Water-Efficient Technology Opportunity: On-site Wastewater Treatment Systems

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Image shows the tanks, pipes, and water holding areas of a wastewater treatment plan. Trees, shrubs, and a body of water are in the background.
A traditional brick-and-mortar wastewater treatment plant.

The Federal Energy Management Program (FEMP) identified on-site wastewater treatment systems as a technology that can provide a source of alternative water that is relevant to the federal sector, is commercially available, and offers a significant opportunity to offset freshwater use.

This overview provides agencies with key information to deploy innovative products and systems that may otherwise be overlooked. It also helps agencies identify water-efficient technologies for consideration when entering into energy savings performance contracts and utility energy service contracts.   

FEMP considered the following when selecting this technology.

  • Underutilized in the federal sector
  • Broad applicability across the federal sector
  • Lack of information available to agencies on alternative water systems
  • Offset of freshwater
  • Market availability
  • Produced by multiple manufacturers

Technology Description

Treated effluent from an on-site wastewater treatment system can be reclaimed and used in non-potable applications, providing a consistent source of alternative water to federal facilities. An important component of a site’s water management plan is identifying sources of alternative water to offset the use of freshwater from surface and groundwater sources, which helps to lower the water risk of a site making it more water secure.

Uses for treated wastewater effluent include (but are not limited to) landscape irrigation, vehicle wash, construction-related applications, dust suppression, ornamental pond and fountain filling, cooling tower makeup, and toilet and urinal flushing.

Several different wastewater treatment processes and technologies are available. The selection of the appropriate treatment technology depends on the volume and composition of the wastewater treated, the quality requirement of the effluent, and the land space available.

This table provides an overview of several available technologies, with the following considerations.

  • Information in the table is primarily based an evaluation of wastewater treatment technologies that modeled the performance of specific systems, treating wastewater discharged from a small community (population less than 2,000) with varying levels of waste concentration. (For more information, see Assessment of Wastewater Treatment Plant Design for Small Communities: Environmental and Economic Aspects).
  • All of the technologies listed—except the traditional wastewater treatment plant—are considered secondary treatment technologies that supplement primary treatment filtration or solids/liquid separation. Additional treatment (called tertiary treatment) and filtration may be required depending on the quality of the effluent and the requirements for reuse.
  • Primary waste constituents considered for removal are suspended solids, chemical oxygen demand, nitrogen, and phosphorous. High oxygen demand is an indirect indication of high organic content.  Some inorganics, such as ammonia will also contribute to oxygen demand.
  • Capital and operation costs are presented as high, moderate, or low for relative comparison. Actual costs will depend on the capacity and size of the system.

 

