# Physico-chemical characterization of Residual Household Waste for energy recovery in insular territories: Case study of Reunion Island

Mathilde Maillot, Dominique Morau

► To cite this version:

Mathilde Maillot, Dominique Morau. Physico-chemical characterization of Residual Household Waste for energy recovery in insular territories: Case study of Reunion Island. Environmental Quality Management, 2023, 33 (1), pp.107 - 119. 10.1002/tqem.21989. hal-05482871

HAL Id: hal-05482871

https://hal.science/hal-05482871v1

Submitted on 29 Jan 2026

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
# Physico-chemical characterization of Residual Household Waste for energy recovery in insular territories: Case study of Réunion Island

Mathilde Maillot

Dominique Morau

PIMENT Laboratory, Université de La Réunion,
Le Tampon, La Réunion, France

**Correspondence**

Dominique Morau, PIMENT Laboratory,
Université de La Réunion, 117 rue du Général
Ailleret, Le Tampon, 97430 La Réunion, France.
Email: dominique.morau@univ-reunion.fr

**Funding information**

This article is the result of research work by
the SYNBIOZER project financed by European
funds (FEDER) and the Réunion Regional
Council

**Abstract**

Waste-to-energy is a promising approach to face the current challenge of waste over-production in Reunion Island, a French territory. In this particular context of an isolated and tropical territory, it is essential to study the properties of potential feedstocks to choose the most appropriate conversion process. This article reports on the composition of Residual Household Waste from Reunion Island and its physico-chemical parameters. Twelve representative samples of Residual Household Waste were subjected to thermal and elemental analysis. The results showed that their composition had a significant influence on the physico-chemical properties, including calorific value. Residual Household Waste from the selective sorting (rich in wood, plastic, and sanitary textiles) as well as dry mixed RHW are the most interesting for energy recovery. Due to their high volatile matter and high carbon content, and their low moisture content, these types of waste have a high calorific value exceeding 18 MJ/kg. Furthermore, the RHW sample comply with the environmental and health criteria applied by French regulations concerning halogen and heavy metal. Thus, it seems that Residual Household Waste can be an alternative to conventional fuels used in incineration or pyro-gasification processes. However, the study also points the need for a pre-treatment process for these wastes. Indeed, it is necessary to sort them correctly in order to avoid the risks of pollution and important maintenance. And more importantly, drying beforehand is unavoidable to improve combustibility and obtain optimal energy conversion.

**KEYWORDS**

energy perspectives, heating value, tropical territory, waste characterization, waste pollutants

# 1 | INTRODUCTION

## 1.1 | Waste management in island territories and in Reunion Island

Waste management is a matter of great concern for small territories especially islands. Due to their insular nature and remoteness from the

mainland, some small territories such as Reunion Island have to deal with a large amount of waste generated by the economic, touristic, or local activities. It is also facing a dynamic demographic growth. In most cases, waste is landfilled or dumped illegally because these regions lack sustainable technological means for waste management (Mohee et al., 2015).

<footnote>This is an open access article under the terms of the [Creative Commons Attribution-NonCommercial-NoDerivs License](https://creativecommons.org/licenses/by-nc-nd/4.0/), which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
© 2023 The Authors. *Environmental Quality Management* published by Wiley Periodicals LLC.</footnote>
<figure><img src="image_2.png" /><figcaption>**EXHIBIT 1** Residual solid waste (RSW) streams and existing treatment platforms in Reunion Island. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

<table><caption>**EXHIBIT 2** Grid of waste categories according to ADEME</caption><tr><td>1. Putrescible</td><td>Food waste, animal carcasses, garden waste...</td></tr><tr><td>2. Paper</td><td>Office paper, newspaper, book...</td></tr><tr><td>3. Carboard</td><td>Food packaging, moving boxes, postcard...</td></tr><tr><td>4. Composite</td><td>Food packaging (milk, juice, chips, coffee), wire, toy...</td></tr><tr><td>5. Textile</td><td>Natural or synthetic clothing, curtains...</td></tr><tr><td>6. Sanitary textile</td><td>Diapers, towels, tissues, cotton</td></tr><tr><td>7. Plastic</td><td>Plastic bag, packaging, plastic film, bottles, polystyrene</td></tr><tr><td>8. Combustible</td><td>Wood packaging, shoes, leather goods, furniture, tires</td></tr><tr><td>9. Glass</td><td>Bottle, jar, other packaging</td></tr><tr><td>10. Metal</td><td>Can, packaging, furniture, iron and other metals</td></tr><tr><td>11. Nonfuel</td><td>Clay pot, plaster, rubble, marble, rock...</td></tr><tr><td>12. Hazardous waste</td><td>Varnish, stripper, paint, battery, medical waste...</td></tr><tr><td>13. Small part</td><td>All waste &lt;2 cm</td></tr></table>

In France, a law called "Loi de Transition Énergétique pour la Croissance Verte" (LTECV) intends to act for the climate by committing to green growth and establishing a new energy model. It aims to fight against waste and promote the circular economy in order to reduce landfill by 50% and involves the development of renewable energies (Ministère de la Transition écologique, 2020).

