Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong

Waste Management xxx (2017) xxx–xxx

Contents lists available at ScienceDirect

Waste Management journal homepage: www.elsevier.com/locate/wasman

Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong Md. Uzzal Hossain, Zezhou Wu, Chi Sun Poon ⇑ Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

a r t i c l e

i n f o

Article history: Received 21 February 2017 Revised 8 June 2017 Accepted 30 July 2017 Available online xxxx Keywords: Building construction waste Environmental evaluation Life cycle assessment Waste sorting systems

a b s t r a c t This study aimed to compare the environmental performance of building construction waste management (CWM) systems in Hong Kong. Life cycle assessment (LCA) approach was applied to evaluate the performance of CWM systems holistically based on primary data collected from two real building construction sites and secondary data obtained from the literature. Different waste recovery rates were applied based on compositions and material flow to assess the influence on the environmental performance of CWM systems. The system boundary includes all stages of the life cycle of building construction waste (including transportation, sorting, public fill or landfill disposal, recovery and reuse, and transformation and valorization into secondary products). A substitutional LCA approach was applied for capturing the environmental gains due to the utilizations of recovered materials. The results showed that the CWM system by using off-site sorting and direct landfilling resulted in significant environmental impacts. However, a considerable net environmental benefit was observed through an on-site sorting system. For example, about 18–30 kg CO2 eq. greenhouse gases (GHGs) emission were induced for managing 1 t of construction waste through off-site sorting and direct landfilling, whereas significant GHGs emission could be potentially avoided (considered as a credit 126 to 182 kg CO2 eq.) for an on-site sorting system due to the higher recycling potential. Although the environmental benefits mainly depend on the waste compositions and their sortability, the analysis conducted in this study can serve as guidelines to design an effective and resource-efficient building CWM system. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction A considerable amount of construction and demolition (C&D) waste is generated globally. So far, the majority of the C&D waste is landfilled without any further treatment (Bovea and Powell, 2016). Nevertheless, C&D waste could be reused as raw materials for the manufacturing of secondary materials/products (Rodrigues et al., 2013). Recycling and reusing of C&D materials has a twofold beneficial effect of avoiding landfill disposal and conserving non-renewable natural resources (Vieira and Pereira, 2015). Thus, high priority has been given to C&D waste minimization from both waste management and resource efficiency perspectives (Pacheco-Torgal et al., 2013). The management of C&D waste has received increasing attentions from both practitioners and researchers worldwide, as resource efficient management is a challenging issue globally (Lu and Yuan, 2011; Yuan and Shen, 2011). However, C&D waste is not effectively managed in many countries (Cheng and Ma, ⇑ Corresponding author. E-mail address: [email protected] (C.S. Poon).

2013). There are substantial opportunities for improving C&D waste management in terms of technical, environmental and economic points of views (Bovea and Powell, 2016). The effective and efficient minimization of building construction waste is a challenging issue (Tam, 2008; Wu et al., 2016). Waste sorting is considered one of the most effective measures for waste minimization and materials recovery (Saez et al., 2013). During the waste sorting process, different waste fractions are sorted and recovered before the residuals are sent for disposal (Lu and Yuan, 2012). But most building construction participants are reluctant to conduct on-site waste sorting in Hong Kong (Poon et al., 2013). In addition, Yu et al. (2013) showed that the use of waste reduction practices on building construction sites in Hong Kong is still not common even after the implementation of construction waste disposal charging scheme. In order to support the decision making process on the selection of effective and resource-efficient CWM, the evaluation of environmental performance of CWM through different sorting systems using life cycle assessment (LCA) technique is therefore necessary. The LCA approach following the guidelines provided by ISO 14040-44 has increasingly been used to identify strategies that

http://dx.doi.org/10.1016/j.wasman.2017.07.043 0956-053X/Ó 2017 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043

2

M.U. Hossain et al. / Waste Management xxx (2017) xxx–xxx

may improve the environmental performance of waste management systems (ISO, 2006a, 2006b). Recently, LCA techniques have been widely applied to the C&D waste management sector, especially for materials recovery and reuse (e.g., Hossain et al., 2016a, 2016b; Butera et al., 2015; Dahlbo et al., 2015; Kucukvar et al., 2016). Mercante et al. (2012) conducted an LCA study on C&D waste management systems with emphasis on inert waste processing and treatment facilities. An overview of C&D waste management using LCA was conducted by Yeheyis et al. (2013). Dahlbo et al. (2015) assessed the environmental and economic performance of the common C&D waste management system in Finland in order to identify the recycling potential of materials to meet the overall EU target (70%) by 2020. Butera et al. (2015) assessed the environmental performance of utilizing C&D waste as road based materials. A review on the application of LCA methodology to overall C&D waste management, recycling and applications was conducted by Bovea and Powell (2016). Mastrucci et al. (2016) used the LCA approach to develop a framework of building material stocks and the potential environmental impact of end-of-life of buildings at the urban scale as a supporting decision tool. Rodrigues et al. (2013) assessed the mineralogical and physicochemical properties of recycled aggregates generated from C&D waste. In addition, Neto et al. (2016) analyzed the economic viability of different types of processing (e.g., sorting) in C&D waste recycling platforms. From the above review of the literature, most studies assessed the environmental performance of materials recycling and utilizations for secondary applications. But little has been done on assessing the use of different waste sorting strategies on the environmental performance of building CWM systems. To bridge this research gap, this study focuses on evaluating the environmental performance of different building CWM systems incorporating different sorting strategies using Hong Kong as a case study. 2. Construction waste management systems in Hong Kong A huge amount of C&D waste is generated each year in Hong Kong. According to the Hong Kong Environment Protection Department (HKEPD), about 58,000 tonnes per day of C&D waste was generated in 2014, of which 93% was delivered to public fill reception facilities (for land reclamation), and 7% was sent to landfills (for landfill disposal), and the latter made up 27% of the total landfilled waste in Hong Kong (HKEPD, 2015). As a result, the management of this kind of waste is becoming a serious problem in Hong Kong because both of the disposal outlets (public fills and landfills) are running out. In Hong Kong, C&D waste is categorized into inert (such as soil, sand, bricks and concrete, which is disposed of at public fills for land reclamation) and non-inert materials (e.g., wood and timber, bamboo, plastics, glass, paper, and other materials, which is disposed of at landfills) (Poon et al., 2001). Usually, C&D waste is a mixture of inert and non-inert construction materials, thus waste sorting is a good practice before it is disposed of in landfills or public fills, respectively (Lu and Yuan, 2012). Three strategies can be used for CWM, i.e., off-site sorting, on-site sorting and direct landfilling (without sorting). The typical C&D waste management structure in Hong Kong is shown in Fig. 1. 2.1. Building CWM system through off-site sorting In Hong Kong, the most common form of waste sorting of building construction waste is by off-site sorting (Lu and Yuan, 2012). The off-site sorting process is presented in Fig. 2. First, contractors send mixed waste materials from construction sites to off-site sort-

