Wastewater Treatment

Wastewater Treatment

Quick Facts
  • Wastewater treatment is needed so that we can use our rivers and streams for fishing, swimming and drinking water.
  • The 1972 Amendments to the Federal Water Pollution Control Act (Public Law 92- 500), known as the Clean Water Act (CWA), established the foundation for wastewater discharge control in this country.
    • The CWA’s primary objective is to ‘restore and maintain the chemical, physical and biological integrity of the nation’s waters.’
    • The CWA established a control program for ensuring that communities have clean water by regulating the release of contaminants into our country’s waterways.
      • Permits that limit the amount of pollutants discharged are required of all municipal and industrial wastewater dischargers under the National Pollutant Discharge Elimination System (NPDES) permit program.
    • The 1987 Amendments to the CWA established State Revolving Funds (SRF) to replace grants as the current principal federal funding source for the construction of wastewater treatment and collection systems.
  • Over 75 percent of the nation’s population is served by centralized wastewater collection and treatment systems.
    • The remaining population uses septic or other onsite systems.
    • The use of sewage collection systems brought dramatic improvements to public health.
  • Approximately 16,000 municipal wastewater treatment facilities are in operation nationwide.

Pretreatment

The National Pretreatment Program, a cooperative effort of Federal, state, POTWs and their industrial dischargers, requires industry to control the amount of pollutants discharged into municipal sewer systems.

Primary Treatment

  • Coarse solids are removed from the wastewater in the primary stage of treatment.

Preliminary Treatment

Screening
  • A screen removes large floating objects, such as rags, cans, bottles and sticks that may clog pumps, small pipes, and down stream processes.
Grit Chambers
  • sand, grit, cinders, and small stones settle to the bottom

Primary Sedimentation

  • suspended solids gradually sink to the bottom.
  • This mass of solids is called primary sludge
Primary Sedimentation Pages

Secondary Treatment

Secondary treatment can remove up to 90 percent of the organic matter in wastewater by using biological treatment processes

Secondary Treatment Pages

Attached Growth Processes (fixed film)

Attached Growth Proceesses Pages

Suspended Growth Processes

Suspended Growth Processes Pages

Lagoons ( treatment pond)

  • a scientifically constructed pond, three to five feet deep, that allows sunlight, algae, bacteria, and oxygen to interact.
  • Biological and physical treatment processes occur in the lagoon to improve water quality.
Lagoon Pages

Land Treatment

  • the controlled application of wastewater to the soil where physical, chemical, and biological processes treat the wastewater as it passes across or through the soil.
  • The principal types of land treatment are:
    • slow rate
      • the most commonly used land treatment technique.
      • can be applied to the land by spraying, flooding, or ridge and furrow irrigation.
    • overland flow
      • has been used successfully by the food processing industries for many years to remove solids, bacteria and nutrients from wastewater.
    • rapid infiltration
      • most frequently used to polish and recover wastewater effluents for reuse after pretreatment by secondary and advanced treatment processes.

Disinfection

Basic Wastewater Treatment Processes

Advanced Methods of Wastewater Treatment

Nitrogen Control

Nitrifying bacteria biologically convert ammonia to the non-toxic nitrate through a process known as nitrification.
  • an additional biological process can be added to the system to convert the nitrate to nitrogen gas.
    • The conversion of nitrate to nitrogen gas is accomplished by bacteria in a process known as denitrification.
Nitrogen Control pages

Phosphorus Control

Removal can be achieved through chemical addition and a coagulation sedimentation process
  • Alum, lime, or iron salts are chemicals added to the wastewater to remove phosphorus.
    • Can reduce the concentration of phosphate by more than 95 percent 
Phosphorus Control pages

Carbon adsorption

Can remove organic materials from wastewater that resist removal by biological treatment remove more than 98 percent of the trace organic substances.

Carbon Adsorption pages

Use or Disposal of Wastewater Residuals and Biosolids

  • more than half of the biosolids produced by municipal wastewater treatment systems is applied to land as a soil conditioner or fertilizer
  • the remaining solids are incinerated or landfilled.

Land Application

Properly treated and applied biosolids are a good source of organic matter for improving soil structure and help supply nitrogen, phosphorus, and micronutrients that are required by plants.

Incineration

  • burning the dried solids to reduce the organic residuals to an ash that can be disposed or reused.

Beneficial Use Products from Biosolids

  • Heat dried biosolids pellets have been produced and used extensively as a fertilizer product for lawn care, turf production, citrus groves, and vegetable production for many years.
  • Composting of biosolids is also a well established approach to solids management that has been adopted by a number of communities.

Decentralized (Onsite and Cluster) Systems

Onsite System

An onsite system is a wastewater system relying on natural processes, although sometimes containing mechanical components, to collect, treat, disperse or reclaim wastewater from a single dwelling or building. A septic tank and soil adsorption field is an example of an onsite system.

Cluster System

A wastewater collection and treatment system under some form of common ownership that collects wastewater from two or more dwellings or buildings and conveys it to a treatment and dispersal system located on a suitable site near the dwellings or buildings is a cluster system

Additional areas on this site for Wastewater Treatment Information


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