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Journal of Cleaner Production 99 (2015) 275e285

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Journal of Cleaner Production

journal homepage: www.elsevier .com/locate/ jc lepro

Valorization of thermal treatment residues in Enhanced LandfillMining: environmental and economic evaluation

Maheshi Danthurebandara a, b, *, Steven Van Passel b, Lieven Machiels c, Karel Van Acker a

a Department of Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, 3001, Leuven, Belgiumb Center for Environmental Sciences, Faculty of Business Economics, Hasselt University, 3590, Diepenbeek, Belgiumc High Temperature Processes and Industrial Ecology, Department of Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, 3001, Leuven, Belgium

a r t i c l e i n f o

Article history:Received 3 June 2014Received in revised form4 March 2015Accepted 5 March 2015Available online 14 March 2015

Keywords:Enhanced Landfill MiningPlasma gasificationPlasmastoneLife cycle assessmentLife cycle costing

List of acronyms: ELFM, Enhanced Landfill Minintential; IRR, Internal rate of return; LCA, Life cyclecosting; NPV, Net present value; OPC, Ordinary Poderived fuel.* Corresponding author. Department of Materials E

teelpark Arenberg 44, Bus 2450, 3001 Leuven, Belgium494152559 (mobile).

E-mail address: mdanthurebandara@gmail.com (M

http://dx.doi.org/10.1016/j.jclepro.2015.03.0210959-6526/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

Enhanced Landfill Mining is an innovative concept which allows the recovery of land, re-introduction ofmaterials to the material cycles and recovery of energy from a considerably large stock of resources heldin landfills. Plasma gasification is a viable candidate for combined energy and material valorization in theframework of Enhanced landfill Mining. Besides energy production, plasma gasification also delivers anenvironmentally stable vitrified residue called plasmastone, which can be converted into building ma-terials. This paper presents an environmental and economic evaluation of the valorization of thermaltreatment residues (plasmastone) in the context of Enhanced Landfill Mining. The most common valo-rization route, that is, the treatment of plasmastone via production of aggregates, is compared with twoother possible, higher added value applications, which are inorganic polymer production and blendedcement production. The evaluation is based on life cycle assessment and life cycle costing. The studysuggests that the environmental and economic performances of the valorization routes depend mainlyon the quality and quantity of the final products produced from a certain amount of plasmastone. Thematerials with the greatest contribution to potential global warming and to the net present value of thevalorization scenarios are the process input materials of sodium silicate, sodium hydroxide and cement.The study concludes that the plasmastone valorization via inorganic polymer production yields higherenvironmental benefits, while the blended cement production provides higher economic profits. Plas-mastone valorization via aggregates production does not yield economic or environmental benefits.Given the trade-off between environmental and economic performances, we conclude that the decisionsregarding the selection of appropriate valorization routes should be made cautiously to obtain optimalenvironmental benefits and economic profits.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

The concept of landfill mining has been practiced around theworld for more than 50 years as a way to reintroduce buried re-sources into the material cycle and minimize the environmentalburden of landfill emissions (Hogland, 2002). However, most

g; GWP, Global warming po-assessment; LCC, Life cyclertland cement; RDF, Refuse

ngineering, KU Leuven, Kas-. Tel.: þ32 16 37 34 72, þ32

. Danthurebandara).

landfill mining studies have focused on conservation of landfillspace and remediation, since getting permission to develop newlandfills is increasingly difficult (van der Zee et al., 2004; Krooket al., 2012; Fr€andegård et al., 2013). Moreover, traditional landfillmining is often limited to reclamation of land, methane and alimited number of metals such as copper or aluminum (van der Zeeet al., 2004; Jones, 2008). In the context of rapidly growingcompetition for resources, increasing raw material prices anddeclining availability of natural resources, Enhanced Landfill Min-ing (ELFM) has emerged. Related to the new perspective ofextracting valuable material and energy resources from landfills,ELFM emphasizes intentional storage of currently non-recyclablematerials and energy resources that can be valorized in the future(Hogland et al., 2010; Jones et al., 2013). As Jones et al. (2013)explained, ELFM is defined as “the safe conditioning, excavation

M. Danthurebandara et al. / Journal of Cleaner Production 99 (2015) 275e285276

and integrated valorization of (historic and/or future) landfilledwaste streams as both materials (Waste-to-Material, WtM) andenergy (Waste-to-Energy, WtE), using innovative transformationtechnologies and respecting the most stringent social and ecolog-ical criteria”.

Jones et al. (2013) and Danthurebandara et al. (2015) describedthe major process steps of ELFM, including vegetation and topsoilremoval, conditioning, excavation, separation, transformation ofintermediate products, and land reclamation. As these authorsexplained, the separation process results in many waste fractionsthat can be sold directly. In addition, intermediate products (frac-tions that need further treatment in order to obtain higher marketprices) also are sorted out in the separation process. Refuse derivedfuel (RDF) is an important intermediate product that can be valo-rized in a thermal treatment with energy recovery (Quaghebeuret al., 2013). Although many existing thermal treatment technolo-gies can be used in processing RDF, an objective of the novel ELFMconcept is to find integrated technologies that aim for ‘‘zero waste’’processes, incorporating recycling, recovery, and upgrade of (res-idue) materials, in addition to energy production (Spooren et al.,2013). Bosmans et al. (2013) recently analyzed and comparedseveral thermal treatment technologies, including incineration,gasification, pyrolysis, plasma technologies, and their combina-tions, for their suitability in ELFM. They concluded that plasmagasification/vitrification is a viable candidate for combined energyand material valorization in the framework of ELFM.

Plasma gasification offers a number of advantages, such as highheat and reactant transfer rates, formation of cleaner and highenergy synthesis gas containing mainly hydrogen and carbonmonoxide, and the use of low-energy fuels such as household andindustrial waste (Chapman et al., 2010; Ray et al., 2012; Bosmanset al., 2013). Taylor et al. (2013a, b) highlighted that the plasmagasification technology is able to efficiently produce a clean syn-thesis gas and an environmentally stable vitrified product (plas-mastone) from historically landfilled materials. The synthesis gascan be used for production of electrical energy and/or heat or assecond-generation liquid fuels. In addition, several valorizationpossibilities have been proposed for plasmastone (Iacobescu et al.,2013; Pontikes et al., 2013; Machiels et al., 2014).

The residues (bottom ash) produced in traditional thermaltreatment processes like incineration are disposed of directly tolandfills inmany cases. This material needs to be pretreated if it is tobe utilized as a secondary aggregate. In contrast, plasmastone has agreat potential and can be designed for use in rather diverse ap-plications, mainly in the construction materials industry (Joneset al., 2013; Spooren et al., 2013). Leaching tests have indicatedthat plasmastone may be safely used as an aggregate/gravelreplacement (Chapman et al., 2011). Hence, the most evidentvalorization route is the use of plasmastone as an aggregate for roadconstruction or building blocks. Nevertheless, ELFM targets highervalue applications. Jones et al. (2013) highlighted that depending onthe RDF chemistry and the cooling method applied, the followinghigher added value products can be developed from plasmastone:glass-ceramic monoliths for use as building materials or glass-ceramic aggregates for use in high-strength concrete; hydraulicbinders, pozzolanic binders, or inorganic polymer precursors.

According to the International Energy Agency's (IEA) Green-house Gas R&D Program (Hendriks et al., 2000), ordinary Portlandcement (OPC) production generates an average world carbonemission of 0.81 kg of CO2 per kilogram of cement produced. Onaverage, one tonne of concrete is produced each year for everyhuman being in the world (Lippiatt and Ahmad, 2004). Productionof alternatives for cement can mitigate this heavy CO2 burden. Sofar, fly ash and other by-products of the energy and materials in-dustry, currently disposed of as waste, have been used to produce

these alternative products (Huntzinger and Eatmon, 2009; Turgut,2012; Van den Heede and De Belie, 2012). Machiels et al. (2014) andIacobescu et al. (2013) explained the possibility of developingbinding materials from plasmastone to be used as low-carbon al-ternatives for OPC in construction applications.