Hence, Reunion Island such as the other French territories must rapidly draw up a regional waste prevention and management plan to comply with national and European obligations. Currently on the island, Household and Similar Waste (HSW) represents 12% of the 4.3 Mt of waste generated on the island per year, it means over 530,000 tons per year (ADEME, 2019a). It includes Residual Household Waste (RHW), Dry Recyclable Waste (DRW), Green Waste (GW), bulky items, and waste from economic activities (Exhibit 1).

They are mainly collected either door-to-door or at the recycling centers by the five local public establishments (CINOR, TCO, CIVIS,

CASud, CIREST) and sent to the existing treatment platforms which are managed by the two waste treatment syndicates on the island (SYDNE and ILEVA). Sixty five percent of HSW goes to landfill (mainly mixed RHW), 21.3% is composted (such as organic waste and GW), and only 13.7% is sent for recycling (glass, metal, plastic from DRW and from some bulky items) (INOVEST; SUEZ).

Despite this structure, sustainable waste management remains a challenge on the island because of its economic and geographical situation, but also its relief and its tropical and humid climate. As the two non-hazardous waste storage facilities are close to saturation and as there are few ways to treat RHW on the island, there is an urgent need to find new solutions. To limit waste disposal in landfills, local authorities are developing material recovery centers and trying to introduce new processes to produce energy from Residual Household Waste. A local study considered several scenarios and it suggested that multiple waste treatment (sorting, recycling, energy
conversion, composting) is the most appropriate solution in terms of environmental impact and surface area used (Lebon et al., 2020). In this context, several possibilities exist: incineration with energy recovery, gasification recommended by the Region's "zero waste" scenario, and energy recovery from Solid Recovered Fuel (SRF). Among them, incineration is one of the alternatives chosen to address the issue of waste treatment and energy production (ILEVA, 2019). The plant will be operational by 2023 and will only process one specific type of waste such as SRF. Energy recovery from SRF offers the advantage of additional waste separation for maximum material recovery and a better energy balance. However, the question of the final waste from this facility (flue gas cleaning residues and residual ashes) but also those resulting from the sorting to produce SRF is still to be resolved. Other processes such as gasification and pyrolysis emerge as a solution to produce storable energy (H₂) with better efficiency and less final waste. But the lack of technical means and the absence of sufficient economic elements to evaluate the profitability of these installation projects remains a problem (Gabbar et al., 2018). From an environmental point of view, these three categories of installations are subject to the same requirements regarding the limit values for emissions of various pollutants into the air and it should be remembered that the emission standards for these installations have recently been tightened by European regulations (Ministère de la Transition écologique, 2020).

## 1.2 | Waste for energy use

Waste characterization is a crucial phase in the selection, evaluation, and implementation of a waste treatment process (Coutin et al. 2007).

> Waste characterization is a
crucial phase in the selection,
evaluation, and
implementation of a waste
treatment process

Current R&D work on waste-to-energy is mainly focused on processes using biomass (Hatik and Gatina, 2017) or "mono-waste" such as tires, wood, plastics, or even rigorously prepared waste such as SRF (Vonk et al., 2018; Han et al., 2022). SRF is mainly composed of wood, plastic, and cardboard/paper in variable quantities and is used in furnaces and incineration plants. It must meet specific requirements such as being prepared from non-hazardous waste, having a high calorific value (over 12 MJ/kg) and having chemical characteristics that indicate they can safely replace conventional fuels (ADEME, 2015).

Regarding Residual Household Waste itself, few studies exist on its energy conversion due to its heterogeneity and its temporal and spatial variation. Indeed, RHW is composed of mixed materials in different proportions. Previous work by the ADEME has classified waste in a grid

of 12 material categories (Exhibit 2). The ADEME also determined the average composition of a typical RHW bin in Reunion Island: 25%–35% putrescible, 15% plastics, and 14% sanitary textiles. The other fractions are papers, cardboards, composites, textiles, glass, metals, and other combustibles and non-combustibles as shown in the Exhibit 3 (ADEME, 2019a).

From a regulatory point of view, it is important to assess the hazardous nature of RHW when they are subjected to processing (incineration, pyro gasification, methanization). For this purpose, it is necessary to study the elements that can generate dangerous or harmful products during the energy transformation such as halogens and heavy metals. Halogens, such as chlorine cause corrosion and their compounds (HCl, Cl₂) can be hazardous to health and the environment as well as some heavy metals like mercury (ADEME, 2019b). Other elements such as nitrogen and sulfur are verified. Indeed, nitrogen can be converted in nitrogen oxides (NOx) and sulfur to sulfur oxides (SOx) and sulfuric acid (H₂S), which are responsible for pollution and corrosion (ADEME, 2015). In France, the regulation currently concerns only four pollutants on SRF (ADEME, 2015): chlorine content must be less than 15,000 mg/kg on dry product, bromine content must be less than 15,000 mg/kg, the total halogen content must be less than 20,000 mg/kg and the mercury content must be less than 3 mg/kg on dry product. Cadmium is also monitored but is not regulated for the moment.

