water spray wets and captures particles + gases	0.5–100 µm; also SO₂, HCl	70–99% (varies)
Catalytic converter	Oxidises CO, HC; reduces NOx (3-way catalyst)	Gaseous; vehicles	>90% for CO, HC

10.5 Atmospheric Dispersion — Gaussian Plume Model

Concentration at point (x, y, z) downwind of a stack:
C(x,y,z) = Q / (2π × σ_y × σ_z × U) × exp(−y²/2σ_y²)
× [exp(−(z−H)²/2σ_z²) + exp(−(z+H)²/2σ_z²)]

At ground level (z = 0) on centreline (y = 0):
C(x,0,0) = Q / (π × σ_y × σ_z × U) × exp(−H²/2σ_z²)

Where: Q = emission rate (g/s); U = mean wind speed at stack height (m/s)
H = effective stack height = physical height + plume rise (Δh)
σ_y, σ_z = horizontal and vertical dispersion coefficients (function of stability class and x)

Maximum ground level concentration:
C_max = Q / (π × e × U × σ_y × σ_z) at x where σ_z = H/√2

10.6 Pasquill-Gifford Stability Classes

Class	Stability	Condition	Dispersion
A	Extremely unstable	Strong insolation, low wind (<2 m/s)	Rapid, wide dispersion; large σ
B	Unstable	Moderate insolation	Good dispersion
C	Slightly unstable	Slight insolation	Moderate
D	Neutral	Overcast or windy (>6 m/s)	Average; most common
E	Slightly stable	Clear night, moderate wind	Poor dispersion
F	Stable	Clear night, low wind	Very poor; fumigation possible

10.7 Noise Pollution

Sound Pressure Level (SPL): L = 20 × log₁₀(P/P_ref)
P_ref = 20 µPa (threshold of hearing); L in dB

Sound Intensity Level: LI = 10 × log₁₀(I/I_ref); I_ref = 10⁻¹² W/m²

Addition of decibels (incoherent sources):
L_total = 10 × log₁₀(Σ10^(Li/10))
For two equal sources: L_total = L + 3 dB (NOT 2L)

Equivalent Sound Level (L_eq): energy-averaged noise level over a period
L_eq = 10 × log₁₀[1/T × ∫₀ᵀ (P/P_ref)² dt]

10.8 Noise Standards (CPCB / IS 4954)

Zone	Day (6am–10pm) dB(A)	Night (10pm–6am) dB(A)
Industrial	75	70
Commercial	65	55
Residential	55	45
Silence zone (hospitals, schools)	50	40

10.9 Health Effects of Noise

<70 dB: Conversation normal; no health risk
70–85 dB: Prolonged exposure → hearing fatigue; TTS (Temporary Threshold Shift)
85–100 dB: Risk of PTS (Permanent Threshold Shift / NIPTS) — occupational noise
>120 dB: Pain threshold; immediate damage
140 dB: Eardrum rupture
Non-auditory effects: stress, hypertension, sleep disturbance, impaired concentration

ℹ️ NIPTS (Noise-Induced Permanent Threshold Shift) occurs at 4000 Hz first (4 kHz notch in audiogram is characteristic). OSHA permissible: 90 dB(A) for 8 hours/day; each 5 dB increase halves the permissible exposure time (5 dB exchange rate in US; 3 dB in WHO/India).

★Solid Waste Management & Quick Revision►

A. Solid Waste Management

A.1 Classification of Solid Wastes

Type	Sources	Examples	Characteristics
Municipal Solid Waste (MSW)	Household, commercial, institutional	Food waste, paper, plastic, glass, metals	Mixed; 50–60% biodegradable in India
Industrial solid waste	Factories, power plants	Fly ash, slag, packaging, process waste	May contain hazardous substances
Biomedical waste	Hospitals, labs, clinics	Sharps, body fluids, infected material	Hazardous; special handling (BMW Rules 2016)
Hazardous waste	Chemical industries; EV batteries	Solvents, heavy metals, pesticides	Toxic; special treatment and landfill (Hazardous Waste Rules)
Construction & demolition (C&D)	Building demolition, excavation	Concrete rubble, steel, brick, soil	Inert; large volume; recycling possible
E-waste	Consumer electronics	Computers, mobiles, batteries	Contains heavy metals (Pb, Hg, Cd, Cr); E-waste Rules 2022

