LCIA OF IMPACTS ON HUMAN HEALTH AND ECOSYSTEMS

Life cycle assessment of adsorbents for fluoride removalfrom drinking water in East Africa

Teshome L. Yami1 & Junyi Du1& Laura R. Brunson1

& Jim F. Chamberlain1&

David A. Sabatini1 & Elizabeth C. Butler1

Received: 30 June 2014 /Accepted: 13 June 2015 /Published online: 30 June 2015# Springer-Verlag Berlin Heidelberg 2015

AbstractPurpose Various fluoride adsorbents have been studied forremoval of excess fluoride from drinking water to meet theWorld Health Organization (WHO) Guideline value of1.5 mg/L. Production of these adsorbents emits contaminantsthat can affect human health and the environment, but theextent of these impacts is currently unknown. This study eval-uates the environmental impacts of four low-cost and easy touse adsorbents: activated alumina, aluminum oxide amendedwood char, bone char, and treated alum waste.Methods The environmental impacts of these adsorbents wereevaluated using life cycle assessment (LCA). The life cyclestages considered were raw material acquisition, adsorbentmanufacturing, and waste management. The functional unitwas defined as the quantity of adsorbent necessary to reducethe fluoride concentration of 100,000 L of water from 10 mg/Lto theWorld Health Organization recommended drinking waterlevel of 1.5mg/L. Eco-indicator and the Tool for Reduction andAssessment of Chemicals and other Environmental Impacts(TRACI) were used to interpret the environmental impacts.Results and discussion The results indicate that the environ-mental impacts of these adsorbents vary greatly using a com-mon functional unit of treating 100,000 L (100 m3) offluoride-impacted water. A key determining factor for the

impacts is the fluoride adsorption capacity of the adsorbentmaterial because this affects how much material is required toproduce safe water. Aluminum oxide amended wood char hadthe highest overall negative environmental impact in all im-pact categories, and the lowest adsorption capacity. The twoadsorbents that performed the best (lowest environmental im-pact) were the bone char and the treated alum waste.Conclusions The environmental impacts of the adsorbentscan be reduced by increasing their fluoride adsorption capac-ity and/or carefully selecting key process components, such asthe distance and means of transportation, particularly for acti-vated alumina. Regeneration and reuse of spent adsorbentshas the potential to minimize impacts to ecosystem quality.

Keywords Activated alumina . Bone char . Drinking watertreatment .Fluorideadsorbents .Lifecycle assessment .Woodchar

1 Introduction

It is estimated that more than 200 million people worldwideconsume water with fluoride concentrations above the WorldHealth Organization (WHO) recommended threshold of1.5 mg/L (Amini et al. 2008). Consumption of water withfluoride above this concentration affects human health, rang-ing from dental to skeletal fluorosis (Dissanayaka 1991;Fawell et al. 2006). Other health disorders include musclefiber degeneration, neurological symptoms, repeated miscar-riage or stillbirth, andmale sterility (Maheshwari 2006). Theseconditions can be physically debilitating and painful.

In most cases, fluoride in groundwater is geogenic, i.e., itresults from local geological formations that are naturally richin fluoride (Apambire et al. 1997). For such areas, it is impor-tant to either find an alternative water source or to implement

Responsible editor: Sonia Valdivia

Electronic supplementary material The online version of this article(doi:10.1007/s11367-015-0920-9) contains supplementary material,which is available to authorized users.

* Teshome L. YamiTeshome.L.Yami-1@ou.edu

1 School of Civil Engineering and Environmental Science, Universityof Oklahoma, Norman, OK 73019, USA

Int J Life Cycle Assess (2015) 20:1277–1286DOI 10.1007/s11367-015-0920-9

fluoride removal techniques. Treatment methods such as co-agulation, adsorption, membrane processes, and electrolyticdefluoridation have been investigated for removal of excessfluoride from drinking water (Fawell et al. 2006; Ayoob et al.2008; Mohapatra et al. 2009). Previous studies indicate thatadsorption is currently the best option for fluoride removal,especially for developing countries, due to its high efficiencyand low cost of operation and maintenance (Jagtap et al.2012). However, the production of common fluoride adsor-bents has potential negative health and environmental impactssuch as cancer risks, respiratory infections, and globalwarming (Classen et al. 2009; Martin and Griswold 2009).These impacts should be scientifically modeled and estimated.

