Life cycle assessment of polychlorinated biphenyl contaminated soil remediation processes
Post on 15-Jul-2016
LCA OF WASTE MANAGEMENT SYSTEMS
Life cycle assessment of polychlorinated biphenylcontaminated soil remediation processes
Guillaume Busset & Matthieu Sangely &Mireille Montrejaud-Vignoles & Laurent Thannberger &Caroline Sablayrolles
Received: 10 June 2011 /Accepted: 6 December 2011 /Published online: 11 January 2012# Springer-Verlag 2012
AbstractPurpose A life-cycle assessment (LCA) was performed toevaluate the environmental impacts of the remediation ofindustrial soils contaminated by polychlorobiphenyl (PCB).Two new bioremediation treatment options were comparedwith the usual incineration process. In this attributionalLCA, only secondary impacts were considered. The con-taminated soil used for the experiments contained 200 mg ofPCB per kilogram.Methods Three off-site treatment scenarios were studied: 1)bioremediation with mechanical aeration, 2) bioremediationwith electric aeration and 3) incineration with natural gas.Bioremediation processes were designed from lab-scale,scale-up and pilot experiments. The incineration techniquewas inspired by a French plant. A semi-quantitative uncertainty
analysis was performed on the data. Environmental impactswere evaluated with the CML 2001 method using the SimaProsoftware.Results and discussion In most compared categories, thebioremediation processes are favorable. Of the bioremediationoptions, the lowest environmental footprint was observed forelectric aeration. The uncertainty analysis supported theresults that compared incineration and bioremediation butdecreased the difference between the options of aeration.The distance of transportation was one of the most sensitiveparameters, especially for bioremediation. At equal distancesbetween the polluted sites and the treatment plant, bioremedi-ation had fewer impacts than incineration in eight out of 13categories.Conclusions The use of natural gas for the incinerationprocess generated the most impacts. Irrespective of theaeration option, bioremediation was better than incineration.The time of treatment should be taken into account. Moreprecise and detailed data are required for the incinerationscenario. More parameters of biological treatments shouldbe measured. LCA results should be completed using eco-logical and health risk assessment and an acceptabilityevaluation.
Keywords Attributional LCA . CML-method .
Environmental evaluation .Midpoint category .
The management of contaminated soil requires the selectionof the most adapted technology from a wide range ofoptions (Suer et al. 2004). Remediation techniques take
Responsible editor: Shabbir Gheewala
G. BussetCATAR-CRITT Agroressources,4 Allee Emile Monso,31030 Toulouse, France
M. Sangely : L. ThannbergerVALGO,81 rue Jacques Babinet,31100 Toulouse, France
M. Sangely : C. SablayrollesUniversite de Toulouse, INP, LCA (Laboratoirede Chimie Agro-Industrielle), ENSIACET,4 Allee Emile Monso,31030 Toulouse, France
M. Sangely :M. Montrejaud-Vignoles : C. Sablayrolles (*)INRA, LCA (Laboratoire de Chimie Agro-Industrielle),31029 Toulouse, Francee-mail: firstname.lastname@example.org
Int J Life Cycle Assess (2012) 17:325336DOI 10.1007/s11367-011-0366-7
place on site, either in situ or ex situ, or off-site and includethermal treatments, biological treatments, soil washing,landfill, electrodialysis, bioleaching, biosparging treatments,chemical treatments (such as oxidation or reduction) andsolvent extraction among many others (Cadotte et al. 2007;Lemming et al. 2010). In practice, ex situ techniques appear tobe the most commonly used (Lemming et al. 2010). Thesetechnologies also diverge in their results. They could lead toimmobilization, separation, concentration or destruction of thepollutants (Rahuman et al. 2000). The primary differences liein their technology, but their cost, efficiency and duration arealso considered.
Pollutants are either inorganic, such as metals, or organic,and their physical and chemical properties, such as volatility,persistence, solubility and conductivity influence the choice ofremediation technique.
Until now, polychlorobiphenyl (PCB) contaminants havemost often been destroyed by incineration. However, thededicated incinerators used for this process require a largeamount of energy to limit dioxin formation, and few effi-cient alternatives are available. Chemical oxidation hasshown a low efficiency (Zhou et al. 2004). Supercriticalwater oxidation exhibits high destruction efficiency butrequires high pressure and temperature conditions (Zhou etal. 2004). A phytoremediation technique using methylated--cyclodextrins has been the subject of a recent study (Shenet al. 2009). The results are conclusive: the impact ofmethylated--cyclodextrins must be investigated. To inves-tigate the biological breakdown of PCBs, Sangely et al.(2009) have tested the combination of Phanerochaete cry-sosporium, a fungus capable of breaking down PCBs underanaerobic conditions, and Burkholderia xenovorans, a bac-terium implicated in PCB breakdown under aerobic condi-tions. The combination of aerobic and anaerobic steps hasgiven rise to a new process of bioremediation of PCB-contaminated soils and has been developed on both thelaboratory scale and as a pilot project.
