study on compact device for waste processing based on mechanical biological treatment in dong van town, duy tien district, ha nam province, vietnam

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, D

-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

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

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

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 29th, 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 ]

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

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)

• Dumps and poorly operated landfills

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 tem porally 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 e xample, 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:%

It depends on their size and population Nowadays, some private companies begin

Waste

sources

Collecting organization

Treat ment Transfer

station Collection

Transfer stations of wastes collected daily

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]

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 i n 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 consi der 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 hospit als 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

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

collecting

groups

Sidewalk depots operators

Itinerant buyers

Recycling industry

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 o f

Facility

Capacity (tons/day) Opened

Source of Organic Waste

Status

Nam Dinh

Mixed municipal waste

Operating Compost provided

to farmers free of charge

Closed due to difficulties in selling compost

Thuy Phuong,

Mixed municipal waste

Operating Sells compost for

1100 VND/kg to coffee and rubber farmers

Operating Selling three products with different quality for 800, 1200, and

2000 VND/kg Phuc Khanh,

Operating

Trang Cat, Hai

Sewers, mixed municipal waste

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

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 scale in Vietnam However, there have some difficulties during waste treatment in townships in small- and medium-scale due to the followings reasons:

large- 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

 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 ec onomy, 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

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 m2 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 400m2 [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

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 intocomposting tower and mature tower, moving inert waste into combustor, packaging and transporting compost materials, transporting classified nylon

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

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

Anaerobic stage Optional

35%

20%

40%

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]

Mechanical separ ati on

Inert to landfill Biologica l treatment

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]

The main goals of the mechanical treatment are the recovery of valuabl e 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

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:

 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

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 nit rogen 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 45oC [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 70oC 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

destroyed Thermophilic decompositions continue as long as sufficient nutrients and oxygen exist

1.3.3 Applying of MB T

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

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) matur e 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

Figure 7: Flow chart of CD-Waste processing in Dong Van town

[Tam Sinh Nghia, 2007]

Receiv ing area

Shredder and magnetic separation 1

Manual sorting

Vibrat ing screen

Milling

Tro mme l Magnetic separation 2

Mixing

Additive Mould

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 tr eated 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

Waste was picked up by crane into the bunker where use heat from combustor

to reduce moisture, and then waste will be separated in next morning day

Moisture of waste is an important factor when waste is treated in Vietnam If waste is too wet, it will stick lots sand and stone It leads to have difficulty during treatment Therefore moisture of waste is checked before waste is separated The moisture of waste is around 50-55% before feeding into shredder

Shredder has not only function as cutting to reduce size of feedstock but al so

as adjusting the feeding speed that ensures feedstock spread out on conveyor (continuously) with the thickness less than 15cm in accordance with speed of conveyor and suitable with manual sorting stage

Magnetic separator

Thank to shredder at the first step, the material was reduced the size and the ferrous material from all the other parts was separated The MSW particle size for magnetic separator is from 10 to 100mm

Manual sorting

When waste is on the conveyor, 2-4 workers stand at two sides of conveyor belt to sort out the large waste such as: shoes, wheel, grass bottle, nonferrous, porcelain and the other things (including hazardous waste)

Manual sorting takes advantages of the individual physical characteristics of each waste type This is a step that has a very important role in the whole technology system of municipal solid waste collection and treatment

 Waste stream between two layers of screen (the size from 10 to 40mm): organic waste stream using for biological treatment

 Waste stream on the top of screen (larger than 40mm): large organic waste, plastic

Then, waste stream on the top of vibrating screen goes into air classification system to separate light fraction In this system most of plastic which has light weight will be separated The organic stream that has heavy weight will go down into a mill under air classification system to cut and to reduce the size After that, this organic stream moves into trommel In which organic stream is separated into 2 waste streams:

 Waste stream on trommel (larger than 35mm): organic fibre, and inert stuff used as material for combustion

 Waste stream under trommel (smaller than 35mm): organic waste used as a feedstock for composting