Based on these premises, several valorization routes for plas-mastone have been tested at KU Leuven, Belgium, in the frameworkof the first comprehensive ELFM project (“Closing the Circle”project by Group Machiels, Belgium). These valorization routesmainly include production of inorganic polymer and blendedcement products out of plasmastone. To bring ELFM from theconceptual to the operational stage, knowledge about the criticalfactors of environmental and economic performance of the asso-ciated technologies is important. Nonetheless, because of thenovelty of the ELFM concept, such evaluations for plasmastonevalorization in ELFM have not yet been reported, although severalother studies have evaluated the products based onwastematerialsand by-products. For example, Weil et al. (2009) conducted adetailed life cycle analysis of geopolymers produced both fromresource-intensive materials like metakaolin and less resource-intensive materials like fly ash, and McLellan et al. (2011) exam-ined the environmental and economic impacts of the life cycle ofgeopolymers produced from fly ash. In addition, several studieshave discussed the environmental performance of blast furnaceslag used in geopolymer production (Habert et al., 2011; Van denHeede and De Belie, 2012). Although these studies explain thepossible environmental impacts of transformation of waste mate-rials into alternatives to OPC, a more detailed evaluation is requiredfor plasmastone valorization to identify its usability in ELFM.

This paper addresses the current lack of environmental andeconomic evaluation for valorization of thermal treatment residuesin ELFM. The study comprises life cycle assessment (LCA) and lifecycle costing (LCC). Themost common valorization route, aggregateproduction, was compared with two other higher added valueapplications, inorganic polymer production and blended cementproduction. This paper identifies and discusses the environmentaland economic drivers of plasmastone valorization, analyzes therelative advantages and disadvantages of different scenarios, andsuggests possible improvements in design and operating parame-ters. In addition, a trade-off analysis indicates the most beneficialvalorization options to be used in ELFM.

2. Materials and methods

This section describes the studied plasmastone valorizationroutes and the LCA and LCC methodologies.

2.1. The system studied

The excavated landfill waste is subjected to a series of separationprocesses to sort different waste fractions. As shown in Fig. 1, theRDF fraction obtained by the separation process is directed to athermal treatment process. In this study, plasma gasification wasthe thermal treatment technology considered (Chapman et al.,2010; Bosmans et al., 2013; Taylor et al., 2013a, b). The mainproducts identified were synthesis gas and plasmastone. Synthesisgas can be used mainly for energy production (electrical energyand/or heat), although other valorization options include produc-tion of liquid fuels. Plasmastone, which is recovered from theplasma convertor, is fully vitrified, mechanically strong, environ-mentally stable, and inert. ELFM focuses broader attention on thevalorization of all types of landfill wastes, even wastes and by-products generated during processing of landfill waste. Therefore,the obtained plasmastone is subjected to additional various treat-ments in order to obtain valuable products. Although the entire

Fig. 1. Interactions of ELFM (focus of the current study is outlined by the dotted line).

M. Danthurebandara et al. / Journal of Cleaner Production 99 (2015) 275e285 277

ELFM system presents a multitude of complex interactions, thefocus in this study was only on the subsystem of plasmastonevalorization, which is the step highlighted by the dotted line inFig. 1. Different valorization options were compared to identifythe best option, according to environmental and economicconsiderations.

Fig. 2. Process flow diagram for valorization of plasmastone via production of inor-ganic polymer (Scenario 1).

2.2. Valorization/treatment routes

This study included three main scenarios: Valorization of plas-mastone via (1) production of inorganic polymer cement/block, (2)production of blended cement/block, and (3) production of aggre-gates. The process flow diagrams were developed according to theliterature data and lab scale experiments conducted at KU Leuven.

Scenario 1. Valorization of plasmastone via production of inor-ganic polymer cement/ block

Inorganic polymers, alternatively termed geopolymers, are aclass of materials formed by the reaction between an alkaline so-lution and a reactive precursor material, rich in silica andcommonly alumina (Provis and Deventer, 2009; Deventer et al.,2010; Davidovits, 2011). Inorganic polymers display outstandingtechnical properties, such as high strength, high acid resistance,and high temperature resistance. These materials form a hard,durable body that can be used as an alternative to OPC for standardor more demanding applications, including in environments withhigh temperature or acid conditions, as well as for the encapsula-tion and disposal of hazardous wastes (Davidovits, 2011). Well-performing inorganic polymers also can be obtained using sec-ondary raw materials, such as industrial by-products like fly ash orslag. The use of these materials as input for inorganic polymerproduction not only could solve the waste problem, but also reduceconsumption of primary raw materials.

As explained above, this study focused on inorganic polymerproduction from plasmastone. Currently, inorganic polymercement and a precast product are being developed at the Depart-ment of Materials Engineering, KU Leuven. Plasmastone is an idealprecursor for a inorganic polymer cement because it can bedesigned to be composed of more than 90 percent glass, whichensures a very high reactivity in an inorganic polymer cement(Pontikes et al., 2013). Work is in progress on the optimization ofthe plasmastone chemistry and of the inorganic polymer cementblend composition, and partial results have been published(Machiels et al., 2014). This study utilized data from Machiels et al.(2014) regarding the optimal blend composition for cement pro-duction, which is a blend composed of more than 90 percentplasmastone that can deliver superior properties, such as highercompressive strength, compared to traditional OPC. This plasma-stone composition can be obtained by treatment of a mixture ofindustrial and household waste RDF, derived from ELFM, in aplasma gasification system (Spooren et al., 2013).

Fig. 2 is the process flow diagram for Scenario 1, depicting thefollowing major steps (see also Machiels et al. (2014)).

� Milling: The size of the plasmastone received from the plasmagasification process after application of water quenching toobtain the required reactivity is approximately 0.5 cm onaverage (Pontikes et al., 2013). Milling of the plasmastone is thefirst step of the treatment process and is needed to obtain therequired uniform grain size.

� Pre-mixing: Milled plasmastone is mixed with an alkali source(NaOH) and a silicate solution (Na2SiO3) to produce an inorganicpolymer cement.

� Mixing: The resulting mixture of plasmastone and alkali andsilicate solutions (inorganic polymer cement) is then mixedwith water and aggregates to obtain an inorganic polymermortar or concrete that can be shaped to blocks as an alternativeto OPC-based concrete blocks and bricks.

� Curing: In this study, curing was done at room temperature(20 �C) because inorganic polymers based on reactive materialsactivated with a Na-silicate solution can achieve the desiredtechnical properties within a few hours or days at room tem-perature without any heat curing (Bakharev et al., 1999; Duxsonet al., 2007).

Two sub-scenarios emerged from the process shown in Fig. 2:Scenario 1a e valorization of plasmastone via inorganic polymercement production; and Scenario 1b e valorization of plasmastonevia inorganic polymer block production.

Scenario 2. Valorization of plasmastone via production ofblended cement/ block

Cement and concrete terminology defines blended cement ashydraulic cements that are consisting of an intimate and uniformblend of a number of constituent materials, generally termed sup-plementarycementitiousmaterials (SCM) (ACI, 2005; Snellings et al.,2012). To produce blended cements, Portland cement clinkermay be

Fig. 3. Process flow diagram for valorization of plasmastone via production of blendedcement (Scenario 2).

Fig. 4. Process flow diagram for valorization of plasmastone via production of aggre-gates (Scenario 3).

M. Danthurebandara et al. / Journal of Cleaner Production 99 (2015) 275e285278

either intergrinded or blended with the SCM, or a combination ofboth.Blendedcementshave theadvantagesof improvedworkability,improved resistance to sulfate attack and chloride penetration,improved resistance to alkaliesilica reactions, and improved long-term strength development. Plasmastone has good potential asSCMbecause ithasahighglass content andanappropriate chemistry(high silica content, and substantial calciumandaluminumcontent),which enables it to react with OPC clinker to form calcium silicatehydrate binding phases (Iacobescu et al., 2013). Fig. 3 depicts theprocess flow for treatment of plasmastone via blended cementproduction. The milled plasmastone and cement were blended

Table 1Inputs and outputs of the different treatment scenarios.

