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Review
. 2023 Feb 14;57(6):2235-2247.
doi: 10.1021/acs.est.2c05846. Epub 2023 Jan 31.

Greenhouse Gas and Air Pollutant Emissions from Composting

Sarah L Nordahl  1   2 , Chelsea V Preble  1   2 , Thomas W Kirchstetter  1   2 , Corinne D Scown  1   3   4   5
Affiliations
Review

Greenhouse Gas and Air Pollutant Emissions from Composting

Sarah L Nordahl et al. Environ Sci Technol. .

Erratum in

Abstract

Composting can divert organic waste from landfills, reduce landfill methane emissions, and recycle nutrients back to soils. However, the composting process is also a source of greenhouse gas and air pollutant emissions. Researchers, regulators, and policy decision-makers all rely on emissions estimates to develop local emissions inventories and weigh competing waste diversion options, yet reported emission factors are difficult to interpret and highly variable. This review explores the impacts of waste characteristics, pretreatment processes, and composting conditions on CO2, CH4, N2O, NH3, and VOC emissions by critically reviewing and analyzing 388 emission factors from 46 studies. The values reported to date suggest that CH4 is the single largest contributor to 100-year global warming potential (GWP100) for yard waste composting, comprising approximately 80% of the total GWP100. For nitrogen-rich wastes including manure, mixed municipal organic waste, and wastewater treatment sludge, N2O is the largest contributor to GWP100, accounting for half to as much as 90% of the total GWP100. If waste is anaerobically digested prior to composting, N2O, NH3, and VOC emissions tend to decrease relative to composting the untreated waste. Effective pile management and aeration are key to minimizing CH4 emissions. However, forced aeration can increase NH3 emissions in some cases.

Keywords: Air Quality; Ammonia; Anaerobic Digestion; Composting; Greenhouse Gases; Methane.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Breakdown of the 140 composting scenarios and study methods associated with the reported emission factors collected for analysis. Emission factors are categorized by (a) composted material, (b) aeration method, and (c) measurement method.
Figure 2
Figure 2
Distributions of (a) CH4 and (b) N2O emission factors for composting reported in the literature and relative contribution to total GWP100 based on (c) mean values and (d) median values. The sample size (n) of data points contributing to each boxplot is indicated in the x-axis labels for parts (a) and (b); the first value refers to the sample size of CH4 emission factors, and the second value refers to that of N2O emission factors. Parts (a) and (b) have two y-axes: the left axis indicates the per-tonne mass of the specified pollutant emitted (exact values), and the right axis shows the CO2-equivalent emission factor (rounded values), so that CH4 and N2O emissions can be compared with respect to GWP100. The mean values for the boxplot data are indicated by the open point symbols, while outliers are shown as closed circles.
Figure 3
Figure 3
Distributions of (a) CH4 and (b) N2O emission factors for OFMSW composting based on the aeration method. The sample size (n) of data points contributing to each boxplot is indicated in the x-axis labels. Each figure has two y-axes: the left axis indicates the per-tonne mass of the specified pollutant emitted (exact values), and the right axis shows the CO2-equivalent emission factor (rounded values). The mean values for the boxplot data are indicated by the open point symbols, while outliers are shown as closed circles.
See this image and copyright information in PMC

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