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Data Entry: June 2011
Name of Technology Energy Recovery from Sewage Sludge and Biomass with Synchronous Digestion
Technology Owner Tsukishima Kikai Co., Ltd.
General Description This technology aims to construct a system that reduces the power generating cost of digestion gas below the price of purchasing electric power at wastewater treatment plants. Viewing a wastewater treatment plant as a facility for using local biomass, this technology processes kitchen refuse produced outside the plant along with sewage sludge in the existing digestion tank to produce digestion gas for power generation. Ultrasonic solubilization of sewage sludge improves sludge digestion efficiency and mitigates the effects of kitchen refuse fed into the tank. Since the energy self-sufficiency rate is greatly improved, the wastewater treatment plant emits less carbon dioxide, thus mitigating global warming.
Components of Technology

Conceptual system diagram


Descriptions of components

Receiving/Pretreatment equipment Receives kitchen refuse from outside the plant, removes foreign matter, and mixes and crushes the kitchen refuse with sludge.  The mixture is fed into the existing digestion tank.
Sludge solubilization equipment  Performs ultrasonic treatment and processes sludge ready for digestion.
Digestion tank Processes sludge and kitchen refuse at the same time (synchronous digestion).
Digestion gas refining equipment Removes hydrogen sulfide via a dry-desulfurization process (existing equipment included).
Removes hydrogen sulfide via a dry-desulfurization process (existing equipment included). Generates power and heat (hot water).
Generates power and heat (hot water). Dewaters digested sludge
Features of Technology

The system has the following features (differences from conventional systems).
(1) Receives kitchen refuse from outside the wastewater treatment plant and feeds it into the existing sludge digestion tank.
(2) Performs ultrasonic sludge solubilization to improve sewage sludge digestion efficiency, reduce solids and increases digestion gas output.
(3) Increases digestion gas output to benefit from economies of scale of digestion gas power generating equipment.
(4) Reduces power generation cost by considering the reduction in cost of treating regular kitchen refuse as revenue from the present system.
Ultrasonic sludge solubilization is a technique used to create cavitation effects to make thickened excess sludge soluble. This ultrasonic process improves the efficiency of sludge digestion and raises the capacity of the existing digestion tank. Consequently, the tank can handle the higher organic matter load of kitchen refuse fed into the tank. Since the proliferation of advanced wastewater treatment processes is expected to increase the output of excess sludge, ultrasonic processing is anticipated to reduce sludge output by reducing solids.
Furthermore, the power generation cost is reduced, since kitchen refuse fed into the tank produces more digestion gas, the size of the digestion gas power generating equipment increases, and the reduction in the cost of treating regular kitchen refuse can be regarded as revenue from the system. Moreover, the raw materials for digestion gas carried in from outside the plant improve the energy self-sufficiency rate of the wastewater treatment plant and reduce carbon dioxide emissions

Features of the equipment components

Receiving/pretreatment equipment Comprises a hopper, bag opener-separator and mixing-crushing tank.Removes foreign matter from kitchen refuse carried in on refuse trucks, mixes kitchen refuse with thickened sludge and feeds it into the existing digestion tank.
Sludge solubilization equipment Comprises a sludge pump and ultrasonic sludge solubilizer.An ultrasonic oscillator in contact with thickened excess sludge creates cavitation effects, making the sludge soluble and ready for digestion.
Digestion gas power generating equipment Comprises gas compressor, siloxane-removing, gas engine and heat recovery modules to produce electricity and heat (hot water).The generated power is used by plant equipment, and the generated heat is used to heat the digestion tank.
Evaluation of Technology

This technology was developed in the LOTUS Project (Lead to Outstanding technology for Utilization of Sludge Project) and evaluated and reviewed by the Sewerage Technology Development Project Committee under the Ministry of Land, Infrastructure and Transport in Japan in 2007.

[Link to the technology evaluation report]

Contact Information Water Environmental Business Headquarters, Tsukishima Kikai Co., Ltd.

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