This study concerns the physico-chemical characterization of RHW in order to use it in a thermal-conversion process. The first step is to prepare 12 waste samples of known composition. They will be analyzed in an external laboratory to determine their elemental chemical composition, calorific value, and physical parameters (moisture, volatile matter, and ash). The results obtained will be compared with the literature in order to get an idea of the potential thermo-conversion of this RHW. The analysis of the pollutants present in these samples will also be carried out in compliance with environmental and health regulations. Finally, certain categories of waste will be highlighted as they would be particularly effective in the implementation of a thermal-conversion process on Reunion Island.

## 2 | MATERIALS AND METHODS

### 2.1 | Collection and preparation of samples

In this study, samples are composed of wood and/or waste. Wood is the material the most studied for thermo-conversion process. In this study, it will serve as a reference. Two types of wood were analyzed: Cryp-toeria wood chips from a local wood product and a mixture of wood from different trees located on the university campus. RHW is mainly collected on the university campus for this study. It is mainly composed of putrescible (food waste and green waste), paper (office paper, food packages), cardboard (food packages, boxes), composites (food packages), textiles (jacket, hat), sanitary textiles (baby nappies, tissues, hand towel, masks), plastics (bottles, food packages), other fuels (wood) and small part under 2 cm (food waste, cigarette butts). Non-combustible materials including glass, metals, and Special Household Waste (SHW)
<figure><img src="image_3.png" /><figcaption>**EXHIBIT 3** Average composition of Residual Household Waste (RHW) in Reunion Island. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>**EXHIBIT 4** Protocol for physico-chemical characterization. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

such as medical waste, PVC are removed since they are of no interest in energy conversion and may be hazardous.

From these raw materials, 12 samples were selected as shown on Exhibit 4. To obtain the most representative samples, their conditioning was based on the different compositions obtained during the waste characterization in 2018 by ADEME (ADEME, 2019a).

ECH1 and ECH7 are composed of cryptomeria wood and mixed wood, respectively. ECH2 and ECH8 have the same composition and are based on the composition of the local bin for non-recyclable household waste. They were collected at different times. ECH3, ECH4, ECH5, ECH9 show the influence of small particles (all waste >2 cm), putrescible, plastics, and cardboard/paper, respectively. ECH6 has the
approximate composition of a waste bin if all the sorting instructions were followed, cryptomeria wood (30%) is used for the smallest fractions of non-recoverable waste. The amount of putrescible is lower in ECH10 and ECH11 compared to ECH2 and ECH8. ECH12 contains about 80% mixed wood and 20% waste in the same proportions as ECH2. Their composition is summarized in Exhibit 5.

## 2.2 | Physico-chemical analysis

The physico-chemical parameters were then determined by an external laboratory SOCOR according to the European standards. In this paper, the parameters studied are: moisture content (W), Volatile Matter content (VM), Ash content (AC), and Fixed Carbon content (FC) as well as elemental contents such as carbon (C), hydrogen (H), nitrogen (N), sulfur (S), oxygen (O), halogens, and heavy metals. The calorific value is also important especially Low Heating Value (LHV) and High Heating Value (HHV). These analyses were carried out on the undried raw samples (raw basis) as well as on the dried samples (dry basis). The Exhibit 6 gives the parameters of some local RHW (ILEVA, 2015) and SRF (Vonk et al., 2018; Han et al., 2022) found in the literature.

**Moisture Content (W)** is characterized by the amount of water evaporated from the material after drying. It is an important economic and energy factor in the thermal-conversion process. Indeed, high humidity requires more energy to initiate combustion, which may reduce conversion efficiency. It is recommended to have a humidity lower than 20% (ADEME, 2019a; Komilis et al., 2014). The standard for measuring the humidity of household and similar waste is NF X30-466 (NF X30-466).

**Ash content (AC)** represents the mass of solid residue obtained after total combustion of the sample. The quantity and quality of ash, as well as its behavior at high temperatures, informs on the type of ash treatment system to be implemented after thermo-conversion. A high AC exceeding 10% can lead to process operating issues and therefore very regular monitoring (agglomeration in the pipes, waste management) (Vonk et al., 2018). The AC is measured according to the ISO 1171 standard relating to solid mineral fuels (ISO 1171:2010).

**Volatile Matter content (VM)** is the chemical species that are expelled from the fuel when it is subjected to high temperatures in an inert atmosphere. They are composed of non-condensable (mainly CO, H₂, and CH₄) and condensable gases (oils and char). This parameter gives information on the fuel reactivity: combustible with a high VM is more flammable. A minimum of 60% VM is recommended. The standard ISO 562 describes the operating procedure to measure the VM content (ISO 562:2010).

