Unlocking the potential of walnut husk extract in the production of waste cooking oil-based biodiesel

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

Contents lists available at ScienceDirect

Renewable and Sustainable Energy Reviews journal homepage: http://www.elsevier.com/locate/rser

Unlocking the potential of walnut husk extract in the production of waste cooking oil-based biodiesel Zahra Khounani a, Homa Hosseinzadeh-Bandbafha b, c, Abdul-Sattar Nizami d, Alawi Sulaiman e, Sayed Amir Hossein Goli f, Elham Tavassoli-Kafrani f, Akram Ghaffari a, Mohammad Ali Rajaeifar c, g, Ki-Hyun Kim h, i, ****, Ahmad Farhad Talebi j, ***, Mortaza Aghbashlo b, **, Meisam Tabatabaei a, c, e, k, * a

Microbial Biotechnology Department, Agricultural Biotechnology Research Institute of Iran (ABRII), Agricultural Research, Education, and Extension Organization (AREEO), Karaj, Iran b Department of Mechanical Engineering of Agricultural Machinery, Faculty of Agricultural Engineering and Technology, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran c Biofuel Research Team (BRTeam), Karaj, Iran d Center of Excellence in Environmental Studies (CEES), King Abdulaziz University, Jeddah, Saudi Arabia e Faculty of Plantation and Agrotechnology, Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia f Department of Food Science and Technology, College of Agriculture, Isfahan University of Technology, Isfahan 84156-83111, Iran g School of Engineering, Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom h Department of Civil and Environmental Engineering, Hanyang University, 222 Wangsimni-Ro, Seoul, 04763, South Korea i Henan Province Engineering Research Center for Forest Biomass Value-added Products, Henan Agricultural University, Zhengzhou 450002, China j Genetic Department, Faculty of Biotechnology, Semnan University, Semnan, 35131-19111, Iran k Faculty of Mechanical Engineering, Ho Chi Minh City University of Transport, Ho Chi Minh City, Vietnam

A R T I C L E I N F O

A B S T R A C T

Keywords: Biodiesel Walnut waste valorization Bio-antioxidant Life cycle assessment Oxidation stability index Propyl gallate

Biodiesel has a lower oxidation stability index (OSI) than mineral diesel fuel. Its consequential oxidation products and deteriorated physical and chemical properties of fuel are associated with engine operation chal­ lenges such as the formation of insoluble gums that can plug fuel filters. Given the fact that oxidation leads to barriers for commercial use of biodiesel, addition of appropriate antioxidants into biodiesel is a promising and cost-effective approach to overcome this challenge. Although synthetic antioxidants such as propyl gallate (PG) are frequently used to counter the oxidation process of biodiesel, PG is a designated carcinogen. In light of that, this study was conducted aiming at introducing walnut husk methanolic extract (WHME) as a more sustainable antioxidant to replace PG in waste cooking oil (WCO) methyl esters. Moreover, to facilitate the commerciali­ zation of the new product, a comprehensive environmental investigation and comparison with the conventional counterpart, i.e., PG, was performed using life cycle assessment (LCA) approach. To enhance the eco-friendly features of the natural antioxidant, a solar photovoltaic-driven extraction process based on methanol (as re­ agent) was used in extracting polyphenols from walnut husk. The results showed that the induction period of WCO methyl esters was prolonged from 1.2 h to more than 3 h (meeting the ASTM D6751 standards) using 5000 ppm and 250 ppm of WHME and PG, respectively. More specifically, 20-fold more natural antioxidants would be required to meet the international standards. However, since walnut-producing countries are responsible for 42.4% of global biodiesel production on one hand and the cost-effectiveness of walnut husks on the other hand, their valorization could attract the attention of the global biodiesel industry. Moreover, this study highlights the considerable environmental and health benefits of turning this bio-waste product into a valueadded antioxidant fuel additive. The LCA results showed that the developed bio-antioxidant was more

* Corresponding author. Universiti Teknologi MARA (UiTM), Malaysia. ** Corresponding author. University of Tehran, Iran. *** Corresponding author. Semnan University, Iran. **** Corresponding author. Hanyang University, South Korea. E-mail addresses: [email protected] (K.-H. Kim), [email protected] (A.F. Talebi), [email protected] (M. Aghbashlo), meisam_tabatabaei@ uitm.edu.my, [email protected] (M. Tabatabaei). https://doi.org/10.1016/j.rser.2019.109588 Received 1 July 2019; Received in revised form 8 November 2019; Accepted 9 November 2019 1364-0321/© 2019 Elsevier Ltd. All rights reserved.

Please cite this article as: Zahra Khounani, Renewable and Sustainable Energy Reviews, https://doi.org/10.1016/j.rser.2019.109588

Z. Khounani et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

effective in different damage categories compared with PG, i.e., 0.32% in ecosystem quality, 12.13% in human health, 8.37% in climate change, and 614% in resource. Overall, the WHME obtained through solar photovoltaicdriven extraction process could outcompete PG from the environmental perspective.

List of abbreviations ANOVA ASTM α-T Barrel/d BHA BHT C2H5OH C3H6O C4H8O2 CAT CH3OH CO2 CO DNA DPPD DPPH e.g. EN F FU GAE H2SO4 i.e. IP IPCC ISO KOH LCA Na2CO3 NaOH OBPA –OH OSI PM PG p-value

PY R2 Sc-1 Sc-2 SOD TAA TBHQ TBP TPC UHC US v/v vs w/v% WCO WHME wt.%

Analysis of variance American society for testing and materials α-tocopherol Barrels per day Butylatedhydroxyanisol Butylatedhydroxytoluene Ethanol Acetone Ethyl acetate Catalase Methanol Carbon dioxide Carbon monoxide Deoxyribonucleic acid N,n0-diphenyl-p-phenylenediamine 2, 2-diphenyl-1-picrylhydrazyl Exempli gratia European standard specifications Stabilization factor Functional unit Gallic acid equivalents Sulfuric acid Introduce examples Induction period Intergovernmental panel on climate change International organization for standardization Potassium hydroxide Life cycle assessment Sodium carbonate Sodium hydroxide Octylated butylated diphenyl amine Hydroxyl Oxidation stability index Particulate matter Propyl gallate Probability value

Propyl 3,4,5 trihydroxybenzoate Coefficient of determination First scenario Second scenario Inhibiting superoxide dismutase Total antioxidant activity Tert-butyl hydroxyquinone Tert-butylated phenol derivative Total phenolic content Unburnt hydrocarbons United states Volume/volume percent Versus Weight/volume percent Waste cooking oil Walnut husk methanolic extract Percentage by weight

List of units C Celsius μPt Micropoints DALY Disability-adjusted life-years g Gram h Hour kg Kilograms kg CO2eq Kilograms carbon dioxide equivalent L Liter m3 Cubic meter mg Milligram min Minutes MJ Megajoule mL Milliliter mM Micromolar nm Nanometer PDF*m2*yr Potentially disappeared fraction of species over a certain amount of square meters during a certain amount of year ppm Parts-per-million �

a cost-effective and environmentally sound transportation fuel [9]. Biodiesel is primarily synthesized by transesterification of vegetable oils and animal fats with monohydric alcohols (ethanol-C2H5OH, meth­ anol-CH3OH) [10] using various basic/acidic catalysts (mostly potas­ sium hydroxide-KOH or sodium hydroxide-NaOH) [11]. Currently, industrial production of biodiesel relies primarily on vir­ gin oil feedstock [12] which has led to major challenges including high cost of feedstock as well as feedstock procurement [13]. Nevertheless, it has been well documented that the application of waste-product oil resources such as waste cooking oil (WCO) can significantly enhance the economics of biodiesel production [14] while resolving fuel supply is­ sues in remote areas [15]. Meanwhile, WCO is discharged inappropri­ ately into soils, water, and sewerage systems in many parts of the world [16]. As such, its reuse as biodiesel feedstock could lead to a reduction of WCO releases into nature. In spite of its advantages, biodiesel’s relatively poor thermooxidative stability and short shelf life compared with mineral diesel due to its ester-based chemistry must be addressed to increase its

1. Introduction One of the most significant current discussions in the world is the growing fossil fuel demands [1] and the concerns associated with the rapid depletion of these non-renewable energy carriers [2]. In addition, there exists increasing concerns about the consequent unfavorable environmental impacts caused by the resultant toxic emissions [3] as well as emissions contributing to climate change such as carbon dioxide (CO2) [4]. These have spurred an intense search in both developed and developing countries for renewable energy carriers that could partially or completely replace fossil fuels [5]. Among these energy carriers, a blend of several fatty acid methyl or ethyl esters also known as biodiesel [6] has attracted a great deal of attention because of its biodegradable and nontoxic characteristics [7]. Biodiesel also promises to reduce problematic emissions such as par­ ticulate matter (PM), unburnt hydrocarbons (UHC), and carbon mon­ oxide (CO) [8]. During the last decade, biodiesel has been recognized as 2

