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International Journal of Performability Engineering Vol. 10, No. 4, June, 2014, pp. 347-356. © RAMS Consultants Printed in India

Recycling Waste Cooking Oil into Biodiesel: A Life Cycle Assessment M. RIPA*, C. BUONAURIO, S. MELLINO, G. FIORENTINO, S. ULGIATI Department of Science and Technology, Parthenope University of Naples, ITALY (Received on Sept.05, 2013, revised on Oct.10 and Oct.18, 2013, and finally on Jan.23, 2014) Abstract: Production activities are always accompanied by energy consumption and waste generation; the basic environmental issue in industrial and developing countries worldwide still is how to best identify and manage waste streams while at same time recovering their energy content. In this paper, starting from the evidence that the conventional disposal of waste cooking oil (WCO) causes severe environmental problems, a new way to recover and reuse this oil is explored. Collection of cooking oils and fats from residential and commercial facilities and treatment to biofuel is investigated as a case study in the Campania Region (Italy). There have been recent developments in recycling techniques for conversion of WCO into biodiesel: in such a way, environmental damage can be minimized by also meeting the need for alternative fuels. The aim of this study is dual. Firstly, it assesses the environmental effectiveness of biodiesel production from WCO, secondly, it identifies hotspots throughout the entire biodiesel production chain and suggests future improvements. Keywords: Life Cycle Assessment, Waste Cooking Oil, Waste Management, Biofuels, Biorecycling.

1.

Introduction

Converting waste streams into valuable resources represents a three-win solution, dealing simultaneously with human security, pollution, and, last but not least, energy recovery. The European Directive 2009/28/EC, establishing a substitution corresponding to 10% of biofuels in the total consumption by the year 2020 [1], generated an emerging interest in replacing fossil feedstock with biomass-based raw materials. At the same time the European Directive 2008/98/EC [2] dictates a precise hierarchical order in the waste management (prevention, re-use, recycling, recovery and final disposal) with the aim of reducing the amount of waste delivered to landfill and the improper disposal of waste streams. Both aspects require a re-thinking of our systems of production. Biodiesel is a diesel fuel defined as mono-alkyl esters of vegetable oils or animal fats. It is recommended as a substitute for petroleum-based diesel mainly because of its claimed renewable nature [3-8]. However, concerns have also been raised concerning its real production cost from oilseed crops and extent of benefits. In fact, the use of a food source (edible oil and fertile land) to produce biodiesel while millions of people face hunger and starvation around the world has received harsh criticism worldwide [9-13], due to the resultant increase in the demand for vegetable or edible oil and unnecessary clearing of forests for plantation. The use of waste cooking oil (WCO) as a biodiesel feedstock has been identified as an alternative source of fatty materials for the production of biofuels [14]. WCO is a domestic waste generated from households and restaurants, as the result of using edible vegetable oil for cooking and frying. WCO causes hard negative environmental impacts caused by the uncontrolled disposal of such products. Diverting WCO from improper _____________________________________________________ *Corresponding author’s e-mail: [email protected]

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disposal extends the product life cycle and prevents the contamination of groundwater supplies with this harmful liquid waste: very often, this residue is poured in sanitary sinks and toilets, going to stop in the sewer systems causing damages in the clogging of the pipes and increasing the price of the processes of the stations of treatment, causing the pollution of the aquatic environment. This causes additional energetic and economic costs: 3 kWh and about 1 €, respectively, per kg of WCO delivered to the sewer system [15]. As a consequence, collecting and recycling WCO contributes to solve simultaneously three environmental problems: waste reduction by product reuse/recovery, reduction of the fossil fuels energy dependence and reduction of pollutant emissions [16-20]. The present work is based on case study data about collection, sorting, recovery and treatment phases of WCO in Campania Region. 2.

