California Integrated Waste Management Board

Threats to Organic Recycling Programs

Emissions Reduction from Composting and Related Facilities

Background

In California, local air pollution districts set operational rules and limitations for any business which emit significant amounts of "criteria pollutants." In many rural areas, district boundaries follow county lines. In other areas, districts are multi-county entities that address air problems regionally. Two of the largest districts are the South Coast Air Quality Management District (South Coast AQMD), which covers most of urban Southern California (except San Diego and the deserts), and the San Joaquin Valley Unified Air Pollution Control District (San Joaquin Valley UAPCD), which covers eight counties in the southern half of the Central Valley, California's agricultural heartland.

Those two districts are charged with cleaning up some of the most polluted air in the nation. As expected, the rules for entities that emit pollution into these air basins as part of their regular business activities are among the strictest of any place in the world. Local air pollution districts are led by their own executive boards, typically comprised of county supervisors and city council persons. The districts are supervised by the U.S. Environmental Protection Agency. Under the federal Clean Air Act, they are required to produce and implement plans for cleaning up any pollutant which exceeds federal standards.

Local air districts are not able to enact rules which restrict "mobile sources," which include cars, trucks, locomotives, and other mobile vehicles. Only "stationary sources" of air pollution fall under the control of local air pollution districts. Mobile sources are exclusively regulated by the California Air Resources Board.

Stationary sources include industrial sources. As the obvious sources of pollution--like power plants or refineries--get cleaned up, local air pollution districts increasingly look toward less obvious sites, such as organic recycling operations, as potential places to reduce emissions of either criteria pollutants or their precursor chemicals, which are also subject to regulation. This includes composting and chip-and-grind operations. The South Coast AQMD has enacted rules to regulate biosolids co-composters and to prevent inadvertent composting at chip-and-grind sites. The San Joaquin Valley UAPCD also regulates co-composters, and is now implementing regulations intended to reduce emissions from greenwaste composters and chip-and-grind sites. They may also seek to place composters within the federal permitting programs set up to apply the Clean Air Act.

The most important emissions from composting operations are volatile organic compounds (VOC). VOCs react in the atmosphere with oxides of nitrogen (NOx) to make ground-level ozone a criteria pollutant. VOCs can also react with ammonia (NH3) to create fine particulates (alternatively referred to as particulate matter PM) another criteria pollutant.

VOCs are a class of over 1,000 chemicals with greatly varying degrees of reactivity and toxicity. Some VOCs may be considered desirable, such as the ones which give off the scent of lemons or pine, or an expensive perfume. Others, like cadaverine, are extremely offensive. VOCs may be man-made (anthropogenic) or may occur naturally (biogenic). In the San Joaquin Valley, it is estimated that there are 1,000 tons of biogenic VOCs created daily, compared to some 300 tons per day of man-made VOCs.

Scientists disagree how much VOC or ammonia is actually released by composting. The types of VOCs being released are poorly understood, and because the reactivity of VOCs varies greatly, it is also not proven that VOCs from composting operations are reacting with other pollutants and making a significant contribution to regional air pollution.

Rules Listed by Air District

South Coast AQMD

Rule 1133. Adopted on January 10, 2003, this rule covers chipping and grinding operations, as well as biosolids co-composting operations. Composters who process exclusively greenwaste are currently exempt from Rule 1133; however, the South Coast AQMD indicates it may start work later in 2008 on a new section of the rule to cover greenwaste composting.

San Joaquin Valley UAPCD

Rule 4565. Adopted on March 15, 2007, this rule covers "all facilities whose throughput consists entirely or in part of biosolids, animal manure, or poultry litter and the operator who landfills, land applies, composts, or co-composts these materials."

Rule 4566. In April, 2008, the San Joaquin Valley UAPCD introduced its draft version of Rule 4566, covering greenwaste operations, including composters, as well as chip-and-grind and land application operations. Workshops were conducted in April, with a second round tentatively scheduled for August. The air district has indicated it intends to adopt Rule 4566 in the first quarter of 2009.

Mojave Desert AQMD

Rule 1133. The Mojave Desert Air Quality Management District (Mojave Desert AQMD) released a draft rule for composting and related operations in June 2008 The District began hearings on the proposed rule in August 2008, and adopted the rule on October 27, 2008. All organics materials handlers must register with the District by December 26, 2008. Mojave Desert AQMD Rule 1133 includes a set of raw materials holding-time limitations identical to South Coast AQMD Rule 1133.1, and a series of best management practices for bio-solids co-composters very similar to those found in San Joaquin Valley UAPCD Rule 4565.