Z. Khounani et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

viability as an alternative fuel [17]. Moreover, the oxidative stability of biodiesel depends on the physicochemical features of the oil feedstock used [18]. In comparison with virgin oil, WCO is generally far more sensitive to oxidative and thermal degradation [19]. Gums, aldehydes, alcohols, carboxylic acids, insoluble sediments, and other products of biodiesel oxidation can foul injectors and clog fuel filters and lead to the fusion of moving parts, failure of fuel systems, combustion chamber deposition, and tightening of rubber components [20]. Various ap­ proaches have been proposed to increase the oxidation stability index (OSI) (or the induction period (IP), i.e., the time period until the appearance of secondary reaction products [21]) of biodiesel, including storage in an inert nitrogen atmosphere [22], distillation [23], use of different raw materials [24], and application of antioxidants [25]. Among the mentioned approaches, special emphasis has been placed on the application of antioxidants to combat the free radicals generated in the initiation and propagation phase of fatty acid esters oxidation [26]. This is because antioxidants reduce the need for costly treatments as well as new storage tanks and fuel-handling systems [27]. Synthetic antioxidants, including tert-butyl hydroxyquinone (TBHQ) [28], N, N0-diphenyl-p-phenylenediamine (DPPD) [29], butylatedhydrox­ yanisol (BHA) [30], butylatedhydroxytoluene (BHT), propyl 3,4,5 tri­ hydroxybenzoate (pyrogallol or PY) [31], propyl gallate (PG) [27], and other commercial products such as Baynox (Lanxess) [32], Ethanox 4760E (Albemarle) [33], and Bioextend (Eastman) [34], are frequently used to prevent oxidation in biodiesel and other fuels. All these anti­ oxidants donate hydrogen from their hydroxyl (–OH) group(s) to free radicals, preventing progression of the oxidation process. As determined by the number of OH groups, these antioxidants are ranked as BHA, BHT < DTBHQ ¼ TBHQ < PY ¼ PG. Both PG and PY contain three OH groups linked to an aromatic ring [27]. While both PY and PG have more liable hydrogen, PY is less effective, probably owing to lower solubility in some biodiesels [27]. PG is now the most widely used antioxidant in the biodiesel industry. However, synthetic antioxidants, including PG, have been criticized because of reported adverse side effects. For instance, a National Toxicology Program study revealed a direct relation between PG and cancerous tumors in rats (US Department of Health and Human Services) [35]. Moreover, synthetic materials are often consid­ ered environmental pollutants as they are more complex compared with their natural counterparts, taking longer to biodegrade [35]. The search for alternatives to synthetic antioxidants has resulted in the investiga­ tion of numerous antioxidants found in plants such as olive leaf extract [36], rosemary (Rosmarinus officinalis L.), oregano (Origanum vulgare), and thyme (Thymus vulgaris) [37]. Unlike their synthetic counterparts, natural antioxidants are generally recognized as safe, and their appli­ cations are less limited [38]. Various studies have been performed to investigate the OSI of natural antioxidants vs. their synthetic counterparts. The OSI of soybeanoriented biodiesel supplemented with a number of alcoholic plant ex­ tracts such as rosemary, oregano, and basil has been assessed [39]. Soybean biodiesel samples containing antioxidants individually or in combination displayed higher resistance to oxidation as determined by Rancimat vs. control. A 1:4 mixture of rosemary and oregano extracts was found to be the most favorable treatment. The antioxidant effects of ginger extract on the stability of biodiesel produced from pongamia (a non-edible energy crop) have also been studied [40]. Accordingly, a minimum ginger extract concentration of 250 ppm was required to meet the European standard specifications (EN 14214) for biodiesel OSI. In a similar work, Devi et al. [41] evaluated potato peel extract in the range of 100‒250 ppm as an antioxidant for Mesua ferrea L. biodiesel. They argued that potato peel extract was more effective than the synthetic antioxidant TBHQ in enhancing the OSI of the investigated biodiesel. In a recent investigation, Ahanchi et al. [17] compared the effectiveness of pistachio hull extracts of different varieties in enhancing canola methyl ester OSI, with the synthetic antioxidant PG used as a reference. The results showed that pistachio hull extracts and PG concentrations of 2500 ppm and 250 ppm, respectively, were sufficient to prolong the IP of

straight methyl esters from 1.53 h to over 3 h as per the American So­ ciety for Testing and Materials (ASTM) D6751 standards for biodiesel OSI. Despite the superior performance of the synthetic antioxidant, the authors concluded that pistachio hull extracts are a more favorable option from the human health point of view [10]. The environmental effects of newly identified natural antioxidants have also been scrutinized to further their sustainable production. Rodríguez-Meizoso et al. [42] introduced a novel method called water extraction and particle formation on-line to extract antioxidants from rosemary leaves. They used LCA approach to compare the environ­ mental performance of their method with the other methods used to obtain antioxidants. They claimed that their method was associated with lower environmental impacts and energy consumption because it was carried out in a single step. They also highlighted the importance of the primary energy sources of the electricity used in the antioxidant pro­ duction process [42]. In another study, the environmental aspects of astaxanthin production by microalgae were evaluated using LCA approach from lab to pilot scale [43]. The results identified electricity requirements as a major factor that affect the environmental impacts of the production process. It also claimed that the environmental impacts were greatly reduced in the pilot-scale production due to changes implemented following a lab-scale environmental assessment. Ahanchi et al. [17] used LCA approach to evaluate the environmental perfor­ mance of antioxidant production from pistachio hulls and concluded that use of the produced natural antioxidant was promising from climate change and human health standpoints as compared with a synthetic antioxidant like PG. The authors stated that the implementation of a hexane recovery step (throughout the antioxidant production process) was the main reason for the reductions in the environmental impacts. Overall, there are many methods to deal with agro-wastes in modern agriculture, however, their valorization into valuable biomaterials including natural antioxidants is regarded as a very promising strategy. This has led to a widespread search to identify agro-wastes containing significant amounts of phenolic compounds, which could be used for sustainable production of natural antioxidants. In line with that, anti­ oxidant characteristics of different parts of the walnut plant (fruit, stem, leaf, and husk) have been investigated [44]. However, to the best of our knowledge, there is no reports published on the use of walnut husk methanolic extract (WHME) as a biodiesel fuel additive. Therefore, this study for the first time set out to explore the application of WHME as a natural antioxidant for WCO biodiesel. On the other hand, despite the high efficacy of solvent extraction, it suffers from high non-renewable energy consumption during solvent recovery which would undoubt­ edly be attributed to adverse environmental consequences. Therefore, a solar photovoltaic-driven extraction process was implemented in the present study to address this challenge. Following an investigation of the antioxidant properties of the extract, WHME was compared with the most commonly employed synthetic antioxidant, PG, using the Ranci­ mat method based on the EN 14214 standard by measuring the OSI, as detailed in our previous study [17]. Finally, an LCA of the environ­ mental burdens associated with the synthesis and utilization of the investigated antioxidant as a biodiesel fuel additive was performed. Considering the health risks associated with PG exposure and the fact that walnut husks (inexpensive and readily available agricultural waste products) could serve as an ideal antioxidant source, the outcomes of this survey could be of great interest to the biodiesel industry. In fact, the findings presented here could be of value in improving the health ben­ efits of waste-oriented biodiesels around the world while also contrib­ uting to the integration of waste valorization and renewable energy implementation with waste-oriented biodiesel production. 2. Materials and methods Fig. 1 presents the general methodology used in the present study.

3

Z. Khounani et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

Fig. 1. The general methodology used in this study.

2.1. Materials preparation

sample was then centrifuged at 4200 rpm for 7 min after filtering using Whatman filter paper no. 41. A rotary evaporator was employed to completely recover the utilized solvent in vacuum conditions at ambient temperature. The purified extract was transferred to dark-colored glass bottles and refrigerated to hinder any further chemical or physical modifications.

Husks of Persian walnut (Juglans regia L.) variety, known as the “Sefid” cultivar (collected from Semnan, Iran) were used in this inves­ tigation. Walnut husks are rich in phenolic constituents in concentra­ tions ranging from 2 to 4 wt% fresh weight [45]. The husks were freeze-dried for 48 h to preserve the antioxidant activity of the bioac­ tive compounds. The analytical-grade chemicals and solvents used in this study were obtained from Sigma (Germany).

2.4. Measurement of total phenolic content and total antioxidant activity TPC of the extract was measured using a Folin–Ciocalteu reagent after slight modifications of the procedure introduced by Nickel et al. [49], in which 10 mg of the extract was dissolved in 10 mL of methanol. After 0.5 mL of the diluted sample was blended with 2 mL of sodium carbonate (Na2CO3) (7% w/v). After 5 min, 2.5 mL of 10x distilled water-diluted Folin–Ciocalteu reagent was added to the mixture, reacted for 20 min at ambient temperature, and the absorbance was measured spectrophotometrically at 735 nm. Gallic acid (10–250 ppm) was applied as a standard. Accordingly, TPC was measured in mg gallic acid equivalents/g extract (mg GAEs/g extract) using the following calibra­ tion curve (R2 ¼ 0.99):

2.2. Waste cooking oil (WCO) biodiesel production To maximize methyl ester yield and avoid saponification reactions, a two-step process was employed using acid-catalyzed esterification fol­ lowed by alkaline-catalyzed transesterification [46]. Briefly, the esteri­ fication process (at industrial scale) of WCO (collected from Karaj, Iran) was conducted in the presence of methanol and sulfuric acid (H2SO4) for 1 h at 60 � C. One hour after completion of the reaction, the top phase, i. e., the methanol-water fraction, was separated, and the acid value of the remaining bottom phase was analyzed. The transesterification process of the pretreated WCO was carried out using methanol in the presence of a KOH catalyst. The reaction slurry was continuously stirred for 1 h at a temperature of 60 � C. The obtained biodiesel was purified, washed, and dehydrated, according to Aghbashlo et al. [47].