A.2 Municipal Solid Waste — Composition (India)

Typical Indian MSW: 40–60% biodegradable (food/organics), 15–20% inert (dirt/ash),
5–10% paper, 3–5% plastic, 3–5% glass, 2–4% metals, rest miscellaneous

Per capita waste generation: 0.3–0.6 kg/person/day (urban India)
Calorific value: 1000–2500 kcal/kg (low due to high moisture and inert content)

A.3 Integrated Solid Waste Management (ISWM)

ISWM follows the waste hierarchy (3R principle):

Reduce: Minimise waste generation at source (packaging design, consumer behaviour)
Reuse: Use items multiple times before disposal
Recycle: Material recovery — paper, glass, metals, plastics recycled
Recover energy: RDF (Refuse Derived Fuel), WTE (Waste-to-Energy) plants, biogas
Dispose: Sanitary landfill for residuals only (last resort)

A.4 Disposal Methods

Method	Description	Advantage	Disadvantage
Open dumping	Waste thrown in open without treatment	None (cheap short-term)	Illegal; vermin, leachate, gas; prohibited under SWM Rules 2016
Sanitary landfill	Compacted waste in lined cells; covered daily; leachate collected; gas managed	All waste types; low cost per tonne	Land intensive; 30+ year liability; leachate treatment needed
Composting	Aerobic decomposition of organics; produces compost (soil conditioner)	Reduces waste; produces useful product	Needs source segregation; market for compost
Vermicomposting	Worms (Eisenia) decompose organics; high-quality worm castings	High N compost; decentralised	Sensitive to temperature; lower volume capacity
Incineration (WTE)	Combustion at high temperature; residue to landfill; energy recovered	90%+ volume reduction; energy	Air pollution; expensive; needs high calorific value waste
Biomethanation	Anaerobic digestion; biogas (CH₄) + compost	Energy + compost; closed system	Needs organics segregation; technical operation
Pyrolysis / Gasification	Thermal decomposition without air; produces syngas, char, oil	Handles mixed waste; energy rich products	Complex; expensive; emerging technology in India

A.5 Sanitary Landfill Design

Key components: liner system (HDPE), leachate collection, gas collection, monitoring wells, cover

Liner: HDPE geomembrane (1.5 mm min) + compacted clay (K ≤ 10⁻⁷ cm/s, 60 cm thick)
or composite liner (HDPE + clay)

Leachate: L = P × A × R_c / 1000 (m³/day)
P = precipitation (mm/day), A = area (m²), R_c = runoff coefficient (0.3–0.5 for covered landfill)

Landfill gas: 50% CH₄ + 50% CO₂ (approx); generated 1–5 m³/tonne refuse over 10–30 years
Gas: fire/explosion hazard within 300 m; must be collected or flared

Daily cover: minimum 15 cm soil or alternative cover (geosynthetic, tarps)

B. Quick Revision — All Key Numbers

Water Supply

Per capita demand: 135 lpcd (domestic); 200 lpcd (total design, IS 1172)
Peak factors: MDD = 1.8×ADD; MHD = 2.7×ADD
Design period: 30 yrs (dams), 15–20 yrs (treatment), 10 yrs (distribution)
Kuichling fire formula: Q = 3182√P (L/min; P in thousands)
Hardy-Cross: ΔQ = −Σh_L / (n×Σ|h_L/Q|) [n=1.85 HW, 2 DW]
Balancing storage = 1/3 daily demand + fire reserve + emergency reserve

Ground Water

Darcy's law: Q = KiA
Unconfined: Q = πK(H²−h²)/ln(R/r_w)
Confined: Q = 2πKb(H−h)/ln(R/r_w) = 2πT(H−h)/ln(R/r_w)
T = Kb; Sichardt: R = 3000(H−h)√K

Water Quality (IS 10500:2012)

pH: 6.5–8.5; Turbidity ≤ 5 NTU; TDS ≤ 500 mg/L
Total hardness ≤ 300 mg/L; Fluoride ≤ 1.0 mg/L; Nitrate ≤ 45 mg/L
Arsenic ≤ 0.01 mg/L; Iron ≤ 0.3 mg/L; Chloride ≤ 250 mg/L
Residual Cl₂ ≥ 0.2 mg/L (at tap); No coliforms in 100 mL treated water