CIWMB Research on Compost Emissions

The Modesto Study

In 2006, the CIWMB launched the largest study to date of composting VOC emissions, collecting and analyzing 100 emissions samples from four compost windrows built and managed at the City of Modesto's composting facility. The study calculates a life-cycle VOC emissions factor for greenwaste and food waste windrows, and also tests the emissions-reducing potential of two best management practices. The study was released in December 2007.

Compost vs. Biogenic Emissions

The CIWMB funded research at San Diego State University to determine whether emissions from the decay of organic materials vary based on whether the materials are composted or allowed to decay in an uncontrolled environment. The study concluded that VOCs are "very likely to be biodegraded within the composting matrix, and thus result in lower emissions when composted than if the materials were to be handled differently." This research was first published in the Winter 2006 issue of Compost Science and Utilization.

Best Management Practices (BMP)

The most cost-effective way to reduce emissions from compost operations may be to carefully control operational variables in order to provide the best possible environment for the aerobic organisms which power composting. Most composters do these things purposefully; others may do it unwittingly, inconsistently, or not at all. Everyone knows that poorly managed piles smell bad and attract bugs; it is also likely they produce more air pollution than well-managed piles.

Even well-managed piles can have sections which go "anaerobic." That means a lack of oxygen has depleted the desirable microbes which break down organic wastes, and has allowed other microorganisms which break down organic molecules without the presence of oxygen to take their place. Emissions of methane, ammonia and other VOCs like cadaverine or putrescine seem to be related to anaerobic conditions.

While the types and amounts of emissions may be closely related to actual feedstocks (which vary seasonally), it is thought that the following variables influence emissions, and that optimizing these variables may significantly reduce composting emissions.

  • Initial carbon-nitrogen ratio: Piles which have too much nitrogen may lose nitrogen to the atmosphere in gaseous form. Excessive carbon may slow or halt decomposition.
  • Moisture content: Piles which are too wet may go anaerobic. Piles which are too dry may not compost well or may get too hot. In California, composters must add water to piles during the warm months and when aerating. In other sections of the country, piles must be protected from excessive rain.
  • Temperature: Piles which are too hot may volatize more compounds than is optimal. Cold temperatures may indicate an anaerobic pile. Composters are already required to maintain pile temperatures greater than 131ºF for 15 days in order to kill pathogens.
  • Oxygen content: Lack of oxygen impedes or kills aerobic organisms, leading to anaerobic conditions. Blowers and windrow turners both inject oxygen deep into the pile.
  • Initial pH: Acidity or alkalinity of the feedstocks may help or hinder beneficial organisms.

CIWMB Research on Best Management Practices

In 2002, CIWMB completed emissions tests on greenwaste composting designed to evaluate emission reductions that could be achieved by controlling feedstock mixtures and aeration techniques. Two blends of feedstock were used: a woody blend (high carbon-to-nitrogen ratio) and a grassy blend (low carbon-to-nitrogen ratio). Two levels of aeration were evaluated as well: static windrows (natural convection only) and mechanically turned windrows using a Scarab. The tests were conducted at Tierra Verde Industries in Irvine, in Southern California. Test results indicated that ammonia emissions were extremely low and should not be an issue of concern for greenwaste composting. The results also indicated that controlling feedstock blends can effectively reduce VOC emissions. The results associated with aeration techniques show different emission profiles over time; however, it is difficult to conclude whether aeration techniques can lower total emissions. Overall, the Tierra Verde tests supported the concept of using best management practices to lower emissions.

The two emissions-reducing best management practices tested at Modesto included a "pseudo-biofilter compost cap," and a pair of commercial inoculants blended into and sprayed upon a windrow. The compost cap, a 4-6" layer of finished compost covering the newly formed windrow, acts as a biofilter to destroy emissions. The inoculants stimulated beneficial microbes and helped form a crust on the active compost pile. Both practices resulted in emissions reductions during the initial two weeks of composting. However, the pseudo-biofilter was more effective, reducing emissions by about 75 percent during the first two weeks. This is significant because the Modesto study suggests that roughly 80 percent of all emissions occur during the first two weeks of composting.

Presentations

CIWMB staff periodically participate in panels and conferences where the compost emissions issue is discussed with operators and other regulatory agencies. These presentations serve as an excellent introduction to the complex regulatory dilemma:

CIWMB Contact

Bob Horowitz

Threats Home

Last updated: November 4, 2008
Organic Materials Management http://www.ciwmb.ca.gov/Organics/
Contacts: http://www.ciwmb.ca.gov/Organics/Contacts.htm