C&D waste generation

> 50% inert

< 50% non-inert On-site sorting

Off-site sorting

Mixed waste

Landfill disposal

X-inert waste

Public fill disposal

Inert waste

X-inert waste Inert waste

Materials recycling Fig. 1. C&D waste management structure in Hong Kong.

Construction waste generated at building construction sites Mixed construction waste Transport

Off-site sorting facilities Manual sorting Vibratory grizzly feeder (VGF) Magnetic separator Heavy duty scalping screening Rotary trommel screening Sorting by hand picking (to remove non-inert waste)

Wood, timber, plastic, paper, etc.

Landfills

To remove ≥ 250 mm waste

Public fills

Metallic waste

Recycling

To remove ≥ 150 mm waste

Public fills

To remove ≥ 50 mm waste

Public fills

To remove noninert waste

Landfills

Inert waste (<50 mm)

Public fills

Fig. 2. Building CWM through off-site sorting in Hong Kong.

ing facilities, in which inert and non-inert waste materials are separated. However, the sorting facilities only accept construction waste which contains more than 50% of inert materials (by weight) with the purpose of maximizing its service efficiency (Lu and Yuan, 2012). After receiving by the sorting facilities, the mixed waste goes through several manual and mechanical processes (Fig. 2). The separated inert and non-inert waste fractions are then disposed of at public fill sites and landfill sites, respectively. 2.2. Building CWM system through on-site sorting On-site sorting is considered as an effective approach to manage building construction waste, as it could increase the reuse and recycling rates and reduce associated disposal costs (Poon et al., 2001; Hao et al., 2008; Wang et al., 2010). When implementing on-site sorting, the workers separate the generated building waste at source in order to prevent waste being mixed. Yuan et al. (2013) described several on-site management strategies for sorting building construction waste: (i) recyclable waste such as paper, cardboard, plastics and aluminum cans are collected and transferred to designated recycling bins, (ii) inert waste is collected and transported to a designated area after some preliminary source separation on each construction floor, (iii) other non-inert waste

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043

3

M.U. Hossain et al. / Waste Management xxx (2017) xxx–xxx

Construction waste generation at construction sites

Store in open place or in large containers Recyclable waste

Direct reuse (on-site)

Transport to recycled plant for processing

Landfills Public fill reception facilities

Collect and transport of separated waste

Non-recyclable waste

Source separation by workers (hand picking and mechanical handling)

Fig. 3. Building CWM system through on-site sorting in Hong Kong.

with no recyclable values are collected and transported to waste skips. Different bins and containers are required to be placed at specific areas around the site. An illustration of the common onsite sorting arrangement is shown in Fig. 3. 2.3. Direct landfill Construction waste containing more than 50% non-inert materials would be sent directly to landfills for disposal (existing practice in Hong Kong). The stored mixed waste generated from building construction activities is transported to landfill sites directly without any treatment (after retrieving of metallic waste if any) for disposal. 3. Methodology

management practices (e.g., storage, on-site and off-site sorting, recycling, etc.), waste handling and transportation, methods of waste disposal, etc. The compositions of the waste generated from the two sites were quantified using detailed manual sorting and weighing. The waste can be broadly classified into inert (soil, rock, concrete, aggregate, brick, tiles, etc) and non-inert waste. The noninert waste was then sub-grouped as wood and timber (included bamboo), metals, paper and cardboard, plastic and rubber, and others (e.g. domestic waste, glass, textile, etc) (shown in Fig. 4 and Table 1). An example of the generated and sorted waste in both sites is illustrated in Fig. 5. Based on the off-site sorting process being practiced at a waste sorting facility (described in section 2.1), the material flow processes of the wastes generated from Sites 1 and 2 are given in Fig. 6 when they are sent to the off-site sorting facility. However, if on-site waste sorting process (described in Section 2.2) is practiced, the material flow processes of the wastes generated are shown in Fig. 7 (where recycling indicates the recovery of materials to be reused in producing the secondary materials or products). Several assumptions were made in this LCA study: (i) the energy consumption for manual/mechanical handling during on-site sorting, and on-site handling (including onsite transport) for storing towards transporting to off-site sorting and landfill sites were considered as normal construction activities and practice, and thus was excluded from this analysis; (ii) about 50% of the recovered materials from on-site sorting can be recycled (based on the on-site sorting practice at the both construction sites). However, it can be varied based on the materials due to the process of construction. Therefore, the results of the influence of materials recovery rate for on-site sorting system were also evaluated; (iii) no material can be recovered from off-site sorting and direct landfilling except metals (current practice), and (iv) 100% of the metals can be recovered for all scenarios. The influence of recovery rates on the net environmental profile has also been assessed.

