Characterisation of excavated fine fraction and waste composition from a Swedish landfill

Abstract

The present research studies the characterisation and the physico-chemical properties of an excavated fine fraction (<10 mm) from a Swedish landfill, the Högbytorp. The results showed that the fine fraction represents 38% by mass of the total excavated wastes and it contains mainly soil-type materials and minerals. Higher concentrations of zinc, copper, barium and chromium were found with concentrations higher than the Swedish Environmental Protection Agency (EPA) for contaminated soil. The found moisture and organic contents of the fine fraction were 23.5% and 16.6%, respectively. The analysed calorific value (1.7 MJ kg⁻¹), the potential of CH₄ (4.74 m³ t⁻¹ dry matter) and Total Organic Carbon (TOC) (5.6%) were low and offer low potential of energy. Sieving the fine fraction further showed that 80% was smaller than 2 mm. The fine represents a major fraction at any landfill (40%–70%), therefore, characterising the properties of this fraction is essential to find the potential of reusing/recycling or safely redisposing.

Keywords

Landfill mining Högbytorp landfill characterisation of wastes fine fraction physico-chemical properties waste composition

Introduction

Serious discussions regarding scarcity of important natural resources have been carried out throughout the world (European Commission, 2010). Natural constituents like copper, iron, zinc and the earth rare metals are depleted in their primary sources, while there is a huge increasing demand owing to the development of the standard of living (Jani et al., 2014). As an example, about 50% of the primary mined iron and copper are unusable now owing to landfilling and dumping in other waste streams (Krook and Baas, 2013). However, supplying industries with raw materials in an economic, environmental and sustainable way highlighted the need to shift from the open loop practice (where all the wastes are landfilled) into the circular economy closed loop model, where all the waste materials (the new and the dumped wastes) are considered as secondary resources that must be recovered and recycled again in different industries. In response to that demand of materials, the recycling and recovery of materials from landfills through the landfill mining approach has gained growing interest (Greedy, 2015). The landfill mining main idea is to consider the landfill sites as temporary reservoirs for the recovery of future resources and also to recover land value spaces, which are important within the current situation of increasing the rate of population and fast urbanisation process (Wolfsberger et al., 2015b).

On the other hand, not only the recycling of materials and the recovery of energy are responsible for the interest in landfill sites, but also the environmental threats of landfills that can occur. Therefore, local and the European Union (EU) legislation framework (such as Directive 2008/98/EC) put forward national and regional regulations about landfill managements and secure operations. These regulations take into account the potential environmental risks of landfill leachate and high emission of greenhouse gases (Scharff, 2012).

The landfill fine fraction (frequently 10 or 20 mm) represents 40%–70% of the total excavated waste materials (Hull et al., 2005; Mönkäre et al., 2016; Quaghebeur et al., 2013). Typically, fines contain mainly soil with different quantities of landfilled materials (Hogland, 2002). Owing to the lack of economic value, the characterisation properties of the fine fraction have not been studied well (Mönkäre et al., 2016). To identify the recovery, the recycling and the final disposal methods of this fraction, the physico-chemical properties must be characterised. Recently, thermochemical techniques like incineration and gasification have assessed the use of different landfilled wastes with small particle sizes like the fine fraction (Bosmans et al., 2013). Therefore, properties like the calorific value and the potential of CH₄ must be also identified.

In Sweden there is a lack of information about the physico-chemical properties of the fine fraction and the recycling options. Therefore, the goal of the present study is to characterise the properties of the fine fraction from a Swedish landfill (the Högbytorp) by specifying the physico-chemical properties, like moisture content, organic content, total metal content and other properties, as an essential step in the evaluation of the possibility of recovering or recycling the excavated fine fraction (<10 mm). In addition, the mass balance of the total waste materials was also studied after the sieving of the excavated waste materials to three different fractions: Coarse fraction (>40 mm), medium-size fraction (between 40 and 10 mm) and fine fraction (<10 mm). However, the composition of the excavated medium-size fraction (between 40 and 10 mm) was also studied by hand sorting to 13 different categories.

