1. Waste Storage Unit

 

The first stage of waste
treatment comprises of Bio-waste and garden waste storage. Bio-waste and garden
waste are received and managed separately at this stage. G1 It
is necessary to have a dedicated storage space for waste to ensure a continuous
supply of feed, G2 which
is the municipal waste, to the plant and G3 avoid
any disruption or halt in operations that may be caused otherwise. G4 

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

Incoming waste is brought into
the reception area where eachG5 
loaded truck is weighed and registered before entering the facility.  Three different entry points with reception
and registration are considered to accommodate multiple vehicular entries into the
plant simultaneously. This is also G6 necessary
to evade any congestion at the entrance of the facility.G7 

A separate storage
area is allocated for the two different types of waste wherein weighed and
registered G8 delivery
trucks unload bio-waste and garden waste respectively.  There is a possibility of foul smell being
emitted should the waste be piled up on open space and in order to minimize
this issue as well as maintain hygienic conditions within the plant,
construction of closed area is to be done for storing both bio waste and garden
waste indoors. From the data given in contract, the total quantity of bio-waste
and garden waste is calculated. Seasonal variations of waste are consideredG9 
rather than an average values of bio-waste and garden waste throughout the
year. The data of the city of Kaunas, Lithuania 2009 are used and tons of waste
generated for primarily four seasons – spring, summer, autumn, and winter – are
calculated. The results are G10 as shown in Table 1. (Denafas et al., 2014)G11 G12 

Table 1: Total yearly waste and
seasonal variations

 

Bio-waste (Tons)

Garden waste (Tons)

Spring

16922.51

155.16

Summer

22445.94

372.42

Autumn

24407.16

263.79

Winter

16274.11

108.63

Total waste per annum

80049.71

900

 

To size the storage facility, it
is important to estimate the daily peak flow of both types of waste. This can
be calculated by averaging the incoming waste throughout each season and arrive
at the volume of waste for each day. Following which, the peak volume is now
considered to select the dimensions of waste storage area. The results are
depicted in Table 2.

 Table 2: Tons and volume of waste generated
per day

 

Bio-waste

Garden waste

Daily peak weight (tons)

268.21

4.05

Daily peak volume (m3)

670.53

26.99

Density (tons/m3)

0.4

0.15

 

 

The storage unit is designed to
store bio-waste and garden waste for a maximum period of two and five days
respectively. The peak volume calculated is used to size the storage facility
and dimensions are tabulated in Table 3.

 

Table 3: Dimensions of storage
facility

 

Bio-waste Storage Facility

Garden waste Storage Facility

Length (m)

40

4

Breadth (m)

9

9

Height (m)

4

4

Area (m2)

360

36

Volume (m3)

1440

144

 

2. Pre-treatment Unit

 

The aim of including
pre-treatment unit operations is to eliminate the unwanted substances present
in the incoming waste. As mentioned in the contract, bio-waste is expected to
have impurities between 2.6% to 5.4% and the content of it in garden waste is
estimated around 4.5%. The separation of these impurities is vital to
maintaining end pG13 roducts of uniform quality which may
otherwise cause disruptions in downstream processes, disturb the fermentation
process or affect the overall quality of compost.

The technologies available for
pre-treatment in the market are very specific and the luxury of a G14 large variety of options is not available, as in the
case of other industries. This is because waste management industry in itself
is in its nascent stage and the concepts of waste management have picked up
momentum only in the recent past. G15 In our pre-treatment unit, we’re
considering processes primarily for the purpose of separation and size
reduction and to achieve this, we are selecting machinery
which is well proven and belong to the category of best available technologies
for their respective operations.G16 G17  G18 G19 G20 

There are two possibilities of
treating the different types of incoming waste, i.e. bio-waste and garden
waste. One way to do this is to have two separate
treatment lines for each category of waste. However, G21 it is more appropriate to choose
this technique when the plant is treating a higher quantity of garden waste. In
this case, daily peak flow of garden waste is about 1.48% of overall peak daily
waste (4.04 tons out of 272.26 tons) and it makes much more sense to first
treat bio-waste followed by garden waste using the same pre-treatment machines.
So, for this proposed plant design, one single line treatment for both types of
incoming waste is chosen. This has quite a few advantages over two line
treatment system. For example, space, power consumption and extra investment on
equipment can be saved.G22 G23 G24 

 

 

 

 

 

2.1 Pre-treatment Process Flow

To remove ferrous metals    

To open larger plastic bags    

 

 

Magnetic
Separation

Bag Opener

Incoming Waste

 

 

Density Separator

Trommel Screen

Fine Shredder

To Fermenter /
Compost

 

 

To separate remains of plastics, paper, film from
upstream processes      

Larger particles separation from finer particles      

 

 

Figure 1: Pre-treatment Process Flow Diagram

 

The complete single-line
pre-treatment processes are depicted in Figure 1. Bio-waste and garden waste
are treated in batches one after the other using same conveyor belt systems and
equipment. Waste from the storage unit is loaded using wheel loaders into G25 feeders which feed the waste onto conveyors
transporting waste to the processing unitG26 . The
description of equipment involved in carrying out above mentioned operations is
discussed in section 2.2 in detail.G27 G28 G29 G30 

