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By technology classification

Osaka Gas believes that technologies serve as the foundation of corporate competitiveness, and considers R&D to be one of the most important elements in the strategy to make a difference.
For this reason, Osaka Gas works actively on R&D and commercialization of new technologies, as presented below.

Energy-creating wastewater treatment process: hydrothermal gasification process

Overview

The hydrothermal gasification process can produce fuel gas mainly composed of methane, while treating wastewater, thereby achieving both substantial CO2 emission and treatment cost reductions.

Japan has a medium-term goal of reducing greenhouse effect gas emissions by 25% by 2020 from the 1990 level. To achieve this goal, it is necessary to develop novel technologies for energy savings and CO2 emission reductions.
Semiconductor foundries and chemical plants emit wastewater that contains phenols and other organic substances, which are difficult to treat through conventional biological treatment processes. Such wastewater has been incinerated using fuel such as heavy oil. A problem with this method is the use of a large amount of fuel, which leads to increase CO2 emissions and treatment cost.
To address this challenge, Osaka Gas has worked on developing a hydrothermal gasification process that can purify wastewater on the one hand and can produce fuel gas for beneficial use on the other, by using a catalyst for decomposing organic matter contained in wastewater and converting it to fuel gas, with the main component being methane.
The hydrothermal gasification process is designed to break down organic matter contained in wastewater, in a high-temperature high-pressure liquid phase, to low-molecular weight substances, such as methane, other hydrocarbons and hydrogen. A proprietary catalyst developed by Osaka Gas enables efficient breakdown reaction.

Fig. 1: Comparison between hydrothermal gasification process and incineration process (existing technology)

24/ Fig. 2: Scanning electron micrograph (SEM) of hydrothermal gasification catalyst Fig. 3: Transmission electron micrograph (TEM) of hydrothermal gasification catalyst

Features

The hydrothermal gasification process developed by Osaka Gas uses a catalyst to chemically decompose organic matter contained in wastewater and efficiently converts it into fuel gas. Compared with conventional wastewater treatment technologies such as incineration and biological processes, the hydrothermal gasification process offers the following advantages:

1. Substantially Reduced CO2 Emissions and Treatment Cost
The incineration process treats wastewater by oxidizing organic matter contained therein, producing CO2 from all kinds of organic matter. Furthermore, wastewater evaporation performed as preliminary treatment requires a huge amount of heat, resulting in wasteful burning of fuel at a high cost and inevitable emissions of a vast amount of CO2. In contrast, the hydrothermal gasification process treating wastewater in its liquid phase requires no extravagant heating intended for evaporation. In addition, decomposition of organic matter taking place in the absence of atmospheric oxygen converts organic matter into fuel mainly composed of methane, which can be collected and used efficiently as an energy source. Consequently, the hydrothermal gasification process simultaneously reduces cost and CO2 emissions, which would otherwise be produced as a result of treatment.

2. Suitable for Wastewater in Cases Where No Other Treatment Processes Are Effective
The traditional biotreatment process is not suitable for wastewater that contains high-concentration substances or components that may possibly act as biotoxins. Designed to chemically decompose organic matter contained in wastewater, the hydrothermal gasification process can be used to treat such wastewater. The newly-developed catalyst speeds the decomposition.

Fig. 4: Advantages of hydrothermal gasification process (wastewater treatment rate: 200 m3/day)

Achievements and future efforts

The hydrothermal gasification process has proven capable of treating wastewater safely and stably for an extended period through various tests using laboratory and bench scale apparatuses. A demonstration test was conducted with a pilot plant built in a factory discharging wastewater to verify the process performance. This demonstration test was subsidized by a Grant for General Promotion of Environmental Research provided by the Ministry of the Environment. The pilot plant continues operating in the factory to treat the wastewater after the demonstration test.

Fig. 5: Pilot plant set up at actual factory

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