January 25, 2009 | General

Controlling Composting Emissions

BioCycle January 2009, Vol. 50, No. 1, p. 32
California air district authorizes research project to examine which composting factors will reduce VOC emissions from compost piles.
Robert Horowitz

THE San Joaquin Valley Air Pollution Control District (District), which covers eight rural counties at the southern end of the San Joaquin Valley in California, has authorized a research project that will attempt to show which composting factors – such as temperature, moisture content, and porosity – will reduce Volatile Organic Compounds (VOC) emissions from compost piles. The District released a Request for Proposals for the project on December 30, 2008. If all goes as expected, field work would begin in spring 2009.
The District is planning to issue permits and place operational controls on green waste composting piles. Many composting facilities already have air quality permits for diesel- or gas-powered equipment, but this would be the first time that emissions controls were applied to green waste compost piles. The VOC emissions from the compost piles are thought to mix with nitrogen oxides (NOx) from cars and trucks and other combustion by-products and exacerbate the District’s ground-level ozone levels, among the worst in the nation.
Along with its decision to release the RFP, the District’s governing board unanimously agreed to delay – by 18 months – passage of a new rule affecting “chip-and-grinds” (primarily mulch and biomass fuel operations), green waste composters and related organics recycling operations. That measure, Rule 4566, is in draft form but is still scheduled to take effect in 2012, despite the delay in its passage from the first quarter of 2009 to the third quarter of 2010.
In 2007, the District adopted Rule 4565, which offered biosolids and manure cocomposting facilities with throughput under 100,000 tons/year the option of carefully monitoring temperatures, moisture, oxygen and carbon-to-nitrogen ratios in lieu of expensive aeration systems. Facilities processing more than 100,000 tons/year are required by 2010 to aerate their piles, and capture and destroy 80 percent of the associated VOC emissions. That rule spared facilities that only handle green or wood waste.
Rule 4566, whose passage was delayed last month, imposes a similar menu of aeration vs. process controls, but with a threshold of 50,000 tons/year before emissions capture and destruction become mandatory. The District’s rationale for the lower cutoff was that studies of green waste composting undertaken by another air district seemed to indicate that green waste composting produced twice the amount of VOCs for each ton of feedstock composted, compared to biosolids.
In late 2007, the California Integrated Waste Management Board (CIWMB) published a study of VOC emissions at a green waste facility within the District’s borders (see “Measuring And Controlling Composting Emissions,” BioCycle March 2008). That research indicated green waste and food waste composting emissions rates might be substantially lower than previously estimated, even lower than biosolids or manure cocomposting.
As the rulemaking process proceeded, the Waste Board also pointed out that the District’s estimate of compost
production within its borders was inflated, thereby overstating the potential impact of composting to San Joaquin Valley air quality.
More recent research at privately run composting facilities in California, however, seems to suggest emissions rates might be substantially higher than earlier measurements. The District is reviewing the conflicting research, and is supposed to release a proposed “emissions factor” by Spring 2009, when it will begin issuing “in house” permits for existing compost operations. That emissions factor, when coupled with both permitted and actual throughputs, will determine annual pollution totals, which determine whether composters also must get a federal Title V “major source” permit for their existing operations.
Ongoing discussions with stakeholders revealed that, while maintaining excellent process controls is known to produce good compost, additional research is needed to clarify which practices actually clear the air by emitting fewer VOCs. This led the District to issue its RFP at the end of December. It wants to find out whether variations in compost pile temperature, moisture content, pH, carbon-to-nitrogen ratio, or oxygen might produce measurable emissions reductions. At least $200,000 was appropriated from a special research fund; CIWMB also is considering providing some funds for the study. At a January committee meeting, CIWMB tentatively approved providing $30,000 for the study.
Prospective researchers have until January 29 to submit proposals. The District will review those during early February, with the goal of picking a winning proposal by February 18, and placing a research team in the field by early spring 2009. If all goes according to plan, field testing would conclude by fall 2009, and a final report would be ready before 2010. District staff plans to use the data to support or modify Rule 4566 before putting it out for final approval in the third quarter of 2010.
Bob Horowitz is a senior integrated waste management specialist at the California Integrated Waste Management Board. To find out more about these subjects, visit He will be presenting at the BioCycle International Conference 2009 in San Diego, April 27-30. The SJVUAPCD’s Request for Proposals, can be viewed at

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