ĐẠI HỌC QUỐC GIA HÀ NỘI
TRƯỜNG ĐẠI HỌC KHOA HỌC TỰ NHIÊN
o0o


NGUYỄN VĂN THÁI


STUDY ON COMPACT DEVICE FOR WASTE PROCESSING
BASED ON MECHANICAL BIOLOBICAL TREATMENT
IN DONG VAN TOWN, DUY TIEN DISTRICT,
HA NAM PROVINCE, VIETNAM

CHUYÊN NGÀNH: QUẢN LÝ CHẤT THẢI VÀ XỬ LÝ VÙNG Ô NHIỄM
(CHƯƠNG TRÌNH ĐÀO TẠO QUỐC TẾ)

LUẬN VĂN THẠC SĨ CÔNG NGHỆ HÓA HỌC

NGƯỜI HƯỚNG DẪN KHOA HỌC:
PGS. TS NGUYỄN THỊ DIỄM TRANG







HÀ NỘI- NĂM 2007

HANOI UNIVERSITY OF SCIENCE DRESDEN UNVERSITY OF TECHNOLOGY





NGUYEN VAN THAI


STUDY ON COMPACT DEVICE FOR WASTE PROCESSING
BASED ON MECHANICAL BIOLOBICAL TREATMENT
IN DONG VAN TOWN, DUY TIEN DISTRICT,
HA NAM PROVINCE, VIETNAM



MASTER THESIS

Field: waste management and contaminated site treatment




Supervisor: Assc. Prof. Dr. Nguyen Thi Diem Trang








HANOI, DECEMBER 2007




1

INTRODUCTION
The rapid economic development has resulted in the difficult task of
identifying way to manage the increasing waste generation, especially solid waste
problem. Solid waste is generated from production and life activities in all sectors
such as households, industry, hospitals, commerce, and agriculture.
Vietnam, a developing country, is certainly facing with a big problem of
rapid waste generation. Therefore, finding out effective solutions of waste
management and treatment has become an important issue in Vietnam. Actually, the
Vietnamese government has tried to carry out preliminary steps in order to control
waste generation in recent years. However, most of these steps just focus on
available technologies in large-scale applications in industrial cities. Whereas waste
treatment technologies in small-scale applications has not been paid much attention.
The main reasons are due to high cost and skillful requirements of operation and
management.
Moreover, there has not any effective waste management model for small
capacity in townships where the population is not so big and amount of waste is 20
– 40 tons/day [Dong Van URENCO, 2006]. If waste management does not
implement well in these areas, risks from pollution will, as a result, be highly
serious. Therefore, finding out the best solutions to protect environment is a very
necessary and urgent matter in townships.

Taking that serious problem into account, one of model companies named
Hydraulic and Machine Company Ltd. has completely manufactured an effective
system, which was named Compact Device, for municipal solid waste treatment
(so-called CD-Waste System). This system was designed based on mechanical
biological treatment system which has been applied since long time before. It has
considered to be suitable in small-scale applications in townships. Besides, another
company named Dong Van Urban Environment Company Ltd. has also been
established in Dong Van town, Hanam province in order to respond to national




2

policies of socialization in environmental protection. The two companies have
closely cooperated to implement a project named “Waste Collection and Treatment
System Using CD-Waste Technology with Capacity 20-30 tons per day” in Dong
Van town, Duy Tien district, Hanam Province.
Based on this project, I had carried out this study named “Study on
Compact Device for Waste Processing based on Mechanical Biological
Treatment in Dong Van town, Duy Tien district, Hanam province, Vietnam”.
This study aims at:
 Completion of clearness about theoretical and practical issues from
CD- Waste Technology applications.
 Assessment of CD-Waste Technology applicability in Dong Van town,
Duy Tien District, Hanam Province
 Cost planning and pre-calculation of waste treatment Plant in Dong
Van Town, Duytien District, Hanam Province.