Inputs and outputs Scenario 1a Scenario 1b

InputsPlasmastone (t) 1.000 1.000NaOH (t) 0.064a 0.064a

Na2SiO3 (t) 0.078a 0.078a

Water (t) 0.308a

Aggregates (t) 3.000a

OPC (t)Electrical energy (kWh) 20.000c 55.000c

Output productsInorganic polymer cement (t) 1.142a

Inorganic polymer block (t) 4.142a

Blended cement (t)Blended cement block (t)Aggregates (t)

a Machiels et al. (2014).b Iacobescu et al. (2013).c Measured value.

together to produce blended cement. In addition, water and aggre-gates can be added to the blend to produce a pre-cast product orblended cement blocks. As in Scenario 1, curing was done at roomtemperature. As defined by Iacobescu et al. (2013), we considered amixture of 20 percent plasmastone and 80 percent OPC in this study.

Two sub-scenarios emerged from the process shown in Fig. 3:Scenario 2a e valorization of plasmastone via production ofblended cement; and Scenario 2b e valorization of plasmastone viaproduction of blended cement block.

Scenario 3. Valorization of plasmastone via production ofaggregates

Most materials for aggregate production come from bedrock orfromunconsolidated deposits. The vastmajority ofmaterials used inthe mineral aggregate industry are obtained from surface-minedstone quarries or from sand and gravel pits. In addition, increasingamounts of recycledmaterials are being used to supplement naturalaggregates (Ray et al., 2012; Taylor et al., 2013a, b). Plasmastone'sunique combination of high mechanical strength and hardness, aswell as its extremely high resistance to chemical leaching, make it aperfect secondaryaggregatematerial for use in road paving andpipebedding (Ray et al., 2012; Taylor et al., 2013a, b). Use of secondaryraw materials as aggregates avoids the long production process ofnatural aggregates, includingextractionormining, transportation tothe processing plants, separation, crushing, scrubbing, andscreening (Kellenberger et al., 2007). As shown in Fig. 4, Scenario 3comprised only two simple processes: crushing and sieving.

2.3. Life cycle assessment (LCA) method

LCA is a technique to quantify the environmental and healthimpacts associated with manufacturing a product or carrying out aprocess or activity from raw material extraction through materialprocessing, product manufacturing, distribution, use, repair andmaintenance, and disposal or recycling (ISO14040, 2006, ISO14044,2006).

The goal of this LCA study was to use the scenarios mentioned inSection 2.2 to evaluate the environmental impacts of the valoriza-tion of a certain mass of thermal treatment residues (plasmastone)obtained in the plasma gasification process, and thus, to identifythe most beneficial treatment option to be used in ELFM. The studyfollowed the international standard for LCA (ISO 14040, 14044) andused SimaPro 7 (PR�eConsultants, 2010) as the software tool to setup the LCA model. Figs. 1e4 show the system boundaries, and thematerial inputs and outputs under the study's different scenarios.

Scenario 2a Scenario 2b Scenario 3

1.000 1.000 1.000

2.500b

15.000b

4.000b 4.000b

20.000c 55.000c 10c

5.000b

22.250b

1.000c

Table 2Input values used in cash flow model.

Description Value Sources

General dataPlasmastone treatment

capacity (t/y)100,000 case study

Life time (y) 20 case studyDiscount factor (%) 15 Case studyScenario 1Investment cost (V/t plasmastone)Scenario 1a 5 calculated value (mentioned

in the text)Scenario 1b 10 calculated value (mentioned

in the text)Materials pricesPrice of plasmastone (V/t) 0 Case studyPrice of water (V/t) 4 industrial referencePrice of NaOH (V/t) 275 ICIS (2010)Price of Na2SiO3 (V/t) 405 ICIS (2008)Price of aggregates (V/t) 10 Gardiner and Theobald (2012)

Energy pricePrice of electrical energy(V/MWh)

97 Europe's Energy Portal (2013)

Maintenance and repair cost(% from investment cost)

10 calculated value

Other cost (labor þ other unforeseen costs) (V/t plasmastone)Scenario 1a 17 calculated valueScenario 1b 19 calculated value

RevenuesSelling price of inorganicpolymer cement (V/t)

150 case study

Selling price of inorganicpolymer block (V/t)

70 case study

Scenario 2Investment cost (V/t plasmastone)Scenario 2a 20 calculated value(mentioned

in the text)Scenario 2b 40 calculated value(mentioned

in the text)Materials pricesPrice of plasmastone (V/t) 0 Case studyPrice of water (V/t) 4 industrial referencePrice of cement (V/t) 77 industrial referencePrice of aggregates (V/t) 10 Gardiner and Theobald (2012)

Energy pricePrice of electrical energy(V/MWh)

97 Europe's Energy Portal (2013)

Maintenance and repair cost(% from investment cost)

10 calculated value

Other cost (labor þ other unforeseen costs) (V/t plasmastone)Scenario 2a 30 calculated valueScenario 2b 39 calculated value

RevenuesSelling price of blendedcement (V/t)

100 case study

Selling price of blendedcement block (V/t)

50 case study

Scenario 3Investment cost (V/t plasmastone) 3 industrial referenceOperational þ maintenance þ other

costs(V/t plasmastone)2 industrial reference

RevenuesSelling price of aggregates (V/t) 5 case study

M. Danthurebandara et al. / Journal of Cleaner Production 99 (2015) 275e285 279

In this study we used a unitary functional unit (¼ reference flow) asexplained in the ILCD handbook (2010) and Laurent et al. (2014).Using a unitary functional unit or a reference flow is very commonin LCAs of waste treatment (Consonni et al., 2005; Fr€andegård et al.,2013). Examples include ‘treatment of 1 tonne of municipal solidwaste’. Similarly, to provide information that could readily bescaled to any application, we used a functional unit of ‘treatment of1 tonne of plasmastone’ for this analysis, since the study's objectivewas to evaluate the treatment process rather than the product. Inthis way, we could identify the best valorization route to process allplasmastone generated in a certain ELFM project. The results couldbe different if the focus was on production of 1 tonne of product.But the key objective of ELFM is to use innovative transformationtechnologies to valorize the total waste in a landfill while mini-mizing the environmental burden and maximizing the economicreturn. We did not include the production phase of plasmastonebecause the amount of plasmastone to be treated in all scenarioswas equal.

All values were quoted per tonne of plasmastone, and thesevalues could be readily used to calculate the environmental impactsof valorization for a requested functional unit of plasmastone.Table 1 shows the process inputs used in all scenarios and thevariation of the quantities of the output products of different sce-narios, as follows: Treatment of 1 tonne of plasmastone produces1.142 tonnes inorganic polymer cement (Scenario 1a), 4.412 tonnesinorganic polymer blocks (Scenario 1b), 5 tonnes blended cement(Scenario 2a), 22.250 tonnes blended cement blocks (Scenario 2b),and 1 tonne of aggregates (Scenario 3). For the background pro-cesses, such as the production of electrical energy and raw mate-rials, the life cycle inventory data published in the ecoinventdatabase was used (Ecoinvent, 2010). Transportation of input ma-terials was not included because we assumed all input materials tobe manufactured within Belgium where the study took place.

As described previously, the alternative products obtained inplasmastone valorization can mitigate the heavy CO2 burdencaused by OPC-based products. Therefore, we selected globalwarming potential (GWP) as the priority impact category for theenvironmental impact assessment of this study because it directlyrelates to the CO2 burden. IPCC 2007 GWP 100a method(PR�eConsultants, 2008) was used as the assessmentmethod. On theother hand, the valorization methods can affect several otherimpact categories. To investigate this influence, we used the ReCiPemidpoint method (Goedkoop et al., 2013) to assess the impactcategories of climate change, ozone depletion, terrestrial acidifi-cation, freshwater eutrophication, marine eutrophication, humantoxicity, photochemical oxidant formation, particulate matter for-mation, terrestrial ecotoxicity, freshwater ecotoxicity, marine eco-toxicity, ionizing radiation, agricultural land occupation, urban landoccupation, natural land transformation, water depletion, metaldepletion, and fossil fuel depletion.