The United Nations Conference on Environment and De-velopment indicated that environmental impact should beevaluated for proposed activities that are likely to have signif-icant adverse impacts on the environment (Montalembert et al.1992). In accordance with this principle, the focus of this workis to present a life cycle assessment (LCA) of adsorbents forfluoride removal that illustrates the environmental impacts ofthe adsorbents. The aim of LCA is to perform a comprehen-sive analysis of the life cycle of a product, including rawmaterial acquisition, manufacturing, use, and waste manage-ment (ISO 2006a). LCA can help to select processes andtechnologies that have lower environmental impacts. Forexample, Gabarrell et al. (2012) compared the environmentalimpacts of textile dye treatment processes and identified aprocess with environmental advantages using LCA.

In this study, the Bora district in the Rift Valley of Ethiopiain East Africa was used as the study area with correspondingmodel inputs coming from this location. This area was selecteddue to the high naturally occurring fluoride concentrations ingroundwater which is the main source of drinking water, ob-served fluoride health impacts among the residents, and also thecurrent implementation of some fluoride treatment technologiesin the region (Rango et al. 2012; Brunson and Sabatini 2014).Four adsorbents were considered in this analysis: (1) commer-cially available activated alumina (α-Al2O3); (2) aluminum ox-ide amended wood char, produced by firing wood in a furnaceand impregnating it with aluminum oxide; (3) bone char pro-duced by charring cow bone, with the main constituent beinghydroxyapatite; and (4) a waste product from alum production,referred to hereafter as Btreated alum waste.^

The study was performed using the protocol of the Interna-tional Organization for Standardization (ISO) 14040/44,which consists of four phases: (1) goal and scope definition,(2) life cycle inventory, (3) life cycle impact assessment, and(4) interpretation (ISO 2006a, b). The objective of this studywas to provide a better understanding of environmental im-pacts associated with fluoride adsorbents through the quanti-fication and comparison of impacts. This understanding willprovide a greater contribution towards solving the globaldrinking water crisis in a way that minimizes the potential

for negative environmental impacts. To our knowledge, nospecific investigation has evaluated the environmental im-pacts of these adsorbents for fluoride removal.

2 Methods

2.1 Goal and scope definition

The goal of this LCA was to compare the environmental im-pacts of four fluoride adsorbents suitable for emerging regions:activated alumina, aluminum oxide amended wood char, bonechar, and treated alumwaste, and to identify the life cycle stagesor processes associated with these adsorbents that have thelargest negative impacts. The functional unit was defined asthe quantity of adsorbent necessary to reduce the fluoride con-centration of 100,000 L of water from 10 mg/L to the WHOrecommended drinking water level of 1.5 mg/L (WHO 2011).An initial fluoride concentration of 10mg/Lwas selected in thisstudy since the mean fluoride concentration in wells in the RiftValley of Ethiopia has been reported to 10 mg/L (Rango et al.2012). The scope of the study included all stages from cradle tograve except the use phase, which was determined to be com-mon for all adsorbents. These stages included raw materialacquisition, adsorbent manufacturing, transportation, and wastemanagement (Fig. 1). It was assumed that during use, the ad-sorbents are packed in a column through which fluoride-containing water is passed until an effluent fluoride concentra-tion of 1.5 mg/L is reached. Then, the spent adsorbents areremoved from the column and taken to awaste pile for disposal.The use phase was excluded from the analysis since (i) it isexactly the same for all four materials and (ii) the total wasteemissions associated with this stage are negligible.