Material and methods

Site description

Högbytorp landfill is Ragn-Sells AB largest waste treatment facility and is located 40 km northwest of Stockholm (60°32’N, 17°37’E, Sweden). The landfill was established in 1964, occupies an area of around 30 ha and contains municipal as well as industrial wastes. This landfill receives 700,000 t of waste yearly, making the landfill the largest landfill in Sweden with total wastes amount of about 4m t. The landfill has different waste units and cells addressed to contaminated soil, oily sludge from car washes, organic materials, PTP (paper tape perforator) – paper, wood and plastics, metals scrap, ash, medical waste, hazardous waste disposal, and wastes from municipalities, industries and households. Therefore, the landfill consists of a complex mixture of organic and inorganic wastes.

Excavation and sampling

The excavated area was a temporary waste heap of approximately 1000 t and contained municipal, construction and demolition waste that have been stored since 2009. The sampling was done in April 2014 by excavating four test pits (hole1:H1, hole2:H2, hole3:H3, hole4:H4) using a bucket excavator with 1 m³ excavation capacity, which were further divided into four different depth layers (B1, B2, B3, B4) reaching an approximate total depth of up to 4 m from the top of the landfill. Therefore, each layer had an approximate thickness of about 1 m. The total amount of the excavated waste for sampling was about 32,830 kg with 6550 kg, 9000 kg, 6650 kg and 10,630 kg from H1, H2, H3 and H4, respectively.

As soon as excavation was done, excavated waste was then fed into screening equipment (TEREX model 883, UK) to separate the wastes into three different fractions: Coarse fraction >40 mm, medium-size fraction between 40 mm and 10 mm and the fine fraction <10 mm.

A total of 16 samples were collected (one sample from the combination four holes and for layers) for the hand sorting (which was directly done at the site after excavation) of the medium-size fraction (10–40 mm). A total of 48 samples with about 10 L each (triplicate from each one of the 16 layer and hole combinations) from the fine fraction <10 mm was collected for laboratory analysis. The 48 samples were transferred and stored at 4 ^oC in the laboratory during the performance of analyses.

Hand sorting of the medium size fraction (10–40 mm)

The 16 collected samples were directly sorted manually into 13 different categories: Soft plastic, other plastic, rubber, ferrous metals, non-ferrous metals, stone, wood, glass, paper, textile, asphalt, limestone and soil-type material (sorting residue that could not be identified by visual inspection). The results of the hand sorting of the medium size fraction of the four holes are shown in Table 1 (and Figure 2, detailed later). The total amount of the hand-sorted waste was about 84 kg with 15.57 kg, 21.26 kg, 18.85 kg and 28.34 kg from H1, H2, H3 and H4, respectively.

Table 1.

Results of sorting analyses conducted in the past and the present study in wt%.

Fraction	% Waste in UKSiddiqui et al. (2012)	% Waste in GermanySiddiqui et al. (2012)	% Waste in USAHull et al. (2005)	% Waste in SwedenPresent study
Type of waste	MSW	MSW	MSW, construction and demolition	MSW, construction and demolition
Total waste amount	—	—	3.8m t	4m t
Soft plastic	4.57	2.4	17.13 (1.68)	0.66 (0.15)
Other plastic	6.27	5.91	0.54 (0.15)	6.81 (0.55)
Rubber	0.18	0.25		0.19 (0.09)
Ferrous metals	—	—	7.17 (0.89)	0.47 (0.11)
Non-ferrous metals	Both metals:0.49	Both metals: 1.49	0.3 (0.17)	0.45 (0.33)
Stones	1.73	3.17	3.5 (1)	28.07 (5.39)
Wood	1.57	3.22	20.5 (5.37)	15.20 (1.41)
Glass	25.06	28.61	0.67 (0.31)	5.62 (1.12)
Paper	0.43	0.18	And cardboard 21.17 (4.86)	4.48 (1.2)
Textile	1.33	0.63	And rubber 8.47 (2.1)	2.73 (1.03)
Asphalt	0	0	0	3.21 (1.85)
Limestone	0	0	0	4.81 (2.77)
Bones	0.27	0.37	Food and yard: 2.63 (0.25)	0
Hazardous	0	0	0.2 (0.1)	0
Soil-type material (not-identified)	58.1	53.77	17.77 (8)	27.30 (1.11)
Total weight in kg	25	25	80	84.02

The value between brackets represents the standard deviation.