Water Treatment

Alum: optimal pH 6.5–7.5; G×t = 10⁴–10⁵ (flocculation)
Sedimentation overflow rate: 12,000–18,000 L/m²/day (plain); 30,000–40,000 (coag.)
SSF rate: 0.1–0.4 m/hr; RSF rate: 4–12 m/hr; RSF backwash: 12–15 m/hr
Chick's law: N = N₀e^(−kt); Free residual Cl₂ ≥ 0.2 mg/L at tap

Sewerage

Sewage = 80% water supply; Peak = 3×DWF (small sewers)
V_min = 0.75 m/s; V_max = 3.0 m/s; Manning n = 0.013 (RCC)
Q_max in circular pipe: at d/D = 0.94; V_max at d/D = 0.81
Manhole spacing: 30–50 m (straight); at all junctions and bends

Sewage Quality

BOD₅ domestic: 150–300 mg/L; COD: 250–600 mg/L
BOD_t = L₀(1−e^(−k_d t)); k_d at 20°C ≈ 0.23/day (base-e)
DO_sat at 20°C = 9.08 mg/L; at 25°C = 8.26 mg/L
Streeter-Phelps: D_t = k_d L₀/(k_r−k_d)×(e^(−k_d t) − e^(−k_r t)) + D₀e^(−k_r t)

Sewage Treatment

Primary: BOD 25–40%; Secondary (ASP): 85–95%
ASP: MLSS 2000–4000; SRT 5–15 days; HRT 4–8 hrs; SVI 80–120 (good)
Biogas: 60–70% CH₄; Anaerobic digestion SRT: 20–30 days
CPCB effluent standard: BOD ≤ 30 mg/L; SS ≤ 100 mg/L for discharge to rivers

Air Pollution

NAAQS: PM₁₀ ≤ 100 µg/m³; PM₂.₅ ≤ 60 µg/m³; SO₂ ≤ 80 µg/m³; NO₂ ≤ 80 µg/m³
Gaussian plume: C(x,0,0) = Q/(π×σ_y×σ_z×U) × exp(−H²/2σ_z²)
Stability class A (most unstable) → F (most stable)

Noise

SPL: L = 20 log₁₀(P/20µPa) [dB]
Two equal sources: L_total = L + 3 dB
CPCB Residential: Day 55, Night 45 dB(A)
CPCB Silence zone: Day 50, Night 40 dB(A)
Pain threshold: 120 dB; 4000 Hz notch = NIPTS signature

C. Mnemonics

Water treatment sequence: "Screens Are Cleverly Set For Distribution"
Screening → Aeration → Coagulation → Sedimentation → Filtration → Disinfection

IS 10500 key limits (the "5-5-300" rule):
Turbidity ≤ 5 NTU | TDS ≤ 500 mg/L | Hardness ≤ 300 mg/L | Fluoride ≤ 1.0 | Nitrate ≤ 45

Peak factors: "1.8 and 2.7"
MDD = 1.8× ADD; MHD = 2.7× ADD → "1.8 and 2.7 — drink at Maximum Daily (1.8) and Maximum Hourly (2.7)"

RSF vs SSF: "Rapid is Raw — needs coagulation; Slow is Schmutzdecke — biological film"
RSF rate = 4–12 m/hr; SSF rate = 0.1–0.4 m/hr (30× slower)

Well equations — "UC for Unconfined, C for Confined":
Unconfined: Q∝(H²−h²); Confined: Q∝(H−h) — note squared vs linear

Activated sludge SVI: "80 to 120 = good sludge; above 200 = bulking (bad)"

Noise zones (D–C–R–S): "75–65–55–50 day; 70–55–45–40 night"
Industrial–Commercial–Residential–Silence zone

Air pollution control (increasing efficiency):
Gravity chamber → Cyclone → Wet scrubber → Baghouse → ESP
"Gravity Catches Some Big Elephants"

Sewer self-cleansing: "0.75 m/s min; 3 m/s max"
"Sewage must at least Walk (0.75) but not Sprint (3) through the pipe"

