A REVERSE LOGISTICS COST MINIMIZATION MODEL FOR THE TREATMENT OF WEEEDoan Thi Truc Linh 1, Nguyen Thi Le Thuy2, Tran Thi My Dung3

Department of Industrial Management, Can Tho University, Viet Nam

ABSTRACT: Attention with Waste Electrical and Electronic Equipment (WEEE) has become increased during last

decade since accelerating technological changes and market expansion of EEE products. In order to prevent

negative effects of WEEE on the environment, humans, and the valuable materials that can be reused in them, the

WEEE need to be handled, disposed, reused, recycled, remanufactured or treated properly. Based on the analysis of

the WEEE reverse logistic network and the characteristics of its planning, this paper presents a recycling network

which has a cost minimization model for multi-products reverse logistic system. The factors considered in the

proposed model include the cost of collection, treatment, sales income as well as transportation cost with different

fractions of returned products. Especially, the proposed model is solved by an algebraic modeling package AMPL

(A Mathematical Programming Language). The proposed optimization model can help determine the optimal

facilities and the material flows in the network. In addition, Radio Frequency Identification (RFID) technology is

suggested to manage the information of returned products at collection points that can help managers increase

efficiency of logistic operations in collection facilities

Keywords: Recycling, Reverse Logistics, WEEE, RFID.

1. Introduction

According to Environmental Protection Agency

(EPA), there are 20 to 50 million metric tons of

WEEE generating worldwide every year, comprising

more than 5% of all municipal solid waste.

Developing countries are estimated to triple their

output of WEEE by 2010. In the US alone, some 14

to 20 million PCs are thrown out every year. In

Western Europe, 6 million tons of WEEE (waste of

electrical and electronic equipment) were generated

in 1998 and the amount of WEEE is expected to

increase by at least 3-5% per annum. By 2010, the

European Union will be producing around 12 million

tons of electrical and electronic waste annually. It

was estimated that about 1.6 million obsolete EEE

were generated in 2003 in China with TV accounting

for nearly half of the total [Liu et al. (2006)].

WEEE is a non-homogeneous and complex in terms

of materials and components. Many of the materials

are highly toxic (Dimitrakakis et al., 2009; Hicks et

al, 2005), as well as WEEE has high residual value.

In view of the negative effects of WEEE on the

environment, humans, and the valuable materials that

can be reused in them, legislations in many countries

have focused their attention on the management of

WEEE, and new techniques have been developed for

the recovery of WEEE. In particular, the European

Union (EU) adopted the 2002/96/EC and 2002/95/EC

(Restriction of Hazardous Substances- RoHS

directive), which causes essential changes in the field

of electronic scrap recycling. Producers are requested

to finance the collection, treatment, recovery, and

environmentally sound disposal of WEEE. The

directive imposes a high recycling rate for all targeted

products. The directive imposes a high recycling rate

of all targeted WEEE products. Reuse, recycling and

recovery rates ranging from 50% to 80% according to

the category of equipment considered, must be

achieved by producers of EEE [He et al, 2006].

The recycling of WEEE is an important step of the

end-of-life strategies for WEEE treatment. Although

there is an increasing amount of research on material

recycling models and specific products (Krikke,

1998; Barros and Scholten, 1998; Ammons and

Realff, 1999; Newton, 2000; Nunes et al., 2009;

Reynaldo, 2009), as well as reverse logistics

networks (Mutha, 2009; Reynaldo, 2009; Kannan,

2010), studies specifically addressing WEEE

problems (Assavapokee, 2004; Deepali, 2005;

Rahimifard, 2009; Grunow, 2009; Geraldo, 2010;

Achillas, 2010; Jang and Kim, 2010; Silveria and

Chang, 2010) are rare and still limited to some

specific areas of WEEE reverse logistics.In view of

lack of in-depth with respect to WEEE reverse

logistics operations in the literatures, this paper

presents a recycling network for multi-products

reverse logistic system as well as to analyze the

material and component flows of returned products at

treatment and final stage particularly so that the cost

of the recycling can be achieved effectively. The

factors considered in the proposed model include the

cost of collection, treatment, sales income as well as

transportation cost with different fractions of returned

products. Specially, the proposed model is solved by

an algebraic modeling package AMPL. In addition,

RFID technology is suggested to manage the

information of returned products at collection points

that can help managers increase efficiency of logistic

operations in collection

2. Recycling sequence

Figure1.Flow of returned products in recycling model

Figure 1 shows Flow of returned products in

recycling model. There are four layers of recycling

model from left to right. Each layer has its own

function which can be described as follows:

First Layer (Collection Site): Returned products are

received from collection points such as retailers,

permanent drop-off sites by classified groups. They

are then transported to disassembly site

- Second Layer (Disassembly Site):

This site receives the collected wastes from collection

sites. It has two main functions; the first one is to

separate the recycled product into fractions (different

components and parts). Second, determine whether a

component (or part) is in fact re-usable and in which

way through the inspection activity. The re-usable

component (or part) will be transported to a

secondary market; the rest of the parts will be

transported to an extraction facility for further

treatment. Also, through the separation processing,

some fractions that belong to the same type of

materials could be compressed leading to a smaller

transportation volume. In other words, it can reduce

the recycled product volume which means the

truckload utility increases. The disassembly site can

also collect large quantities of components (parts), to

ensure that transportation vehicles are fully loaded.

-Third Layer (Extraction Facility): An extraction

facility receives the disassembled fractions which

need further treatment from disassembly sites. The

following typical fractions can be extracted and can

be reused or disposed in different ways: ferrous metal

tractions are used in iron smelters; most non-ferrous

metals go to copper smelters, aluminum smelters, and

lead smelters; plastics can become regenerated

material; hazardous materials would be disposed of in

special landfills properly.

- Fourth Layer (Termination Site-reuse/resell or

disposal):

This layer is for the reuse or resell of the

regenerated material and components (parts). For

non-recyclable material and hazardous materials,

they will be disposed of properly.

We summarize the sequences as follows: an

end-of-life product will be sent to an initial collection

site which is the closest point to the customer. After a

period of time, all products from the collection site

will be transported to a disassembly site for

separation. Next, the re-usable components (parts)

would be transported to a secondary market directly,

and the fractions which needed further treatment

would be sent to an extraction site to be processed.

The regenerated materials and hazardous materials

will be extracted from those fractions. Finally, the

regenerated raw materials will be sold to

manufacturers or material suppliers for reuse or

reselling. The non-recyclable wastes and hazardous

materials will be properly disposed of.

It has to be mentioned that the product’s total

transportation cost changes alone with the recycling

process. When a product is sent to disassembly site

and to be disassembled into many different parts, the

total volume of sending those parts to a disposal site

and termination site may change. There are three

kinds of situation and what would happen depends on

the different product types. The first case is the

product volume remains the same, like recycling

books. The second case is the volume decreases, for

example some plastic part could be compressed into a

smaller volume. The third case, when a product is

disassembled the total volume increase due to the

separated parts needing more space to be delivered.

For a Less Than Truckload (LTL) carrier, the

transportation cost that will be charged depends on

the freight’s volume or weight. The unit

transportation cost change is due to the different

product (or component) rate of weight and volume.

The recycling process leads to the total transportation

cost changes. A simple product is used to be a

sample to illustrate the variation of the transportation

cost more clearly. Figure 2 is a disassembly tree of

product , and the transportation cost related with

each component

.

Figure 2. Disassembly tree of product

Product is being transported from collection

sites to disassembly sites; the unit transportation cost

is 40 dollars. At the disassembly site, product

will be disassembled into four parts (component ,

component , sub-assembly , disposable item

). For component , it is a shell of product ,

the volume is equal to the original volume, although

the weight is less than product , it is still be

charged by the volume, which is 40 dollars. In the

case of component , sub-assembly , disposable

item , they are all charged by weight. And sub-

assembly will be transported to extraction sites

for further treatment, after which extraction process

material and hazardous material are generated.

The transportation cost of these two types of material

is also charged by weight.

3. Recycling system network model

Based on the recycled goods processing

sequence mentioned in the previous section, a

recycling system network configuration model was

constructed for solving recycling management

problems. A mixed integer programming model is

proposed to create an optimal reverse logistics system

for recycling EOL products

.

Figure 3.Recycling System Network

There are four layers of sites in this recycling

system network: collection site, disassembly site,

extraction facility, and termination site. The arcs

represent the flow of resource waste, sorted waste

and regenerated material, and hence there are arcs

between each adjacent level. In our problem, m kinds

of products are to be transferred from a set of

collection sites to a set of Termination sites (Disposal

site and reuse/resell site) (see figure 3). The objective

is to minimize the total cost as well as the income

from selling the reclaimed materials.