Methodology

The environmental assessment was performed according to the Life Cycle Assessment methodology, described in the standards ISO 14040 and 14044 [21-22]. The data utilized for the analysis were provided by a network of companies that operate in Campania Region (collection and pre-treatment phase [23-24]) and Lazio Region (transesterification phase [25]). 2.1 Goal and Scope 2.1.1 Objectives and Functional Unit The goal of this study is, firstly, to compare different options for biodiesel production and, secondly, to analyze the production of biodiesel from WCO under an environmental perspective. An identification of the most significant and sensitive steps in the production system is also pursued in order to evaluate the most crucial ones in terms of environmental impacts and energy requirements and improve their performance. At this aim, an attributional LCA was performed in order to illustrate the environmental impacts of the analyzed process. The functional unit chosen for this assessment is 1 kilogram of diesel/biodiesel produced. In order to allocate the environmental load to biodiesel and glycerine, delivered by trans-esterification phase, an economic allocation is pursued. The allocation by economic value is based on average market prices of final products [26]. 2.1.2 System Description and Boundaries In this study WCO is considered as a waste stream. In so doing, the agricultural production of oil is not included, according to standard procedure for the life cycle of waste [27-29]. Since the agricultural phase is responsible for the greatest environmental impacts, according to most LCA studies [30, 12, 34], calculated indicators of the recycling process are expected to show potentially large benefits. The approach used in this analysis is ‘from gate to gate’. The environmental loads associated with the use of biodiesel are not taken into account, since they do not have any influence on the comparative study of different production systems. 2.1.3 Biodiesel Production from WCO The system under examination consists of four stages: 1) collection of WCO, 2) pretreatment, 3) delivery of treated oil to the biodiesel facility and 4) its conversion into biodiesel through trans-esterification. WCO is firstly collected in plastic containers of different capacities from restaurants, hotels and agro-food industry by Papa Ecologia S.r.l. (Campania Region, Italy). Then, WCO is supplied to a pre-treatment company (Proteg

Recycling Waste Cooking Oil into Biodiesel: A Life Cycle Assessment

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S.p.A, Campania Region, Italy) and mechanically pre-treated to lower the content of solid waste by means of decantation and centrifugation. The purified WCO is transported by truck to a biodiesel production plant (DP Lubrificanti, Lazio Region, Italy). The final stage is the trans-esterification reaction of the triglyceride with an alcohol (methanol) in the presence of a catalyst, yielding a mixture of fatty acid alkyl esters (biodiesel) and glycerine. The crude methyl ester is washed to remove traces of methanol, glycerine, catalyst, etc., and then dried to become usable biodiesel. 2.2 Life Cycle Inventory (LCI) and Impact Assessment (LCIA) The Life Cycle Inventory (LCI) is a crucial step, since the quality of the whole study depends on the representativeness, consistency, accuracy and geographical specifications of the data collected, in accordance with the ISO 14040 standards. The inputs and outputs for each stage have been obtained from different sources. Primary local data were personally communicated by Papa Ecologia S.r.l. and Proteg S.p.A. They refer to a process survey made in year 2012 for the above-mentioned phases (collection and purification); adjusted average industrial operational inputs from Ecoinvent v. 2.2 database are used for the trans-esterification phase instead of those specific for DP Lubrificanti S.r.l. in the nearby Lazio Region, due to incomplete inventory information. Wastewater treatment and related environmental impacts are also included in the analysis. Fuels, machinery, water, electricity, process chemicals, plant construction materials for the industrial conversion phase as well as the main intermediate and final products are shown in Table 1. All the values are calculated with reference to a functional unit of 1 kg of biodiesel produced over one year. 2.3 Life Cycle Impact Assessment (LCIA) Comparative LCIA has been carried out with reference to biodiesel from rapeseed and fossil diesel: key data for the quantification of inputs (chemicals, water, electric and thermal energy demands, etc.) and outputs were derived from Ecoinvent database. Materials and energy carriers are selected within the database from processes and geographical areas as similar as possible to the Campania Region. Worldwide production mix is chosen for some chemicals, as a proxy for European production, considering that these processes are based on similar technologies worldwide. LCIA is performed by means of the LCA software OpenLCA 1.3 (www.openlca.org) and Ecoinvent v 2.2 using the CML 2001 and the CED (Cumulative Energy Demand) methods. For the CML 2001 method, the following categories were explored: Abiotic Depletion Potential (ADP, in kg Sb eq), Acidification Potential (AP, in kg SO 2 eq), Eutrophication Potential (EP, in kg PO 4 3- eq), Global Warming Potential (GWP, in kg CO 2 eq), Human Toxicity Potential (HTP, in kg 1,4-DB eq), Photochemical Oxidation Potential (POP, in kg C 2 H 4 ). All the analyzed categories are referred to the CML 2001 baseline version. The second method (CED, Ecoinvent version 2.2 [31]) is applied to investigate the use of non-renewable (fossil, nuclear, biomass from primary forests) and renewable (biomass from agriculture, wind, solar, geothermal, water) sources involved in the production system, to be interpreted as patterns of energy resource investment and depletion. For sake of clarity, it is important to point out that the energy content of the feedstock is taken into account (as primary use) in the case of biodiesel from rapeseed and fossil diesel whilst, it is not considered in the case of WCO because, according to CED method: "Wastes, which are used for energy purposes are dealt with a cut-off approach. Thus they are non accounted for in the CED values. Their energy content and thus the demand is allocated to the primary use" [31].