2.2 Life cycle inventory

A life cycle inventory (LCI) of inputs and outputs of materialsduring raw material acquisition, manufacturing, and disposalof the fluoride adsorbents was obtained using the Ecoinvent v.2.2 databases (Ecoinvent Center 2010) and a literature review.SimaPro v. 7.3.3 was used to build life cycle models. A massbalance method was used to estimate the system input andoutput data when appropriate datasets were not available fromEcoinvent (Table S1 and Section 2 calculations in theElectronic Supplementary Material).

The fluoride adsorption capacity at an equilibrium dis-solved fluoride concentration of 1.5 mg/L (referred to hereaf-ter as Q1.5, with units of mg F−/g adsorbent) is a crucial factorfor comparing the magnitude of environmental impacts, be-cause the quantity of adsorbent required for fluoride removal(the functional unit) is governed by the fluoride adsorptioncapacity. The Q1.5 is pertinent to field applications since1.5 mg/L is the WHO recommended fluoride treatment goal.

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Using Langmuir isotherm parameters reported in the litera-ture, a range of Q1.5 values was estimated for each adsorbentusing the Langmuir isotherm (Eq. (1)):

Q1:5 mg=gð Þ ¼ Qmax � K � Ce

1þ K � Ceð Þ ð1Þ

where Qmax (mg F−/g adsorbent) is the maximum adsorptioncapacity, K (L/mg F−) reflects the adsorption affinity, andCe—the equilibrium concentration of the treated water—wasset equal to 1.5 mg/L. These Q1.5 values, along with the me-dian Q1.5 value for each adsorbent, are reported in Table S2(Electronic Supplementary Material). Median Q1.5 valueswere then used to estimate values of the total mass of eachadsorbent required to treat 100,000 L of water to reduce fluo-ride from 10 to 1.5 mg/L using Eq. (2):

Totalmass gð Þ ¼ Co−Ceð Þ � V

Q1:5ð2Þ

whereCo is the initial fluoride concentration before adsorption(10 mg/L), Ce is the final concentration (1.5 mg/L), and V isthe total volume (100,000 L). These values of total adsorbentmass are reported in Table 1 and were used as the functionalunit for the LCI.

2.2.1 Life cycles of the fluoride adsorbents

The processes involved in the life cycle of the four fluorideadsorbents are illustrated in Fig. 1 and summarized in thefollowing section.

Activated alumina Activated alumina is created by calciningaluminum-based materials at a high temperature. In Ethiopia,activated alumina is primarily imported from South Africa andthen directly applied for fluoride adsorption without furthertreatment. Therefore, the existing module of aluminum oxidein the Ecoinvent database, which represents themanufacturingprocess of commercialized activated alumina, was used withprocesses of transportation, packaging, and waste manage-ment added to complete the module. Typically, activated alu-mina is transported to Addis Ababa, Ethiopia, by aircraft andthen delivered to point-of-use (POU) sites in the Rift valley ofEthiopia by van over an average distance of 100 km.

Aluminum oxide amended wood char Aluminum oxideamended wood char is a locally available and low-cost adsor-bent prepared by amending wood char (which has low fluo-ride adsorption capacity) with aluminum oxide in order toimprove its fluoride adsorption capacity. The raw materialsfor production of aluminum amended wood char are alumi-num sulfate and wood chips which are obtained from an alumfactory and the forest management project located in the Riftvalley, respectively. The raw materials are transported usingtractor and trailer to the production sites. Wood chips arecharred at a temperature ranging from 500–600 °C (Brunsonand Sabatini 2014). The wood charring is done in a furnace forone hour using kerosene and charcoal for ignition. Aluminumis produced from bauxite and is transported to smelting sites.Caustic soda is mixed with bauxite for production of sodiumaluminate which is later treated with CO2 to produce Al(OH)3.