Abs ​ 735 ¼ 0:004mg gallic ​ acid ​ þ 0:028

(1)

The methodology described by Nickel et al. [49] was considered with some modifications to determine the total antioxidant activity (TAA) of WHME. After 20 mg of the extract was dissolved in 10 mL of methanol, 0.2 mL of the methanolic solution of 0.15 mM 2, 2-diphenyl-1-picrylhy­ drazyl (DPPH) was added to 2.8 mL of the diluted sample. The obtained slurry was stirred and left in the dark at ambient temperature for 1 h. A reduction in absorbance was determined spectrophotometrically at 517 nm. A blank sample was prepared in the same manner without WHME. PG was used as positive control under the same assay condi­ tions. The DPPH radical–scavenging activity was measured based on the following equation:

2.3. WHME preparation and characterization Polyphenolic extract of walnut husks was obtained as described by Jakopi�c et al. [48] using a solar photovoltaic-driven extraction system. Briefly, 10 g of freeze-dried husk powder was transferred to an Erlen­ meyer flask containing 100 mL of pure methanol. The flask was wrapped with aluminum foil to block light. This blend was incubated in an ul­ trasonic bath for 45 min and further refluxed at 30 � C for 24 h. The 4

Z. Khounani et al.

Scavenging ​ activityð%Þ ¼ 100 �

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

�

Absblank

�� � Abssample ​ Absblank :

step in an LCA; an inappropriate definition of system boundaries will result in misleading conclusions [56]. The system boundary throughout this study, including the entire manufacturing process from extracting raw materials to producing final products (i.e., WCO biodiesel supple­ mented with WHME or PG), is shown in Fig. 2. A functional unit (FU), or base unit for inventory data, was also defined to facilitate comparisons of the environmental performance of different systems [57]. The FU selected in the present study was 1 kg of WCO biodiesel augmented by WHME or PG. In the second step of an LCA (inventory analysis), the inputs and outputs of a production system should be determined and compiled [58]. Two types of databases, foreground, and background, were used to compile inventory data. The first group of data was obtained from lab experiments (amounts of materials and energy carriers used in the production of WHME and PG alongside the generated emissions during the processes). The second group of data included production of inputs and energy carriers as well as their associated emissions obtained from the Ecoinvent database (v3.5). The third phase of the LCA (impact assessment) was conducted once the inventory data concerning the primary material extraction and pollutant emissions related to a prod­ uct’s life cycle were compiled [54]. Throughout this study, the IMPACT 2002þ method, with the aid of SimaPro 8.2.3 software, was used to model the inventory data. This method not only allows the imple­ mentation of a consolidated mid-point/damage approach but also links all types of inventory analysis results through 15 mid-point impact categories to four end-point damage categories [59]. The results of LCA studies generally face uncertainties because of erroneous measurements, unrepresentative or missing data, wrong es­ timations, modeling assumptions, and data variability [60]. To address this problem and to improve the decision making in LCA studies, sto­ chastic modeling is frequently used [61]. In this method, probability distributions are propagated by random sampling such as Monte Carlo analysis. Therefore, to determine the uncertainty of distributions of the LCA results obtained in this study, the Monte Carlo (1000 runs) method was employed.

(2)

2.5. Thermal OSI analysis of WCO biodiesel Briefly, a Rancimat apparatus (743 Rancimat, Metrohm AG, Herisau, Switzerland) was used to measure the OSI of the WCO biodiesel samples containing different concentrations of WHME (in the range of 1000 ppm to 10,000 ppm) based on the ENE 14214 biodiesel standard. A comparative study was conducted by incorporating PG into biodiesel at concentrations of 250–1000 ppm [17]. During the measurements, pu­ rified air at a flow rate of 0.02 m3/h flowed into a sample (2.5 g) held at 110 � C and then into 60 mL of deionized water in a measuring vessel. The samples were kept at 110 � C to simulate the accelerated oxidation of biodiesel, and the volatile oxidation products carried by the air stream were transferred to another container filled with distilled water. The oxidation curve was obtained by continuously measuring the conduc­ tivity in the vessel. PG and phenolic extracts were incorporated into biodiesel using an ultrasonic bath. To this end, biodiesel containing antioxidants was sonicated for 30 min at 40 � C [17]. A WCO biodiesel sample without an antioxidant additive served as a control. Duration of the IP (h) was considered an indication of OSI; accordingly, a stabili­ zation factor was defined to determine the effectiveness of antioxidant incorporation [17]: F ¼ IPX =IP0

(3)

where IPX and IP0 denote the IP in antioxidant presence and absence, respectively [17]. 2.6. Statistical analysis and environmental assessment All the data were averaged and presented as the average � standard deviation. Statistix 8 software was used to carry out analysis of variance (ANOVA). A least significant difference test at p-value < 0.05 was used to compare mean values. All experiments were repeated three times. LCA was used to weigh and compare environmental sustainability with respect to the production of WHME and PG as well as their respective environmental burdens. Two scenarios were considered:

3. Results and discussion In this section, the preparation of the polyphenolic extract of walnut husks is first explained followed by presenting the TPC and TAA of WHME. Subsequently, the results obtained on the effect of WHME on the OSI of WCO methyl esters are reported and compared with those of the synthetic antioxidants (i.e., PG). Finally, the environmental impacts of the investigated antioxidants through LCA are presented and compared. The practical implications of this study are also presented.

First scenario (Sc-1): WCO biodiesel augmented by WHME Second scenario (Sc-2): WCO biodiesel augmented by PG. Awareness of the environmental impacts of goods and services through their life cycle, e.g., their overall contributions to deforestation, species extinction, and/or increasing atmospheric carbon dioxide con­ centrations, is growing [50], along with demands for more environ­ mentally benign products [51]. Sustainability considerations are now routinely applied to the manufacture of products from the raw material purchase stage to product distribution and utilization [52]. In some cases, social, economic, resource, or environmental sustainability may contradict the technological and technical aspects of a given product. Hence, when introducing a new product or comparing competing products, both technological/technical and sustainability features should be taken into account to meet the above-mentioned criteria in a balanced manner [17]. LCA is one of the most appealing approaches to addressing the sustainability aspects of newly developed products [53]. International organization for Standardization (ISO) 14040 defines LCA as a systematic research tool for measuring the environmental conse­ quences of production systems from primary material procurement to waste utilization [54]. The LCA consisted of four interrelated steps: goal and scope defini­ tion, inventory analysis, impact assessment, and interpretation [55]. In this study, the goal was to conduct an environmental impact assessment of the production processes for WHME and PG, while comparing their associated environmental burdens as WCO biodiesel additives. Deter­ mination of a boundary for the system under investigation is a critical

3.1. Preparation of phenolic extracts of walnut husks To obtain phytochemicals such as phenolic compounds from plant materials, milling, grinding, homogenization, and extraction must be carried out. Here, the final step is considered the most critical [62]. Among various extraction procedures for isolating phytochemicals, solvent extraction is the most widely used [63]. It is well documented that the efficiency of a solvent extraction method depends significantly on the solvent used, mainly owing to the different polarities of the compounds to be extracted [64]. Apart from extraction efficiency and polyphenolic content, the antioxidant activities of the obtained extract could also be strongly affected by the type of solvent, as certain anti­ oxidants may not be soluble in certain solvents [63] due to the different chemical characteristics and polarities of the compounds. It has been shown that polar solvents such as ethanol, methanol, acetone (C3H6O), and ethyl acetate (C4H8O2) are suitable choices for polyphenol extrac­ tion from plant tissues [63]. Among these solvents, methanol is more efficient in extracting polyphenols from green walnut fruits [65]. This was also confirmed by Anokwuru et al. [63], who argued that methanol is much more efficient than ethanol or acetone in terms of absolute 5

Z. Khounani et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

Fig. 2. The system boundary considered in this work, including WCO biodiesel supplemented with WHME (Scenario 1) or PG (Scenario 2).

solvent extracts [63]. Absolute methanol was used here to prepare the polyphenolic extracts of walnut husks.

respectively. The antioxidant capacity of the WHME investigated here is promising, considering the comparatively lower concentration needed to achieve favorable results.

3.2. TPC and TAA of WHME

3.3. Influence of WHME on the OSI of WCO methyl esters

The TPC and TAA of WHME are summarized in Table 1. The TPC of the WHME measured in this study (i.e., 102.59 mg GAEs/g extract) was significantly higher than that reported by Oliveira et al. [35] and �ndez-Agullo � et al. [66] for green walnut husks using water Ferna (32–74 mg GAEs/g extract) and water/ethanol (1:1) (84.46 mg GAE/g extract) as solvents, respectively. Similarly, Goli et al. [67] experimen­ tally revealed that the extraction method, plant cultivar, and type of solvent used for extraction could play key roles in the efficiency of TPC extraction. A constant concentration of 200 ppm, the antioxidant capacity of the obtained WHME, was comparable to that of the synthetic antioxidant PG (87.6% vs. 89.1%) (Table 1). This indicated a strong TAA for WHME despite an unpurified extract that could have experienced interference with its antioxidant capacity. The findings of this study were also in line with those of Oliveira et al. [35], who also claimed to have found strong antioxidant potentials of the extracts of green walnut husks of 5 different cultivars (ranging from 83.1 to 93.9%). However, Oliveira et al. [35] tested at concentrations 5 times higher than those of the present study (i. e., 1000 ppm). They also compared green walnut husk extract with other conventional antioxidants, i.e., BHA and α-tocopherol, and reported antioxidant capacities of 96% and 95% at 3600 ppm and 8600 ppm,