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Table 1: Inventory of Input Flows to Collection, Pre-treatment and Trans-esterification Phases INPUT FLOWS Collection phase Diesel1 Truck (van 32t 5 Heat, natural gas, at industrial furnace Methanol Posphoric acid, 85% in H 2 O Potassium hydroxide, at regional storage Water Electricity, medium voltage Vegetable oil esterification plant Treatment sewage to wastewater treatment plant FINAL PRODUCTS (all phases) Collected oil Purified oil Biodiesel Glycerin

VALUE

UNIT (unit/kg/yr)

3.34E-02 6.07E-02 1.16E-02

kg t*km kg

1.93 6.40E-05 2.47E-02 9.52E-08 2.26E-05 1.19E-02 1.18E-08 4.89E-11

m2 kg kWh item item kg kg item

0.22 0.99 0.12 4.97E-03 1.22E-02 2.92E-02 4.08E-02 1.01E-09 6.75E-05

t*km MJ kg kg kg kg kWh item m3

1.34 1.11 1 0.11

kg kg kg kg

1

Diesel is an input of the operation process in the truck. Truck includes also the van and road maintenance and disposal. It includes also the local emission delivered by engine combustion. 3 For electricity, the reference is to the Italian production mix of medium voltage electricity. 4 Wastewaster treatment plant is considered in the analysis based on the typology of the analyzed plant. All local emissions are also included in the analysis. 5 The transport covers the distance Caivano-Aprilia (200 km) and includes the diesel consumption and the local emissions. Due to the lack of specific data, the diesel consumption is referred to operation process, transport, lorry>32t in the Ecoinvent database. 2

3.

Results and Discussion

3.1 A Comparison with Biodiesel from Rapeseed and Fossil Diesel In order to assess the suitability of biodiesel from WCO as an alternative fuel, a comparison among biodiesel from WCO, biodiesel from rapeseed and fossil diesel was accomplished. All the inputs and outputs were referred to the production of 1 kg of biodiesel from rapeseed and diesel from fossil resources, appropriately adjusted from the Ecoinvent database; the processes taken into account were “diesel, at refinery” and “rape methyl ester, at esterification plant”. In order to make the processes more fit to the Italian context, in both cases the Italian electricity mix was included. The impacts calculated throughout the CML 2001 and the CED methods for the different type of diesel are listed below. Table 2 and 3 show the environmental impact associated to the different production processes. In each impact category, the total impacts


351

associated with biodiesel production from WCO are much lower than those associated with biodiesel production from rapeseed and fossil diesel. Furthermore, biodiesel from rapeseed shows the highest impact in Global Warming category in comparison to the other diesel production processes. Global Warming impacts are mainly generated by the agricultural phase (fertilizers, pesticides, machinery, among others) requiring a large amount of fossil resources, whilst the impacts generated by the industrial steps are much lower [32, 30, 12]. This evidence, confirmed by previous studies [13, 33, 34], underlines that the use of dedicated biomass is not feasible for energy production only (biodiesel and heat). Comparison among CML impact categories is made possible by means of a normalization procedure. By applying the CML 2001 normalization factors Western Europe 1995 [35], the highest contributions to all the impact categories are from biodiesel from rapeseed, excepted for Abiotic Depletion which is higher for fossil diesel (Figure 1). This result reflects the fact that fossil diesel itself is accounted as an abiotic resource. Table 2: CML 2001 Characterized Impacts Calculated for the Comparison among Biodiesel from WCO, Rapeseed and Fossil Diesel. Impact Category

Abiotic depletion Acidification Eutrophication Global warming Human toxicity Photochemical oxidation

