CETvol87


 
 

 

                                                                    DOI: 10.3303/CET2187074 
 

 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Paper Received: 28 September 2020; Revised: 3 February 2021; Accepted: 3 April 2021 
Please cite this article as: Amado M., Carrasco J., Ochoa L.D., Rangel C.J., Becerra A.P., Cabeza I.O., Acevedo P.A., 2021, Technical and 
Environmental Analysis of Large-scale Pig Manure Digestion Through Process Simulation and Life Cycle Assessment, Chemical Engineering 
Transactions, 87, 439-444  DOI:10.3303/CET2187074 

 CHEMICAL ENGINEERING TRANSACTIONS 
VOL. 87, 2021 

A publication of 

The Italian Association 
of Chemical Engineering 
Online at www.cetjournal.it 

Guest Editors: Laura Piazza, Mauro Moresi, Francesco Donsì
Copyright © 2021, AIDIC Servizi S.r.l. 
ISBN 978-88-95608-85-3; ISSN 2283-9216

Technical and Environmental Analysis of Large-Scale Pig 
Manure Digestion through Process Simulation and Life Cycle 

Assessment 
Mónica Amado a,b, Jessica Carrasco c, Laura D. Ochoa c, Carol J. Rangel a*, Ana 
P. Becerra c, Iván O. Cabeza c, Paola A. Acevedo c,d 
aFacultad de Ingeniería, Universidad EAN, Bogotá D.C., Colombia 
bAix Marseille Univ, CNRS, Centrale Marseille, M2P2, Marseille, France 
cEngineering Department, Universidad Santo Tomás, Bogotá, Carrera 9 No 51-1, Colombia 
d Deparment of Industrial Engineering, Universidad Cooperativa de Colombia, Bogotá, Avenida Caracas 37 - 63, Colombia 
crangel46372@universidadean.edu.co 

The biogas and by-products production from anaerobic digestion of pig manure was evaluated technically, 
economically, and environmentally in an industrial park in Bogotá, Colombia, in order to generate economic 
opportunities and to reduce environmental impacts. Mass and energy balances were performed using data 
from literature and developing a simulation of the AD process in Aspen Plus software based on stoichiometric 
balances. The environmental evaluation of this process was developed using LCA methodology. Also, the 
economic viability of the process was evaluated by calculating the internal rate of return and the net present 
value considering 10 years of life of the plant and equipment. The results of the environmental evaluation 
show that the stages of transport, and consumption of electrical and thermal energy contribute to the 
categories of acidification, abiotic, and ozone layer depletion, for both scenarios of interest according to the 
allocation of the final product. Furthermore, it is established that the project is viable as it has an internal rate 
of return of 26% and a payback time of 5 years, according to the results of the economic evaluation. 

1. Introduction

The anaerobic digestion (AD) is a feasible response to Colombia's energy demand in order to increase the 
percentage of biogas participation within the energy matrix through the use of the large amount of biomass 
available; according to Piñeros, V.et al, (2018), there is availability of substrates such as pig manure (PM) that 
has a high potential for bio-methanation. In Colombia, currently the increase in pig production generates 
approximately eight million tons of manure per year in just one department. Then, bioprocesses can be one of 
the answers within the Nationally Appropriate Mitigation Actions for the mitigation of greenhouse gases 
(GHG); promoting the generation of biogas of agricultural origin for energy use, through the recovery of waste 
generated in this economic sector (Ministerio de minas y energía, 2019). Since the AD process is not 
unrelated to the scale’s economy, it is necessary to engage large amounts of organic residues in one place to 
improve profitability, which might represent a threat to the environment in which they are disposed of, treated, 
and transformed. For this reason, possible environmental impacts are being evaluated, using methodologies 
such as process simulation and its environmental analysis. The different scenarios can be modelling by 
scaling processes, allowing the generation of balances through the data obtained; and the environmental 
analysis can be carried out using Life Cycle Assessment (LCA) methodology, where potential environmental 
impacts are quantified and identified from the beginning to the end of a process. This study of biomass 
conversion and its uses aims to determine the technical, economical, and environmental viability of producing 
electric energy (EE) through the biogas generated by the AD of pig manure. It also evaluates the scenario in 
which the manures of several pig farms in the department of Cundinamarca are coupled, and an electric 

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power generating plant which could be built in an industrial park located near Bogotá, including in the analysis 
the production of digestate to be marketed as fertilizer.  