**Fixed Carbon content (FC)** is the solid residue remaining after the release of the VM, apart from the ash and humidity. It represents non-converted carbon in the tar. The FC content is calculated from the formula (LECO, 2019): $FC (\%) = 100 - (VM + C + W)$.

**Calorific Value** is the amount of chemical energy that is released as thermal energy during the combustion reaction. This parameter is influenced by W, AC, and the oxygen flow in the process.

<table><caption>EXHIBIT 5 Summary of the sample composition</caption><thead><tr><th>Sample</th><th>Composition</th><th>ECH1<br>Cryptomeria Average<br>wood</th><th>ECH2<br>RHW bin</th><th>ECH3<br>Small<br>part</th><th>ECH4<br>No<br>putrescible</th><th>ECH5<br>No sanitary<br>textile</th><th>ECH6<br>Ideal sorted<br>bin</th><th>ECH7<br>Mixed<br>wood</th><th>ECH8<br>Average<br>RHW bin</th><th>ECH9<br>No paper/<br>cardboard</th><th>ECH10<br>Less<br>putrescible<br>influence</th><th>ECH11<br>Average<br>DRW bin</th><th>ECH12<br>80% wood +<br>20% RHW</th></tr></thead><tbody><tr><td>(%w)</td><td>1. Wood</td><td>100</td><td></td><td></td><td></td><td></td><td>29.6</td><td>100</td><td></td><td></td><td></td><td>79.1</td></tr><tr><td></td><td>2. Putrescible</td><td></td><td>32.5</td><td>28.9</td><td></td><td>47.8</td><td></td><td></td><td>32.1</td><td>40.7</td><td>16.0</td><td>3.4</td></tr><tr><td></td><td>3. Paper</td><td></td><td>8.6</td><td>6.9</td><td>13.1</td><td>14.5</td><td></td><td></td><td>8.8</td><td></td><td>10.6</td><td>2.3</td></tr><tr><td></td><td>4. Cardboard</td><td></td><td>9.9</td><td>8.6</td><td>14.5</td><td>15.2</td><td></td><td></td><td>9.6</td><td></td><td>12.1</td><td>2.7</td></tr><tr><td></td><td>5. Composite</td><td></td><td>4.4</td><td>3.2</td><td>4.7</td><td>5.5</td><td></td><td></td><td>3.6</td><td>4.0</td><td>4.7</td><td>1.0</td></tr><tr><td></td><td>6. Textile</td><td></td><td>3.5</td><td>2.1</td><td>5.0</td><td>8.3</td><td></td><td></td><td>3.8</td><td>3.4</td><td>5.0</td><td>0.9</td></tr><tr><td></td><td>7. Sanitary textile</td><td></td><td>18.8</td><td>17.2</td><td>26.7</td><td></td><td></td><td>21.4</td><td>17.6</td><td>22.3</td><td>21.9</td><td>4.4</td></tr><tr><td></td><td>8. Plastic</td><td></td><td>17.8</td><td>17.1</td><td>27.1</td><td></td><td></td><td>48.9</td><td>19.2</td><td>23.5</td><td>23.3</td><td>4.5</td></tr><tr><td></td><td>9. Other combustible</td><td></td><td>4.6</td><td>4.1</td><td>8.9</td><td>8.6</td><td></td><td></td><td>5.3</td><td>6.2</td><td>6.5</td><td>1.8</td></tr><tr><td></td><td>10. Small part</td><td></td><td></td><td>11.9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>
<table><caption>**EXHIBIT 6** Physico-chemical data of some fuels and household waste.</caption><thead><tr><th>Sample</th><th></th><th>Wood</th><th>SRF</th><th>RHW Tampon</th><th>RHW St-Pierre</th><th>RHW St-Paul</th></tr><tr><th>Reference</th><th></th><th>(Vonk et al., 2018)</th><th>(Han et al., 2022)</th><th>(ILEVA, 2015)</th><th>(ILEVA, 2015)</th><th>(ILEVA, 2015)</th></tr></thead><tbody><tr><td rowspan="4">Immediate analyses</td><td>W (%w)</td><td>10.2</td><td>4.4</td><td>49.4</td><td>45.6</td><td>41.6</td></tr><tr><td>AC (%w dry)</td><td>1.3</td><td>9.2</td><td>26.5</td><td>20.7</td><td>10</td></tr><tr><td>VM (%w dry)</td><td>81.7</td><td>86.7</td><td>21.5*</td><td>75.4*</td><td>87.3</td></tr><tr><td>FC (%w dry)</td><td>17.0</td><td>4.1</td><td>NA</td><td>NA</td><td>NA</td></tr><tr><td rowspan="7">Elemental analyses</td><td>C (%w dry)</td><td>47.9</td><td>68.9**</td><td>40.5</td><td>40.5</td><td>48.3</td></tr><tr><td>H (%w dry)</td><td>5.8</td><td>8.9**</td><td>5.18</td><td>5.38</td><td>6.72</td></tr><tr><td>N (%w dry)</td><td>0.12</td><td>0.40**</td><td>1.15</td><td>0.95</td><td>0.91</td></tr><tr><td>S (%w dry)</td><td>0.00015</td><td>0.14**</td><td>0.13</td><td>0.20</td><td>0.21</td></tr><tr><td>O (%w dry)</td><td>46.2</td><td>21.3**</td><td>26.2***</td><td>31.7***</td><td>33.5***</td></tr><tr><td>Cl (%w dry)</td><td>0.0048</td><td>0.32</td><td>0.34</td><td>0.59</td><td>0.41</td></tr><tr><td>HHV (MJ/kg dry)</td><td>NA</td><td>NA</td><td>17.0</td><td>16.7</td><td>19.8</td></tr><tr><td>Thermal analyses</td><td>LHV (MJ/kg dry)</td><td>18.7</td><td>24.7</td><td>15.9</td><td>15.6</td><td>18.4</td></tr></tbody></table>

