LANDIFILL MINING AND ITS POTENTIAL ROLE IN THE CIRCULAR ECONOMY

PROF. RAFFAELLO COSSU, AVV. ANDREA FANTAPPIE’

General objectives

Landfill mining (LFM) consists of excavating and treating waste from landfills. Interest in LFM has grown steadily in Italy since the 1990s (Cossu et al., 1995).

The reasons for carrying out LFM may be one or more of those shown in Figure 1.

Figure 1: Graphic representation of the main motivations for the use of the “Landfill Mining” technique.

The removal of a source of contamination, whether potential or confirmed, is particularly important in cases where a landfill presents risks or critical issues attributable to:

• outdated design models based on obsolete standards and regulations;
• inadequate management, lacking effective quality control of the waste delivered;
• design or construction errors;
• physiological degradation of containment barriers;
• intrinsic deficiencies in the landfill system itself which, as currently regulated, allows materials that are likely to generate and mobilise contaminants to be released into the soil.

In this context, landfill mining represents a decisive intervention, as it eliminates the risk of pollution at source, remediates existing contamination, overcomes the technical and administrative problems associated with post-operational landfill management, and relieves operators of the legal and economic responsibilities assigned to them by current legislation.

The recovery of soil and available volumes can generate significant advantages in several respects:

• availability of areas for expansion or urban redevelopment;

• availability of new volumes for the construction of controlled landfill facilities, without further land consumption, as well as for the temporary storage of fractions deriving from separate collections which, for territorial or market reasons, cannot be immediately placed and remain awaiting subsequent valorisation (Wagner and Bilitewski, 2009);
• recovery of energy and materials from previously delivered waste.

The recovery of resources represents, more than a strictly economic advantage, a benefit in terms of an increase in the volumes useful for the controlled burial of waste. In fact, the greater the amount of material excavated and destined for outside the landfill, the greater the volume recovered and reusable.

However, recovery and recycling operations present significant challenges. On the one hand, there are technical difficulties in achieving quality standards suitable for the commercialisation of recovered materials (e.g. washing gravel and sand); on the other hand, treatment plants located at economically sustainable distances are required, as in the case of incineration of combustible fractions (plastic, paper, wood, rubber, etc.).

LFM projects must be properly planned and based on solid technical, economic and financial foundations. In order to assess their feasibility, it is therefore necessary to examine various aspects such as the infrastructure and plant context of the surrounding area, the composition of the waste, the environmental conditions of the landfill, any need for conditioning prior to excavation, possible destinations for the excavated fractions, as well as expected costs and revenues.

 

Preliminary investigations for the characterisation of waste and landfill sites

 The characterisation of the deposited material includes the assessment of the composition of the waste and its biochemical and physical characteristics, which are relevant for the design of the LFM process and with a view to material and energy recovery (Cossu et al., 1996; Krook et al., 2012; Masi et al., 2014; Cossu and Grossule, 2022).

It is also necessary to assess the environmental conditions of the landfill, in order to prevent technical difficulties that may arise during excavation due to high levels of leachate and/or significant biogas emissions, which could lead to mechanical instability of the waste and accumulation of biogas in the excavation area, hindering operations and causing safety risks (Raga and Cossu, 2014; Raga et al., 2015; Raga and Cossu, 2018).

For these reasons, before starting LFM, a series of specific investigations are necessary to obtain detailed information on the following aspects:

• Morphological and geomechanical characteristics of the landfill. Especially in the case of old uncontrolled landfills, with no records of disposal activities, geophysical investigations can provide an assessment of the thickness and extent of the deposited waste, as well as the presence of saturated leachate layers. In addition, based on the results of geophysical investigations, geotechnical investigations are carried out to provide detailed information on the stratigraphy of the site, the physical characteristics of the deposited material (e.g. moisture content, density) and the expected mechanical stability of the waste during excavation (Cossu et al., 2009; Cossu and Grossule, 2022).
• Characterisation of waste. The analysis of the material composition and particle size distribution, conducted on representative samples of waste as is, is preliminary to the assessment of the potential for material and energy recovery from the excavated waste. Data on the original composition of the waste at the time of delivery are generally scarce or unreliable; moreover, the composition itself is subject to changes over time due to the biodegradation processes that take place in the body of the landfill (Prechthai et al., 2008). For these reasons, targeted sampling campaigns are necessary, distributed across different areas of the site. It is also essential to verify the quality of the selected fractions in order to assess their suitability for subsequent treatment and recycling. Potential residual emissions must also be quantified and the appropriateness of stabilisation processes for fractions destined for further disposal must be assessed.
• Environmental conditions of the landfill. The levels of leachate production and the extent of its accumulation, if any, must be determined, and the potential for biogas generation and current emission rates must be assessed. This information is essential for planning any pre-treatment of the landfill prior to excavation, for selecting the most suitable operational technologies and for defining specific measures to prevent environmental impacts and ensure worker safety.

