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

TECHNISCHE uy UNIVERSITAT DRESDEN HANOI UNIVERSITY OF SCIENCE DRESDEN UNVERSITY OF TECHNOLOGY NGUYEN VAN THAI STUDY ON COMPACT DEVICE FOR WASTE PROCESSING BASED ON MECHANICAL BIOLOBI

ĐẠI HỌC QUỐC GIA HA NOT TRUONG DAI HOC KHOA HOC TU NHIEN

—— — - oữa ——-: —

NGUYÊN 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

CHUYEN NGANH: QUAN LY CHAT THAI VAXU'LY VUNG 6 NHIEM

(CHUONG TRINH DAO TAO QUOC TE)

LUAN VAN THAC Si CONG NGHE HOA HOC

NGƯỜI HƯỚNG DẪN KIIOA HỌC:

PGS TS NGUYEN THỊ DIỄM TRANG

HÀ NỘI- NĂM 2007

TECHNISCHE uy) UNIVERSITAT

DRESDEN

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: Asse Prof Dr Nguyen Thi Diem Trang

HANOI, DECEMBER 2007

TNTRODUCTION

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 honschalds, 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

Tmanagerment and treatment has become an important issue in Vielnam AcLually, the

Vietnamese government has tried to carry out preliminary steps in order to control wanle generalion in recenl, years, However, most af these sleps 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 amaunt 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 Ihe best solutions to proiecl environment is a very

necessary and urgent matter in townships

Taking that serious problem into account, one of model companies named Ilydraulic and Machine Company Lrd has completely manufactured an effective

syslem, which was named Compact Device, for municipal solid wasle treatment

(so-called CD-Waste System) This system was designed basod 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 Td 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 distriot, Hanam Province

Rased on this project, T 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 eleamess about theerclical 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-calculalion of waste treatment Plant in Dong

Van Town, Duytien District, [lanam Province

wm

Chapterl: 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", 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, ie 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]

In Vietnam, big and industrial cities are major waste generation sources

According to nalional statistical report in 2064, big cilies and urban areas keep only 24

porcent 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

duc (o an affluent lifestyle, larger quantitics of trade and commercial activities, and

more intense industnalization aud whanization 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 lotal

naliomwide populalion but produce jusi less than half of waste generalion tale of those

in urban areas As shown in waste generation rate is approximately 0.3 ke/cap/day in rural areas compared to 0 ke/capiday in urban areas,

Table 1; Municipal solid waste generation at the glance [VEM, 2004]

Number of solid waste disposal facilities

Vietnam will reach the same level of |.2 kg/cap/day as big cities in other Asian countries [Pham Ngoc Dang, 2000]

Wasle composition varies spalially 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 tunes 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 arc lwo main componenis in DSW in Vietnam: (i) bio-waste (making up 30-50%), and (i) 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 activitics 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 insome cities in Vietnam in 2002 (NEA, 2003]

Unit.%

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

ta

to take part in implementation of waste collection in some cities and towns This trend is expanding in many urban areas in accordance to he Government's policy as

an altraction of all cconomic sectors to take parl in mumicipal wasie collcotion and

treatment

Waste collection rate has been improving, however it remains low in many cities The national average collection sate 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 Jown the wasle colleclion rate is only 20-30% of

the (otal volume of solid waste discharged [Nguyen Loan Thi, 2003]

In addition, funding sources for the operation of waste collecting and transporting organization in urhan 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 sities Figure 2 shows the model of solid waste

collection and treatment in urban areas in Vietnam in which mainly whan

environment organizations collect and transport waste to landtills

hospital cooperatives collected daily

roads somifation tem

Figure 2; Model of collection and treatment of municipal solid waste in Viewam

[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 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

wbanization 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 swrounding 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

domestic waste from households (waste paper, plastic, metal and glass), dealing poinls of collected waste materials and recycling establishments

For municipal wasto, the Victnameso goverment can subsidize recycling and treatment facilities and it is important to build up municipal capacity to recycle waste The private sector should be encouraged (o manage and reeyele 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 arcas in Viclnam can be imagined as shown in figure 3

Waste ‘Waste pickers ‘Waste pickers Household

collecting on the streets at the landfills goods not used

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 Lo 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 inlensive agriculture is

hecossary

The effectiveness of centralized composting facilities could ¡merease

considerably Centralized composting facilities are large-scale waste treatment plants

that draw on an urban area for their organic waste supply Several of these facilities

are currently operaling in Vietnam, but no dala are available on their cosl-

Nan Dith 250 2003 mamieipal | tofarmer fee ofcharpe

"ty waste

1982, Mixed | Cloeed due to difficulties in

_ 159 2004 mmniipal | 1100 VND/kg Lo coffee and

waste nuibber farmers 199% Operating Selling three

Cau Dien, 140 ° ade a Market and | products wilh different

Hanoi woooestteet waste | quality for 800, 1200, and

Phu Tho 35 1998 with different quality for 200,

Operal Pine Hea Vung Tau cily 30 NA A nang

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 countrics have failed when relying on mixed municipal wasle as their main

feedstock, source separation initiatives are being tested in Vietnam In Hanoi, for

example, waste from markets or separated houschold waste from tos! areas arc

being wed 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 or use as a soil condi ioner