D. Exam-Angle Comparison

Topic	GATE Focus	ESE Focus	SSC JE Focus
Water demand	Per capita values; peak factors; population methods	Detailed demand calculations; fire demand; design period	Per capita; MDD and MHD values
Well hydraulics	Numerical: unconfined/confined well equations; T = Kb	Theis method; Thiem; test analysis; Sichardt R	Types of aquifers; formula recognition
Water quality	IS 10500 key limits; hardness types; BOD kinetics; Chick's law	Jar test; coagulant chemistry; Langelier index; breakpoint Cl	IS 10500 key limits only
Water treatment	SSF vs RSF rates; sedimentation overflow rate; disinfection CT	Tank design calculations; filter media specs; G×t for flocculation	Sequence of treatment; types of filters
Sewer design	Manning eq; self-cleansing velocity; Q at d/D=0.94; sewer types	Full sewer design; storm water; rational method; storm overflows	Manning equation; sewer materials; manhole spacing
Sewage quality	BOD-COD; Streeter-Phelps; DO sag; SVI; F/M	Full river quality analysis; critical DO calculations	BOD definition; COD concept
Sewage treatment	ASP design parameters; SRT; HRT; MLSS; biogas CH₄%	Complete STP design; ETP; ZLD; NRC formula for TF	Types of treatment; primary vs secondary
Solid waste	Sanitary landfill components; composting; 3R hierarchy	Landfill design; leachate; gas collection; EIA	Types of waste; disposal methods
Air pollution	Gaussian plume formula; NAAQS limits; stability classes	Stack design; control device selection; photochemical smog	Pollutant sources and effects; NAAQS limits
Noise	dB addition; Leq; CPCB limits	dB(A) calculations; noise control measures; barrier attenuation	Zone-wise noise limits; health effects

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Environmental Engineering – Complete Study Notes

1.1 Sources of Water

1.2 Types and Per Capita Demand

1.3 Factors Affecting Water Demand

1.4 Variation in Demand — Peak Factors

1.5 Design Period and Population Forecasting

1.6 Fire Demand Formulae

2.1 Pipe Flow — Manning's and Hazen-Williams Equations

2.2 Pipe Materials for Water Supply

2.3 Distribution System Layout

2.4 Hardy-Cross Method for Pipe Network Analysis

2.5 Service Reservoir (Storage)

3.1 Types of Aquifers

3.2 Darcy's Law

3.3 Well Hydraulics — Steady State

3.4 Well Discharge Equations

3.5 Transient Well Flow — Theis Method

3.6 Types of Wells

4.1 Physical Characteristics

4.2 Chemical Characteristics

4.3 Biological Characteristics

4.4 Hardness of Water

4.5 Chlorine Demand and Breakpoint Chlorination

5.1 Flow Chart of Water Treatment Plant

5.2 Aeration

5.3 Coagulation and Flocculation

5.4 Sedimentation Tanks

5.5 Filtration

5.6 Disinfection

6.1 Sewerage Systems — Types

6.2 Quantity of Sewage

6.3 Sewer Hydraulics — Design

6.4 Hydraulic Elements — Circular Pipe

6.5 Sewer Appurtenances

7.1 Composition of Domestic Sewage

7.2 BOD — Biochemical Oxygen Demand

7.3 Dissolved Oxygen and Streeter-Phelps Equation

7.4 Sludge Volume Index (SVI)

8.1 Land Disposal Methods

8.2 Dilution and Self-Purification in Rivers

8.3 Septic Tank Design

8.4 Wastewater Irrigation Standards (IS 11624)

9.1 Levels of Sewage Treatment

9.2 Activated Sludge Process (ASP)

9.3 Trickling Filter (Biological Filter)

9.4 Waste Stabilisation Ponds (WSP)

9.5 Sludge Treatment and Management

9.6 Industrial Effluent Treatment (ETP)

10.1 Composition of Clean Air

10.2 Major Air Pollutants and Sources

10.3 Effects of Air Pollution

10.4 Air Pollution Control Devices

10.5 Atmospheric Dispersion — Gaussian Plume Model

10.6 Pasquill-Gifford Stability Classes

10.7 Noise Pollution

10.8 Noise Standards (CPCB / IS 4954)

10.9 Health Effects of Noise

A. Solid Waste Management

A.1 Classification of Solid Wastes

A.2 Municipal Solid Waste — Composition (India)

A.3 Integrated Solid Waste Management (ISWM)

A.4 Disposal Methods

A.5 Sanitary Landfill Design

B. Quick Revision — All Key Numbers

Water Supply

Ground Water

Water Quality (IS 10500:2012)

Water Treatment

Sewerage

Sewage Quality

Sewage Treatment

Air Pollution

Noise

C. Mnemonics

D. Exam-Angle Comparison