**4. Results and discussion**

ASTM–D 3173 standard (105°C) using moisture analyzer (Precisa, XM 50), whereas the heat value of the bio-dried material was determined using IKA C-7000 model calorimeter (IKA Laboratory Equipment, Werke Staufen, Germany), in accordance with EN 15400 standard. It is worth mentioning that, due to the heterogeneous nature of the waste, the weighted average method was employed in determining the initial moisture content of the waste matrix, since it was impossible to get a typical sample from the heterogonous mixture of the waste, a similar procedure employed by Shuqing et al. [48]. Elemental analysis was analyzed with Thermo Scientific Flash 2000 Elemental Analyzer (Thermo Fisher Scientific Inc., Bremen, Germany). Three different methods are employed for the determination of biogenic content of solid recovered fuels/bio-dried materials according to the technical specifications CEN/TS 15440:2006 (CEN, 2006). These include Selective Dissolution Method (SDM), Manual Sorting Method (MSM) and 14C Method. In the present study, the biogenic and non-biogenic content of the waste matrix

(a.r) 464.18 100.46 346.50 204.14

**Parameter Unit Food waste Paper Plastic Pruning waste**

**Biogenic mix Non-biogenic mix**

Moisture content % (a.r) 91.48 5.40 0.94 8.43 Ash content % (a.r) 25.33 18.64 2.05 6.36 Biogenic content % (a.r) 72.73 72.34 — 92.31 Non-biogenic content % (a.r) 1.94 9.02 96.44 1.33

Calorific value MJ/kg (a.r) 0.11 12.51 44.65 16.01

Bulk density kg/m3

**Table 2.** Composition of waste.

**Mixture Composition (%)**

96 Agricultural Waste and Residues

T1 85 15 T2 65 35 T3 50 50 T4 80 20 T5 75 25 T6 90 10 T7 80 20 T8 94 6 T9 84 16 T10 100 — T11 — 100

**Table 3.** Physico-chemical properties of raw material.

It is an established fact that combustible non-biogenic materials are characterized by higher heat content per unit weight than combustible biogenic materials. Consequently, the ratio of biogenic to non-biogenic material proportion can have a considerable effect on the heat content of a waste material intended for combustion purpose [40, 49]. **Figure 1** shows the relationship between moisture content and calorific value. The moisture content is a key parameter, as it affects both the biogenic carbon content and the effective heating value of the combustible waste. The moisture content of the bio-dried material varied between 8.59 and 50.93%, whereas that of the extreme conditions was 91.48 and 0.94% for biogenic (food waste) and non-biogenic materials, respectively (**Table 3**). It should be pointed out that the two extreme conditions were just raw materials without been subjected to bio-drying process. It can be seen that as the share of biogenic waste in the waste matrix gradually decrease, a corresponding trend in moisture content could be expected. Additionally, depending on the amount of food waste in the waste mix of the biogenic material, a decrease or increase in moisture content could be envisaged since the food waste contributes the highest initial moisture content to the biogenic waste mix.

The results revealed a positive correlation between moisture content and calorific value (R<sup>2</sup> = 0.85). As indicated earlier, the amount of biogenic waste had a significant impact on the former and latter. A discrepancy was observed in T3 and T5 in terms of moisture content and calorific value. Even though T3 had the lowest moisture content, T5 had the highest calorific value. The possibly reason was that the difference in food waste in both trials versus the other waste types in the biogenic mix was high enough to induce significant difference in the observed levels of calorific value, with approximately same non-biogenic mix. This suggest that, depending on the amount of food waste in the biogenic mix, the moisture content and calorific value of the bio-dried material could be significantly affected, regardless of the amount of non-biogenic waste in the waste matrix.