114 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 Vicinam They were combined lo treat solid

waste, wastewater as well as polluted air Technologies which meet Vietoamese environment standards are 1/2 - 2/9 cheaper than those of imported technologies

For example, some waste treatment plants in Vietnam have been designed and built

by Vietnamese cngincers 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 im landfills and no leachate releases

[INEST, 2003]

Ilowever, the manufacture of equipments and technologies remain in private

sector Most of technologies have been designed and installed by institulss and

environment centers and/or environmental consultant companics 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 [lowever, 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 (ons/day,

10

Y Tlighrequirements of operation skills

¥ Tack of money for waste collection, transport and treatment [Deng Van

URENCO, 2006]

Thus, it is really necessary to produce optimal technalagies for waste trealment in (ownships Taking this problem inlo concern, Hydraulie 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 lons/day This technology has demonstrated to be effective and suitable with

small-scale applications it lownships [Dong Van URFNCO, 2006]

1.2 Current situation of waste management in Dong Van town, Duy Tien

district, Ila Nam province

1.2.1 Introduction to Dong Van town,

Boing a town located in the Wost 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 inchiding 1,344

households, in which 858 households Lhat make up 64% are small scale industry,

commerce and service, 388 houscholds rely on agricultural based ce 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 Ti also has potentialities for indusirial development and urbanization, in which

a pat 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 ta be carried out for waste collection and treatment activities of the town

Groups of environment sanilalion were spontancously established in the town Daily

collection capacity was about 2.5 to 3 tons of waste Actually, there is a landfill in

lown This landfill of (he town had an area of aboul 1,000 m* Ti has deep of 2.5 — 3m It is located 2k far from the town Up to now, the covered area of this landfill

is 400m” [Dong Van URENCO, 2006], However, because landfill does not strictly

manage, scrious pollution has bocn caused Resides, bad odor was rcleascd, leachale

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 arcas have to face up with many difficulties in waste

Tmanagement because there is no wasle Lreaiment system in (he 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

cslablished “Dong Van urban environment company Td,” in October, 2006 Lrading

in waste collection and weatment within the town area and other surrounding

communes This company has cooperated to Ilydraulic Machine Company Lid in

pilot operation of waste collechon and trealment syslem wilh Compacl 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 anew approach of waste management in local area

During 10 months period, Dong Van Urban Environment Company (Dong

Van URBNCO) is a new company, its collection scale is still small The existing sumber of collection workers is 19 people and divided into three groups

1 Waste collection group by handerafts (consisting of seven people):

collecting waste from wards, quarters and markets by handerafts and after

Ibal waste was concentrated in ceriain areas

12

2 Transportation group (consisting of three people): collecting waste from

collection system point on small trucks and transporl Lo Irealmeni area

3, Waste scparation and treatment group (consisting of nine people): carrying

out visual inspection and pick up waste on conveyors, putting waste into

composling tower and mature tower, moving inert waste inlo 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 al roads’ sides Collection lime is from 15h—-18h

With present capacity, the company can only collect waste al 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 perind the waste treatment using CD-Waste technology is

achieved good result Tl has reduced environmental pollution Some materials are

secycled and reused This model has brought a deep change in waste management

method in town It has associated waste collection, transportation and treatment

syslem 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 mevhanival biological treatment method that was applied for long time in the world Ilowever, this system has not been considered about the

theoretical of mechanical biological treatment Therefore, it is necessary to study on

this system in order (o reach aslandard as mechanical biological Ireatmient

13 Introduction of mechanical biological treatment

13.1 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

13

processes (eg crushing, sorting, screening) and biological processes (aerobic

‘yotting”; 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

(100%) material flow separation Glass (optional)

Non- ferrous metals

High calorific fraction (RDF)

rich material

Anaerobic stage onal (optionally max 10% as biogas)

Pre treated waste for deposition

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

of the mass, volume, toxicity and biological reactivity of waste, in order to

minimize environmental impacis from waste deposition such as landfill gas and

leachale cmissions as well as sctUlements of the landfill body Concernmg 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

iuinimization of the waste amounts

In recent years, the recovery of waste camponents for industrial reuse has

become an integral part in development of MBT, especially concerning the production

of refused derived fuels (RDF) Thus MRT is now an inlegraled technology for the

material flow managemen| of MSW, where almost half of the input Now is recovered

for industrial reuse and only one third remains for deposition Figure 1 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 combmation thereof (figure 5)