The organic waste stream from the middle layer of vibrating screen (number

5 in figure 8) and from under layer of trommel (number 8 in figure 8) are taken out

at the same outlet of separating system

Waste stream after moving through the separating system is separated into different components: inorganic waste, organic waste and inert stuff or fibre

2.3 Biological treatment system

Organic waste stream that was separated at the first step will be continuously treated in composting tower and mature tower The main steps for organic waste treatment are shown in figure 9

Figure 9: Flow chart of organic waste treatment process

[Tam Sinh Nghia, 2007]

Before organic waste is fed into composting tower, it will be optimized all of factors affecting to the biological treatment such as moisture, C:N ratio

In CD-Waste system, the moisture of waste is optimized at 55% before feeding into composting tower and C: N ratio was balanced at 30:1 However, because there is

no laboratory for checking these factors, most of the way to check moisture and C:N ratio are by using the experiences of workers and staffs there

After complementing microorganisms and optimizing C:N ratio, moisture content Mixing process is implemented for homogenizing the material

Organic stream was lifted up to the top of composting tower

Optimization of moisture (40-50%) and adding microorganism decomposing lignin

Composting product

Quality - checking

Not qualified yet

Crushing Dòng hữu cơ thô

2.3.1 Composting tower

2.3.1.1 Structure of composting tower

The structure of composting tower includes 9 parts as shown in figure 10

Notes:

(1) Inlet (2) Gear (3)Composting tank (4) Lobby

(5) Fan (6) Airsupplying (7) Operating centre (8) Rotary

Figure 11: Structure of sidewalls in composing tower in Dong Van town

(from Hydraulic Machine Ltd Company, 2007)

2.3.1.2 Operation of composting tower

In composting tower, aerobic composting consumes large amounts of oxygen, particularly during the initial stages If the supply of oxygen is l imited, the composting process may turn anaerobic, which is a much slower and odorous process So there must be adequate oxygen to support the dominance of the aerobic microorganisms The air is provided through slots in the side walls The sidewalls play an important role in composting towers It supplies air for composting and keeps temperature in composting

According to Hydraulic Machine Ltd Company, depending on the season in

a year temperatures are maintained in composting tower from 20 to 70oC as shown figure 12 [Tam Sinh Nghia, 2007] The thermophilic temperatures are desirable because they destroy more pathogens, weed seeds and fly larvae in the composting materials

0 10 20 30 40 50 60 70 80

Figure 12: Flow chart of temperature in composting tower at different seasons Composting in composting tower is operated in accordance with the mechanism with multi layers as shown in figure 13 The feedstock was supplied air circulation Thus, nutritive substances are retained in closed towers and they are not lost during evaporating when mass volume is thermogenetic

Figure 13: Composting mechanism of composting tower (from Hydraulic Machine Ltd Company, 2007)After composting tower is full and the composting product at the bottom layer is mature The pre-composted feedstock is taken out through an outlet at the bottom of the tower after a retention time of 10-11 days Because of insufficient mixing and aeration inside the tower, the decomposition quality of the organic material is not very good

2.3.2 Crushing and separating system for organic waste

The composted that is taken out from composting tower is moved to organic waste crushing and separating system in order to remove fibre, nondegradable

substances (figure 14)

Figure 14: Structure of crushing and separating system for organic waste

(from Hydraulic Machine Ltd Company, 2007)

The composted product is fed into organic waste crushing and separating system in which organic waste that is degraded is crushing into small pieces Organic waste moves into vibrating screen in this system This vibrating screen has

2 layers (one layer has slot of 15mm and one layer has slot of 5mm) to separate organic waste into 3 streams:

 Waste stream on vibrating screen (larger than 15mm): organic fibre, and inert stuff used as a feedstock for combustion

 Organic waste stream in middle layer (size from 5 to 15mm): organic waste This organic waste stream is not composted It needs to recompost in compost tower

 Organic waste stream under vibrating screen (smaller than 5mm): composted used as feedstock in mature tower

Organic waste that is degraded has smaller size than 5mm will be continuously picked up in top of mature tower to compost