In order to evaluate and compare the environmental performance of the above-mentioned building CWM systems, a case study was conducted using two real building construction sites with the following three scenarios: Scenario 1 – CWM through off-site waste sorting system (existing system) Scenario 2 – CWM through on-site waste sorting system (proposed system) Scenario 3 – CWM through direct landfilling (existing system) Specific waste sorting practices can vary from one site to another, depending on the compositions of the waste, and the compositions can also vary with different stages of the construction process. Therefore, two residential building construction sites (namely, Site 1 and Site 2) were used as cases in this study, in which Site 1 was at the finishing stage and Site 2 was at the mid stage of construction. The construction of nine blocks of low-rise 7 to 11-storeyed building with commercial podium, clubhouse, basement car park and associated external works were included in Site 1. The site was located at the eastern part of Hong Kong. The construction of five blocks of high-rise 40-storeyed building was included in Site 2, and was located at the western part of the city. Several visits were conducted at both sites in order to identify and estimate the sources, types and quantities of waste, and scrutinize waste

Type of waste (%)

3.1. Evaluation of building CWM systems

80

Inert waste

Non-inert waste

61.9

61.5

60 40

38.5

38.1

20 0 Site 1

Site 2

Fig. 4. Compositions of building construction waste.

Table 1 Compositions of non-inert waste generated from two building construction sites. Waste material

Wood and timber Plastic and rubber Metals Paper and cardboard Others

Composition (%) Site 1

Site 2

51.2 8.1 17.1 13.4 10.2

86.9 1.5 8.4 0.6 2.6

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043

4

M.U. Hossain et al. / Waste Management xxx (2017) xxx–xxx

Site 1

Sorted waste

Site 2

Sorted waste

Fig. 5. Generated and sorted waste in Sites 1 and 2.

(Fig. 8). The substitution approach due to the utilization of recovered waste materials was used in the LCA study.

3.2. Aim and scope of the study This study aimed to compare the environmental impacts of building CWM in Hong Kong through different waste sorting systems. The study included all stages of the life cycle of building construction waste, i.e., from its generation (building construction sites) to its disposal in landfills or public fills, and its transformation into recycled materials and valorization into secondary products/materials. Hence, the considered system boundary was ‘cradle-to-grave’ with a reference flow of 1 t of construction waste

Waste generation at construction sites Mixed waste transportation to off-site sorting facilities Manual and mechanical sorting

Inert materials (61.9%) a (38.5%) b

Non-inert materials (38.1%) a (61.5%) b

Public fills (100%) a b

Site 1 Site 2

Metal recycling (100%)

Landfill disposal

Fig. 6. Material flow considered for off-site sorting system.

3.3. Life cycle inventory (LCI) and impact assessment The LCI was performed by following the guidelines provided by ISO 14040-44 standards (ISO, 2006a, 2006b). The first-hand inventory data (waste compositions, etc.) were collected from the two selected construction sites. In addition, the secondary data were collected from various literature (e.g., Mercante et al., 2012; Hossain et al., 2016c). Different databases (e.g., the China Light and Power (CLP), the Chinese Life Cycle Database (CLCD), European reference Life Cycle Database (ELCD), and Ecoinvent) were used as upstream data (e.g., for electricity and fuel consumption, transportation, waste landfilling, etc.). The details of the data sources used are listed in Tables 2–4. The landfill disposal of different waste constituents was modeled separately, and the total impacts were assessed based on the waste compositions. According to the system boundary described in Fig. 8, the transportation distances were calculated from the construction sites to the processing and transformation sites, and then to the reuse or disposal sites (shown in Table 2). Based on the volume of the trucks and their carrying capacities, the input values for transport was calculated by multiplying the mass of the materials transported by the distance with the use of transport correction factors (calculated based on Marca, 2010, and Mercante et al., 2012). The factor was 1.40, 1.00, 6, 22, 19, and 4 for mixed, inert, wood, plastic, paper, and metal, respectively. The life cycle stages of 1 t construction waste were modeled and assessed by using the SimaPro 8.1.0 software. The inventory data regarding the materials recycling and recovery based on flow of the materials, as shown in Figs. 6 and 7 were used. The substitutional LCA approach was applied in this study. The substitution approach deals with co-products or

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043

5

M.U. Hossain et al. / Waste Management xxx (2017) xxx–xxx

Waste generation at construction sites

Inert materials (61.9%) a (38.5%) b

Non-inert materials (38.1%) a (61.5%) b a

Public fills (100%)

b

Metals (17.1%)a (8.4%) b

Wood & timber (51.2%) a (86.9%) b

Paper & cardboard (13.4%) a (0.6%) b

Site 1 Site 2

Plastic & rubber (8.1%) a (1.5%) b

Others (10.2%) a (2.6%) b

Plastic & rubber

Others

On-site sorting

Metals

Wood & timber

Recycling (100%)

Recycling (50%)

Paper & cardboard

50%

Recycling (50%)

50%

Recycling (50%)

100%

50%

Landfill disposal Fig. 7. Material flow considered for on-site sorting.

Construction waste from building construction activities

On-site sorting

Non-inert materials

Off-site sorting

Inert materials

Inert materials

Non-inert materials

Transport

Recyclable waste

Non-recyclable waste Transport

Wood & timber waste

Public fills Landfill

Paper & cardboard Transport

Transport

Mixed waste

Metals

Transport

Plastic & rubber Transport

Metals Transport

Bio-fuel production plant

Paper and cardboard recycling facilities

Plastic & rubber recycling facilities

Metal recycling facilities

Bio-energy generation from wood pellet & use in the cement industry

Use in producing secondary sulphate pulp

Use in producing secondary Polyethylene (HDPE)

Use in producing secondary steel

Polyethylene (HDPE)

Iron ore replacement

Substitution

Use of coal replaced by bio-energy

Sulphate pulp replacement

Fig. 8. System boundary for CWM systems considered.