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

15

compost It is an imegral part of full-scale resources recovery facilities It plays an

important role in wasle 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 onthe 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 parlicle size range Thus screens can also be used for separation [B

Rilitewski et al., 2600]

The screen’s efficiency sating 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 1 generally uses an overhead magnelic separation

system that attracts ferrous material and conveys it away cither perpendicular or parallel to the waste trans portation 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 orgarue materials

Therefore thank to mechanical treatment municipal sclid 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 Tudwig et al., 1999],

16

The main goals of the mechanical treatment are the recavery 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 maller is composled in drums or bins as well as in tunnels ar 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 cnergy

secovery or dis posed in landfills In this part aerobic composting will be considered

Composting is a microbial process in which organic materials are aerobically

decomposed under controlled canditions to praduce humus like product, compost

The composting feadstock can have a varicly of sources: residences, restaurants,

and other commercial establishmenl, and agricultural sources among others The use of acrobic composting has become an cffective 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 comiposting is implemented, there are some factors effecting on

composting process

» Nutrient

Since the decomposition of organic substances 1s 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,

aerobic aclivity 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 wot weight of the malerial

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 dosirable [Christian

Ludwig et al, 1999] Moisture contents above 65-70% interfere with desired

oxygen levels If the moisture content drops below 15- 50% it will interfere with

35:1 is generally agreed upon as optimal for composting [Andi F.et al., 1997], In

the case of a heterogenons 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 1s too much carbon, biological activity will decrease’ if there is too

18

much nitrogen the excess will be released as ammonia both a source of ordors and

loxic Lo microorganism

« Air pore volume

The air pore volume should be in the range of 25 to 35% [Bernd Dilitewski et

al, 2000] Air pore volume and water contont are therefore competing parameters

« pH

During composting (he pH will follow a progressive pallern corresponding lo

the type of microbial activity taking place The pH will drop during the unitial 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 ulilizing 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 TL should be noted thal if the pH rises to 9 nilrogen is

converted to ammonia and becomes unavailable to microorganisms [Christian

Ludwig ct 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

lemperaures belween 25 and 45°C [Doedens H ef al., 1999] As the

microorganisms metabolize the organic matter, carbon dioxide is genoratcd, the

temperature of the composting mass rises Under less than optimal temperatures

belween 45 and 76°C so as Lhe temperalure of the composting pile rises, Lhe

thermophilic microorganism dominates [Doedens H et al., 1999], The phase in

which the thermophiles are generating heat is the point at which pathogens are

19

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 len years, especially in Gorman, Australia and Switzerland on technical sale, but also in several developing and emerging countries ona pilot plant scale

Today, there are over 70 plants operating in Europe using some form of

mechanical biological Irealment on residual waste [Hecrman, 2002] This total

includes several composting plants, parlicularly in Tlaly, thal 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 info a single process system, and which incorporate

sophisticated environmental control systems, number over 30 in Furope 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 segregaled residual waste

20

Chapter 2: CD-WASTE SYSTEM

2.1 Overview ofCD—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

21

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

[Tam Sinh Nghia, 2007

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

" 3

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

to reduce moisture, and then wasle will be separated im nexl momung 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

(reaiment Therefore moisture of waste is checked before wasic is separated The

moisture of waste 1s around 50-55% before feeding into shredder

Shredder has not only [nnetion as culting lo reduce size of feedstock bul also

as adjusting the feeding speed that ensures feedstock spread out on conveyor (continuously) with the thickness less than 150m 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 sive and the ferrous

material from all the other parts was separated The MSW particle size for magnetic separator is from 10 to LOUmm

« Mamual 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 umportant role m the whole technology system of municipal solid waste collection and treatment

* Screening

The waste stream that separated ferrous metal by magnetic separator and is sorted on conveyor will continuously move into the vibrating screen with two layers

in which waste was separaled into three streams with the different sive: more Ihan

40mm, from 10 to 40mm and smaller than 10mm

«= Waste stream al the lowest (less [han 10mm): such as sand, stone, slag, brick They were taken out and transferred to inorganic acceptance area

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

"Waste stream on the fop of screen (larger than 10mm): 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

" Wasle stream under (rommel (smaller than 35mm): orgamic waste used as a

feedstock for composting

The organic waste sircam 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 Libre

2.3 Biological treatment system

Organic waste stream that was separated at the first step will be

continously treated in composting tower and mature tower The main steps for

organic waste treatment are shown in figure 9

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Coarse organic waste

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

Tieue 9: Flow chart of oreanie waste treatteiit pEocess

[Tam Sinh Nghĩa, 2007]