3

Chapter 1: OVERVIEW
1.1 Waste
1.1.1 Definitions and concepts
The term waste is defined in the Vietnamese law on environmental
protection of November 29
th
, 2005. According to this definition “Waste means
materials that take solid, liquid, gaseous, or other forms, are discharged from
production, service, daily life or other activities [Environment law, 2005].
Municipal solid waste (MSW) includes the solids discarded by the end of
consumers, i.e. private households, small business and public areas and typically
collected by public authorities for disposal. Normally, separated collected waste for
recycling such as paper, metals, aluminum, glass etc. is included in the MSW
quantities given. MSW refers specifically to that part of MSW which is sent to
landfill, incineration, or other final treatment [Christian Ludwig et al., 1999].
Waste management refers to all activities engaged with waste segregation,
collection, transport, reduction, reuse, recycling, treatment and disposal
[Environment law, 2005].
1.1.2 Waste generation in Vietnam
Solid waste generation in Vietnam is approximately 15 million tons per year.
Among them, municipal waste generation is about 12.8 million tons (making up
80%), and industrial and agricultural waste generation normally contribute the rest
2.2 million tons per year (making up 20%) as shown in figure 1 [VEM, 2004].
80%
1.40%

17%
1.60%
municipal waste
hazardous
healthcare waste
industrial waste
others

Figure 1: Different waste generated (by percent) in Vietnam, 2003




4

In Vietnam, big and industrial cities are major waste generation sources.
According to national statistical report in 2004, big cities and urban areas keep only 24
percent of the total nationwide population; however, they produce over 6 million tons
of municipal waste (making up 50% of nationwide municipal waste amount). This is
due to an affluent lifestyle, larger quantities of trade and commercial activities, and
more intense industrialization and urbanization. Along with, these activities also
increase high proportion of hazardous waste (such as batteries and chemical solvents)
and non-degradable waste (such as plastic, metal, and glass) normally found in
municipal solid waste. In contrast, people living in rural areas make up 76% of the total
nationwide population but produce just less than half of waste generation rate of those
in urban areas. As shown in waste generation rate is approximately 0.3 kg/cap/day in
rural areas compared to 0.4 kg/cap/day in urban areas.
Table 1: Municipal solid waste generation at the glance [VEM, 2004]
Municipal solid waste generation (tons/y)
• National

• Urban areas
• Rural areas

12,800,000
6,400,000
6,400,000
Municipal waste generation (kg/per/day)
• National
• Urban areas
• Rural areas

0.7
0.4
0.3
Collection of waste (% of waste generated)
• Urban areas
• Rural areas
• Among urban poor

71%
<20 %
10-20%
Number of solid waste disposal facilities
• Dumps and poorly operated landfills
• Sanitary landfills

74
17
Generally, comparing to the standard on domestic solid waste (DSW) in
other countries, the amount of domestic in Vietnam is much lo wer [Luu Duc Hai,

2001]. Forecasting in 15-20 years, domestic solid waste amount in big cities in




5

Vietnam will reach the same level of 1.2 kg/cap/day as big cities in other Asian
countries [Pham Ngoc Dang, 2000].
Waste composition varies spatially and temporally based on life and
industrial activities. Each city has its own lifestyle, civilization level, and
development rate. As a result, they have different waste composition. Besides,
waste composition normally varies in different times of the year. For example, in
holidays and festive occasions such as Lunar New Year, organic and yard waste
ratios are commonly higher than those in the rest of the year [Nguyen Khac Kinh et
al., 2001].
Generally, there are two main components in DSW in Vietnam: (i) bio-waste
(making up 30-50%); and (ii) soil, sand, construction materials and other inorganic
stuffs (making up 20-40%) [Nguyen Thanh Yen, 2004]. Compared to those of many
other countries, increasing rates of glass, plastic, metal, paper are lower due to
waste activities of potential scavengers (garbage pickers) in Vietnam [Nguyen Thuy
Thu Thi, 2005]. Table 2 shows domestic solid waste compositions in some big
cities in Vietnam.
Table 2: Composition of MSW in some cities in Vietnam in 2002 [NEA, 2003]
Unit:%
Composition
Provinces, cities

Hanoi
Viet Tri

Ha Long
Tay Ninh
Organic
53
55.0
49
63
Rubber, plastic
9
4.5
3
8-12
Paper
1
7.5
5
5-6
Metal
5
0.2
1
1-4
Glass, ceramics
3
0.6
4
2-4
Construction waste
28
32.1

39
13-22
1.1.3 Municipal solid waste management in Vietnam
1.1.3.1 Waste collection
Municipal solid waste collection in urban areas in Vietnam has been
systematically organized. And, state-owned companies so-called Urban
Environment Companies (URENCOs) in the whole country are responsible for
waste collection. Each city and/or town has either one or more than one URENCOs.
It depends on their size and population. Nowadays, some private companies begin




