Water supply and sewerage - Mitigation

In addition to handling waste water in a manner that is safe for health and the environment, the purpose of water supply and sewerage is to secure one the basic needs of humans – supply of fresh water. On a national level, wastewater treatment produces small amounts of greenhouse gas emissions, while water supply and sewerage is also an indirect energy consumer, when a notable share of consumed heat energy is transferred outside residences along with wastewater.

Water supply and sewerage services produce drinking water for the needs of urban areas and handle the purification of their wastewater. Three quarters of the emissions of water supply and sewerage services originates in sewage disposal and the rest from the manufacture of drinking water.

Emissions from wastewater treatment are created when the nitrogen included in the wastewater is removed with the help of microbes. In addition to methane created in oxygen-free conditions, the handling processes release nitrogen compound breakdown products produced by microbes in the air. The evaporating methane and nitrous oxide form approximately 0.3% of the national greenhouse gas emissions. This amount corresponds to half of the greenhouse gas emissions for the entire water supply and sewerage.

In addition to evaporative emissions, emissions are created in the production of energy needed by the treating processes. Direction and treatment of water require amply of electrical pumps and mixers. Drinking water manufacture emissions and approximately a third of the wastewater treatment emissions are caused by energy consumption. Compared to wastewater treatment, energy need per treated drinking water cubic metre is approximately a third smaller.

Digestion of wastewater sludge reduces emissions

By preventing evaporative emissions of wastewater in air, greenhouse gas emissions produced by water supply and sewerage could be most effectively mitigated. However, no experience exists of such solutions but controlling the gasses in underground facilities should be more successful than in facilities above ground.

In addition, emissions could be effectively reduced by utilising the organic matter in wastewater sludges better, and producing energy from it either through digestion or incineration. Harnessing the current digestion plant using flaring to the production of electricity and heat includes a notable mitigation potential.

Furthermore, emissions can be reduced by decreasing the energy consumption of pumps, mixers and other equipment and buildings with new technical solutions and by selecting low emission fuels for the production of electricity and heat. Emissions are also reduced when the sludges are used as a source of nutrients in urban landscaping or fields instead of filling the need with other products.

References [1], [2]



  1. Tilastokeskus 2010. Suomen kasvihuonekaasupäästöt 1990-2008. 4. korjattu painos. http://www.stat.fi/tup/khkinv/suominir_2010_4.pdf
  2. Tenhunen, J., Oinonen, J. ja Seppälä, J. 2000. Vesihuollon elinkaaritutkimus. Tampereen vesilaitoksen vaikutukset ympäristöön. Suomen ympäristö 434. Tiivistelmä saatavissa osoitteesta: http://www.environment.fi/default.asp?contentid=84636&lan=fi