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043

6

M.U. Hossain et al. / Waste Management xxx (2017) xxx–xxx

Table 2 Transport data of different materials and systems. Considered sites

Materials

Locations

Transport type

Distance (km)

Upstream database

Site 1

Inert and mixed waste Non-inert and mixed waste

Construction Site 1 to public fill site (Tseung Kwan O Area 137 fill bank) Public fill site to landfill site (South East New Territories Landfill, Junk bay) Construction Site 1 to landfill site Construction Site 1 to waste recycling sites (Tuen Mun recycling facilities) Off-site sorting facilities to recycling facilities (Tuen Mun waste recycling facilities) Construction Site 2 (Tseun Wan) to public fill site (Tuen Mun fill bank) Public fill site to landfill site (West New Territories Landfill, Tuen Mun) Construction Site 2 to landfill site Construction Site 2 to waste recycling sites (Tuen Mun recycling facilities) Off-site sorting facilities to recycling facilities (Tuen Mun waste recycling facilities) Recycling sites to secondary products processing sites (Tuen Mun waste recycling facilities to mainland China)

Trucks (30 t) Trucks (30 t)

18.0 4.0

CLCD (2010a) CLCD (2010a)

Trucks (30 t) Trucks (30 t)

20.0 36.0

CLCD (2010a) CLCD (2010a)

Trucks (30t)

45.0

CLCD, 2010a

Trucks Trucks Trucks Trucks

26.0 9.0 32.0 25.0

CLCD (2010a) CLCD (2010a) CLCD, 2010a CLCD, 2010a

Trucks (30t)

1.0

CLCD (2010a)

Inland barge; Trucks (30t)

120: 30

CLCD (2010a, 2010d)

Non-inert waste Non-inert waste Non-inert waste Site 2

Inert and mixed waste Non-inert and mixed waste Non-inert waste Non-inert waste Non-inert waste

Recycling sites

Non-inert waste (metal, plastic and paper)

(30 (30 (30 (30

t) t) t) t)

Table 3 Energy requirements for sorting and recycling of construction waste. Management practices

Materials

Activity

Energy requirements

Sources of data

Upstream database

On-site sorting Off-site sorting

Wood and timber, steel scrap and metals, plastic and rubber, and paper and cardboard Inert, metals and other non-inert

On-site waste sorting manually in separate bins, containers and designated locations Off-site sorting manually and mechanically (screening and on-site handling)

Negligible

Field visits

Not applicable

5 MJ/t (electricity) & 11 MJ/t (diesel)

CLP (2014); CLCD (2010b, 2010c)

Public fills

Inert waste

Processing and disposal in public fill site

Refers to database

Landfills

Non-inert waste (wood waste)

Processing and disposal in landfill site

Refers to database

Non-inert waste (plastic waste)

Processing and disposal in landfill site

Refers to database

Non-inert waste (paper and cardboard)

Processing and disposal in landfill site

Refers to database

Mercante et al. (2012) Inert waste landfill Wood waste landfill Plastic waste landfill Paper waste landfill

Ecoinvent (2013a) Ecoinvent (2013b) Ecoinvent (2013c) Ecoinvent (2013d)

Table 4 Substitution of secondary materials obtained in recycling. Recovered material/product

Avoided product/material

Substitution ratio

Sources of data

Upstream database

Bio-energy (from wood and timber) Metals Plastic Paper & cardboard

Coal energy Iron ore Polyethylene (HDPE) Sulphate pulp

1: 1: 1: 1:

Hossain et al. (2016c) WSA (2016) Mercante et al. (2012) Mercante et al. (2012)

Ecoinvent Ecoinvent Ecoinvent Ecoinvent

multi-functional processes, and includes credits for burdens that are avoided (Brander and Wylie, 2011; Rigamonti et al., 2009). This study assessed and compared the building CWM through different sorting processes, where different waste materials/ products are included inside the processes that can be (potentially) recycled and used to replace primary materials. Therefore, recycled materials have been credited, and the credits are ultimately given to the corresponding processes. For example, three processes (off-site, on-site and direct landfilling) were credited due to the recycling and reuse of metal scraps, whereas on-site sorting was credited for some other materials as the potentiality of wastes recovery is increased. In this process, the environmental impacts due to recycling and recovery, and transportations were taken into account as induced impacts, and the savings due to the substitution of primary raw materials/ products with recovered materials were considered as avoided impacts by considering the substitution ratio. This approach has

0.81 1.40 0.81 0.83

(2013e) (2013f) (2013g) (2013h)

been widely applied in the waste management systems (e.g., Mastrucci et al., 2016; Dahlbo et al., 2015; Butera et al., 2015; Mercante et al., 2012). For the inclusion of the recycling benefits that can be obtained from recovered waste materials, the system was expanded with processes that could be avoided by recovering the materials or energy of the outputs from the waste treatment lines (Fig. 8). The data and substitution ratio regarding bio-energy (e.g., heat) generated from wood pellets produced from recycled wood and timber waste, replacing coal as an energy source for industrial use (e.g. in the cement industry) has been collected from Hossain et al. (2016c). According to the World Steel Association (WSA), 1 t of scrap steel can save 1.40 t of iron ore for the production of 1 t new steel (WSA, 2016). The recovered materials and their avoided materials/products, substitution ratio, sources of data are shown in Table 4.

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043

7

M.U. Hossain et al. / Waste Management xxx (2017) xxx–xxx

In addition, the downstream users of waste materials were also considered in this study. For example, the user of wood and timber waste (e.g., wood pellets producer) is available in Hong Kong, and thus the transportation distance was modeled from Sites 1 and 2 to the wood pellet manufacturing site (for the recovered portion) and to the landfill sites (for the residual waste requiring landfill disposal). As there is no local downstream users of other recovered materials (e.g., paper and cardboard, plastic and rubber, and metals) in Hong Kong, this study considered the nearest downstream user (i.e., located in Guangdong Province in mainland China) and the transportation distances were modeled accordingly (Table 2). In this study, a midpoint (impact categories) and damage approach (single score) was selected in order to assess the environmental impacts. By using the characterization and other factors provided by IMPACT 2002+ method, seven mid-point impact categories were selected and assessed (e.g., respiratory effects caused by inorganics, ozone layer depletion, acidification (terrestrial and aquatic), aquatic eutrophication, global warming, non-renewable energy consumption) (Jolliet et al., 2003). In addition, a single score was obtained by applying the damage and weighting factors in order to compare the net environmental burden for the three CWM systems effectively (the factors are given in the supplementary information, S1–S3).