Resource recovery

The potential for resource recovery from LFM depends on:

• the composition of the waste deposited;
• the quality of the different materials;
• the characteristics and efficiency of the technologies used to separate and treat the different material flows;
• the available destinations for the recovered fractions.

In terms of composition, municipal solid waste (MSW) landfills managed before the introduction of separate collection are generally more suitable for the adoption of LFM.

Considering a specific case relating to an MSW landfill (Cossu and Grossule, 2022), the composition, divided into three particle size classes and averaged over several large-diameter (80 cm) boreholes, was as shown in Table 1.

Table 1: Composition of three particle-size fractions, obtained using two sieves (50 mm and 20 mm), analyzed in an municipal solid waste (MSW) landfill in Central Italy (Cossu and Grossule, 2022).

 

Based on this product analysis, the most interesting fractions, which are likely to be used, are as follows:

• medium-fine material fraction <20 mm, which could allow for the recovery and recirculation of medium and fine gravel and sand, with a residue consisting of clayey silt and other fine fractions. If this fraction does not meet the criteria set out in current legislation (release test referred to in Annex 3 of Ministerial Decree 186/2006), it could be subjected to a washing process
• fraction with a grain size between 50 and 20 mm, consisting of 70% aggregates (63% gravel, stones, shards; 7% glass, etc.) and 30% miscellaneous waste. If its quality is acceptable, this fraction could be used directly in a new controlled landfill site as raw material to improve the overall hydraulic conductivity of the mass, while for use as material for the construction of drainage systems in the new plant, it would need to undergo treatment to improve its quality and performance.
• fraction of coarse material >50 mm, in which metals and materials with high calorific value are concentrated.

Metals consist of approximately 80% ferrous metals and 20% non-ferrous metals, with a predominance of aluminium. They are highly recyclable and their sales are well remunerated by the market.

The flow of materials with high calorific value, consisting of paper, cardboard, plastics, rubber, wood, textiles, leather, etc., is generally concentrated in the coarse fractions and can be used for energy recovery in a thermal treatment plant, with a calorific value ranging from approximately 10 to 20 MJ/kg (Hogland et al., 1995, Obermeier and Saure, 1995; Cossu et al., 1995; Rettenberger, 1995; Quaghebeur et al., 2013; Wanka et al., 2017; Cossu and Grossule, 2022), allowing energy to be used without auxiliary fuels.

An alternative may be the production of Secondary Solid Fuel (Passamani et al., 2016).

 

The fine fraction (under 10–20 mm), which is richer in organic matter, could be considered as a possible compost amendment, but this option is generally hindered by strict regulatory requirements for agricultural use. This fraction may contain high concentrations of heavy metals (Cu, Cr, Ni, Zn).

Alternative uses, such as daily covering in future controlled landfill sites, the construction of embankments, the filling of depressions in the ground or landscaping operations, must consider the quality of the materials and compliance with the specific regulations governing such applications.

A residual fraction, resulting from the separation and treatment of excavated materials, will always be present and will constitute an additional stream to be sent for final disposal in the new controlled landfill facility.

Depending on the intended use of the excavated material, the sorting process may produce streams that combine different fractions, as shown in Figure 2, considering a sorting and treatment plant based on different treatment options.

Figure 2: Layout of a sorting and treatment plant for Landfill Mining material from an MSW landfill, where different treatment options are combined. The mass balance is based on the waste composition reported in Table 1 (Cossu and Grossule, 2022).

Pre-conditioning of the waste pile, excavation operations and mechanical treatment of excavated waste

In order to mitigate the risks associated with uncontrolled biogas emissions that may occur during excavation operations — such as odorous emissions and potential fire or explosion phenomena may be necessary to pre-condition the landfill by means of in situ aeration, to be carried out before the start of Landfill Mining activities (Cossu et al., 2003).

