Regeneration of Activated Carbon Using Dimethyl Ether for Water Treatment
Mitsuhiro Matsuzawa* and Tadashi Sano*
*Center for Technology Innovation – Mechanical Engineering, Research & Development Group, Hitachi, Ltd.
The water industry, which includes systems such as water supply and sewage systems, seawater desalination systems, and reclamation water systems, has been expanded with the increasing growth of the world’s population and progress of industrialization. In the water treatment process, using activated carbon has been expected to remove the organic matters dissolved in the wastewater. The most common process for the regeneration of activated carbon is the thermal method. In this method, the used activated carbon is heated up to approximately 800 ºC to 900 ºC for several hours and the organic matters absorbed by the activated carbon are decomposed and detached from it. However, the thermal method needs the much time, energy, and costs to regenerate the activated carbon, so the used activated carbon generated in the water treatment process has frequently been disposed without being regenerated in reality. Therefore more efficient method to regenerate the activated carbon has been needed.
Dimethyl ether (DME) is an organic compound which is gas at normal temperature and pressures. DME is liquefied when it is pressurized up to approximately 0.5 MPa at normal temperature and liquefied DME has unique characteristic to dissolve both water and organic solvents . Therefore, we investigated the method to regenerate activated carbon by using the characteristic of DME in this study. Especially, both batch and flow method to regenerate the used activated carbon using the liquefied DME were investigated and the regeneration rates were evaluated.
In batch method, the regeneration rate of the used activated carbon was approximately 70% and it was confirmed that the regeneration rate was kept at 70% when the activated carbon was regenerated at least 5 times.
On the other hand, the regeneration rate of the used activated carbon was approximately 80% in flow method when the contact time between DME and the activated carbon was 300 s. Moreover, the regeneration rates did not almost change when the regeneration process was repeated at least 5 times.
Finally, we estimated the cost needed in the regeneration process of the activated carbon using DME and compared it to that needed in the process using virgin activated carbon. The estimates indicated that the cost needed in the regeneration process using DME could be decreased by at least 79% compared to that needed in the process purchasing virgin activated carbon.
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