With the use of new technologies and energy-optimising equipment, the aim was to make the plant energy self-sufficient, and even produce 50% more energy than is consumed.
The renovation of Egaa Wastewater Treatment Plant was initiated to gain a maximum energy output, and a fruitful collaboration with leading suppliers of technologies, processes and components made this possible. Vatech 2000 was among the suppliers and has delivered Vatech penstocks and ball valves for the project along with AVK butterfly valves and knife gate valves with linear actuators. The linear actuators were chosen, since they are energy efficient compared to actuators using compressed air.
Cleaning of nitrogen with anammox bacteria
With the establishment of a DEMON® anammox reject water plant, the electricity consumption for nitrogen cleaning is reduced. From the bottom of the clarification zone in the DEMON® tank, sludge is pumped back to the process as return sludge, and excess sludge is pumped into a cyclone, where anammox bacteria generated in the cleaning process are sifted out. In addition to cleaning reject water, the anammox bacteria also clean the wastewater in the process tanks without any use of carbon.
Carbon filtering with Salsnes® filters
Norwegian Salsnes® has developed strip filters that are used early in the process to filter carbon from the wastewater. These filters reduce aeration energy consumption, previously accounting for about 40% of total energy consumption, since less carbon is discharged to the process tanks. The concentration of solid in the primary sludge which is extracted from the strip filters is so high that pre-dewatering can be avoided. Primary sludge and biological sludge are both pumped into the digestion tank, where it is recirculated through a heat exchanger and biogas is generated. After fermentation, the sludge is transported to a sludge buffer storage before final dewatering.
Utilisation of biogas and excess heat energy
Optimum utilisation of biogas is ensured by installing a highly efficient gas generator plant, where biogas is used for the production of electricity and heat. Also, excess heat energy is used to produce an additional 10% electricity by using an Organic Rankine Cycle (ORC). This helps reach the objective of an energy production that is 50% higher than energy consumption.