**Figure 1.** Calorific value as a function of moisture content of bio-dried materials.

However, a relatively slight deviation was observed in the trend for certain composition of waste particularly in instances where there is an absence of pruning waste and slightly decrease in food waste. This is probably attributed to the pruning waste having the highest proportion of biogenic carbon content of all the waste types, thus having a proportionally greater impact on biogenic carbon content of the waste matrix relative to its calorific value.

waste had the highest sulfur content relative to the other raw materials. Oxygen was dominant in pruning and food waste with lowest oxygen content recorded in paper (10.79%), indicating the presence of inorganic or low oxygen content organic molecules in papers. The results of the elemental analysis obtained in this study are consistent with those reported by Komilis et al. [49]. **Figure 3** shows the relationship between calorific value and biogenic carbon content of the different composition of waste. The different compositions resulted in a wide range of biogenic carbon content and calorific value. The non-biogenic carbon content in the waste matrix ranged between 1 and 7%, with T2 having the highest non-biogenic content (**Figure 2**). This was attributed to the low contribution of paper and pruning waste to the waste matrix of the biogenic mix, which were the major contributors to the biogenic carbon content of the bio-dried materials. On the other hand, T7 had the highest biogenic carbon content of 91.84%. The reason was associated with the amount of food waste relative to the other the biogenic waste materials in the biogenic mix. Similarly, two extremes conditions of biogenic (T10) and non-biogenic (T110 waste were considered. It is evident that the proportion of the different waste components in the waste matrix had significant impact on the biogenic content and the calorific value as well. It can be seen that the former reduces as the amount of biogenic source in the waste mix reduces whiles the latter increases as the calorific value of non-biogenic source due to the high moisture content. The results revealed a very highly positive correlation between biogenic content and calorific value (R<sup>2</sup> = 0.87). It should be pointed out that the amount of food waste as a biogenic material in the waste mix impacted on the calorific value of the bio-dried materials due to its high initial moisture content. Additionally, it should also be emphasized that pruning waste and paper were the major contributors to the biogenic content of the bio-dried materials. For instance, it is clearly that T1 contained higher proportion of pruning waste and paper as compared to bio-dried material obtained in T9. The biogenic content herein refers to the non-fossil based carbon content. It is suggested that any material with a calorific value that

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**Figure 2.** Biogenic and non-biogenic carbon content of bio-dried materials.

As shown in **Table 2**, a range of waste composition was developed to examine their impact on biogenic content and calorific value. The elemental analysis of carbon, hydrogen, oxygen, nitrogen and sulfur are presented in **Table 4**. The results indicated that carbon and oxygen were the most dominated elements in the raw materials, with biodegradable waste such as food waste, pruning waste and paper composed at 32.55, 37.14 and 64.72% of the total weight, respectively. The non-biogenic material (plastic) had the highest carbon content of 68.55%. Nitrogen was measured in high contents in food waste with paper as the lowest. The hydrogen content of the raw materials ranged from 5.17% to 12.90%, with plastic having the highest hydrogen content. Food


**Table 4.** Elemental composition of raw materials.

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**Figure 2.** Biogenic and non-biogenic carbon content of bio-dried materials.

However, a relatively slight deviation was observed in the trend for certain composition of waste particularly in instances where there is an absence of pruning waste and slightly decrease in food waste. This is probably attributed to the pruning waste having the highest proportion of biogenic carbon content of all the waste types, thus having a proportionally greater impact on biogenic carbon content of the waste matrix relative to its calorific value.

As shown in **Table 2**, a range of waste composition was developed to examine their impact on biogenic content and calorific value. The elemental analysis of carbon, hydrogen, oxygen, nitrogen and sulfur are presented in **Table 4**. The results indicated that carbon and oxygen were the most dominated elements in the raw materials, with biodegradable waste such as food waste, pruning waste and paper composed at 32.55, 37.14 and 64.72% of the total weight, respectively. The non-biogenic material (plastic) had the highest carbon content of 68.55%. Nitrogen was measured in high contents in food waste with paper as the lowest. The hydrogen content of the raw materials ranged from 5.17% to 12.90%, with plastic having the highest hydrogen content. Food

**Parameter Food waste Paper Plastic Pruning waste**

Carbon 32.55 64.72 68.55 37.14 Nitrogen 2.97 0.32 0.99 1.10 Hydrogen 5.17 5.49 12.90 8.09 Oxygen 33.85 10.79 15.46 47.30 Sulfur 0.07 0.04 0.05 0.01

**Figure 1.** Calorific value as a function of moisture content of bio-dried materials.

98 Agricultural Waste and Residues

**Table 4.** Elemental composition of raw materials.

waste had the highest sulfur content relative to the other raw materials. Oxygen was dominant in pruning and food waste with lowest oxygen content recorded in paper (10.79%), indicating the presence of inorganic or low oxygen content organic molecules in papers. The results of the elemental analysis obtained in this study are consistent with those reported by Komilis et al. [49].

