Wastewater collection entails collecting wastewater from end users and transporting it to a final discharge point, usually a wastewater treatment facility. Depending on the type of system, energy and/or GHG emissions from wastewater collection will be related to the following:
- Pumping efficiency and operation.
- The amount of infiltration or rain water entering the collection system and being pumped.
- Energy source (renewable, fossil fuels, grid energy mix) for pumping.
- Combined Sewer Overflow (CSO) events leading to direct GHG emissions from receiving waters.
- Direct discharges to receiving waters where there is no wastewater treatment coverage.
- Fuel consumption from truck pickup/deliveries.
- Methane emissions from methane produced in sewers under anaerobic conditions (from sediment buildup and/or long detention times).
- Recovering Energy (Heat and topographical).
The distance and elevation of the wastewater treatment facilities dictates whether wastewater needs to be pumped (as opposed to gravity flow).
The wastewater treatment energy depends on the volume and concentration of the water collected. Collection systems with high infiltration and rain water collection lead to less efficient treatment. Collection systems with long detention times allowing for anaerobic organic matter decay, may lead to the use of chemicals in the treatment to ensure nitrogen removal.
When there is no wastewater treatment, the distance and elevation of the final discharge point dictates whether wastewater needs to be pumped.
The type of collection system affects the amount of water used in the homes (dry or flush toilets, greywater separated from blackwater).
The less water entering the collection system from end users, the less pumping energy is required (in pumped systems). However, reduced flows in the collection system network can lead to greater detention times, which can possibly result in greater methane emissions from the collection system.