Epsilon Archive for Student Projects

Abstract

Främby wastewater treatment plant, a 50 000 population equivalent (pe) municipal sewage treatment plant in Falun, faces large changes as aging technology, increasing load and stricter effluent quality requirements lead to a demand for upgrading the plant. The owner of the plant, Falu Energi & Vatten (FEV), have a vision of an energy neutral plant in the future. That is, a plant that produces at least as much energy as it consumes. Achieving energy neutrality therefore requires a combination of more efficient use of electricity and heat and better utilization of the plant’s resources, for example by biogas production from sludge.

An energy audit of the sewage treatment processes on the Främby plant showed that the yearly electricity use and heat use was 1,9 GWh and 1,5 GWh respectively. Approximately 66 % of the electricity was used in the biological treatment process, which is similar to other sewage treatment plants but still indicates that there is potential for energy saving measures.

By using the results of the energy audit of the existing plant and a description of the future plant provided by FEV, the likely energy consumption of the future plant with a load of 70 000 pe was calculated. With the same processes as today, the energy consumption will increase by 47 % to 4,9 GWh per year. If nitrogen removal with Membrane BioReactors (MBR) is implemented on the future plant, the energy consumption can instead increase to three times of today’s use, to 10,3 GWh per year.

An evaluation of the biogas production on the Främby plant showed that the biogas yield is high, despite that no optimization of the digestion process has been made. The possible biogas production on the future plant was calculated from the biogas yield of today, resulting in a production of 3 900 Nm3 per day. The biogas can be used to produce 7,3 GWh heat per year, 2,6 GWh electricity and 5,2 GWh heat per year or be upgraded to 660 tons of vehicle fuel per year. A literature review and calculations indicated that the best option for a plant the size of Främby is to use the biogas for combined heat and power production. This alternative is also the best according to FEV’s vision of an energy neutral plant.