The design, management, and control of landfills has changed considerably in recent years in response to a better understanding of the pollution potential of wastes and of more effective means of control.
‘Sustainable’ and ‘fail-safe’ concepts are based upon landfills that continue to accept mixed MSW, but in full recognition of the fact that long-term pollution exists. Control may be achieved either by accelerating the rate of waste degradation to produce a stable residue, or by pre-treating the waste prior to landfill. In a recent report, the findings of a feasibility study to assess the potential of developing a bioreactor cell rotation landfill in which both options are utilized have been presented.54 This scheme differs from previous schemes, such as
‘Landfill 2000’,55 in that it incorporates waste separation with homogenization of waste prior to emplacement, in this way ‘providing a predictable gas generation rate and a high quality residue as part of a controlled process’. The removal of recoverable materials such as metals, plastics, glass, paper, and textiles ensures that only low calorific value (CV) wastes are landfilled, while high CV wastes are incinerated with energy recovery.
51 H. Pearce, Land Contam. Reclam., 1993, 1, 172.
52 Ends Rep., 1994, 230, 35.
53 Ends Rep., 1994, 229.
54 Applied Environmental Research Ltd., ‘The Sustainable Landfill: A Feasibility Study to Assess the Potential of Developing a Bioreactor Cell Rotation Landfill’, ETSU Report B/B3/00242/REP, Harwell, Oxfordshire, 1993.
55 K. Bratley and Q. Khan, ‘Proceedings AMA Environment Conference ‘‘Caring for the future’’ ’, Newcastle-upon-Tyne, 1989.
In keeping with this theme, Kent County Council (in South-East England) have launched a waste management strategy to reduce the proportion of MSW (650 000 tonnes) and Civic Amenity (CA) waste that goes to landfill. Proposals56 included an anaerobic digestion plant to handle 40 000 tonnes annum~1, with 200 000 tonnes annum~1 going to a waste-to-energy incineration plant.
The option proposed by Kent County Council is similar to that described above but using more traditional anaerobic digestion of the organic waste component rather than the ‘bioreactor cell rotational landfill’. Anaerobic digestion (AD) plants such as the DRANCO and VALORGA processes have been reviewed elsewhere.57 While it is clear that anaerobic digestion after pre-sorting of wastes is receiving more interest, a number of uncertainties relating to the capacity, reliability of the processes, and the marketability of the final product, are still to be resolved. For example, it is possible that if a market cannot be found for the final product of AD, the cost of pre-treatment, together with potential costs associated with segregation and collection at source, may be too high to sustain as a permanent waste management option. Also, if no market can be found for the final product, disposal to landfill would still result in the production of landfill gas and leachate and the benefits of pre-treatment would be negated to a large extent. Thus, while in theory schemes such as those described above seem both feasible and practicable, they have yet to be proven and the full ramifications may not have been realized. The composting of waste (aerobic digestion, not anaerobic digestion) is also receiving increasing interest as a waste treatment option, but at the moment uncertainties similar to those for anaerobic digestion are restricting its use on a commercial scale. The success of these pre-treatment processes may well be dependent upon the willingness of the public to effectively sort waste ‘at source’ and to ensure, for example, that glass is not allowed to contaminate sorted vegetable material.
Even if the products of AD and composting are marketable, landfill will still be required for the final disposal of wastes (ash) from incineration (approximately 15% by weight of input). Such wastes may be landfilled directly, although there is an argument that for the Best Practicable Environmental Option (BPEO)58 to be achieved, these wastes, which may be high in heavy metal concentration, should be further treated to minimise the pollution risk. This will be especially true if organic wastes are removed from wastes to landfill. In this event, pH control of the environment (achieved through bacterial processes in organic waste degradation) will be significantly reduced, thereby increasing the risk of metal migration to the surrounding environment.
The removal of organic wastes from landfill will also have important ramifications for co-disposal, for without organic material there will be no substrate for growth of the bacteria that effect the degradation of co-disposed wastes. Thus, even if co-disposal is allowed as a waste management option in the future, practical problems may prevent its use.
56 Warmer Bull., 1993, 39, 2.
57 J. Coombs, ‘The Prospects for Methane Recovery from the Anaerobic Digestion of Municipal Solid Waste in the UK’, ETSU Report B1234S, Harwell Laboratory, Oxfordshire, 1990.
58 Royal Commission on Environmental Pollution, ‘Twelfth report: ‘Best Practicable Environmental Option’, 1988, Cmd. 310, HMSO.