As mentioned earlier, biodiesel OSI has been a subject of consider­ able research over the last two decades [23]. Given the growing interest in applications of organically oriented compounds, the antioxidant properties of various herbs and spices containing natural components like phenolic, have been scrutinized [68]. Among these feedstocks, Slatnar et al. [69] reported strong antioxidant and free radical­ –scavenging capacities of the phenolics contained in walnuts. Recently, Wenzel et al. [70] pointed out that walnut husks also contain a considerable quantity of phenolic compounds with both antioxidant and antimicrobial properties. Meanwhile, Sulistyo et al. [24], Sundus et al. [27], Botella et al. [71], De Sousa et al. [72], Mittelbach et al. [73], Buosi et al. [74], García et al. [75], and Zhou et al. [76] have shown that the oxidative stability of biodiesel fuels of different origins can be enhanced significantly by adding various natural (or synthetic) antiox­ idants. However, to the best of our knowledge, there have been no published reports on the application and antioxidant effects of walnut extract as a fuel additive. Accordingly, in the present work, the perfor­ mance of a phenolic extract of walnut husks as a natural antioxidant was compared with a conventional synthetic biodiesel antioxidant, PG, after being added to WCO biodiesel at different concentrations (1000, 2500, 5000, and 10,000 ppm). Table 2 summarizes a comparison of the results obtained in the current study with those of the other studies reported in the published literature where natural/synthetic antioxidants were used as additive in biodiesel. Fig. 3 presents the effects of different doses of PG and WHME on the OSI of WCO methyl esters using the Rancimat method (air volume flow rate of 0.02 m3/h and temperature of 110 � C). The OSI of WCO biodiesel was dramatically improved by increasing the WHME concentration. The OSI of WCO biodiesel was improved by almost three times owing to the

Table 1 TPC and TAA of WHME. TPC (mg gallic acid equivalent/g sample)

TAA (%)

WHME

PG

WHME

102.59 � 4

89.06 � 1.5a*

87.6 � 0.4a

* Different letters indicate significant difference (p-value < 0.05). 6

Z. Khounani et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

Table 2 A summary of the studies conducted previously on the effects of natural/synthetic antioxidants on oxidation stability of biodiesel vs. the results of the present study. Type of biodiesel

Oxidation stability (h)

Oxidation stability (h) following antioxidant inclusion

Natural antioxidant/s (conc.)

Synthetic antioxidant/s (conc.)

Temperature

Standard specifications

Ref.

WCO Biodiesel

1.2

3.41

PG (250)

110 � C

EN 14214

Present study

Beef tallow methyl ester

0.55

BHT and TBHQ (5000 mg/kg)

110 � C

EN 14112

[77]

Canola methyl ester

1.53

4.9 for natural antioxidant and >74 for synthetic antioxidants 3

Walnut husk methanolic extract (5000 ppm) Cashew nut shell liquid (5000 mg/kg)

PG (250 ppm)

110 � C

5.51

9

BTE (2000 ppm)

110 � C

ASTM D6751-12 EN14112

[17]

Commercial biodiesel (30% soybean þ30% tallow þ40% cotton) High oleic sunflower methyl ester.

Pistachio hull extract (2500 ppm) Moringa oleifera Lam leaf (4000 ppm)

5

Mixed tocopherols (1000 ppm)

Hindered phenol/amine, Hindered phenol, and PG (1000 ppm)

110 � C

EN 14214

[79]

Jatropha methyl ester

3.95

35 for natural antioxidants and between 15 and 30 for synthetic antioxidants 6

α-tocopherol (α-T)

110 � C

EN 14112

[80]

Palm methyl ester

8

Mixed tocopherols (1000 ppm)

BHT (150 ppm), TBHQ (200 ppm tert-butylated phenol derivative (TBP), and octylated butylated diphenyl amine (OBPA) (300 ppm) Hindered phenol/amine, Hindered phenol, and PG (1000 ppm)

110 � C

EN 14214

[79]

Palm oil methyl esters Rapeseed methyl ester.

3.5

α-T (1000 ppm)

BHT and TBHQ (50 ppm)

110 � C

EN 14214

[81]

Mixed tocopherols (1000 ppm)

Hindered phenol/amine, Hindered phenol, and PG (1000 ppm)

110 C

EN 14214

[79]

Soybean methyl ester Soybean methyl ester

n,a

Rosemary, oregano and basil extracts Mixed tocopherols (1000 ppm)

TBHQ

110 � C

EN 14112

[74]

Hindered phenol/amine, Hindered phenol, and PG (1000 ppm)

110 C

EN 14214

[79]

Soybean oil methyl ester

4.04

–

110 � C

EN 14112

[82]

5

3

43 for natural antioxidants and between 21 and 65 for synthetic antioxidants >6 13 for natural antioxidants and between 10 and 12.5 for synthetic antioxidants >6 12 for natural antioxidants and between 5.5 and 9.5 for synthetic antioxidants 8.18

(600 ppm)

Barley waste (13 g L 1) and Moringa oleifera leaves extract (9 g L 1)

incorporation of 5000 ppm WHME. The IP can be linearly correlated with antioxidant dosage (R2 ¼ 0.9449). Fattah et al. [23] also claimed that the OSI of biodiesel increased linearly with the concentration of antioxidants to a certain amount. It is observed that at least 4000 ppm of WHME could be used to prolong the IP of straight WCO biodiesel (control fuel) from 1.2 h to over 3 h as per the ASTM D6751 standard. The influence of increasing WHME dosage on OSI was also shown by the stabilization factor (F); for example, the F10000 was 2.6 times higher than the F1000 (Table 3). The lowest concentration of PG, 250 ppm, enhanced the OSI to 3.48 h, which was well above the minimum standard requirement. The F value for 250 ppm of PG was equal to that of 5000 ppm of WHME. Comparing the effects of 10 different synthetic antioxidants (PG, PY, TBHQ, etc.) at doses ranging between 100 and 1000 ppm on the OSI of biodiesel, Chen and Luo [33] also found that low doses of synthetic antioxidants result in substantial improvement in the OSI of biodiesel. Similar to the WHME, elevating PG concentration markedly improved IP. The highest PG concentration, 1000 ppm, improved the OSI of WCO biodiesel to 10.39 h (Fig. 2). Similar findings have also been reported in previous reports by Dunn [22], Fattah et al. [23], and Focke et al. [26], arguing that synthetic antioxidants were much more efficient than natural antioxidants in enhancing the OSI of biodiesel. Pinto et al. [83] found that the capability

�

�

[78]

of TBHQ for improving the OSI of peanut oil-based biodiesel was higher than the ethanol extract of green tea and α-tocopherol. In a different study, Buosi et al. [74] comparatively assessed the OSI of neat soybean oil biodiesels when supplemented with a mixture of rosemary, oregano, and basil extracts and the synthetic antioxidant TBHQ. Based on their observations, the synthetic antioxidant was ranked higher in terms of effectiveness compared with the natural ones. Based on the study findings, higher concentrations of the natural antioxidant would be required to meet the international standards as compared with the synthetic antioxidant. Nevertheless, walnut husk valorization through natural biodiesel antioxidant production could still be of wide industrial interest due to the growing demand for organically oriented substitutes for synthetic antioxidants, PG in particular. More­ over, walnut husks are inexpensive and readily available agricultural waste products that could enhance the economic features of biodiesel supplemented with the resultant natural antioxidant. Fig. 4 presents the quantity of walnut husks generated around the world. Walnutproducing countries account for 42.4% of the global biodiesel produc­ tion rate (Table 4), highlighting the considerable potential of valorizing this biowaste material into a value-added product, i.e., fuel antioxidant additive.

7

Z. Khounani et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

greater than the environmental damage resulting from the fabrication of the products using bio-waste. This was done to clarify how the use of bio-waste vs. virgin materials could change the associated environ­ mental impacts. According to IMPACT 2002þ, “carcinogenic,” “non-carcinogenic,” “respiratory organic,” “respiratory inorganic,” “ionizing radiation,” and “ozone layer depletion” are the mid-points categorized in the human health damage category [84]. Biodiesel production from WCO contrib­ uted to improvements in the human health damage category in both Sc-1 and Sc-2 (Table 5). This can be ascribed to avoid the production of soybean oil as the main oil feedstock used for biodiesel production. More specifically, WCO biodiesel production led to 3.03E-07 (caused by the collection, transportation, purification and transesterification stages) disability-adjusted life-years per kilogram (DALY/kg), while avoiding the production of soybean oil led to a decrease of 1.33E-06 DALY/kg in biodiesel production. The emissions released to the air during WCO biodiesel production (caused by the collection, transportation, purifi­ cation and transesterification stage) and their contribution to the human health damage category were particulates < 2.5 μm (1.05E-07 DALY/kg), hydrocarbon aromatic (8.16E-08 DALY/kg), sulfur dioxide (6.06 E-08 DALY/kg), and nitrogen oxides (3.73E-08 DALY/kg). While the avoided production of soybean oil led to reductions in the above-mentioned emissions during biodiesel production (particu­ lates < 2.5 μm (1.07E-06 DALY/kg), hydrocarbon aromatic (2.81E-08 DALY/kg), sulfur dioxide (1.27 E-08 DALY/kg), and nitrogen oxides (3.09E-08 DALY/kg)). Furthermore, the production of 5000 mg WHME had a positive impact (negative emissions) on human health damage category due to avoiding the production of 250 mg PG (5.77E-08 DALY/250 mg caused by PG production was deducted from 7.29E-12 DALY/5000 mg caused by WHME production). Overall, the burdens imposed on the human health damage category were estimated to be 12.13% higher for Sc-2 vs. Sc-1, resulting from synthetic antioxidant production. The main reason for this difference was the higher electricity consumption at the production stage of gallic acid, that is one of the main ingredients used in PG synthesis. Techni­ cally, gallic acid is produced by combining wood powder (50 g) with a methanol-water solvent (1000 mL), followed by tannic acid extraction electrochemically (5 h) and solvent recovery through vacuum distilla­ tion (60 min). Finally, tannic acid is electrolyzed with sulfuric acid (7.5 h) to generate gallic acid (produced at a laboratory scale). Fig. 5 shows the relative and cumulative relative frequency plots according to the Monte Carlo simulation for two scenarios. Based on the data presented in the figure, the probability that the Sc-2 would obtain 1.07E-06 DALY/FU (as simulated minimal damage to human health) is 0%, while the probability that the damage to human health for the Sc-1 would be equal to 1.07E-06 DALY/FU is more than 80%. IMPACT 2002þ, an ecosystem quality damage category consisting of four mid-points — “aquatic ecotoxicity,” “terrestrial ecotoxicity,” “terrestrial acidification/nutrification,“,” and “land occupation” — was used to investigate the level of disruption in ecosystems [84]. Based on the results tabulated in Table 5, it can be deduced that the second sce­ nario made a higher contribution (0.32%) to the ecosystem quality damage category compared to the first one. More specifically, in Sc-1, 2.76E-03 PDF*m2*yr caused by PG production (250 mg) was deducted from 2.67E-05 PDF*m2*yr caused by WHME production (5000 mg). Like the human health damage category discussed above, the main reason for the burdens imposed on the ecosystem quality damage category was emissions of electricity consumption during antioxidant production (gallic acid production in PG production). For instance, in Sc-2, each 250 mg of PG produced led to 2.76E-03 PDF*m2*yr of damage to the ecosystem, out of which 9.58E-04 PDF*m2* yr (35%) was attributed to nitrogen oxides emission to air. Fig. 6 shows that the probability for the Sc-2 to reach 3.48 PDF*m2* yr/FU (simulated minimal damage to ecosystem quality) would be 0%, while this value stands at approximately 0% for the Sc-1 as well. Therefore, there is no significant preference for scenario selection.