Fig. 1 Flow diagrams showing steps for raw material acquisition, manufacturing, use, and waste management for four fluoride adsorbents

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Sulfuric acid is mixed with Al(OH)3 to obtain Al2(SO4)3 forwood char amendment. For charring, wood chips are assumedto be obtained from sawn hardwood timber since it is easier tohandle than softwood in Africa (Seidel 2008). Wood charringis conducted in a kiln and wood chips are used as both acharring material and energy source. Wood charring involvesemissions of gases such as CO2, SOx, NOx, CO, and volatileorganic compounds (VOCs), as well as particulates(Table S1). However, due to unavailability of dioxins andfurans emission data from kilns for wood charring, they werenot included in this analysis. Wood chars are then crushed andfurther amended by soaking them in a solution of Al2(SO4)3 atroom temperature for 5 days, followed by rinsing. The alumi-num oxide amended wood char is then packaged in wovenbags and transported to POU sites.

Bone char Bone char is produced from waste cow bones,which are collected from slaughterhouses and transported tocharring facility using tractor and trailer. The Ecoinvent data-base lacks data on animal bones and thus a bone char module,which is a set of independent units or processes involved toproduce the bone char, was created in SimaPro v. 7.3.3 usingbone char data complied in Table S1. Emissions data fromcow bone and meat meal combustion in a fluidized bed wereutilized in lieu of bone charring emissions data, which areunavailable in Ecoinvent. The gaseous emissions from thebone charring processes are similar to the wood charring pro-cesses. In the bone char module, part of the environmentalimpact of cattle raising was allocated to bone char production.An allocation factor of 17 %, which is equal to the weightfraction of bone in the animal (Terry et al. 1990), was used.The animal bone charring process is initiated in a kiln usingkerosene and charcoal for ignition after which the bone burnson its own without requiring additional energy (CDN et al.2007). Brunson and Sabatini (2009) conducted cow bonecharring at a temperature of 400 °C. The bone char is crushedand rinsed using NaOH solution to remove impurities (CDNet al. 2007; Arrenberg 2010) and is then packaged in wovenbags for transportation to POU sites.

Treated alum waste The residue generated during the manu-facture of alum from kaolin by the sulfuric acid process con-tains abundant aluminum sulfate and exhibits fluoride adsorp-tion capacity (Nigussie et al. 2007). The alum waste was

obtained from a waste pile close to the premises of the alumproduction factory located in the Rift Valley of Ethiopia, and itwas transported to the adsorbent manufacturing center using atractor/trailer. The process of obtaining alum waste from thewaste pile and the corresponding impacts from transportationwere included in the scope of this study. The use of sulfuricacid in alum production is described by (Ismail 2010 Eq. (3)):

Al2O3 � 2SiO2 � 2H2Oþ 3H2SO4→Al2 SO4ð Þ3 þ 2SiO2 þ 5H2O

ð3Þ

The process results in alum waste containing excess sulfu-ric acid (pH 3.5) and large volumes of water. These propertiesare undesirable for fluoride adsorption and thus the wasterequires pH adjustment and thermal treatment at a temperatureranging from 100 to 700 °C in a furnace for 1 h (Nigussie et al.2007). The thermally treated alum waste is later neutralizedusing 0.1 M NaOH, packaged in woven bags, and transportedto POU sites.

2.2.2 Assumptions

The following assumptions were made in this LCA:

& Infrastructure, such as production facilities (e.g., mixersand tractors) that are repeatedly used, are common to allprocesses and thus were not included in the assessment.

& No adsorbents are lost during processing and treatment,except where noted. Minute adsorbent particles escapingfrom the treatment processes were not considered due todata unavailability.

& Regeneration of adsorbents was not considered. The wastedisposal scenario considered in this study was that thewaste is piled on the ground, spread out, and dried, withsome additional land required for access to the site. Con-sidering a waste density of 1000 kg/m3 (Doka 2009), a 1-m average height of a waste pile, and the need for addi-tional space and access for waste dumping, spreading, anddrying (based on our observation in the Rift Valley ofEthiopia on July 27, 2013), an area of 0.002 m2 kg wastewas assumed. Emissions from waste piles were omitteddue to lack of relevant data.

Table 1 Total mass of adsorbents needed to lower the fluoride concentration of 100,000 L of water from 10 to 1.5 mg/L

Adsorbent Median Q1.5 (mg/g) (from Table S2) Total mass of adsorbent equal to the functional unit (kg)

Activated alumina 0.8 1063

Bone char 1.71 496

Aluminum oxide amended wood char 0.13 6538

Treated alum waste 3.4 250

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& Woven bags were used for packaging all of the adsorbentsand 0.01 kg of woven bag was required per kilogram ofadsorbent.