First, HHV is measured according to standard NF EN 15400 (NF EN 15400). HHV represents the total quantity of heat produced during the complete combustion of a fuel unit under oxygen with particular atmospheric conditions. LHV is then calculated from HHV, W and hydrogen content. It corresponds to the thermal energy released during the complete combustion of a combustible unit, excluding the latent heat resulting from the water vapour. The calorific value is an essential parameter. In practice, the calculation of HHV or LHV helps to compare the efficiency of different fuels (Selectra).

Elemental analysis (CHNO) is used to measure the content of C, H, N and O contained in a sample and sometimes S. These parameters are very useful to predict the reactivity of the fuel. The content of C, H and N is measured according to NF EN ISO 21663 relating to SRF. S is measured according to NF EN 15582 and O is determined by calculated at the end.

The determination of halogens and heavy metals is very important for regulations and process maintenance. This study considers: four main halogens (Cl, F, I, and Br) and eight heavy metals (Hg, Cd, Pb, As, Cr, Cu, Ni, Zn). The operating procedure for halogens is given in the standard NF EN 14582 relating to waste characterization. Currently, there is no standard for heavy metal analysis. They are measured by Inductively Coupled Plasma (ICP) spectroscopy.

# 3 | RESULTS AND DISCUSSION

## 3.1 | Energy perspective

In this first part of the result, the possible use of these samples in a thermal-conversion process is discussed.

The Exhibit 7 shows the samples classified by decreasing humidity and their calorific value especially LHV on dry basis and raw basis.

The lower the humidity, the higher the calorific value of the raw samples. Indeed, the calorific value strongly depends on the humidity (Vonk et al., 2018; ADEME, 2019a). These examples clearly show that humidity in RHW is particularly high, more than 30% when it consists of putrescible and small part (ECH5, ECH3, and ECH8). Correspondent LHV is below 12 MJ/kg (minimum value for SRF). Obviously, humidity decreases when the sample is composed mainly of plastic, wood, and other dry waste such as cardboard and paper (ECH7, ECH11, ECH12). Dry samples have higher LHV and are very similar to SRF. The dry ECH2 has a much higher LHV than the raw state, it has the second highest LHV after ECH6 and before the wood samples. They can reach more than 19 MJ/kg.

Volatile matter and ash content also influence the calorific value (Santos and Alencar, 2020). The Exhibits 8 and 9 show the samples classified by decreasing order in VM, respectively, on a raw and dry basis. Their corresponding LHV is also represented. Raw samples with a high volatile matter and a low ash content tend to have a high LHV. Decreasing moisture has a significant relationship with this effect. Once dry, the volatile matter content is of the same order of magnitude, therefore the samples have a higher LHV than the raw samples. As their moisture content has no influence, it is assumed that their nature determines the value of their LHV. Indeed, the cryptomeria wood-rich (ECH1 and ECH6) and plastic-rich (ECH9, ECH10, ECH4, and ECH6) samples have the highest LHV. Note the difference between wood samples 1 and 7, the dry mixed wood produces less volatile matter than cryptomeria. Ash content in RHW is very variable, from 1% to 12%. Plastic and wood samples (ECH1, ECH7, ECH6, and ECH9) generate less ashes than putrescible and cardboard/paper (ECH2, ECH8, ECH3, ECH5, ECH11, ECH12). In addition, dry RHW produces more ashes than wet ones that exceed 10%. Regarding the fixed carbon contents, woods are richer in fixed carbon than RHW. It would therefore appear that RHW does not produce more coke than wood.

<footnote>*organic matter; **dry and no ash; ***calculated value.</footnote>
<figure><img src="image_5.png" /><figcaption>**EXHIBIT 7** Calorific value as a function of decreasing humidity. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

Tanner diagram (or ternary waste diagram) in Exhibit 10 shows the suitability of a material or waste to combustion based on their AC, W, and combustible material content on a wet basis (Komilis et al., 2014; Tanner, 1965). It is used to assess the self-sustained combustibility (shaded area) of HSW during incineration. The samples are represented on this diagram as well as the South Korean SRF and the Runeva's RHWs from Exhibit 5. All the samples are in the grey zone, which implies that their combustion can be carried out without external heat input. They are viable materials for a thermo-conversion process. The South Korean SRF is very close to wood samples as well as ECH11 and ECH12, due to their very low humidity. In this area, the reactivity of the materials is greater and the calorific value higher. However, Runeva's RHWs are located at the edge of the grey zone, which makes them poorer fuels, on wet basis.