6

Waste
sources
Collecting
organization
Treatment
Transfer
station
Collection
Handcart
Handcart
Transport
Transport
truck
Household
office

school
hospital
market
roads
URENCOs and
Environment
sanitation
cooperatives
environment
sanitation team
Transfer
stations of
wastes
collected daily
Landfills
to take part in implementation of waste collection in some cities and towns. This
trend is expanding in many urban areas in accordance to the Government‟s policy as
an attraction of all economic sectors to take part in municipal waste collection and
treatment.
Waste collection rate has been improving, however it remains low in many
cities. The national average collection rate of municipal waste in urban areas rose
from 65% to 71% between 2000 and 2003. Collection rates are typically higher in
larger cities, and range from 45% in Long An to 95% in Hue City in 2003 [NEA,
2003]. But in small and medium town the waste collection rate is only 20-30% of
the total volume of solid waste discharged [Nguyen Loan Thi, 2003].
In addition, funding sources for the operation of waste collecting and
transporting organization in urban and rural areas is somewhat dependent on the
budget of local administration and contribution of households as user‟s fee (the
contribution rate is decided by the local administration and often is VND 2,000-
3,000/person/month in major cities. Figure 2 shows the model of solid waste

collection and treatment in urban areas in Vietnam in which mainly urban
environment organizations collect and transport waste to landfills.
















Figure 2: Model of collection and treatment of municipal solid waste in Vietnam
[Nguyen Danh Son et al., 2005]




7

Besides, complete separation of solid waste at source has not yet been done
widely in Vietnam at present. Waste separation at source is being experimented in
some major cities (Hanoi, Da Nang, Ho Chi Minh…) and will be expand in the
future to reduce the pressure for treatment of solid waste (disposal, reusing,

recycling, composting etc.)
1.1.3.2 Municipal solid waste disposal
Waste recovery, recycle and reuse are somewhat limited in state level. Most
of the solid waste is treated by disposal at landfills. Landfills in all localities
including major cities which have already been built do not reach sanitary standards
and are not planned to match the rapid development of industrialization and
urbanization. Of the 91 disposal sites in the whole country, only 17 are consider as
sanitary landfills [VEM, 2004]. By the middle of 2004 only half of the provinces
and cities in the country (32/64) had the investment projects on the construction of
sanitary landfills, of which 13 cities have already started construction [VEM, 2004].
The existence of landfills in different localities has caused urgent environmental
problems to not only surrounding communities but also people in the areas where
waste is collected.
Incinerating waste is not a common practice in Vietnam. A few hospitals in
the country have incinerators which they use but overall the healthcare industry‟s
waste is primarily disposed in landfills. For the hospital waste that is incinerated,
little data is available on the amount or type of waste being incinerated because they
do not keep records [Nguyen, 2005]. Whatever the case, even though the
incinerators are assessed by the government for technical standards and gas
emissions, Vietnam lacks the technology to be able to analyze dioxin concentrations
emitted by the incinerators [Nguyen, 2005].
1.1.3.3 Reusing and recycling
Reusing and recycling of solid waste are a trend of development in
environmental management in general and waste management in particular. A
network of recycling waste has been formed for many decades with collectors of




8


domestic waste from households (waste paper, plastic, metal and glass), dealing
points of collected waste materials and recycling establishments.
For municipal waste, the Vietnamese government can subsidize recycling
and treatment facilities and it is important to build up municipal capacity to recycle
waste. The private sector should be encouraged to manage and recycle industrial
and hazardous waste, which are usually not managed by municipalities.
The Vietnamese government is advocating the establishment of a new
industry that is waste recycling industry. The channel of reusing and recycling of
solid waste in urban areas in Vietnam can be imagined as shown in figure 3.