This intervention could then be extended to promote an increase in the biological stability of the organic fraction, with positive effects on the subsequent treatment phases and the final placement of the recovered materials.

In the frequent cases where leachate is present in the waste to be excavated, aeration can be effectively integrated with its extraction, preferably using pneumatic ejectors (Raga et al., 2015).

The technologies that can be used for excavation depend on the quality and nature of the waste delivered.

Parameters such as the age and depth of the deposit, degree of degradation, moisture content, presence of leachate, morphology of the landfill body and stability conditions of the stockpile must be carefully evaluated when defining the operational plan and choosing the machinery (hydraulic excavators, rippers, bulldozers, loaders, dumpers, etc.).

If there is a suspicion of the presence of hazardous materials (e.g. waste containing asbestos), the excavated material must be temporarily stored in special storage bays to allow for the necessary checks and analyses to be carried out before proceeding to the next stages of treatment.

The extracted material may be highly compacted or of such a size that, before screening and separation of recyclable fractions, it must first be reduced in size using shredders specifically designed for waste treatment.

Downstream of screening — generally carried out with rotary screens — the waste can undergo various unit operations: densimetric classification for the separation of light and heavy fractions, magnetic separation of ferrous metals and, more generally, all the technologies commonly used in recovery and recycling plants for recoverable fractions. However, it should be noted that, in the case of waste from landfill mining, the effectiveness of these technologies is often lower than for conventional waste streams (Ford et al., 2013).

 

Costs and financing

The application of a cost-benefit analysis is an essential tool for assessing the economic feasibility of landfill mining (LFM). Despite the potential benefits associated with this system and the growing interest shown over the last two decades, the number of full-scale interventions is still limited. This is mainly due to the difficulty of ensuring an adequate economic and financial balance in each specific case

At present, financially favourable situations for the application of landfill mining, where revenues can exceed costs, have materialised in the following particular situations:

• the need to build infrastructure of great public interest – as in the case of the LFM project carried out at the old Modena landfill – to allow the construction of a trench for the passage of the high-speed railway line (Raga et al., 2015).
• Recovery of areas for redevelopment and urban expansion in areas with high land costs or recovery of new volumes to extend the useful life of existing landfills (van der Zee, 2004; Goeschl and Rudland, 2007; Raga and Cossu, 2014, Cossu and Grossule, 2022).
• Single-waste landfills that may contain, in suitable quantities, materials of commercial interest, such as incinerator bottom ash landfills from which metals can be conveniently recovered (Wagner and Raymond, 2015).
• Areas where a waste thermal treatment plant can benefit from an additional supply of other waste. A well-known case is that of the Aosta Valley, where an LFM intervention was envisaged to allow an adequate feed rate for the optimal operation of an incineration or pyrolysis plant, which was not guaranteed by the low waste production of the population in the region (Cossu et al., 2009).

At present, however, interventions based on Enhanced Landfill Mining (ELFM), where the main motivation is the recovery and recycling of materials, do not appear to be financially realistic (Jones et al., 2016; Raga and Cossu, 2018). This is due to the unfavourable balance between the high costs of the current treatment technologies needed to ensure the standards required for End of Waste and the limited revenues from the sale of recycled materials.

However, as mentioned above, the recovery of resources can be synergistic with the maximisation of the recovery of useful volumes for controlled landfilling which, as seen in the previous paragraphs, is essential for closing the mass balance of the Circular Economy in a virtuous manner. The availability of useful volumes, without further land consumption, could make LFM decidedly advantageous in view of the increasing difficulty in finding new areas that are suitable in terms of urban planning, the environment and society.

This aspect, linked to the resolution of the many administrative, financial and legal issues involved in post-landfill management and the long-term environmental responsibilities that current legislation places on operators, could make Landfill Mining increasingly attractive, especially if incentivised by public financial contributions, which would be appropriate given the enormous social and environmental benefits that the system can bring to the community.

 

Authorisation regimes

 First of all, it should be noted that LFM projects do not fall within any specific framework in Italian state legislation.

Italian legislation, and in particular Legislative Decree No. 152/2006 (Consolidated Environmental Act), outlines two main procedural paths within which the authorisation process for such projects could be framed:

1. a) the remediation procedure (Title V, Part Four, Legislative Decree 152/2006):
2. b) the waste management procedure (Title I, Part Four, Legislative Decree 152/2006):

The choice between the two procedures (first by the proponent in the application and then, above all, by the administration called upon to authorise the project) affects the authorisation procedure, the timing and the authorities responsible for issuing the authorisation.