MSW: municipal solid waste.

Analysis

To reduce the time and the number of samples, the fine fraction (<10 mm) analyses were divided into two parts. In each part, all the analyses were repeated three times (to insure the results) and the average was taken as the final result.

In the first part, 40 L of fine fraction (<10 mm) from all the holes and buckets was mixed to form an aggregate. Then the leachate from the fine fraction was analysed to find the Chemical Oxygen Demand (COD), metals content and Total Organic Carbon (TOC) according to the EN 12457-4: 2002 (Characterisation of waste. ISBN: 0 580 40580 X, United Kingdom), EN 12457-3: 2002 (Characterisation of waste. Leaching. ISBN: 0 580 40580 X, United Kingdom) and SS-EN 13137: 2001 (Characterisation of waste. Determination of total organic carbon (TOC) in waste, sludges and sediments. ISBN: 0 580 38053 X, United Kingdom)-A standards, respectively, for the liquid to solid ratio (L/S) of 10 (which was obtained by mixing the fine fraction with distilled water in a one-stage shaking leaching test for 24 h). The pH and the electrical conductivity were analysed by shaking 10 g of fine fraction with 100 ml distilled water (10 L/S) for 30 min (Hull et al., 2005). The pH was measured by the pH-meter Radiometer PHM 210 (HQ40d, Germany) and the electrical conductivity by the Radiometer CDM 210 (HQ40d, Germany). The calorific value was measured with an automatic bomb calorimeter, the IKA 200C, and the fine fraction’s bulk density was found according to the ASTM E1109-86(2009) standard. The results of these analyses are shown in Table 2.

Table 2.

Physical and chemical properties of the studied fine fraction (<10 mm).

Property	Value
TOC (%)	5.6
COD mg kg⁻¹ L/S = 10	2390
Bulk density (kg m⁻³) for dry matter	690
Calorific value (MJ kg⁻¹)	1.7
Volume of CH₄ (m³ t⁻¹ dry matter)	4.74
pH	7.7
Electrical conductivity (mS m⁻¹)	350

COD: chemical oxygen demand; L/S: liquid to solid ratio; TOC: total organic carbon.

In the second part, more focus was laid on the specification of physico-chemical properties of the excavated fine fraction by analysing moisture content, organic content, particle size distribution and metal content by using X-ray fluorescence (XRF) analysis.

Moisture content

About 500 g was taken from each one of the 48 samples to analyse the moisture content according to the SS-EN 14346:2007 standard. Each sample was dried in an oven at 105 ±5 ^oC until reaching a constant weight. The moisture content was found by calculating the weight difference before and after drying.

Organic content

The organic content was found according to the SS-EN 15169:2007 standard by heating about 100 g of dried weight (the samples were taken directly after finishing the moisture content tests) from the 48 samples in a furnace at 550 ^oC and for 1 h. The organic content was determined by calculating the weight difference before and after heating.

Particle size distribution and XRF analysis

About 500 g of fine fraction from each of the 48 samples was first dried and then sieved by a mechanical sieve for 15 min for the following particle sizes (>8, >4, >2, >1, >0.5, >0.25, >0.125 and <0.125 mm).

Semi-quantitative XRF analysis, Olympus DS-4000 (Innov-X system, USA), was used to analyse the samples using an XRF spectrometer and a Semi Q-program with a typical detection limit of 0.01% (w/w).