& One third of the energy input to thermal treatment process-es was considered lost as waste heat to the environment(Hendricks and Choate 2006).

& Land transportation of adsorbents was by tractor with trail-er unless otherwise indicated. The average transportationdistance from the location of adsorbent production to thePOU site was assumed to be 100 km, so a round tripdistance of 200 km was used.

& All bones considered in this study were cow bones. A cowon good pasture supplemented with grain gains about0.9 kg per day (Wilson and Beall 1979). An average Ethi-opian cowweighs 300 kg (Tesfaye 2006). Therefore, cowswere considered to have an average lifespan of 1 yearbefore being slaughtered. Only 50 % of total cow boneswere assumed suitable and available for charring (e.g.,hooves, tail, bone marrow, and horns are assumed notsuitable for charring). Damage of bones by wildlife andlow collection efficiency are also reasons for less thancomplete bone recovery.

& The allocation factor for treated alumwaste was 20% (i.e.,20 % of the emissions associated with alum productionwere assigned to the waste) based on an interview madewith the Manager of Awash Melakasa aluminum sulfateproduction factory, Ethiopia (personal communication onJuly 27, 2013).

2.3 Impact assessment methods and impact categories

Eco-indicator, one of the most widely used damage assessmentmethods for life cycle impact assessment (Mark and Renilde2000) and the Tool for Reduction and Assessment ofChemicals and other Environmental Impacts (TRACI) (Bareet al. 2003) were used to interpret the environmental impactsin this study. TRACI is a midpoint-oriented method that char-acterizes impact categories based on the impacts that are direct-ly caused by emitted pollutants, while Eco-indicator is anendpoint-oriented method in which damages to human health,ecosystems, and resources are assessed at the endpoint-level byanalyzing the midpoint impact categories (Bare et al. 2000).According to Bare and Gloria (2008), TRACI has the advan-tage of representing a mid-point on the cause-effect chain be-tween stressors (e.g., air quality, water quality, extreme temper-ature) and endpoints. The analysis at the midpoint minimizesdamage forecasting since the endpoint estimation is constrainedby the incompleteness of model coverage. The midpoint anal-ysis also simplifies complexity of modeling and communica-tion (Bare 2002). Eco-indicator, an endpoint method, was se-lected in this analysis since the impacts from the two methodsshow similar trends and it has an additional advantage in that it

enables grouping of the categories to better understand the im-pacts to the major impact categories of damage to humanhealth, eco-system quality, and resources.

In Eco-indicator, the human health damage category in-cludes the following impact categories: climate change, ozonelayer depletion, carcinogenic substances, respiratory effects(organics), respiratory effects (inorganics), and ionizing radi-ation. The ecosystem quality damage category includes thefollowing impact categories: land use, acidification/eutrophi-cation, and ecotoxicity. The resources damage category in-cludes the depletion of fossil fuel and depletion of mineralsimpact categories.

3 Results and discussion

3.1 Overview

The results from the two impact assessment methods showedsimilar trends in terms of the impact in each category (Fig. 2a–b). Specifically, aluminum oxide amended wood char pro-duced the highest impact in nearly all impact categories,followed by activated alumina, regardless of the method used(Fig. 2a–b), indicating overall agreement between the mid-point (TRACI) and endpoint (Eco-indicator) methods. Whilemidpoint methods have the advantage of lower uncertainty,the endpoint method Eco-indicator allows grouping of impactcategories into a smaller number of damage categories (humanhealth, ecosystem quality, and resources) that have commonunits (disability adjusted life years (DALYs), potentially dis-appeared fraction (PDF)×m2×year, and MJ surplus energy,respectively) that can then be quantitatively compared. Thus,Eco-indicator was used for subsequent analyses in this project.

