People living near wastewater and sewer treatment plants often complain about the odors that emanate from them. Now some of those plants are becoming better, less odiferous neighbors. The FRP biotrickling filters (BTFs) supplied by California-based Daniel Company are helping to eliminate noxious odors in an environmentally friendly way by capturing fugitive emissions and putting them through biological air scrubbers.
The wastewater treatment process releases hydrogen sulfide and other volatile organic compounds that can be poisonous in high concentrations and that have a very distinct, unpleasant smell. Treatment plants in Europe have been using BTF-type technology for many years, but it’s only during the last five to 10 years that it’s been embraced by U.S. facilities.
“In the past, wastewater treatment facilities in the U.S. have used reagents – a combination of sodium hydroxide and sodium hypochlorite – in what is called a wet pack tower,” says Tim Malki, Daniel Company president. These chemicals break down the odorous compound hydrogen sulfide in the emission into free hydrogen and free sulfur elements. Wastewater treatment plants may also use carbon to absorb volatile organic compounds (VOCs). Both processes require the storage and use of large quantities of chemicals and activated carbon.
“These systems are not necessarily eco-friendly,” says Malki. “So what’s been developed in Europe is a means of using a bio-organism called Thiobacillus bacterium that’s found in great proliferation throughout the wastewater treatment plant. The strain feeds on hydrogen sulfide and some other long-chain reduced sulfuric compound, breaking them down with very little byproducts.” Daniel Company’s BTF system creates a small ecosystem inside an FRP vessel filled with a special media in which the Thiobacillus bacterium thrives.
Europe was an early adopter of the micro-organism treatment system because it made economic sense; the chemicals required for treatment plants are very expensive there. In the United States, however, plants did not use this type of filter in a vapor phase application because they could obtain chemicals at a lower cost.
But things have changed in recent years. “People have become more and more cognizant and sensitive to minimizing their environmental footprint, and the price of chemicals has gone up,” says Malki. “Plus, the storage of chemicals has become more of an ordeal.” Environmental regulations and community perceptions also have altered the way that odiferous discharges are handled. In remote parts of the country, treatment plants previously would vent emissions into the atmosphere with minimal treatment. That is no longer acceptable. So the biotrickling filter provides a way that plants can treat the discharge in a cost-effective, environmentally responsible way.