Figure 3: Channels of Municipal Waste Reuse [Nguyen Danh Son et al., 2005]
1.1.3.4 Composting and recovery
Composting is a very useful form for recycling of organic wastes to produce
a clean soil conditioner and could help to increase the recovery rate of recyclable
materials. Composting also is a good way to reduce environmental pollution at
landfill if organic waste was disposal. This could contribute to a more efficient
municipal solid waste treatment, but it is not yet widespread for a number of reasons
such as: inadequate attention to the biological process requirements; poor feed stock
and poor quality of the fertilizers; poor marketing experiences. To support
composting, the development of a strong market for intensive agriculture is
necessary.
The effectiveness of centralized composting facilities could increase
considerably. Centralized composting facilities are large-scale waste treatment plants
Waste pickers
on the streets
Waste pickers
at the landfills
Household
goods not used

Waste
collecting
groups
Sidewalk
depots
operators
Itinerant
buyers
Recycling industry




9

that draw on an urban area for their organic waste supply. Several of these facilities
are currently operating in Vietnam, but no data are available on their cost-
effectiveness (Table 3).
Table 3: Status of selected Centralized Composting Facilities in Vietnam [VEM, 2004]
Location of
Facility
Capacity
(tons/day)
Opened
Source of
Organic
Waste
Status
Nam Dinh
City

250
2003
Mixed
municipal
waste
Operating. Compost provided
to farmers free of charge.
Hoc Mon, Ho
Chi Minh City
240
1982;
closed
1991
Mixed
municipal
waste
Closed due to difficulties in
selling compost
Thuy Phuong,
Hue
159
2004
Mixed
municipal
waste
Operating. Sells compost for
1100 VND/kg to coffee and
rubber farmers.
Cau Dien,
Hanoi

140
1992;
expanded
in 2002
Market and
street waste
Operating. Selling three
products with different
quality for 800, 1200, and
2000 VND/kg
Phuc Khanh,
Thai Binh1
75
2001
N/A
Operating
Trang Cat, Hai
Phong City
50
2004
Sewers, mixed
municipal
waste
Trial period
Viet Tri City,
Phu Tho
Province
35
1998
N/A

Operating. Selling 3 products
with different quality for 200,
250 and 900 VND/kg
Phuc Hoa –
Vung Tau city
30
N/A
N/A
Operating

The compost produced at these plants often contains broken bits of glass,
metals and is therefore difficult to sell. Since centralized composting plants in other
Asian countries have failed when relying on mixed municipal waste as their main
feedstock, source separation initiatives are being tested in Vietnam. In Hanoi, for
example, waste from markets or separated household waste from test areas are
being used as clean sources of organic matter for composting plant. Thank to source
separation the quality of composting product is improved. In addition, old landfills
have been used as sources of income. Organic waste decomposes naturally in




10

landfills and, if it is not contaminated by glass, heavy metals, or other pollutants, it
can be recovered for use as a soil conditioner.
1.1.4 Situation of Vietnamese technology for domestic waste treatment
Some waste treatment technologies in large-scale applications in urban areas
have been designed and installed in Vietnam. They were combined to treat solid
waste, wastewater as well as polluted air. Technologies which meet Vietnamese

environment standards are 1/2 - 2/3 cheaper than those of imported technologies.
For example, some waste treatment plants in Vietnam have been designed and built
by Vietnamese engineers such as: Dong Vinh Waste Treatment Plant in Vinh City-
Nghe An Province. This plant uses Seraphin technology with the capacity from 80-
100 tons/day. In Hue City there is another plant named Thuy Phuong Waste
Treatment Plant. It applies technology of An Sinh Company (ASC technology) with
the capacity of 300 tons/day. By applying this technology, 85 – 90% waste can be
recycled, and only 10-15% waste was disposed in landfills and no leachate releases
[INEST, 2003].
However, the manufacture of equipments and technologies remain in private
sector. Most of technologies have been designed and installed by institutes and
environment centers and/or environmental consultant companies. There has no
professional producing firm so far to produce environmental equipments and there
has also no trademark related to environmental industry. Although, big demand on
waste treatment is really necessary, capital for investment is insufficient and there
has no professional investor for manufacturing, business of environment
equipments.
Moreover, most of waste treatment technologies have been applied in large-
scale in Vietnam. However, there have some difficulties during waste treatment in
townships in small- and medium-scale due to the followings reasons:
 Scales of applications as designed are only for treating big waste amounts
(for 80-100 tons/day), whereas, amounts of waste generated in townships are
around 30 tons/day.




11

 High requirements of operation skills.

