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Wind energy has been considered as one of the greenest renewable energy sources over the last two decades. However, attention is turning to reducing the possible environmental impacts from this sector. We argue that wind energy would not be effectively "green" if anthropogenic materials are not given attention in a responsible manner. Using the concept of the circular economy, this paper considers how anthropogenic materials in the form of carbon fibers can reenter the circular economy system at the highest possible quality. This paper first investigates the viability of a carbon-fiber-reinforced polymer extraction process using thermal pyrolysis to recalibrate the maximum carbon fiber value by examining the effect of (a) heating rate, (b) temperature, and (c) inert gas flow rate on char yield. With cleaner and higher quality recovered carbon fibers, this paper discusses the economic preconditions for the takeoff and growth of the industry and recommends the reuse of extracted carbon fibers to close the circular economy loop.
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A circular economy approach to green energy:
Wind turbine, waste, and material recovery
Siqi HAO1
University of Nottingham Ningbo China
Adrian T. H. KUAH, PhD 2 *
James Cook University Australia, Singapore Campus
Christopher D. RUDD, PhD 2
James Cook University Australia, Singapore Campus
Kok Hoong WONG, PhD1
University of Nottingham Ningbo China
Nai Yeen Gavin LAI, PhD1
University of Nottingham Ningbo China
Jianan MAO1
University of Nottingham Ningbo China
Xiaoling LIU, PhD1
University of Nottingham Ningbo China
Declarations of interest: none
1 University of Nottingham Ningbo China (UNNC), Ningbo, 315100, China
2 James Cook University (JCU), 149 Sims Drive, Singapore 387380, Singapore
*Corresponding author: Associate Professor Adrian Kuah (
College of Business Law and Governance
James Cook University Australia, Singapore Campus
149 Sims Drive
Singapore 387380
Wind energy has been considered as
one of the greenest renewable energy
sources over the last two decades.
However, attention is turning to
reducing the possible environmental
impacts from this sector. We argue
that wind energy would not be
effectively “green” if anthropogenic
materials are not given attention in a
responsible manner. Using the
concept of the circular economy, this
paper considers how anthropogenic
materials in the form of carbon fibers can reenter the circular economy system at the highest
possible quality. This paper first investigates the viability of a carbon-fiber-reinforced polymer
extraction process using thermal pyrolysis to recalibrate the maximum carbon fiber value by
examining the effect of (a) heating rate, (b) temperature, and (c) inert gas flow rate on char
yield. With cleaner and higher quality recovered carbon fibers, this paper discusses the
economic preconditions for the takeoff and growth of the industry and recommends the reuse
of extracted carbon fibers to close the circular economy loop.
Four economic preconditions ensure re-entry of recovered fiber into circular system
Rapid heating rate and high temperature reduce char formation on carbon fiber
Effect of inert gas flow on reduction of char residues is only obvious at 550°C
Improved pyrolysis conditions increase char intrinsic reactivity and oxidation rate
circular economy, wind turbine, carbon fiber, pyrolysis, recovery, recycling
Hao S, Kuah A.T.H, Rudd C.D., Wong K.H., Lai N.Y.G., Mao J and Liu X (2019) A circular
economy approach to green energy: wind turbine, waste, and material recovery. Science of the
Total Environment (In Press)
1. Introduction
Wind energy has been considered as one of the greenest renewable energy sources over the
last two decades (Liu and Barlow 2017; Liu et al., 2019). As a result, national and regional
energy policies have encouraged the development of onshore and offshore wind farms, where
installed capacity has grown rapidly from 7,600 MW in 1998 to 591,000 MW in 2018 (Global
Wind Energy Council [GWEC], 2015; 2019). Amidst this growth, attention turns naturally to
the environmental impact of end-of-life turbine blades, especially when the end-of-life blades
and associated structures end up in landfills and negate the “green” credentials of the industry.
This is a pertinent challenge because the annualized growth rate in wind power over the
first decade of the 21st century exceeded 12% (GWEC, 2014) and based on projection, 14.9–
18% of global electricity demands will be supplied by wind energy between 2020 and 2050
(European Wind Energy Association [EWEA], 2014; International Energy Association [IEA],
2011). A steady growth scenario of new installation wind farms around the world has been
reported by Liu and Barlow (2017) in China, the United States, Europe, and the rest of the
world, as shown in Fig. 1. New global installation capacity grew to 51.7 GW in 2014, then 63.8
GW in 2015 but stayed fairly consistent for the next 3 years (54.9 GW in 2016, 53.5 GW in
2017, and 51.3 GW in 2018) in a report by the GWEC (2019).
Figure 1: Annual new wind turbine installations by region
Source: Adapted from Liu and Barlow (2017)
With the rapid growth in wind energy capacities, and considering the typical turbine design
lifespan of 20 years, Liu and Barlow (2017) have projected that the end-of-life waste from
turbines becomes a critical global problem by 2028. Albers (2009) predicted around 50,000
tons of blade waste in 2020, with the amount exceeding 200,000 tons by 2034. Similarly,
Andersen et al. (2014) predicted 400,000 tons of blade waste being generated between 2029
and 2033. Liu and Barlow (2017) estimate the blade material usage in China reaching
1,500,000 tons by 2050. Therefore, there is a pressing need to consider this very significant
waste stream.
A typical horizontal-axis unit consists of four main components: a foundation, a tower, a
nacelle, and three blades. The nacelle is fabricated from steel and copper. The tower is
fabricated from concrete or steel and the foundation is made solely from concrete, with the
rotating blades made from composite materials to minimize inertial and windage losses.
Considering the anthropogenic materials used, composite is one of the most problematic
materials because there are currently no mature recycling channels (Job, 2013; Pimenta and
Pinho, 2011).
The composite found in the blades is of fiber-reinforced polymer composite for ease of
manufacture into aerodynamic shape and high mechanical performance. However, because of
the cross-linked polymer chains in the thermoset matrix, recycling remains a significant
challenge, particularly reusing the ingredients in other high-grade applications. Most of the
older blades are made of glass-fiber-reinforced polymer (GFRP) composites because of their
relatively low manufacturing and material costs. However, this imposes a constraint for
recycling options because cost must be tightly controlled to make the recycling process
economically viable. To date, the only recycling route that is commercially active is where
GFRP waste is shredded and consumed in cement kilns. The value of the waste stream is
reduced to that of calcium carbonate, making this approach only viable where landfill is
prohibited, as in the case of Germany (Job, 2013).