2.4. Life cycle costing (LCC) method

LCC is a tool to determine the most cost-effective option amongdifferent competing products, when each is equally appropriatefor implementation on technical grounds. Apart from the initialinvestment cost, LCC takes into account all costs related to oper-ating, future periodic maintenance, and rehabilitation of a projectover a defined time period. Payback time, internal rate of return(IRR), and net present value (NPV) are the most important eco-nomic indicators associated with LCC to verify whether or notinvestment in a project is worthwhile financially (Brealey et al.,2010).

To perform LCC for the study's selected scenarios (Section 2.2), ahypothetical treatment plant was considered with a capacity to

treat a 100,000 tonnes of plasmastone per year and a having alifetime of 20 years. A cash-flow model was developed for the 20-year period, including all costs and revenues associated with thescenarios (see Table 2). The cost advantages due to size, output, orscale of operation (economies of scale) were considered to deter-mine the investment and operational costs of the scenarios. Currentinvestment costs of cement productionwere used to determine theinvestment costs under Scenarios 1a, 1b, 2a, and 2b. Unlike in themanufacture of Portland cement, a kiln and other infrastructure arenot needed to produce inorganic polymer or blended cement;

M. Danthurebandara et al. / Journal of Cleaner Production 99 (2015) 275e285280

consequently, the investment cost of Scenario 1a and 2a wereassumed to be 30 percent of the reported investment cost of acement production plant (V263 per tonne cement/year for a plantwith a capacity of 1 million tonnes/year and a 20-year lifetime)(ETSAP, 2010). The ratios of plasmastone to inorganic polymercement and plasmastone to blended cement were used to convertthe units into euros per tonne of plasmastone. The investment costsof Scenario 1b and 2b were assumed to be twice those of Scenario1a and 1b. Materials and energy costs were estimated according tothe market prices in Belgium where all materials were to be pro-duced. However, a sensitivity analysis was performed for all theseassumptions and estimations.

Similar to the LCA study, the LCC study did not consider theproduction phase of plasmastone; therefore, a value is not given forthe price of plasmastone. The next challenge was to determine theselling prices of the products, according to their physical andchemical characteristics. Because inorganic polymer cement offershigher compressive strength than traditional Portland cement, theselling price of inorganic polymer cement was estimated at V150/t.Considering the proportion of cement and aggregates of inorganicpolymer block, we calculated the selling price of inorganic polymerblock atV70/t. In the sameway,V100/t andV50/t were assigned forblended cement and blended cement block. According to theirquality, aggregates were priced at V5/t.

Because our main objective was to compare the different sce-narios, we used NPV as the major economic indicator, which wecalculated by subtracting the investment cost from the discountedcash flows. For this private assessment, we applied a 15 percentdiscount factor (Van Passel et al., 2013). For the simplicity, we useda 0% inflation rate.

To examine how the NPV varies when the value of uncertainassumptions is modified, a Monte Carlo simulation approach wasused, as explained by Van Passel et al. (2013). This approach helpsto identify the uncertainties of the input parameters as well as theirimportance.

In general, private investors consider projects with an IRR of 15percent to be profitable (Van Passel et al., 2013), a fact used tocalculate the minimum selling prices of the products andmaximum buying price of plasmastone. As IRR is the discount rateat which the NPV is zero, we used Equation (1) to calculate theminimum selling prices of the products and Equation (2) tocalculate maximum buying price of plasmastone.

NPV ¼X20

t¼0

ðcos ts� ðx*amount of product per yearÞÞð1þ Discount rateÞt ¼ 0 (1)

Where t is time and x indicates unit selling price of a product.

NPV ¼X20

t¼0

ðððy*annual treatment capacityÞ þ other costsÞ � RevenuesÞð1þ Discount rateÞt ¼ 0 (2)

Where t is time and y indicates unit price of plasmastone.

3. Results and discussion

Sections 3.1 and 3.2 include the results of the LCA and LCCstudies.

3.1. Environmental evaluation of valorization of plasmastone

Influence of the process inputs and the substituted products ofeach scenario are discussed below.

3.1.1. Influence of the process inputsApart from the processing conditions, the input raw materials

selected are important parameters that determine the final prod-ucts' setting behavior, workability, and chemical and physicalproperties. In addition, they largely define the environmentalprofiles of the treatment processes.

Fig. 5 shows the influence of process inputs on the impactcategory of GWP. The graph presents the greenhouse gas emissionin terms of kilograms of CO2 equivalent per valorization of 1 tonneof plasmastone. Clearly, there are significant differences betweenresource intensive and less resource intensive primary raw mate-rials. In Scenario 1b, aggregates contribute only a little to GWP,despite their highmass proportion compared to NaOH and Na2SiO3.The provision of water also does not noticeably contribute to GWP.NaOH and Na2SiO3 significantly contribute to the GWP, and Na2SiO3dominates the environmental profile of both sub-scenarios ofScenario 1. These results agreewith other studies on environmentalevaluation of inorganic polymer production (Weil et al., 2009;Habert et al., 2011).

The impact of aggregates used in Scenario 2b is only 1 percent ofthe total impact, although the quantity of aggregates used wasmore than three times higher than the quantity of OPC. Comparedwith Scenario 1, Scenario 2 shows significantly higher greenhousegas emission due to process inputs, 216e223 kg of CO2 equivalentcompared with 3350e3387 kg of CO2 equivalent, because Scenario2 used OPC. To treat 1 tonne of plasmastone, 4 tonnes of OPC mustbe used, and OPC production generates an average greenhouse gasemission of 0.81 kg of CO2 per kilograms of cement produced(Hendriks et al., 2000). Although NaOH and Na2SiO3 productionhave higher emissions, like 1.1 and 1.59 kg of CO2 per kilogram(Althaus et al., 2007), the need for these chemicals is comparativelylow to treat 1 tonne of plasmastone (0.064 tonne NaOH and 0.078tonne Na2SiO3). Compared with Scenarios 1 and 2, the greenhousegas emission is very low in Scenario 3 because electrical energy wasthe sole input to this process, and the energy requirement wascomparatively low.

3.1.2. Influence of the substituted products (avoided environmentalburden)

One key objective of the novel ELFM concept is to avoid primarymaterial production to a certain extent by reintroducing buriedresources in the material cycle. Hence, the quality of the productsobtained in ELFM must be identified in order to determine clearlywhichmaterials can be replaced and towhat extent. ELFM productshave an “avoided burden“, meaning that these recycled materials

avoid the impact of virgin material production. Hence, the overallenvironmental impact of the valorization scenarios can be calcu-lated by subtracting the avoided environmental impact from theenvironmental impact of process inputs shown in Fig. 5.

To define the substituted products, we analyzed the ELFMproducts to determining their compressive strengths, porosity,

Fig. 5. Greenhouse gas emission of process inputs of plasmastone valorizationscenarios.

M. Danthurebandara et al. / Journal of Cleaner Production 99 (2015) 275e285 281

consistence upon water immersion, and so on. The inorganicpolymer cement obtained from Scenario 1a was found to exceedthe quality of traditional OPC (a higher 28-day compressivestrength). Hence, the substituted product of Scenario 1a was OPC,strength class 52.5 (CEM I, 52.5) (Kellenberger et al., 2007). Simi-larly, concrete blocks and bricks were the substituted products ofScenario 1b. Note that OPC is used in concrete production, but notin brick production. The quality checks indicated that the resultingblended cement in Scenario 2a had a compressive strength of32.5 MPa (Iacobescu et al., 2013); therefore, we used CEM II 32.5(Kellenberger et al., 2007) to calculate the avoided environmentalimpact under Scenario 2a. The selected substituted products todetermine the avoided burden of Scenario 2b are OPC-based con-crete blocks and non-OPC-based sand-lime bricks. The productionmethods and emissions of these products are clearly explained inecoinvent report number 7 (Kellenberger et al., 2007). Finally, weassumed that Scenario 3 could replace the conventional gravelproduction. Fig. 6 represents the net environmental profiles,including the avoided environmental burden of all scenarios. Thered lines (in web version) indicate the net environmental impact(environmental impact of process inputs-avoided environmentalburden) of the scenarios.

