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Data Entry: June 2011
Name of Technology Anaerobic Co-digestion System with Low Running Cost of Power Generation
Technology Owner JFE Engineering Corporation
Daiki Ataka Engineering Co., Ltd.
Kajima Corporation
Dainen Co., Ltd.
General Description This technology uses existing digestion tanks to digest kitchen refuse and other organic waste (hereinafter "kitchen refuse"), viewing a wastewater treatment plant as a facility for using local biomass. The aim of this technology is to produce biogas from previously untapped energy sources which can then be used to generate power.
In comparison with conventional incineration at refuse incineration plants, this technology processes refuse at a lower cost. Consequently, the costs of conventional treatment and disposal can be allocated to sewerage projects to improve the project balance sheet.
This technology also allows biogas power to be generated at low cost, benefiting from economies of scale, since the increased biogas output in comparison with sewage sludge-only systems leads to larger-capacity power generation equipment. Moreover, incorporating bio-desulfurization, this technology refines the produced digestion gas more cheaply than the conventional technology and improves the reliability of digestion gas power generation by also removing siloxane.
Combining these features, this technology greatly reduces the cost of effectively using sewage sludge.

Conceptual diagram of newly developed technology

Components of Technology The major components of this technology are: (1) Receiving/pretreatment equipment, (2) Digestion tank, (3) Digestion gas refining equipment, (4) Digestion gas power generation equipment and (5) Dewatering equipment. These components have the following features.

(1)Receiving/pretreatment equipment
Receives kitchen refuse and carries out pretreatment for feeding into the digestion tank.

(2)Digestion tank
Transforms received organic matter to digestion gas. This technology uses existing equipment.

(3)Digestion gas refining equipment
Refines digestion gas by removing siloxane and hydrogen sulfide contents to make digestion gas suitable for use by power generation equipment.

(4)Digestion gas power generation equipment
Comprises a gas engine or micro gas turbine to use digestion gas for power generation.

(5)Dewatering equipment
Dewaters sludge produced in the digestion tank. This technology uses existing dewatering equipment.

Schematic image of the technology

Features of Technology

This technology processes received kitchen refuse in a suitable pretreatment process and produces an increased amount of digestion gas using the existing digestion tank. Furthermore, it incorporates bio-desulfurization to refine the produced digestion gas at a lower cost than by the conventional technology and combines siloxane removal to improve the reliability of digestion gas power generation.
By combining these techniques, power is generated at lower cost than the conventional simple power generation technology.

The features of this technology are detailed below.
(1) Anaerobic co-digestion system
Mixes kitchen refuse into sewage sludge (thickened sludge). Kitchen refuse is expected to increase the gas output since its solid concentration is high and it contains a higher proportion of organic matter than sewage sludge. This technology incorporates newly installed pretreatment equipment, receives and processes kitchen refuse in a pretreatment process at the wastewater treatment plant and feeds kitchen refuse into the digestion tank.
The pretreatment equipment incorporates a bag opener-separator to separate and remove foreign matter. The kitchen refuse is then fed into the digestion tank with thickened sludge. A mixing tank circulation pump (crushing pump) carries out wet crushing. These processes ensure stable crushing and mixing. A fixed quantity of thickened sludge is mixed to facilitate handling.

(2) Digestion gas power generation systemIt is assumed that at medium-sized to large treatment plants, the digestion gas power generation system uses a gas engine and at small treatment plants, a micro gas turbine. The technology of these power generation systems has already been established. Nonetheless, the use of siloxane-removing equipment will improve reliability.

(3) Bio-desulfurizerThe bio-desulfurizer oxidizes and removes hydrogen sulfide from biogas, using the activity of microorganisms (sulfur-oxidizing bacteria). The basic principle is the same as in bio-deodorization at wastewater treatment plants to remove hydrogen sulfide. One advantage of the present system is that the maintenance cost is extremely low compared with conventional dry or wet desulfurization (alkali cleaning). Moreover, it is a highly safe and stable system. The systems that have already been installed in food factories are working well.
The bio-desulfurizer reduces the desulfurization cost and thus the power generation cost.

Filter material in bio-desulfurizer

(4) Siloxane-removing equipment
Two problems associated with a power generation system using digestion gas produced in a wastewater treatment plant are that the system is more prone to "flame-out" than when using utility gas, and that the system requires inspection and maintenance at shorter intervals.
The cause of these problems is organosilicon compounds (siloxane) in the digestion gas. It is known that when burned in the engine combustion chamber, siloxane produces silica (silicon dioxide, SiO2), which affects the service life of the components of the gas engine.
This technology solves these problems by incorporating siloxane-removing equipment using a digestion gas refining agent to selectively adsorb siloxane from digestion gas. The siloxane-removing equipment removes almost all siloxane from digestion gas, improves the reliability of the digestion gas power generation system to a level comparable with utility gas power generation systems, and reduces the cost of maintaining the gas engine or micro gas turbine, thus suppressing the power generation cost.

 Siloxane (molecular structure of D4)
Siloxane-removing equipment
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

Environmental Industrial Engineering Division, JFE Engineering Corporation

For inquiry:

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