Because the wind power industry is working toward larger turbines capable of producing
10 MW or greater, weight saving is a primary concern because blade mass increases in
proportion to the cube of the rotor radius (Igwemezie et al., 2019). This makes carbon fiber an
ideal material because of its high specific stiffness and reduced fatigue sensitivity (Veers et al.,
2003). However, the main disadvantage is its high initial cost (Liu and Barlow, 2017). For this
reason, carbon-fiber-reinforced polymer (CFRP) has only displaced GFRP in manufacturing
structural elements, such as the spar, for blades longer than 45 m. For the next generation of
10 MW units with blades of length 100 m, Wood (2010) notes that the total mass can be reduced
by 30% if carbon fiber is used to make blade skins. This mass reduction can potentially mitigate
the high cost impact of the material (Veers et al., 2003). Thus, it is recognized that the
proportion of carbon fiber composite usage will increase and a trend toward fully carbon
composite blades is expected (McKenna et al., 2016). Because carbon fibers are energy
intensive to produce and have high intrinsic value, there are both environmental and economic
motivations for recovering carbon fibers from CFRP (Shuaib et al., 2015).
In this study, the concept of Circular Economy (CE) is used to consider how the valuable
carbon fiber can be recovered from the end-of-life blades and what economic preconditions are
required to allow the fiber to reenter the cycle at the highest possible quality. The CE is defined
as “an industrial system that is restorative or regenerative by intention and design. It replaces
the end-of-life concept with restoration, shifts towards renewable energy, elimination of toxic
chemicals which impair reuse and return to the biosphere, and aims for the elimination of waste
through the superior design of materials, products, systems, and business models” (Ellen
MacArthur Foundation, 2013). The CE creates a closed-loop system in which resources can be
kept in a continuous cycle of production and utility, thereby allowing precious and finite
resources to generate more value for an extended period of time (United Nations Environment
Program [UNEP], 2006). Hence, moving toward CE necessitates changes in the way we design,
produce, consume, use (and reuse), and manage waste.
Some common CE approaches include: (1) recycling and recovery, where used materials
are processed or treated so that they can be reused (Hamzaoui-Essoussi and Linton, 2010); (2)
remanufacturing, in which worn-out, damaged, or end-of-life products are restored (Wang and
Kuah, 2018); (3) sharing or collaborative consumption for optimization of utility (Belk, 2014);
and (4) product life extension, in which products are ultimately designed to have a longer
lifetime (Tse et al., 2015). These practices require technological improvements and changes to
processes, hence most innovation is driven by industry.
This paper does not consider lifetime extension or collaborative consumption possibilities
covered by the CE concept, but rather how carbon fiber could reenter the circular economy
system at the highest possible qualityeither in the forms of a product (reuse/repurpose or
resize/reshape) or as recycled “raw” or intermediate material (recycle, recovery, and
conversion). Sending end-of-life wind turbine blades to landfill is not a long-term viable
solution, where many European Union countries legislate against composite waste being sent
to landfills (Pickering, 2006). In response, Asmatulu et al. (2013) explored the reuse of these
materials as structural components in bridges, buildings, or artificial reefs. Other ways to
repurpose blades may involve bridges or urban furniture, but the key challenge remaining in
the reuse of composites in public amenity infrastructure is to ensure structural integrity. In
terms of composite blade recycling, the valuable output streams are fiber, filler, resin, and
energy recovered (Liu et al., 2019). Blades’ recycling typically involves jaw cutters for
sectioning before crushing or shredding. Shredding reduces fiber length and strength while
hammer milling reduces the composite to smaller fragments, generating noise and dust. The
recyclates still contain polymer residue, quality is variable, and applications therefore limited
to low-grade structures.
From the CE’s perspective, material loop needs to be closed and this very much depends
on the quality of the recovered carbon fiber and the technicalities involved (Hahladakis and
Iacovidou, 2018; Kasprzyk and Gajewska, 2019). Clean carbon fibers can be recovered
through three known thermal decomposition processes. First, a pyrolysis process, which
extracts fibers, energy, and pyrolysate at high temperature in an inert environment. The trade-
off of this process is the use of the lowest possible temperature to devolatilize the polymer to
avoid fiber degradation (Fraisse et al., 2016). Second is the “fluidized bed” process (Pickering
et al., 2015) to decompose the polymer composite thermally. The feedstock is heated to 450–
550 °C on a layer of silica sand, fluidized by a flow of hot air, thereby oxidizing and
decomposing the polymer matrix. Solvolysis is an alternative process performed using sub- or
supercritical fluids. This strips the polymer matrix via a chemical reaction in an aggressive
solvent attack. Pure carbon fibers, an inorganic residue, and low molecular weight
hydrocarbons are the typical output streams (Sokoli et al., 2018).
Among the three recovery options, pyrolysis has been the process of choice in recent
decades. Unlike the fluidized bed process technology, which burns off the organic matrix for
energy recovery, the pyrolysis process recovers both fiber and a hydrocarbon stream for
potential reuse. Although low-cost solvents are used in solvolysis, a high energy intensity of
up to 101 MJ/kg (La Rosa et al., 2016) is required to achieve the high pressure and temperature
conditions, thus limiting their progress to the laboratory scale. In contrast, the energy
requirement for a typical pyrolysis process is much lower at around 30 MJ/kg (Witik et al.,
2013) and compares favorably to virgin carbon fiber production, which consumes 704 MJ/kg
(Das, 2011). Microwave-assisted heating may also yield energy saving compared with
conventional convective furnaces (Jiang et al., 2015). Fiber recovered from the pyrolysis
process is relatively clean, with low levels of char residue, and around 90% property retention
(McConnell, 2010). These fibers also bond well to epoxy resin (Jiang and Pickering, 2016),
making them reusable in new composites.
Despite its growing popularity, few reports address the effect of pyrolysis conditions on the
quality of the recovered fiber. Meyer et al. (2009) focused on the effects of pyrolysis
temperature, dwell time, and oven atmosphere on the performance of recovered carbon fibers,
while Lyon (1998) studied char residuals and their dependence on resin chemistry. A
conventional pyrolysis process will result in char formation, which requires a second oxidative
treatment (Meyer et al., 2007) because it inhibits free fiber handling and dispersion quality in
intermediate products such as nonwoven mat (Wong et al., 2012) and compromises adhesion
strength. Lower oxidation temperature and short oxidation times seem to assist char
minimization and fiber strength retention (Yang et al., 2015). Clearly, minimizing char residues
is critical, along with minimizing oxidative damage to the fiber.
It is evident that carbon fiber recovery from end-of-life blades is a critical issue for greener
and more sustainable wind energy production, where successful carbon fiber recovery through
pyrolysis is very promising to create and close the circular economy loop. The presence of char
residues affects the quality of recovered carbon fibers and posttreatment processes are needed,
which add additional cost and complexity to the recovery of fibers. To achieve this, we
determine the pyrolysis conditions that lead to ideal recovered fibers, which could reenter the
circular economy system at the highest possible quality and without any secondary cleaning.