Results and discussion

Screening of the waste materials

As shown in Figure 1, the screening results showed that the medium and fine fractions have the same mass portion of 38% each. According to different studies (Kaartinen et al., 2013; Mönkäre et al., 2016; Wolfsberger et al., 2015a) the percentage of the fine fraction represents about (40%–70%) of the total excavated waste material and depends mainly on the excavation procedure, the waste age and the chosen particle size (usually between 10–20 mm). The fine fraction in the current study (38% by mass) is less than that of Mönkäre et al. (2016) at Kuopio and Lohja landfills in Finland, with 45% and 58%, respectively. In Mönkäre et al. (2016) the sampling was done by drilling, which can cause a reduction in the particle sizes of the waste owing to crashing (Sormunen et al., 2008). In addition, the amount of the fine fraction seems to increase with the age of the waste owing to the decomposition of the organic wastes. The waste age at Kuopio and Lohja landfills was 10 and 13 years, respectively, while it was only 5 years in this study. Furthermore, the chosen particle size was <20 mm in Mönkäre et al. (2016), while it was <10 mm in the current study. However, the present results (38%) were slightly less than that of Quaghebeur et al. (2013), with 44% at REMO landfill for the same particle size of <10 mm and an age of 14 years; compared with Hogland et al. (2004) who indicate the portion of fines (<18 mm) at the Måsalycke landfill in Sweden (age: 22 years) with 19.7%.

Composition of the excavated waste materials

One of the key factors in studying the potential of mining any landfill is to study the composition of the mined waste materials. However, the waste composition at any landfill depends on different parameters, like waste legislations, differences in the waste management systems, recycling systems, standard of living and on society and culture (Quaghebeur et al., 2013). As an example, the variation of the composition of the excavated waste materials from four different landfills in Sweden, USA, UK and Germany are shown in Table 1. The comparison between the waste materials in these four countries shows that the soil-type material is dominating the waste composition in UK and Germany. While the paper and cardboard fraction dominates the waste composition in USA and stones is the largest fraction in Sweden. However, the variation in the waste composition can appear even at different landfills in the same country, like the situation at Lohja and Kuopio landfills in Finland (Kaartinen et al., 2013; Mönkäre et al., 2016).

Figure 2 and Table 1 display the composition of the waste material for the medium-size fraction (between 40 and 10 mm) after hand sorting of the 16 samples according to the distribution of these waste fractions within each hole. The results showed that stones (28.0%), soil-type materials (27.3%) and wood (15.2%) dominate the composition of the waste materials in all four holes. This can be owing to the source of the waste materials, which contains municipal waste with construction and demolition wastes. High mass fractions of soil-type material (54.5%), stones (13.7%) and wood (10.0%) were also reported in Sweden at the Måsalycke landfill by Hogland et al. (2004). The same results were also found by Quaghebeur et al. (2013) in Belgium with soil-type material (70.0%), stones (20.0%) and wood (13.0%). On the other hand, the percentages of plastics (7.5% soft and others), paper (4.5%) and metals (0.9 ferrous and non-ferrous) were low compared with that of Hull et al. (2005) for paper (15.5%), plastics (17.7%) and metals (6.8%); while the present results are in agreement with that of Hogland et al. (2004) for metals (1.7%), paper (9.7%) and plastics (4.9%). This low percentage of plastics, paper and metals might be owing to the high-quality performance of the Swedish waste management system in collecting and recycling of the household waste materials (Avfall Sverige, 2015).

The present results show a high potential for the recycling of the excavated waste as ‘Waste to Material’ owing to the high concentration of stones, asphalt and limestone (36.1%) and also as ‘Waste to Energy’ owing to the concentration of plastics, wood, paper and textile (29.9%).

Laboratory analyses of the fine fraction (<10 mm)

The results of laboratory analyses of fines are presented in Table 2. The fines average pH value was 7.7, which was slightly higher than the fine fraction (<20 mm) pH value at Kuopio and Lohja landfills with 7.2 and 7.5, respectively (Mönkäre et al., 2016). However, the found pH was in the pH range (between 7 and 8) at different landfills (Hogland et al., 2004; Xiaoli et al., 2007). It is important to highlight that a neutral pH range is one of the European demands for the recycling of wastes in construction sectors (IPTS, 2009).

