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Waste water treatment facilities have big operational cost as a consequence of meeting their discharge permit requirements. Waste treatment processes include energy-intensive operations such as aeration and pumping. As a result, waste water treatment plants (WWTPs) require significant energy consumption. As electrical prices increase, plant operators are facing higher energy costs.

 

As the cost of energy rises and emphasis on renewable energy increases, local authorities search new ways of recovering energy from sustainable sources that will lead to cost saving and financial surplus. GE Jenbacher offer gas engines that provide a renewable energy solution through combined heat and power production (CHP) systems, or simply “cogeneration systems” that result in long-term savings for wastewater treatment plants.

A large proportion of the world’s sewage systems do not recover value from the sewage in the form of electricity and heat. But the renewable energy fuel source derived from sewage gas can be converted, using reciprocating gas engines, to electricity and heat, compensating a large fraction of the facility’s electric power demand and eliminating the need to purchase fossil fuels for plant heating processes.

 

Clean energy derived from waste water treatment plant

 

The process of biogas generation and utilization follows the next steps:

1. Preparation of the input material including removal of physical contaminants.

2. Digestion (fermentation), consisting of hydrolysis, acetogenesis, acidogenesis and methanogenesis.

3. Clean electric power and heat generation through cogeneration (CHP) systems.

4. Post-treatment of the digestate.

 

Municipal sewage systems collect the sewage and send it to the waste water treatment plant. From here it is sent to the sewage digesters, after a first stage preparation. In the digestion tanks a series of biological processes are harnessed in order to produce biogas. Hydrolysis is the process where the organic material is solubilised into the digestion liquid. It then undergoes the intermediate steps of acidogenesis and acetogenesis which create the precursor molecules for methanogenesis. Methanogens feed off these precursors and produce methane as a cellular waste product. The biogas containing this biologically-derived methane is contained and captured in a gas storage tank which is typically located separately to the main digester. The gas storage tank acts as a buffer in order to balance fluctuations in the production of gas in the digesters. Where gas production levels are low or highly variable, dual fuel mixing can be used to supplement the sewage gas with natural gas from the mains distribution network.

 

Benefits of cogeneration in Sewage Treatment

 

  • A waste material is used to generate renewable energy through cogeneration (CHP).

  • Environmental benefits from the reduction in carbon emissions compared to aerobic sewage treatment.

  • Transmission loss free and economical electric power generation on site.

  • Production of a low-carbon fertilizer.

  • Technology that is proven and cost effective.

  • Seamless dual fuel mixing maximizes renewable energy output and smoothens gas production fluctuations by supplementing with natural gas as required.

  • High electrical efficiency. More electricity generated per unit of sewage gas used. The electrical efficiency can rise up to 43%.

  • LEANOX controls with turbocharger bypass ensure the correct air-to-gas ratio under all operating conditions to minimize exhaust gas emissions while maintaining stable operation.

  • Longer overhaul schedule. The maintenance cost is minimized with 60,000 operating hour overhaul intervals.