This research addresses the problem of

efficiently transporting multiple types of recycled

products from multiple sources and in the process

satisfying the demand on the recycled items at a

number of destinations. The recycling system

problem can be formulated as follows:

Given:

(a) Locations of each site (collection,

disassembly, extraction, termination).

(b) Capacities of these disassembly sites and

extraction facilities.

(c) Processing efficiency of these extraction

facilities.

(d) Cost structures (transporting, processing,

operating, and disposal costs).

(e) Availability of reusable material for each

reuse/resell site.

Find:

Which facility should be used and how the

recycled goods should be delivered so that the total

cost of the system is minimized.

The mathematical formulation of the model

follows while explanation of the notations is included

in the next section.

3.1 Assumption and Notations

The optimization model of the recycling

network is based on the following assumptions:

1. All recycled products must enter the

recycling system through collection

sites.

2. The recycled product at the collection

site must be recyclable, reusable or

recoverable.

3. The capacities of disassembly and

extraction facilities are limited.

4. The transportation cost is linearly

related to distance.

5. The location of collection sites,

disassembly sites, extraction facilities

and termination sites are fixed

Following notations to formulate the recycling system network problem:

Number of collection sites;

Number of disassembly sites;

Number of extractions sites;

Number of reuse/resell sites;

Number of disposal sites;

Number of product types;

Number of sub-assembly types;

Number of directly reuse parts;

Number of disposable items;

Number of regenerated materials;

Number of non-recyclable materials;

The amount of components or material of type n necessary to produce every unit of product

type m. .

The unit transportation cost. For different product or component types m.

The distance between outgoing site i and incoming site j,

The extracted rate at extraction facility for .

The unit operation cost at site j (disassembly and extraction) for product type (or component)

m. ,

Maximum storage and processing capacity of handling product m at disassembly site j=

for , for .

Maximum storage and processing capacity at extraction facility for

for handling integral sub-assembly m,

Unit cost of dispose of disposable item and non-recyclable material

. For the revenue of directly

reusable components and material fractions per unit,

.

The supply at collection site i for recycled product m.,

0-1 variable, =1 represents reuse/resell site j has the demand for component part m or

=0. ,

.

If site (collection or extraction) can handle product(or sub-assembly) type m, =1;

otherwise =Z;

Note: Z is set to some arbitrarily high value.

Decision variables:

The unit of product(or component) type m is transported from outgoing site i to incoming site j

; i,j ,

3.2 Model Formulation

In this section, we formulate the problem of

minimum cost of the recycling system. The system

which considered transportation cost, capacity and

operating cost of disassembly sites and extraction

facilities, and the demand of the secondary market.

This formulation is based on the single objective of

minimum cost of transporting cost, operating cost,

and disposal cost

.

Total cost = Transportation cost+ operation cost+ disposal cost- revenue of sell reclaimed materials and

components.

(1)

Eq. (1) represents the objective functions. The objective function is constrained by various requirements,

which will be addressed individually. To ensure that all the recycled products leave the collection site, Eq. (2) is

imposed as follows.

for ,

(2)

This means all recycled products collected at the collection site will be processed through the entire recycling

system.

To ensure the flow balance between each site, Eq. (3) to (7) is imposed as follows.

(3)

(4)

(5)

(6)

(7)

Eq. (3), (4), and (5) ensures the incoming flow of recycled products at the disassembly site j multiple is

equal to the outgoing flow from disassembly site to extraction site, reuse/resell site, and disposal site respectively .

Eq. (6), and (7) ensures that the outgoing flow from the extraction facility j is equal to the incoming flow from the

disassembly site i multiple and extraction rate .

To ensure the reuse/resell site has the demand for different components and materials or not, Eq. (8) and (9) is

imposed as follows.

(8)

(9)

=1 represents reuse/resell site j has the demand for component part m or =0.

To ensure the capacity of each site will not be exceeded, Eq. (10) and (11) is imposed as follows.

(10)

(11)

Eq. (10) limits the units sent from collection site i through disassembly site j to the capacity of disassembly

site j. Eq. (11) limits the unit which is sent from disassembly site i to extraction facility j to the capacity of extraction

facility site j.

Eq. (12) deals with non-negative decision variables. Eq. (13) means all types of products, integral sub-

assemblies, directly reusable parts, and directly disposable items are integers.

for all m, i , j. (12)

as an integer. (13)

4. RFID at collection points:

Supply in reverse logistic is typically considered as a

fluctuant factor since the timing, quality, quantity of

returned products may be difficult to control.