Fig. 3. Effect of antioxidant incorporation (WHME and PG) at different doses on the OSI of WCO methyl esters using Rancimat at air volume flow rate of 0.02 m3/h and temperature of 110 � C. Table 3 The stabilization factor (F) of WHME. WHME Concentration (ppm)

Stabilization Factor (F)

1000 2500 5000 10000

1.35 1.96 2.84 3.54

3.4. Environmental comparison of the investigated antioxidants using LCA Two scenarios were considered in the present study, i.e., 5000 ppm of WHME and 250 ppm of PG incorporated into 1 kg of WCO biodiesel (first and second scenarios, respectively). To compare the scenarios from an environmental perspective, four end-point damage categories were taken into consideration. Table 5 summarizes the results obtained from the LCA of both scenarios. The first scenario, in which electricity pro­ duced by photovoltaic cells was used for walnut husk processing and WHME production, had higher environmental compliance in all four damage categories. It should be noted that the use of WCO and walnut hull in the production of biodiesel and antioxidant, led to avoided pro­ duction soybean oil and PG, respectively. Therefore, soybean oil was considered as an avoided product in both scenarios. Moreover, in Sc-1, PG was considered as an avoided product. More specially, the environ­ mental damage caused by the production of soybean oil and PG were deducted from the environmental damage caused by the production of WCO biodiesel and WHME. In line with this, in Table 5, the sign ( ) of the numerical results implies a positive environmental impacts caused by the use of bio-waste compared to virgin materials. In better words, the amount of environmental damage associated with not producing the avoided products (i.e., soybean oil in both scenario and PG in Sc-1) is 8

Z. Khounani et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

Fig. 4. Major walnut-producing countries.

In better words, when the decision is to be made based on this damage category, neither of the scenarios would be superior. Resource damage category mid-points — “non-renewable energy consumption” and “mineral extraction” — represent primary energy utilization in a given activity or production process [84]. As shown in Table 5, production of 1 kg of WCO biodiesel supplemented with WHME was associated with 3.36 MJ of primary energy consumption that is approximately 614% lower than biodiesel supplemented with PG. Negative value is due to avoided production of soybean oil for biodiesel production as well as avoided production of 250 mg PG as antioxidant. More specially, 6.81 MJ of primary energy was attributed to WCO bio­ diesel production but it avoided 8.72 MJ of primary energy by avoiding using soybean oil for biodiesel production. In addition, 1.44 MJ of pri­ mary energy was attributed to the production of 250 mg PG vs. 4.31E-05 MJ of primary energy used for the production of 5000 mg WHME based on Sc-1. This difference could be ascribed to the solar photovoltaic-driven extraction process used for the natural antioxidant production vs. fossil electricity driven production process used for its synthetic counterpart. Based on the data presented in Fig. 7, the probability for Sc-2 to reach 0.89 MJ of primary energy (simulated minimal damage to resource) would be 0% while this value for the Sc-1 would be equal to 100%. This result emphasizes that when the aim would be to reduce resource depletion, Sc-1 is strongly preferred compared to scenario Sc-2. Based on the IMPACT 2002þ, the only mid-point category contrib­ uting to the climate change damage category is global warming impact category with a characterization factor of 1 [84]. Hence, the results presented for climate change damage category are similar to the results of global warming impact category in the IMPACT 2002þ. As shown in Table 5, the second scenario exhibited higher GHG emissions compared with the first. More specifically, 1 kg of WCO biodiesel augmented by 5000 mg WHME was responsible for 2.33 kg CO2eq. The negative value is due to avoided production of soybean oil for biodiesel production (2.46 kg CO2eq.) and avoided production of 250 mg PG as an antioxidant. Whereas 1 kg of WCO biodiesel augmented by 250 mg PG led to 2.15 kg CO2eq. (negative value is due to avoid the production of soy­ bean oil). More than 90% of the climate change damage category in cases of PG production was attributed to CO2 originating from fossil-oriented energy carriers used for electricity generation. This

electricity was subsequently used for extraction of gallic acid (used for PG production). Overall, WHME outperforms PG from a climate change viewpoint. Based on the Monte Carlo simulation, the probability that Sc-2 rea­ ches 2.37 kg CO2eq/FU (simulated minimal damage to climate change) would be 0%, while this probability for Sc-1 stands at about 40% (Fig. 8). The Sc-1. was found more environmentally advantageous than the Sc-2 based on the obtained LCA results in all the investigated damage categories, i.e., 0.32% in an ecosystem quality, 12.13% in human health, 8.37% in climate change, and 614% in the resource. In addition, the uncertainty propagation using the Monte Carlo analysis emphasized on the superiority of Sc-1 vs. Sc-2, especially in terms of the resource damage category. Sc-1 was found superior to Sc-2 in all damage categories, however, given the different unit used in different damage categories, it would be difficult to compare these scenarios in term of their total environmental damages. Therefore, the values associated with different damage cate­ gories (Table 5) were weighted according to the IMPACT 2002þ method to achieve a single score. Based on the weighted results presented in Table 6, the single score for Sc-2 was 587.95 μPt/FU while the single score for Sc-1 stood at 641.35 μPt/FU, confirming the environmental superiority of Sc-1. Moreover, by replacing PG with WHME, the total environmental damage of Sc-1 was reduced by 9.08% vs. Sc-2. Moreover, given consumption and exposure to PG, and the conse­ quent potential health hazards, careful consideration of the biosecurity and teratogenicity aspects of this synthetic compound is warranted [85]. Numerous studies have been devoted to the impacts of PG on different model organisms (such as abnormalities in Alium cepa L.) [86] and its mitogenic [87] and cytogenetic effects [88,89]. According to a report by Han and Park [90], depending on dose and duration, exposure to PG could reduce cellular glutathione level and increase the amount of reactive oxygen species by inhibiting superoxide dismutase (SOD) and catalase (CAT) activities [90]. The cytotoxicity of PG in several cell types has been described as a disturbance of the redox cycle and induction of deoxyribonucleic acid (DNA) strand breaks [91]. Because of the destructive effects of PG on human health, the use of safer alternatives such as WHME has been advised.

9

Z. Khounani et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

electricity consumption by eliminating the solvent recovery stage, and 2) changing solvent type (e.g., using solvents that increase extraction speed and consequently, reduce electricity consumption per mg of WHME produced). Future studies could scrutinize the environmental impacts associated with these recommendations. Overall, WHME is favorable as a cleaner antioxidant in both pro­ duction and consumption phases, while it could serve as a suitable replacement for the potentially hazardous PG. Moreover, production and use of WHME as a natural fuel antioxidant could lead to more sus­ tainable waste management of walnut plantations. PG is a phenolic antioxidant used extensively to improve the stability of biodiesel fuels by avoiding its oxidative degradation. However, the biosecurity and teratogenicity aspects of this compound and the consequent potential health hazards upon exposure necessitate its substitution with safer al­ ternatives. Throughout this study, the use of a naturally sourced, solar photovoltaic-driven substitute for PG, i.e., WHME in WCO biodiesel, was studied. Finally, the present findings seem to be consistent with those of the other research works claiming that synthetic antioxidants could be replaced with their natural counterparts to improve the oxidative sta­ bility of biodiesel (see Table 2). Nevertheless, previous studies were mostly focused on the technical aspects of using natural antioxidants vs. synthetic antioxidants neglecting the environmental aspects of

Table 4 Contribution of walnut-producing countries to global biodiesel production*. Rank

Country

Biodiesel production (1000 barrel/d in 2014) a

1 United States 2 Brazil 3 Indonesia 4 Germanya 5 Argentina 6 Francea 7 Thailand 8 Spaina 9 Poland 10 Netherlands 11 Chinaa 12 Belgium 13 Colombia 14 Malaysia 15 Italya 16 Finland 17 United Kingdom 18 Portugal 19 Canada 20 Korea, South 21 Austriaa 22 Czech Republic 23 Denmark 24 Sweden 25 Greecea 26 Romaniaa 27 Hungary 28 Lithuania 29 Slovakia 30 Philippines 31 Indiaa 32 Latvia 33 Norway 34 Australia 35 Belarusa 36 Bulgaria 37 Croatia 38 Ireland 39 Turkeya 40 Uruguay Overall global production

83 59.66 58.76 56.56 50.21 36.19 20.45 14.67 13.11 12.71 12.61 11.74 9.86 9.76 6.75 6.49 6.31 6.14 5.49 5.28 4.69 4.28 3.91 3.52 3.3 3.29 2.85 2.42 1.98 1.93 1.58 1.42 1.14 1.12 1.08 1.06 0.77 0.54 0.53 0.4 529b

a

Among major walnut-producing countries (Fig. 4). 224.25 from 529 (1000 barrel/d), i.e., 42.4% of the total biodiesel produced in major walnut-producing countries. * Source: http://www.eia.gov. b

3.5. Practical implications of this study The favorable environmental aspects of antioxidant production from walnut husk investigated herein could be further enhanced by consid­ ering a series of recommendations, including 1) changing the antioxi­ dant extraction method from walnut husk, e.g., the use of microwaves instead of solvents could result in higher extraction rates and decreased

Fig. 5. The difference between the two scenarios in terms of the human health damage category (in DALY/FU).