Life-cycle assessment (LCA) appears to be a method welladapted for the evaluation of the impacts of remediationtechniques (Morais and Delerue-Matos 2009). LCA can beattributional or consequential, particularly in the soil remedi-ation domain (Lesage et al. 2007a; Lesage et al. 2007b).Attributional LCA evaluates the primary impacts from resid-ual contamination and/or the secondary impacts from thetechnique life cycle. Consequential LCA takes into accountenvironmental and economic impacts after remediation(Volkwein et al. 1999). Most authors have limited their studiesto secondary impacts (Lemming et al. 2010). LCA has beenapplied to contaminations of lead (Page et al. 1999), polycy-clic aromatic hydrocarbons, chromium and mineral oils(Volkwein et al. 1999), sulfur (Blanc et al. 2004), diesel fuel(Toffoletto et al. 2007; Cadotte et al. 2007) and trichloroethene(Lemming et al. 2010). These studies show that LCA is a
relevant management tool for evaluation of the environ-mental impacts of soil remediation techniques of differ-ent pollutants.
A life-cycle assessment was undertaken to compare dif-ferent treatments of PCB waste in Ohio, USA. This completestudy investigated environmental impacts and economic,technologic and health risks (Morris et al. 2000). At thattime, biological treatments were only in the R&D stage;therefore, they were not included among the evaluated tech-niques. Another recent LCA investigated PCB treatmenttechniques but compared a high-temperature process with abase-catalyzed decontamination (Hu et al. 2011). No LCAhas been performed on the new biological process used inthis study.
The objectives of this study are (a) to evaluate, via attribu-tional LCAmethodology, the potential environmental impactsof the bioremediation process for PCB-contaminated soils, asrecently established by Sangely et al. (2009), and (b) tocompare the bioremediation impacts to the impacts of thecurrent incineration technique.
The life-cycle assessment was undertaken using the ISO14040(2006) and ISO 14044(2006) standards
2.1 LCA goal and scope
The evaluated systems function was to restore soil PCB con-tamination levels to waste acceptance criteria (50 mg kg1 ofsoil) in hazardous (French class 1) waste landfill sites in France(http://www.ineris.fr/aida/?q0consult_doc/consultation/126.96.36.199.8.2283). The reference flow was taken as theamount of moist soil (20% moisture) that can be excavated in1 day under pilot-project conditions; this quantity correspondsto 600 t per day. Laboratory results have shown a potential ofPCB degradation in soil of 556 g kg1 per day. Therefore, thePCB concentration can be reduced from 200 mg kg150 mg kg1 of soil in 265 days (Sangely 2010). The functionalunit was therefore defined as treating 600 t of PCB-contaminated moist soil (20% moisture) to reduce its PCBconcentration from 200 mg kg150 mg kg1 of soil.
The processes taken into consideration for the studiedsystems included excavation and transport to the landfill siteafter the treatment phase. A detailed description is given inthe next section. For all of these processes, infrastructureconstruction, worker transport and landfill site maintenancewere not taken into account, primarily because the share ofimpacts by soil remediation treatments was negligible. Theremediation activity of PCB-contaminated soils is not themost important part of the enterprises activity. Systemsboundaries are discussed in Section 4.
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2.2 Life-cycle inventory
2.2.1 Systems description
The life-cycle assessment was used to compare two PCB-contaminated soil remediation processes: soil incinerationand biological treatment. Three scenarios were defined: BM,treatment by bioremediation with mechanical aeration; BE,treatment by bioremediation with electric aeration; and Inc,treatment by incineration.
Biological treatment The biological treatment is an inno-vative and original process based on experimentallaboratory-scale and pilot-scale trial results. The treat-ments procedure consisted of alternating aerobic andanaerobic phases. The aerobic conditions favor the devel-opment of the bacteria B. xenovorans, and the anaerobicconditions favor the fungi P. crysosporium; each is capa-ble of partially breaking down PCB. Bacteria broke downthe less-chlorinated PCBs, whereas fungi broke down themore highly chlorinated PCBs (Sangely et al. 2009).When the bacteria and fungi were broken down in tan-dem, PCB was broken down to the target concentrationor lower. In practice, the treatment of PCB-contaminatedsoils required three cycles; each cycle consisted of2 months under anaerobic conditions and 1 month underaerobic conditions.
