Sewerage: Definition & Professional Guide
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Sewerage is the complete infrastructure system of pipes, manholes, pump stations, and treatment facilities used to collect, transport, and treat wastewater from buildings and discharge the treated effluent to the environment. While “sewage” refers to the wastewater itself, “sewerage” refers to the physical network that conveys it. A municipal sewerage system connects every building’s plumbing to a centralized treatment facility through a network of progressively larger collection pipes.
Laterals, Collection Mains, Trunk Sewers & Treatment Plant Sequence
A sewerage system consists of four functional components that work in sequence. Building sewer laterals carry wastewater from individual properties to collection mains. Collection mains run through streets and easements, gathering flow from hundreds or thousands of laterals. Trunk sewers and interceptors are large-diameter pipes that consolidate flow from multiple collection mains and route it toward the treatment plant. The treatment plant processes the combined wastewater before discharging treated effluent.
The design of a sewerage system must account for peak flow conditions, which occur when many users simultaneously generate wastewater — typically during morning and evening hours. Pipe sizing must handle these peak flows while maintaining minimum velocity during low-flow periods to prevent solids from settling in the pipes. Engineers use flow projections based on population density, commercial activity, and per-capita water usage to size each component appropriately.
Infiltration and inflow (I&I) are persistent challenges for sewerage systems. Infiltration occurs when groundwater enters the system through cracked pipes, deteriorated joints, and damaged manholes. Inflow occurs when stormwater enters through illegal connections, defective manhole covers, or cross-connections between storm and sanitary systems. In areas with high water tables and heavy rainfall, I&I can increase sewage volumes dramatically during wet weather, potentially overwhelming treatment plant capacity.
Separate, Combined, Pressure Force Main & Vacuum Sewer Types
Separate sewerage systems maintain completely independent pipe networks for sanitary sewage and storm water. This is the standard in modern construction and most municipalities, where sanitary and storm systems are separate.
Combined sewer systems carry both sanitary sewage and storm water in a single pipe network. During heavy rain, the combined flow can exceed system capacity, causing combined sewer overflows (CSOs) that discharge untreated sewage to waterways. Combined systems exist in older cities in the Northeast and Midwest but are not used in newer developments.
Pressure sewerage systems use grinder pumps at individual properties to pressurize wastewater through small-diameter force mains. A force main is a pressurized sewer pipe that moves wastewater from a pump station to a gravity sewer or treatment facility, enabling sewage transport across flat terrain or uphill where gravity flow is impossible. These systems are cost-effective alternatives to gravity sewerage in flat terrain or areas with high water tables.
Vacuum sewerage systems use centralized vacuum stations to draw wastewater through sealed pipes. These are used in specific applications where gravity and pressure systems are impractical.
Lateral Inspection, Septic Connection & Backflow Prevention Services
Bonded Plumbworks works at the intersection where building plumbing connects to the municipal sewerage system. The building sewer lateral — the pipe from the foundation to the municipal main — is the property owner’s responsibility. Bonded Plumbworks’ drain and sewer services include lateral inspection, repair, replacement, and new connections when homes transition from septic systems to municipal sewerage.
When the municipal sewerage system experiences problems such as main line backups, the backwater protection installed by Bonded Plumbworks through backflow prevention and sump pump and flood prevention services prevents sewage from entering the home.
Clean Water Act, NPDES Permits & ASCE/WEF MOP No. 9 Standards
The Clean Water Act governs sewerage system design and discharge standards nationally. The state department of environmental protection regulates sewerage system construction, operation, and discharge permits. ASCE/WEF Manual of Practice No. 9 provides design standards for gravity sanitary sewers. The Ten-State Standards (GLUMRB) establish minimum design criteria referenced by many local utilities.
ADS, Hobas, Vylon HDPE & Xylem Flygt Pump Station Products
Advanced Drainage Systems (ADS) manufactures HDPE sewer pipe for gravity and pressure applications. Hobas provides fiberglass-reinforced sewer pipe for aggressive soil conditions. Vylon manufactures PVC sewer pipe. Xylem (Flygt) produces pump stations and lift station equipment for sewerage systems.