Germany-headed biogas technology provider Weltec Biopower GmbH has announced that following a public tender it was awarded the contract for an anaerobic stage for the municipal sewage treatment plant in Bückeburg, North Germany. Apart from the earthworks and the electrical installations, the contract entails supervising the construction of the new sludge thickener, the engine room for the cogeneration power plant, and the digester with its gas storage roof.
The budget for the various modernization measures on the premises totals EUR 4.14 million. The anaerobic stage will be ready to go live in October 2021. Within the framework of the European Regional Development Fund (ERDF), the investment and development bank of Lower Saxony (NBank) rewards the carbon savings with a subsidy of EUR 1 million.
Environmental and economical benefits
Until now, the 33 000 population equivalents (pe) sewage treatment plant in Bückeburg has applied aerobic wastewater treatment. The conversion to anaerobic sludge stabilization will put the entire plant on track towards economic and ecological success.
The new wastewater treatment solution to be supplied from Weltec Biopower is set to optimize operating processes and deliver significantly higher energy efficiency. Moreover, the new process is expected to reduce the sewage treatment plant’s greenhouse gas (GHG) emissions by 664 tonnes per annum.
Besides the ecological improvement, Weltec’s anaerobic wastewater treatment will result in a significant cost reduction. The amount of sludge that accumulates every year will be reduced by around 1 000 tonnes to 1 800 tonnes. Additionally, overall power consumption will be reduced by some 5 percent.
The greatest savings potential, however, lies in the use of the sewage gas produced from the sludge.
With the 465 000 kWh of power that we will gain from the sewage gas every year, we will be able to cover 40 percent of our own power demand, said Rainer Klenke, Technical Manager Operations for the municipality of Bückeburg.
The technical manager of the wastewater operations of the municipality of Bückeburg according to Rainer Klenke’s calculations, the yearly power bill for the WWTP will drop by two-thirds, from EUR 195 000 to EUR 65 000.
Drawing on optimization expertise
Using its expertise from biogas technology Weltec Biopower will implement the digester as a stainless-steel tank in the tried-and-tested segmental design with a double-paddle mixer. The digester will have a height of 6.3 m, a diameter of about 19 m, and a capacity of 1 823 m3.
The sewage gas will be stored in the flexible double-membrane roof with a volume of approximately 600 m3. This design stands out with much lower investment costs than a conventional digester and, according to the company, is an optimum solution for smaller wastewater treatment plants.
The new static sludge thickener, which is equipped with a submersible mixer and boasts a capacity of 342 m3, is also made of stainless steel. A 226-kW cogeneration unit will ensure efficient utilization 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 in order to ensure the heat supply of the digester even during maintenance work on the cogeneration power plant.
Efficiency gains through process improvements
The municipal sewage treatment plant will thus experience an efficiency boost thanks to technological and process-related improvements. Apart from the anaerobic stage, a primary clarifier will be integrated into the process.
In this way, primary sludge will be extracted from the wastewater, reducing the chemical oxygen demand (COD) by a third. The lower this value, the easier the water can be treated. This reduces the aeration period in the aeration tank and thus the energy costs.
Aerobically stabilized sludge contains a higher organics load and is more difficult to dewater. With the anaerobic process, the dewatered sludge has about 35 percent less volume, which saves sludge transportation and disposal costs, explained Thomas Sextro, Sales Manager at Weltec Biopower.
Such smart combinations of wastewater treatment, energy generation, and climate protection make existing sewage treatment plants future-proof. The cost-efficient technologies and proven concepts from the field of biogas are suitable to counteract fluctuating energy prices and increasing sludge utilization costs.
In Bückeburg, for example, this enables the municipality to keep its wastewater and surface water drainage costs steady without burdening the citizens with extra fees.