Turning wastewater into green energy at Marselisborg WWTP, Denmark
In 2016 Marselisborg WWTP produced 50 percent more electricity than it needed and 2.5 GW of heat for the district heating system without adding external organic waste or carbon. Marselisborg wastewater treatment plant has increased plant efficiency and reduced energy consumption by optimizing all its processes. The excess energy produced is enough to serve the needs of the drinking water supply and wastewater treatment facilities in the region.
Solution to which problem
Water and wastewater facilities are usually high energy consumers. Typically, water and wastewater-treatment processes account for 25 – 40 percent of the municipality’s electricity bill. Nowadays the technology and knowledge is available to make water-management systems energy neutral. Marselisborg wastewater treatment plant has increased plant efficiency and reduced energy consumption by optimizing all its processes. In addition, Aarhus Vands goal is an energy neutral water cycle in which WWTP energy production is able to offset the energy consumption of operations within its catchment area.
Technical conditions
In 2006 there were fourteen smaller WWTPs around Aarhus. Aarhus Vand began with consolidation of these smaller WWTPs, from 14 plants to just 4 today, Marselisborg WWTP remaining the largest. Centralization was the best solution for this area. It is more energy and cost efficient to treat wastewater at larger plants, operating fewer but larger plants also decrease operation and maintenance costs. Marselisborg WWTP has a capacity of 220 000 PE and in 2016 the average daily inflow rate was about 27,500 m3/day.
Implementation
Over the past years there has been great focus on energy savings and energy production at Marselisborg WWTP.
Energy saving technologies:
- SCADA control system: online control based on ammonium load and advanced control of blowers;
- Improved efficiency of aeration: replacement of HV Turbo blower with ABS HST Compressor;
- Replacement of old centrifuge (Alfa Laval 550 series) with new energy efficient (Alfa Laval G3);
- Sludge liquor treatment based on the anammox process.
- Optimized energy production, with replacement of old gas engines with high efficient engines;
- Utilization of surplus heat for district heating system.
Result
In 2015, Marselisborg WWTP had a total energy production of 9,628 MWh/ year and an energy consumption of 6,311 MWh/year, equivalent to a net energy production of 153%. It means that the plant’s energy production was 53% higher than the consumption. Surplus heat is directed towards Aarhus district heating.
In 2016, the plant produced 50% more electricity than it needed and 2,5 GW of heat for the district heating system without adding external organic waste or carbon. This excess energy is enough to serve the energy need for the drinking water supply and wastewater facilities in the catchment area.
The energy production has been improved through implementation of new energy efficient biogas engine (CHP) resulting in an increase in electricity production of 1 GWh/year.
Optimization with SCADA has brought many benefits. The system produced a reduction in annual electricity consumption of around 700 000 kWh, corresponding to annual saving of 61 000€.
Replacement of blowers for the aeration system resulted in a reduction in power consumption of 300 000 kWh/year and annual savings of 26 000€.
Altogether, saving measures at the plant led to an overall reduction in power consumption of approximately 25%. The total consumption was 4,2 GWh/year in 2005 while 3,1 GWh/year in 2016.