Increasingly stringent air-emission regulations and demands to better control odors has put an economic strain on industries that recycle large amounts of organic materials, such as compost facilities, dairies, and feedlots. ECS has recently introduced an affordable composting technology to greatly improve facility compliance and odor control. This technology is the AC Composter™.

Air Quality Issues

National and state air quality standards are bringing increased scrutiny on composting facilities (see Appendix I for a more complete discussion). While this is especially true in so-called “nonattainment” areas where Federal clean-air standards are frequently not met, it also holds for areas with more pro-active regulations as well. These regulations are already quite restrictive in some places, and the trend is toward increasing emission control requirements nationwide.

Odor Issues

Compost facilities across North America have been closed due to nuisance odors crossing property lines and beyond. Many of these facilities operated for years before their rural buffer zones were replaced by housing developments, hobby farms, or commercial enterprises. Most of these facilities were open air type (windrow, giant piles or ASP) with little or no odor control technology. The threat of closure has forced permitting agencies, banks, and facility owners to put odor control at the top of the facility design requirements. The traditional methods used to contain (enclose) and control odors universally pushed up the costs of facilities. So much so, that numerous planned facilities “didn’t pencil” and were never been built.

Traditional Approach for Controlling Odors & Air Emissions

Controlling compost emissions is done by enclosing process and/or capturing air. Enclosing the process is done with buildings and/or with in-vessel technology. ECS and others have successfully implemented these methods at numerous facilities feedstocks such as biosolids and source separated organics. However the precludes them from being widely adapted. The open-pile in-building approach, capital cost advantages over in-vessel methods, has other draw backs. These building ventilation rates required to meet health and safety requirements unusual); in-building facilities need large air handling systems, water hungry biofilters with comparable footprints to the compost piles themselves.

AC Composter™

For years ECS has designed and built traditional in-vessel and ASP systems. But as the concern for emissions has grown, we have received more inquiries from compost facility designers and operators whose business model would not support traditional enclosed approaches. With this incentive ECS set out to develop a technology with in-vessel like emission capture efficiencies, but at a greatly reduced system cost. In the spring of 2007 ECS introduced the AC Composter™ (patent pending), a covered ASP system that has achieved these design goals.

The AC Composter™ (shown in detail in Appendix II) is designed to control both the VOC’s and the NH3 emissions from the compost pile and captured in the process exhaust gas stream. It has four major components:

The cover is made of a fabric that is impermeable to both VOCs and NH3. This fabric is medium weight, highly UV resistant, and readily repaired in the field. The cover has single-direction air ports that allow continuous aeration of the biomass under negative aeration. The result is an enclosed compost pile with near zero fugitive emissions from the surface, and relatively small volume of process exhaust air that can be effectively scrubbed.

The AC Composter™ has the added advantages (over an open and standard ASP) of significantly reducing O&M costs; and, facility footprint. In traditional aeration system design large air flow volumes are used to control pile temperatures and maintain Oxygen levels at or above 16%. This approach minimizes odor generation within the pile, but requires a large mechanical system with significant energy costs and a commensurately sized biofilter. The high capture efficiency of the AC Composter means that these traditional design constraints don’t apply to odor control. Our results show that slightly slower biodegradation rates (due to higher temperatures and lower Oxygen levels) are easily outweighed by vastly improved moisture control, lower energy costs, and a much smaller biofilter.

AC Composter™ Installations

The AC Composter was put into large scale operation in Washington State in April of 2007, and is currently in pilot scale operation in Wyoming, Texas, and California. In Washington State, regulators with the Olympic Region Clean Air Agency (ORCAA) granted the AC Composter™ an emission capture rate of 100% (based on SCAQMD data – Appendix I), along with the BACT standards of 80% control efficiency for biofilters.

In California ECS has teamed with Cal State University in Fresno, through a USDA SBIR grant, to study the efficacy of the AC Composter™ at controlling emissions while stabilizing manure for use as bedding and compost. The trials are taking place at CSUF’s research dairy facility. Air emissions from the system are being measured by the experts from the College of Agricultural Sciences and Technology, Air Quality Lab. This data will be used to determine compliance visà- vis BACT. The Phase I research is scheduled to be completed by January 2008. Initial data has demonstrated a high capture rate and good process outcomes.

Appendix I - Air Quality Issues and Their Impact on Compost Facilities

Nationwide, regional air control districts have enacted tighter air-emission regulations to respond to the federal Clean Air Act and to improve ozone standards. The Environmental Protection Agency has identified the counties that are not attaining air-quality standards for Ozone and fine particulates (PM). Many of these counties center on large urban areas with impacted zones that stretch into surrounding countryside.

California

California seems to be the leader in setting and implementing air quality standards. The San Joaquin Valley (SJV) is one region whose air quality meets neither federal nor state standards for ozone emission control. Composting operations in the San Joaquin Valley Air Basin emit an annual estimated 511 tons of volatile organic compounds (VOC) which are an Ozone precursor (Source: San Joaquin Valley Unified Air Pollution Control District, 2005). The San Joaquin Valley Air Basin has been charged under the federal Clean Air Act to attain new 8-hour standards for ozone by 2013. (This date subject to an on-going debate).

