LA EXTERNALIZACIÓN DEL PODER ESTATAL POR LA ECONO- ECONO-MÍA

Releases to atmosphere can occur at every stage of waste transport, handling and treatment. For example, during transport the potential exists for the following emissions to occur:

f Dust; from tracking of contamination on the wheels of the vehicle.

f Dust; from the payload, from dry and finely dispersed material that has not been sufficiently damped or sheeted.

f Odours; from open loads, leaking valves, biological or organic sludges.

f Adventitious releases of gases or fumes as a result of accidents and fires.

Similarly, during landfilling of wastes, releases to atmosphere can be characterized as follows:

f Dust; tracking of vehicles on the site, working of the landfill, and of the cover material.

f Litter; from loose, unbagged waste and uncovered working areas.

f Odours; landfill gas, decomposing waste, chemicals.

f Pathogens and microbial emissions; release of bacteria and pathogens through disturbances of the waste during landfilling and compaction.

f Combustion gases from the flaring or utilization of landfill gas.

f Adventitious fumes from fires, gas explosions, and uncontrolled chemical reactions.

8 Commission of the European Communities, ‘Proposal for a Council Directive on Hazardous Waste Incineration’, COM(92)9 Final-SYN 406, Off. J. Eur. Communities, C130, 21 May 1992.

9 Commission of the European Communities, ‘Proposal for a Council Directive on the Landfill of Waste’, (91/C190/01), Off. J. Eur. Communities, C190/1-18, 22 July 1991. Amended proposals COM(93)275, 1993.

10 Commission of the European Union, ‘Draft Directive on Incineration of Waste’, 21 April 1994.

Table 2 Relative

Emissions/kg y~1 Contribution to glc*/%

Chemical Stack Fugitive Stack Fugitive

Chloroform 11 42 15 85

Ethylene dichloride 35 47 32 68

Hexachlorobutadiene 17 0.2 98 2

Methyl styrene 37 3 90 10

*glc\ ambient air ground level concentration at point of maximum impact.

Emissions sources from waste management processes such as incineration and physicochemical treatment are similar to those encountered in the chemical and process industries; namely, process vents and stacks, scrubbers, etc. In addition to deliberate and controlled discharges (such as via a tall stack), fugitive emissions can occur from pumps, valves, seals, waste handling and transfer operations, opening and sampling of drums, displacement of headspace in storage tanks, etc.

The cumulative magnitude of these fugitive releases has often been overlooked when compiling an inventory of releases from a site. In one study of an incineration facility11 an attempt was made to characterize fugitive release from waste handling and storage operations associated with rotary kiln and liquid injection combustion systems fed with pesticide wastes, oily sludge, and phenol/acetone distillation wastes. Table 2 summarizes the annual emissions of representative chemicals in the wastes streams from the stack and from fugitive sources during the operation of a hypothetical medium-sized liquid injection combustor. It can be seen that fugitive releases can reach significant proportions relative to emissions from the stack and, for the more volatile chemicals, can be the main contributor to ambient air ground level concentrations.

In another study, annual emissions of five metals from the stack of an MSW incinerator were compared against annual fugitive emissions of these metals in dust released during the landfilling of the ash residue.12 For the landfill scenario,it was assumed that dust emissions derived from three sources: placement of the ash (including transport over the landfill), spreading and compaction of the ash, and wind erosion. The latter source accounted for approximately 75% of the metals emitted from the landfill. However, the annual emissions of metals from the stack exceeded the annual fugitive emissions from the landfill by a factor of 50—500.

11 C. C. Travis, E. L. Etnier, G. A. Holton, F. R. O’Donnell, D. M. Hetrick, E. Dixon, and E. S.

Harrington, ‘Inhalation Pathway Risk Assessment of Hazardous Waste Incineration Facilities’, Report ORNL/TM-9096, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1984.

