August 2009, Vol. 21, No.8

Research Notes

Nanocomposite Adsorbent Found To Treat Dyes in Wastewater

Textile, paper, leather, dye processing, molasses, and plastic industries that use dyes to color their products produce wastewater containing dyes that are resistant to microbial and chemical degradations and can be converted into toxic or carcinogenic compounds. This industrial wastewater can be treated using nanotechnology, according to a report from the Indian Institute of Technology Madras (Chennai, India) describing new nanotechnology designed to treat this wastewater.

The Indian Institute of Technology Madras filed for a patent for nanotechnology that uses a nanocomposite adsorbent to treat this wastewater. Sundara Ramaprabhu, a professor in the institute’s Alternative Energy and Nanotechnology Laboratory and Department of Physics, led the research for this nanotechnology. He found three different hybrid nanocomposite adsorbents that can be used to treat dye, textile, leather, and molasses industrial wastewaters, the executive summary of the report says.

For the nanotechnology, selective functional groups of nanomaterials are attached to the surfaces of other different dimensional nanomaterials to absorb the dye molecules. The nanocomposite groups include nanometal, nanometal-oxide materials, or both.

“The nanocomposite adsorbents result in the complete removal of organic [and] inorganic molecules and color and odor from industrial wastewaters so that the purified water can be reused,” Ramaprabhu said. The new patent-pending technology shows the ability of three different nanocomposite adsorbents to absorb color, trap gas molecules and odor, and completely remove the dye molecules from the wastewater stream, according to the report.

In addition, the nanocomposite adsorbent does not release any of the dye molecules when allowed to react with the wastewater, and it can be reactivated by selective fluid treatment, the report says. “Wastewater absorbed nanocomposite adsorbent can be reactivated by simple suitable fluid treatment,” Ramaprabhu said.

The process was tested on effluent from the tannery and textile industries and on wastewater from the leather and molasses industries using different nanocomposites. Studies for the new nanotechnology finds that use of the nanocomposites can be a suitable alternative to current treatment methods, the report says.

The nanocomposite adsorbents would be inexpensive because they are made up of about 90% graphite, and the remaining portion is made up of nanometal, nanometal-oxide, or both, and carbon-based materials. The process could be changed to treat wastewater from other industries or clean polluted water supplies. 

Tracking Methylmercury in Pacific Waters

Scientists studying mercury levels in the Pacific Ocean have published a study identifying the source of
methylmercury, a particularly toxic form of mercury, according to a news release from the U.S. Environmental Protection Agency (EPA).

The study cites biological decomposition by bacteria as the producer of methylmercury. The study also models mercury cycles in the Pacific, compares past and present levels, and predicts future levels.

Though the danger in consuming mercury has been known for some time, the process behind the creation of methylmercury has until now been a mystery. Previous explanations gave methylmercury a geologic origin. However, this recent study points to a biological process as the likely cause.

Mercury methylation begins when surface algae die and begin to sink to deeper waters, a process known as “ocean rain.” At greater depths (200 to 700 m), bacteria decompose the dead algae. This decomposition in the presence of mercury inadvertently creates methylmercury, the news release says.

The scientists tracked the circulation and methylation of mercury from 16 hydrographic stations between Honolulu and Kodiak, Alaska, according to the news release.

“It appears the recent mercury enrichment of the sampled Pacific Ocean waters is caused by emissions originating from fallout near the Asian coasts,” said co-author of the study and U.S. Geological Survey scientist David Krabbenhoft. “The mercury-enriched waters then enter a long-range eastward transport by large ocean circulation currents.”

The study also noted that mercury levels in the North Pacific have risen 30% since the mid-1990s. Furthermore, the researchers created a model which predicts a 50% increase in mercury levels in the Pacific by 2050, based on mercury emissions projections, transport and deposition, and ocean circulation models.

The study is the first to link atmospheric mercury emissions to methylmercury levels in marine life. Rising future mercury levels could have hazardous consequences for methylmercury concentrations.

©2009 Water Environment Federation. All rights reserved.