Hence, this paper investigates the potential of CFRP recovery and the quality of the
recovered materials. To close the CE loop, the technicalities and economics of extraction are
considered, alongside the potential applications of recovered fibers. The paper is organized as
follows: Section 2 presents the method to determine the pyrolysis conditions that lead to ideal
recovered fibers, which could reenter the circular economy system at the highest possible
quality. Section 3 presents the results; while Section 4 discusses the recovery costs, economic
preconditions, and considerations for fiber applications. Section 5 concludes.
2. Methodology
The effects of pyrolysis temperature, heating rate, and nitrogen flow rate on char volume
were investigated using a thermogravimetric analyzer (TGA). Then, the oxidation rate of the
produced char, as expressed in terms of intrinsic reactivity, was measured via a nonisothermal
approach. The morphology of the char was then studied via a scanning electron microscopy
(SEM) analysis.
2.1 Materials
Unidirectional prepreg Toray® T700s carbon fibers and 37 wt% epoxy resin were supplied
by Aojing Composite Company, Shanghai, China. The prepreg was cut to 200 mm by 200 mm
and cured at 140 °C in air for 2 h. The release film and backing paper were removed before the
prepreg was pyrolyzed using a TGA. To study the char oxidation rate, epoxy was squeezed out
from the as-received prepreg between hot platens at 5 MPa and 80 °C. The resin was cured at
the previous schedule and subjected to thermal analysis, as described below.
2.2 Thermal analysis
Thermal and degradation properties of the cured prepreg were investigated using an SDT
Q600 TGA from TA Instruments, Delaware, US, on approximately 20 mg samples in a nitrogen
environment according to the heating profiles summarized in Fig. 2. Samples were heated from
ambient to either 550 °C or 650 °C, after which the samples were held isothermally for 30 min
before cooling to room temperature. A range of heating rates were used in this study. The
slowest heating rate was decided according to the common practice in lab-scale pyrolysis
studies on composite waste, which is between 10 and 30 °C/min (Onwudili et al., 2016; Song
et al., 2017), thus it was set to 20 °C/min. The highest heat rate was determined by the capability
of the TGA unit, i.e., 200 °C/min. Other selected heating rates were 80 and 100 °C/min, which
are common in fast pyrolysis studies on biomass (Wang et al., 2019) and coal (Jiang et al.,
2019). The weight loss profile of the degrading sample under these four different heating rates
was recorded. These tests were undertaken at a constant nitrogen gas flow rate of 50 ml/min.
However, in the later stage of the study, the nitrogen gas flow rate was increased to 100, 200,
and 400 ml/min with other process variables unchanged.
Char oxidation kinetics was studied by subjecting the neat epoxy to the same thermal cycles
as shown in Fig. 3 to create different grades of char. The gas flow was maintained at 50 ml/min.
The pyrolytic chars were later dried and subjected to an intrinsic reactivity test and SEM
analysis, as detailed below.
Figure 2. Thermal treatment profile used in TGA test
Figure 3. Effect of heating rates and pyrolysis temperatures on CFRP’s TG curves
2.3 Char analysis
The combustion characteristics of carbonaceous residue were determined using an intrinsic
reactivity analysis with nonisothermal heating in air (Unsworth et al., 1991). Pyrolytic char
samples were heated from ambient temperature to 105 °C inside an air-filled chamber at a
heating rate of 20 °C/min. The temperature was maintained for 30 min for moisture removal
and then ramped to 900 °C at the same heating rate to complete the intrinsic reactivity study.
Mass loss profile (TG) and the first derivative of the mass loss profile (DTG) were analyzed to
identify peak temperature (PT) and burnout temperature (BT) of the pyrolytic char sample. The
peak of the DTG curve was used to determine the PT value because it is defined as the
temperature at which the highest combustion rate occurs. The BT is defined at 1 wt%/minute
of combustion rate. A Zeiss@ Sigma VP scanning electron microscope was used to study the
morphology of pyrolytic char with a 10 kV accelerating voltage.
3. Results
3.1 Effects of heating rates and pyrolysis temperatures
TGA mass loss profiles are shown in Fig. 4, which clearly demonstrate that after a marginal
drop during early-stage heating, each of the profiles undergoes a sharp drop in mass before
finally reaching a plateau region. The initial drop was mainly due to moisture loss, while
conversion of the epoxy matrix into volatiles produced the sharp loss in mass and the rate of
conversion, which is accelerated at higher pyrolysis temperatures. A portion of the epoxy
matrix was converted into pyrolytic char and remained on the surface of the carbon fiber.
Together, they contributed to the final masses at the plateau region as shown in Fig. 3, which
vary with heating rates and pyrolysis temperatures. Because the carbon fiber reinforcement was
relatively unaffected by the pyrolysis process, the variations in final mass loss corresponded to
the extent of char retention.
Figure 4: Effect of heating rates and pyrolysis temperatures on CFRP’s mass loss
The variations in mass loss are further illustrated in Fig. 5, recalling the initial epoxy
loading of 36.4 wt%. A mass loss exceeding 36.4 wt% suggests degradation of the carbon fiber,
but a lower value indicates the presence of pyrolytic char. At 550 °C, a mass loss of 28.0 wt%
was recorded at 20 °C/min and a further 5 wt% reduction was achieved by ramping the heating
rate to 200 °C/min, which suggested the fiber residue entrained 3.5 wt% of char. Lower char
contents were obtained at the higher pyrolysis temperature of 650 °C and again, higher heating
rates resulted in greater mass loss, but the rate effects were lower than that at 550 °C.
Bridgwater and Peacocke (2000) have reported the significance of these two factors on the
mass distribution of char and volatiles from biomass, typically a higher heating rate and
pyrolysis temperature favored the production of gaseous products and the reverse conditions
favored char formation due to secondary coking and repolymerization reactions. These agree
with the findings reported in Fig. 4, and because the aim of the project is to reduce char
formation, this can be achieved with higher heating rate and/or increasing the pyrolysis
temperature from 550 °C to 650 °C. The former factor is preferable because higher
temperatures are likely to degrade the carbon fiber performance.
3.2 Effect of nitrogen gas flow rate
Fig. 5 shows the mass loss curve for prepreg at different nitrogen gas flow rates for two
different pyrolysis temperatures. It can be seen in Fig. 5(a) that at a pyrolysis temperature of
550 °C, more volatiles were released, or fewer char residues were left on the fiber when the
gas flow rate was increased from 50 ml/min to 200 ml/min for both 20 °C/min and 80 °C/min
heating rates. Higher flow rate suggests shorter residence time within the heating chamber for
volatiles and this reduces secondary reactions that promote char formation (El-Harfi et al.,
1999; Pütün et al., 2006; Uzun et al., 2007) or cracking of the primary volatiles and
repolymerization in hot char particles (Lanzetta et al., 1997). However, no further significant
mass loss was observed with gas flow rate higher than 200 ml/min. In contrast, the dependency
of mass loss on gas flow rate became less extensive at a heating rate above 100 °C/min.