2. Methodology

2.1 Mass balances and simulation of the process 

The available PM in the department of Cundinamarca was calculated according to the study by Piñeros, V. et 
al,(2018). The first unit process included the harvesting and transportation of the raw material, which included 
diesel fuel consumption calculations, according to Garbs & Geldermann, (2018). A 32 tons of load capacity 
and Euro 3 emission standard truck was defined. The following unit processes data were based on the 
simulation of an AD large-scale process, carried out in Aspen Plus. For this, a stirred semi-batch reactor was 
considered, with 21 days, in mesophilic conditions (35 °C), atmospheric pressure, and with the following 
characterization of the PM: 22.83% of TS, 19.79% of VS, 4.98 g/L of COD, 1.88% of total Kjeldahl nitrogen 
and 82.30% of content of organic matter (Amado et al., 2021). From the simulation results, the production and 
sizing of the equipment are obtained. It was considered that the reactors are fed with conveyor belts, which 
collect the material stored in hoppers. Biogas requires a process of desulfurization and dehydration before 
being transformed into electrical energy. This process is carried out in a coupled unit, which has a compost 
biofilter and a dehydrator with removal efficiencies between 80 and 97% (Navarro et al., 2007; Vikrant et al., 
2018). Once the biogas has been treated, with removal efficiencies between 80 and 97%.in a combustion 
engine by increasing the pressure to the inlet of the engine. The electrical energy generated was calculated 
based on Eq. (1)-(2) (Espejo et al., 2019). 

  ( ) = ℎ  ( ) ∗   ( ℎ/ )  ∗  0,65 ∗ 0,35  (1) ℎ  ( ) =   ( /  )  ∗     (2)
Where 0.65 is the factor to determine the amount of biogas available to produce electrical energy, and 0.35 is 
the efficiency factor of the generator motor. The bio-methanisation potential (BMP) of the PM used was 437.33 
m3/CH4/ton VS (Rodríguez et al., 2017) and the specific heat of the biogas (6 KWh/m

3), based on the methane 
fraction (0.5-0.6) (Indrawan et al., 2018). To calculate the combustion gases, the concentrations measured in 
the report of the Inter-American Development Bank (Blanco et al., 2017) were used. Furthermore, CO2 and 
CO emissions were taken from the Ecoinvent 3 database and from the technical report by Nielsen et al., 
(2010) respectively. The digestate, which leaves the biodigester as a muddy mixture of PM with water, was 
treated in the decantation and centrifuge processes to remove the water. In the decanter, 80% of water is 
poured with soluble substances such as fatty acids, amino acids, carbon dioxide, among others. The 
remaining sludge is transferred to a centrifugal dehydrator that maintains 80% humidity in the final digestate.  

2.2 Economic evaluation 

The economic evaluation was carried out based on determining the viability of the AD process of PM for the 
generation of electrical energy and digestate. For the development of this, a 10-year cash flow (2019 to 2029) 
was calculated considering income, from the sale of AD products, the costs of raw materials, and necessary 
supplies, maintenance, and payroll. Additionally, the depreciation of the equipment, the annual taxes (profit 
and equity), the total investment of the project and the salvage (20% total investment of the equipment). 
Finally, viability was determined from the net present value (NPV) and the internal rate of return (IRR). 

2.3 Life cycle assessment 

Following the International Organization for Standardization (ISO 14040), this study uses the LCA 
methodology which proposes four main stages: definition of aim and scope, life cycle inventory, life cycle 
impact assessment, and finally interpretation (ISO, 2006). The aim of this work was to evaluate the generation 
of electricity and digestate from the biogas resulting from AD of PM, and to identify and quantify the potential 
environmental impacts of two possible scenarios based on the data obtained from the simulation of this 
process. For this, a door-to-door approach is established where the necessary raw materials and the required 
industrial services were taken from the EcoInvent 3 databases.  
The starting point of the established study was the transport of the PM, from the municipality of San Antonio 
de Tequendama to Bogotá, and ends with the generation of electric power and digestate. The first scenario is 
based on a 100% allocation for biogas since the study has the purpose of generating electrical energy. For 
this scenario, a functional unit (FU) of 1 kWh of electrical energy generated was selected. For the second 
scenario, the allocation percentage is changed to 100% of the digestate obtained; since, in the results of the 

