International Review of Waste Management Policy - Department of ...

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3. Bioaerosols
Of these, the first two impacts differ depending on the nature of the composting
process. This is discussed in Sections 63.8.3.1 and 63.8.3.2. Bioaerosols are
discussed in Section 63.8.3.3.
63.8.3.1 Air Quality Impacts in Windrow Composting
As was previously indicated in Section 63.8.1, our analysis assumes that 10% of the
total nitrogen content of the waste is released in some form and that of this 10%,
88% is released as NH3 in windrow systems that operate without the use of a biofilter.
This results in NH3 emissions of 795 g of NH3 per tonne of waste to the facility.
Although relatively few studies have investigated emissions of VOCs from composting
processes, the UK’s Environment Agency did measure emissions from sites. These
are shown in Table 63-25.
Table 63-25: Emissions of VOCs from Monitoring of Compost Facilities
Compounds Compounds Detected Detected
g / / tonne tonne of of MSW
MSW
m,p Xylene [108-38-3; 106-42-3] 0.81
Nonane [111-84-2] 0.44
o Xylene [95-47-6] 0.54
Beta.-Pinene [127-91-3] 3.7
Ocimene [13877-91-3] 3.0
D-Limonene [5989-27-5] 10.5
Undecane [1120-21-4] 2.4
Dodecane [112-40-3] 1.2
Methyl-(methylethyl)-Cyclohexane [99-82-1] 1.5
Total 24.0
Source: Environment Agency (2000) Life Cycle Inventory Development for Waste Management
Operations: Composting and Anaerobic Digestion, R&D Project Record P1/392/4
We have used the total Environment Agency figure – of 24 g of emission per tonne of
waste to the facility - with regard to the emission of VOCs from windrow composting
processes.
63.8.3.2 Air Quality Impacts In Vessel Composting Systems
In in-vessel composting systems, NH3 is usually treated in biofilters. In biofilters, the
nitrogen in the ammonia is converted to, in varying proportions, N2, NO and N2O.
One study looking at MBT processes suggests a mass balance for a biofilter as shown
in Figure 63-1. The figure suggests that, as regards N, for every 500 g of N entering
the biofilter as NH3, an additional 111 g of N is emitted as N2O. This would imply a
conversion ratio of 22%. On the other hand, the above figure suggests a low overall
rate of destruction of NH3.
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