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Weltec Biopower to build AD unit for German sewage facility

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Weltec Biopower has been contracted to build an energy-efficient wastewater treatment unit for a sewage treatment plant in Bückeburg, North Germany.

Apart from the earthworks and the electrical installations, the German biogas manufacturer will supervise the construction of the new sludge thickener, the engine room for the cogeneration power plant and the digester with its gas storage roof.

Until now, the sewage treatment plant, with a capacity of 33,000 (population equivalents) has used aerobic wastewater treatment. The conversion to anaerobic sludge stabilisation will optimise the operating processes and deliver higher energy efficiency. It is expected to reduce the plant’s greenhouse gas emissions by 664 tonnes per year.

Weltec’s anaerobic wastewater treatment will result in ‘significant’ cost reduction. The amount of sludge that accumulates annually will decrease from 2,800 tonnes to 1,800 tonnes.

“With the 465,000 kWh of power that we will gain from the sewage gas every year, we will be able to cover 40% of our own power demand,” said Rainer Klenke, technical manager of wastewater operations in Bückeburg. Klenke estimates the annual power bill will drop by two-thirds, from €195,000 to €65,000.

With Weltec Biopower’s installation, the sludge will undergo anaerobic digestion in a stainless steel digester. The firm will implement the digester as a stainless steel tank in the ‘tried and tested’ segmental design with a double-paddle mixer. The digester will be 6.3 m high, with a diameter of around 19 m, and a capacity of 1,823 m3.

The sewage has will be stored in a flexible double-membrane roof with a volume of approximately 600 m3. This design stands out with much lower investment costs than a conventional digester, according to Weltec, and, therefore, is an optimum solution for smaller wastewater treatment plants.

The new static sludge thickener, which is equipped with a submersible mixer and has a capacity of 342 m3, is also made of stainless steel. A 226-kW CHP unit will ensure efficient utilisation of the gas. Both the generated power and the heat will be used on the plant premises. Additionally, a gas boiler with an output of 170 kW will be installed in the engine room to ensure the heat supply of the digester, even during maintenance work on the cogeneration power plant.

Thomas Sextro, sales manager at Weltec Biopower, said: “Aerobically stabilised sludge contains a higher organics load and is more difficult to de-water. With the anaerobic process, the de-watered sludge has about 35% less volume, which saves sludge transportation and disposal costs.”

Such smart combinations of wastewater treatment, energy generation, and climate protection making existing sewage treatment plants ‘future-proof’, according to Weltec. The cost-efficient technologies and proven concepts from the biogas sector are suitable to counteract fluctuating energy prices and increasing sludge utilisation costs.

The unit will be ready to go live in October.