Based on this grouping of impact categories, aluminum ox-ide amended wood char had the greatest adverse impacts in thehuman health, ecosystem quality, and resources damage cate-gories (Figs. 3 and 4). The life cycle stage that contributed themost (more than 60%) to the adverse impacts for this adsorbentwas raw material acquisition (Fig. 3). Raw material acquisitionincludes the processes illustrated in Fig. 1. The high impacts foraluminum oxide amended wood char are mainly due to its lowQ1.5 value compared to the other adsorbents (Table 1), meaningthat a larger mass of adsorbent, and therefore more materialsprocessing and waste management activities are needed to meetthe treatment goal for this adsorbent.

Activated alumina was next in terms of adverse impacts inmost damage categories, with the principal impacts comingfrom the adsorbent manufacturing stage for the human healthand resources damage categories and from the waste manage-ment life cycle stage for the ecosystem quality damage cate-gory (Fig. 3). Bone char and treated alum waste had lowerimpacts in all damage categories compared to aluminum oxideamended wood char and activated alumina, with raw material

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acquisition contributing the most to the human health andwaste management to ecosystem quality damage categoriesfor bone char and treated alum waste (Fig. 3).

For the adsorbents studied here, a relationship was observedbetween environmental impacts and adsorption capacity i.e., alu-minum oxide amended wood char > activated alumina > bonechar > treated alum waste. This trend in environmental impactcan be explained by the fact that a smaller mass of each succes-sive adsorbent was required to meet the treatment goal, and thus,smaller corresponding emissions were generated from materialsproduction and processing (see Table 1). Thismeans that in orderfor low cost, locally available adsorbents like aluminum oxideamended wood char to compare favorably with other adsorbentsin terms of environmental impacts, a significant increase in theirspecific adsorption capacity or adsorption capacity per mass isneeded. This underscores the need for research to enhance andoptimize the adsorption capacity of wood chars and other locallyavailable materials that could serve as fluoride adsorbents.

3.2 Process contribution and dominant impact categoryanalyses

Next, the relative contribution of specific life cycle processesand specific impact categories to the overall damages were

Fig. 2 Impact comparison using(a) Eco-indicator and (b) TRACI.The y-axis value for the adsorbentthat had the maximum impact ineach category was set equal to100 %, and other values werenormalized to this maximumvalue

Fig. 3 Damage assessments for the adsorbents at each life cycle stage.Abbreviations used are activated alumina (AA), aluminum oxideamended wood char (AOWC), bone char (BC), and treated alum waste(TAW)

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assessed for each adsorbent. For three of the four adsorbents(activated alumina, bone char, and treated alum waste), wastemanagement activities contributed the most to the ecosystemquality damage category (Fig. 5). For the fourth adsorbent(aluminum oxide amended wood char), waste managementcontributed more than a third of the damages in this category.The significant contribution of waste management activities tothe ecosystem quality damage category for all adsorbents in-dicates the need for research on and implementation of regen-eration and reuse of spent adsorbents.

For all adsorbents except bone char, the specific impactcategory that contributed the most to the human health dam-age category was respiratory inorganics, while for bone char,climate change and respiratory inorganics both contributedsignificantly to the human health damage category (Fig. 4).These impacts were due to transportation (air and land), char-ring, cattle raising, and thermal treatment (data not shown).Except for activated alumina, the land use impact categorywas the biggest contributor to the ecosystem quality damagecategory for all adsorbents (Figs. 4 and 5), due primarily towaste management activities (data not shown). Finally, thefossil fuels impact category was the largest contributor to theresources damage category for all adsorbents (Fig. 4), due touse of fossil fuels throughout adsorbent acquisition andmanufacturing (data not shown).

Bone char and aluminum oxide amended wood char hadhigher impacts in the climate change impact category thanactivated alumina and treated alum waste (Fig. 2a) mainlydue to CO2 emissions from charring—a step that is not in-volved in the production of activated alumina and treated alumwaste. Emissions of CO2 from wood and cow bone charringcontributed the most to impacts in the climate change impactcategory (data not shown). While these impacts can, in theory,be mitigated by carbon offsets, development of adsorbentswith higher adsorption capacities is likely to be a more

effective strategy for mitigating climate change impacts forchar-based adsorbents.