The processing unit comprises of
the following processes –

1.      Bag
opening

2.      Magnetic
separation

3.      Screening

4.      Air
separation

5.      Fine
shredding

 

2.2 Pre-treatment EquipmentG31 

This section comprises of
descriptions and specifications of all technical equipment involved in the
pre-treatment process.G32 

 

2.2.1 Bag Opener

The possibility of waste coming
in plastic bags facilitates the inclusion of a bag opener at the start of
pre-treatment process. Albeit manual checking is common in most of the waste
treatment plants, particularly in developing countries where cheap manpower is
available, it is planned to eliminate this considering state-of-the-art nature G33 and location of the proposed waste
treatment plantG34 . The bag opener decided upon for this
plant is BOS 4000 which shall be supplied by a sub-vendor namely Environmental
Marketing Solutions Ltd. and it has the following specifications.

Table 4: Bag opener
specifications

Equipment Details

Length

3.972
m

Breadth

1.999
m

Height

2.781
m

Throughput per hour

35
tons

 

 

 

 

 

 

 

 

 

Figure 2: Bag opener

 

 

(EMS Turnkey Waste Recycling Solutions, 2018)

 

The above equipment yields an
opening efficiency of over 95% according to claims of the supplier and is
effective in opening both wholly as well as partially bagged waste. It consists
of special ripper knives to work upon even the smaller bags. The bags present
in the waste stream are opened and the product is conveyed to the downstream
processes using a chain conveyor in the discharge hopper. (EMS Turnkey
Waste Recycling Solutions, 2018)

 

2.2.2 Magnetic Separator

Some of the impurities in waste
stream are expected to be metals. Thus, a magnetic separator is incorporated to
remove ferrous metals from the waste stream conveyed after bag opener operation.
It is also important to remove the metals in order to protect the down-stream
sizing equipment, i.e. shredder, from being harmed. Out of several options, an
over-head magnetic separator is chosen for this process because of its
flexibility, simple construction and overall good performance.

The working principle is quite
simple and is depicted in figure 3. A permanent magnet is installed at a fixed
distance, 900 mm in this case, from the conveyor belt with waste stream having a
working width of 2 metersG35 . 
All ferrous metals being conveyed along with the waste stream are
attracted to the magnetic field generated by the over-head magnet and segregate
from rest of the waste. In this plant, the permanent magnet is proposed to be
positioned over pulley instead of over belt in the conveyor system as the metal
tramps are removed easily when magnets are placed over pulley because this
position takes the aid of the natural break-up of the metal flow as it leaves
the head pulley.G36  Thus, a sG37 ignificant performance improvement is
reported whenever a magnet is positioned this way. (Steinert GmbH, 2015)G38 

Over-head Magnet

Figure 3: Magnetic Separator

 

 

 

 

 

Magnetic Field

 

Ferrous materials

Conveyor belt

Non-ferrous materials

 

(Steinert GmbH, 2015)

2.2.3 Trommel Screen

The next stage in pre-treatment
is size separation. A trommel is included in the processing unit to perform
screening of the waste based on their particle size.G39  It is used to sort the waste as per size
requirements and is nothing but a rotating drum. It has been used successfully
in numerous waste recycling plants around the world and hence, is an
established equipment to be used for pre-treatment of waste. Its
downside of occupying more footprint, the intermittent formation of plaits and
dust emissions are balanced by the advantages of decompressions, thorough
mixing, minimal risk of clogging and it is a G40 G41 rugged, heavy-duty system in general. A
basic working principle of a trommel screen can be observed in figure 4.G42 G43 

Figure 4: A typical trommel screen

 

 

 

 

 

 

                                                                                                                                                            (Christensen, 2011)

A drum screen such as trommel can
handle municipal waste effectively and desired size separation can be obtained
by selecting appropriate screen size with optimum tilt position. For the
proposed municipal waste treatment plant, we’re procuring heavy-duty trommel
screen from Krause Manufacturing, Inc. To suit the need of the system, a screen
with specifications, as mentioned in table 5, is selected.G44 

Table 5: Trommel screen specifications

Equipment Details

Length

15 m

Diameter

2.4 m

Throughput per hour

35 tons

Drum inclination

4o

(Krause Manufacturing, Inc., 2012)

Figure 5: An installation of trommel screen by Krause
Manufacturing, Inc.

 

 

 

 

 

 

 

 

 

(Krause Manufacturing, Inc., 2012)

A screen size of 70 mm is used
with deflectors to increase the overall efficiency of the trommel. When garden
waste is being pre-treated, separated smaller fractions can be taken directly
to compost after removal of lighter fractions in air classification process
whereas, the over-size fractions of garden waste are then shredded to reduce
particle size before feeding into composting unit. However, for bio-waste, it
is necessary to subject G45 the smaller fractions to fine shredding as
per system requirements of the fermenter.