 Lack of money for waste collection, transport and treatment [Dong Van
URENCO, 2006].
Thus, it is really necessary to produce optimal technologies for waste
treatment in townships. Taking this problem into concern, Hydraulic Machine
Company Ltd., a company designs synchronous equipments as well as specific
equipments for industries, has introduced an equipment system for waste treatment
in small- and medium-scale named CD-Waste technology with small capacity of 20
- 30 tons/day. This technology has demonstrated to be effective and suitable with
small-scale applications in townships [Dong Van URENCO, 2006].
1.2 Current situation of waste management in Dong Van town, Duy Tien
district, Ha Nam province
1.2.1 Introduction to Dong Van town
Being a town located in the West of Duy Tien District, Ha Nam province,
Dong Van covers a natural area of 383.15 ha, in which 222.82 ha is for agriculture,
47.5 ha is urban land. Total population of the town is 5,202 people including 1,344
households, in which 858 households that make up 64% are small scale industry,
commerce and service, 388 households rely on agricultural based economy, making
up 29%. Average income per capita is VND 4.56 million /year in 2005. And
21.61% of GDP mechanism is from agriculture and 78.39% is from industry, small
scale industry and service [Dong Van URENCO, 2006].
Dong Van has advantage in traffic with train station and highway running
over. It also has potentialities for industrial development and urbanization, in which
a part of Dong Van is industrial zone. Industrial zone invested by 33 units and
companies with more than 2000 workers.
Previously, Dong Van was named as “waste town” because waste was not
collected. Sanitary landfills are not planned. Landfilling was a traditional method
that used to be carried out for waste collection and treatment activities of the town.
Groups of environment sanitation were spontaneously established in the town. Daily





12

collection capacity was about 2.5 to 3 tons of waste. Actually, there is a landfill in
town. This landfill of the town had an area of about 1,000 m
2
. It has deep of 2.5 –
3m. It is located 2km far from the town. Up to now, the covered area of this landfill
is 400m
2
[Dong Van URENCO, 2006]. However, because landfill does not strictly
manage, serious pollution has been caused. Besides, bad odor was released, leachate
that infiltrates into underground water system also cause pollution. More seriously,
waste is discharged in to highway sides, it makes lots of nylon bags and the other
dirty things flying to the roads. It caused dangerous for transportation vehicles on
the town. Dong Van and other areas have to face up with many difficulties in waste
management because there is no waste treatment system in the whole district.
Moreover, the district is far from the center of province, thus it is difficult to
transport waste into landfill.
With this situation, a citizen in Dong Van town whose name Do Phat Trien
established “Dong Van urban environment company Ltd.,” in October, 2006 trading
in waste collection and treatment within the town area and other surrounding
communes. This company has cooperated to Hydraulic Machine Company Ltd. in
pilot operation of waste collection and treatment system with Compact Device
technology (CD-Waste technology). This system has been operating for more than
10 months.
1.2.2 Dong Van Urban Environment Ltd. Company
The establishment of urban environment company connecting waste
collection, transportation and treatment (by using CD–Waste processing) at small

and medium scale in towns is a new approach of waste management in local area.
During 10 months period, Dong Van Urban Environment Company (Dong
Van URENCO) is a new company, its collection scale is still small. The existing
number of collection workers is 19 people and divided into three groups.
1. Waste collection group by handcrafts (consisting of seven people):
collecting waste from wards, quarters and markets by handcrafts and after
that waste was concentrated in certain areas




13

2. Transportation group (consisting of three people): collecting waste from
collection system point on small trucks and transport to treatment area.
3. Waste separation and treatment group (consisting of nine people): carrying
out visual inspection and pick up waste on conveyors, putting waste into
composting tower and mature tower, moving inert waste into combustor,
packaging and transporting compost materials, transporting classified nylon
to sell to purchasers.
Waste collection activities are taken place along streets. Waste is put in
plastic buckets and placed at roads‟ sides. Collection time is from 15h –18h.
With present capacity, the company can only collect waste at residential
areas close to big roads and markets. The estimated collection efficiency is 50%-
60%. The collected waste amount is about 2.5-3 tons/day.
In the first pilot period, the waste treatment using CD-Waste technology is
achieved good result. It has reduced environmental pollution. Some materials are
recycled and reused. This model has brought a deep change in waste management
method in town. It has associated waste collection, transportation and treatment
system in an enterprise.