For activated alumina, transportation by air and land con-tributed the most to the human health, ecosystems quality andresources damage categories (Fig. 5). Also, for activated alu-mina, the process that contributed the most to both the respi-ratory inorganics and fossil fuel impact categories was the useof aircraft to transport activated alumina from Johannesburg,South Africa, to Addis Ababa, Ethiopia, followed by wastemanagement (data not shown).

For aluminum oxide amended wood char, charring contrib-uted the most to the human health damage category, and ac-quisition of wood chips contributed the most to the ecosystemquality and resources damage categories (Fig. 5).

For bone char, cattle raising produced the majority of im-pacts in the human health and ecosystem quality damage cat-egories, and obtaining cow bone (mainly transportation) con-tributed the most to the resource damage category (Fig. 5).The respiratory inorganics and climate change impact catego-ries contributed the most to the human health damage categorydue to emission from the charring process, transportation, andcattle raising, which leads to methane emissions.

For treated alum waste, sulfuric acid production contribut-ed the most to the human health damage category and alummanufacturing contributed the most to the ecosystem qualitydamage category (Fig. 5). The process that contributed thehighest impact to the resource damage category was the pro-cess of obtaining the alum waste due to the use of land forwaste storage followed by thermal treatment to remove mois-ture and activate the adsorbent.

3.3 Sensitivity analysis

A sensitivity analysis was conducted to evaluate the process-es with the greatest environmental impacts, and thus the

Fig. 4 Specific impact categoriescontributing to the human health,ecosystem quality, and resourcesdamage categories for eachadsorbent. Abbreviations used areactivated alumina (AA),aluminum oxide amended woodchar (AOWC), bone char (BC)and treated alum waste (TAW)

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greatest potential for improvement. Initial review of the LCIindicated that there was potential improvement in the respi-ratory organics and fossil fuels impact categories for activat-ed alumina. Thus, processes contributing to emissions inthese impact categories, particularly transportation, were se-lected for sensitivity analysis.

The assumed process of transporting activated aluminafrom Johannesburg, South Africa, to Addis Ababa, Ethio-pia, by plane (5000 km—a process called BSouth Africa byair^ in Fig. 6) contributed the most to the respiratory inor-ganics and fossil fuels impact categories (Fig. 4) due to thesubstantial fuel consumed during the long-distance flight.To reduce the impact, the following reasonable alternativescenarios involving more energy efficient means of trans-portation and/or a closer supplier of activated alumina thanJohannesburg were evaluated:

1. Transporting activated alumina from the port city of Dur-ban, South Africa, to the Republic of Djibouti in East

Africa by ship (6500 km) and then land transportation toAddis, Ababa, Ethiopia, by van (500 km) (denoted BSouthAfrica by ship^ in Fig. 6);

2. Transporting activated alumina from the port city of Mum-bai, India, to Addis Ababa, Ethiopia, by aircraft (4000 km)(denoted BIndia by air^ in Fig. 6);

3. Transporting activated alumina from the port city of Mumbai,India, to the Republic of Djibouti in East Africa by ship(3500 km) and then land transportation to Addis Ababa, Ethi-opia, by van (500 km) (denoted BIndia by ship^ in Fig. 6).

The modeling results indicate that scenario 3, i.e., India byship, led to the lowest environmental impacts in both the re-spiratory organics and fossil fuels impact categories. Compar-ison of India by air and India by ship shows the significantimpact of mode of transportation on the respiratory organics(Fig. 6a) and fossil fuels (Fig. 6b) impact categories, since thetotal transportation distance for these two scenarios is identi-cal. Likewise, when both the mode of transportation and the

Fig. 5 Processes contributing to each damage category for each adsorbent

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distance were varied (compare South Africa by air and SouthAfrica by ship, the respiratory organics impact category waslowered significantly (Fig. 6a), and the fossil fuels impactcategory was lowered by about 75 % (Fig. 6b), indicatingthe importance of transportation distance on environmentalimpacts, particularly fossil fuel depletion. These observationssuggest that some of the adverse impacts of activated aluminaillustrated in Figs. 2 and 3 would be decreased in cases wherethe adsorbent was used closer to where it is manufactured.