In our opinion, the regulatory framework and the authorisation procedure for LFM projects depend primarily on the essential purpose of the intervention, but above all on the environmental status of the site where the project is to be carried out. In particular, the classification of an LFM project depends crucially on the presence or absence (at the landfill site) of confirmed or potential contamination exceeding the Contamination Threshold Concentrations (CSC) defined by the regulations. In this regard, the position taken by the Ministry of the Environment and Energy Security is clear, according to which:

• in the case of in situ safety measures, carried out without waste removal, or even in the case of ex situ measures involving the removal and transfer of waste to a new waste disposal area, but where a remediation plant is involved, the relevant project must be authorised in accordance with Article 242, paragraph 7, Legislative Decree No. 152 of 2006, the approval of which replaces all acts of consent and, for SINs, pursuant to Article 252, paragraph 4, of the same legislative decree;
• however, if the attention values are not exceeded, the procedure laid down by the legislator for the adoption of the relevant administrative measures for the approval of the waste management project and for the issue of the necessary permits for the implementation of the measures must be followed (Ministry of the Environment and Energy Security, response to request for ruling of 24 September 2025, in mase.gov.it).

Secondly (and this is a decisive factor), it is important to note whether the landfill is authorised or not. If the landfill is authorised and regularly managed, it is considered that LFM’s activity can be classified as waste treatment and must be authorised in accordance with Articles 208 et seq. of the Consolidated Environmental Act (Landonio S., Sciunnach D., Cappa S., 2018).

The following provisions of Legislative Decree 152/20026 support this view:

• Article 183, in its definition of waste “management”, also includes “actions following the closure of disposal sites”, which could therefore include those relating to LFM projects;
• Article 239, paragraph 2, excludes the applicability of the regulations on remediation even to the phenomenon of abandonment and uncontrolled waste disposal; this provision delimits the scope of application of the regulations on remediation, which only come into force again when it is ascertained that the attention values have been exceeded following the removal, recovery or disposal of the waste; This is a clear sign that, on the contrary, the regulations on remediation are not directly applicable to the phenomenon of controlled waste abandonment (in landfills).
• Article 240 defines various concepts, including those of “site” relevant to the application of the regulations in Title V and “remediation”. However, although it can be assumed – as mentioned above – that a landfill site may represent a polluted environmental matrix (which must therefore be subject to remediation), there cannot be any equivalence between a contaminated site and a landfill site.

It follows that:

1. aa) the remediation process must be applied when the LFM intervention is motivated by the need to remove a source of pollution to secure and remediate the landfill site or is carried out on an unauthorised landfill site;
2. bb) on the contrary, if the intervention on an authorised and regularly operated landfill site is not triggered by the exceeding of the CSC, but is mainly aimed at recovering soil, volumes or resources (secondary raw materials or energy), it would fall under the general rules on waste management. The excavated materials will be considered waste for all intents and purposes, and their treatment, recovery or disposal must follow the ordinary procedures. In this regard, however, it should be noted that if the fractions recovered from the LFM, following a treatment process, acquire the characteristics of a “by-product” within the meaning of Article 184-bis of Legislative Decree 152/2006, they may cease to be classified as waste. However, this classification requires a rigorous case-by-case verification of the existence of all the conditions laid down by law (see, for example, Lombardy Regional Administrative Court, Brescia, No. 400 of 2017).

Finally, it should be noted that the application for authorisation for an LFM project may, and in many cases must, follow the Single Regional Authorisation Procedure (PAUR), governed by Article 27-bis of Legislative Decree No. 152/2006.

An LFM project, in fact, by its very nature, involves the construction and management of a complex waste treatment plant. Activities include excavation, sorting, mechanical-biological treatment, material and/or energy recovery, and waste disposal. These activities fall within the project categories listed in the annexes to Part Two of Legislative Decree No. 152/2006, which define the applicability of EIA or EIA screening.

Non-hazardous waste disposal and recovery facilities are subject to screening or EIA when certain capacity thresholds are exceeded. Given the typical operational scale of an LFM intervention, it is highly likely that these thresholds will be exceeded, making at least the screening procedure necessary. If the outcome of the screening determines the need for an EIA, and the competence is regional, the application of the PAUR procedure becomes mandatory.

 

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