TERMINOLOGIES (SANITARY)
Sewer – An underground conduit or drain through which sewage is carried to a point
of discharge or disposal.
Sewerage – A system of structures, devices, and equipment used for the collection,
transportation, and pumping of sewage and liquid waste (excluding treatment
works).
Sewage / Wastewater – Liquid waste generated from a community, including
sullage, latrine discharge, urinals, industrial waste, and stormwater.
Domestic Sewage – Wastewater from residential buildings, offices, schools,
theatres, etc.
Industrial Sewage – Wastewater generated from industrial and commercial
establishments.
Storm Water – Surface runoff water caused by rainfall in a locality.
Sullage – Wastewater from kitchens, bathrooms, and wash basins (non-foul,
contains negligible organic matter).
Sanitary Engineering – Branch of civil engineering dealing with sewage, wastewater,
and waste management systems. Ensures protection of public health and
environment.
Wastewater / Sewage – Liquid waste generated from communities including
domestic, industrial, and stormwater. Needs collection, treatment, and disposal.
Sanitary Sewage (Dry Weather Flow, DWF) – Wastewater flow during non-rainfall
periods; basis for design of sewer systems.
Storm Sewage (Wet Weather Flow, WWF) – Wastewater generated during rainfall
due to runoff; determines capacity of storm sewers.
Peak Flow – Maximum expected sewage discharge; used for sizing sewers and
treatment units.
Catchment Area – Surface area contributing runoff; essential for stormwater flow
estimation.
Runoff – Water flow over land reaching sewers; impacts design of stormwater
systems.
Rational Method – Empirical formula to estimate stormwater runoff; used for small
catchment hydrology.
Sewerage Systems & Appurtenances
Separate System – Two sewers: one for sewage, one for stormwater; reduces
treatment load.
Combined System – Single sewer carries both sewage and stormwater;
economical in narrow urban areas.
Partially Combined System – Carries sewage and part of stormwater; compromise
between cost and efficiency.
Manhole – Access structure on sewers for inspection and cleaning; facilitates
maintenance and ventilation.
Street Inlets – Openings on streets to collect stormwater; prevent street flooding.
Catch Basin – Chamber to trap grit, sand, and debris before sewer entry; prevents
clogging.
Flushing Devices – Tanks or chambers that discharge water to clean sewers; avoid
clogging due to low velocity.
Inverted Siphon – Depressed sewer constructed to cross obstacles; allows sewage
passage under pressure.
Ventilation Shaft – Vertical pipe provided in sewers to release foul gases; prevents
hazardous accumulation.
Sewer Outlet – Final discharge point of sewage into treatment or disposal site.
Drop Manhole – A manhole designed to connect sewers at different elevations by
dropping the higher flow into the lower one.
Lamp Hole – Small vertical shaft for inspection and cleaning of small-diameter
sewers.
Side Connection – Junction allowing house sewer lines to connect with the main
sewer.
Storm Relief Sewer – Auxiliary sewer that diverts excess flow during heavy rainfall.
Hydraulic Design & Formulas
Hydraulic Mean Depth (R) – Ratio of flow area to wetted perimeter; used in
Manning’s formula.
Manning’s Formula – Empirical formula for velocity in open channels or sewers.
Chezy’s Formula – Hydraulic relation between velocity, slope, and hydraulic radius.
Bazin’s Formula – Formula for Chezy’s constant based on surface roughness.
Kutter’s Formula – Empirical refinement for hydraulic design of sewers.
Self-Cleansing Velocity – Minimum velocity required to prevent deposition in
sewers.
Non-Scouring Velocity – Maximum velocity that avoids abrasion and erosion of
sewer walls.
Hydraulic Gradient Line (HGL) – Line showing pressure head in a hydraulic system.
Energy Grade Line (EGL) – Line representing total energy in a hydraulic system.
Invert Level – The inside bottom elevation of a sewer pipe.
Gradient of Sewer – Slope of a sewer line to maintain self-cleansing velocity.
Wastewater Treatment Processes
Preliminary Treatment – Screening, grit removal, skimming; removes large particles
and debris.
Primary Treatment – Sedimentation to remove suspended solids; reduces organic
load.
Secondary Treatment – Biological treatment processes (activated sludge, trickling
filters) for dissolved and colloidal organics.
Tertiary / Advanced Treatment – Polishing processes (filtration, reverse osmosis,
nutrient removal) for final effluent quality.
Screening – Removal of floating materials using bar racks.
Grit Chamber – Tank to remove sand, gravel, and grit.
Flotation / Skimming Tank – Removes oils, grease, and lighter solids.
Sedimentation – Settling of suspended solids under gravity.
Discrete Settling – Particles settle individually without interaction.
Flocculent Settling – Particles form flocs during settling.
Zone Settling – Particles settle as a mass or blanket.
Compression Settling – Lower layer compresses under weight of particles above.
