ALTERNATIVE METHODS FOR ASSESSING BIOFILTER PERFORMANCE
Abstract:The South Coast Air Quality Management District (SCAQMD) requires affirmative demonstration of ammonia and volatile organic compound (VOC) emissions reductions by cocomposting operations (SCAQMD, 2003). Operations that compost biosolids and green wastes blends may have air emissions from pile and, if present, biofilter surfaces. Sampling these surface emissions traditionally involves the use of flux chambers (Kienbusch, 1986), an established sampling method that is expensive, cumbersome and not easily applied by inexperienced users. Additionally, the SCAQMD stipulated analysis methods for VOCs (SCAQMD, 2000) and ammonia (SCAQMD, 1993) involve expensive, off-site laboratory analyses.
This paper compares test results from alternative methods of sample collection, flow determination and ammonia analysis performed at biofilters. Sample collection methods were compared for their ability to assess biofilter surface advective flows, i.e., flows passing through a defined surface area. Dynamic (using sweep gas) emissions isolation flux chamber (EIFC) results were compared to an alternative inverted cone sampler. Comparisons of ammonia analyses by SCAQMD draft Method 207.1 versus field measurements using colorimetric tubes and a hand-held instrument were also made.
Direct velocity measurements of biofilter exhaust with the inverted cone sampler came the closest to matching the biofilter inlet flow compared to flux chamber derived measurements.
A standard EIFC design with limited venting capability was not effective where significant advective flows through porous media exist. A modified EIFC design with larger openings more closely matched the inlet flow assuming even flow distribution through the biofilter.
Both surrogate methods for ammonia consistently under predicted ammonia emissions when compared to the SCAQMD proposed method involving impingers and laboratory analysis by HPLC/IC (draft Method 207.1). Of the methods tested, the colorimetric tube was more responsive to changes in ammonia concentration and closer to draft SCAQMD Method 207.1 than the hand-held electronic instrument.
This paper recommends that further verification of the inverted cone sampler be performed. For surfaces with extremely low advective flows (surface velocity < 2 fpm or 0.01 mps), the inverted cone sampler may not offer an advantage to the standard design EIFC. Further work is needed to establish a rigorous criteria for determining the extent of the modifications needed for the flux chamber in applications where significant advective flows are present. Finally, alternatives to rigorous and expensive source tests are needed to meet maintenance and compliance demands by air regulatory agencies.
Document Type: Research Article
Publication date: 2004-01-01
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