to produce various secondary materials/products. Similarly, about 3–9% lower aquatic eutrophication impacts were found for scenario 3 than that of scenario 1, and higher eutrophication impacts could be avoided for scenario 2. It is also estimated that about 20–33% lower GHGs emission was associated with scenario 3 than scenario 1. However, for scenario 2, about 126 kg CO2 eq. GHGs emission could be avoided for Site 1, and the savings was much higher (about 31%) for Site 2 due to higher amount of materials recovery. Similar trends were found in previous studies (Dahlbo et al., 2015; Coelho and de Brito, 2013; Mercante et al., 2012). For example, the overall climate change impact reduction was about 350 kg CO2 eq./t of C&D waste management in Finland due to recycling of useful materials such as metals, timber and concrete (Dahlbo et al., 2015). For scenario 1, about 314–423 MJ non-renewable energy was needed, which was about 33–35% higher than that of scenario 3. However, a significant amount of non-renewable energy (about 1562–2204 MJ) can be avoided for scenario 2. Due to the higher percentage of recyclable materials generated in Site 2, about 29% higher non-renewable energy savings were observed than that in Site 1.

4. Results and discussion

Based on the IMPACT 2002+ method, the net environmental burden was assessed for all scenarios (shown in Fig. 9). The net environmental burden (also called eco-point) is a dimensionless figure, measured in units of milli-points (mPt), which indicates the potential number of people affected by the environmental impacts in a period of one year. The eco-point is calculated based on the standardization factors (Jolliet et al., 2003). Fig. 9 shows that about 47–54% higher eco-point was associated with scenario 1 than the scenario 3. For scenario 2, about 39–65 mPt could be avoided after deducting the induced impacts due to materials recovery and utilizations. The LCA results demonstrated that significant net environmental impacts could be avoided if on-site sorting can be practiced in Hong Kong.

The results of the selected impact categories for managing 1 t of building construction waste are given in Table 5. The LCA results showed that the management of construction waste generated from building construction activities through off-site sorting system associated with significantly higher environmental impacts than that of on-site sorting system and direct landfilling. Much lower impacts were associated with direct landfilling than the off-site sorting system in most of the impact indicators, as it requires shorter transport distances and no further processing before disposal of at landfills. From Table 5, the LCA results show that scenarios 1 and 3 had a much higher impact than scenario 2 in the category of respiratory inorganics. Negative values were found for all scenarios in this category as the avoided impacts were much higher than the induced impacts. Similarly, about 27% higher impact in the category of ozone layer depletion (OLD) was found in scenario 1 than in scenario 3. In both sites, much higher OLD impacts could be avoided due to material recovery for scenario 2. In addition, higher savings was observed for Site 1 than Site 2 due to the higher amount of noninert waste landfill disposal for scenario 2. In relation to the acidification impacts, it was found that scenario 1 was about 46–48% higher than scenario 3. However, about 1.44–2.20 kg SO2 eq. acidification impact could be avoided for scenario 2 due to material recycling and their subsequent valorization

10

Environmental burden (mPt/t construction waste)

4.1. Environmental profile of the CWM systems

4.2. Comparative environmental evaluation of building CWM systems

4.02 5.92

2.12 2.74

0 -10

Scenario 1

Scenario 2

Scenario 3

-20 -30 -40

-38.84

-50 -60

Site 1

Site 2 -65.16

-70

Fig. 9. Comparison of total environmental burden of 1 t of CWM.

Table 5 LCA results of 1 t of CWM for the studied scenarios. Impact indicator

Respiratory inorganics (kg PM2.5 eq.) Ozone layer depletion (kg CFC-11 eq.) Aquatic eutrophication (kg PO4P-lim.) Acidification (kg SO2 eq.) Global warming (kg CO2 eq.) Non-renewable energy (MJ primary)

Scenario 1

Scenario 2

Site 1

Site 2

0.01164 6.85E 07 0.00362 0.72 30 314

0.00349 9.69E 07 0.00198 0.98 27 423

Site 1 0.15874 6.4E 07 0.02981 2.20 126 1562

Scenario 3 Site 2

Site 1

Site 2

0.32585 4.89E 07 0.05871 1.44 182 2204

0.01757 5.00E 07 0.00350 0.39 24 212

0.00950 7.09E 07 0.00180 0.51 18 277

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043

8

M.U. Hossain et al. / Waste Management xxx (2017) xxx–xxx

portation to sorting facilities (14%), recovered metal transportation to material recycling sites and then to utilization sites (for recycling/remanufacturing) (7%) and waste sorting (5%) for the waste generated from Site 1 for off-site system. The corresponding contributions of GHGs emission was 58%, 11%, 22%, 3% and 6% for Site 2 respectively. In addition, about 9–11 kg CO2 eq. GHGs emission could be saved due to metal recycling and use for substituting iron ore for the production of new steel.

4.3. Contribution analysis The contributions on the total GHGs emission for 1 t of CWM through different scenarios are shown in Figs. 10–12. It can be seen from Fig. 10 that transportation (from construction sites to off-site sorting facilities, and then to landfill sites) and landfilling of noninert waste contributed the highest GHGs emissions (about 57%), followed by inert waste public filling (17%), mixed waste trans-

-9 -11

Avoided impacts (iron ore)

Site 2

Site 1

1

Recovered material transport

3 21

Non-inert waste transport & landfill disposal

24 4

Inert waste public fill disposal 2 2

Waste sorting Mixed waste transport to off-site facilities -15

-10

-5

7

6 0

5

8 10

15

20

25

30

kg CO2 eq. GHGs emission Fig. 10. Process contributions of total GHGs emission for CWM through scenario 1.

Fig. 11. Process contributions of total GHGs emission for CWM through scenario 2.