Chemical Precipitation – Addition of chemicals (lime, alum) to aggregate colloids.
Coagulation – Neutralization of particle charges using chemicals.
Flocculation – Gentle mixing to form larger flocs.
Aeration – Process of supplying air into wastewater for oxidation of organics.
Diffused Aeration – Air supplied by perforated pipes or diffusers.
Mechanical Aeration – Aeration using paddles or mechanical devices.
Activated Sludge Process (ASP) – Aeration of wastewater with microbial biomass
to degrade organics.
Trickling Filters – Wastewater trickled over media to support biofilm growth.
Rotating Biological Contactor (RBC) – Rotating discs with attached biofilms for
secondary treatment.
Membrane Bioreactor (MBR) – Advanced process combining biological treatment
with membrane filtration.
Sludge & Byproducts
Sludge – Settled solids removed from wastewater.
Scum – Floating fats, grease, and lighter solids.
Primary Sludge – Solids removed in primary sedimentation.
Secondary Sludge – Biomass from biological treatment.
Chemical Sludge – Solids produced by chemical precipitation.
Sludge Thickening – Process of concentrating sludge solids.
Sludge Digestion – Biological stabilization of sludge.
Conventional Digester – Single-tank digestion.
High-Rate Digester – Heated and mixed tank for rapid digestion.
Two-Stage Digester – First tank for digestion, second for thickening/storage.
Humus Sludge – Well-stabilized sludge from trickling filters.
Digestate – Residue from anaerobic digestion.
Biogas – Gas (CH₄ + CO₂) produced during anaerobic digestion.
Dewatering – Removal of water from sludge using drying beds or machines.
Composting (Sludge) – Biological conversion of sludge into soil conditioner.
Incineration (Sludge) – Burning of sludge solids at high temperatures.
Natural Disposal & Stream Terms
Dilution Method – Disposal of sewage into water bodies where natural forces purify
it.
Self-Purification of Streams – Natural recovery of rivers through aeration, sunlight,
and bacterial action.
Oxygen Sag Curve – Graph of DO variation downstream of wastewater discharge.
Zones of Pollution – Four zones: degradation, active decomposition, recovery, clear
water.
Assimilative Capacity – Ability of a water body to dilute and purify wastewater.
Outfall – Point of final discharge of sewage.
Mixing Zone – Area in receiving waters where effluent first mixes.
Dissolved Oxygen (DO) – Oxygen content in water, indicator of stream health.
Biochemical Oxygen Demand (BOD) – Oxygen required by microbes to degrade
organics.
Chemical Oxygen Demand (COD) – Oxygen required to chemically oxidize
organics.
Eutrophication – Nutrient enrichment of water bodies leading to algal blooms.
On-Site Sanitation Systems
Septic Tank – Underground watertight tank for sedimentation and anaerobic
digestion of sewage.
Imhoff Tank – Two-story tank with sedimentation above and sludge digestion below.
Cesspool / Leaching Pit – Underground pit where wastewater percolates into soil.
Soak Pit / Leach Pit – Porous pit for septic tank effluent disposal.
Evapotranspiration Bed – Shallow system where wastewater evaporates and is
absorbed by plants.
Solid Waste Management
Solid Waste – Discarded materials from domestic, industrial, or commercial
sources.
Garbage – Putrescible solid waste, mainly food residues.
Rubbish – Non-putrescible waste like paper, plastics, and wood.
Ashes – Residues from fuel combustion.
Bulky Waste – Large items like furniture, appliances.
Leachate – Polluted liquid draining from solid waste.
Sanitary Landfill – Controlled disposal of waste in layers with soil cover.
Open Dumping – Uncontrolled disposal of waste in low-lying areas.
Controlled Tipping – Method of dumping with periodic soil covering.
Transfer Station – Facility where waste is transferred from small to large vehicles.
Refuse-Derived Fuel (RDF) – Processed waste converted into fuel pellets.
Composting (Solid Waste) – Biological decomposition of organic waste into
humus.
Incineration (Solid Waste) – Burning of solid waste at high temperatures.
Pyrolysis – Thermal decomposition of waste in absence of oxygen.
Gasification – Conversion of waste into syngas with limited oxygen.
Advanced Treatment & Disinfection
Nitrification – Biological oxidation of ammonia to nitrites and nitrates.
Denitrification – Biological reduction of nitrates to nitrogen gas.
Phosphorus Removal – Removal of phosphates by biological or chemical methods.
Chlorination – Use of chlorine for disinfection.
Ozonation – Use of ozone gas for disinfection.
Ultraviolet (UV) Disinfection – Use of UV light to kill microorganisms.
Granular Activated Carbon (GAC) – Adsorption process for advanced wastewater
polishing.
Green Sand Filter – Filter medium used for iron and manganese removal.
Reverse Osmosis (RO) – Membrane filtration process for high-quality water.