Previous studies again support this finding, e.g., a shortened volatilesresidence time was
observed by Montoya et al. (2015) in depolymerization reactions of cellulose and
hemicellulose. In another case, which focused on pyrolytic behavior of rapeseed, Haykiri-
Acma et al. (2006) found that a higher heating rate reduced volatiles’ residence time, which
could further reduce secondary reactions such as cracking, repolymerization, and
recondensation. Our results are consistent with these studies because greater mass loss
accompanied higher heating rates and the volatiles’ residence time was expected to be greatly
reduced and become independent of nitrogen flow rate for a heating rate above 100 °C/min.
Similar tests on the effect of gas flow rate were repeated at a higher pyrolysis temperature
of 650 °C. However, as plotted in Fig. 5(b), a rather complex relationship is observed. At 20
and 80 °C/min heating rates, char mass loss increased gradually to 32.4% and 33.6%,
respectively, with increasing gas flow rate to 200 ml/min, but the mass loss started to decline
with further increase in flow rate to 400 ml/min. A general trend toward higher mass loss,
despite not being as evident as the results at 550 °C, can be identified for 100 and 200 °C/min
heating rates. Overall, the impact of the gas flow rate was less apparent at 650 °C.
Figure 5. Effect of nitrogen gas flowrate s on CFRP’s mass loss with (a) 550°C and (b) 650°C
pyrolysis temperature
3.3 Intrinsic reactivity analysis of char oxidation rate
Fig. 6 shows the effects of pyrolysis temperature and heating rate on chars’ intrinsic
properties; at either 550 °C or 650 °C, both PT and BT reduce with higher heating rates, which
indicates char resulting from higher heating rate was more reactive and could be oxidized at a
lower temperature. In addition, higher pyrolysis temperatures increased the BT value provided
the heating rate was less than 100 °C/min. Consistent with this, Chitsora et al. (1987) reported
such an effect in relation to German bituminous coal char produced in a fluidized bed, similarly
on lignite char by Ashu et al. (1978).
Figure 6. Effect of heating rates on intrinsic reactivity of char generated at 550 and 650 ºC.
3.4 Scanning electron microscopy
The effects of heating rates and pyrolysis temperatures on the morphologies of pyrolytic
char are depicted in SEM images shown in Fig. 7. It is evident that the combination of low
heating rate and low pyrolysis temperature, as shown in Fig. 7(a), created char with a rough
but continuous appearance. However, at 650 °C, as shown in Fig. 7(b), porosity became
apparent, increasing with higher temperature and heating rate. Fushimi et al. (2003) suggested
that a high heating rate caused a rapid evolution of volatiles, which in turn increased the porous
structure. Fast volatile release rate produced considerable overpressure, which encouraged void
coalescence and greater porosity levels (Guerrero et al., 2005). Septien et al. (2018) reported
that a high porosity level would enhance gas species diffusion within the char open structure,
which facilitated penetration of oxygen and better evacuation of reaction products from the
porous structure. Char created from the epoxy matrix in this study reinforced their findings
because a high intrinsic reaction was found from char with a high porosity.
Figure 7. SEM images of pyrolytic chars produced at different temperatures and heating rates
(a) 550°C, 20°C/min (b) 650°C, 20°C/min (c) 550°C, 200°C/min and (d) 650°C, 200°C/min
4. Discussion
Section 3 reported that a rapid heating rate caused a substantial reduction of pyrolytic char
volume, particularly for pyrolysis at 550 °C. The inert-gas flow rate was another contributing
factor to char yield and the level at which it affected the char content depended on the pyrolysis
temperature and heating rate. Higher gas flow rate promoted devolatilization and reduced the
char content provided the heating rate was less than 100 °C/min and the pyrolytic temperature
was 550 °C. However, the positive effect became insignificant at higher temperature and
heating rate. The intrinsic reactivity of the char was significantly influenced by the pyrolytic
reaction conditions. Char with higher intrinsic reactivity was associated with high heating rates
and temperature and this implied the char had a faster oxidation rate. These findings are of
commercial relevance to the carbon fiber recycling industry with high priority in cost control
because with a lower char volume and faster oxidation kinetics, the energy-intensive oxidation
process can be shortened and the carbon fiber can potentially be recovered with a higher
mechanical performance due to the compressed thermal cycle. The importance of recovery cost
and the reuse options available for the recovered carbon fiber will be discussed in subsequent
4.1 Recovery costs
Presently, there is no industrial-scale recycling of end-of-life turbine blades; therefore, the
costs and actual commercialization procedure have not been well-defined (Larsen, 2009).
Research on recycling and remanufacturing of these items is still ongoing. Pyrolysis is a mature
fiber recovery approach and has been considered suitable for mass-scale commercial efforts
use (Rybicka et al., 2016). Existing pyrolysis practices require size reduction and progressively
shorter fibers (and lower value) as the number of cycles increases. Thus, the hierarchy of
applications ranges from initial, continuous fiber composites, ultimately to milled fiber fillers
for lower grade structures. This potential circular economy flow is illustrated in Fig. 8.
Figure 8. Circular economy for end-of-life wind turbine blades
The materials CE loop sets some economic preconditions for the retrieval of carbon fibers.
At the initial stages, without a demand-side pull, legislative drivers, or standards in the reuse
of materials, private sector investments are unlikely. Furthermore, implementing recycling and
recovery comes at a price, including the collection costs, pretreatment and sorting costs, and
the costs of final recovery.
However, the market value of the recovered carbon fiber and concomitant by-products
could offset many of these costs. This is because the production process of virgin carbon fibers
is energy intensive, and incurs high manufacturing cost, especially in the case of high-grade
carbon fiber (used for structural applications such as blades). Therefore, there is a greater
economic incentive to recover these carbon fibers. Moreover, the costs of commercially
available fibers reclaimed through pyrolysis have been reported by industry sources to be about
10 Euros per kg while the market value of virgin product is 18–50 Euros per kg (ELG Carbon
Fiber, 2016).
Industry perspectives also agree that the cost to recover carbon fiber will be a fraction of
that for producing virgin carbon fiber (Carberry, 2008). The energy requirement to recover
carbon fibers (Cherrington et al., 2012; Vo Dong et al., 2018) is typically <10% that of virgin
fiber production1. Previous studies also highlighted the importance of throughput in reducing
the unit cost through a recycling plant (Meng et al., 2018). Clearly, the energy requirements,
efficiency, and cost associated with recycling the carbon fibers from blades would improve
beyond the current reported (laboratory) figures in mature, mass production settings.
4.2 Economic preconditions needed
As the technology for recovery and up-scaling of recycling continues to be developed,
there are four considerations that need to be addressed to enable the takeoff and growth in the
recovery of carbon fibers from end-of-life blades.
