Municipal wastewater treatment
(Kommunal spildevandsrensning)


Most wastewater generated in Denmark is subject to significant treatment in municipal wastewater treatment plants.

Process description

The present data refer to wastewater treatment at the Wastewater Treatment Plant Damhusåen in Copenhagen, Denmark. The treatment process comprise following steps: 1) mechanical screening, 2) grit and grease removal 3) primary settling of suspended matter (primary sludge), 4) activated sludge treatment including nitrification, denitrifikation and biological phosphorus removal, 5) chemical phosphorus removal with Fe(III), 6) final settling of suspended matter (excess sludge), 7) production of biogas from primary and excess sludge 8) centrifugation of digested sludge 9) production of heat and electricity from biogas combustion. The dewatered sludge is transported to the Wastewater Treatment Plant Lynetten in Copenhagen where it is incinerated. The technology is modern with a high degree of automatic process control and much focus on energy management.

The law regulates emissions from municipal wastewater treatment plants (tax incentives and maximum emissions) and the marginal emissions of substances such as N, P and organic matter (BOD) are independent of the characteristics of the wastewater entering the plants. Thus, a change in the amount of wastewater delivered to the treatment plants will not affect the emissions of N and P to the environment, but rather the energy- and chemical consumption at the plants.

Data collection and treatment

Data on electricity production and consumption as well as heat production have been derived from the wastewater treatment plant's 2002 records and from the 2001 green account.

The electricity consumption for pumping of water (about 0.02 kWh/m3) is low compared with electricity for aeration (about 0.2 kWh/m3 average wastewater) and electricity consumption is determined primarily by the concentration of N and organic matter in the wastewater (except for extremely dilute wastewater such as rainwater). Wastewater from food products is usually relatively rich in organic matter and N and all energy consumption associated with the treatment has been allocated to the two groups of substances.

Technical scope

The present data include energy exchanges (consumption as well as production) in all units of the Damhusåen wastewater treatment plant. Chemical consumption, handling of sludge as well as emissions of heavy metals and xenobiotic organic substances have not been considered. Specific energy consumption for P removal is negligible and not taken into account.


The present data are derived from a major wastewater treatment plant located in an urban area (Copenhagen). The total capacity of the plant is 350,000 person equivalents (PE) corresponding to about 3% of the total treatment capacity in Denmark. The plant is highly energy efficient and smaller plants may be somewhat less energy efficient.


The processes in modern municipal wastewater treatment plants are complex and considerable investigations are required before accurate, specific and detailed data can be provided. A previous study by Weidema et al. (1996) has suggested an electricity consumption of 1.3 kWh per kg BOD in wastewater treated in a typical provincial wastewater treatment plant (100.000 PE) which is the same order of magnitude as observed here.

Inputs and outputs

Marginal emissions of organic matter and nutrients (N and P) are independent of input concentrations in wastewater and hence zero. The net electricity consumption associated with treatment of general organic matter and nutrients is in the order of 1.1 kWh per kg BOD and 4 kWh per kg N removed, respectively.


Lynettefællesskabet I/S (2001): Grønt regnskab 2001.

Weidema BP, Pedersen RL and Drivsholm TS (1996): Lifecycle screening of food products - two examples and some methodological proposals. Danish Academy of Technical Sciences (ATV).  

Administrative information

Data URL:
Version no.: 1.00
Authors: Per H. Nielsen, 2.0 LCA consultants
and Kim R. Jørgensen, development engineer, Lynettefællesskabet I/S.
Data entry: Per H. Nielsen
Data completed: 
July 2003.