Orange County Sanitation District
Orange County, California
Major sources of emissions at a wastewater treatment plant typically include combustion sources
(internal combustion engines, boilers, flares, emergency diesel generators and turbines). At the
two wastewater treatment plants owned and operated by the Orange County Sanitation District
(OCSD), natural and digester gas-fired internal combustion (IC) engines are the major emitters
of toxic air contaminants (TACs). Plant 1 has three, 2.5 megawatts (MW) IC engines and Plant 2
has five, 3 MW IC engines. The IC engines are fueled primarily by digester gas and
supplemented by natural gas. TAC, namely formaldehyde, emitted by the IC engines was found
to be the major contributor to health risk to neighborhood residents and businesses.
In order to address compliance with California Air Resource Board (CARB) and South Coast Air
Quality Management District (SCAQMD) air toxics regulations, a facility wide health risk
assessment was performed. The results of the risk assessment determined formaldehyde from
the IC engines as the major contributor to the facilities’ health risk to surrounding communities.
Therefore, control of the air toxics from the gas-fired IC engines would result in the greatest
reductions in risk levels from both plants.
Alternatives for reducing emissions from the gas-fired IC engines were identified and evaluated.
Two alternatives to reduce the health risk levels at Plant 1 and Plant 2 were pilot tested: 1) Precombustion
chamber (PCC) timing and air-to-fuel control optimization for pilot gas system; and
2) post combustion control using a catalytic oxidizer. The purpose of the pilot testing program
was to evaluate the long term effectiveness of the proposed alternatives and to determine the
technical and economic feasibilities of the alternatives for reducing air toxics emissions. This
paper presents results of an emission evaluation for IC engines, the health risks, and details of the
pilot testing programs.
Posted: May 3rd, 2011 | Filed under: >1M, Sanitary Sewer, Waste Water Treatment | Tags: Air-to-Fuel Control Optimization, Reduced Air Pollutants, Reduced Emissions, Reduced Formaldehyde Concentrations, Reduced Health Risk, VOC Reduction | No Comments »
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.
Posted: May 3rd, 2011 | Filed under: Uncategorized | Tags: Biofiltration, Reduced Air Pollutants, Reduced Greenhouse Gas Emissions, Reduced Odors | 1 Comment »
In this paper, the results of the process of designing, installing and commissioning the
full-scale biofilter systems will be discussed. All of the biofilter system utilized an
inorganic synthetic media. The objective of this paper is to emphasize major pitfalls in
specifying full-scale biofilter systems, wherein the impact of inlet concentration on
treatment efficiency is often ignored, and simultaneous treatment requirements of exit
odor levels as well as treatment efficiencies for hydrogen sulfide and each of the major
reduced sulfur compounds are required to be met by the full-scale system. The major
differences between the performances of a biofilter, thermal oxidizer and chemical
treatment systems will be discussed, with special emphasis on correctly specifying
biofilter systems to meet the goals of odor control at a wastewater treatment plant.
Posted: May 3rd, 2011 | Filed under: Uncategorized | Tags: Improved Installation and Operation for Biofiltration, Increased Efficiency, Reduced Air Pollutants, Reduced Odors | No Comments »
Santa Clara Valley Water District
San Jose, California
The Santa Clara Valley Water District (District), the primary water agency for Santa Clara
County, which encompasses the southern part of the San Francisco Bay, provides water supplies
for an expanding urban population containing 1.8 million resident, hosting 200,000 commuters,
and harboring Silicon Valley, a major economic driver for California.
To help meet increasing water demands, the District has developed a comprehensive suite of water
conservation and water recycling programs that have resulted in cumulative savings of 427,000
acre-feet (AF) of new water supplies between fiscal year (FY) 92-93 and FY 06-07. In addition to
saving water, water conservation and water recycling programs save energy and reduce air
pollutant emissions due to the significant quantities of energy required (and air pollutants
generated by energy production) for the water supply chain: 1) Water conveyance; 2) Water
treatment; 3) Distribution; 4) End use; and 5) Wastewater treatment.
Air pollutants generated include (depending on energy source) the following: reactive organic
gases, sulfur oxides, nitrogen oxides, particulate matter, and carbon dioxide. The latter is a greenhouse
gas that contributes to global warming.
The climate changes and other impacts that occur as a result of global warming present challenges
for water agencies. Sea level rise (including saltwater intrusion into the freshwater San Francisco
Bay-San Joaquin Delta levee system), a decrease in snow pack in the Sierra Nevada mountain
range (which supplies water for much of the state), and increased drought are all possible outcomes
of global climate change. The District is committed to responding to these challenges through
adaptation (preparing for future changes) and mitigation (reducing the District’s role in global
warming through more efficient use of resources).
With regard to the mitigation of global climate change, the District recently completed an analysis
of the energy saved by its water conservation and water recycling programs, which have been in
operation since FY 92-93. For FY 92-93 through FY 06-07, the District has saved approximately 1.62
billion kilowatt-hours (kWh) of energy, which represents a financial savings of approximately $208
million and is equivalent to the annual electricity required for 236,000 households. Through saving
energy, the emissions of approximately 381 million kg of carbon dioxide, a greenhouse gas, were
eliminated, which is the equivalent of removing 82,000 passenger cars from the roads for one year.
Posted: August 24th, 2010 | Filed under: >1M, Waste Water Treatment, Water Treatment | Tags: Cost Savings, Energy Savings, Increased Plant Efficiency, Reduced Air Pollutants, Reduced Carbon Footprint, Reduced Greenhouse Gas Emissions, Water Conservation, Water Recycling | No Comments »