First, there must be a network to ensure a consistent supply of feedstock for fiber recovery
that would deliver economies of scale. The current lack of infrastructure for collecting end-of-
life blades is a key challenge. Ideally, recycling facilities should be located close to wind farms;
alternatively, mobile recycling units have been trialed in some regions. Sorting and
classification will also improve value streams. Nonstandard construction (Brøndsted et al.,
2005) means that traceability would help to identify ideal processing parameters, likely yield,
Second, a marketplace must be created for secondary or recovered materials (Stahel, 2013)
to centralize demand for recyclates or fibers produced. The market demand for the materials
will help to offset the cost of decommissioning and collecting end-of-life blades. The concept
of CE necessitates that there is a ready market to receive and reintroduce the recovered
materials into the economic cycle (Wang and Kuah, 2018). There could be an issue if the cost
of virgin materials is already low as in the case of glass fibers. The recovered materials must
have a value higher than the cost needed to retrieve them, i.e., using recovered fibers must be
cheaper than the cost of using virgin materials directly. This is the most likely case for carbon
The recent agreement in providing composite waste from Boeing’s aircraft manufacturing
facilities to ELG Carbon Fiber signaled both the value of composite waste supply and the
availability of a marketplace for the recovered fiber (Zazulia, 2018). Fiber recovered from the
manufacturing wastes and growing end-of-life parts can potentially help in mitigating the
1 286 MJ/kg (Suzuki and Takahashi, 2005) and 704 MJ/kg (Das, 2011)
shortage in virgin fiber supply, particularly in the demand for discontinuous fibers. Recyclers
have been developing scalable conversion technologies to enlarge the supply-side capacity for
recovered fiber. For example, a new hybrid nonwoven mat containing recovered carbon fiber
and polyamide 6 resin was developed for making seatbacks for the high-volume automotive
applications (Milberg, 2017). Driven by the affordability (Nicolais and Pisanova, 2012) and
more environmentally friendly recovery process, more reuse applications in the near future are
Third, quality standards for the fibers or recyclates must be established to build confidence
(Carberry, 2008; Finnveden et al., 2013; Job, 2013; Pickering, 2006; Wood, 2010). The design
of a product, the material retrieval system, efficiency of sorting, and the recovery technology
are fundamental in increasing the quantity, quality, and usability of recovered materials
(Gregson et al., 2015).
Fourth, key legislation and government policy intervention need to mandate both operators
and end-users into the reuse of recovered carbon fiber with accompanying fiscal penalties and
benefits. Cherrington et al. (2012) outlined some of the key examples of legislation and
directives relevant to end-of-life blades. Landfill and incineration disposal are increasingly
penalized (Cherrington et al., 2012) whilst R&D incentives for sustainable product design and
technologies that enhance the recycling process (Söderholm and Tilton, 2012) are increasingly
important. Extended Producer Responsibility (EPR) is another important initiative to
encourage further recycling, where producers play a more proactive role in supporting recovery
and reuse. EPR has been successfully utilized for end-of-life vehicles and waste electrical and
electronic equipment (Cherrington et al., 2012).
4.3 Recovered carbon fibers’ applications and considerations
Low-grade application:
Granulation of CFRP scrap requires the lowest energy of all recovery methods (Wong et
al., 2017). These recyclates can be sorted into resin-rich and fibrous-rich groups, but both have
low commercial value because the recyclates still contain a high level of resin residues, limiting
their usage to low-grade applications, such as being used as a filler for polymer resin or
construction materials (Thomas et al., 2014) and concrete (Mastali and Dalvand, 2016).
Medium-grade application:
To maximize the value of recovered carbon fibers, they should be separated from the
polymer matrix and the fiber should retain enough mechanical performance for the next
application. To date, this can be achieved via the common pyrolysis process and with the use
of adequate pyrolytic conditions; as discussed in this paper, cleaner and stronger carbon fibers
can potentially be recovered. However, blades are bulky, and to reduce logistical cost,
decommissioned blades are sectioned in situ to a manageable size for transportation to
recycling facilities, at which, further size reduction has taken place prior to feeding to the
pyrolysis process.
As a result, the recovered fibers are generally short and fluffy and cannot be processed in
the same way as the virgin fibers. To allow the fibers to reenter the circular economy system
at the highest possible quality, they should be converted into intermediate forms suitable for
industrial molding processes.
Nonwoven mat is a common intermediate form widely offered by the recycling industries,
which can be made by carding and spinning or papermaking. Both are cost-effective processes,
suited to mass volume production and with versatile combinations of thermoplastic filaments
or powders suitable for thermoforming (Wolling et al., 2017). Because of the random
orientation of fibers, the fiber packing density is limited to around 30% (Wong et al., 2017).
Nonwovens are typically used in nonstructural applications, such as tooling for aerospace parts
(Gardiner, 2014), heating elements (Pang et al., 2012), and electromagnetic interference
shielding (Wong et al., 2010).
Higher-grade application:
Fiber alignment is a necessary intermediate step for higher-value applications because the
presence of a close-packed structure greatly increases the reinforcing potential of the fibers.
Hydrodynamic alignment was originally developed in the 1970s (Bagg et al., 1977) but more
recent innovations (e.g., van de Werken et al., 2019; Wong et al., 2009) optimize streamline
velocities to deposit an aligned fiber slurry onto a moving mesh. Clean, free-flowing filaments
are essential here, underlining the need for a char-free feedstock, because char carryover
inhibits uniform dispersion, hence the need for upstream control of pyrolytic conditions, as
reported here.
Other alignment technologies include electrostatics (Ravindran et al., 2018), air streaming
(Ericson and Berglund, 1993), and the dry carding process (Miyake and Imaeda, 2016). Fiber
alignment plays an important role in upgrading the value of the recovered carbon fiber but,
clearly, production economics remains to be established for any of these secondary operations.
5. Conclusions and Recommendations
This paper is the first to consider urban mining of carbon fiber from end-of-life wind turbine
blades to close the CE loop. Using the concept of CE in reusing, repurposing, recycling, and
recovering, this paper investigates CFRP recovery and the quality of the recovered materials.
Our investigation revealed that pyrolytic reaction conditions were important in controlling
char formation volume and its oxidation rate. A rapid heating rate caused a substantial
reduction of pyrolytic char volume, particularly for the pyrolysis process undertaken at 550 °C.
Nitrogen gas flow rate also affected the char content at a specific combination of pyrolysis
temperature and heating rate. At 550 °C and less than 100 °C/min heating rate, a higher gas
flow rate favored the devolatilization process and reduced the char content. High heating rate
and pyrolysis temperature produced char with higher intrinsic reactivity, suggesting a faster
oxidation rate. This is beneficial to shorten the post-processing step, thereby leading to lower
energy costs. These findings are of commercial significance to the carbon fiber recycling
industry with high priority in cost control as with lower char volume and faster oxidation
kinetics, and hence the carbon fiber can potentially be recovered with a higher mechanical
performance due to the shortened thermal cycle.