In Exhibits 11 and 12, elemental composition is represented in decreasing order of carbon content, respectively, on a raw and dry basis. This parameter affects the calorific value which is also represented in the figures (Santos and Alencar, 2020). In Exhibit 12, carbon decreases while oxygen increases due to the presence of water, so LHV of water-rich samples (ECH5, ECH3) are lower than drier samples (wood and ECH6). Dry RHW samples have high C values (> 42%). But unlike coal and oil which have a very low oxygen content (less than 10%), RHW is also rich in oxygen. In Exhibit 12, wood samples ECH6 and ECH2 have the highest carbon content and the lowest oxygen content on a dry basis, and thus the highest LHV. Thus, carbon-rich materials would be better fuels and the presence of oxygen would inhibit combustion.

The Van Krevelen diagram represented in Exhibit 13 supports these observations. It illustrates the H/C ratio of a dry fuel as a function of O/C ratio. It reflects the degree of carbonization of a solid fuel. H/C and O/C ratios are high for fuels with a low degree of carbonization

like peat and biomass. These ratios decrease with increasing degree of carbonization (Agraniotis et al., 2017). In addition, a lower O/C ratio leads to a higher LHV close to that of hydrocarbons. As expected, most of RHW samples are located in the biomass domain corresponding to high H/C and O/C ratios. South Korean SRF and ECH6 are less oxygen-rich and have a higher degree of carbonization hence their higher LHV. Dried ECH2 and Runeva samples also approach the SRF's properties. Contrary to the observations made on Tanner diagram, on a dry basis, these samples would be good fuels.

**3.2 | Regulatory perspective**

In this second part of the result, the regulatory approach is studied and therefore the potential pollutants present in the waste samples.

In Exhibit 14, N, S, and Cl contents are illustrated on a dry basis (the contents on raw material are generally similar). Chlorine is the most important halogen. Fluorine, iodine, and bromine have a low content, less than 40 mg/kg in the samples, they are not represented in the figure. Wood contains the least amount of chlorine unlike the RHW samples which contain more than 1000 mg/kg. ECH6 is the richest sample containing more than 18,000 mg/kg probably due to the composition of the plastics (with perhaps the presence of a chlorine-rich element). This element generally comes from putrescible materials, sanitary textiles (ADEME, 2007), certain plastics (PVC) (Riber et al., 2009), or even printed papers since the inks may contain chlorine (ADEME, 2015). Nitrogen contents in the samples are variable but all less than 1%. Cryptomeria wood contains very little unlike the ECH7 (mixed wood) and samples ECH2, ECH9 and ECH12 are the richest. Most of the time, nitrogen comes from putrescible, papers or certain plastics (Vonk et al., 2018; ADEME, 2007) or glues (Pizzi and Mittal).
<figure><img src="image_6.png" /><figcaption>**EXHIBIT 8** Calorific value as a function of decreasing volatile matter content (VM) on raw basis. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**EXHIBIT 9** Calorific value as a function of decreasing volatile matter content (VM) on dry basis. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**EXHIBIT 10** Ternary diagram of Tanner on raw basis, samples of the study are represented by the small color dots. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**EXHIBIT 11** Evolution of the low heating value (LHV) with decreasing carbon content on raw basis. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>**EXHIBIT 12** Evolution of the low heating value (LHV) with decreasing carbon content on dry basis. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**EXHIBIT 13** Van Krevelen diagram for various solid fuels, samples of the study are also represented with the small color dots. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

Sulfur contents are also very low, less than 0.13%. The richest samples are ECH2, ECH12 and ECH11. Very often sulfur comes from putrescible and/or certain plants (ADEME, 2007; Coutin et al., 2007) and also from some plastics, resins or glues (Vonk et al., 2018; ADEME, 2015).

The Exhibit 15 shows the heavy metal contents. Only Cr, Cu, Ni, Pb, and Zn are represented. The other elements Cd, As, and Hg are not shown in the figure because they are not detected by the analysis method used. Their content is, respectively, lower than 1, 2, and

0.1 mg/kg. These metals are often derived from printed packaging inks (Coutin et al., 2007), textiles, or leather goods (Riber et al., 2009). Wood contains very few heavy metals, unlike mixed RHW. The most important element is zinc, especially in the sample ECH6. Zinc is often found in putrescible such as meat or plant residues, sanitary textiles and other fuels (ADEME, 2015). Copper is the second most important element with contents between 3 and 95 mg/kg. The contents of the other elements are generally less than 25 mg/kg. Thus, once the metal materials have been removed, heavy metals might be therefore very little present in RHW.

