SIMAP guidance for wastewater

What is wastewater treatment?

Wastewater treatment is the treatment of sewage by a central wastewater treatment facility or through the use of septic tanks for rural areas. There are many different methods for treating wastewater, and each method has different emissions associated with it. The following wastewater treatment methods are available in SIMAP and can be selected on the Data Entry tab > Wastewater page: 

  • Aerobic
  • Aerobic + Anaerobic Sludge Digestion
  • Anaerobic
  • Anaerobic + Anaerobic Sludge Digestion
  • Septic

Wastewater.png

How have wastewater methods changed in SIMAP? [February 2022]

In February 2022, we updated the historic wastewater methods to better reflect the available wastewater treatment methods. We hope this makes it easier to match your treatment plant with the methods in SIMAP! Here are the changes:

  • Septic: No change
  • Aerobic: Added CH4 emissions factor to 2021 version of emissions factors. Previous EF versions assumed 0 emissions from CH4.
  • Anaerobic: No change
  • Anaerobic digestion: Renamed to Aerobic + Anaerobic digestion
  • Anaerobic + Anaerobic digestion: New category

What does this mean for your inventory? If your wastewater treatment facility uses aerobic, anaerobic, or septic treatment, then you are all set! If your facility has an anaerobic digestion step, then please read on to see which method would be the best fit for your campus.

Where can I find my campus's wastewater data?

Data on what type of treatment your campus employs and how much water is treated can be found on the bills received from your local wastewater treatment plant (WWTP) or on the treatment plant's website. Some campuses use their water bill to calculate the amount of wastewater they produce by assuming that a certain percentage of the water they use will be discharged into the sewer system after use.

What are the stages of wastewater treatment?

  1. Influent
    • Wastewater (sewage), collected from a designated population by a pipe system, enters a wastewater treatment plant (WWTP) as an influent.
  2. Preliminary
    • The influent flows through a screen that removes large debris such as flushable wipes before entering a grit chamber where sand and small stones settle out of the water.
  3. Primary Treatment
    • The wastewater enters a sedimentation tank where the speed of the flow decreases, and small sediment particles settle to the bottom of the tank creating a mass called raw primary biosolids.
  4. Secondary Treatment
    • This stage in the treatment process removes about 85 percent of the organic matter in the wastewater by the use of trickling filters and the activated sludge process. Existing bacteria in the wastewater are used in these processes to remove the organic matter.
  5. Disinfection
    • Chlorine is added to the secondary treatment effluent to kill pathogenic bacteria and reduce odor. Ozone and ultraviolet light can be used as alternatives to chlorine in the disinfection process.
  6. Tertiary Treatment
    • When higher water quality is required of the effluent entering a body of water, advanced water treatment techniques are employed. This tertiary level of treatment removes additional heavy metals, nutrients, and toxic substances from the wastewater through physical-chemical processes including filtration, carbon adsorption, distillation, and reverse osmosis. While not all wastewater is treated to this higher level, the need for tertiary treatment is increasing.
  7. Effluent to Receiving Water Bodies
    • The treated effluent is pumped into a nearby body of water or used as the influent for a water treatment plant in water-poor regions.

What categories are included in SIMAP?

  • Aerobic
  • Aerobic + Anaerobic Sludge Digestion
  • Anaerobic
  • Anaerobic + Anaerobic Sludge Digestion
  • Septic

Which category should I use?

Information about the type of wastewater treatment system can sometimes be found on the website for your municipality or wastewater utility but it is always recommended to reach out to confirm with your wastewater treatment provider.

What does each category mean?

Aerobic

  • Treatment systems that contain little to no anaerobic zones, or zones where there is no oxygen present in the wastewater
  • Examples include: aerated lagoons, activated sludge, and bardenpho systems
    • Constructed wetlands are classified as aerobic systems despite exhibiting both aerobic and anaerobic treatment
  • The aerobic methane emission factor (kg CH4/gallon) is calculated by multiplying the amount of biological oxygen demand (BOD) in the wastewater by the percent of the BOD that was not removed by primary treatment. This value is then multiplied by the percent of the wastewater that accidentally experiences anaerobic degradation. Finally, this value is multiplied by the emission factor for aerobic systems (kg CH4/kg BOD) to find the final methane emission factor.