2.3.3 Mature tower

2.3.3.1 Structure of mature tower

The structure of mature tower includes 8 parts as shown in figure 1 5

(1) Inlet (2) Operating center (3) Air supplying pipe

(4) Fan (5) Frame (6) Motor to take out feedstock

(7) Outlet (8) Air box

Figure 15: Structure of mature tower (from Hydraulic Machine Ltd Company, 2007)

2.3.3.2 Operation of mature tower

The size-reduced biowaste is fed into the top section of the maure tower The feedstock is moved and dumped through an opening to the next lower floor

The principle of operation is to supply air continuously and to combine with agitation These processes are characterized by continuous movement and aeration

of the feedstock Because the material is never static, dynamic composting processes have the advantage of contributing to the homogenization of the feedstock The microelement was retained in mature tower and not lost during evaporating when mass volume is thermo genetic Bad odors are adsorbed through biofilter layers in towers In addition, during the operation, the parameters affecting

to composing process such as temperature and moisture must be contro lled The moisture is about 45-47% and the temperature depends on the maturity of composting product after composting If the maturity is less than 70%, the temperature in tower is higher 22oC -25oC than temperature at outside If the maturity is more than 70%, the temperature in tower is higher 15-20oC than temperature at outside (from Hydraulic Machine Company, 2007)

After continuous mature composting in mature tower about 22 days, composing process will complete and form as mature product (figure 16) Then mature product is sold to farmer or professional fertilizer enterprises Mature compost has particle size from 2 to 3 mm It is dark brown color

The composting product does not purify because the waste treatment station has not system for purifying the composting product

Figure 16: Composting product (from Hydraulic Machine Ltd Company, 2007)

2.4 Waste combustion

2.4.1 Treatment step for waste that has combustible organic fibre

Bulky waste (rag, scraps of fabric, branches, wooden waste etc.) and other types of combustible waste are manually separated at receiving area, mixed with the other nondegradable substances from separation steps after organic waste treatment steps will be used as a material for combustor (figure 17)

Figure 17: The combustor (from Hydraulic Machine Ltd Company, 2007)

Firstly, materials are cut in small pieces and to minimize the moisture of waste through an equipment group for cutting and crush Then waste is put into combustor Inside a furnace, combustion occurs in two phases: primary combustion and secondary combustion In primary combustion, the temperature is 6500C, moisture is driven off then the burnable waste is volatilized and ignited In the secondary stage of combustion, the temperature is 8500C the remaining unburned gases and particulates which are entrained in the airstreams after primary combustion are oxidized The secondary stage of combustion helps to eliminate odors and reduces the amount of unburned particulates in the exhaust gases Auxiliary gas or fuel oil is used for furnace warm-up and to initiate primary combustion when refuse is very wet Auxiliary fuel also facilities complete secondary combustion and provides additional smoke and ordor control in exhaust

gases Ash is collected to combine with inert waste flow for compacting or level foundation

2.4.2 Control of particulates

As shown in figure 18, exhaust gases from combustions at around 800 -900oC flow through a tank This tank is reduced the temperature due to a fan under the tank The fan will supply air into tank At this time, the temperature will be reduced

to less than 400oC The exhaust gases go out of tank for reducing temperature will

be collected into a cyclone The aim of this cyclone is to remove dust in exhaust gas Dust has large weight will be separated at the bottom of cyclone The gases that have light weight go through the cyclone coming into a tower In this tower water is pumped in order to clean the gases before release out to environment

Figure 18: Process of control particulates [Tam Sinh Nghia, 2007]

2.4.3 Functions of combustion

Combustion step‟s functions are regulated as follows:

 Thank to combustion the waste volume decreases

 Energy that is generated from combustor is used for drying waste surface in receiving area

 Exhaust gas from combustor after treatment satisfies discharging standard (TCVN 5939-05)

2.5 Plastic waste treatment step

Nylon and plastic waste are valuable resource in municipal solid waste After being separated, they are preliminary cleaned They are continuous ly separated and subjected to preliminary treatment for useful products