Excavation, the first phase, was followed by transportto the bioremediation site, where the soil was immedi-ately put onto a waterproof concrete platform (not takeninto account in the LCA). This soil was then coveredwith a low-density polyethylene sheet, supplied withnitrates and flooded with water to create anaerobic con-ditions. The aerobic phase was facilitated by soil aera-tion. The two techniques being studied were given twodifferent bioremediation scenarios. These scenarios weredesigned to allow a comparison of two technical alter-natives and determine the best one. The first technique(BM) involved turning the soil over four times per cycleusing a 5-t mechanical digger. The second technique(BE) involved the electrical pumping of air throughthe soil for 25% of the aerobic phase. An 11-kWcompressor was used. The first anaerobic/aerobic cyclewas followed by two more identical cycles. After threecycles, the soil was transported to the nearest hazardouswaste landfill site. For this stage, the residual amount ofPCB met the landfills waste acceptance upper limitationcriteria. It was considered as an emission to the soil. Aflow diagram of the bioremediation procedure and thetwo aeration options is shown in Fig. 1.
The potential direct emissions from anaerobic and aero-bic PCB decomposition were not known and were notconsidered.
Treatment by incineration Soil treatment by incinerationconsisted of excavation followed by transport to the incin-eration site. At the incineration site, the soil was put into arotating oven where soils and other organochloride wasteswere burned at a high temperature (1200C) (Sch 2010).The gaseous waste was burned in a second combustion at1200C, followed by a rapid cooling to 70C to avoid theformation of dioxins and furans (Sch 2010). The gas wasthen washed with sodium hydroxide in two gasliquid con-tactors. Dust was then removed by a Venturi followed by anelectric filter (Sch 2010). Waste water was treated withlime and complexing and flocculating agents. Solid residuesfrom the incinerated soils and the wash-water treatmentsludges were sent to a hazardous waste landfill. Althoughnot all of the PCB was destroyed by incineration, we assumedthat there were no emissions due to the very low residualconcentration. The incineration procedure and process flow-chart is shown in Fig. 2.
2.2.2 Data collection
Inventory data about the bioremediation processes weretaken from laboratory-scale and pilot-scale experiments.When results from the pilot scale were not available,laboratory-scale data from Sangelys dissertation were usedfor extrapolation (Sangely 2010).
Data about incineration were taken from the RegistreFranais des missions Polluantes (French pollutant emis-sion register) website (http://www.pollutionsindustrielles.ecologie.gouv.fr/IREP/index.php), which provided informa-tion on the main direct emissions for the overall process atthe incineration site. A large amount of natural gas was usedfor the incineration; the LCA impact from its productionwas taken into account by calculating the quantity of naturalgas Eq. 1 from the amount of CO2 emitted.
Volume of natural gas used per incineration calculatedfrom the quantity of CO2 emitted:
Vgnv mCO2 Ipa 1
Vgnv is the volume of natural gas assumed to beconsumed by the functional unit in cubic meter
mCO2 is the mass of CO2 emitted in kg UF1
Ip is the percentage CO2 emitted attributed to thenatural gas combustion
is the conversion coefficient (mass of CO2 per volumeof burned natural gas: in kilogram per cubic meter).
Finally, all the product and energy inventory data used inthe procedure were obtained from the Ecoinvent Europeandata table.
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2.2.3 Uncertainty analysis
Uncertainty analysis was applied to all inventory dataaccording to the method in Frischknecht et al. (2007). Foreach data set, six parameters were qualitatively evaluated ona scale of 16, and an uncertainty factor was attributed toeach evaluation using a correspondence table. The evaluatedparameters and the corresponding uncertainty factors aregiven in Table 1 (Jolliet et al. 2005). If a parameter did notapply to the data, it was assigned a value of 1. The variancewas calculated using Eq. 2.
U1 the uncertainty factor for the reliability parameterU2 the uncertainty factor for the exhaustivity parameterU3 the uncertainty factor for the temporal correlation
U4 the uncertainty factor for the geographical correlationparameter
U5 the uncertainty factor for the technological correlationparameter
U6 the uncertainty factor for the sample size parameterU7 the basic uncertainty factor. It depends on the
emissions measuring and modelling techniques.
The uncertainty factors have no units.The Ecoinvent data used were primarily evaluated as a
function of the different correlations. The relative uncertaintyof the data was found using Eq. 3.
Calculation of relative uncertainties:
where I% is the relative uncertainty of the data...