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.

National and state air quality standards are bringing increased scrutiny on composting facilities. While this is especially true in designated “non-attainment” areas where Federal clean-air standards are not met, it also holds for areas with more pro-active regulations as well.

These regulations are already quite conservative in some places, and the trend is toward increasing emission control standards nationwide.

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 or giant static piles) 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 and control odors universally pushed up the costs of facilities. So much so, that numerous planned facilities “didn’t pencil out” and were never built.

Controlling compost emissions is done by enclosing process and/or capturing exhausted process air. The enclosing process is done with buildings and/or with in-vessel technology.

Engineered Compost Systems (ECS) and others have successfully implemented these methods at numerous facilities for higher-revenue feedstocks such as biosolids and source-separated organics. However, the cost of these approaches precludes them from being widely adapted.

The open-pile in-building approach, which can have capital cost advantages over in-vessel methods, has other drawbacks. These include the high building ventilation rates required to meet health and safety requirements (10 ACH is not unusual); in-building facilities need large air handling systems, water-hungry scrubbers, and biofilters with comparable footprints to the compost piles themselves.

ECS has developed the AC Composter 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 and a biofilter.

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.

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

In Washington State, regulators with the Olympic Region Clean Air Agency (ORCAA) granted the composter an emission capture rate of 100 percent (based on SCAQMD data), along with the BACT (best available control technology) standards of 80 percent control efficiency for biofilters.

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 contaminant most likely to exceed threshold limits.)

Since the facility used the composter with impermeable covers and with continuous negative aeration, the collection (capture) of the NH3 was assumed to be effectively 100 percent. (Open positive and negative ASP are less than 33 percent.)

Using the 78 percent 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 per year (SQER), and the facility was granted necessary permits to proceed.

In California, ECS has teamed with Cal State University in Fresno, through a USDA SBIR grant, to study the efficacy of the composter at controlling emissions while stabilizing manure for use as bedding and compost. The trials are taking place at CSUF’s research dairy facility.

This data will be used to determine compliance vis-à-vis BACT (Best Available Control Technology). Initial data has demonstrated a high capture rate and good process outcomes.

In the next issue of Ag Nutrient Management ECS will share the findings from CSUF VOC emission testing; and review the process in a commercial dairy application. ANM

—From Engineered Compost Systems