Wastewater Treatment Technologies
TechnologyDescriptionConsiderations
Traditional Wastewater Treatment PlantA conventional brick-and-mortar plant that consists of a series of filtration, settling, and biological treatment stages (see figure below)Requires significant land area, high capital and operational costs, reduces primary waste constituents to low levels, appropriate for large campus-style sites with high wastewater flows
Pond SystemEngineered lagoons that rely on natural processes (sunlight, wind, microorganisms, algae, etc.) to treat the wastewaterRequires significant land area, low capital and operational costs, reduces nitrogen and phosphorous to low levels, may require additional treatment if the wastewater is high in chemical oxygen demand or suspended solids
Intermittent Sand FilterLayered bed of clean, durable, granular material that filters the wastewater as it percolates through the media and facilitates chemical and biological treatment of the wastewater; for more information, see the EPA Wastewater Technology Fact Sheet: Intermittent Sand Layers.Requires significant land area, low capital and operational cost, reduces suspended solids to low levels, reduces nitrogen and phosphorous to moderate levels, may require additional treatment if the wastewater is high in chemical oxygen demand
WetlandsEngineered lined marsh that provides filtration and settling followed by bacterial treatment through natural processes (sunlight, wind, microorganisms, algae, etc.) to treat the wastewaterRequires significant land area, low capital and operational cost, reduces suspended solids to low levels, reduces nitrogen and phosphorous to moderate levels, may require additional treatment if the wastewater is high in chemical oxygen demand
Membrane BioreactorCombination of a suspended growth bioreactor that breaks down waste with microbes followed by membrane filtrationPackage unit that requires less land area than a traditional wastewater treatment plant, moderate capital investment, high operational cost, reduces waste constituents to low levels and produces high-quality effluent
Sequencing Batch ReactorFill and draw single batch activated sludge system where wastewater is added to a single reactor, treated, and then discharged; depending on the wastewater characteristics and the desired effluent, two or more batch reactors can be used in parallel; for more information see the EPA Wastewater Technology Fact Sheet: Package Plants listed in the Additional Resources sectionPackage unit that requires relatively less land area than a traditional wastewater treatment plant; high capital cost; moderate operational cost; reduces suspended solids, nitrogen, and phosphorous to low levels; may require additional treatment if the wastewater is high in chemical oxygen demand; suited for low or intermittent wastewater flow conditions
Extended AerationModified activated sludge process for small loads where diffusers provide air to sustain the aerobic biological process required to breakdown organics; for more information see the EPA Wastewater Technology Fact Sheet: Package PlantsPackage unit that requires relatively less land area than a traditional wastewater treatment plant, high operational cost; moderate capital investment, reduces suspended solids to low levels, reduces nitrogen and phosphorous to moderate levels, may require additional treatment if the wastewater is high in chemical oxygen demand
Moving Bed Biofilm ReactorsUses thousands of moving polyethylene biofilm carriers in an aerated treatment process to biologically break down waste; for more information see the Moving Bed Biofilm Reactor TechnologyPackage unit that requires relatively less land area than a traditional wastewater treatment plant, moderate capital and operational cost, reduces suspended solids to low levels, reduces nitrogen and phosphorous to moderate levels, may require additional treatment if the wastewater is high in chemical oxygen demand
Rotating Biological ContactorsFixed-bed reactors with a series of partially submerged disks mounted on a horizontal shaft that slowly rotate as the wastewater flows through the reaction vessel to maximize the surface area for biological breakdown of waste constituents; for more information see Rotating Biological ContactorsPackage unit that requires relatively less land area than a traditional wastewater treatment plant, moderate capital and operational cost, reduces chemical oxygen demand and suspended solids to low levels, reduces nitrogen and phosphorous to moderate levels
Submerged Fixed Bed Biofilm ReactorTreatment system using bio-films attached to submerged, fixed open structure plastic media that treats the wastewater as it flows through the reaction vessel; for more information see EPA: Emerging Technologies for Wastewater Treatment and In-plant Wet Weather ManagementPackage unit that requires relatively less land area than a traditional wastewater treatment plant, moderate capital and operational cost, reduces suspended solids to low levels, reduces nitrogen and phosphorous to moderate levels, may require additional treatment if the wastewater is high in chemical oxygen demand
Trickling FilterWastewater flows by gravity over a biofilm-covered, permeable fixed bed of rock, slag, or plastic where waste constituents are broken down biologically; for more information see the EPA Wastewater Technology Fact Sheet: Trickling FiltersPackage unit that requires relatively less land area than a traditional wastewater treatment plant, moderate capital and operational cost, reduces chemical oxygen demand to low levels, reduces nitrogen and phosphorous to moderate levels, may require additional treatment if the wastewater is high in suspended solids

Technology Considerations

The following are important considerations when selecting the appropriate technology and implementing an on-site wastewater treatment system.

  • Wastewater flow: The volume of wastewater flow must be known to size the wastewater treatment technology.
  • Wastewater composition: The characteristics of the wastewater stream must be quantified in terms of suspended solids, pH, and molecular composition (organics, chemical oxygen demand, biological oxygen demand, pharmaceuticals, nitrogen, phosphorous, heavy metals, etc.).
  • Reuse quality: The required quality of the reused water must be known to determine the technologies needed to meet the quality requirements.
  • Site location: The land area needed for the technology must be considered as well as interconnections with existing sewer or discharge piping.
  • Reuse options: The applications that can use the reclaimed water should be evaluated, including comparing the application’s water use demand to the volume of reclaimed water and application’s vicinity to the wastewater treatment system.
  • Water rates: Areas with higher water rates will make alternative water projects more economically viable.
  • Permits: Environmental and operating permits will be required. Check with local or state government.
  • Solids removal: The solids collected by filtration and settling will need to be properly disposed of at a landfill or composting location.
  • Operation and maintenance: Different technologies require different commitment levels for ongoing operation and maintenance. At a minimum, the following needs to be considered:
    • Monitoring system performance
    • Cleaning and maintaining system parts
    • Monitoring for leaks
    • Testing discharge water quality.

Additional Resources

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