A sample of potassium dichromate, also known as the mineral lopezite. About 10 mm long, probably synthetically grown. (Credit: A13ean, http://commons.wikimedia.org/wiki/User:A13ean)
Sumitomo Heavy Industries, Ltd., in collaboration with the National Institute for Environmental Studies, Japan, successfully developed an organic wastewater treatment process at ambient temperatures that is based on methane fermentation. When this technology is put into practical implementation it will be the world’s very first case example.
The wastewater discharged by domestic industries in Japan amounts to approximately 11.1 billion tons and most of it is comprised of organic effluent that includes a relatively low concentration of organic matter. The majority of such wastewater is currently treated using a method referred to as aerobic biotreatment (known also as the activated sludge method). According to the press-release, issues of this method include the consumption of large amounts of electric power and the production of excessive activated sludge in copious quantities. Such produced volumes can be significantly reduced using the methane fermentation process however the process has not been widely adopted since the wastewater for treatment has to contain medium to high concentration of organic matter and because this method can only be applied with lukewarm liquids at medium temperatures.
The recently-developed technology can treat wastewater with low concentrations of organic matter and facilitates the treatment of methane fermentation in ambient temperatures. This not only extends the range in which the method can be applied but also enables a reduction in operating energy of about 75% in comparison with the conventional activated sludge organic wastewater treatment process. The development is expected to move into evaluations of the validation performance, aiming for practical implementation in the future. Practical implementation is expected to be achieved within one to two years at the earliest and this can potentially become the world’s very first case example.
According to the developers of the technology, treatment can be applied to low concentrations of organic matter in wastewater and also at ambient temperatures. Conventional methane fermentation treatment can only be applied to effluent containing organic matter at concentrations of 2 to 20 grams CODCr/L and only at temperatures between 35 and 37°C. The recently developed technology can be applied to effluent containing organic matter at concentrations of about 0.3 to 1 g CODCr/L (see footnote) and also at ambient temperatures (10 to 25°C). Most sewage corresponds to these conditions.
In environmental chemistry, the chemical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water. Its value is expressed in milligrams per liter (mg/L) and represents the amount of oxygen consumed when organic matter in water is oxidized by an oxidant. This value is used to represent the level of contamination in an aquatic environment and also used as a water quality standard or environmental standard. Among derivative values, CODCr involves a method that uses potassium dichromate, K2Cr2O7, a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications.The activated sludge method, which is currently the mainstream treatment, requires a large amount of energy for aeration operations (supplying oxygen in water to activate microbes) and excess activated sludge treatment. Aeration is not required with the methane fermentation treatment and smaller amounts of excess activated sludge are produced, therefore the operating energy required for the new organic wastewater treatment process in an experiment was reduced by about 75%. Furthermore, it is also possible to dramatically reduce expenses for treating excess activated sludge.