## 3.3 | Discussion

From the above observations, it appears that the calorific value of RHW is highly dependent on its humidity, volatile matter content and intimately on its elemental composition (C and O). These parameters are related to the nature of the different materials that constitute the samples.

Generally, a high value of VM and C and low moisture content indicate that the material has a high energy conversion capacity. Indeed, dry waste, containing mostly plastic, wood, and sanitary textiles (ECH6, ECH9, ECH12), would be good fuels as they have low humidity, high volatile matter, high C content and high LHV, especially on a raw basis. Nevertheless, they are likely to cause environmental and regulatory
<figure><img src="image_12.png" /><figcaption>**EXHIBIT 14** Nitrogen, sulfur, and chlorine contents in local Residual Household Waste (RHW) on dry basis. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**EXHIBIT 15** Heavy metals contents (Cr, Cu, Ni, Pb, and Zn) in local Residual Household Waste (RHW) on dry basis. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>
problems (ash management and pollutant emissions). For instance, sample ECH6 has a composition close to SRF, which could explain its high calorific value despite its moisture content. However, its CI content can be a significant problem as it is higher than the regulations. Paper and cardboard waste as well as putrescible waste (ECH5, ECH11) are the least useful for energy production. These materials generally add moisture and produce a lot of ashes that can be problematic for the process operation. Moreover, they can be recycled or recovered by composting.

The physico-chemical analyses of samples ECH2 and ECH8, having the same composition, give different results, in particular their humidity, their ash or their CI, Cu, or Pb contents. This shows the variability of RHW over time and space. Indeed, RHW is made up of many different materials (although they are classified by categories). As seen above, this greatly influences the calorific value as well as the amount of any pollutants present. It is therefore impossible for two samples taken at different times and places to have the same physico-chemical composition. This makes characterization difficult. However, these two samples and more generally mixed RHW (ECH2, ECH3, ECH8, ECH10) containing a majority of putrescible, non-recyclable plastics and sanitary textiles seem to meet the fuel criteria (good calorific value and few pollutants) but only in a dry state. Dried samples have actually higher calorific value than raw samples and are comparable to SRF. Similarly, the Tanner and Van Krevelen diagrams confirm that these samples of RHW can be used as fuel for a thermal-conversion process since they fall within the study areas of the usual fuels. However, these figures highlight that they would be better fuels when dried. This implies a drying treatment of RHW that would improve their combustibility. The removal of small particles can also be considered to improve conversion (differences between ECH2 and ECH3).

## 4 | CONCLUSION AND PERSPECTIVES

Despite the variability in waste properties, this study indicates that mixed RHW from Reunion Island are potential feed-stock for thermo-conversion processes such as pyro-gasification that could be an alternative to landfill. For optimal energy conversion, mixed wood /plastic/sanitary textiles (ECH6) and mixed dry waste (ECH2) seem to be the most appropriate. However, the study also highlights the importance of conditioning upstream of the conversion process to increase the energy potential of these materials and reduce the risks of pollutant emissions. Indeed, meticulous sorting is necessary in order to eliminate irrelevant materials (metals, glasses, small elements) and dangerous materials (PVC, explosive materials). Then, the humidity of RHW must be constantly checked for the best energy conversion efficiency. In a tropical area such as Reunion Island, where humidity varies greatly, the moisture content of waste is likely to be problematic. The installation of a drying or roasting device should be considered before the thermal conversion process.

## ACKNOWLEDGEMENTS

The authors are grateful for the financial support and information provided by the FEDER, the Région Réunion, and technical support of the University of Reunion Island.

## DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.

## REFERENCES

* ADEME. (2015). COMBUSTIBLES SOLIDES DE RECUPERATION (CSR). Technical Report. www.ademe.fr/mediatheque

* ADEME. (2019). CARACTERISATION DES DECHETS SUR L'ILE DE LA REUNION. Technical Report. www.ecogeos.fr

* ADEME. (2019). INCINERATION HAUTE TEMPERATURE DE DECHETS HALOGENES/SOUFRES ET NANODECHETS. Technical Report. www.ademe.fr/mediatheque

* ADEME. (2007). La composition des ordures ménagères et assimilées en France. www.ademe.fr/mediatheque/publications

* AFNOR. (2010). Solid mineral fuels-Determination of ash. Technical Report.

* AFNOR. (2010). Hard coal and coke: Determination of volatile matter.

* AFNOR; NF EN 14582. Characterization of waste, Halogen and sulfur content, Oxygen combustion in closed systems and determination methods. Technical Report.

* AFNOR; NF EN 15400. Solid recovered fuels Determination of calorific value. Technical Report.

* AFNOR; NF EN ISO 21663. Solid recovered fuels - Methods for the determination of carbon (C), hydrogen (H), nitrogen (N) and sulphur (S) by the instrumental method. Technical Report.

* AFNOR; NF-X30-466: Déchets ménagers et assimilés : Méthode de caractérisation - Analyse sur produit sec. Technical Report.

