Wastewater Sewerage Engineering

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A comprehensive set of vocabulary flashcards covering key terms, materials, hydraulics, design criteria and operational issues discussed in the wastewater engineering lecture.

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68 Terms

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Water Pollution

Degradation of a water body by addition of materials until it becomes unfit for its intended use.

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Point-Source Pollution

Contaminants discharged directly into a water body via a single, identifiable outlet such as a pipe or sewer.

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Nonpoint-Source Pollution

Pollutants carried indirectly to water bodies over land, e.g., fertilizer washed from fields; harder to monitor and control.

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Sewerage

The system of collecting wastewater from occupied areas and conveying it to a disposal or treatment point.

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Separate Sewer System

Collection network in which sanitary sewage and stormwater are carried in totally separate pipes.

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Sanitary Sewer

Pipeline that conveys domestic, commercial and industrial wastewater to a treatment plant.

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Storm Sewer

Gravity-flow pipe network that conveys stormwater runoff directly to receiving waters, excluding sanitary sewage.

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Combined Sewer System

Single pipe network that carries both sanitary sewage and storm runoff; now obsolete in new construction.

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Gravity Sanitary Sewer

Most common collection pipe; relies on elevation difference so wastewater flows by gravity.

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Pressure (Pumped) Sewer

System in which wastewater is transported under pressure through force mains—common in flat or low-lying areas.

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Vacuum Sewer

Collection system using negative pressure to move wastewater where gravity flow is not feasible.

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Domestic (Sanitary) Wastewater

Wastewater originating from residences and similar establishments.

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Industrial Wastewater

Waste stream in which industrial wastes predominate; may require on-site pre-treatment.

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Stormwater Runoff

Rain or snowmelt water that runs off roofs, streets and other impervious surfaces.

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Infiltration

Groundwater that enters a sanitary sewer through defects such as cracked pipes and joints.

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Inflow

Surface water that enters a sanitary sewer from sources like roof leaders, manhole covers and cross-connections.

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I&I (Infiltration / Inflow)

Combined extraneous water that increases sanitary sewer flow beyond design capacity.

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Sanitary Sewer Overflow (SSO)

Uncontrolled discharge of raw sewage from separate sanitary systems, often due to blockages or excess I&I.

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Acid Attack Corrosion

Deterioration of concrete sewer surfaces by low-pH industrial wastes contacting the pipe below water line.

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Hydrogen Sulfide Corrosion

Biologically generated H₂S gas oxidizes to sulfuric acid on sewer crowns, corroding concrete above the water line.

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Building Sewer (Connection Pipe)

Pipe that conveys wastewater from building plumbing to the public lateral or branch sewer.

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Lateral (Branch) Sewer

First public pipe in the street or easement that collects flow from one or more building sewers.

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Main Sewer

Pipe that conveys wastewater from several laterals to a trunk or interceptor sewer.

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Trunk Sewer

Large conduit carrying flow from many mains to treatment, disposal or an interceptor sewer.

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Interceptor Sewer

Very large sewer that intercepts numerous trunks/mains and conveys flow to a treatment facility.

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Manhole

Vertical shaft that provides access for inspection, cleaning and maintenance of sewers.

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Drop Inlet

Manhole inlet where influent drops from a higher pipe to a lower sewer to dissipate energy.

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Catch Basin

Storm-sewer inlet with a sump for settling sand/grit and a trap to retain floatables and odors.

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Grease Trap

Appurtenance installed in kitchen or garage waste lines to remove grease, oil, mud and sand before discharge.

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Regulator (Sewer)

Device that diverts flow from one sewer to another, often separating dry-weather flow from storm flow.

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Inverted Siphon

Pressurized sewer segment that dips below hydraulic grade line to pass under obstacles such as waterways.

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Marston’s Equation

Formula W = C w B² used to calculate earth load on a buried conduit based on trench geometry and soil.

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Manning Equation

v = (1/n) R^{2/3} S^{1/2}; common hydraulic-design formula for gravity sewers (n ≥ 0.013 for new pipe).

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Darcy–Weisbach Formula

Headloss h_f = f (L/D)(v²/2g); relates friction losses to pipe length, diameter and velocity.

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Hazen-Williams Coefficient (C)

Empirical roughness factor used in Hazen-Williams equation for water flow; varies with pipe material and condition.