The fines calorific value, methane gas potential and TOC were also analysed. These parameters can specify the energy potential of the fine fraction. The found calorific value (1.7 MJ kg⁻¹) was slightly higher than that of Hogland et al. (2004) (0.9 MJ kg⁻¹) for the fine fraction <18 mm. This could be owing to the difference in the wastes age (5 and 22 years, respectively) and moisture content (23.5% and 29%, respectively). However, the result was slightly less than that of Quaghebeur et al. (2013) with (2.2 MJ kg⁻¹) for the 14 years mined fine fraction (<10 mm). The found methane gas potential was 4.74 m³ t⁻¹, which is in the range of the reported results for the fine fraction <11.2 mm (2.7–8.7 m³ t⁻¹) (Kim and Townsend, 2012; Mönkäre et al., 2016). The analysed TOC (5.6%) was in agreement with the result of Mönkäre et al. (2016) with (5.2%), but it was less than that of Quaghebeur et al. (2013) with 10%. The calorific value, methane gas potential and TOC decreased with increasing the waste storage time owing to the decomposition of the organic waste materials in the older landfill layers. Despite that the age of the studied waste was 5 years, both calorific value and TOC were lower in comparison with Quaghebeur et al. (2013), who have studied MSW fine fraction stored for 14 years, suggesting this could be owing to differences caused by the presence of not only MSW but also construction and demolition waste in the present study.

The COD is an important parameter to specify the possibility of recycling the excavated fine fraction. A high COD in the leachate means that the fine must be treated before recycling as a cover layer. A high COD concentration was reported by Sormunen et al. (2008) for the shredded and sieved <50 mm fraction at Kujala and Ämmässuo landfills in Finland with (5600 mg kg⁻¹) and (19,300 mg kg⁻¹), respectively. However, a low COD was found in the present study (2390 mg kg⁻¹), which was in agreement with that of Mönkäre et al. (2016) (2578 mg kg⁻¹) at Kuopio landfill in Finland.

One of the important parameters in designing the system of handling and reusing any waste materials is the bulk density (Hull et al., 2005). Limited information is found in literature about the fine fraction bulk density. The found bulk density (690 kg m⁻³) was slightly less than that of Hull et al. (2005) with 742 kg m⁻³. The difference in the results can be owing to the differences in the composition of the waste materials or the moisture content.

Moisture and organic content

The most influencing factor in the degradation of any waste materials is the moisture content, which plays vital role in the metabolism of all micro-organisms (Bäumler and Kögel-Knabaner, 2008). The moisture content is also important when considering the recycling of wastes to produce energy through biological or thermal methods (Brunner and Rechberger, 2015). In addition, it increases the dissolution of the organic and the inorganic of different chemical compounds like metals and hence increases the leaching of these compounds to the environment like water recipients (Qi et al., 2013). According to different studies, the wastes moisture content in Europe and USA ranged between 20% and 30%, while it is between 30% and 60% in China (Hull et al., 2005; Meng et al., 2012; Sormunen et al., 2008). This variation is mainly because of the high content of kitchen wastes in China, which represents 60% of the total waste materials (Meng et al., 2012). However, the moisture content in any landfill is affected by different interconnected parameters, like the composition, type and properties, the climatic conditions, landfill operating system and the soil cover layer, which are recommended to be 30–50 cm (Hull et al., 2005) for closed landfills. The results showed that the average moisture content was 23.5%, which is in agreement with that of Hull et al. (2005) with 25.9% and Mönkäre et al. (2016) at Lohja landfill 28.3%, and less than that at Kuopio landfill (43.3%) in the same study.