2.2.4 Density Separator

Following screening where the particle is separated based on size, a
final separation equipment is incorporated which segregates the waste into two
fractG46 ions based on density. This helps in
removing any plastic, film, paper or other lighter unwanted materials that may
have passed through up-stream pre-treatment processes. A density separator
utilizes air stream for material separation. Smaller and or denser materials
are segregated by air and drop down onto the discharge conveyor. Since air is
being blown to perform separation, emissions of foul odor is a disadvantage. This is
minimized by circulating most G47 of the aiG48 r stream. Another possible reduction in
efficiency can be observed when bio-waste with high moisture content is passing
through the density separator. Thus, a very robust system is chosen which shall
be designed, engineered and supplied by our sub-vendor EMS Turnkey Waste
Recycling Solutions to segregate all kinds of municipal waste, including bio-waste.
G49 G50 G51 G52 

 

 

 

 

 

 

 

 

 

 

 

Figure 6: Schematic of Density Separator

 

(EMS Turnkey Waste Recycling Solutions, 2018)

The model DS 3500 is selected taking into
consideration the system requirements of the plant and to match the throughput
of up-stream equipment. The specifications are as mentioned in table 6.G53 G54 

 

Table 6: Density Separator Specifications

Equipment Details

Length

6.09 m

Width

1.51 m

Height

7.82 m

Throughput per hour

35 tons

(EMS Turnkey Waste Recycling Solutions, 2018)

2.2.5 Shredder

The last unit operation included
in the proposed waste management facility is size reduction. A fine shredder is
used for this process. Impurities are eliminated before feeding waste stream
into the shredder and it is vital in particular to remove metals from the waste
stream owing to the fact that they have the potential to disrupt the operation
of shredder by clogginG55 g the cutting blades. This may also lead to
complete shut-down of the equipment and subsequently bring the entire process
to a halt.

Shredding of sorted waste is an
important stage here because of the requirement of downstream process of dry
fermentation wherein particle size is warranted to be less than 40 mm. It shall also
facilitate enhanced microbial activity by shredding the waste results into
increase in surface area of the particles. G56 Thus, we shall procure a shredder from our
sub-vendor WEIMA Maschinenbau GmbHG57  which can carry out fine shredding of
municipal waste of any sort. It is made up of knife-like blades, one rotating
clockwise and the other anti-clockwise and in between the two, particles are
shredded and fall underneath the blades through a screen onto a belt
conveyor. G58 The model selected is WEIMA Powerline and
it is capable of shredding the waste down to 30 mm particle size. The
specifications are as depicted in table 7.G59 G60 

Table 7: Shredder Specifications

Equipment Details

Length

5.25 m

width

2.0 m

Height

4.39 m

Rotor knives

80 x 80 mm

Rotor diameter

800 mm

Throughput per hour

35 tons

Figure 6: Installed WEIMA Powerline shredders MBT plant
in Waterbeach, England

 

 

 

 

 

                                                                         

 

Figure 6: Installed WEIMA Powerline shredders MBT plant
in Waterbeach, England

 

(Weima Maschinenbau GmbH, 2017)

 

 

References

Bilitewski, B., Härdtle, G., Marek, K., &
Wissbach, A. (1997). Waste Management. Springer.
Christensen, T. H. (2011). Solid Waste Technology
and Management. Blackwell Publishing Ltd.
EMS Turnkey Waste Recycling Solutions. (2018). EMS
Turnkey Waste Recycling Solutions. Retrieved from
http://www.emswasterecycle.com/products/bag-opener-system-bos2500-4000/.
Krause Manufacturing, Inc. (2012). Krause
Manufacturing – A Division of the CP Group. Retrieved from
http://www.krausemanufacturing.com/material-recovery-facility/single-stream-recycling/commercial-and-industrial-recycling/krause-trommel-screens/.
Ludwig , C., Hellweg, S., & Stucki, S. (2003). Municipal
Solid Waste Management. Springer.
Steinert GmbH. (2015). Steinert . Retrieved
from http://www.steinertglobal.com/grp/en/.
Weima Maschinenbau GmbH.
(2017). Weima Industrial Shredders and Briquette Presses. Retrieved
from https://weima.com/en/shredding/waste/.
 

 

Inserted: at

Inserted: a

Inserted: the

Deleted:in

Inserted:  the

Inserted: ies

Deleted:y

Inserted: A s

Inserted: are

Inserted: ,

Deleted:S

Deleted:is

Inserted: ing

Inserted:  a

Inserted: ve

Inserted: is

Inserted: y

Deleted:s

Deleted:ies

Deleted:are

Inserted: s

Deleted:is

Deleted:ve

Deleted:s

Inserted: the

Inserted: the

Inserted: is

Deleted:s

Deleted:s

Deleted:are

Deleted:s

Deleted:s

Inserted: –

Inserted:  the

Inserted: r

Inserted: the

Inserted:  a

Deleted:r

Inserted: ing

Inserted: s

Inserted: the

Deleted:be

Deleted:ng

Inserted:  the

Inserted: ,

Inserted: e th

Inserted: s

Inserted:  the

Deleted:,

Deleted:aj

Deleted:ri

Deleted:y

Inserted: e th

Deleted:s

Inserted:  the

Inserted: by

Inserted: s

Inserted:  a

Deleted:as

Deleted:-