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economic evaluation, most of the income corresponds to its sale. The selected FU is 1 Kg of digestate 
produced. 
For the LCIA, SimaPro software was used and the inputs and outputs were entered, the latter being the 
products of the process or environmental aspects (wastewater and emissions), obtained in the construction of 
the mass and energy balances. The LCIA profile was estimated using the CML baseline methodology for the 
following impact categories: acidification (AC-KgSO2eq), abiotic depletion (AbD- KgSbeq), eutrophication (EP- 
gPO4eq), climate change (GWP-KgCO2eq), ozone layer depletion (OLD- KgCFC-11eq) and photochemical 
oxidation (PO-KgC2H4eq). 

3. Results

Figure 1 shows the process diagram, where the black lines show the flow of mass currents, while the red lines 
represent the energy consumption of the equipment used. The values shown are calculated for a 21-day 
anaerobic digestion modelling process. 

Figure 1: Diagram of AD process for PM 

A distance of 32.5 km and 73 trips were estimated for the collection of the PM of a batch, from the pig farms to 
Bogotá. The collection of the PM is done once before each batch begins and stored in four hoppers with a 
capacity of 850 m3 each. The stored biomass is transported to the reactors using two conveyor belts. Due to 
the large amount of PM for AD, it was established that the process will be carried out in two biodigesters, each 
of 3702 m3. From the first treatment given to biogas, a removal of H2S (g) is obtained, the value of which was 
excluded from the evaluation due to the low concentration obtained. In addition, for obtaining electricity, two 
internal combustion engines of 300 kW each with their respective compressor are used. It is important to 
consider the use of heat exchangers. The first one has the functionality of increasing the temperature of the 
water entering the stirred reactor, so that the temperature conditions are obtained for AD reactions to be 
carried out. The second exchanger takes advantage of the combustion gases from the generator engine to 
heat thermal oil.  

3.1 Economic evaluation 

The economic evaluation of the process was carried out based on 10-year cash flow, in which the values of 
the income from the sale of electricity and digestate were calculated. Additionally, the process costs 
considered correspond to the payroll, equipment maintenance, and water consumption and price (Ministerio 
de Vivienda, Ciudad y Territorio, 2010). There are also the costs of purchasing PM, the consumption of oil to 
heat the reactor (Priboloc, 2019), and diesel for the truck and forklift  (Ministerio de minas y energía, 2019). 
The price of energy was taken the same as both the sale price and the cost and corresponds to the reported 
market value of the (UPME, 2019). Also, the consumption of electrical energy for lighting was taken from EPM 

441



data (EPM, 2019). The quantity data for income and costs were taken from the results obtained in the 
balances, and their value increased annually based on the CPI (Sintraprevi, 2018); for which the average of 
the index was taken from 2015 to 2018. The results show, the sale of the digestate represents the highest 
income for the project, while the highest costs are reflected in the purchase of PM. It was established that the 
depreciation of the equipment and the salvage of the project is 10% and 20% respectively, of the total 
investment less the cost of the land. Taxes calculated are taxes on profits (33%) and wealth tax. Taking these 
data into account, the net operating profit (UNO) was calculated, which was subsequently used together with 
the minimum attractive rate TAM (10%) and the value of the corrected equity, to estimate the annual NPV and 
the IRR. The results of the economic evaluation shown that for a purchase value of $ 14 per Kg of EC and a 
sale value of digestate of $ 2000, the recovery time of the project investment (equipment and land) is five 
years. On the other hand, an IRR of 26% was obtained, this being higher than the TAM, which indicates that 
the project is profitable and that apart from recovering the investment, profits will be generated. 

3.2 Life cycle assessment 

3.2.1 Life cycle impacts assessment LCIA 
Figures 2 shows the contribution of the stages of the AD process to each of the impact categories evaluated 
for the first and second scenario proposed. Figure 2a shows that in the first scenario the stages that contribute 
to the evaluated impact categories are the generation of electrical energy, PM transport, process water 
consumption, temperature increase of the water entering the biodigester (steam) and energy consumption of 
the process, which for this scenario, the equipment that consumes energy are the hopper, the conveyor belt, 
the biodigester agitators and the compressor. 