kg CH4 / gallon = (kg BOD / gallon) * %accidental anaerobic degradation * (1 - % BOD removed by primary treatment) * (kg CH4 / kg BOD)

  • The aerobic nitrous oxide emission factor (kg N2O /gallon) is calculated by multiplying the total nitrogen entering the treatment system by the emission factor for aerobic systems (kg N2O/kg N). This value is multiplied by the molecular weight ratio of nitrous oxide and nitrogen gas to convert the emission factor to the desired units.

kg N2O / gallon = TN * EFaerobic * (44 / 28)

Aerobic + Anaerobic Sludge Digestion

  • Aerobic treatment systems where the solids removed (sludge) are treated onsite using anaerobic sludge digestion. 
  • Anaerobic digestion is for solids treatment and is used in addition to liquid wastewater treatment, at some facilities. Not all facilities treat the solids removed (sludge) onsite.
  • The anaerobic sludge digestion methane emission factor (kg CH4 / gallon) is calculated by multiplying the volume of gas in the wastewater by the amount of methane present in the gas. This value is multiplied by the percentage of gas in the wastewater that was not combusted.
  • The methane emission factor for this category is equal to the sum of the aerobic methane emission factor and the anaerobic sludge digestion methane emission factor.

kg CH4 / gallon = [(kg BOD / gallon) * %accidental anaerobic degradation * (1 - % BOD removed by primary treatment) * (kg CH4 / kg BOD)]

+ [m3 gas / gallon wastewater * (kg CH4 / m3 gas) * (1 - % gas combusted)]

  • The nitrous oxide emission factor for this category is equal to the aerobic nitrous oxide emission factor.

Anaerobic

  • Treatment systems that consist of a majority of zones where there is no oxygen present in the wastewater
  • Examples include: anaerobic lagoons, anaerobic sludge blanket reactors, and anaerobic filter reactors
  • The anaerobic methane emission factor (kg CH4 / gallon) is calculated by multiplying the amount of BOD in the wastewater by the percent of the BOD that was not removed by primary treatment. This value is then multiplied by the emission factor for anaerobic systems (kg CH4 / kg BOD) to find the final methane emission factor.

kg CH4 / gallon = (kg BOD / gallon) * (1 - %BOD removed by primary treatment) * (kg CH4 / kg BOD)

  • The anaerobic nitrous oxide emission factor (kg N2O / gallon) is calculated by multiplying the total nitrogen entering the treatment system by the emission factor for anaerobic systems (kg N2O / kg N). This value is multiplied by the molecular weight ratio of N2O and N2 to convert the emission factor to the desired units.

kg N2O / gallon = TN * EFanaerobic * (44 / 28)

Anaerobic + Anaerobic Sludge Digestion

  • Anaerobic treatment systems where the solids removed (sludge) are treated onsite using anaerobic sludge digestion. 
  • Anaerobic digestion is for solids treatment and is used in addition to liquid wastewater treatment, at some facilities. Not all facilities treat the solids removed (sludge) onsite.
  • The methane emission factor for this category is equal to the sum of the anaerobic methane emission factor and the anaerobic sludge digestion methane emission factor.

kg CH4 / gallon = [(kg BOD / gallon) * (1 - %BOD removed by primary treatment) * (kg CH4 / kg BOD)]

+ [(m3 gas / gallon wastewater) * (kg CH4 / m3 gas) * (1 - % gas combusted)]

  • The nitrous oxide emission factor for this category is equal to the anaerobic nitrous oxide emission factor.

Septic

  • On-site treatment systems composed of a septic tank and a soil dispersion system that are generally buried in the ground
  • The methane emission factor (kg CH4 / gallon) is calculated by multiplying the per capita methane emission factor (kg CH4 / capita / day) for septic systems by the wastewater produced per person per day.

kg CH4 / gallon = (EFSeptic * 100 gal / person / day)

  • The septic nitrous oxide emission factor (kg N2O / gallon) is calculated by multiplying the total nitrogen entering the septic system by the emission factor for septic systems (kg N2O / kg N). This value is multiplied by the molecular weight ratio of N2O and N2 to convert the emission factor to the desired units.

kg N2O / gallon = TN * EFSeptic * (44 / 28)

Sources