The wastes moisture content is highly interrelated with the organic content at any landfill (Bäumler and Kögel-Knabaner, 2008). The moisture content increased with the decrease of the organic content owing to the biological degradation of the organic materials. As shown in Figure 3, high levels of moisture content was related to a low percentage of organic contents owing to biodegradability, as clearly shown in hole 4 and hole 2. The average organic content was 16.6%, which is in agreement with that at Kuopio landfill with 12% and higher than that at Lohja landfill with 8.7% for the fine fraction <20 mm (Mönkäre et al., 2016). In contrast, high organic content (30%) was reported by Hull et al. (2005) for the fraction <25.4 mm. The variation in the moisture and the organic contents between the present and the former results can be owing to the differences in the studied particle sizes, the climatic, the landfill age and the waste composition.

Particle size distribution

The particle size distribution is one of the key parameters in specifying the physico-chemical properties of the landfill wastes. Studying this parameter helps to estimate the relevant methods of recycling and processing the fine fraction. The results of the dry sieving of the fine fraction to the particle sizes (>8, >4, >2, >1, >0.5, >0.25, >0.125 and <0.125 mm) are shown in Figure 4. The results showed similar behaviours in all holes. A total of 98% of the excavated fine fraction was of the size <4 mm, while 80% was within the particle size <2 mm. These results were in agreement to that of Hogland et al. (2004), with 90% of the fine fraction (<18 mm) being less than 10 mm. And also in agreement to that of Mönkäre et al. (2016) with 90.5% of the fine fraction (<20 mm) being in the size <11.2 mm and 70% under the particle size <5.6 mm. In contracts, Hull et al. (2005) reported that 50% of the fine fraction (<25.5 mm) was in the particle size <4.8 mm, while Kaartinen et al. (2013) found that 51% of the fine fraction (<20 mm) was within the size <4 mm. The difference in the results between the present and the reviewed researches might be owing to the difference in the chosen particle size of fine fraction, which was <10 mm in the present study and <18–20 mm in the former studies. In addition, the high percentage of small particle sizes could be owing to the drying and mechanical sieving (both were used), as these processes can crack bigger particles into smaller ones (Kaartinen et al., 2013).

Metals content

To evaluate the utilisation possibility of the excavated fine fraction identifying contaminants like heavy metals are essential. The fine fraction metals content was analysed by scanning all the 48 samples with XRF and the results are shown in Table 3. According to the found results, the zinc, copper, barium and chromium were in concentrations higher than that of the Swedish Environmental Protection Agency (EPA) metal limits for contaminated soils (SEPA, 2002). Therefore, the leachate from this fine fraction must be controled for future utilisations as a cover layer.

Table 3.

Heavy metal concentrations of fines obtained in past examinations and the present study.

Metalppm of dry matter	REMO, Belgium fraction <10 mmQuaghebeur et al. (2013)	Burlington, USA fraction <25.4 mmHull et al. (2005)	Högbytorp, Sweden fraction <10 mmPresent study	SEPA (2002) limits values for contaminated soil
Cr	495.7 (118)	26 (24)	254 (54)	150
Co	NM	NM	23.3 (5.8)	35
Ni	176.3 (60.7)	NM	111.4 (33.7)	120
Cu	339.3 (55.3)	NM	1460 (684)	200
Fe	27,000 (750)	NM	28,724 (8108)	—
Zn	667 (211)	487 (406)	1848 (488)	500
Ba	291 (167)	NM	468 (143)	300
Pb	NM	55 (46)	240 (65.3)	400
As	27.1 (15)	9.1 (8.6)	5.1 (1.7)	25
Cd	5.9 (3.8)	1.2 (1.2)	2.1 (0.6)	15
Hg	0.7 (0.5)	0.4 (0.4)	0.7 (0.2)	2.5
V	NM	NM	42.9 (10.8)	200
Sb	NM	NM	5.7 (2.1)	30
Mo	NM	NM	18.8 (3.9)	100

Note: Values between brackets represent the standard deviation.

NM: not measured.