Creating a market and closing the CE loop requires several issues to be overcome so that
recovered carbon fibers can be accepted as an environmentally friendly, reliable, and cost-
effective material. The industry would require establishment of standards for the recycled
carbon fiber products and to regulate pyrolysis operations. In addition, a labeling scheme such
as those used in recycled plastics would yield greater user acceptance and support. This
addresses the demand-side conditions. Further fiscal incentives and penalties by governments
would also push the supply side so that companies might engage more responsibly in closing
the circular loop.
Our investigation also identifies scope for future studies. This investigation looked into
maximum carbon recovery for first-time recycled carbon fiber. Carbon fiber physical and
mechanical properties will degrade over time after multiple thermal treatments, hence affecting
their reuse value. Therefore, a more detailed study is recommended to encompass this complex
scenario of having different stages of recovered fiber content to ensure long-term sustainability.
Second, the thermal pyrolysis of carbon fiber produces two other by-products—oil and gas
that have good calorific and some economic value. Clearly, further study of these by-products
would assist a full loop recycling solution for the composite wastes.
The experimental work was done in the “ACC TECH-UNNC joint laboratory in Sustainable
Composite Materials”. The authors would like to acknowledge the financial supported by
Ningbo S&T Bureau Industry collaboration Project (project code 2017D10030), and Ningbo
3315 Innovation team Scheme “Composites Development and Manufacturing for Sustainable
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... In RE policies, the government needs to mandate the cost of project decommissioning after a 25-30-year lifespan for the developer, for example, collecting 78 million tons of PV panels or recycling 43 million tons of wind turbine blades by 2050 (USAID 2021). Possible solutions are lifetime extension or increasing funding for research in raising the recovery rate of decommissioned equipment, according to the 4R principle in CE: reusing,repurposing,recycling,and recovering (or reusing,remanufacturing,refurbishment,repairing,or even 6Rs,namely: reuse,recycle,reduce,recover,remanufacture and redesign) (Mutezo and Mulopo 2021;Hao et al. 2020). CE is related to processes such as Manufacturing, Supply Chain Management, Biogas for Electrification, and Waste Management (Hao et al. 2020). ...
... Possible solutions are lifetime extension or increasing funding for research in raising the recovery rate of decommissioned equipment, according to the 4R principle in CE: reusing,repurposing,recycling,and recovering (or reusing,remanufacturing,refurbishment,repairing,or even 6Rs,namely: reuse,recycle,reduce,recover,remanufacture and redesign) (Mutezo and Mulopo 2021;Hao et al. 2020). CE is related to processes such as Manufacturing, Supply Chain Management, Biogas for Electrification, and Waste Management (Hao et al. 2020). ...
This chapter provides a comprehensive overview of global policies pertaining to the circular economy and renewable energy. The concept of a circular economy, which aims to minimize waste and maximize resource efficiency, has gained significant attention in recent years. Simultaneously, the importance of renewable energy sources in mitigating climate change and ensuring sustainable development has become increasingly evident. This study examines the interplay between these two critical areas and explores the policies implemented to promote their integration. By analyzing key initiatives and strategies, this paper aims to shed light on the current state of global policy frameworks and identify potential areas for improvement. It contributes to a better understanding of the challenges and opportunities associated with transitioning towards a more sustainable and energy-efficient future.
... Thermal recycling processes cover the processes where the polymers in the matrix are decomposed under high temperature, high pressure, and no oxygen, such as pyrolysis [28]- [30] and microwave [24], and fluidized bed technology [31]. Pyrolysis has received increasing interest in academic literature since the process allows for the separation of cured resin and glass fibers. ...
... The process produces multiple products with multiple applications in other industries. However, the pyrolysis processing technology is yet to be tested on an industrial scale for WTB waste [28]. In the majority of the reviewed studies, fiber recycling is considered, but upcycling of higher-value products, e.g., fuel and chemicals, is scarcely investigated [32]. ...
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This study presents a sustainable end-of-life (EoL) value chain scenario assessment framework for decommissioned wind turbine blades (WTBs) to address the challenge of increased volumes of WTBs reaching their EoL. Findings from the previous studies highlight that WTBs EoL scenarios and their upscaling are yet to be addressed environmentally and economically. The scenarios investigated herein are mechanical shredding, pyrolysis, and cement co-processing that can be industrially upscaled. Together with the industrial partners, end-of-life scenario value chains are identified, to assess their sustainability through material flow analysis (MFA), life cycle assessment (LCA), and techno-economic assessment (TEA). A prospective consequential LCA model is proposed for scenarios with different technology readiness levels (TRL) expected to be commercialized at different timeframes. IPCC’s Shared Socio-economic Pathways (SSPs) will be used to describe foreground and background systems in 2030, 2040, and 2050. More specifically, SSP1 (i.e., green road), SSP2 (i.e., middle road), and SSP5 (i.e., fossil-fueled development) will be employed and quantified based on integrated assessment models (IAM). Furthermore, environmental impacts, economic criteria, Social sustainability, and circularity cannot directly be compared to evaluate the scenarios. Thus, this research proposes multi-criteria decision-making (MCDM) method to evaluate the three end-of-life scenario value chains considering a prospective scheme and addressing the key challenges related to the assessment of emerging technologies. Furthermore, a full conceptual framework of the methodology is presented.
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... Accounting and assessment of production waste generation usually is not carried out due to its absence at an operational stage. However, a significant part of waste, including industrial waste, is generated at the stage of shutdown or reconstruction of energy facilities, which is especially important for solar and wind power facilities [14,15,[34][35][36][37]. ...
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The need to reduce the negative environmental impact of energetics with the growing energy demand in the world is the core objective of the industry for the upcoming decades. The global agenda in the field of environmental protection increases the requirements for evaluation of the energy investment projects, in particular for their environmental efficiency. Currently, much attention is paid to assessing the impact of the project on atmospheric air, water bodies and land resources, including the formation of industrial waste during the operational stage. The formation of production and consumption waste at other stages of the project life cycle is not considered either when generating cash flows or when conducting the assessment pf environmental efficiency. It might significantly reduce the reliability of assessment results. The purpose of this study is to develop a system of integrated accounting for all types of waste generated and the environmental costs incurred for handling them during the environmental and economic assessment of energy projects. The paper discusses modern waste management practices at energy enterprises, waste generation at various stages of investment projects implementation, and provides recommendations on waste accounting when assessing their environmental and economic efficiency.
