The characteristics of MSW will determine the options in waste recycling and the viability of incineration option as a disposal strategy.

The importance of the waste characteristics for a waste to energy plant is a central issue that need to be addressed as it has numerous implications, inter alia:

• High organics/vegetable wastes fraction and high moisture content are determinant factors that affect the viability of a WTE plant;

• The waste characteristics will determine whether the Net Calorific Value (NCV) of the waste is sufficient to sustain energy production;

• In the event that the NCV is not sufficient to sustain energy production; then auxiliary fuel will be required to make good the shortfall in NCV;

• The characteristics of the gaseous emissions are strongly dependent on the waste characteristics, in particular with respect to Dioxins and Furans (PCDD/PCDF), heavy metals, PCB, and other priority organic pollutants (POPs)

Several studies have reported solid waste characteristics in Mauritius.

Table 5.1.1 shows the reported characteristics
of MSW in Mauritius.

The composition of MSW as reported by SIDEC11 is not based on an actual characterisation study on MSW and in fact these are only estimates based on visual inspection of waste at the transfer stations for the urban zones of Plaines Wilhems, Port Louis, discussions with private and public waste operators and their experience in the field of MSW.

In contrast, Fichtner (2000) and Mohee (2002) reported MSW characteristics based on actual characterisation study.

Fichtner (2000)12 carried out an extensive characterisation study that took into account socio economic aspects (population density, income level, urban/rural areas, etc.), sources of wastes (household, commercial, tourist, etc.) etc. Average composition of MSW from eight districts of the island was determined and the average composition for MSW for Mauritius was derived subsequently.

Fichtner (2002) concluded that the dominant fractions in both MSW and commercial wastes were vegetables and organic waste, paper and cardboard, plastics and plastic bottles and fine ash and that the compostable fraction was 70% for both wastes.

Mohee (2002)13 carried out a characterisation study on MSW from a residential area in an urban region to assess the recovery potential of solid wastes in Mauritius.

Mohee concluded that, in the main:

• The composition of the MSW is largely organic in nature with vegetable and green waste occupying more than 60percent;

• The moisture content of the wastes was around 48percent and have a low calorific value;

• The incineration option should be studied further as the heating value of mixed MSW is quite low, however if the organic part of the stream is removed and composted, the remaining part of the wastes will have a higher calorific value and this will render incineration suitable;

• The characteristics of the wastes suggest that recovery of solid waste through composting of the organic fraction, either through home composting or centralised composting of green waste should be considered first;

• Composting will help to divert more than 60% of the wastes from the waste stream and lead to enormous cost savings in terms of waste collection, transport and disposal.

Carl Bro (2005)14 did not carried out any MSW characterisation study but instead provided a review of the MSW characterisation studies in particular focussing on the work of Mohee (2002) and the investigations of the University of Mauritius. Carl
Bro concluded that:

• MSW in Mauritius is dominated by the organic component consisting of kitchen/vegetable wastes, garden (yard) green waste and waste paper. This is unlike the waste characterisation of most European or North American municipal disposal authorities. Carl Bro further concluded that this difference in waste composition has implications for the possible incineration of the waste as an alternative to landfill.

When comparing with the reported waste characteristics in Developing countries and Developed Countries, the local waste characteristics conform in the main to those of Middle Income Countries as per Table 5.1.2.

Table 5.1.2: Characteristics of Municipal Solid waste by level of industrialization 15

From the above the most significant point is that developing and middle income countries typically have waste streams of significantly moisture content and organic composition.

5.1 Moisture Content of MSW
and its Impact on Calorific Value

Increase in moisture content in the MSW decreases the NCV of municipal solid waste.

The moisture content in MSW in Mauritius is considered very high. Fichtner (2000) reported average moisture content of 47% for MSW16 from their characterization study whereas Mohee (2002) indicated that moisture content is around 48%.