Table 5 Results obtained from LCA for both scenarios per FUa. Scenario Human health Sc-1 Sc-2 Ecosystem quality Sc-1 Sc-2 Climate change Sc-1 Sc-2 Resources Sc-1 Sc-2 a

Unit

Walnut hull processing

Antioxidant production

DALY DALY

1.46E-13 –

5.77E-08 5.77E-08

1.03E-06 1.03E-06

1.09E-06 9.72E-07

PDF*m2*yr PDF*m2*yr

5.35E-07 –

2.74E-03 2.76E-03

3.17Eþ00 3.17Eþ00

3.17Eþ00 3.16Eþ00

kg CO2eq. kg CO2eq.

5.83E-08 –

8.79E-02 8.79E-02

2.24Eþ00 2.24Eþ00

2.33Eþ00 2.15Eþ00

MJ primary MJ primary

8.63E-07 –

1.44Eþ00 1.44Eþ00

1.91Eþ00 1.91Eþ00

3.35Eþ00 4.70E-01

Sc-1: WCO biodiesel augmented by WHME and Sc-2: WCO biodiesel augmented by PG. 10

Biodiesel production

Grand total

Z. Khounani et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

Fig. 6. The difference between the two scenarios in terms of the ecosystem quality damage category (in PDF*m2*yr/FU).

Fig. 8. The difference between the two scenarios in terms of the climate change damage category (in kg CO2eq/FU). Table 6 The weighted results of the LCA for both scenariosa according to the IMPACT 2002þ. Scenario

Unit

Human health Sc-1 μPt Sc-2 μPt Ecosystem quality Sc-1 μPt Sc-2 μPt Climate change Sc-1 μPt Sc-2 μPt Resources Sc-1 μPt μPt Sc-2 Total impact Sc-1 μPt Sc-2 μPt

Walnut hull processing

Antioxidant production

Biodiesel production

Grand total

2.06E-05 –

8.13 8.13

144.99 144.99

153.12 136.86

3.90E-05 –

0.20 0.20

231.30 231.30

231.50 231.10

5.89E-06 –

8.87 8.88

225.81 225.81

234.68 216.93

5.68E-06 –

9.49 9.49

12.55 12.55

22.04 3.06

7.12E-05 –

26.70 26.70

614.65 614.65

641.35 587.95

a Sc-1: WCO biodiesel augmented by WHME and Sc-2: WCO biodiesel augmented by PG.

4. Conclusions The results revealed that, at a constant concentration of 200 ppm, the antioxidant capacity of WHME was comparable to that of the synthetic antioxidant PG (87.6% vs. 89.1%). This was indicated by the strong TAA of the WHME despite the possibility of the unpurified extract containing impurities that interfered with its antioxidant capacity. Overall, 5000 ppm of WHME should be incorporated into WCO biodiesel to prolong the IP from 1.2 h to over 3 h as per the ASTM D6751 standard compared with 250 ppm for PG. Despite the higher concentrations required, the growing interest in substitution of synthetic antioxidants (that come with potential health hazards) such as PG with naturally sourced antioxidants and the fact that walnut husks are an inexpensive and readily available agricultural waste product suggest that its use as an antioxidant could be of special interest to the world’s biodiesel in­ dustry. In addition, 42.4% of global biodiesel volume is produced in countries where a large amount of walnut husks is generated. It was also

Fig. 7. The difference between the two scenarios in terms of the resource damage category (in MJ/FU).

antioxidants production. Overall, despite their technical success, natural antioxidants production suffers from a number of shortcomings such as high solvent and energy consumption. Therefore, in the absence of a thorough environmental analysis, the application of these compounds may not be sustainable compared with their synthetic counterparts. The findings presented herein not only looked into the technical aspects of using natural antioxidant but also studied the associated environmental aspects and provided recommendations to enhance their sustainability features as promising safe eco-friendly alternatives to synthetic antiox­ idants such as PG whose application is associated with health issues.

11

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx

Z. Khounani et al.

revealed that the environmental burdens of WHME additives at 5000 ppm are lower than those associated with PG production at 250 ppm. More specially, the LCA result showed that Sc-1 was more environmentally advantageous than Sc-2 in all the investigated damage categories, i.e., 0.32% in an ecosystem quality, 12.13% in human health, 8.37% in climate change, and 614% in the resource. Moreover, weighting of the environmental damage categories showed that the replacement of PG with WHME led to 9.08% reduction in the total environmental damage compared. Overall, in addition to its favorable technical aspects, the natural antioxidant (WHME) obtained through solar photovoltaic-driven extraction process was found a promising ecofriendly alternative to PG whose application is associated with health concerns.

[10] [11]

[12] [13] [14]

[15]

Author Contributions

[16]

Z.K. produced WCO biodiesel; Z.K., A.G., and A.F.T produced the natural antioxidant; S.A.H.G., E.T-K., and A.S. characterized the natural antioxidant; H.H.B. and M.A.R. performed the LCA; A.F.T., A-H.K., A-S. N, M.A., and M.T. developed the idea of the project and provided the required funds; Z.K., H.H.B, A-H.K., A-S.N, M.A., and M.T. contributed to the drafting of the manuscript; M.T. supervised and led the overall flow of the various stages of the project.

[17] [18] [19] [20]

Declaration of competing interest Authors declare no conflict of interest.

[21] [22]

Acknowledgments

[23]

The authors would like to extend their sincere appreciation to the Biofuel Research Team (BRTeam), Agricultural Biotechnology Research Institute of Iran, University of Tehran, Universiti Teknologi MARA (UiTM), and the Iranian Biofuels Society for supporting this study. KHK acknowledges support by the R&D Center for Green Patrol Technologies through the R&D for Global Top Environmental Technologies funded by the Ministry of Environment (Grant No:2018001850001) as well as by a grant from the National Research Foundation of Korea funded by the Ministry of Science, ICT, & Future Planning (Grant No: 2016R1E1A1A01940995).

[24] [25] [26] [27] [28]

References

[29]

[1] Dhinesh B, Raj YMA, Kalaiselvan C, KrishnaMoorthy R. A numerical and experimental assessment of a coated diesel engine powered by high-performance nano biofuel. Energy Convers Manag 2018;171:815–24. [2] Dhinesh B, Annamalai M, Lalvani IJ, Annamalai K. Studies on the influence of combustion bowl modification for the operation of Cymbopogon flexuosus biofuel based diesel blends in a DI diesel engine. Appl Therm Eng 2017;112:627–37. [3] Lalvani JIJ, Parthasarathy M, Dhinesh B, Annamalai K. Pooled effect of injection pressure and turbulence inducer piston on performance, combustion, and emission characteristics of a DI diesel engine powered with biodiesel blend. Ecotoxicol Environ Saf 2016;134:336–43. [4] Nanthagopal K, Ashok B, Garnepudi RS, Tarun KR, Dhinesh B. Investigation on diethyl ether as an additive with Calophyllum Inophyllum biodiesel for CI engine application. Energy Convers Manag 2019;179:104–13. [5] Lalvani JIJ, Parthasarathy M, Dhinesh B, Annamalai K. Experimental investigation of combustion, performance and emission characteristics of a modified piston. J Mech Sci Technol 2015;29:4519–25. [6] Aghbashlo M, Tabatabaei M, Rastegari H, Ghaziaskar HS. Exergy-based sustainability analysis of acetins synthesis through continuous esterification of glycerol in acetic acid using Amberlyst® 36 as catalyst. J Clean Prod 2018;183: 1265–75. [7] Aghbashlo M, Tabatabaei M, Khalife E, Najafi B, Mirsalim SM, Gharehghani A, et al. A novel emulsion fuel containing aqueous nano cerium oxide additive in diesel–biodiesel blends to improve diesel engines performance and reduce exhaust emissions: Part II–Exergetic analysis. Fuel 2017;205:262–71. [8] Aghbashlo M, Tabatabaei M, Khalife E, Roodbar Shojaei T, Dadak A. Exergoeconomic analysis of a DI diesel engine fueled with diesel/biodiesel (B5) emulsions containing aqueous nano cerium oxide. Energy 2018;149:967–78. [9] Aghbashlo M, Tabatabaei M, Rastegari H, Ghaziaskar HS, Roodbar Shojaei T. On the exergetic optimization of solketalacetin synthesis as a green fuel additive