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043

9

M.U. Hossain et al. / Waste Management xxx (2017) xxx–xxx

25

21

Site 1

kg CO2 eq. GHGs emission

20

13

15 10 5

4.4. Influence of material recovery on the on-site CWM system

9

7

5

4

Based on the waste compositions and materials flow from both sites, the influence of material recovery rates and utilizations on the net environmental profile through the on-site sorting systems (scenario 2) is shown in Fig. 13. The figure provides an overall CWM direction based on environmental point of view. It has already been mentioned that about 4–6 mPt net environmental burden is associated for the management of 1 t of construction waste for scenario 1 for both sites. Even with only 10% material recovery (including 100% metals), about 8–12 mPt net environmental burdens could be saved for 1 t construction waste in both sites after deducting the induced impacts. With the increase of the recycling rate, the environmental saving was also gradually increased for both sites. The possibilities of energy recovery and reuse were high due to the high amount of wood and timber wastes generated in Site 2, and thus significantly higher net environmental savings were observed for Site 2. However, changes in the waste composition influenced the environmental profile of CWM. Based on the compositions, it can also be seen that a higher amount of non-inert waste had a higher potential of recycling, and thus higher environmental benefits were observed.

-9 -8

0 -5

sorting saved some landfill space when compared with direct landfilling.

Site 2

Inert waste

Non-inert waste

Transport

Avoided impact

-10 -15 Fig. 12. Process contribution of GHGs emission for CWM through scenario 3.

For scenario 2, about 41% of the total GHGs emission was associated with non-inert waste transportation and landfilling, 22% for inert waste transportation and public fills, and 37% for recovered materials transport to recycling sites and then to utilization sites for Site 1. However, about 167 kg CO2 eq. GHGs emission could be avoided due to materials recovery and recycling, in which 72% by bio-energy for replacing coal energy, 7% by recycled metals for replacing iron ore production, 13% by recycled plastic for replacing polyethylene production, 8% by paper and cardboard for replacing sulphate pulp production. Similarly, high GHGs emission (about 219 kg CO2 eq.) could be avoided for Site 2. In Site 2, high percentage of wood and timber waste was generated, and thus contributed to 95% of the total GHGs savings. The rest (about 5%) was due to plastic, paper and metal recycling and utilizations (Fig. 11). For scenario 3, non-inert waste landfilling associated with highest GHGs emission (50–64%), followed by inert waste disposal (15– 21%) and mixed waste transport to disposal sites (15–35%) (Fig. 12). Although less quantity of non-inert waste was associated with Site 1, high GHGs emission was observed for non-inert waste landfilling than Site 2. This is because the GHGs emission associated with the landfill disposal of paper waste is significantly higher than that of plastic and wood waste (higher amount of paper waste was generated in Site 1). Based on the above analysis, it can be seen that, on-site sorting showed apparent environmental advantages over off-site sorting, regardless of the composition of the construction waste. The worst environmental performance was found for CMW through off-site sorting, even worse than the direct landfilling. However, off-site

4.5. Comparative analysis due to attributional LCA approach Fig. 14 shows the comparative results of CWM for different scenarios due to the use of attributional LCA approach. The figure shows that scenario 3 had the lowest environmental impacts for most of the categories compared to scenario 1 and 2, as a relatively shorter transport distance was associated with this scenario. In addition, the transport correction factor was lower for the mixed waste (directly transport to landfill sites), but the factors for individual wastes were much higher (transporting to landfill sites after both off-site and on-site sorting). Compared to scenario 1, higher impacts were observed in the categories of respiratory impact (15%), ozone layer depletion (7%), acidification potential (21%) and non-renewable energy consumption (20%) for scenario 2 for Site 1. This is because the recyclable materials transportation from generation site (Site 1) to recycling sites (processing sites) and then to utilization sites contributed significantly higher impacts. However, significant environmental gains still could be achieved in the category of aquatic

Environmental burden (mPt/t)

100

Site 1

90

91.03

Site 2 77.85

80 65.16

70 60

51.63

50

54.28 38.29

40 30 20

38.84

25.29

30.91 23.24

12.14

10

7.76

46.42

15.51

0 10%

20%

30%

40%

50%

60%

70%

Materials recovery rate Fig. 13. Influence of materials recovery rates on the environmental profile (all values are negative, meaning net environmental savings).

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043

M.U. Hossain et al. / Waste Management xxx (2017) xxx–xxx

Comparative impacts (%)

10

Scenario 1

Scenario 2

Scenario 3

100 90 80 70 60 50 40 30 20 10 0

Impact categories (Site 1)

Comparative impacts (%)

Scenario 1

Scenario 2

Scenario 3

100 90 80 70 60 50 40 30 20 10 0

Impact categories (Site 2) Fig. 14. Comparative results for attributional LCA approach.

eutrophication (36%), and similar impact of global warming, when the environmental impacts due to the utilization of recovered materials in secondary products were not accounted for (for Site 1). For Site 2, considerable lower impacts were associated for the impact categories (e.g., ozone layer depletion and aquatic eutrophication), and slightly higher impacts were found for other categories than the scenario 1 (Fig. 14). By applying attributional LCA approach on CWM systems in Hong Kong (with assumptions taken in this study and excluded the recycled benefits, but included the transport impacts of recyclable materials), it can be observed that the environmental impacts were comparable for both scenario 1 and 2 (net environmental burden were about 11.39–11.78 mPt and 12.94–12.35 mPt, respectively) which was much higher than scenario 3 (8.18–8.62 mPt). Although significant environmental advantages were observed for CWM through on-site system (scenario 1), off-site sorting is a common practice in Hong Kong. Most of the relevant parties such as clients, contractors and sub-contractors are reluctant to carry out on-site sorting in Hong Kong because on-site sorting activities are hindered by space limitation and the tight construction schedule (Yu et al., 2013). In addition, management efforts, labour, cost and interference with normal construction activities are other limiting factors for on-site sorting practice (Poon et al., 2001). To provide incentives for carrying out on-site sorting of waste, the Government has implemented a construction waste charging