The comparison of the current and former results of metals content in different landfills is also indicated in Table 3. The iron concentration was in agreement with that of Quaghebeur et al. (2013) and Kaartinen et al. (2013) for the fine fraction (<10 mm) and (<20 mm), respectively. While the concentrations of zinc and copper were higher than that of Quaghebeur et al. (2013) and Hull et al. (2005). The reason behind the higher concentrations of zinc and copper maybe owing to the degradation of plastics, papers and construction and demolition wastes, as suggested by Long et al. (2011). The barium concentration was slightly higher than that of Quaghebeur et al. (2013), while the concentrations of chromium and nickel were lower than that of Quaghebeur et al. (2013). Furthermore, the arsenic concentration was lower than that in all the reviewed studies.

Leaching test and recycling potential

According to the Swedish EPA, the leachate composition is an essential test to identify the recycling possibilities of waste materials like the fine fraction (SEPA, 2010). The leachate composition is presented in Table 4, compared with the Swedish EPA limits for recycling the wastes as construction materials, a cover layer (daily or final) inside landfills or for the re-deposition as an inert waste.

Table 4.

Leachate composition compared with the SEPA leachate limits for cover layer, deposition and construction material.

Metal (mg l⁻¹)	Fine fraction present study	SEPA (2010) leachate limits for:
Metal (mg l⁻¹)	Fine fraction present study	Construction material outside the landfill	Landfill cover layer	Landfilling as inert material
Cr	0.05 (0.01)	1.0	2.0	10
Ni	3.10 (0.28)	0.4	4.0	10
Cu	5.18 (0.57)	0.8	2.0	50
Zn	16.15 (4.74)	4.0	11.0	50
Ba	0.46 (0.18)	—	—	100
Pb	0.61 (0.40)	0.20	2.0	10
As	0.04 (0.005)	0.10	0.9	2
Cd	0.02 (0.01)	0.02	0.04	1
Hg	Not detected	0.01	0.02	0.2
Mo	2.91 (0.05)	—	—	10
Chlorides	2185 (219)	130	11,000	15,000
Fluorides	8.02	—	—	150

Note: Values between brackets represent the standard deviation.

The results showed that the recycling of the fines as a construction material is not possible owing to the concentrations of zinc, copper, nickel and lead, which were higher than the Swedish EPA limits. Furthermore, using the fines as a cover layer can be only possible if the concentrations of zinc and copper are reduced to the Swedish EPA limits. This can be done by using the washing method (Wang et al., 2015) (this method will be studied further in a future planned study). The final chosen solution was to re-dispose the fine fraction as an inert waste, which was in accordance with the Swedish EPA limits.

Conclusions

In this article, the characterisation properties of excavated fine fraction (<10 mm) from a Swedish landfill was studied. The mass percentage of the fine fraction was 38%. The study shows that 98% of the total fines were <4 mm and 80% were <2 mm. The visual inspection of the fine fraction showed that it is a heterogeneous material dominated by soil-like materials and minerals. The moisture and the organic contents of fines were 23.5% and 16.6%, respectively. The results of the calorific value (1.7 MJ kg⁻¹) and the methane gas potential (4.74 m³ kg⁻¹) with the low organic content 16.6% showed a low potential for recovering energy. High concentrations of zinc, copper, barium and chromium were found, which could offer an opportunity for metals extraction. Comparing the fines leachate composition with the Swedish limits for recycling the waste as a cover layer, construction materials or to safely redispose, emphasised that the best scenario is to redispose the fine fraction owing to the high concentrations of zinc and copper. Furthermore, the hand sorting of the medium size fraction (between 10 and 40 mm) showed a high potential of recycling Waste to Materials with 36.1% (stones, asphalt and limestone) and of Waste to Energy with 29.9% (plastics, wood, paper and textile). Waste characterisation is an essential first step during the planning and suggestions of the recycling/recovering technologies that can be used after mining the landfills.

Footnotes

Acknowledgements

The authors would like to acknowledge the financial support from the Swedish Institute-SI. We are grateful for the help obtained during the excavation and field work from the MSc and PhD students of Kaunas University of Technology (Department of Environmental Technology), Estonian University of Life Sciences (Institute of Agricultural and Environmental Sciences and the Department of Water Management), Linnaeus University (Environmental Science and Engineering Group) and to the support given by Ragn-Sells AB.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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