Although, CD-Waste system has just applied in small scale in Dong Van
town, the effectiveness is quite good. This system was designed by Vietnamese
engineering based on mechanical biological treatment method that was applied for
long time in the world. However, this system has not been considered about the
theoretical of mechanical biological treatment. Therefore, it is necessary to study on
this system in order to reach a standard as mechanical biological treatment
1.3 Introduction of mechanical biological treatment
1.3.1 Definition of mechanical biological treatment
Mechanical biological treatment (MBT) of municipal solid waste is defined
as the processing or conversion of waste from human settlements (household…)
which include biologically degradable component by a combination of mechanical




14

processes (eg. crushing, sorting, screening) and biological processes (aerobic
“rotting”; anaerobic fermentation) [Christian Ludwig et al.,1999].
Mechanical biological treatment is primarily considered as a method for
dealing with the residues of mixed waste once the dry-recyclable fraction (eg.
paper, card, plastics cans, glass etc. and to an extent garden waste) has been reduced
and in some cases largely removed, through separate collection systems from
households. The MBT process is normally considered as a “pre-treatment” for
landfill but as technologies improve and legislation becomes clearer, other
applications geared more to recovery and recycling may be possible. However,
MBT also plays a key role in strategies including separate collection of food waste.
















Figure 4: Flow chart of mechanical biological treatment [Christian Ludwig et al., 1999]
At the beginning of the development MBT, it was applied as a pre treatment
technology for residual waste before landfilling. It aimed primarily at the reduction
Pre treated waste for deposition





Mechanical processing &
material flow separation
Biological treatment
Input
material
MSW
(100%)

55% organic

rich material
Anaerobic stage
Optional
35%

20%

35-
40%

Fe- metals
Non- ferrous metals
Glass (optional)
<4%

<1%

<4%

Process losses
(optionally max.
10% as biogas)
High calorific
fraction (RDF)




15


of the mass, volume, toxicity and biological reactivity of waste, in order to
minimize environmental impacts from waste deposition such as landfill gas and
leachate emissions as well as settlements of the landfill body. Concerning these
points MBT completed with waste incineration. The recovery of reusable waste
components such as metals and plastics then was only an incidental to the
minimization of the waste amounts.
In recent years, the recovery of waste components for industrial reuse has
become an integral part in development of MBT, especially concerning the production
of refused derived fuels (RDF). Thus MBT is now an integrated technology for the
material flow management of MSW, where almost half of the input flow is recovered
for industrial reuse and only one third remains for deposition. Figure 4 shows an
example about an MBT plant to separate and to treat waste.
1.3.2 Technology of mechanical and biological treatment
Mechanical biological treatment comprises several mechanical and
biological process steps and combination thereof (figure 5).










Figure 5: Typical MBT Process [Heerman, 2002]
1.3.2.1 Mechanical pretreatment
The first step of the treatment consists of a mechanical process. The main
step of mechanical process is shown as following:
Size reduction

Size reduction is the unit operation used to reduce the size of the materials in
municipal solid waste. Size reduction is used to process materials for direct use for
Waste
input
Size
reduction

Screening
Mechanical
separation
Mechanical
separation
Metals
Other recyclables
Inert to
landfill
Biological
treatment




16

compost. It is an integral part of full-scale resources recovery facilities. It plays an
important role in waste processing, since it typically is one of the first in the series
of unit processes. Therefore, type and degree of size reduction has the major effect
on the performance of all equipment used in subsequent handling and separation.
Screening
Screening segregates material of various sizes into specific particle size

categories. Waste can be screened according to the size and at the same time
separated based on material characteristics, assuming that the materials remain in
the same particle size range. Thus screens can also be used for separation [B.
Bilitewski et al., 2000].
The screen‟s efficiency rating is based on the effective separation of the
screening process and is identified by the relationship between the fine fraction that
passes through the screen and the fine fraction in the initial feed.
Magnetic separation
Magnetic separation is the most commonly used technology for separating
ferrous from non ferrous metals. The removal of ferrous components is achieved by
using a permanent magnetic field. It generally uses an overhead magnetic separation
system that attracts ferrous material and conveys it away either perpendicular or
parallel to the waste transportation direction.
Density separation
Density separation is a technique widely used to separate materials based on
applied to the separation of shredded waste into major components: (1) the light
fraction, composed primarily of paper, plastics and organics and (2) the heavy
fraction which contain metals, wood, and other relatively dense inorganic materials.
Therefore thank to mechanical treatment municipal solid waste is sorted,
sieved, shredded, magnetically separated and homogenized. As result waste is
classified in several fractions, namely reusable materials, a fraction of high calorific
value, a heavy mineral fraction and a fraction rich inorganic which is readily
biodegraded [Christian Ludwig et al., 1999].




