Waste incineration concerns

Concern has been raised, lately, about the possibility of resorting to large-scale mass burn incineration as part of implementing Malta's national waste management strategy.

Malta's municipal waste generation is projected to increase up to 60 per cent by 2020 compared to baseline year 2005, with overall EU27 projections envisaging a much lower 25 per cent. Objective 4 of the May 2010 Solid Waste Management Strategy states that the government will work towards recycling 70 per cent of all construction and demolition waste by 2020.

The Landfill Directive limits the amount of biodegradable waste that can ultimately be landfilled. Directive 2009/28/EC classifies waste as a renewable resource from which energy can be derived. In this regard, the options are basically threefold: either resort to mechanical biological treatment (MBT) plants for the generation of biogas, which, in turn, can be used for the generation of electricity; resort to waste incineration to dispose of so-called residual waste fractions with a relatively high calorific value; or both. On a cautious note, the SWMS mentions Delimara as a site with the potential for constructing mass burn incinerator.

Despite the state-of-the-art technology installed in the Marsa incinerator plant in recent times, Malta's experience with waste incineration so far has been far from positive. It was only after years of protests and complaints by residents that the St Luke's Hospital incinerator was closed down. According to the project description statement submitted to the Malta Environment and Planning Authority by the Ministry of Health in March 2003, the SLH waste incineration facility consisted of a diesel-fired INCINCO H 500-A static grate, single chamber incinerator, also equipped with afterburner. The latter device served to inject more fuel onto the incinerating mass and, hence, by raising combustion temperatures, a more efficient thermal treatment of the clinical waste was ensured. The SLH plant was commissioned from a UK company in the 1970s.

Waste incineration technology has evolved rapidly over the last three decades. The now-defunct SLH engine represented a totally inconceivable technology by today's standards whereby the operating conditions of such plants is regulated by Article 6 of Directive 2000/76/EC on the incineration of waste, requiring that incineration plants should be capable of raising temperatures as high as, 1100˚C. On page 11 of the abovementioned PDS it is stated that the SLH incinerator was estimated to be capable of reaching a temperature of just 400˚C and that the treatment of clinical waste resulted in "approximately 120kg of potentially hazardous flyash and other unburnt residues on a daily basis".

The chemical composition of flyash, consisting of micrometer-range particulates, largely depends on the chemical nature of the waste being burnt. Apart from various oxides and heavy metals, soot, essentially elemental black carbon, is usually another particulate component released with flyash. Of major environmental and human health concern is the release of noxious substances such as polyaromatic hydrocarbons (PAHs), and maybe even dioxins, which are generally associated with soot formation. Considerable amounts of soot are also emitted by vehicles and fossil fuel power stations.

Environment impact assessment specialists usually rely on computer modelling to assess the impacts of chimney stack emissions such as the plume that generations of residents close to the ex-SLH incinerator had grown to live with. Technical data on the ex-SLH engine, thankfully, now shut down for good, are provided in Table 1.

The computer model gives ground-level concentrations in microgrammes per cubic metre, μgm-3, and it is assumed that the SLH plant used to operate on a continuous six-hour daily basis. The final model outcome for one particular atmospheric stability scenario is produced in Figure 1.

The insistence on a flue gas exit temperature of 906˚C from the plant, now decommissioned, seems inexplicable given the PDS affirmation that the maximum temperature that could have been reached by the engine was just 400˚C. Altering the computer model to factor in a 400˚C instead of the "official" 906˚C gives the outcome in Figure 2.

Several details aside, not least the fact that one would expect the flue gas exit velocity to alter depending on flue gas temperature, the fundamental difference in the two modelled outcomes are the peaks reached in flyash ground-level concentrations as dispersed downwind over a distance of 4,500 metres. The lower the flue gas exit temperature, the higher these peak concentrations result to be. In both cases, it is apparent that the most hard-hit site with respect to these emissions from the plant - which is no longer there - should have been at a distance of 400 metres downwind. The exact location would obviously be variable, depending on wind direction and a variety of meteorological conditions.

The modelled outcome should be interpreted in the context of EU Directive 1999/30/EC, which has now been superseded by Directive 2008/50/EC, the CAFE Directive, but which was applicable at the time when the SLH incineration plant was in operation. The relevant PM10 air pollution limits were set as follows in Table 2.

The model assumes a flat topography in the chimney stack surroundings - which is not the case for SLH with respect to Guardamangia, Ħamrun, Msida and Ta' Xbiex. A quick analysis of the modelled outcomes suggests that ground-level PM10 concentrations resulting from stack emissions were quite close to the 40μgm-3 limit annual average for 2005 under a 3ms-1 wind speed and this was surely to be exceeded had the plant remained operational until 2010 when the annual average was lowered to 20μgm-3 and assuming a daily six-hour continuous operation. The envisaged situation gets worse if it is assumed that the flue gas exit temperature is 400˚C (Figure 2), a temperature which, arguably, should be more likely, if not less, despite the official data tabled in Parliament. Note that the highest peak obtained in Figure 2 well exceeds the 45μgm-3 mark.

Modelled outcomes such as these should be interpreted with caution. Whereas they provide the assessor with a reasonably good indicative picture of a certain environmental situation, there are considerable limitations that should be taken into account and, in any case, computer modelling outcomes should always be subject to factual environmental sampling verification. This analysis on the ex-SLH incinerator does not factor in one important feature: the cumulative health and environmental effects that could have arisen due to the regular daily operation of the plant for over 30 years.

The proposed Delimara waste incinerator should be a different story. The technology will be different and the ultimate target shall be generating electrical power from waste. State-of-the-art technology still requires that detailed environmental analysis is done, factoring in all aspects, not least airborne emissions.

In the case of a hypothetical mass burn incinerator at Delimara, however, the scenario considered must be more complex since the incineration facility will operate in tandem with a much bigger oil-fired power station. The total disregard of the potentially-affected communities and a lack of understanding between the competent authorities and all stakeholders involved shall be unforgivable despite the fact that waste incineration has probably become a necessary evil, given Malta's waste crisis on the horizon.

The author specialises in environmental management.

sapulis@gmail.com