Fig. 6. Net environmental profile of plasmastone valorization scenarios.

In Fig. 6, the dotted column indicates the environmental impactthat could be avoided under Scenario 1a. In this scenario, valori-zation of 1 tonne of plasmastone produces 1.142 tonnes of inorganicpolymer cement. This amount of inorganic polymer cement avoidsthe production of the same amount of OPC, strength class 52.5(CEM I, 52.5) or avoids greenhouse gas emission of 950 kg of CO2equivalent; hence, the net savings of valorization of 1 tonne ofplasmastone via inorganic polymer cement production is 748 kg ofCO2 equivalent. In Scenario 1b, 1 tonne of plasmastone resulted in4.142 tonnes of inorganic polymer blocks, which avoid the pro-duction of an equal amount of bricks or concrete blocks. Thecheckered and vertically striped columns in Fig. 6 illustrate theavoided environmental impacts under Scenario 1bwhen bricks andconcrete blocks are the substituted products. These substitutionsprevent an emission of 985 and 501 kg of CO2 equivalent, respec-tively. The net CO2 equivalent savings under Scenario 1b is 762 kgfor the substitution of bricks, and 278 kg for the substitution ofconcrete blocks. The overall environmental impact of Scenario 1aand 1b do not show a significant difference when bricks are thesubstituted product under Scenario 1b. On the other hand, whenconcrete blocks are replaced, the net impact of Scenario 1b is 2.5times less than that of Scenario 1a. Nevertheless, all described sub-scenarios are credited with the GWP impact category.

The diagonally striped column in Fig. 6 indicates the avoidedenvironmental burden under Scenario 2a. This avoided emission of3591 kg of CO2 equivalent resulted from replacing the production of5 tonnes of CEM II 32.5 with the same amount of blended cementvia valorization of 1 tonne of plasmastone. In this way, 249 kg of netCO2 savings is possible under Scenario 2a. In Scenario 2b, valori-zation of 1 tonne of plasmastone produced 22.25 tonnes of blendedcement blocks. This amount can replace the same amount of eithersand-lime bricks or concrete blocks. The higher environmentalburden from the process inputs under Scenario 2b is largely offsetby the avoided environmental burden, although the net environ-mental impact still remains as a burden. In this study, we used astandard cement-to-aggregate ratio of 1:3 for blocks produced,according to ECS EN-196 (1994), without any optimization of thecement-to-aggregate ratio and the aggregate particle-size distri-bution. In commercial concrete, this optimization is made, whichresults in much lower cement content and a lower environmentalimpact. Hence, the replaced impact also is lower when commercialconcrete blocks are used as the substituted product under Scenario2b, which explains that scenario's burden level.

Despite the high mass production, Scenario 2 has less environ-mental benefits than Scenario 1 mainly because of the higherenvironmental burden from the OPC used Scenario 2. The envi-ronmental profiles of Scenario 1 suggested that all its sub-scenariosare favorable for the valorization of plasmastonewith respect to theenvironmental impact. In contrast, only Scenario 2a shows envi-ronmental friendly conditions in plasmastone valorization.

As shown in Fig. 6, the overall environmental impact of Scenario3 is a burden for two main reasons. First, unlike Scenarios 1 and 2,in Scenario 3, 1 tonne of plasmastone produces only 1 tonne ofaggregates. Second, the greenhouse gas emission of conventionalgravel production is comparatively low, and hence, the avoidedenvironmental burden is also low. Nevertheless, the net burden ofScenario 3 is significantly smaller than that of Scenario 2b.

As defined by Jones et al. (2013), ELFM implies that landfilledwaste should be processed using innovative transformation tech-nologies respecting themost stringent social and ecological criteria.For that reason, the best option for valorization of plasmastoneobtained in ELFM activities must be identified. Based on the anal-ysis of this study's scenarios, Scenario 1 is clearly themost favorabletreatment option for obtaining the maximum environmentalbenefit; however, this analysis was based on only one impact

M. Danthurebandara et al. / Journal of Cleaner Production 99 (2015) 275e285282

category and not all potential environmental impacts wereincluded in this impact assessment method. Another environ-mental analysis was performed to identify the effect of the valori-zation scenarios on other impact categories.

Table 3 displays results obtained from an environmental impactassessment using the ReCiPe midpoint method (hierarchistversion) with European normalization. Similar to the previousassessment, plus values represent burdens and minus values ben-efits. The highest burdens and benefits of each impact category arehighlighted in the table. Among all scenarios, Scenario 1a isresponsible for the highest negative impact on freshwater eutro-phication, human toxicity, terrestrial eco toxicity, freshwater ecotoxicity, marine eco toxicity, andmetal depletion. Scenario 1b (withbricks replacement) creates the highest positive impact on climatechange, terrestrial acidification, marine eutrophication, photo-chemical oxidant formation, and particulate matter formation. Thehighest burden on the ozone depletion impact category is attrib-uted to Scenarios 1a and 1b, with concrete block replacement, andScenario 2b (with sand-lime brick replacement) has the maximumpositive impact on the same impact category. Ionizing radiation andfossil depletion impact categories are influenced negatively, mainlybecause of Scenario 1b with concrete block substitution. Moreover,Scenario 2b (with sand-lime brick substitution) is responsible forthe maximum negative impact on terrestrial acidification, marineeutrophication, and the formation of photochemical oxidant andparticulate matter, and for the highest negative impact on ozonedepletion, terrestrial eco toxicity, agricultural land occupation,natural land transformation, and fossil depletion impact categories.In addition, Scenario 2b (with concrete block replacement) has ahigh positive influence on freshwater eutrophication, humantoxicity, freshwater eco toxicity, marine eco toxicity, urban landoccupation, and metal depletion impact categories. Notably,Scenarios 2a and 3 are not responsible for any of the highest pos-itive or negative impacts on any impact category.

This preliminary analysis suggests that the studied scenariosinfluence not only the impact category of GWP, but also severalother impact categories. Hence, a detailed study is necessary toidentify the reasons for the impact distribution.

3.2. Economic evaluation of valorization of plasmastone

Using the cash-flow model, we investigated the sensitivity ofNPV to a wide range of parameters, including the amount of

Table 3Normalized environmental impact of different scenarios on different impact categories (Tand underlined text respectively).

Impact category Scenario

1a 1b-bricks 1b-concrete bloc

Climate change �0.0667 ¡0.0680 �0.0248Ozone depletion �0.0003 �0.0019 0.0006Terrestrial acidification �0.0194 ¡0.0406 �0.0069Freshwater eutrophication 0.2308 �0.0156 0.1851Marine eutrophication �0.0015 ¡0.0052 0.0001Human toxicity 0.1395 0.0316 0.1067Photochemical oxidant formation �0.0224 ¡0.0415 �0.0128Particulate matter formation �0.0210 ¡0.0365 �0.0123Terrestrial ecotoxicity 0.0008 �0.0010 0.0007Freshwater ecotoxicity 0.1433 0.0064 0.0860Marine ecotoxicity 0.1898 0.0088 0.1118Ionizing radiation 0.0003 0.0055 0.0082Agricultural land occupation 0.0000 �0.0045 �0.0046Urban land occupation �0.0010 �0.0042 �0.0056Natural land transformation �0.0220 �0.5823 �0.1034Water depletion 0.0000 0.0000 0.0000Metal depletion 0.0158 �0.0037 �0.0441Fossil depletion �0.0104 �0.0960 0.0060

different input materials, the investment and operational costs ofthe different valorization scenarios, and the revenues of differentproducts. Table 4 illustrates the parameters' influence on the vari-ation in NPV and the direction of their influence obtained fromMonte Carlo simulations using triangular distributions. Positivecontributions indicate that an increase in the parameter is associ-ated with an increase in the economic indicator. Negative contri-butions imply the opposite situation. We calculated the maximumand minimum values of the considered ranges as follows: For thematerial prices, we decided the price ranges based on publishedliterature (ICIS, 2008; ICIS, 2010; Gardiner&Theobald, 2012) andcommunication with experts in the relevant industries. 10 percentand 50 percent from the investment cost of OPC industry wasconsidered to set the minimum and maximum values of the in-vestment costs of the scenarios (The respective calculation isexplained in detail in Section 2.4). A 10 percent margin from theaverage value was set to the maximums and minimums of thequantities of process inputs and product prices.