Figure 19: Plastic waste and extruder in Dong Van The plastic feedstock may enter the extruder in a molten state but it usually is solid upon entering and is melted and pressurized inside the extruder The incoming feed may be in the form of granulated state after crush The plastic extruder consists

of a horizontal screw feeder that rotates inside a thick cylinder with the infeed hopper located at one end and the shaping die attached to the discharge area at the other end A combination of externally applied heat (when needed) and work done

on the plastic by the shearing and compressive forces of the screw feeder melts the plastic and at the same time mixes it to create a uniform temperature before it is forced through the die Profile extrusion is a variation of the general extrusion process In this case, products having a continuous length are made

recommendations

2.6.1 Applying of CD-Waste technology

CD-Waste technology is a domestic waste treatment technology suitable with small and medium scale of townships where amount of waste was discharged from

20 to 30tons/day It was selected to apply for some reasons as following:

Waste collection, transportation and treatment are closely connected in a plant

The area for installation of equipment is quite small (400m2)

The equipments look as modules When amount of waste is increasing, these equipments are easy to connect wit h other modules

It meets the demand of domestic waste treatment in town and village with capacity of 20-30tons/day

Domestic waste doesn‟t have to transport with the long distance to landfill Therefore, it saves the cost of transportation

In addition, domestic waste is instantaneously checked the moisture when it

is transported to waste treatment station Hence, it is easy to sort and separate waste components In addition, there is no leachate during treatment process Waste can be daily treated It therefore will not release the odor

Organic waste is separated most of impurities Thus, it is very convenient to compost in towers

Waste treatment is implemented in closed towers so as to minimize environment pollution The towers with 2 sidewalls can be used to keep the temperature and to supply enough air whole composting process

Effect of technology that was shown at Dong Van town, Duy Tien District,

Ha Nam province is very good It did not cause environmental pollution and created recycling products for living

The factors affecting on the biological treatment are not checked carefully before feeding into biological treatment system However, if these factors are not checked, it is difficult to get good composting product Therefore, in order to apply CD-Waste technolgoy better it is necessary to have a laboratory to test the bio -chemcial criterial such as water content, pH, impurities, C/N before feeding into biological treatment system

Composting product is not purified after maturation The quality of composting product will be higher if a system for purification is installed in CD-Waste system

The procedure for plastic waste treatment is quite urdimentary Platic waste after separating does not divided into different kinds of plastic Therefore quality of platic composting is not high Recycling plastic product has not been used widely

Chapter 3: IMPLEMENTATION OF EXPERIMENTS

3.1 Introduction

The main target of application CD-Waste system is to treat municipal solid waste effectively and to produce recycling products as well as to reduce amount of waste to landfill

The experiments were implemented during the writing master thesis in order

to assess the ability of waste treatment as well as to consider the practical issue of applying CD-Waste system Therefore, there are four experiment were conducted in Dong Van town

3.2 Composition of input w aste

Firstly, the composition of waste was checked before feeding into CD-Waste system The experiment was implemented on July 18th, 2007

The procedure of experiment is the following:

Step 1: Taking 306 kg waste stream

Step 2: Waste is sorted by using the two sieves

 Sieve has slot 40mm: waste is sorted according to the size: > 40mm,

<40mm

 Sieve has slot 10mm: waste is sorted according to the size: >10mm, and

<10mm

Step 3: Picking up each waste faction into a bucket

Step 4: Weighing for each waste composition

Step 5: The moisture content of waste materials were determined from the loss of weight after drying in an oven at 105oC

The procedure of this experiment is shown in figure 20

Figure 20: Flow chart of experiment to define waste composition

3.3 Composition of waste after separating system

Secondly, with the aim of checking the effectiveness of separating system, the composition of organic waste stream after separating is defined The procedure for defining composition of waste is shown as following:

Step 1: Taking 100 kg of organic stream

Step 2: Sorting out of impurities such as nylon, textile, paper, glass and other inorganic waste

Step 3: Weighing each type of impurity

Step 4: The remained organic stream was put into drum (200lit)

Step 5: Adding water until full of drum,

Step 6: Mixing to separate sand, stone, glass at the bottom of the drum

Manual sorting

Sampling

Drying Weigh