Uncertainty is an important characteristic of returned

product so this issue should be additional research

effort. Lee (2009) mention that the information of

returned product was estimated by forecasting and

simulation in the past. However, those methods lack

for accurate and efficient information which leads to

the higher reverse logistic cost. Therefore, RFID

technology is utilized to manage the amount and

quality of returned product that can provide real data

to improve shipment schedule from collection points

to collection facilities of recycling network

The steps of returned products from collection points

to collection facilities are shown in the figure 4.When

returned products from customers are arrived at

collection points such as retailers or permanent drop-

off sites, RFID tags are attached to the items,

containing the information of items such as product

name, the returned address and the status of returned

product. Information on quality and types of returned

items stored at collection point is transmitted to the

database by RFID readers. With the collected data,

recyclers will prepare a collection schedule which

will be stored in database. Then returned products are

put into the cartons with RFID attachment and the

information data on a carton label consists of the type

of items, amount of items and destination

Then, cartons are put in trucks and RFID readers are

installed there to detect and transmit the good

information to database that help managers to know

the quantity of returned to have efficient routing and

supply to collection facility. They keep track of the

inventory level in each collection point as well.

Figure 4. The steps of returned products from collection points to collection facilities

5. Conclusions:

In this paper, the reverse logistic network design

problem for WEEE has built. A mixed integer

programming model has established to minimize the

total costs while operating the reverse logistic

network and used AMPL to get an optimal solution.

The model considers fourth stages such as collection

sites, disassembly sites, extraction sites and

termination Sites

Compare to existing researches on reverse logistic,

this paper has attempted to apply the recycling

network with analyzing detailed treatment and final

stage for multi-type WEEE. Moreover, the

transportation cost of each type is estimated related to

its characteristic as well. Besides, the RFID

technology is suggested to keep track the quantity

and quality of return goods to increase shipment

route efficiently from collection points to collection

facilities.

MÔ HÌNH TỐI ƯU HÓA CHI PHÍ CHUỖI CUNG ỨNG NGƯỢC CHO VIỆC XỬ LÝ

PHÊ PHÂM THIÊT BI ĐIỆN VÀ ĐIỆN TỬ

Đoàn Thị Trúc Linh 1, Nguyễn Thị Lệ Thủy 2, và Trần Thị Mỹ Dung 3

Bộ môn Quản lý Công Nghiệp, Đại học Cần Thơ, Việt Nam.

Tom tăt: Phê phâm thiêt bị điện và điện tử đa và đang đươc đươc quan tâm nhiêu trong thập kỷ qua kể từ khi sư

phat triển công nghệ ngày càng cao và việc mở rộng thị trường của cac sản phâm điện và điện tử. Để ngăn chặn tac

động tiêu cưc của cac loai phê phâm này đối với môi trường, con người, và cac tài nguyên có gia trị mà có thể

đươc sử dụng lai, cac phê phâm này cần phải đươc xử lý, tai sử dụng, tai chê, tai sản xuất hoặc đươc xử lý hơp lý

đung quy định. Dưa trên phân tích tính chất của phê phâm thiêt bị điện, bài bao này trình bày mô hình tai chê với

chi phí tối ưu cho nhiêu sản phâm trong hệ thống chuôi cung ưng ngươc. Những nhân tố đươc xem xét trong mô

hình gồm có chi phí sản xuất, chi phí xử lý, lơi nhuận thu đươc từ việc tai chê, chi phí vận chuyển tùy theo những bộ

phận khac nhau của phê phâm. Đặc biệt, mô hình đê xuất đươc giải bằng một ngôn ngữ lập trình toan học. Mô hình

tối ưu này sẽ xac định số nhà may cần xây dưng và số lương phê phâm từ nhà may này đên nhà may khac trong

chuôi cung ưng ngươc một cach tốt nhất Ngoài ra, công nghệ tần số vô tuyên (RFID) đươc đê nghị để quản lý thông

tin của phê phâm tai cac tram thu gom điêu này có thể giup cac nhà quản lý nâng cao hiệu quả của hoat động hậu

cần.

Từ khoa: tai chê, chuôi cung ưng ngươc, phê phâm thiêt bị điện và điện tử, công nghệ tần số vô tuyên

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