17

The main goals of the mechanical treatment are the recovery of valuable and

reusable components and create the conditioning of the waste (volume reduction,
particle size reduction, concentration of certain compounds) for an optimal
subsequent biological or thermal treatment.
1.3.2.2 Biological treatment
In the second step, a biological treatment under either oxy or anoxic
conditions follows mechanical treatment. Under oxygen conditions, the fraction rich
in organic matter is composted in drums or bins as well as in tunnels or windrows
requiring periodical agitation (turning). Fermentation under anoxic conditions
requires a closed system where resulting gases (mainly methane) can be collected.
The gas can be utilized for heating or as energy source advantage of this
technology. The finally residual fractions originating from the mechanical
biological pretreatment can be incinerated for volume reduction and energy
recovery or disposed in landfills. In this part aerobic composting will be considered.
Composting is a microbial process in which organic materials are aerobically
decomposed under controlled conditions to produce humus like product, compost.
The composting feedstock can have a variety of sources: residences, restaurants,
and other commercial establishment, and agricultural sources among others. The
use of aerobic composting has become an effective landfill diversion tool for
organic materials and a viable recovery and management option for municipalities.
Composting system of various types has become an important part of many
integrated management systems.
When composting is implemented, there are some factors effecting on
composting process.
Nutrient
Since the decomposition of organic substances is performed by
microorganism, a balanced nutrient ratio is required. Therefore, in addition to the
decomposable organic substances, the following mineral substances are also
desirable:





18

 Nutrients (e.g., nitrogen, phosphorus, potassium),
 Trace elements for microorganisms and plants,
 Alkaline buffers for the neutralization of CO2 and organic acids,
 Adsorption surfaces for the intermediate and final products of the
decomposition process,
 Growth media for numerous type of microorganisms [B. Bilitewski et al.,
2000].
Moisture
The presence of waste is necessary to the composting process, however the
balance of water to solids is a delicate parameter that can have a large impact on
aerobic activity. For the purpose of composting and organic feedstock analysis,
moisture content is expressed as the weight of water as a percentage of the total or
wet weight of the material
Moisture content = [(wet weight – dry weight)/wet weight] * 100
The literature reports a variety of ranges for optimum moisture content. This
number greatly depends on the type of feedstock, its particle size and the rate and
type of composting desired. Generally, ranges of 50-60% are desirable [Christian
Ludwig et al., 1999]. Moisture contents above 65-70% interfere with desired
oxygen levels. If the moisture content drops below 45- 50% it will interfere with
microbial activity.
C:N ratio
There is a significant amount of data and information in the literature
recognizing the importance of the carbon to nitrogen ratio (represented as C:N) to
the composting process. Attainment of an adequate ratio will produce significant
biological activity and minimize the potential for odors. A ratio between 25:1 and
35:1 is generally agreed upon as optimal for composting [Andi. F.et al., 1997]. In

the case of a heterogenous feedstock, the combination of many materials of varying
C:N ratios can be balanced to produce a mix with an overall ratio in the desirable
range. If there is too much carbon, biological activity will decrease‟ if there is too




19

much nitrogen the excess will be released as ammonia both a source of ordors and
toxic to microorganism.
Air pore volume
The air pore volume should be in the range of 25 to 35% [Bernd Bilitewski et
al., 2000]. Air pore volume and water content are therefore competing parameters.
pH
During composting the pH will follow a progressive pattern corresponding to
the type of microbial activity taking place. The pH will drop during the initial stages
of the composting cycle as microorganism breakdown the carbonaceous material
and produce organic acids. The synthesis of organic acids is accompanied by the
development of a population of microorganism capable of utilizing the acids as
substrate. This will cause the pH to microorganism have an optimal pH range of 6
to 7.5. Fungi have a wider optimal range from ph 5.5 to 8 and can more easily
tolerate changes in pH. It should be noted that if the pH rises to 9 nitrogen is
converted to ammonia and becomes unavailable to microorganisms [Christian
Ludwig et al., 1999].
Temperature
Like pH temperature is not usually a controlled variable but is an indicators
of the microbial activity existing in the decomposing mass. Both mesophilic and
thermophilic organisms are necessary for successful composting and these organism
are naturally present in organic material. Mesophilic microorganisms grow best at

temperatures between 25 and 45
o
C [Doedens H. et al., 1999]. As the
microorganisms metabolize the organic matter, carbon dioxide is generated; the
temperature of the composting mass rises. Under less than optimal temperatures
between 45 and 70
o
C so as the temperature of the composting pile rises, the
thermophilic microorganism dominates [Doedens H. et al., 1999]. The phase in
which the thermophiles are generating heat is the point at which pathogens are