Unit

kg Sb eq kg SO 2 eq kg PO 4 3-eq kg CO 2 eq kg 1,4-DB eq kg C 2 H 4

Biodiesel from WCO 4.66E-03 1.19E-03 1.74E-04 0.32 9.66E-02 7.58E-05

Biodiesel from rapeseed 1.11E-02 1.70E-02 5.47E-03 2.62 1.12 1.18E-03

Fossil Diesel

2.37E-02 5.40E-03 2.76 -04 0.49 0.25 3.39E-04

Concerning the CED method, Table 3 shows that biodiesel production from WCO and fossil diesel are mainly relying on non-renewable fossil sources, accounting for 98% and 99% of the total energy demand, respectively. Although the biodiesel production from rapeseed is only partially dependent on non-renewable energy sources (34%), in absolute values it represents the most demanding diesel production process, showing the highest energy consumption and the highest values in almost all impact categories. Biodiesel production from WCO shows the lowest energy demand and it requires 10.31 MJ/kg of energy, of which 9.59 MJ/kg from fossil fuels, 0.56 MJ/kg from nuclear (indirectly, through imports from France) and only a minor contribution (0.16 MJ/kg) from renewables, 81% of which from Renewable, hydro. Table 3: CED Impacts Calculated for the Comparison among Biodiesel from WCO, Rapeseed and Fossil Diesel. Impact Category

Unit

Non-renewable, fossil Non-renewable, nuclear Non-renewable, biomass Renewable, biomass Renewable, wind, solar, geothermal Renewable, hydro

MJ MJ MJ MJ MJ MJ

Biodiesel from WCO 9.59 0.56 1.44E-04 2.32E-02 7.80E-03 0.13

Biodiesel from Rapeseed 22.5 2.78 1.23E-03 47.6 3.26E-02 0.47

Fossil Diesel 53.4 0.60 6.33E-05 2.21E-02 1.13E-02 7.07E-02

This positive balance suggests that the biodiesel production from WCO is also feasible from an energy perspective. As observed, the biodiesel production from WCO potentially entailed a much more desirable environmental profile than the current petrol or biomass diesel production processes, and despite current techno-economic limitations, WCO is set

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to play a role for the achievement of the targets established by the Directive 2009/28/EC. An additional value is also represented by the economic viability of the process since it presents a reasonable payback period despite the high fixed investment and the lowest overall environmental impact [36].

Normalized values

1.60E-13

1.20E-13

8.00E-14

4.00E-14

0.00E+00

ADP

AP

EP

GWP

HTP

POP

Biodiesel from WCO

2.98E-14

3.70E-15

1.32E-15

7.71E-15

1.69E-15

7.88E-16

Biodiesel from Ra peseed

7.09E-14

5.29E-14

4.14E-14

6.31E-14

1.96E-14

1.23E-14

Fossil Diesel

1.51E-13

1.68E-14

2.09E-15

1.18E-14

4.38E-15

3.53E-15

Figure 1: CML 2001 Normalized Impacts Calculated for the Comparison among Biodiesel from WCO, Rapeseed and Fossil Diesel.

3.2 Environmental Impact of Biodiesel from WCO Phases In order to highlight the contribution of each phase of the system, the environmental impacts of biodiesel production from WCO on CML 2001 and CED categories were explored step by step. Table 4 shows that the impacts associated to pre-treatment stage is negligible in comparison to the impact of collection and trans-esterification. This is in line with the fact that the pre-treatment phase only consists of mechanical treatment. In contrast, the trans-esterification is the stage with greater impact in all impact categories. The normalized results (not shown here) confirm that the most impacted categories are Abiotic Depletion and Global Warming. Table 4: CML 2001 Characterized Impacts Calculated for the Comparison among Different Phases of Biodiesel from WCO Impact Category

Unit

Collection Phase

Pretreatment Phase

Delivery of WCO

Transesterification Phase

Abiotic depletion Acidification Eutrophication Global warming Human toxicity Photochemical oxidation

kg Sb eq kg SO 2 eq kg PO 4 3-eq kg CO 2 eq kg 1,4-DB eq kg C 2 H 4

1.19E-03 3.60E-04 3.12E-05 6.76E-02 3.92E-02

1.10E-04 7.00E-05 4.90E-06 1.54E-02 6.09E-03

1.90E-04 1.60E-04 2.52E-05 2.65E-02 4.57E-03

3.17E-03 6.00E-04 1.09E-04 2.15E-01 4.67E-02

2.49E-05

3.20E-06

4.11E-06

4.35E-05

Figure 2 proves that, also regarding the energy supply, the most energy demanding phase is the trans-esterification phase, showing a significant requirement of fossil sources (95% of the total energy consumption), mainly due to the use of fossil chemicals.