As described in the LCA study, the quality of the products of thevalorization scenarios essentially contributes to the net environ-mental and economic impact, which the substituted products ineach scenario explained. In the LCC study, the selling price of theproduct measured this contribution, which logically results in ahigher NPV when selling prices are higher. Table 4 shows that theselling price of the products is of key importance for the economicfeasibility of the treatment scenarios. In addition, the investmentcosts, and operational costs such as materials prices (Na2SiO3, ag-gregates and OPC) also have an important impact on NPV. Never-theless, the range definitions of the different parameters (Table 4)highly influence the final impact of the different parameters on theNPV.

As shown in Table 4, the input materials with the highest eco-nomic impact are Na2SiO3 in Scenarios 1a and 1b and OPC inScenario 2a. Remarkably, these materials also cause the highestenvironmental impact (Fig. 5). Although the amount of aggregatesused in Scenarios 1b and 2b do not show a significant environ-mental impact in the LCA study, their price makes 11 percent % and18 percent contribution to NPV in these respective scenarios. Whencalculating the net environmental impact, the total amount ofproducts has a very important influence. In Scenario 1b and 2b, thisinfluence is largely caused by the amount of aggregates. Similarly,in the economic evaluation, the amount of aggregates has a verysignificant contribution on the variation of NPV.

he highest burden and benefit on each impact category are highlighted by bold italic

ks 2a 2b-sand lime bricks 2b-concrete blocks 3

�0.0228 0.0449 0.0618 0.0001�0.0001 ¡0.0068 0,0006 0.0001�0.0111 0.0160 �0.0111 �0.0002�0.0135 �0.2420 ¡0.4169 �0.0022�0.0018 0.0046 �0.0039 �0.0001�0.0254 �0,1738 ¡0,3653 �0.0016�0.0097 0.0151 �0.0080 �0.0003�0.0108 0.0012 �0.0260 �0.0004�0.0006 ¡0.0215 �0.0043 0.0000�0.0133 �0.3517 ¡0.4392 �0.0018�0.0195 �0.5663 ¡0.5922 �0.00260.0039 0.0009 0.0070 0.0000

�0.0004 ¡0.0521 �0.0269 0.0000�0.0020 �0.0295 ¡0.0332 �0.0011�0.0931 ¡2.2125 �0.9278 �0.05650.0000 0.0000 0.0000 0.0000

�0.0042 �0.3073 ¡0.3403 �0.0008�0.0129 ¡0.1725 �0.0120 0.0000

Fig. 7. The impact of variations in selling prices of the products on NPV in Scenario 1b(top) and Scenario 2b (bottom).

Table 4Most sensitive parameters to the NPV.

Parameter Minimumvalue

Maximumvalue

Contributionto NPV (%)

Scenario 1aPrice of Na2SiO3 (V/t) 180 630 45.6 (�)Price of NaOH (V/t) 250 300 0.2 (�)Amount of Na2SiO3 (t/t plasmastone) 0.07 0.086 0.5 (�)Amount of NaOH (t/t plasmastone) 0.058 0.07 0.1 (�)Selling price of inorganic polymer

cement (V/t)135 165 43.9 (þ)

Investment cost (V/t plasmastone) 3 8 9.7 (�)Scenario 1bPrice of Na2SiO3 (V/t) 180 630 14.4 (�)Price of NaOH (V/t) 250 300 0.1 (�)Price of aggregates (V/t) 5 15 11.3 (�)Amount of Na2SiO3 (t/t plasmastone) 0.07 0.086 0.6 (�)Amount of NaOH (t/t plasmastone) 0.058 0.07 0.2 (�)Amount of aggregates (t/t plasmastone) 2.7 3.3 17.2 (þ)Selling price of inorganic polymer

block (V/t)63 77 42.7 (þ)

Investment cost (V/t plasmastone) 6 16 13.3 (�)Scenario 2aPrice of OPC (V/t) 70 84 13.7 (�)Amount of OPC (t/t plasmastone) 3.6 4.4 1.0 (þ)Selling price of blended cement (V/t) 90 110 52.3 (þ)Investment cost (V/t plasmastone) 7 32 32.9 (�)Scenario 2bPrice of OPC (V/t) 70 84 2.9 (�)Price of aggregates (V/t) 5 15 18.4 (�)Amount of OPC (t/t plasmastone) 3.6 4.4 0.4 (þ)Amount of aggregates (t/t plasmastone) 13.5 16.5 11.7 (þ)Selling price of blended cement

block (V/t)45 55 43.9 (þ)

Investment cost (V/t plasmastone) 14 64 22.6 (�)Scenario 3Selling price of aggregates (V/t) 3 7 7.6 (þ)Investment cost (V/t plasmastone) 1 5 90.7 (�)Operational þ maintenance þ othercosts

(V/t plasmastone)1 3 1.8 (�)

M. Danthurebandara et al. / Journal of Cleaner Production 99 (2015) 275e285 283

Varying the amount of aggregates yields an impact in twodifferent ways. On one hand, it changes the quality of the product,which in turn leads to changes in selling price. On the other hand, itgenerates variations in the quantity of product that can be gener-ated from 1 tonne of plasmastone. Eventually, both these changeswould influence the NPV. Fig. 7 illustrates the variation in NPV fordifferent selling prices of the products for three different amountsof aggregates in Scenarios 1b and 2b. The different lines representthe variation of NPV according to the changes in selling prices fordifferent levels of aggregates. A 10 percent increase in the sellingprice leads to a 18 to 20 percent gain in NPV under Scenario 1b, andof 22e25 percent under Scenario 2b. A 10 percent increase in theamount of aggregates results in increments of 12 percent and 13percent in NPV for Scenarios 1b and 2b, respectively.

To make the valorization routes more profitable, it is importantto know the product's lowest possible selling price. Equation (1)(Section 2.4) provided minimum selling prices of V77/t for inor-ganic polymer cement (Scenario 1a), V33/t for inorganic polymerblock (Scenario 1b), V82/t for blended cement (Scenario 2a), V30/tfor blended cement block (Scenario 2b), and V12/t for aggregates(Scenario 3). Because these values lay below the existing marketprices of OPC and OPC-based concrete blocks, we could assumethese products would be economical alternatives to OPC-basedproducts.

In this study, we omitted the cost of plasmastone becauseplasma gasification and plasmastone valorization take place at thesame premises and are components of one project. If plasmastoneis purchased in order to produce suggested products, it would beimportant to know the maximum purchase price to keep the

project at the lowest profit margin. Using Equation (2), (Section2.4), we calculated the maximum purchase price for Scenarios 1a,1b, 2a, and 2b to be 83, 152, 91, and 468 V/t plasmastone, respec-tively. However, these numbers are valid only with the data used inTables 1 and 2, and depend not only on the selling price of theproducts, but also the quantity of the products. If the company orthe authority responsible for the ELFM project wants to sell theproduced plasmastone to an outside company to produce sug-gested building materials, then these values can be considered asmaximum selling prices.

