As we have learned in this lesson, operation costs of wastewater treatment plants are influenced by many factors and can differ in a wide range. Accordingly, reliable cost calculations can only be worked out on the basis of detailed data from the plant.

Running through the whole of one particular wastewater treatment project as an exercise would go beyond the scope of this E-Learning course. That’s why the following exercise is based only on few data and shall mainly put you into the position to successfully deal with the relevant costs components and to investigate the most important influencing factors.

Please estimate the possible range of operation costs per year (€/a) of a new municipal wastewater treatment plant with a capacity of 10,000 p.e.. Discuss the main influencing factors on the operation costs.

The exercise should be carried out considering the following assumptions:

• The plant is located in southern Europe. It is operated as a conventional activated sludge system without sludge digestion. The produced sludge is utilized in agriculture as fertilizer.

• The costs to the employer of an annual salary, including insurance, is assumed to be 20,000 € per year.

• The investment costs amount to 2.7 m €. They are divided up into 50/35/15 % on construction/mechanical equipment/electrical equipment. Maintenance costs are assumed to amount up to 15 – 25 % of the total operation costs.

• The average energy tariff amounts up to 0,10 €/kWh.

• The daily volume of wastewater per p.e. is assumed to be 75 l.

Results

Figure 10: Results of exercise / Average composition of operation costs