Odor from wastewater treatment plants is an everyday challenge for utilities. Typically, utilities choose between chemical scrubbers and earthen biofilters for their odor solutions—deciding which better fits their specific requirements. Now, there is a third option: microbe-lined biotrickling filters. Although odor-eating microbes for air quality control is not a new technology, the rate at which these bugs work their magic is.
The bug of choice is the thiobacillus—small bacteria that call sewage or soil home and reduce hydrogen sulfide into odorless sulfate. In this form of a biotrickling filter, thiobacillus-covered sponges are installed in what used to be a chemical scrubber. Certain conditions, such as proper moisture, pH, temperature, and pressure, must be maintained within the scrubber to keep the microbes functioning optimally.
Considering a conversion to a biotrickling filter over chemical scrubbers or earthen biofilters for hydrogen sulfide control may be a good idea. In fact, microbes have proven to be as effective at removing hydrogen sulfide as a chemical scrubber. Use of microbes eliminates the procurement efforts, maintenance, and concern over hazardous chemicals related to scrubbers. Furthermore, biotrickling filters need about 100 times less the space than earthen biofilters need to effectively maintain air quality. Therefore, for larger, urban plants, biotrickling filters may be the answer to ever-pressing space constraints.
However, as is most often the case, the benefits of using biotrickling filters are situational. Their continued operation requires a large amount of power. Therefore, a facility's power expenses play a major role in determining if this is a cost-effective solution. Those plants that enjoy low power costs or recovered energy may have an easier time transitioning to biotrickling filters over those that incur high electricity bills. In regard to costs, chemical scrubbers tend to be more reliable and consistent over time, while earthen biofilters are often the least expensive option possible. As such, different facilities must consider their own factors in the equation when developing future air quality strategies. The difference now, though, is that biotrickling filter use will be in the mix of choices and stands as a viable means for air quality control.
Bob Gaudes, vice president and CDM's technology leader for odor and VOC control, specializes in managing air emissions projects and developing expertise in emerging technologies and their applications.