Figure 2: Contribution of stages to the impact categories in (a) scenario 1 (biogas); (b) scenario 2 (digestate) 

According to the LCIA profile of the first scenario evaluated, the AC and OLD categories present similar 
contributions, since the consumed steam stage is the one that most influences these categories with 44.8% 
and 49.7% respectively, followed by the PM transport and the electrical energy process. The AC contribution 
is assigned to the composition of the emission gases (ammonia, nitrogen oxides and sulfur oxides), impacting 
the acidity of the air (Antón, 2004). Those gases are probably generated in the processes of burning of fossil 
fuels and the generation of electrical energy. For the OLD category, the contribution is due to the emissions of 
chlorofluorocarbons and halons, possibly generated in the production of diesel, electric power and steam, 
which are the precursors of the decrease in the ozone layer (Antón, 2004). The stages of PM transport, 
consumption of electrical energy in the process and the steam consumed are those that contribute 
significantly to category AbD with 43.7%, 27.2% and 19.2% respectively. This is related to resource depletion 
factors such as gold, cadmium, copper, silver and zinc (Antón, 2004) due to the extraction of fossil fuels 
necessary for the production of diesel, the generation of electrical energy and the production of industrial 
steam. For the EP category, the stages that contribute significantly are the consumption of electrical energy 
(42.2%), the transport of PM (28.1%) and the steam generated (26.4%), due to the wastewater and increase 
of the chemical demand (oxygen, nitrate, nitrogen, and phosphate in the water) which generates an increase 
in algaes. For the GWP and PO categories, the stage that contributes the most is the generator engine or the 
generation of electrical energy with 72.6% and 99.5% respectively, due to the combustion of biogas within the 
engine, which generates emissions of GHG like CO2 and VOCs like butane, propane and toluene, which react 
with nitrogen oxides and produce tropospheric ozone (Antón, 2004). 

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Figure 2b shows the stages of contribution to benefits and/or environmental impacts, which are PM transport, 
water consumption, temperature increase to the water entering the biodigester (steam), energy consumed in 
the process, settling and dewatering of sludge for the second scenario. Furthermore, the steam used to heat 
the water entering the digester has high influence on at least four of the six impact categories, highlighting the 
GWP and OLD with percentages impact of 49.3% and 49.6% respectively. This is due to the emissions of 
compounds such as CO2, CH4 and chlorofluorocarbons, which increase GHG and contribute to the 
degradation of the ozone layer (Antón, 2004). These emissions are connected with the fossil fuels used in the 
harvesting. This case also applies to the consumption of electrical energy and transportation, as they 
contribute to the impacts generated in these categories. On the other hand, steam does not have the greatest 
impact on the category EP. 
The greatest contributions to macronutrient impacts are found in the dehydrator tank when generating 
discharges of substances such as ammonia together with phosphate and nitrogenous compounds. After the 
review of the substances present in the discharge of this stage, a high presence of glucose was found, which 
together with the above mentioned substances, would contribute to the increase in biomass production in the 
water source, which brings with it a decrease in available oxygen, causing anaerobic conditions in the 
environment (Antón, 2004). Regarding the PO and AC categories, the stage that presents the greatest 
contribution to impact, after steam, is the consumption of electrical energy, with a percentage of 30.8% and 
27.4%; This is due to the NOx and sulfur emissions to the atmosphere that increase the production of photo-
oxidants, which cause, on the one hand, in the presence of VOCs, the generation of tropospheric O3, and on 
the other hand, the decomposition of acids causing acidification of the medium (Antón, 2004). 
For the AbD category, the stage that presents the greatest contribution is the transport of PM with a 43.5% 
value related to resource depletion factors such as cadmium, chromium, copper, gold and lead (Antón, 2004); 
extracted to obtain the necessary infrastructure for the transport and obtaining of electrical energy. According 
with the analysis of the scenarios, the same behaviours are send for AbD, AC and ODP, resulting on the use 
of steam, PM transport and energy consumption. As the other scenarios differ based on the allocation, a 
greater air damage is generated when AD to energy generation; and water and soil depletion when AD to 
digestate. According with the Mano et al. (2019) and Lijó et al. (2014) results the transport, as a unit process 
stage, generates an important contribution in the OLD, AC and AbD categories for CO2, NH3, nitrogen oxides 
and sulfur oxides. In addition, contributions to ozone depletion (caused by the production of diesel), 
eutrophication of fresh water (influenced by the production of machinery) and formation of photochemical 
oxidants (affected by the combustion of diesel) respectively. De Vries et al. (2012), conclude that this stage 
contributes little in the category of GWP in AD of CD. These results coincide with those obtained in the 
present study, since, for the two scenarios evaluated, transport contributes in these categories, especially in 
AbD. To increase bioenergy with mono-digestion, additional processing can be applied to the PM as 
separation or pretreatment, which would help to concentrate the available organic matter to increase the 
efficiency of the AD process evaluated in this study, after an analysis considering the increases in energy 
demand (De Vries et al., 2012). Mano et al. (2019), affirm that the impacts of AD plant depend on several 
factors such as technologies or operating practices. In this study, a starter heat exchanger is used, which uses 
steam to heat the water entering the biodigester, which, as evidenced in the two-scenarios, affects in almost 
all categories and significantly. This is an operational practice that is not present in all AD plants. The electric 
energy consumption takes energy from the national grid and contributes to OLD and EP categories with a low 
percentage for both. Different studies conclude that electric power generation contributes significantly to the 
GWP and PO categories (Lijó et al., 2014; Mano et al., 2019) as shown in this study. Regarding the digestate 
generation process Mano et al. (2019), affirm that the separation of the liquid phase and the solid phase, 
reduces the ammonia content, a situation that was evidenced in this study, because in the discharges 
generated in the decanter tank and centrifugal dehydrator, the soluble substances, among these ammonias, 
they are removed, leaving a low content of it in the digestate. 