New compost facilities in the SJV are now required to reduce projected criteria pollutants (including VOCs) emissions, and existing facilities will likely need to be in compliance in the near future. The SJVAPCD boards use the anticipated criteria pollutants emitted as the basis of their permitting process. In cases where the proposed facility is not an accessory to agricultural operations, it is subject to offset requirements according to the New Source Review Rule. Offset thresholds are currently set at 10 tons of emissions per year. Compost facilities whose annual emissions exceed this limit may be required to pay for proportional “pollution offsets”. A relatively modest sized open-air compost facility (approximately 11,250 tons per year) would exceed this limit. There is a clear incentive to implement improved control and capture
technologies.

If a proposed composting project is subject to the California Environmental Quality Act (CEQA) process then ideally a facility it could be granted a finding of “No-Significance” if calculations show a discharge of less than 10 tons per year of non-methane VOCs. (Note: each air district can have different standards for significance - for example, L.A. is a 55 pounds per day.) With such a finding a facility is not required to produce a costly and time consuming Environmental Impact Report (EIR) and submit to a relatively complicated public review process.

The emission volumes are calculated using factors and capture and control efficiencies established by the South Coast Air Quality Management District (SCAQMD) Rule 1133 for co-composting facilities. The emission factors baselines are 1.78 pounds of VOC and 2.93 poundsof ammonia per each ton of waste accepted by the facility. The baseline capture and control efficiencies are based on BACT (best available control technologies), and BACT varies with the composting and air-scrubbing technologies employed. For open aerated static piles (ASP’s) the capture rates are 25% and 33% for positive and negative aeration, respectively. In-vessel systems are credited with 90-100% capture rates. The BACT standards grant 80% control efficiency for biofilters used to scrub the captured air-stream.

These regulations have serious implications for compost operators and large-scale farmers that want to recycle the nutrients produced on their farms.
After evaluating the cost of regulatory upgrades against revenue models, many planned facilities never leave the drawing board. Some facilities that have been in the planning for years—such as L.A. County Sanitation’s Westlake Farms—continue to watch costs go up, in part due to the evolution of regulations that require higher levels of capture and control, and the purchase of pollution offsets. There is clearly a need for a cost effective means of meeting these regulations.

Washington


In Washington the Department of Ecology and the Regional Air-Pollution Control Districts have regulations for limiting emissions; and, new compost facility permit applicants are required to calculate total VOC and NH3 discharge levels based on SCAQMD BACT standards.

If the discharge levels of the proposed facility exceed the high limits, regulations can restrict the facility throughput, with the possibility of making it not viable economically.

For example, recently ECS was asked to calculate discharge levels for a Client facility located in Washington, based on SCAQMD standards. The BACT were based on several existing compost facilities, all with different feedstocks and processes. In performing the calculations, ECS notes choosing BACT standards for facilities with similar feedstocks and process is essential.

The calculations began with determining the total pile surface area of the facility, including planned future expansions; and applying the NH3 emission rate for a static pile from the SCAQMD data. (NH3 was used as the most likely containment most likely to exceed threshold limits.) Since the Client facility used the ECS AC Composter™ with impermeable ASP covers and with continuous negative aeration, the collection (capture) of the NH3 was assumed to be effectively 100%. (Open positive and negative ASP are less than 33%.) Using the 78% NH3 destruction rate in the biofilter sited by the Regional Air District, the resulting estimate for annual pounds of NH3 emitted to the atmosphere was well under the limit of 17,500 pounds/year (SQER), and the facility was granted necessary permits to proceed.

Appendix 2: How the AC Composter™ works

A full sized AC Composter (patent pending) has been in operation since April of 2007 at the Silver Springs Organics (SSO) Facility in Tenino Washington (1.5 hour drive from Seattle). The Phase I installation has 24 separately aerated and controlled zones (piles) and processes about 7,000 tons of source separated organics per month.

One of the largest technical and cost hurdles, especially in a negatively aerated system, is the aeration floor. At SSO the AC Composter was implemented with the new patent-pending ECS pipe-less aerated floor technology—known as the CompDogTM. This design provides a well distributed air-flow under the pile, a clean surface for the front-end loaders when breaking down the piles, and does not require expensive below grade pipes or cast-in trenches; and, it works on any approved and flat surface. The CompDog avoids the limitations and risks found when using unwieldy above grade aeration pipes.

Building the Pile

In preparation for receiving raw compost, two CompDogs are placed stretched to full length in the zone, inflated, and connected to the aeration header. The wheel-loader then builds a pile over them. The pile is allowed to settle 12-24 hours. Then the CompDogs are deflated, and retrieved from under the pile using a powered spool. The pile retains the inflated vault shape of the CompDogs under its entire length.

The aeration vaults are connected to the negative aeration system through a push-wall located at the end of the zone. At the front end the vault is plugged with a small amount of material, the AC Cover is then placed over the entire pile. Two temperature probes are inserted through ports in the AC Cover to provide feedback for the automated aeration control and monitoring system.

Active Composting

During composting, fresh air is drawn through the air inlets in the AC Cover to provide oxygen to the biomass. The air is pulled through the biomass and into the vault,via a modulating damper, and into above-ground stainless steel aeration plenums. The aeration plenums deliver the process air to biofilters. When necessary, the control system automatically adds fresh air to cool process air and keep it below 40°C to prevent overheating the biofilters.

Damper position and fan output are automatically controlled by the ECS CompTroller™ system. The operator's software monitors the process, to record time/temperature data files for regulatory compliance, and to input process settings used by the automatic controls. Real-time technical support is available via Web access. CompTroller™systems are in operation at dozens of facilities in N. America.