Affordable new compost technology provides in-vessel levels of gas emission and odor control


Courtesy of Engineered Compost Systems (ECS)

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:

  • Impermeable cover
  • Negative (suction) aeration floor
  • Automated aeration control and monitoring technology
  • Biofilter

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.

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