... (Cole, 2011;Johl & Toha, 2021;Kirchherr et al., 2017;Salesa et al., 2022;Stahel, 2016;Tisserant et al., 2017;Worldwathc Institute, 2008;Xiang et al., 2020) Sectorial applied approach Circular applied proposals are considered for adapting different sectors to the CE, such as Agriculture, Construction, Energy, Real Estate or banking sector. (Gubeladze & Pavliashvili, 2020;Hao et al., 2020;Ikiz Kaya et al., 2021;Norouzi et al., 2021;Salesa et al., 2023) ...
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The role of commercial banks and financial institutions has been described as crucial for the circular economy since they are key actors in financing companies and projects. The facilitating potential of some financial instruments managed by the financial sector has not been studied in connection to extending the circular economy in the environmental accounting framework. Particularly, the renting contracts service, which has been associated with more sustainable performance, shows interesting circular characteristics for servitization and the sharing economy. By studying the details of renting contracts of a financial institution over 18 years as a case study in Spain, this research demonstrates how this type of service, applied to vehicles, can render important benefits in terms of use of resources, environmental impact, energy efficiency and reduced carbon emissions. Measuring these quantitative impacts and reporting about them is important from an environmental accounting basis and in the framework of the European Union taxonomy for sustainable finance. The results obtained from the stakeholders’ perspective highlight the pivotal role of existing financial instruments and the need for new metrics for reporting linked to the servitization of the economy as a specific circular issue. This paper contributes to the academic literature by bringing empirical results to a still recent line of research. For practitioners, we provide innovative metrics for circular economy in the financial sector, and for policymakers, this research highlights the wider role of financial institutions in promoting circular economy within the sustainability framework.
The term “green human resources management” refers to the application of human resources management techniques to support environmentally sound behaviour and heighten employee dedication to environmental sustainability. The circular economy, green human resource management, and the push for “zero waste” have all received a lot of attention in the previous 10 years as major approaches to addressing environmental challenges. Furthermore, without being impacted by outside variables like market demand, competitor commitment, or technical support for circularity, green human resource management helps the move to a circular economy. Business is crucial to this change, and an increasing number of organizations have made sustainability commitments that include waste reduction goals. The various green human resource management techniques, including green hiring, green training and engagement, and green performance management and rewarding, all have a unique impact on an organization’s success. Tools for sustainable consumption and production have been cited as both supporters of circularity and the accomplishment of sustainable development objectives. The highlighted practices included green employee empowerment and involvement, green incentive and compensation, green performance management and appraisal, green training and development, and green management of organizational culture. However, little research has been done on how green human resource management might aid in the shift to a more circular economy. Therefore, research is required to evaluate how green human resource management affects the circular economy, economic strength, and environmental reputation of a business.
This chapter explores the concept of energy decarbonization and its practical implementation through the adoption of a circular economy (CE) founded on materials. It emphasizes the role of CE principles in mitigating environmental impacts as it analyzes the crucial interplay between energy transition and resource management. In pursuance of decarbonized energy systems, the focus of the discussion is on how CE strategies can mitigate resource scarcity issues. Important considerations include end-of-life management, tradeoffs, and the incorporation of principles of environmental justice. The chapter emphasizes waste reduction and repurposing of abandoned industrial sites as opportunities to reduce environmental costs. It also investigates the potential for technological innovations such as automation and artificial intelligence to improve recycling processes. Policymaking, regulation, and research and development efforts are discussed as essential catalysts for the realization of a CE-focused energy decarbonization strategy. This chapter highlights the global and cross-sector nature of this initiative, as well as its potential to revolutionize resource management while advancing sustainability objectives.
Re-purposing the foundations of older wind turbines to install new and larger wind turbines can reduce the investment costs and carbon emissions of wind energy development projects. In this paper, detailed numerical modeling is used to assess the behavior of a shallow foundation designed for a 5 MW wind turbine under the aerodynamic loads and seismic motions of larger replacement wind turbines. The finite element modeling scheme used for the soil under rocking foundations is validated based on experimental data. Results of this study indicate that maximum gapping and maximum tilting have similar trends of increase with increasing turbine power. Relaxing the no-uplift rule for normal operation conditions allows for installing an 8 MW wind turbine on the foundation designed for 5 MW, without compromising the foundation safety or serviceability requirements. However, the foundation does not perform satisfactorily with the 10 MW wind turbine. The no-uplift rule of design regulations for operational conditions is overly conservative. The limits of capacity increase for individual projects can be determined using the procedure presented in this paper.
Conference Paper
Wind energy has grown in popularity and concomitantly so has the installation of wind turbines. As both alternative and green sources of energy, many may assume that wind energy is replacing fossil fuels such petroleum and natural gas and leading us to a more sustainable future. While renewable energy is part of the sustainability equation, another common attribute of achieving sustainability is the localization of production and consumption. In many ways, this almost automatically occurs with wind turbines because electricity does not transport well over long distances. However, despite this characteristic of electricity, it does not mean that electricity cannot be exported, especially when political geographies are considered. Indeed, this research will examine the U.S. state of South Dakota to demonstrate that wind-generated electricity can be treated from an economic point of view as an export commodity despite any local benefits that it generates. By examining statistics for electricity generation, it will be seen that wind energy is doing much more than replacing local electricity generation by fossil fuels. Further examination will show that a significant amount of wind-generated electricity in South Dakota is exported outside the state.
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While attention on the importance of closing materials loops for achieving circular economy (CE) is raging, the technicalities of doing so are often neglected or difficult to overcome. However, these technicalities determine the ability of materials to be properly recovered and redistributed for reuse or recycling, given the material, component and product (MCP) state and functionality. Materials have different properties that make them useful for various functions and purposes. A transition, therefore, towards a CE would require the utmost exploitation of all available routes that MCPs can be diverted to, based on their design, use and recovery; ideally, enabling a perpetual looping of them in the economy. Yet, this is difficult to succeed. In the present short communication article, the authors explain how the quality and the way it is meant at different stages of the plastic packaging supply chain affects their potential recycling; and outlines the opportunities and constraints offered by some of the changes that are currently introduced in order to improve their circularity. The purpose of this article is to underpin the need for research that integrates systemic thinking, with technological innovations and regulations at all stages of the supply chain, in an effort to promote sustainable practices to become established.