scheme in 2005 but recent studies showed that the construction waste disposal charges were not high enough to increase the awareness for promoting good waste management through onsite practice (Poon et al., 2013). But it was also found that stakeholders were willing to pay higher charges than the existing standards in order to enhance the effectiveness of CWM in Hong Kong (Lu et al., 2015). The present study mainly focused on the selected environmental impacts of the building construction waste management through different sorting systems in Hong Kong. In addition to environmental assessment, it will be valuable to assess the economic feasibility of the building CWM through different sorting systems, and merits particular attention in future study. 5. Conclusion The environmental profile of the CWM systems generated from building construction activities in Hong Kong was evaluated using LCA approach. During the assessment, compositions and materials flow were considered to describe the flow of waste fractions and provide the basis of estimating the waste recovery rates of the system, and then LCA was used to expand the basis to assess the environmental impacts of the CWM systems. In order to better represent the waste scenarios and management strategies in Hong Kong, a case study was conducted using two real construction sites. Based on the findings, the following conclusions can be drawn:

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043

M.U. Hossain et al. / Waste Management xxx (2017) xxx–xxx

(i) Compared to the proposed strategy (scenario 2), the prevailing building CWM systems (i.e., off-site sorting and direct landfilling) in Hong Kong is not effective and induces significant environmental burdens. (ii) Considerable environmental impacts can be avoided for the building CWM through on-site system (scenario 2). These are mainly due to the material recovery and reuse in the secondary materials/products. (iii) Compared to Site 1, higher environmental savings were observed for Site 2 due to the higher recycling potential of non-inert waste, especially for wood and timber waste which has a high potential to energy recovery. (iv) If on-site sorting can be practiced, a considerable amount of waste can be diverted from landfills, and reduced the sorting impacts (for off-site sorting). Thus, the environmental performance of CWM through other two scenarios can be improved. Acknowledgements The authors wish to thank The Hong Kong Polytechnic University (Project of Strategic Importance) for funding support. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.wasman.2017.07. 043. References Bovea, M.D., Powell, J.C., 2016. Developments in life cycle assessment applied to evaluate the environmental performance of construction and demolition waste: review. Waste Manage. 50, 151–172. Brander, M., Wylie, C., 2011. The use of substitution in attributional life cycle assessment. Greenhouse Gas Measure. Manage. 1 (3–4), 161–166. Butera, S., Christensen, T.H., Astrup, T.F., 2015. Life cycle assessment of construction and demolition waste management. Waste Manage. 44, 196–205. Cheng, J.C.P., Ma, L.Y.H., 2013. A BIM-based system for demolition and renovation waste estimation and planning: Review. Waste Manage. 33, 1539–1551. CLCD, 2010a. Heavy-duty diesel truck transportation (30t)–CN–AP. Chinese Life Cycle Database Version 0.8. Sichuan University; IKE Environmental Technology CO., Ltd.. CLCD, 2010b. Fuel combustion-Diesel–CN–AP. Chinese Life Cycle Database Version 0.8. Sichuan University; IKE Environmental Technology CO., Ltd.. CLCD, 2010c. Electricity generation, China Southern Grid. Chinese Life Cycle Database Version 0.8. Sichuan University; IKE Environmental Technology Co., Ltd.. CLCD, 2010d. Bulk cargo shipping (2500 t)–CN–AP. In: Chinese Life Cycle Database Version 0.8. Sichuan University; IKE Environmental Technology CO., Ltd.. CLP, 2014. Sustainability Report 2014. The China Light and Power (CLP), Hong Kong. Coelho, A., de Brito, J., 2013. Environmental analysis of a construction and demolition waste recycling plant in Portugal - Part II: environmental sensitivity analysis. Waste Manage. 33, 147–161. Dahlbo, H., Bachér, J., Lähtinen, K., Jouttijärvi, T., Suoheimo, P., Mattila, T., Sironen, S., Myllymaa, T., Saramäki, K., 2015. Construction and demolition waste management–a holistic evaluation of environmental performance. J. Clean. Prod. 107, 333–341. Ecoinvent, 2013a. Inert waste treatment, inert material landfill (RoW), Alloc Def, U. Ecoinvent System Processes. Swiss Centre for Life Cycle Inventories. Ecoinvent, 2013b. Treatment of waste wood, untreated, sanitary landfill (waste treatment) CH. Ecoinvent System Processes. Swiss Centre for Life Cycle Inventories. Ecoinvent, 2013c. Treatment of waste plastic, mixture (CH), sanitary landfill, Alloc Def, U. Ecoinvent System Processes. Swiss Centre for Life Cycle Inventories. Ecoinvent, 2013d. Waste paperboard treatment (RoW), sanitary landfill, Alloc Def, U. Ecoinvent System Processes. Swiss Centre for Life Cycle Inventories. Ecoinvent, 2013e. Heat production, at hard coal industrial furnace, Alloc Def, U. Ecoinvent System Processes. Swiss Centre for Life Cycle Inventories. Ecoinvent, 2013f. Market for iron ore, beneficiated, 65% Fe GLO. Ecoinvent System Processes. Swiss Centre for Life Cycle Inventories. Ecoinvent, 2013g. Polyethylene, high density, granulate production (RoW), Alloc Def, U. Ecoinvent System Processes. Swiss Centre for Life Cycle Inventories. Ecoinvent, 2013h. Sulfate pulp production (RoW), totally chlorine free bleached, Alloc Def, U. Ecoinvent System Processes. Swiss Centre for Life Cycle Inventories.

