Pilot Study for the Applicability of Biofilter Odor Control Technology for use at New York City Water Pollution Control Plants
Throughout the New York City Department of Environmental Protection (NYCDEP) wastewater treatment system, chemical scrubbers and/or carbon adsorption units have typically been used to treat odorous air emissions. Although these are adequate methods to remove Hydrogen Sulfide (H2S)
and Volatile Organic Compound (VOC) constituents that compose malodorous emissions, the need for simpler, more economical, and environmentally-friendly technologies has come to light.
Preceding major upgrades of the Jamaica Water Pollution Control Plant's odor control system scheduled
to be implemented by 2012, NYCDEP has authorized this Pilot Program utilizing Biofilter technology at the Jamaica plant. The Jamaica Biofilter Pilot Program allows the opportunity to demonstrate the applicability of Biofilters within the rigid NYCDEP wastewater treatment system, proving their
efficiency and cost effectiveness. Future odor control upgrades at Jamaica must provide sufficient treatment to maintain adherence to the New York State Department of Environmental Conservation's regulatory requirement of less than 10 ppb of H2S at the fenceline of the plant
and also NYCDEP guidance that requires less than 1 ppb of H2S at sensitive receptors.
Previous studies of H2S emissions at wastewater treatment plants has shown that the major source of H2S emissions in wastewater treatment is the effluent weir section of
the of the primary clarifier tanks. This is due to the large concentration of reduced sulfur compounds produced within the sludge beds of the clarifier tanks that is then released as H2S when turbulence exposes the sulfur compounds to air allowing the gas to then escape. The outfall
of the effluent weirs is the primary location of this release. For this Pilot Program, the effluent weir section of one primary settling tank at the Jamaica WPCP has been isolated, drawing the odorous air into the Biofilter unit. H2S levels under these tank covers were monitored
in the fall of 2006 and have found an average concentration of 0.5 parts per million (ppm) and a peak concentration of 4.2 ppm H2S.
Based on the amount of airflow expected from this weir section and the target removal efficiency, the Biofilter unit was sized at 600 cubic feet
of organic media. This size unit provides approximately 60 seconds of Empty Bed Contact Time (EBCT). Based on previous studies, this retention time should allow for 99.5% removal efficiency of H2S plus substantial removal of VOC's as well although VOCs were not targeted
for performance criteria.
The Pilot was in operation for one year. As part of the sampling protocol, two rounds of testing were conducted: one in summer, one in winter. This sampling was conducted to verify that the biofilter has the ability to meet strict removal criteria for both hydrogen
sulfide (H2S) and dilutions-to-threshold (D/t) of Total Odor. The criteria are as follows:
Hydrogen sulfide: minimum 99.5% removal or 0.025 ppm H2S maximum outlet concentration.
odor: D/t ≤ 350, or 350 ≤ D/t ≤ 500 with a neutral or positive hedonic tone.
Sampling consisted of 2 days of H2S grab-samples, 7 days of continuous logging of inlet and outlet H2S and 2 days of bag sampling to be analyzed
by an odor panel. All scheduled sampling events for the Jamaica Biofilter Pilot Project have concluded. The hydrogen sulfide removal efficiency met the 99.5% criterion for both grab samples and continuous monitoring. In addition, all outlet D/t were less than 350, also meeting the
sampling criterion. Summarized results from both the summer and winter sampling events are delineated below.
H2S removal efficiency was taken from the results of the 7-day continuous logging of the biofilter inlet and outlet. The averaged inlet concentrations and the averaged
outlet concentrations over this period were used to determine the average removal efficiency. Total Odor analysis was provided by St. Croix Sensory of Minnesota.
Summer Sampling Results:
Average H2S Grab Sample Removal
Efficiency – 99.73%
Average H2S Continuous Sample Removal Efficiency – 99.72%
Average Outlet Total Odor – 145 D/t
Average H2S Grab Sample Removal Efficiency – 99.71%
Average H2S Continuous Sample Removal Efficiency – 98.32%
Average Outlet Total Odor – 127 D/t
It should be noted that for most of the sampling period, the outlet data logger did not record a detectable H2S concentration. The minimum threshold limit for the device
is 0.01 ppm. Because of this, outlet concentrations that weren't detected were assumed to be 0.005 ppm (half the detection limit) to be conservative when calculating removal efficiency. The higher average inlet concentration during summer sampling (<4.0 ppm) led to greater removal
efficiencies when using 0.005 ppm as an outlet concentration for non-detect readings. The biofilter performed as well, if not better when considering total odor, during winter sampling but the lower average inlet concentrations led to an overall lower removal efficiency calculation due to
the conservative outlet assumption.
The results of both sampling events show that the biofilter is performed exceptionally well and exceeds all criteria for removal efficiencies of H2S and total odor.
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