[30]

[31] [32] [33] [34] [35] [36]

[37]

12

through ketalization of glycerol-derived monoacetin with acetone. Renew Energy 2018;126:242–53. Tabatabaei M, Aghbashlo M, Dehhaghi M, Panahi HKS, Mollahosseini A, Hosseini M, et al. Reactor technologies for biodiesel production and processing: a review. Prog Energy Combust Sci 2019;74:239–303. Aghbashlo M, Hosseinpour S, Tabatabaei M, Rastegari H, Ghaziaskar HS. Multiobjective exergoeconomic and exergoenvironmental optimization of continuous synthesis of solketal through glycerol ketalization with acetone in the presence of ethanol as co-solvent. Renew Energy 2018;130:735–48. Bala DD, Misra M, Chidambaram D. Solid-acid catalyzed biodiesel production, part I: biodiesel synthesis from low quality feedstock. J Clean Prod 2017;142:4169–77. Kirubakaran M, AMS V. A comprehensive review of low cost biodiesel production from waste chicken fat. Renew Sustain Energy Rev 2018;82:390–401. Aghbashlo M, Tabatabaei M, Hosseinpour S. On the exergoeconomic and exergoenvironmental evaluation and optimization of biodiesel synthesis from waste cooking oil (WCO) using a low power, high frequency ultrasonic reactor. Energy Convers Manag 2018;164:385–98. Da Silva C�esar A, Werderits DE, de Oliveira Saraiva GL, Guabiroba RCDSG. The potential of waste cooking oil as supply for the Brazilian biodiesel chain. Renew Sustain Energy Rev 2017;72:246–53. Hajjari M, Tabatabaei M, Aghbashlo M, Ghanavati H. A review on the prospects of sustainable biodiesel production: a global scenario with an emphasis on waste-oil biodiesel utilization. Renew Sustain Energy Rev 2017;72:445–64. Ahanchi M, Tabatabaei M, Aghbashlo M, Rezaei K, Talebi F, Ghaffari A, et al. Pistachio (Pistachia vera) wastes valorization: enhancement of biodiesel oxidation stability using hull extracts of different varieties. J Clean Prod 2018;185:852–9. Souza ACD, Comin M, Oliveira LH, Silva CA de A, Muzzi RM, Fiorucci AR, et al. Application of solvent dye in the field of biodiesel preservation. Color Technol 2017;133:165–9. Hajjari M, Ardjmand M, Tabatabaei M. Experimental investigation of the effect of cerium oxide nanoparticles as a combustion-improving additive on biodiesel oxidative stability: mechanism. RSC Adv 2014;4:14352–6. Sundus F, Fazal MA, Masjuki HH. Tribology with biodiesel: a study on enhancing biodiesel stability and its fuel properties. Renew Sustain Energy Rev 2017;70: 399–412. Cursaru D, Neagu M, Bogatu L. Investigations on the oxidation stability of biodiesel synthesized from different vegetable oils. Rev Chim (Bucharest) 2013;64:438–41. Dunn RO. Effect of antioxidants on the oxidative stability of methyl soyate (biodiesel). Fuel Process Technol 2005;86:1071–85. Fattah IMR, Masjuki HH, Kalam MA, Hazrat MA, Masum BM, Imtenan S, et al. Effect of antioxidants on oxidation stability of biodiesel derived from vegetable and animal based feedstocks. Renew Sustain Energy Rev 2014;30:356–70. Sulistyo H, Almeida MF, Dias JM. Influence of synthetic antioxidants on the oxidation stability of biodiesel produced from acid raw Jatropha curcas oil. Fuel Process Technol 2015;132:133–8. Ryu K. Effect of antioxidants on the oxidative stability and combustion characteristics of biodiesel fuels in an indirect-injection (IDI) diesel engine. J Mech Sci Technol 2009;23:3105–13. Focke WW, van der Westhuizen I, Grobler ABL, Nshoane KT, Reddy JK, Luyt AS. The effect of synthetic antioxidants on the oxidative stability of biodiesel. Fuel 2012;94:227–33. Sundus F, Fazal MA, Masjuki HH. Effect of anti-oxidants on the lubricity of B30 biodiesel–diesel blend. Lubr Sci 2017;29:3–15. Squissato A, Richter EM, Munoz RAA. Voltammetric determination of copper and tert-butylhydroquinone in biodiesel: a rapid quality control protocol. Talanta 2019; 201:433–40. Rashed MM, Masjuki HH, Kalam MA, Alabdulkarem A, Rahman MM, Imdadul HK, et al. Study of the oxidation stability and exhaust emission analysis of Moringa olifera biodiesel in a multi-cylinder diesel engine with aromatic amine antioxidants. Renew Energy 2016;94:294–303. Rodrigues JS, do Valle CP, Guerra PDAGP, de Sousa Rios MA, de Queiroz Malveira J, Ricardo NMPS. Study of kinetics and thermodynamic parameters of the degradation process of biodiesel produced from fish viscera oil. Fuel Process Technol 2017;161:95–100. Nishath PM, Sekar K, Shameer PM, Usman KM, Shitu A, Mary JS, et al. Influence of pyrogallol (PY) antioxidant in the fuel stability of Alexandrian Laurel biodiesel. Energy Recover. Process. from Wastes, Springer 2020:51–63. Panagiotopoulos IA, Pasias S, Bakker RR, de Vrije T, Papayannakos N, Claassen PAM, et al. Biodiesel and biohydrogen production from cotton-seed cake in a biorefinery concept. Bioresour Technol 2013;136:78–86. Chen YH, Luo YM. Oxidation stability of biodiesel derived from free fatty acids associated with kinetics of antioxidants. Fuel Process Technol 2011;92:1387–93. Fu J, Hue BTB, Turn SQ. Oxidation stability of biodiesel derived from waste catfish oil. Fuel 2017;202:455–63. Oliveira I, Sousa A, Ferreira ICFR, Bento A, Estevinho L, Pereira JA. Total phenols, antioxidant potential and antimicrobial activity of walnut (Juglans regia L.) green husks. Food Chem Toxicol 2008;46:2326–31. Taghvaei M, Jafari SM, Mahoonak AS, Nikoo AM, Rahmanian N, Hajitabar J, et al. The effect of natural antioxidants extracted from plant and animal resources on the oxidative stability of soybean oil. LWT - Food Sci Technol (LebensmittelWissenschaft -Technol) 2014;56:124–30. Spacino KR, Silva ET Da, Angilelli KG, Moreira I, Gal~ ao OF, Borsato D. Relative protection factor optimisation of natural antioxidants in biodiesel B100. Ind Crops Prod 2016;80:109–14.