4. Conclusions

This study contributes to the technical-economic and environmental study of the AD process to produce 
biogas from residual biomass. The results show that in the department of Cundinamarca, Colombia it is 
feasible to install a plant with a processing capacity of 3.2 tons of biomass where according de LCA, the 
highest contribution are the transport of the PM, the consumption of electrical energy and the use of steam. 
Even though the data of these stages were calculated in relation to the simulation of the process, the 
specifications of these steps were taken directly from the inventory of the SimaPro software; therefore, these 
are included indirectly in the analysis. The results present an alternative treatement to the conventional 
handling of this agro-industrial waste, without additional processing and the process is environmentally viable 

443



due to the fact that similar results were obtained from such studies, where a real scenario of production of 
electrical energy from AD was compared with other forms of obtaining energy, the former being the best 
alternative for reducing GHG and of the impacts in the GWP, PO, OLD and AbD categories. 

References 

Amado, M., Barca, C., Hernández, M.A., Ferrasse, J.-H., 2021. Evaluation of energy recovery potential by 
anaerobic digestion and dark fermentation of residual biomass in Colombia. Front. Energy Res. 9. 

Antón, M.A., 2004. Utilización del Análisis del ciclo de vida en la evaluación del impacto ambiental del cultivo 
bajo invernadero mediterráneo. TDX (Tesis Doctorals en Xarxa). Universitat Politècnica de Catalunya, 
Cataluña. 

Blanco, G., Santalla, E., Córdoba, V., Levy, A., 2017. Generación de electricidad a partir de biogás capturado 
de residuos sólidos urbanos: Un análisis teórico-práctico | Publications (Nota Técnica No. IDB-TN-1260). 
Banco Interamericano de Desarrollo. 

De Vries, J.W., Vinken, T.M.W.J., Hamelin, L., De Boer, I.J.M., 2012. Comparing environmental 
consequences of anaerobic mono- and co-digestion of pig manure to produce bio-energy – A life cycle 
perspective. Bioresource Technology 125, 239–248. 

EPM, 2019. Tarifas, solicitud del servicio, usos inteligente del Servicio Público de Generación, Transmisión y 
Distribución de Energía y Electricidad de EPM por parte de usuarios de hogares [WWW Document]. EPM. 
URL https://www.epm.com.co/site/clientes_usuarios/clientes-y-
usuarios/empresas/energ%C3%ADa/grandes-empresas/tips-para-el-uso-inteligente (accessed 7.20.20). 