Fichtner(2000) even went to the extent of assessing the impact of increased moisture content on the Calorific Value of MSW and concluded that a 15mm rainfall will increase the moisture content from 45 to 59 percent whereas at maximum rainfall of around 148mm, the moisture content of MSW will be 70percent. Fichtner further concluded that at a moisture content of 70%, the NCV of the waste will fall to 3600KJ/kg a value which will not sustain combustion without the addition of auxiliary fuel.

Carl Bro (2005) is even more explicit on the impact of moisture content and states
that the net energy released from each component on combustion depends on
chemical composition but mainly on moisture content and concluded that combustion
of wet wastes such as green wastes with moisture content of 50-90% can even be a
net absorber of heat energy instead of a source of energy release-because of the need
to evaporate the water. Carl Bro (2005) expressed further concern once they were
informed that the moisture content can be as high as 60percent at certain times of the
year.
Carl Bro (2005) indicated that the European experience of MSW mass burn
technology is based on typical composition of around 25-30% moisture content (cf.
45-48% for local MSW) and 20-30% incombustible (ash) component.

5.2 Net Calorific Value (NCV) of the Municipal Solid Waste

In as much as the waste composition and moisture content are concerned, all the cited characterisation studies concluded that the high moisture content and the high fraction of organic/vegetable fraction in MSW will produce a low Net Calorific Value that is closer to the minimum NCV (7000KJ/kg) required for self combustion
of MSW.

Carl Bro argued that although equipment can be designed to deal with high organics and high moisture MSW (hence with low calorific value) with the support of auxiliary fuel17 yet the handling costs for the waste material and energy from waste plant efficiencies would undoubtedly be less favourable to the incineration option than if it were higher and more consistent quality.

Since the predominantly household wastes (stricto senso) do not have the NCV whereas Commercial and Industrial Wastes can have a higher NCV then there will be a reliance on the commercial and industrial sectors to produce more wastes so as to increase the NCV of the combined solid wastes. It is feared that there will be no incentives for commercial and industrial activities to reduce wastes or use different materials that have characteristics suitable for reuse or recycle contrary to policies in most of the Developed Countries. In effect, if the commercial and industrial waste generators in Mauritius have to bear the direct costs of disposal this would serve as a disincentive to produce more wastes. In the present case, a WTE scheme implies that waste generation is good since it means more energy.
Since the NCV of municipal waste is low, to support combustion and energy production, auxiliary fuel (heavy fuel oil, coal for example) is required. The use of auxiliary fuel will increase the operating costs of a WTE Plant and this could lead the way to the use of undesirable materials as fuel supplement such as plastics and other untreated waste oils that have high NCV.

5.3 Use of Auxiliary Fuels

SIDEC and Carl Bro considered that the Net Calorific Value (NCV) of MSW is too close to the minimum reported NCV for the sustainable combustion and release of energy for a WTE Plant, the use of auxiliary fuel is necessary to sustain energy production for base load.

In this regard, SIDEC (1998) recognising that the low NCV of MSW (1545 Kcal/kg wet waste), increased the NCV by the addition of Industrial & commercial wastes (NCV estimated at 3 370Kcal/kg of as received waste) to obtain an NCV of 1 802Kcal/kg as received waste for solid waste in winter and 1 608 Kcal/kg as received waste in winter. Even at these NCV, SIDEC (1998) concluded that for the start up and maintaining electricity production, they made provision for the use of coal as auxiliary fuel and estimated that a total of 6,000tonnes of coal per year will be required.

Carl Bro (2005) also came to the conclusion that auxiliary fuel will be required on the basis of their assessment of the reported data on waste characteristics and also on the fact that MSW as a fuel is inherently variable from minute to minute and seasonally.

The Consultants even went to the extent of estimating the amount of oil required (thermal energy equivalent) as auxiliary fuel at various NCV below the minimum NCV so as to maintain the required thermal output.

5.4 Waste segregation

Although condition (b) of the Letter of Intent from BOI refers to segregated or unsegregated waste, it is not clear whether there is a commitment from GoM to carry out a waste sorting process and the level at which the sorting will be carried out.