20

destroyed. Thermophilic decompositions continue as long as sufficient nutrients and
oxygen exist.
1.3.3 Applying of MBT
The mechanical biological treatment of municipal solid waste has been
applied for approximately ten years, especially in German, Australia and
Switzerland on technical scale, but also in several developing and emerging
countries on a pilot plant scale.
Today, there are over 70 plants operating in Europe using some form of
mechanical biological treatment on residual waste [Heerman, 2002]. This total
includes several composting plants, particularly in Italy, that have been upgraded
with mechanical separation front-ends and could therefore be described as „Basic‟
MBT systems. Purpose-built MBT plants, where the mechanical and biological
processes are integrated into a single process system, and which incorporate
sophisticated environmental control systems, number over 30 in Europe. These

plants are mainly located in Austria, France, Germany and Italy with capacities
ranging from a few thousand tones per annum up to 200,000 tons per year. They
mainly process source segregated residual waste.




21

Chapter 2: CD-WASTE SYSTEM

2.1 Overview of CD–Waste system
Hydraulic Machine Ltd. Company completely manufactured an equipment
system at small and medium scale for waste treatment named CD-Waste technology
(capacity of 20 - 30 tons/day). This technology is considered suitable to townships.
It was registered to National Office of Intellectual Property of Vietnam – Ministry
of Science and Technology for technological copyright protection in July 2006
[Tam Sinh Nghia, 2007]. The principle of this technology based on principle of
mechanical biological treatment as mentioned above. In this part the practical issue
of this technology is considered.
Figure 6: Overall of CD-Waste system in Dong Van town
(from Hydraulic Machine Ltd.Company, 2007)
CD-Waste system consists of main six equipment groups: (1) group of
equipments for sorting and separating: shredder, permanence magnetic separator,
conveyor, screening, trommel; (2) composting tower; (3) group of equipments for
mixing and separating of organic waste after composting; (4) mature tower; (5)
plastic waste treatment system and (6) combustor (figure 6). With those groups of
equipment, the main processes of CD-Waste technology are shown in figure 7.

2

1
6
4
3




22





































Figure 7: Flow chart of CD-Waste processing in Dong Van town
[Tam Sinh Nghia, 2007]
Mixer
Packing
Nylon package
Receiving area and reduce
moisture

COMBUSTOR
RECYCLABLE
WASTE FOR
SELL
WASTE
Receiving area
Shredder and magnetic

separation 1
Manual sorting
Vibrating screen
Milling
Trommel
Magnetic separation 2

Organic waste
Composting tower
Grinder
Mature tower
Sorting
Composting
product
Metal
Metal
Microorganism
Favor, gas
Inorganic waste
Inorganic waste
reception area
Mixing
Additive
Mould
Pellet
Bricks
Nylon, plastic
reception area
Nylon
Landfill

Fibre and inert
stuffs
Bulky waste




23

As shown in figure 7 the CD-Waste technology includes some main
processes. Firstly waste is separated into each component. When waste is separated
into organic waste, inorganic waste, plastic, metal etc., it will be treated by different
way. Organic waste is treated by biological treatment method. Inorganic waste will
be transferred to landfill or pre-treated and then used as material for construction.
And plastic can be recycled. Each step will be shown more in detail below
2.2 Separating system
2.2.1 Main equipments for waste separating
The separating equipment group includes (figure 8): (1) Funnel, (2)
permanence magnetic separator, (3) shredder, (4) conveyor, (5) vibrating screen, (6)
air classification system, (7) mill, (8) trommel.

Figure 8: Separating equipments (from Hydraulic Machine Ltd. Company, 2007)

2.2.2 Waste sorting and separating
Domestic waste in Dong Van town was collected and transported to the
receiving area of CD-Waste treatment station in the evening and at night. In this
area, waste is deodorized by biological production. A visual inspection in the
receiving area is intended to prevent large waste component from entering the
processing equipment in the first place.
2

1
3
4
5
7
8
6
5