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Unit Hydrograph Method

Hydrologic tool that estimates runoff hydrographs for various storm frequencies on a given watershed.

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Rational Method

Q = CIA; calculates peak storm runoff using a runoff coefficient, rainfall intensity and drainage area.

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Pump Horsepower Formula

Power = (γ Q H) / Efficiency; determines brake or motor power needed to lift wastewater against total head.

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Runoff Coefficient (C)

Ratio representing fraction of rainfall that becomes surface runoff for a given land surface.

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Minimum Sewer Velocity

At least 2 ft/s (0.6 m/s) at half-full or full flow to prevent solids deposition.

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Maximum Sewer Velocity

Usually limited to 8–10 ft/s (2.5–3 m/s) to avoid pipe scouring and excessive wear.

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Sewer Slope

Longitudinal grade of a sewer chosen to achieve desired velocities without excessive excavation.

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Ductile Iron Pipe

Strong pressure-resistant sewer pipe (100–1350 mm) good for river crossings; susceptible to acid/H₂S corrosion.

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Reinforced Concrete Pipe

Widely available gravity sewer material (300–3600 mm) but vulnerable to interior H₂S or exterior sulfate attack.

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Prestressed Concrete Pipe

Pressure-rated concrete pipe (400–3600 mm) suited to long mains where leakage control is critical.

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Polyvinyl Chloride (PVC) Pipe

Lightweight, corrosion-resistant plastic pipe (100–375 mm); unsuitable for very large gravity mains.

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Vitrified Clay Pipe

Traditional, corrosion-resistant gravity sewer pipe (100–900 mm); brittle and minimum 200 mm diameter recommended.

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Hydraulic Radius (R)

Cross-sectional area of flow divided by wetted perimeter; key variable in Manning and Hazen-Williams formulas.

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Reynolds Number (Re)

Dimensionless value Re = (ρ v D) / μ indicating laminar (

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Headloss

Energy loss due to friction and minor losses between two points in a pipe or sewer system.

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Equation of Continuity

For incompressible flow, A₁ v₁ = A₂ v₂ = Q; mass conservation across varying pipe sections.

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Bernoulli Equation

Energy balance P/γ + v²/2g + z = constant (plus losses) along a streamline between two pipe points.

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Force Main

Pressurized sewer pipe that conveys wastewater from a pump station to a gravity sewer or plant.

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Wet Well

Sump that collects gravity flow before pumps lift wastewater into a force main.

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Peak Factor

Multiplier (e.g., 2.5) applied to average flow to estimate peak wastewater discharge in design.

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Runoff Coefficient – Asphalt Street

Typical C value 0.80–0.95 indicating high runoff potential for impervious pavement.

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Hydrogen Sulfide (H₂S)

Gas produced under anaerobic conditions that leads to sewer odor problems and concrete corrosion.

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Marston Load Coefficient (C)

Dimensionless factor in Marston’s equation that depends on trench width/depth and soil arching.

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Sewer Appurtenance

Any accessory structure (manhole, inlet, trap, regulator, etc.) that aids sewer operation and maintenance.

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Hydraulic Design Criteria

Set of limits on pipe size, slope, velocity, roughness and headloss used when designing sewers.

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Infiltration Treatment Cost (A.C.)

Annual cost = D × L × I × 365 × U.C.; evaluates economic impact of groundwater entering sewer.

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Root Intrusion

Tree roots invading sewer joints or cracks, causing blockages and increased infiltration.

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Hydraulic Grade Line (HGL)

Line representing the piezometric head (pressure + elevation) in a flowing system; inverted siphons dip below it.

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Trenching Width

Excavation width providing at least ~150 mm clearance each side of pipe for installation.

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Rigid Sewer Pipe

Material like concrete or clay that carries load through its own structural strength rather than soil support.

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Flexible Sewer Pipe

Material such as PVC or ductile iron whose load resistance depends on side support from backfill.

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Minimum Manhole Spacing (<600 mm pipe)

Locate manholes at changes in alignment and no more than 100 m (≈350 ft) apart.

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Hydraulic Loss Components (H = Hs+Hf+Hm+Hv)

Static head, friction loss, minor loss and velocity head summed to obtain total dynamic head.