Air Monitoring Wastewater Treatment Plant Monitors Greenhouse Gas Emissions


In Helsinki, a large underground wastewater treatment works is using a Gasmet FTIR gas analyser for continuous emissions monitoring of pollutants such as greenhouse gases. This helps the plant in its efforts to combat climate change and also helps wastewater treatment process optimisation.


Employing a Gasmet multigas FTIR analyser, the plant’s managers are able to measure the effects of process control on the emissions of greenhouse gases (GHGs) such as carbon dioxide, methane and nitrous oxide. This also provides the team with an insight into the fate of nitrogenous compounds within the wastewater stream.


The Viikinmäki wastewater treatment plant was built almost entirely underground to avoid freezing temperatures. This is common practice in the Nordic countries, providing other advantages such as land availability above the plant and the provision of stable conditions for process control and odour management.


The Viikinmäki plant is the largest wastewater treatment facility in Finland, handling approximately 100 million m³ per year. The wastewater is treated in compliance with the Finnish Wastewater Discharge Permit, which is stricter than the EU Water Framework Directive for parameters such as nitrogen removal, phosphate content, BOD, COD and suspended solids.


The treatment process is based on the activated sludge method and includes three phases: mechanical, biological and chemical treatment. Traditional nitrogen removal has been enhanced with a biological filter that utilises denitrification bacteria. The organic matter contained in the sludge produced in the wastewater treatment process is digested and the biogas generated is collected for further use. As a result, the treatment plant is self-sufficient for heating and about 70% self-sufficient in electricity.


As a result of the size of the plant (E-PRTR reporting) and the commitment of the Helsinki Region Environmental Services Authority (HSY) to environmental protection, it was necessary to monitor gaseous emissions. At the beginning of the E-PRTR reporting requirements (2007) HSY modelled the annual gaseous emissions based on grab samples.


Initially, a portable FTIR analyser from Gasmet was hired for a short period to assess the plant’s emissions and for research. However, as Mari Heinonen, Process Manager at Viikinmäki, reports: “The emissions data were very interesting but they were not representative of the annual emissions, and posed more questions than they answered. We therefore purchased a continuous emissions monitoring system (CEMS) from Gasmet, which was installed in late 2012.


“Very little data has been published on the GHG emissions of wastewater treatment and as far as we are aware, Viikinmäki is the only plant in the world conducting this type of monitoring, so our data is likely to be of major significance.”


The Gasmet CEMS at Viikinmäki continuously displays emissions data for CH4, N2 O, CO2 , NO, NO2 , and NH3. Commenting on its performance, Mari says: “The system has performed very well, with little


maintenance required. Zero point calibration with nitrogen (background) just takes a few minutes each day and is fully automated. Water vapour calibration is conducted at least once per year, but under normal circumstances no other calibration is necessary.”


With the benefit of the monitoring data, Mari has calculated the annual emissions for methane to be around 350 tonnes, and for nitrous oxide around 134 tonnes. This means that the emissions per cubic meter of wastewater equate to 3.5g of methane and 1.34g of nitrous oxide.


Looking forward, Mari believes that it will be possible to use the gas monitoring data to improve process control: “Traditional monitoring/control systems focus on concentrations of oxygen, nitrate and ammonia in the water, but if we detect high levels of N2


that we can use as a feedback control. The monitoring data for gaseous nitrogen compounds (N2 more complete picture of the nitrogen cycle in the treatment process.


“Clearly, further research will be required, but this work may indicate a need to consider the fate of nitrogenous compounds beyond just those in the wastewater; the removal of nitrogen from wastewater is a key objective, but if this results in high N2


O emissions the process may need to be managed in a different way.”


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30792pr@reply-direct.com


O gas for example, this may indicate a problem in the process O, NH3, NOx) complements water analysis and provides a


27


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����� Helsinki FINLAND


Gasmet Technologies Oy Pulttitie � A � ����� Helsinki


Tel: ���� � ��� �� ��� email: contact@gasmet.fi www.gasmet.fi


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