* Agraniotis, M., Bergins, C., Stein-Cichoszewska, M., & Kakaras, E. (2017). High-efficiency pulverized coal power generation using low-rank coals. In *Low-rank coals for power generation; Fuel and chemical production* (pp. 95–124). Elsevier. https://doi.org/10.1016/B978-0-08-100895-9.00005-X

* Coutin, F. A., Philippe, F., & Vermande, P. (2007). Contribution à la caractérisation physico-chimique des déchets de deux marchés de la commune de Port-au-Prince (Haïti): propositions de traitements; Déchets, sciences et techniques. https://doi.org/10.4267/dechets-sciences-techniques.1653

* Direction Générale de la Prévention des Risques. (2020). Note d'explication de la nomenclature ICPE des installations de gestion et de traitement de déchets. Technical Report.

* Gabbar, H. A., Aboughaly, M., Ayoub, N. (2018). Comparative study of MSW heat treatment processes and electricity generation. *Journal of the Energy Institute, 91*, 481–488. https://doi.org/10.1016/j.joei.2017.04.009

* Han, S. W., Tokmurzin, D., Lee, J. J., Park, S. J., Ra, H. W., Yoon, S. J., Mun, T. Y., Yoon, S. M., Moon, J. H., Lee, J. G., Kim, Y. M., Rhee, Y. W., & Seo, M. W. (2022). Gasification characteristics of waste plastics (SRF) in a bubbling fluidized bed: Use of activated carbon and olivine for tar removal and the effect of steam/carbon ratio. *Fuel*, 314, 123102. https://doi.org/10.1016/j.fuel.2021.123102.

* Hatik, C., & Gatina, J. C. (2017). Waste production classification and analysis: A PCA-induced methodology. *Energy Procedia*, 136, 488–494. https://doi.org/10.1016/j.egypro.2017.10.308

* ILEVA. (2015). RAPPORT DE MISSION 1: CARACTERISATION QUANTITATIVE ET QUALITATIVE DES DECHETS Mission 1- Caractérisation quantitative et qualitative des déchets. Technical Report. https://runeva.re/
ILEVA. (2019). Un projet pour une gestion durable et vertueuse des déchets dans les microrégions ouest et sud de La Réunion; Concertation préalable du 21 octobre au 12 décembre 2019, Dossier du Maître d'ouvrage. https://runeva.re/

INOVEST. Accueil-INOVEST. https://inovest.re/

Komilis, D., Kissas, K., & Symeonidis, A. (2014). Effect of organic matter and moisture on the calorific value of solid wastes: An update of the Tanner diagram. *Waste Management*, *34*, 249–255. https://doi.org/10.1016/j.wasman.2013.09.023

Lebon, E., Madushele, N., & Adelard, L. (2020). Municipal solid wastes characterisation and waste management strategy evaluation in insular context: A case study in Reunion Island. *Waste and Biomass Valorization*, *11*, 6443–6453. https://doi.org/10.1007/s12649-019-00860-1

LECO Corporation. (2019). Instrument: TGA801 moisture, volatile matter, ash, and fixed carbon determination in coal. Technical Report. www.leco.com

Mohee, R., Mauthoor, S., Bundhoo, Z. M., Somaroo, G., Soobhany, N., & Gunasee, S. (2015). Current status of solid waste management in small island developing states: A review. *Waste Management*, *43*, 539–549; https://doi.org/10.1016/j.wasman.2015.06.012
[NE EN 15582], AFNOR.

Riber, C., Peterson, C., & Christensen, T. H. (2009). Chemical composition of material fractions in Danish household waste. *Waste Management*, *29*, 1251–1257. URL: https://doi.org/10.1016/j.wasman.2008.09.013

Santos, R. G. d., & Alencar, A. C. (2020). Biomass-derived syngas production via gasification process and its catalytic conversion into fuels by Fischer-Tropsch synthesis: A review. *International Journal of Hydrogen Energy*, *45*, 18114–18132. https://doi.org/10.1016/j.ijhydene.2019.07.133

Selectra. Pouvoir calorifique supérieur (PCS): le comprendre et le calculer. https://selectra.info/energie/guides/comprendre/pouvoir-calorifique-superieur

SUEZ. INOVEST donne une seconde vie aux déchets. https://www.suez.fr/fr-fr/notre-offre/succes-commerciaux/nos-references/inovest

Tanner. (1965). https://www.e-periodica.ch/digbib/view?pid=sbz-002:1965:83::262#2137

Vonk, G., Piriou, B., Felipe Dos Santos, P., Wolbert, D., & Vaïtilingom, G. (2018). Comparative analysis of wood and solid recovered fuels gasification in a downdraft fixed bed reactor. *Waste Management*, *85*, 106–120; https://doi.org/10.1016/j.wasman.2018.12.023

How to cite this article: Maillot, M., & Morau, D. (2023).

Physico-chemical characterization of Residual Household

Waste for energy recovery in insular territories: Case study of
Reunion Island. *Environmental Quality Management*, *33*(1),
107-119. https://doi.org/10.1002/tqem.21989