Wastewater Sewerage Engineering

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

Water Pollution

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

Point-Source Pollution

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

Nonpoint-Source Pollution

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

Sewerage

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

Separate Sewer System

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

Sanitary Sewer

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

Storm Sewer

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

Combined Sewer System

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

Gravity Sanitary Sewer

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

Pressure (Pumped) Sewer

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

Vacuum Sewer

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

Domestic (Sanitary) Wastewater

Wastewater originating from residences and similar establishments.

Industrial Wastewater

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

Stormwater Runoff

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

Infiltration

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

Inflow

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

I&I (Infiltration / Inflow)

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

Sanitary Sewer Overflow (SSO)

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

Acid Attack Corrosion

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

Hydrogen Sulfide Corrosion

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

Building Sewer (Connection Pipe)

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

Lateral (Branch) Sewer

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

Main Sewer

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

Trunk Sewer

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

Interceptor Sewer

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

Manhole

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

Drop Inlet

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

Catch Basin

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

Grease Trap

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

Regulator (Sewer)

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

Inverted Siphon

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

Marston’s Equation

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

Manning Equation

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

Darcy–Weisbach Formula

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

Hazen-Williams Coefficient (C)

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

Unit Hydrograph Method

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

Rational Method

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

Pump Horsepower Formula

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

Runoff Coefficient (C)

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

Minimum Sewer Velocity

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

Maximum Sewer Velocity

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

Sewer Slope

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

Ductile Iron Pipe

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

Reinforced Concrete Pipe

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

Prestressed Concrete Pipe

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

Polyvinyl Chloride (PVC) Pipe

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

Vitrified Clay Pipe

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

Hydraulic Radius (R)

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

Reynolds Number (Re)

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

Headloss

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

Equation of Continuity

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

Bernoulli Equation

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

Force Main

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

Wet Well

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

Peak Factor

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

Runoff Coefficient – Asphalt Street

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

Hydrogen Sulfide (H₂S)

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

Marston Load Coefficient (C)

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

Sewer Appurtenance

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

Hydraulic Design Criteria

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

Infiltration Treatment Cost (A.C.)

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

Root Intrusion

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

Hydraulic Grade Line (HGL)

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

Trenching Width

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

Rigid Sewer Pipe

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

Flexible Sewer Pipe

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

Minimum Manhole Spacing (<600 mm pipe)

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

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

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