**Figure 3** shows the relationship between calorific value and biogenic carbon content of the different composition of waste. The different compositions resulted in a wide range of biogenic carbon content and calorific value. The non-biogenic carbon content in the waste matrix ranged between 1 and 7%, with T2 having the highest non-biogenic content (**Figure 2**). This was attributed to the low contribution of paper and pruning waste to the waste matrix of the biogenic mix, which were the major contributors to the biogenic carbon content of the bio-dried materials. On the other hand, T7 had the highest biogenic carbon content of 91.84%. The reason was associated with the amount of food waste relative to the other the biogenic waste materials in the biogenic mix. Similarly, two extremes conditions of biogenic (T10) and non-biogenic (T110 waste were considered. It is evident that the proportion of the different waste components in the waste matrix had significant impact on the biogenic content and the calorific value as well. It can be seen that the former reduces as the amount of biogenic source in the waste mix reduces whiles the latter increases as the calorific value of non-biogenic source due to the high moisture content. The results revealed a very highly positive correlation between biogenic content and calorific value (R<sup>2</sup> = 0.87). It should be pointed out that the amount of food waste as a biogenic material in the waste mix impacted on the calorific value of the bio-dried materials due to its high initial moisture content. Additionally, it should also be emphasized that pruning waste and paper were the major contributors to the biogenic content of the bio-dried materials. For instance, it is clearly that T1 contained higher proportion of pruning waste and paper as compared to bio-dried material obtained in T9. The biogenic content herein refers to the non-fossil based carbon content. It is suggested that any material with a calorific value that

is efficient at turning that waste into useable energy. Finally, this technology will help mitigate

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The authors would like to thank the Scientific and Research Unit (BAP) of University of

and Ismail Ozbay1

1 Department of Environmental Engineering, University of Kocaeli, Kocaeli, Turkey

[1] EC. 2001. Council Directive 1999/31/EC concerning landfilling of waste on the landfill of waste. Avalable from: <http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELE

[2] Council Directive 1999/31/EC. Council Directive 1999/31/EC of 26 April 1999 0n the landfill of waste. Official Journal L 182, 16/7/1999, pp. 1-19. Available from: http://eurlex. europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:1999:182:0001:0019:EN:PDF. [Accessed:

[3] Stuart T. Waste—Uncovering the Global Food Scandal. London: Penguin Books; 2009.

[4] Gustavsson J, Cederberg C, Sonesson U. Global Food Losses and Food Waste: Extent, Causes and Prevention. Rome, Italy: Food and Agriculture Organization of the United Nations; 2011

[5] UNEP. Waste: Investing in energy and resource efficiency. In Towards a Green Economy: Pathways to Sustainable Development and Poverty Eradication. 2011. pp. 286-329. Available from:http://www.unep.org/greeneconomy/Portals/88/documents/ger/ger\_final\_

environmental pollution from the disposal of biodegradable waste.

\*, Augustine Donkor<sup>2</sup>

2 Department of Chemistry, University of Ghana, Accra, Ghana

X:31999L0031&from=EN> [Accessed: 2016-05-15]

dec\_2011/8.0 WASWaste.pdf. [Accessed: 2017-06-30]

\*Address all correspondence to: mutbaby@gmail.com

**Acknowledgements**

**Conflict of interest**

**Author details**

Mutala Mohammed<sup>1</sup>

**References**

2017-11-10]

ISBN: 978-0-141-03634-2

Kocaeli for the financial support.

The authors declare no conflict of interest.

**Figure 3.** Calorific value as a function of biogenic carbon content of bio-dried materials.

exceeds the range of 1–6 MJ/kg could be considered for combustion purpose [50]. Accordingly, waste-to-energy technology can be applied to recover energy from the bio-dried material.
