BIOFILTRATION OF HIGH-STRENGTH EXHAUST FROM BIOSOLIDS COMPOSTING: LESSONS LEARNED AND DEMONSTRATION OF SUCCESSFUL TREATMENT

Solid Waste Authority of Palm Beach County
Palm Beach County, Florida

The Solid Waste Authority of Palm Beach County, Florida, operates an in-vessel composting
facility that processes 30 dry tons/day of dewatered biosolids combined with shredded yard
waste. The facility consists of 36 aerated agitated bays in three buildings supplied by
International Processes Systems (Now Siemens Water Technology). All exhaust air from the
buildings is treated in three 60,000 cfm biofilter cells. New biofilter cells were commissioned in
December 2002. Design and construction included some innovative features including: use of
locally available limestone for the support plenum, use of locally available finely ground bark
mulch in the media, a pre-humidification system with air-atomizing nozzles, clean-outs for every
perforated lateral, and a fast-track design-build method of delivery.
After start-up the well water used for humidification caused rapid scaling of the laterals, due to
the high mineral content and high evaporation efficiency. Pre-humidification was discontinued
while a water softening and deionization system was under consideration. Since then the filters
have been operated only with surface irrigation. The most recent rounds of performance testing
have indicated that surface irrigation, combined with rainfall, were sufficient to maintain optimal
moisture content throughout the full depth of media. Without pre-humidification, the irrigation
distribution pattern is critical.
The filters have been periodically tested for odor and ammonia removal, most recently in 2006
and scheduled again for 2007. The filter media in the different cells have been in continuous use
for 2.6 to 3.1 years. Typical inlet conditions were:
􀂃 Temperature: dry-bulb range 96-105 deg. F. wet-bulb range 86-92 deg F.
􀂃 Ammonia: 22 – 40 ppm
􀂃 Hydrogen sulfide and methyl mercaptan: neglible or non-detect
􀂃 Odor concentration: 1,500 – 2,400 D/T, using the prEN 13725 olfactometry standard.
The biofilters have consistently removed 100 % of ammonia and 93 – 98 % of odor with outlet
odor concentrations in the range of 66 to 86 D/T. Thus, the biofilter is showing highly effective
performance, despite the high temperature and moisture deficit in the inlet air. As a result, the
composting facility is no longer a significant source of off-site odors.
Ammonia is an alkaline gas and there little acid gas present. The media has a pH in the range of
4.8 – 6.8. The acidic pH indicates that alkalinity is being consumed as a result of nitrification. A
nitrogen mass balance indicated that the biofilters are operating in steady state rather than
accumulating nitrogen, and that nitrogen leaves the biofilters by way of leachate and
denitrification. Denitrification was demonstrated by the detection of nitrous oxide. Nitrous oxide
is of increasing interest due to its effect as a greenhouse gases.

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Posted: May 3rd, 2011 | Filed under: Uncategorized | Tags: Biofiltration, Reduced Air Pollutants, Reduced Greenhouse Gas Emissions, Reduced Odors | 1 Comment »

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