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Preliminary Air Emissions Assessments from Co-Composting of Biosolids and Greenwaste Setting the Stage for Future Work

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In August 2001, the South Coast Air Quality Management District (SCAQMD) proposed a ground-breaking rule aimed at controlling emissions of ammonia and volatile organic compounds (VOCs) from composting facilities. Co-composting was defined by SCAQMD staff as the combined composting of biosolids and/or manure with bulking agents (presumed to be greenwastes). The proposed rule specified aggressive control targets for these pollutants that were likely to require significant composting operation changes and/or the addition of extensive control technologies such as total enclosure followed by offgas treatment such as biofiltration.

In response to this proposed rulemaking, the Southern California Association of POTWs (SCAP) funded the Composting Emissions Testing Study (CETS) to determine if well-operated aerated static pile (ASPs) composting, without further add-on controls, could comply with this proposed rule. SCAP also sought to characterize life-cycle ammonia and VOC emissions from ASPs to both compare those emissions to the SCAQMD's source tests for windrow composting operations that were the basis for their rule, and to evaluate if anything less than total enclosure of the operation would allow compliance.

Concurrently, personnel from the Los Angeles County Sanitation Districts (LACSD) began an investigation of the ammonia release potential of various biosolids/green wastes blends during composting. These carefully controlled drum studies used the same raw materials as in CETS, composted under actively aerated conditions similar to the CETS ASP's.

By every objective (e.g., temperature) and subjective (e.g., odor) standard traditionally used in the compost industry to ascertain success of the composting operation and quality of the final product, the CETS ASP composting study produced excellent quality compost. Nevertheless, the CETS results indicate that an ASP with a biosolids-rich mix could not meet the rule-mandated reductions without some additional containment and treatment of offgases. Many factors including pile mixing and pile geometry were not optimal for emissions reductions during the test program.

The drum studies proved conclusively that initial blend variations can have a significant impact on ammonia releases. The data from this study provide information as to which blend ratios might result in lower emissions that would allow compliance to the proposed rule with partial or no enclosure of the operation and/or treatment of the offgases.

SCAP concluded that a combination of judicious mix selection, pile geometry, tapered aeration and well operating biofilters needed to be optimized to achieve the reductions required in the rule.

Document Type: Research Article


Publication date: January 1, 2004

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