Development of Reduction Decomposition Treatment Technique for Nitrates in Wastewater
(Joint Program to Promote Technological Development with the Private Sectors)

RITE - WAKAMATSU NO.2 LABORATORY in Catalysts & Chemicals Industries Co., Ltd

The environmental problems of red tides, algal blooms etc caused by eutrophication of enclosed water bodies have long been recognized. We are aiming to contribute to the reduction of global environmental load by eliminating one of the causes which is the nitrates in industrial wastewater. This research aims at using catalysts and hydrogen to reduce highly concentrated NO3-N to N2 and then separate the catalyst from the reaction solution in a “Catalyst Recycling Process”.

In 2002, 2003 fiscal years we gathered basic information on the effects of various NO3 concentrations, types and amounts of catalysts, methods of mixing, ways of providing hydrogen, as well as the effects of ceramic filters etc. In addition, we investigated the life-span of catalysts and the prevention of exchange of nitrate nitrogen to the by-product ammonia. We also set up a pilot plant and compared this with our laboratory. NO3 reduction took approximately twice the time it took in the laboratory and we could see that the conversion to ammonia was much greater than that found in the laboratory. The capability of non-calcined catalyst was also found to deteriorate in an extremely short period of time. In the 2004 fiscal year we found that Pd, Cu-C (Carbon)-type catalysts only lasted for one month even when calcined due to the elution of Cu in particular. As we were forced to cease the use of carbon-type catalysts due to their flammable and explosive nature in the presence of oxygen, we turned to a Pd, Cu-Z (Zeolite)-type catalyst. This catalyst has a long life-span with results of over 3000 hours being achieved in the laboratory (life-span tests are continuing). In the reaction tests in the pilot plant, we could see that reaction time per unit weight of NO3 is shorter for higher concentrations of NO3. In addition, there appears to be a relation between speed of H2 supply and treatment time. When treating a solution with 400 ppm N with an H2 supply speed of 10 m³/h, 4 times the necessary amount of hydrogen (6.4m³) is necessary and treatment is finished in 2.5 hours. Where hydrogen supply speed is 2 m³/h, only 1.1 times the amount of hydrogen is needed, however treatment takes 5.2 hours to complete.

We plan to research ways to reduce the amount of conversion to ammonia and reuse catalyst as well as industrialize the process in 2006.