Recycled carbon fibers cost a fraction of virgin fibers and their composites can potentially achieve mechanical properties suitable for a wide range of applications. When recycled, carbon fibers usually become millimeter to centimeter long and emerge as a tangled mass analogous to cotton candy. In this work, recycled carbon fibers were processed into unidirectionally aligned and two-dimensional randomly oriented recycled carbon fiber mats. The surface of the recycled carbon fibers was probed to understand the significance of surface characteristics on the mechanical behavior of recycled carbon fiber composites. Tensile testing was used to determine the influence of fiber surface quality, aspect ratio, and alignment on mechanical properties of the composites. It is concluded that the processing has a significant effect on the properties of recycled fiber composites. An analytical model was validated and subsequently used to provide insight into viable methods for improving mechanical properties in recycled carbon fiber composites. The article can be downloaded for free until March 21, 2019 by following the share link,UwqXNFeO
The chemical properties, pyrolysis behaviors and pyrolysis product distributions of Shenmu (SM) coal were investigated by proximate and ultimate analysis, thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy (TG-FTIR) and Pyrolyzer coupled with gas chromatography/mass spectrometry (Py-GC/MS). The results of the proximate and ultimate analysis indicated that SM coal had less saturated aliphatic structures and more polar components. The coke yield for SM coal during pyrolysis process at 100 °C/min, 300 °C/min, and 500 °C/min was 65.60%, 64.19%, and 63.15%, respectively, which indicating that the increment in heating rates could promote the production of volatile substances. Moreover, there was a lateral shift to high temperature of TG/DTG curves when the heating rates increasing. The main volatile species detected from FTIR in the pyrolysis of SM coal were CO2, CO, CH4, C2H4, C²⁺ aliphatics, light arenes, C–O bond containing species and C[dbnd]O bond containing species. Since the difference in the temperature intervals of those volatile species released, the sources of cleavage or chain scission during pyrolysis process were not the same. According to the fast pyrolysis by Py GC/MS, the volatile species could be divided into eleven species including alkenes, cycloalkenes, alkanes, cycloalkanes, aromatics, phenols, ethers, ketones, alcohols, N-containing species, and other species. The relative contents of alkenes and alkanes were dominant regardless of the variegation of heating rate, residence time and pyrolysis final temperature. Furthermore, the trend of each species under different influence factor conditions achieved different tunes rendered with equal skill.
Wind energy has developed rapidly over the last two decades to become one of the most promising economical and green sources of renewable energy, responding to concerns about use of fossil fuels and increasing demand for energy. However, attention is now turning to what happens to end-of-life wind turbine waste, and there is scrutiny of its environmental impact. In this study, we focus on one aspect of this, the blades. We analyse and compare end-of-life options for wind turbine blade materials (mainly glass fibre reinforced plastic and carbon fibre reinforced plastic) in terms of environmental impact (focusing on energy consumption), using our own data together with results gathered from the literature. The environmental impacts of each end-of-life option are discussed, looking at processing energy consumption, the recycling benefits and the effect of blade technology development trends. There is considerable variability in the results, and lack of consensus on predictions for the future. We therefore analyse the results using a range of different scenarios to show how the ‘optimal’ solutions are influenced by trends in blade composition and end-of-life process development. The most environmentally favourable process is dependent on whether the materials used for the blades are glass fibre composite or carbon fibre composite. The extent to which process improvement might affect the viability of different end-of-life processes has been assessed by looking at ‘crossover’ points for when the environmental impact becomes favourable. This analysis gives new insight into areas where research into process technologies could be targeted to enable significant end-of-life environmental benefits.
In the last few years the idea of circular economy has become essential. Thus, designing methods of nutrients removal should be based on using materials that make it possible to recover those nutrients. Recently, methods applied in wastewater treatment plants cannot provide optimal results; moreover, the application of commercial coagulants like ferric chloride and polyaluminum chloride can cause difficulties in potential recovery of phosphorus from sludge. Sorption materials, both natural and modified, are appearing as successful for wastewater treatment, especially for treatment wetland effluent. To pursue circular economy principles, the capacity of waste materials needs to be tested with regard to nutrients removal. If in addition a possibility to recover them appears, it will be possible to close the circuit. The aim of the investigation, according to HELCOM and EU Water Framework Directive recommendations, was to explore the possibility of ensuring good and stable quality of effluent by the application of natural materials for phosphorous removal with possible minimum energy and material consumption. The objective was to determine the sorption capacity of two selected materials (waste material and chemically modified material) in steady conditions. The research focused also on the time of mixing, a period of sedimentation of absorbent materials, and the influence of used materials on the basic parameters of the solution: pH, temperature, total suspended solids, conductivity, turbidity, and color. M1 was a waste material after thermal treatment of carbonate-siliceous rock in temperature above 700 °C (Rockfos®). Material M2 was lanthanum-modified bentonite, a material of anthropogenic origin. Both selected materials have shown a high ability to reduce phosphates concentration in synthetic wastewater. Sorption capacity of materials M1 and M2 were 45.6 mg/g and 5.6 mg/g, respectively.
The high cost and energy intensity of virgin carbon fibre manufacturing constitute a challenge to recover substantial value from carbon fibre reinforced polymers (CFRP). The objective of this study is to assess the environmental and financial viability of several waste management processes for CFRP. Life cycle costing and environmental assessment models are developed to quantify the financial and environmental impacts of waste treatment pathways comparing a panel of recycling techniques that are now available (grinding, pyrolysis, microwave and supercritical water) and that can be used to substitute different grades of both carbon and glass fibres by recycled carbon fibres at competitive prices compared to landfill and incineration. GWP assessment promotes recycling activities by recovery of carbon fibre due to the high avoided impacts from substitution of virgin fibre, thus highlighting the high interest of recycling over conventional production for environmental purpose. Fibre recovery rate and recycling capacity are pivotal to decrease the unit cost of recycled fibre as well as GWP impacts. The advantages and drawbacks of each technique are analysed through economic and environmental indicators, to better understand the network configuration for optimisation purpose of waste management pathway in a holistic viewpoint.
This study describes the hydrolysis of glass fiber reinforced unsaturated polyester (UP) composites using some of the most employed and efficient additives from the literature. This includes the use of KOH, a mix of KOH/phenol and reference experiments without additives. Sub-critical water in a temperature range of 200–325 °C and a constant pressure of 300 bar were chosen as process parameters to cover a wide temperature range. It was possible to explain the mechanisms producing the majority of the different reaction products identified by GC-MS. The monomer phthalic anhydride was only recovered in the experiments without additives and was most stable at 200–250 °C. The increase or decrease in the production of monomers and other reaction products at different temperatures with and without additives has been clarified by the GC-MS investigations, which introduces new possibilities for tailoring the production of monomers and various chemical compounds via hydrolysis of polymer composites.
The pyrolysis of the Tarfaya (Morocco) oil shale was carried out in a modified Fisher-assay-type apparatus using either nitrogen or steam as a sweeping gas. Differences were observed in the yield and the composition of the obtained oil. Pyrolysis under water vapor gave an increase in the yield as opposed to pyrolysis under nitrogen. In addition, the oils obtained are more paraffinic. Furthermore, the presence of water vapor considerably reduced the amount of sulfur in the residues. Increasing the flow rate of water vapor leads to an increase in the total yield and the amount of paraffins, aromatics and aspahaltenes, and a decrease in the amount of polar compounds.