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

In CD-Weaste system, the moisture of waste is optimized at $5% before feeding inta

composting lower and C: N ralio was balanced al 30:1 However, because there is

no laboratory for checking these factars, most of the way to check moisture and CN

ratio are by using [he experienecs 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 Lo the lop of composting tower

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2.3.1 Composting tower

2.3.11 Structure of composting tower

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

Figure 10: Structure of composting tower

(from Hydraulic Machine Ltd Company, 2007)

Within the composting tank, the sidewalls have 2 layers: Inside layer is made

from recyclable plastic in domestic solid waste (figure 11) It has slots for air flowing through The main function of this layer is to supply air for compost and to keep the

temperature inside the tower and ensure that the effect of compost process Outside

layer is made from stainless steel and the distance between two layers is Sem

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

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(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 limited, 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 70°C 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

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

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"Output

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

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

(from Hydraulic Machine Ltd Company, 2007)

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The composted product is fed into organic waste crushing and separating

syslem in which organic wasle that is degraded is crushing into small pieces

Organic waste moves into vibrating serecn in this system This vibrating screen has

2 layers (one layer has slat af 15mm and one layer has slot of Smm) to separate

organic waste inlo 3 streams:

" Waste stream on vibrating screen (larger than 15mm): organi fibre, and

inert stuff used as a feedstock for combustion

" Organic waste stream in middle layer (size from $ to 15mm): arganic waste

This organic wasic strcam is nol composted Il needs to rccomposl in compost (ower

* Organic waste stream under vibrating screen (smaller than Smm): composted

used as feedstock mm mature tower

Organic waste that is degraded has smaller size than 5mm will be continously picked up in lop of mature lower 10 compost

233 Mature tower

2.33.1 Structure of mature tower

The structure of mature tower includes 8 parts ax shown in figure 15

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 controlled 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 22°C -25°C than temperature at outside If the maturity is more than 70%, the temperature in tower is higher 15-20°C 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 ete.) 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 650°C, moisture is driven off then the burnable waste is volatilized and ignited In the secondary stage of combustion, the temperature is 850°C 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 800-900°C

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 400°C 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 continuously 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

2.6 The convenience of applying of CD-Waste technology and

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:

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

plant

2.6.2

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

The equipments look as modules When amount of waste is increasing, these

equipments arc casy to connect with olher 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

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

is transportedte waste treatment station Hence, it is easy to sort and separate

wasLe components Tn addition, there is no leachate during Ireatment process

Waste can be datly treated It therefore will not release the odor

Organic waste is separated most of impuritics Thus, it is very convenient to composl in towers

Waste treatment is implemented in closed towers so as to minimize

environment pollution The lowers with 2 sidewalls can be used to keep the

temperature and to supply enovgh air whole compostung process

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

Ila Nam province is very good It did not cause environmental pollution and

created recycling products for living

Recommendations

Beside the advantages of CD-Waste technology, this technology still has some difficulties dwing operation as following

To improve the quality of composting product, it is necessary to implement

source separation of household waste Solid waste separation at source is an

effective supporling measurement in he operation of CD-Wasle system Solid

waste will be sorted into sorted into organic and inorganic waste at the waste collection system before being collected ‘This process will make convenience for waste treatment in CD-Waste system

35

The factors affecting on the biological treatment are not checked carefully

before feeding into biological treatment system However, if these faclors are nol

checked, it is difficult to get good composting product Therefore, in order to apply CD-Waste technolgoy better it is necessary ta have a laboratory to test the bio-

chemeial crilerial such as water conlenl, pH, impurilics, 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 systom

The procedure for plastic waste trealment is quite urdimentary Platic wasle

after separating does not divided into different kinds of plastic Therefore quality of platic composting 1s not high Recycling plastic product has not been used widely

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Chapter 3: IMPLEMENTATION OF EXPERIMENTS

3.1 Intreduction

The main target of application CD-Waste system is to treat municipal solid waste effectively and lo produce recycling products as well as lo reduse 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 arc four experiment were conducted in Dong Van town

3.2 Composition of input waste

Tirstly, the composition of waste was checked before feeding into CD-Waste

system The experiment was implemented on July 18" 2007

The procedure of experiment is the following:

Step 1: Taking 306 kp waste stream

Step 2: Waste is sorted by using the two sieves

= Sieve has slot 40mm: waste is sorled according (o the size: > 46mm,

<40mm

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

<10mm

Step3: Picking up each waste faction into a bucket

Step 4: Weighing for each waste composition

Slep 5: The moisture content of waste materials were determined from the

Joss of weight after drying in an oven at 105°C

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 composilion of waste ia shown as following

Step 1: Taking 100 kp of organic stream

Slep 2: Sorting oul of impurities such as nylon, textile, paper, glass and other

inorganic waste

Slop 3: Weighing cach lype of impurity

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

Slop 5: Adding water until full of drum,

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

38