11

Hao, J.L., Hill, M.J., Shen, L.Y., 2008. Managing construction waste on-site through system dynamics modelling: the case of Hong Kong. Eng. Constr. Architect. Manage. 15 (2), 103–113. HKEPD, 2015. Environmental Protection Department (HKEPD), Monitoring of solid waste in Hong Kong; Waste statistics for 2014. Hong Kong Government. Hossain, M.U., Leu, S.Y., Poon, C.S., 2016a. Sustainability analysis of pelletized biofuel derived from recycled wood product waste in Hong Kong. J. Clean. Prod. 113, 400–410. Hossain, M.U., Poon, C.S., Lo, I.M.C., Cheng, J.C.P., 2016b. Comparative environmental evaluation of aggregate production from recycled waste materials and virgin sources by LCA. Resour. Conserv. Recyc. 109, 67–77. Hossain, M.U., Poon, C.S., Lo, I.M.C., Cheng, J.C.P., 2016c. Evaluation of environmental friendliness of concrete paving eco-blocks using LCA approach. Int. J. Life Cycle Assess. 21, 70–84. ISO, 2006a. ISO 14040: Environmental Management- Life Cycle Assessment. Principles and Guidelines, International Organization for Standardization, Geneva. ISO, 2006b. ISO 14044: Environmental Management- Life Cycle Assessment. Life Cycle Impact Assessment, International Organization for Standardization, Geneva. Jolliet, O., Margni, M., Charles, R., Humbert, S., Payet, J., Rebitzer, G., 2003. IMPACT 2002+: a new life cycle impact assessment methodology. Int. J. Life Cycle Assess. 8 (6), 324–330. Kucukvar, M., Egilmez, G., Tatari, O., 2016. Life cycle assessment and optimizationbased decision analysis of construction waste recycling for a LEED-certified university building. Sustainability 8 (89), 1–13. Lu, W., Peng, Y., Webster, C., Zuo, J., 2015. Stakeholders’ willingness to pay for enhanced construction waste management: a Hong Kong study. Renew. Sustain. Energy Rev. 47, 233–240. Lu, W., Yuan, H., 2011. A framework for understanding waste management studies in construction. Waste Manage. 31, 1252–1260. Lu, W., Yuan, H., 2012. Off-site sorting of construction waste: what can we learn from Hong Kong? Resour. Conserv. Recyc. 69, 100–108. Marca, F.L., 2010. Optimization of C&D waste management by the application of life cycle assessment (LCA) methodology: the case of the municipality of Rome. Italy. WIT Transact. Ecol. Environ. 129, 497–508. Mastrucci, A., Marvuglia, A., Popovici, E., Leopold, U., Benetto, E., 2016. Geospatial characterization of building material stocks for the lifecycle assessment of endof-life scenarios at the urban scale. Resour. Conserv. Recyc. http://dx.doi.org/ 10.1016/j.resconrec.2016.07.003. Mercante, I.T., Bovea, M.D., Ibanez-Fores, V., Arena, A.P., 2012. Life cycle assessment of construction and demolition waste management systems: a Spanish case study. Int. J. Life Cycle Assess. 17, 232–241. Neto, R.O., Gastineau, P., Cazacliu, B.G., Guen, L.L., Paranhos, R.S., Petter, C.O., 2016. An economic analysis of the processing technologies in CDW recycling platforms. Waste Manage. http://dx.doi.org/10.1016/j.wasman.2016.08.011. Pacheco-Torgal, F., Tam, V., Labrincha, J., Ding, Y., de Brito, J., 2013. Handbook of recycled concrete and demolition waste. http://dx.doi.org/10.1533/ 9780857096906.3.439. Poon, C.S., Yu, A.T.W., Ng, L.H., 2001. On-site sorting of construction and demolition waste in Hong Kong. Resour. Conserv. Recyc. 32 (2), 157–172. Poon, C.S., Yu, A.T.W., Wong, A., Yip, R., 2013. Quantifying the impact of construction waste charging scheme on construction waste management in Hong Kong. J. Constr. Eng. Manage. 139 (5), 466–479. Rigamonti, L., Grosso, M., Sunseri, M.C., 2009. Influence of assumptions about selection and recycling efficiencies on the LCA of integrated waste management systems. Int. J. Life Cycle Assess. 14, 411–419. Rodrigues, F., Carvalho, M.T., Evangelista, L., de Brito, J., 2013. Physical–chemical and mineralogical characterization of fine aggregates from construction and demolition waste recycling plants. J. Clean. Prod. 52, 438–445. Saez, P.V., Merino, M.R., Gonzalez, A.S., Porras-Amores, C., 2013. Best practice measures assessment for construction and demolition waste management in building constructions. Resour. Conserv. Recyc. 75, 52–62. Tam, V.W.Y., 2008. On the effectiveness of implementing a waste management plan method in construction. Waste Manage. 28 (6), 1072–1080. Vieira, C.S., Pereira, P.M., 2015. Use of recycled construction and demolition materials in geotechnical applications: a review. Resour. Conserv. Recyc. 103, 192–204. Wang, J.Y., Yuan, H., Kang, X.P., Lu, W.S., 2010. Critical success factors for on-site sorting of construction waste: a China study. Resour. Conserv. Recyc. 54 (11), 931–936. WSA, 2016. Fact sheet: steel and raw materials. World Steel Association (WSA). Wu, Z., Yu, A.T.W., Shen, L., 2016. Investigating the determinants of contractor’s construction and demolition waste management behavior in mainland China. Waste Manage. http://dx.doi.org/10.1016/j.wasman.2016.09.001. Yeheyis, M., Hewage, K., Alam, M.S., Eskicioglu, C., Sadiq, R., 2013. An overview of construction and demolition waste management in Canada: a lifecycle analysis approach to sustainability. Clean Tech. Environ. Policy 15, 81–91. Yu, A.T.W., Poon, C.S., Wong, A., Yip, R., Jaillon, L., 2013. Impact of construction waste disposal charging scheme on work practices at construction sites in Hong Kong. Waste Manage. 33, 138–146. Yuan, H., Lu, W., Hao, J.J., 2013. The evolution of construction waste sorting on-site. Renew. Sustain. Energy Rev. 20, 483–490. Yuan, H., Shen, L.Y., 2011. Trend of the research on construction and demolition waste management. Waste Manage. 31, 670–679.

Please cite this article in press as: Hossain, M.U., et al. Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong. Waste Management (2017), http://dx.doi.org/10.1016/j.wasman.2017.07.043