3.4 Effect of adsorption capacity on climate changeimpacts for aluminum oxide amended wood char

We observed that for all materials, the environmental impactswere inversely related to adsorption capacity, and therefore, theadsorption capacity was varied in a break-even analysis. Alumi-num oxide amended wood char and bone char were consideredfor the break-even analysis since they have similar charring pro-cesses, while activated alumina and treated alum waste do not.Also, it would be desirable to increase the adsorption capacity ofaluminum oxide amended wood char so that its impacts wouldbe comparable to those of bone char, which is being used withgreater frequency in East Africa as a result of the installation ofbone charring facilities in the Rift valley of Ethiopia and Kenya.Due in part to charring, these two adsorbents had the largestimpacts in the climate change (Eco-indicator, Fig. 2a) and globalwarming (TRACI, Fig. 2b) impact categories.

The climate change impacts of aluminum oxide amendedwood char and bone char were compared for a range of hypo-thetical Q1.5 values of the wood char, while holding the Q1.5

value of bone char invariant at the value reported in Table 1.The climate change impacts of the two adsorbents were foundto be equal at the break-even point where the Q1.5 of alumi-num oxide amended wood char was approximately eighttimes the value reported in Table 1 (i.e., 1.04 mg/g). Through

use of a different aluminum amendment process, Tchomgui-Kamga et al. (2010) produced an aluminum treated wood charwith a Q1.5 of 1.1 mg/g—an eightfold increase compared tothe Q1.5 value of 0.13 mg/g reported in Table 1. In addition,Du et al. (2014) synthesized a high efficiency aluminum(hydr) oxide with Q1.5 of 22 mg/g—a tremendous increasecompared to the Q1.5 of activated alumina reported in Table 1.These results indicate that significant improvements in Q1.5

are possible for aluminum oxide amended wood char. This isthus targeted as an important focus for future research.

4 Conclusions and recommendations

The results of the LCA study investigating four adsorbentsindicate that treated alum waste provides the alternative withthe least impacts in the three damage areas of human health,ecosystem quality, and resource availability. The life cycleprocesses with the highest impacts were transportation foractivated alumina, wood charring for aluminum oxideamended wood char, bone charring and cattle raising for bonechar, and sulfuric acid production for treated alum waste. Forthe adsorbents examined in this study, those with higher fluo-ride adsorption capacities showed lower environmental im-pacts, perhaps due to the lower corresponding impacts frommaterials processing for the more efficient adsorbents. Furtherresearch is suggested to understand whether this relationshipextends to other adsorbents. Based on the results reportedhere, however, the most effective strategy for minimizing cli-mate change impacts is development of locally available ad-sorbent materials that do not require transportation over longdistances and that have high adsorption capacities. When un-avoidable, transport over long distances by ship is preferableto transport by plane. Regeneration and reuse of spent adsor-bents would minimize the impacts associated with their

Fig. 6 Effects of transportationdistance and means oftransportation of activatedalumina on the a respiratoryinorganics and b fossil fuelsimpact categories

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manufacture, and also reduce adverse impacts to ecosystemquality due to their disposal. Therefore, it is imperative fordeveloping countries to adopt materials and processes withlow environmental impact for water purification and use safertechnologies whenever possible. This and other studies high-light the need for continued development and dissemination oflife cycle inventory data appropriate for developing countriesin order to promote sustainable development.

Acknowledgments This work was funded by the National ScienceFoundation (CBET1066425), the University of Oklahoma Water Tech-nologies for Emerging Regions (WaTER) Center, the Sun Oil CompanyEndowed Chair, and the Ken Hoving Graduate College Fellowship. Theauthors thank Jessica Johnston for review of the manuscript. We alsothank the anonymous reviewers and the editor for their valuable com-ments on the manuscript.

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