Biological Air Emissions Control for an Energy Efficient Forest Products Industry of the Future

Abstract

The U.S. wood products industry is a leader in the production of innovative wood materials. New products are taking shape within a growth industry for fiberboard, plywood, particle board, and other natural material-based energy efficient building materials. However, at the same time, standards for clean air are becoming ever stricter. Emissions of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) during production of wood products (including methanol, formaldehyde, acetylaldehyde, and mercaptans) must be tightly controlled. Conventional VOC and HAP emission control techniques such as regenerative thermal oxidation (RTO) and regenerative catalytic oxidation (RCO) require significant amounts of energy and generate secondary pollutants such as nitrogen oxides and spent carbon. Biological treatment of air emissions offers a cost-effective and sustainable control technology for industrial facilities facing increasingly stringent air emission standards. A novel biological treatment system that integrates two types of biofilter systems, promises significant energy and cost savings. This novel system uses microorganisms to degrade air toxins without the use of natural gas as fuel or the creation of secondary pollutants. The replacement of conventional thermal oxidizers with biofilters will yield natural gas savings alone in the range of $82,500 to $231,000 per year per unit. Widespread use of biofilters across the entire forest products industry could yield fuel savings up to 5.6 trillion Btu (British thermal units) per year and electricity savings of 2.1 trillion Btu per year. Biological treatment systems can also eliminate the production of NOx, SO2, and CO, and greatly reduce CO2 emissions, when compared to conventional thermal oxidizers. Use of biofilters for VOC and HAP emission control will provide not only the wood products industry but also the pulp and paper industry with a means to cost-effectively control air emissions. The goal of this project was to demonstrate a novel sequential treatment technology that integrates two types of biofilter systems – biotrickling filtration and biofiltration – for controlling forest product facility air emissions with a water-recycling feature for water conservation. This coupling design maximizes the conditions for microbial degradation of odor causing compounds at specific locations. Water entering the biotrickling filter is collected in a sump, treated, and recycled back to the biotrickling filter. The biofilter serves as a polishing step to remove more complex organic compounds (i.e., terpenes). The gaseous emissions from the hardboard mill presses at lumber plants such as that of the Stimson Lumber Company contain both volatile and condensable organic compounds (VOC and COC, respectively), as well as fine wood and other very small particulate material. In applying bio-oxidation technology to these emissions Texas A&M University-Kingsville (TAMUK) and Bio•Reaction (BRI) evaluated the potential of this equipment to resolve two (2) control issues which are critical to the industry: • First, the hazardous air pollutant (HAP) emissions (primarily methanol and formaldehyde) and • Second, the fine particulate and COC from the press exhaust which contribute to visual emissions (opacity) from the stack. In a field test in 2006, the biological treatment technology met the HAP and COC control project objectives and demonstrated significantly lower energy use (than regenerative thermal oxidizers (RTOs) or regenerative catalytic oxidizers (RCOs), lower water use (than conventional scrubbers) all the while being less costly than either for maintenance. The project was successfully continued into 2007-2008 to assist the commercial partner in reducing unit size and footprint and cost, through added optimization of water recycle and improved biofilm activity, and demonstration of opacity removal capabilities.