353

Energy consumption (%)

100%

80%

60%

40%

20%

0%

Tra ns-esterifica tion pha se

6.38

0.23

Non ren, bioma ss (MJ) 1.34E-04

Delivery of WCO

0.42

2.23E-02

1.17E-06

7.90E-04

1.94E-04

4.06E-03

Pre-trea tment pha se

0.21

3.00E-02

1.71E-07

2.45E-03

6.44E-04

1.91E-02

Collection pha se

2.58

0.28

5.09E-06

8.01E-03

2.40E-03

4.63E-02

Fossil (MJ)

Nuclea r (MJ)

Ren., bioma ss (MJ) 1.18E-02

Wind, sola r (MJ) 4.56E-03

6.25E-02

Hydro (MJ)

Figure 2: CED Characterized Iimpacts Calculated for Different Phases of Biodiesel from WCO: for each Category (The total impact was assumed as 100%).

In order to identify the most impacting input in the trans-esterification-phase, the Abiotic Depletion Potential, Global Warming Potential, Non-renewable-fossil impact categories were investigated in deeper details. Table 5 shows that the use of methanol itself contributes to Abiotic Depletion by 70%, to Global Warming by 43% and to Nonrenewable, fossil by 71%, whereas a minor contribution comes from the other inputs. This is due to the fact that the methanol production process (steam reforming) is strictly dependent from natural gas, strongly impacting respectively on Abiotic Depletion, Global Warming and Non-renewable-fossil categories. Table 5: Environmental Impacts (expressed as percentage) of the Main Inputs (considering a cut-off of 3%) to the Trans-esterification Phase on Abiotic Depletion Potential, Global Warming Potential and Non-renewable, Fossil. Impact Category ADP GWP Non-renewable, fossil

% % % %

Methanol 69.7 43.3 70.5

Electricity 5.5 11.4 5.1

Heat, natural gas 19.3 34.2 19.5

KOH 5.5 11.1 4.9

3.3 Future Scenarios According to the above results, the biodiesel production from WCO shows the best environmental performance, providing an interesting alternative to the other analyzed biodiesel production options. According to Tsai et al. [37], 90% of the total WCO could be saved by converting it into biodiesel. Considering that in 2010 the Italian CONOE (Consortium for recycling of used cooking oil) (http://www.conoe.it/) reported an Italian WCO production of 2.8E5 tons, the total amount of biodiesel, virtually obtainable, could cover 0.6% of the total Italian fuel consumption per year (considering as a reference the fuel Italian consumption in 2010 reported by Unione Petrolifera: http://www.unionepetrolifera.it/). This evidence makes clear that, from one side, the biodiesel production from WCO cannot be assumed as the solution to the dependence from petroleum fuels, but, on the other side, it represents an important added value considering that biodiesel represents the co-product of a recycling/disposal process of an harmful waste. This awareness calls for optimization strategies aiming at reducing the

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environmental impact of the process, such as by increasing the efficiency of the industrial process, by decreasing the distances among the different process sites and components [38] and by minimizing the use of chemicals (some researchers proposed to improve the trans-esterification reaction by reducing the amount of used methanol via ultrasonics [39, 40]). 4.

Conclusion

The LCA methodology applied in this study helped identify the hotspots throughout the entire biodiesel from WCO production chain, pointing out the trans-esterification phase to be responsible for the largest part of the emissions. Although it is unlikely that biofuel production would be a viable alternative to petroleum fuels, the use of biodiesel from WCO shows promising potential: firstly, it can contribute to the reduction of environmental impacts of WCO disposal; secondly, it reduces the economic load related to the operation problems in municipal sewage treatment plants and, thirdly, it contributes a small but non-negligible fraction of renewable energy to society. References [1]. [2]. [3].

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For Biographies of Maddalena Ripa and Sergio Ulgiati, please see page 336 at the end of Guest Editorial. Ciro Buonaurio obtained his M.Sc. degree at the Faculty of Environmental Sciences, Parthenope University of Napoli, Italy. Research interests include life cycle assessment, environmental quality, recycling processes. Salvatore Mellino, Ph.D. in Environment, Resources and Sustainable Development. He has professional expertise in Life Cycle assessment (LCA), Geographic Information Systems (GIS), Emergy Synthesis. Gabriella Fiorentino is a Post-Doc. Research fellow at Parthenope University of Naples. Italy. Research experience includes biomass conversion, biorefineries and LCA of products and processes.