Evaluation of the energy and cost key figures of processes for the elimination of micropollutants in wastewater treatment plants

Summary

The first plants for the elimination of micropollutants at wastewater treatment plants (WWTPs) have been in operation in Switzerland since 2016. The elimination of micropollutants requires the use of energy and human, material and financial resources and it is of general interest to record this data, evaluate it in the form of key figures and compare it with each other. This study examines 13 WWTPs for the elimination of micropollutants and aims to implement and evaluate uniform data collection in accordance with the VSA recommendation “Definition and standardization of key figures for processes for the elimination of micropollutants in WWTPs” from 2018. Six ozone, five powdered activated carbon (PAC) and two granular activated carbon (GAC) plants were investigated.

The average annual elimination performance of the plants is between 75 % and 90 %, whereby the aim of 80 % is predominantly achieved. As a rule, the tested MP stages reliably fulfill the legally prescribed purification effect.

The specific replacement values of the MP stages vary greatly, between 70 – 300 CHF/PE or 150 – 670 CHF/ P_connected and 9,000 – 65,000 CHF/(l/s) (dimensioning water volume). There are no systematic cost differences between ozone, PAC and GAC systems. The replacement values and operating costs vary widely, which can be attributed to individual circumstances such as wastewater composition, subsoil and plant layout.

The annual operating costs are between 1.5 – 11 CHF/(PE*a) or 2.5 – 17 CHF/(P_connected *a) or 0.02 – 0.09 CHF/m³ (treated wastewater volume). If the capital costs (interest and depreciation costs) are also taken into account, the annual costs range from around CHF 7 to 32/(PE*a), CHF 12 – 55/(P_connected *a) or CHF 0.07 – 0.27/m³ (treated wastewater volume).

The total electricity consumption of the MP stages is between 2 – 9 kWh/PE*a or 0.02 – 0.1 kWh/m³, whereby ozone systems tend to have a higher electricity consumption than activated carbon systems.

The primary energy consumption, which takes into account the imported operating materials, varies between 10 – 80 kWh/PE*a or 0.1 – 0.8 kWh/m³, with no significant differences between ozone, PAC and GAC.

The oxygen consumption of ozonations is 1 – 5 kg/PE*a or 10 – 55 mg/l (treated wastewater volume), while the activated carbon consumption of PAC and GAC systems is between 0.5 – 2 kg/PE*a or 5 – 20 mg/l. No significant differences in activated carbon consumption were found between PAC and GAC plants.

The CO₂ equivalents for ozone systems are in the range of 1 – 4 kg CO₂ /PE*a. Activated carbon systems have a larger CO₂ footprint than ozone systems, especially if carbon from fossil raw materials is used. The CO₂ equivalents for activated carbon plants that use activated carbon from fossil raw materials are 6 – 23 kg CO₂ /PE*a, while lower values of 3 – 7 kg CO₂ /PE*a were observed for biogenic raw materials. The use of biogenic raw materials and the reactivation of carbon therefore offer great potential for reducing CO₂ emissions.

Due to the relatively large observed scatter of the data, it is not recommended to form regression curves or mean values from the key figure data. Each MP stage is an individual case that was designed for individual requirements. This means that planning principles for future plants cannot be derived from the available data. However, the data is well suited for a nationwide analysis.

• Year of publication:  2025

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