Espejo, A., Torres, P., Mosquera, J., Rangel, C., Cabeza, I., Ortiz, N., Becerra, P., Acevedo, P., 2019. 
Evaluation of the environmental, technical and economic performance of anaerobic co- digestion 
processes in Colombian scenarios. p. 10. 

Garbs, M., Geldermann, J., 2018. Analysis of selected economic and environmental impacts of long distance 
manure transports to biogas plants. Biomass and Bioenergy 109, 71–84. 

Indrawan, N., Thapa, S., Wijaya, M.E., Ridwan, M., Park, D.-H., 2018. The biogas development in the 
Indonesian power generation sector. Environmental Development 25, 85–99. 

ISO, 2006. ISO 14040:2006(es), Gestión ambiental — Análisis del ciclo de vida — Principios y marco de 
referencia [WWW Document]. ISO. URL https://www.iso.org/obp/ui#iso:std:iso:14040:ed-2:v1:es 
(accessed 5.22.20). 

Lijó, L., González-García, S., Bacenetti, J., Fiala, M., Feijoo, G., Moreira, M.T., 2014. Assuring the sustainable 
production of biogas from anaerobic mono-digestion. Journal of Cleaner Production 72, 23–34. 

Mano, E.M., Naranjo, A.M., Peçanha, V.P., Vaz, C. do R., 2019. Life cycle assessment of manure biogas 
production: A review. Journal of Cleaner Production 219, 411–423. 

Ministerio de minas y energía, 2019. Sistema de Información de Combustibles Líquidos - Estructura de Precio 
[WWW Document]. Sicom. URL
https://www.sicom.gov.co/precios/precioAction.do?method=pMostrarIpPublicado (accessed 7.20.20). 

Ministerio de Vivienda, Ciudad y Territorio, 2010. Reglamento Técnico del Sector de Agua Potable y 
Saneamiento Básico - RAS. 

Navarro, J.D., Gamarra, Y., Escalante, H., 2007. Diseño de un biofiltro para disminuir la concentración de 
H2S de un reactor anaerobiodede flujo a pistón (rap). Rev. UIS ing. 6, 61–69. 

Nielsen, M., Nielsen, O., Marianne, T., 2010. Emissions from decentralised CHP plants 2007 - Energinet.dk 
Environmental project no. 07/1882: Project report 5 - Emission factors and emission inventory for 
decentralised CHP production. National Environmental Research Institute, Neri Technical Report. 

Piñeros, V.; Melo, k; Acevedo, P.; Cabeza, I., 2018. Integración de Modelos de Evaluación de Viabilidad 
Económica e Impacto Ambiental a Modelos Empíricos y Técnicos del Proceso de Codigestión Anaeróbica. 

Priboloc, 2019. Aceite térmico mineral Pirobloc HTF-Mineral | FluidoTermico.com [WWW Document]. 
Priboloc. URL https://www.fluidotermico.com/es/aceites-minerales/17-pirobloc-htf-mineral.html (accessed 
7.20.20). 

Rodríguez, A., Ángel, J., Rivero, E., Acevedo, P., Santis, A., Cabeza, I., Acosta, M., Hernandez, M., 2017. 
Evaluation of the Biochemical Methane Potential of Pig Manure, Organic Fraction of Municipal Solid Waste 
and Cocoa Industry Residues in Colombia. Chemical Engineering Transactions 57. 

Sintraprevi, 2018. SINTRAPREVI [WWW Document]. Indicadores. URL https://sintraprevi.org/indicadores.php 
(accessed 7.20.20). 

UPME, 2019. Precio bolsa [WWW Document]. UPME. URL http://www1.upme.gov.co/Paginas/default.aspx 
(accessed 7.20.20). 

Vikrant, K., Kailasa, S.K., Tsang, D.C.W., Lee, S.S., Kumar, P., Giri, B.S., Singh, R.S., Kim, K.-H., 2018. 
Biofiltration of hydrogen sulfide: Trends and challenges. Journal of Cleaner Production 187, 131–147. 

444