At present no waste segregation or waste sorting is carried out in Mauritius. Hence the probability of hazardous wastes finding their way into MSW is very high as solid waste from Industrial and commercial zones are mixed with domestic waste at the transfer stations. Hazardous wastes containing precursors of dioxins and furans, Polychlorinated Biphenyls (PCB), Poly aromatic Hydrocarbons (PAH) and others will increase the formation of the toxic compounds in the flue gases as well as in ash residues and the risks of higher concentrations that would normally exist in sorted domestic solid wastes.

A product in itself may not be harmful, but when incinerated the chemicals they are made of are released, and the formation of new chemicals can occur. For example:

• Computer and electronic scrap, containing brominated plastics which can
form dioxin congeners;
• Batteries, PVC, lead and treated timber;
• Plastics and materials with brominated chemicals in them will form brominated dioxin congeners if burned.

To limit the formation and emissions of Dioxins and furans, extensive segregation techniques are required to remove all plastics and other chlorinated compounds such as PVC, rubber, etc.

The only reported information in Mauritius of the hazardous fraction in household waste is from the study carried out by Fichtner (2000) who found that the hazardous waste fraction in household waste at 0.5%. The Consultants recommended the removal of the hazardous fraction in the waste stream.

This hazardous fraction is similar to the household hazardous waste fraction in industrialised countries but in the case of Mauritius, is due to the presence of small and medium enterprises (SME) in the urban regions (such as motor vehicle repair workshops, paint contracting activities, etc.). The hazardous wastes consist
principally of oil-based paints, household cleaners, paint thinners, used motor oils,
batteries (lead, Lithium, Lithium/Cadmium and mercury) and fluorescent lamps.

SIDEC recommended that selective waste separation at domestic level should be encouraged to reduce the precursors of dioxins and furans (PCDD/PCDF) in MSW, namely the reduction of synthetic polymers (plastics, low density poly propylene, PVC, etc) in the municipal wastes. However while the dioxins are undoubtedly the best researched of the chemicals released from MSW incinerators, they are not the only ones of significance as elaborated in the previous sections.

Waste sorting is a prerequisite for MSW Incineration. This is clearly spelt out in the European Directive (Directive 2000/76/EC) on the incineration of waste. Preciselythe EU Legislators have set out the minimum requirements for incineration plants (definition and quality of wastes that can be incinerated, operating and monitoring provisions, etc.) and have not only tightened the emissions to air but is more specific on releases to water and land (see later).

The presence of silica (mainly due to the glass fraction) will increase the maintenance frequency of the WTE plant as vitrification of the moving grates and heat exchanger surface of the furnace will result in poor heat transfer performance.

Conclusions

Thus it can be concluded that without a sorting process upstream of the incineration process, incineration of MSW increases the risks of formation of hazardous by products (PCB, PAH, Dioxins and Furans, Heavy metals, etc.). As a consequence it is uncertain whether GoM or the Promoters is responsible for any liability that results due to the formation of highly toxic and hazardous by products of the incineration of MSW. Statements made by the Promoters in their EIA report will tend to shift this responsibility on GoM.

 

_______________________________
11 Mauritius Sugar Authority (1998): Municipal Wastes/Bagasse/Coal Incineration for Electricity Generation – Feasibility Report. SIDEC – Groupe Charbonnages de France
12 Ministry of Economic Development, Productivity and Regional Development (2000): Environmental Solid Waste Management Program – Feasibility Study. Fichtner
13 Mohee Romeela (2002): Assessing the recovery potential of solid waste in Mauritius in Resources, Conservation and Recycling, 36,33-43 - ELSEVIER
14 Ministry of Local Government and Rodrigues (2005): Feasibility Report – Environmental Solid Waste Management Project – Carl Bro
15 Cointreau, Sandra (2001). Environmental Management of Urban Solid Wastes in Developing Countries: A Project Guide. Urban Development Department, World Bank, Washington, D.C.
16 It must be noted that Fichtner carried out the characterisation study from 30th August to 16th September 1999,i.e, during the dry season where rainfall is expected to be low. However no rain data during the said period were given in the report
17 Bold and underline for emphasis.