Energy self-sufficient sewage treatment

Vienna has taken yet another step towards ecological energy production with its "Energy Optimization Sludge Treatment" (EOS) project. EBS VIENNA’s main sewage treatment plant will be energy self-sufficient by the year 2020.

Conversion and construction

Following their commissioning and permanent service since the year 1980, the mechanical pretreatment and first (of two) biological purification stage of Vienna’s main sewage treatment plant are due for replacement starting in 2015. The facilities will be brought into line with the latest technical standards, which will also mean a reduction in maintenance costs. Optimal synergies can be achieved thanks to the simultaneous construction of a new sludge treatment facility. It goes without saying that the plant must remain fully operational during the construction and conversion phase, but this will mean a construction period of six years. Work will start in the spring of 2015, but will be preceded by the approval procedure (2012) and tendering process (2014).

From sludge to energy

Six 30-metre-high, onion-shaped digestion tanks will be erected for treatment of the sludge. Using the digestion of sewage sludge for the production of methane is an innovative biological process. The objective is to minimize both energy consumption and sewage sludge, whilst at the same time increasing the production of gas for energy generation. A combined heat and power system transforms the sewage gas into energy, thus turning it into a renewable source of energy that - unlike solar and wind power - is available continuously and reliably. With an annual volume of 20 million cubic metres of methane, it is possible to produce 78 gigawatt hours of electricity and 82 gigawatt hours of heat.

From consumer to producer

The main sewage treatment plant currently requires 60 gigawatt hours of electricity for the purification of all Vienna’s sewage - equivalent to about one per cent of Vienna’s entire consumption. Starting in 2020, the plant will produce a surplus of nearly 15 gigawatt hours of electricity as well as a surplus of 42 gigawatt hours of heat a year. The main sewage treatment plant will therefore be energy self-sufficient in operation, benefiting Vienna’s energy balance. The emission of CO₂ equivalents will be reduced by about 40,000 tonnes a year - equivalent to the greenhouse gas emissions of a 4,000-person community, or 6,700 times around the Earth by car.

Sunshine in the tank and the bathroom

In accordance with the Urban Energy Efficiency Programme, the main sewage treatment plant is already very active when it comes to climate protection. In 2010 a new solar filling station went into operation that enables the entire fleet of electric vehicles to be recharged environmentally. The electric bikes are specially equipped for transporting sewage samples - due to the size of the plant (420,000 square metres) and up to 60 litres of sewage per sample, this solar boost to muscle power is more than welcome. And when employees start to sweat at work, a solar thermal plant provides hot water for the showers and kitchen. Renewable energy is also provided by a photovoltaic plant (10,500 kWh per year) and a small wind farm, which produces enough clean electricity for the lighting of the 3,500 metre long collector corridors in the "basement" of the site.

"We clarify everything"

Under the motto of "We clarify everything", the technically innovative enterprise in Simmering purifies all the sewage produced by Vienna - an average of 7,000 litres every second. After mechanical purification, the two biological purification stages are modelled on Mother Nature. The result is that the River Danube leaves Vienna with the same quality of water that it has when it arrives.

Source: wieninternational.at