A trade-off analysis was performed to find the relationship be-tween environmental and economic performances of the scenarios.For Scenario 1b, the same product price (V70/t) was used for bothtypes of substituted products (bricks and concrete blocks). Thesituation was the same for Scenario 2b (product price was V50/t).Fig. 8 shows the relationship between economic and environ-mental impact of different valorization scenarios. Total environ-mental impact in terms of kilograms of CO2 equivalent wascalculated for the hypothetical treatment plant used in the eco-nomic analysis (100,000 tonnes of plasmastone per year of treat-ment capacity and a 20-year lifetime). In fact, the positive values ofNPV imply economic profits, while the negative values of envi-ronmental impact indicate environmental benefits; therefore,Scenarios 1a, 1b, and 2a are viable both environmentally andeconomically. Scenario 2b achieves the highest economic benefitand the lowest environmental benefit. Scenario 1b shows thehighest environmental benefit when bricks are chosen as thesubstituted product, a benefit that is slightly higher than that ofScenario 1a. In addition, Scenario 1a marks the lowest NPV amongthe economically and environmentally viable scenarios. Scenario 3

Fig. 8. Trade off analysis of plasmastone valorization scenarios.

M. Danthurebandara et al. / Journal of Cleaner Production 99 (2015) 275e285284

gives neither economic nor environmental profit; however, theenvironmental burden caused by Scenario 3 is considerably lowerthan that of Scenario 2b. The arrow lines in Fig. 8 illustrate thetrade-off line of plasmastone valorization scenarios, or away to giveup economic benefit to obtain environmental benefit. The trade-offline starts from Scenario 2b with concrete blocks as substitutedproduct, passes Scenario 2b with sand-lime brick as substitutedproduct, and then reaches Scenario 1b with concrete blocks andbricks as substituted products, respectively. These results suggestthat Scenario 1 e valorization of plasmastone via production ofinorganic polymer cement/block is the most worthwhile candidatefor yielding environmental and economic profits in ELFM.

4. Conclusions

This paper includes the results of an environmental and eco-nomic evaluation performed to identify the best scenarios forvalorization of plasmastone in the framework of the novel conceptof ELFM. Based on the LCA study, we found that, despite the highmass production of products, valorization of plasmastone via pro-duction of blended cement/block yields fewer environmentalbenefits compared with valorization of plasmastone via the pro-duction of inorganic polymer cement/block. In addition, the LCAstudy further shows that Na2SiO3, NaOH, and OPC inputs producethe greatest environmental impact in the scenarios. The study il-lustrates that the impact of some parameters are negligible envi-ronmentally, but become key economic drivers, and vice versa.Examples include the negligible influence of aggregates to GWPand its substantial contribution to the NPV. Both the LCA and LCCstudies reveal that the quantity of products obtained from a certainamount of plasmastone are also important when calculating the netimpact of the scenarios. Apart from the quantity, the productquality also creates an essential impact on environmental andeconomic performance of plasmastone valorization. A carefulchoice of the quantity and quality of input materials is needed toobtain a high-quality product and the product quality determinesthe avoided environmental burden and the selling prices of theproducts. In the trade-off analysis, we conclude that decisionsregarding of the appropriate valorization routes should be madecautiously because when economic profits are at the maximum,environmental benefits become the lowest in some scenarios.Nevertheless, valorization of plasmastone via (1) production ofinorganic polymer cement, (2) production of inorganic polymerblock, and (3) production of blended cement are the most viablescenarios both environmentally and economically. In fact, theseresults can be used to assess the actual environmental impact of

plasma gasification process with different residue valorizationoptions. Furthermore, the environmental and economic impacts ofthe discussed scenarios in this study can be used in decisionmakingprocess of future ELFM projects. However, the environmentalimpact discussed in this paper is based mainly on one impactcategory (GWP), although a preliminary analysis suggests that thestudied scenarios would influence several other impact categoriesas well. Hence, potential exists for further research to thoroughlyexamine other impact categories.

Acknowledgment

The authors would like to acknowledge the funding of this studyby the IWT-O&O ELFM project ‘Closing the Circle & EnhancedLandfill Mining as part of the Transition to Sustainable MaterialsManagement’ and the valuable discussions with Group Machiels(Belgium).

References

ACI, 2005. ACI 116R-00: Cement and Concrete Terminology. American ConcreteInstitution, Michigan.

Althaus, H., Hischier, R., Osses, M., Primas, A., Hellweg, S., Jungbluth, N.,Chudacoff, M., 2007. Life Cycle Inventories of Chemicals. Ecoinvent Report No 8.Swiss centre for life cycle inventories, Dubendorf, p. 957.

Bakharev, T., Sanjayan, J.G., Cheng, Y.B., 1999. Effect of elevated temperature curingon properties of alkali-activated slag concrete. Cem. Concr. Res. 29 (10),1619e1625.

Bosmans, A., Vanderreydt, I., Geysen, D., Helsen, L., 2013. .The crucial role of Waste-to-Energy technologies in enhanced landfill mining: a technology review.J. Clean. Prod. 55 (0), 10e23. http://dx.doi.org/10.1016/j.jclepro.2012.05.032.

Brealey, R.A., Myers, S.C., Allen, F., 2010. Principles of Corporate Finance. McGrawHill, Columbus, OH.

Chapman, C., Taylor, R., Ray, R., 2010. The Gasplasma™ process; its applications inenhanced landfill mining. In: International Academic Symposium of EnhancedLandfill Mining. Houthalen-Helchteren, Belgium.

Chapman, C., Taylor, R., Deegan, D., 2011. Thermal plasma processing in the pro-duction of value added products from municipal solid waste (MSW) derivedsources. In: 2nd International Slag Valorisation Symposium. Leuven, Belgium.

Commission, E, 2010. International Reference Life Cycle Data System (ILCD) Hand-book e General Guide for Life Cycle Assessment e Detailed Guidance. Publi-cations Office of the European Union, Luxembourg.

Consonni, S., Giugliano, M., Grosso, M., 2005. Alternative strategies for energy re-covery from municipal solid waste: Part B: emission and cost estimates. WasteManag. 25 (2), 137e148. http://dx.doi.org/10.1016/j.wasman.2004.09.006.

Danthurebandara, M., Van Passel, S., Vanderreydt, I., Van Acker, K., 2015. Assess-ment of environmental and economic feasibility of Enhanced Landfill Mining.Waste Manag. (0) http://dx.doi.org/10.1016/j.wasman.2015.01.041.

Davidovits, J., 2011. Geopolymer Chemistry and Applications. Institute Geo-polymere, Saint-Quentin.

Deventer, J.J., Provis, J., Duxson, P., Brice, D., 2010. Chemical research and climatechange as drivers in the commercial adoption of alkali activated materials.Waste Biomass Valoriz. 1 (1), 145e155. http://dx.doi.org/10.1007/s12649-010-9015-9.

Duxson, P., Mallicoat, S.W., Lukey, G.C., Kriven, W.M., Van Deventer, J.S.J., 2007. .Theeffect of alkali and Si/Al ratio on the development of mechanical properties ofmetakeolin based geopolymers. Coll. Surf. A: Physicochem. Eng. Asp. 292 (1),8e20.

Ecoinvent, 2010. How to Use Ecoinvent Version 2? from. http://www.ecoinvent.org/database/ecoinvent-version-2/.

ECS, 1994. EN 196e1, Methods of Testing Cement e Part 1: Determination ofStrength. European Committee for Standardization.

ETSAP, 2010. Cement Production, Technology Brief I03 IEA Energy TechnologyNetwork. ETSAP (Energy Technology Systems Analysis Program).

Europe'sEnergyPortal, 2013. Energy Prices from Past to Present. Retrieved 12/11/2013, from. http://www.energy.eu/.

Fr€andegård, P., Krook, J., Svensson, N., Eklund, M., 2013. .A novel approach forenvironmental evaluation of landfill mining. J. Clean. Prod. 55 (0), 24e34.http://dx.doi.org/10.1016/j.jclepro.2012.05.045.

Gardiner, Theobald, 2012. International Construction Cost Survey: US$ Version.Goedkoop, M., Heijungs, R., Huijbregts, M., Schryver, A.D., Struijs, J., Zelm, R. v., 2013.

ReCiPe 2008 A Life Cycle Impact Assessment Method Which ComprisesHarmonised Category Indicators at the Midpoint and the Endpoint Level.Retrieved 02, 07, 2013, from. http://www.lcia-recipe.net/.