12 D. A. Kellermayer and S. L. Stewart, Environ. Impact Assess. Rev., 1989, 9, 223.

Odour is perhaps the most common type of fugitive emission released from waste treatment or disposal sites: this is reflected in the predominance of complaints relating to odour nuisance over other types of disamenity which could potentially affect surrounding populations. In most waste management processes and operations associated with handling of waste, odours are released as a result of ineffective or nonexistent fume extraction and odour control measures that ideally should be engineered into the design of the plant or incorporated into the systems of work. In processes such as composting, the act of aeration and/or turning of the waste to encourage microbial activity leads to the generation and release of odours, the intensity of which depends on the state of decomposition of the waste and the method of composting. In one study13 odour emissions for different composting techniques were characterized in terms of Odour Units (OU). The discharges ranged from 1000 OU m~3 before turning of the compost, to 5000 OU m~3 during turning of a 4 weeks old pile. Blowing of air through the bottom of the pile resulted in lower odour emissions (200 OU m~3) than when air was drawn from the top of the pile (20 000 OU m~3)—in the former case, the top layer of waste partly deodorized the air stream prior to its dispersal in the surrounding air. Appropriate working methods and engineered control techniques were suggested to ensure that odours were not detected off-site.

The handling, treatment (for example, composting), and landfilling of Municipal Solid Waste (MSW) can also result in microbial emissions to atmosphere.

Pathogenic bacteria form about 6% of the total bacteria on waste reaching a landfill or compost plant.14 Sampling of air prior to composting of MSW indicated concentrations of 10 000—20 000 Gram-negative bacteria per cubic metre of air, with higher concentrations during subsequent dismantling of the compost pile. These emissions have greater implications for worker safety than for adverse health effects off-site.

The principal and trace components of emissions to atmosphere from a range of waste management activities are shown in Table 3. Other than continuous emissions from thermal processes and from landfills, it is difficult to characterize releases to atmosphere from other processes, since they are either of variable quality (for example, from the scrubber or ventilation system of a physicochemical treatment plant) or are fugitive and of intermittent duration, dependent on the nature of the material processed or handled, and on the work practices observed at any particular time.

A detailed characterization of emissions of organic micropollutants from waste incinerators has been presented in a previous volume in this series.15 Emission factors relating to MSW incineration (kg emitted per tonne of MSW combusted) for polychlorinated dibenzodioxins and dibenzofurans (PCDDs and PCDFs)

13 W. Bidlingmaier, ‘Odour—Emissions from Composting Plants’, University of Stuttgart, 1990;

personal communication.

14 J. Lacey, P. A. M. Williamson, and B. Crook, ‘Microbial Emissions from Composts made for Mushroom Production and from Domestic Waste’, AFRC Institute for Arable Crops Research, Harpenden, UK, 1990.

15 G. H. Eduljee, in ‘Issues in Environmental Science and Technology—No. 2 Waste Incineration and the Environment’, ed. R. E. Hester and R. M. Harrison, The Royal Society of Chemistry, Cambridge, 1994.

Table 3 Principal and secondary emissions to atmosphere from various waste management operations

Activity Type Major components Trace components Other emissions

Thermal processes Stack emissions Carbon dioxide Carbon monoxide Odours

Water Acid gases Adventitious releases from spills, fires, etc.

Metals Organics

Landfilling Landfill gas Methane Volatile and semi-volatile Odours

organics

Carbon dioxide Dust

Litter Pathogens

Physicochemical treatment Scrubber emissions Air, water, vapour Acid gases Odours

Organics

Building ventilation Air Organics Adventitious releases from spills, fires, etc.

Biological treatment Methane (from some processes) Odours

Methane Volatile and semi-volatile

organics Carbon dioxide

totheAtmosphere

77

and polychlorinated biphenyls (PCBs) have been published.16 Emission factors for metals released during MSW incineration are available for a range of combustion technologies.17 Landfill gas entrains over 100 organic compounds in trace quantities, many of which are potentially odorous when present at sufficiently high concentrations.18,19 According to one study,20 about 10% of the trace compounds are likely to present odour problems, the most common types being organosulfurs, esters, organic acids, hydrocarbons such as limonene, and alcohols.