Sewage Treatment: Definition & Professional Guide
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Sewage treatment is the process of removing contaminants, pathogens, and pollutants from wastewater collected through the sanitary sewer system or on-site septic systems before the treated water is discharged to the environment or reused. Municipal sewage treatment plants use a multi-stage process of physical, biological, and chemical treatment to transform raw sewage into effluent clean enough to meet federal and state discharge standards set by the EPA and state environmental agencies.
Primary, Secondary & Tertiary Treatment Stage Processes
The sewage treatment process typically progresses through three stages, each removing a different category of contaminants. Primary treatment uses physical processes — screening, grit removal, and sedimentation — to remove large solids, debris, and settleable material from the incoming wastewater. Screens catch trash and large objects, grit chambers settle sand and heavy particles, and primary clarifiers allow remaining suspended solids to settle to the bottom as primary sludge.
Secondary treatment uses biological processes to remove dissolved and suspended organic material that escaped primary treatment. In the most common method — activated sludge — wastewater is mixed with a concentrated population of aerobic microorganisms in aeration tanks. These organisms consume the organic pollutants, converting them to carbon dioxide, water, and additional biomass. The treated water then passes through secondary clarifiers where the biological solids settle and are either recycled back to the aeration tanks or removed as excess sludge.
Tertiary (advanced) treatment provides additional polishing through filtration, nutrient removal (nitrogen and phosphorus), and disinfection. Chlorination, ultraviolet light, or ozone treatment kills remaining pathogens before the final effluent is discharged to surface water, deep injection wells, or reclaimed water distribution systems. Many treatment plants produce reclaimed water used for landscape irrigation, reducing demand on the potable water supply.
Municipal Plant, On-Site ATU, Package Plant & Reclaimed Water Types
Municipal wastewater treatment plants serve communities through the public sanitary sewer system. These facilities handle millions of gallons per day and are operated by local utilities or water management districts.
On-site sewage treatment includes septic tanks and advanced treatment units that process wastewater at the building location. These systems are used in areas without municipal sewer service and are regulated by the state health department.
Advanced wastewater treatment (AWT) plants achieve higher effluent quality through additional nutrient removal stages. Many states require AWT for facilities discharging near sensitive waterways, springs, and aquifer recharge areas.
Package treatment plants are pre-manufactured, self-contained treatment systems sized for small communities, commercial developments, and rural subdivisions. They perform all treatment stages in a compact footprint.
Reclaimed water systems distribute treated wastewater for non-potable uses including irrigation, industrial cooling, and environmental restoration. Many utilities operate extensive reclaimed water distribution networks.
Sewer Lateral Collection, Septic System Maintenance & Groundwater Protection
While Bonded Plumbworks does not operate treatment plants, the company’s plumbing work connects directly to the treatment system at both ends. On the collection side, drain and sewer services ensure that building sewer laterals deliver wastewater to the municipal collection system without leaks, infiltration, or blockages that overload treatment capacity.
On the on-site treatment side, Bonded Plumbworks’ septic system services maintain septic tanks and drain fields that provide decentralized sewage treatment. Properly maintained septic systems protect groundwater quality — a critical concern in areas where the primary drinking water aquifer sits close to the surface.
Clean Water Act, NPDES Permits & EPA Secondary Treatment Standards
The Clean Water Act establishes the federal framework for wastewater discharge standards. The state environmental protection agency (or equivalent) issues National Pollutant Discharge Elimination System (NPDES) permits for treatment plant discharges. State health departments govern on-site sewage treatment systems. EPA secondary treatment standards require removal of at least 85 percent of biochemical oxygen demand and total suspended solids.
Orenco, Infiltrator, Xylem Sanitaire & Evoqua Treatment Equipment
Orenco Systems produces package treatment plants and advanced on-site systems. Infiltrator Water Technologies manufactures advanced treatment components. Xylem (Sanitaire) provides aeration and biological treatment equipment for municipal plants. Evoqua Water Technologies offers disinfection systems.