9 Conclusion
At a time of great change, the future direction of landfill remains uncertain and difficult to predict. Landfill undoubtedly is, and will continue to be, an essential waste management option. However, it seems likely that current changes in regulation and control, and their economic ramifications will, together with political factors and social pressures, lead to changes in waste management as a whole. It is clear that there is an increasing shift in policy towards the top of the waste hierarchy as identified in the EU Fifth Environment Action Programme.
For example, in the Netherlands59 a target of 10% reduction in waste by the year 2000 has been set. There will also be a reduction in the amount of waste disposed to landfill and incineration while at the same time sending a smaller proportion to landfill and a greater proportion to incineration. Policy at both national and regional levels is currently shifting towards the incineration of high CV waste, with energy recovery. Although options for the pre-treatment of lower CV organic wastes are relatively poorly developed on a commercial scale, there is increasing interest in these methods of waste management. This suggests that the landfill of the future will have an extremely low organic material content. Thus, irrespective of political decisions and scientific suitability, processes such as co-disposal are likely to be considerably restricted in the future, unless undertaken through the use of highly controlled and engineered reactors.
Under this scenario, financial provision for effective control of operational and post-operational phases of landfill could be considerably easier to achieve, and the financial elements of landfill generally may be more easily managed.
59 J. P. V. M. Laurijssens, Wastes Manage., 1993, Nov, 12.
G . H . ED U L J EE
1 Introduction
All waste management activities have the potential to release emissions to atmosphere, perhaps along with releases to other environmental media such as groundwater or surface water. These emissions may be controlled (i.e. managed so as to minimize harm to the environment) or uncontrolled (i.e. not under the direct management of plant or site operators).1 In some waste management processes (for example incineration, gasification, pyrolysis) continuous and controlled emissions to atmosphere are an integral and essential consequence of the treatment, since the aim is to convert wastes to essentially gaseous, non-toxic products which can safely be released to the environment. In other waste management processes (physicochemical treatment, solidification, chemical recovery, etc.) the aim is not to permit releases to the atmosphere, and to contain the products within the reaction vessel. However, adventitious, uncontrolled releases could still occur if the reactions are not adequately monitored. In the landfilling of biodegradable wastes, approximately 6 m3 of gas is released per tonne of waste deposited per year. Two gas management concepts are currently under discussion: maintaining dry conditions within the landfill by preventing the ingress of air and water and thus slowing the generation of landfill gas and leachate (the ‘dry tomb’), or treating the landfill as a bioreactor and maximizing the generation and release of landfill gas by optimizing air and water requirements.2
In addition to these process-related emissions, uncontrolled releases to atmosphere could occur during any stage of the waste management cycle, for example during handling, transportation, inter-plant transfer, etc. Figure 1 illustrates the potential for releases from various types of waste management processes: landfills (representing an area source), combustion plant (stack emissions representing a point source), and traffic (representing a line source).
Emissions can be continuous (as in the case of gases from incinerator stacks or of gas diffusing through the cover material of a landfill) or discontinuous (as in the
1 M. D. LaGrega, P. L. Buckingham, and J. C. Evans, ‘Hazardous Waste Management’, McGraw Hill, New York, 1994.
2 R. W. Maurer, ‘Proceedings of the Conference ‘‘Landfill Tomorrow—Bioreactors or Storage’’ ’, Imperial College Centre for Environmental Control and Waste Management, London, 1993.
Figure 1 Emissions to atmosphere from various types of waste management operations, and uptake of contaminants from the environment
case of releases from physicochemical treatment plants or from fires and accidental spills).
In comparison to soil and ground or surface water, the atmosphere is a far more effective carrier of pollution in that dispersion of emissions into the surrounding environment is multidirectional, relatively fast, and over longer distances.3 To persons living in the vicinity of waste treatment and disposal facilities, emissions to atmosphere are often the most obvious manifestation of waste management operations, because of visible emissions (steam and smoke from an incinerator stack), or because fugitive releases of dust, odours, litter, etc.
have resulted in loss of amenity. Certainly, waste management processes that routinely discharge to atmosphere (in general, all thermal processes) have attracted more attention from environmental groups and the public due to anxieties over serious adverse health effects than have other types of waste treatment and disposal options.
This article presents an overview of emissions to atmosphere from waste management operations. The discussion commences with a brief review of the regulatory control of such emissions, as it pertains in the UK. Next, the releases to atmosphere are characterized in terms of their sources, composition, and scale of release. The environmental impacts of such releases are then examined, differentiating between national or global issues, and near-field effects which have the potential to produce more local impacts. Finally, measures which can be taken to mitigate the potential adverse effects of emissions to atmosphere are discussed.
3 J. Petts and G. H. Eduljee, ‘Environmental Impact Assessment for Waste Treatment and Disposal Facilities’, John Wiley, Chichester, 1994.