Habert, G., d' Espinose de Lacaillerie, J.B., Roussel, N., 2011. An environmentalevaluation of geopolymer based concrete production: reviewing currentresearch trends. J. Clean. Prod. 19 (11), 1229e1238. http://dx.doi.org/10.1016/j.jclepro.2011.03.012.

M. Danthurebandara et al. / Journal of Cleaner Production 99 (2015) 275e285 285

Hendriks, C.A., Worrell, E., dejager, D., Block, K., Riemer, P., 2000. Emission Reduc-tion of Greenhouse Gases from the Cement Industry. IEA Greenhouse Gas R&DProgramme.

Hogland, W., 2002. .Remediation of an old landsfill site. Environ. Sci. Pollut. Res. 9(1), 49e54. http://dx.doi.org/10.1007/BF02987426.

Hogland, W., Hogland, M., Marques, M., 2010. Enhanced Landfill Mining: materialrecovery, energy utilisation and economics in the EU (Directive) perspective. In:International Academic Symposium on Enhanced Landfill Mining. Houthalen-Helchteren, Belgium.

Huntzinger, D.N., Eatmon, T.D., 2009. A life-cycle assessment of Portland cementmanufacturing: comparing the traditional process with alternative technolo-gies. J. Clean. Prod. 17 (7), 668e675. http://dx.doi.org/10.1016/j.jclepro.2008.04.007.

Iacobescu, R., Machiels, L., Pontikes, Y., Jones, P., Blanpain, B., 2013. Hydraulicreactivity of quenched FE, Si rich slags in the presence of Ca(OH)2. In: ThirdInternational Slag Valorisation Symposium. Leuven, Belgium.

ICIS, 2008. Indicative Chemical Prices Aez from. http://www.icis.com/chemicals/channel-info-chemicals-a-z/.

ICIS, 2010. European Chemical Profile: Caustic Soda from. http://www.icis.com/Articles/2010/04/05/9348034/european-chemical-profile-caustic-soda.html.

ISO14040, 2006. Environmental Management- Life Cycle Assessment- Principlesand Framework. International Organisation for Standardization, Switzerland.

ISO14044, 2006. Environmental Management- Life Cycle Assessment- Re-quirements and Guidlines. International Organisation for Standardization,Switzerland.

Jones, P., 2008. Landfill mining: history and current status overview. In: GlobalLandfill Mining Conference. London.

Jones, P.T., Geysen, D., Tielemans, Y., Van Passel, S., Pontikes, Y., Blanpain, B.,Quaghebeur, M., Hoekstra, N., 2013. .Enhanced Landfill Mining in view ofmultiple resource recovery: a critical review. J. Clean. Prod. 55 (0), 45e55.http://dx.doi.org/10.1016/j.jclepro.2012.05.021.

Kellenberger, D., Althaus, H., Kunniger, T., Lehmann, M., Jungbluth, N., Thalmann, P.,2007. Life Cycle Inventories of Building Products-Ecoinvent Report No.7. SwissCentre for Life Cycle Inventories, Dubendorf.

Krook, J., Svensson, N., Eklund, M., 2012. Landfill mining: a critical review of twodecades of research. Waste Manag. 32 (3), 513e520.

Laurent, A., Clavreul, J., Bernstad, A., Bakas, I., Niero, M., Gentil, E., Christensen, T.H.,Hauschild, M.Z., 2014. Review of LCA studies of solid waste management sys-tems e Part II: methodological guidance for a better practice. Waste Manag. 34(3), 589e606. http://dx.doi.org/10.1016/j.wasman.2013.12.004.

Lippiatt, B., Ahmad, S., 2004. Measuring the life cycle environmental and economicperformance of concrete: the BEES approach. In: International Workshop onSustainable Development and Concrete Technology. Beijing.

Machiels, L., Arnout, L., Jones, P.T., Blanpain, B., Pontikes, Y., 2014. Inorganic polymercement from Fe-silicate glasses: varying the activating solution to glass ratio.Waste Biomass Valoriz. 5 (3), 411e428. http://dx.doi.org/10.1007/s12649-014-9296-5.

McLellan, B.C., Williams, R.P., Lay, J., van Riessen, A., Corder, G.D., 2011. Costs andcarbon emissions for geopolymer pastes in comparison to ordinary Portland

cement. J. Clean. Prod. 19, 1080e1090. http://dx.doi.org/10.1016/j.jclepro.2011.02.010.

Pontikes, Y., Machiels, L., Onisei, S., Pandelaers, L., Geysen, D., Jones, P.T., Blanpain, B.,2013. .Slags with a high Al and Fe content as precursors for inorganic polymers.Appl. Clay Sci. 73, 93e102. http://dx.doi.org/10.1016/j.clay.2012.09.020.

PR�eConsultants, 2008. SimaPro Database Manual: Methods Library. PR�e Consul-tants, the Netherlands.

PR�eConsultants, 2010. Introduction into LCA with SimaPro 7. PR�eConsultants, TheNetherlands.

Provis, J.L., Deventer, J.J., 2009. Geopolymers: Structures, Processing, Properties andIndustrial Applications. Woodhead Publishing Ltd.

Quaghebeur, M., Laenen, B., Geysen, D., Nielsen, P., Pontikes, Y., Van Gerven, T.,Spooren, J., 2013. .Characterization of landfilled materials: screening of theenhanced landfill mining potential. J. Clean. Prod. 55, 72e83. http://dx.doi.org/10.1016/j.jclepro.2012.06.012.

Ray, R., Taylor, R., Chapman, C., 2012. .The deployment of an advanced gasificationtechnology in the treatment of household and other waste streams. Process Saf.Environ. Prot. 90 (3), 213e220. http://dx.doi.org/10.1016/j.psep.2011.06.013.

Snellings, R., Mertens, G., Elsen, J., 2012. Supplementary cementitious materials.Rev. Mineral. Geochem. 74 (1), 211e278. http://dx.doi.org/10.2138/rmg.2012.74.6.

Spooren, J., Quaghebeur, M., Nielsen, P., Machiels, L., Blanpain, B., Pontikes, Y., 2013.Material recovery and upcycling within the ELFM concept of the Remo case. In:Second International Academic Symposium on Enhanced Landfill Mining.Houthalen-Helchteren, Belgium.

Taylor, R., Chapman, C., Faraz, A., 2013a. Transformations of syngas derived fromlandfilled wastes using the gasplasma process. In: Second International Aca-demic Symposium on Enhamced Landfill Mining. Houthalen-Helchteren,Belegium.

Taylor, R., Ray, R., Chapman, C., 2013b. Advanced thermal treatment of autoshredder residue and refuse derived fuel. Fuel 106 (0), 401e409. http://dx.doi.org/10.1016/j.fuel.2012.11.071.

Turgut, P., 2012. .Manufacturing of building bricks without Portland cement.J. Clean. Prod. 37 (0), 361e367. http://dx.doi.org/10.1016/j.jclepro.2012.07.047.

Van den Heede, P., De Belie, N., 2012. Environmental impact and life cycle assess-ment (LCA) of traditional and ‘green’ concretes: literature review and theo-retical calculations. Cem. Concr. Compos. 34 (4), 431e442. http://dx.doi.org/10.1016/j.cemconcomp.2012.01.004.

van der Zee, D.J., Achterkamp, M.C., de Visser, B.J., 2004. Assessing the market op-portunities of landfill mining. Waste Manag. 24 (8), 795e804. http://dx.doi.org/10.1016/j.wasman.2004.05.004.

Van Passel, S., Dubois, M., Eyckmans, J., de Gheldere, S., Ang, F., Tom Jones, P., VanAcker, K., 2013. The economics of enhanced landfill mining: private and societalperformance drivers. J. Clean. Prod. 55, 92e102. http://dx.doi.org/10.1016/j.jclepro.2012.03.024.

Weil, M., Dombrowski, K., Buchwald, A., 2009. Life cycle analysis of geopolymers. In:Provis, J.L., Van Deventer, J.S.J. (Eds.), Geopolymers: Structures, Processing,Properties and Industrial Applications. Woodhead Publishing Limited, Cam-bridge, England, pp. 194e210.