Z. Khounani et al.

Renewable and Sustainable Energy Reviews xxx (xxxx) xxx [65] O’Sullivan AM, O’Callaghan YC, O’Grady MN, Hayes M, Kerry JP, O’Brien NM. The effect of solvents on the antioxidant activity in Caco-2 cells of Irish brown seaweed extracts prepared using accelerated solvent extraction (ASE). J Funct Foods 2013;5:940–8. [66] Fern� andez-Agull� o A, Pereira E, Freire MS, Valentao P, Andrade PB, Gonz� alez� Alvarez J, et al. Influence of solvent on the antioxidant and antimicrobial properties of walnut (Juglans regia L.) green husk extracts. Ind Crops Prod 2013; 42:126–32. [67] Goli AH, Barzegar M, Sahari MA. Antioxidant activity and total phenolic compounds of pistachio (Pistachia vera) hull extracts. Food Chem 2005;92:521–5. [68] Chang S, Bassiri A, Jalali H. Evaluation of antioxidant activity of fennel ( foeniculum vulgare ) seed extract on oxidative stability of olive oil. J Chem Heal Risks 2013;3:53–61. [69] Slatnar A, Mikulic-Petkovsek M, Stampar F, Veberic R, Solar A. Identification and quantification of phenolic compounds in kernels, oil and bagasse pellets of common walnut (Juglans regia L.). Food Res Int 2015;67:255–63. [70] Wenzel J, Storer Samaniego C, Wang L, Burrows L, Tucker E, Dwarshuis N, et al. Antioxidant potential of Juglans nigra, black walnut, husks extracted using supercritical carbon dioxide with an ethanol modifier. Food Sci Nutr 2016;5: 223–32. [71] Botella L, Bimbela F, Martín L, Arauzo J, S� anchez JL. Oxidation stability of biodiesel fuels and blends using the Rancimat and PetroOXY methods. Effect of 4allyl-2,6-dimethoxyphenol and catechol as biodiesel additives on oxidation stability. Front Chem 2014;2:1–9. [72] De Sousa LS, De Moura CVR, De Oliveira JE, De Moura EM. Use of natural antioxidants in soybean biodiesel. Fuel 2014;134:420–8. [73] Mittelbach M, Schober S. The influence of antioxidants on the oxidation stability of biodiesel. J Am Oil Chem Soc 2003;80:817–23. [74] Buosi GM, Da Silva ET, Spacino K, Silva LRC, Ferreira BAD, Borsato D. Oxidative stability of biodiesel from soybean oil: comparison between synthetic and natural antioxidants. Fuel 2016;181:759–64. [75] García M, Botella L, Gil-Lalaguna N, Arauzo J, Gonzalo A, S� anchez JL. Antioxidants for biodiesel: additives prepared from extracted fractions of bio-oil. Fuel Process Technol 2017;156:407–14. [76] Zhou J, Xiong Y, Liu X. Evaluation of the oxidation stability of biodiesel stabilized with antioxidants using the Rancimat and PDSC methods. Fuel 2017;188:61–8. [77] Kleinberg MN, Rios MAS, Buarque HLB, Parente MMV, Cavalcante CL, Luna FMT. Influence of synthetic and natural antioxidants on the oxidation stability of beef tallow before biodiesel production. Waste and Biomass Valorization 2019;10: 797–803. [78] França FRM, dos Santos Freitas L, Ramos ALD, da Silva GF, Brand~ ao ST. Storage and oxidation stability of commercial biodiesel using Moringa oleifera Lam as an antioxidant additive. Fuel 2017;203:627–32. [79] Serrano M, Martínez M, Aracil J. Long term storage stability of biodiesel: influence of feedstock, commercial additives and purification step. Fuel Process Technol 2013;116:135–41. [80] Sarin A, Singh NP, Sarin R, Malhotra RK. Natural and synthetic antioxidants: influence on the oxidative stability of biodiesel synthesized from non-edible oil. Energy 2010;35:4645–8. [81] Liang YC, May CY, Foon CS, Ngan MA, Hock CC, Basiron Y. The effect of natural and synthetic antioxidants on the oxidative stability of palm diesel. Fuel 2006;85: 867–70. [82] Valenga MGP, Boschen NL, Rodrigues PRP, Maia GAR. Agro-industrial waste and Moringa oleifera leaves as antioxidants for biodiesel. Ind Crops Prod 2019;128: 331–7. [83] Pinto LM, De Souza AL, Souza AG, Santos IMG, Queiroz N. Comparative evaluation of the effect of antioxidants added into peanut (arachis hypogae l.) oil biodiesel by P-DSC and rancimat. J Therm Anal Calorim 2015;120:277–82. [84] Sajid Z, Khan F, Zhang Y. Process simulation and life cycle analysis of biodiesel production. Renew Energy 2016;85:945–52. [85] Baran A, K€ oktürk M, Atamanalp M, Ceyhun SB. Determination of developmental toxicity of zebrafish exposed to propyl gallate dosed lower than ADI (acceptable daily intake). Regul Toxicol Pharmacol 2018;94:16–21. [86] Pandey H, Kumar V, Roy BK. Assessment of genotoxicity of some common food preservatives using Allium cepa L. as a test plant. Toxicol Reports 2014;1:300–8. [87] Abdo KM, Huff JE, Haseman JK, Alden CJ. No evidence of carcinogenicity of Dmannitol and propyl gallate in F344 rats or B6C3F1 mice. Food Chem Toxicol 1986;24:1091–7. [88] Tayama S, Nakagawa Y. Cytogenetic effects of propyl gallate in CHO-K1 cells. Mutat Res Toxicol Environ Mutagen 2001;498:117–27. [89] Lee JE, Kim JM, Jang HJ, Lim S Young, Choi SJ, Lee NH, et al. Propyl gallate inhibits adipogenesis by stimulating extracellular signal-related kinases in human adipose tissue-derived mesenchymal stem cells. Mol Cells 2015;38:336–42. [90] Han YH, Park WH. Propyl gallate inhibits the growth of HeLa cells via regulating intracellular GSH level. Food Chem Toxicol 2009;47:2531–8. [91] Hamishehkar H, Khani S, Kashanian S, Ezzati Nazhad Dolatabadi J, Eskandani M. Geno-and cytotoxicity of propyl gallate food additive. Drug Chem Toxicol 2014;37: 241–6.

[38] van Aardt M, Duncan SE, Long TE, O’Keefe SF, Marcy JE, Sims SR. Effect of antioxidants on oxidative stability of edible fats and oils:thermogravimetric analysis. J Agric Food Chem 2004;52:587–91. [39] Coppo RL, Pereira JL, da Silva HC, Angilelli KG, Rodrigues PRP, Galvan D, et al. Effect of natural antioxidants on oxidative stability of biodiesel from soybean oil. Applying simplex-centroid design. J Biobased Mater Bioenergy 2014;8:545–51. [40] Devi A, Das VK, Deka D. Ginger extract as a nature based robust additive and its influence on the oxidation stability of biodiesel synthesized from non-edible oil. Fuel 2017;187:306–14. [41] Devi A, Das VK, Deka D. Evaluation of the effectiveness of potato peel extract as a natural antioxidant on biodiesel oxidation stability. Ind Crops Prod 2018;123: 454–60. [42] Rodríguez-Meizoso I, Castro-Puyana M, B€ orjesson P, Mendiola JA, Turner C, ~ ez E. Life cycle assessment of green pilot-scale extraction processes to obtain Ib� an potent antioxidants from rosemary leaves. J Supercrit Fluids 2012;72:205–12. [43] P�erez-L� opez P, Gonz� alez-García S, Jeffryes C, Agathos SN, McHugh E, Walsh D, et al. Life cycle assessment of the production of the red antioxidant carotenoid astaxanthin by microalgae: from lab to pilot scale. J Clean Prod 2014;64:332–44. [44] Kavuncuoglu H, Kavuncuoglu E, Karatas SM, Benli B, Sagdic O, Yalcin H. Prediction of the antimicrobial activity of walnut (Juglans regia L.) kernel aqueous extracts using artificial neural network and multiple linear regression. J Microbiol Methods 2018;148:78–86. [45] Cosmulescu S, Trandafir I, Achim G, Botu M, Baciu A, Gruia M. Phenolics of green husk in mature walnut fruits. Not Bot Horti Agrobot Cluj-Napoca 2010;38:53–6. [46] Pourvosoughi N, Mohammadi P, Goli SAH, Nikbakht AM, Jafarmadar S, Pakzad M, et al. Polysel: an environmental-friendly CI engine fuel. Energy 2016;111:691–700. [47] Aghbashlo M, Hosseinpour S, Tabatabaei M, Dadak A. Fuzzy modeling and optimization of the synthesis of biodiesel from waste cooking oil (WCO) by a low power, high frequency piezo-ultrasonic reactor. Energy 2017;132:65–78. � [48] Jakopi�c J, Veberi�c R, Stampar F. Extraction of phenolic compounds from green walnut fruits in different solvents. Acta Agric Slov 2009;93:11–5. [49] Nickel J, Spanier LP, Botelho FT, Gularte MA, Helbig E. Effect of different types of processing on the total phenolic compound content, antioxidant capacity, and saponin content of Chenopodium quinoa Willd grains. Food Chem 2016;209: 139–43. [50] Llorach-Massana P, Farreny R, Oliver-Sola J. Are Cradle to Cradle certified products environmentally preferable? Analysis from an LCA approach. J Clean Prod 2015;93:243–50. [51] Jang YJ, Kim WG, Bonn MA. Generation Y consumers’ selection attributes and behavioral intentions concerning green restaurants. Int J Hosp Manag 2011;30: 803–11. [52] Zhou Z, Cheng S, Hua B. Supply chain optimization of continuous process industries with sustainability considerations. Comput Chem Eng 2000;24:1151–8. [53] Rajaeifar MA, Hemayati SS, Tabatabaei M, Aghbashlo M, Mahmoudi SB. A review on beet sugar industry with a focus on implementation of waste-to-energy strategy for power supply. Renew Sustain Energy Rev 2019;103:423–42. [54] ISO. 14044 iInternational standard. Environmental management–life cycle assessment–principles and framework. Geneva, Switzerland: International Organisation for Standardization; 2006. [55] Rajaeifar MA, Ghanavati H, Dashti BB, Heijungs R, Aghbashlo M, Tabatabaei M. Electricity generation and GHG emission reduction potentials through different municipal solid waste management technologies: a comparative review. Renew Sustain Energy Rev 2017;79:414–39. [56] Manfredi M, Vignali G. Life cycle assessment of a packaged tomato puree: a comparison of environmental impacts produced by different life cycle phases. J Clean Prod 2014;73:275–84. [57] Bueno G, Latasa I, Lozano PJ. Comparative LCA of two approaches with different emphasis on energy or material recovery for a municipal solid waste management system in Gipuzkoa. Renew Sustain Energy Rev 2015;51:449–59. [58] Altun-Çiftçio� glu GA, G€ okulu O, Kadırgan F, Kadırgan MAN. Life cycle assessment (LCA) of a solar selective surface produced by continuous process and solar flat collectors. Sol Energy 2016;135:284–90. [59] Jolliet O, Margni M, Charles R, Humbert S, Payet J, Rebitzer G, et al. Impact 2002 þ: a new life cycle impact assessment methodology. Int J Life Cycle Assess 2003;8: 324. [60] Clavreul J, Guyonnet D, Christensen TH. Quantifying uncertainty in LCA-modelling of waste management systems. Waste Manag 2012;32:2482–95. [61] Lloyd SM, Ries R. Characterizing, propagating, and analyzing uncertainty in life cycle assessment: a survey of quantitative approaches. J Ind Ecol 2007;11:161–79. [62] Do QD, Angkawijaya AE, Tran-Nguyen PL, Huynh LH, Soetaredjo FE, Ismadji S, et al. Effect of extraction solvent on total phenol content, total flavonoid content, and antioxidant activity of Limnophila aromatica. J Food Drug Anal 2014;22: 296–302. [63] Anokwuru CP, Anyasor GN, Ajibaye O, Fakoya O, Okebugwu P. Effect of extraction solvents on phenolic, flavonoid and antioxidant activities of three nigerian medicinal plants. Nat Sci 2011;9:53–61. [64] Mukherjee S, Mandal N, Dey A, Mondal B. An approach towards optimization of the extraction of polyphenolic antioxidants from ginger (Zingiber officinale). J Food Sci Technol 2014;51:3301–8.

13