1. Waste Storage Unit The first stage of wastetreatment comprises of Bio-waste and garden waste storage. Bio-waste and gardenwaste are received and managed separately at this stage.
G1 Itis necessary to have a dedicated storage space for waste to ensure a continuoussupply of feed, G2 whichis the municipal waste, to the plant and G3 avoidany disruption or halt in operations that may be caused otherwise. G4 Incoming waste is brought intothe reception area where eachG5 loaded truck is weighed and registered before entering the facility. Three different entry points with receptionand registration are considered to accommodate multiple vehicular entries into theplant simultaneously. This is also G6 necessaryto evade any congestion at the entrance of the facility.
G7 A separate storagearea is allocated for the two different types of waste wherein weighed andregistered G8 deliverytrucks unload bio-waste and garden waste respectively. There is a possibility of foul smell beingemitted should the waste be piled up on open space and in order to minimizethis issue as well as maintain hygienic conditions within the plant,construction of closed area is to be done for storing both bio waste and gardenwaste indoors. From the data given in contract, the total quantity of bio-wasteand garden waste is calculated. Seasonal variations of waste are consideredG9 rather than an average values of bio-waste and garden waste throughout theyear. The data of the city of Kaunas, Lithuania 2009 are used and tons of wastegenerated for primarily four seasons – spring, summer, autumn, and winter – arecalculated. The results are G10 as shown in Table 1.
(Denafas et al., 2014)G11 G12 Table 1: Total yearly waste andseasonal 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, itis important to estimate the daily peak flow of both types of waste. This canbe calculated by averaging the incoming waste throughout each season and arriveat the volume of waste for each day.
Following which, the peak volume is nowconsidered to select the dimensions of waste storage area. The results aredepicted in Table 2. Table 2: Tons and volume of waste generatedper 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 tostore bio-waste and garden waste for a maximum period of two and five daysrespectively. The peak volume calculated is used to size the storage facilityand dimensions are tabulated in Table 3. Table 3: Dimensions of storagefacility 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 includingpre-treatment unit operations is to eliminate the unwanted substances presentin the incoming waste. As mentioned in the contract, bio-waste is expected tohave impurities between 2.6% to 5.
4% and the content of it in garden waste isestimated around 4.5%. The separation of these impurities is vital tomaintaining end pG13 roducts of uniform quality which mayotherwise cause disruptions in downstream processes, disturb the fermentationprocess or affect the overall quality of compost. The technologies available forpre-treatment in the market are very specific and the luxury of a G14 large variety of options is not available, as in thecase of other industries. This is because waste management industry in itselfis in its nascent stage and the concepts of waste management have picked upmomentum only in the recent past. G15 In our pre-treatment unit, we’reconsidering processes primarily for the purpose of separation and sizereduction and to achieve this, we are selecting machinerywhich is well proven and belong to the category of best available technologiesfor their respective operations.G16 G17 G18 G19 G20 There are two possibilities oftreating the different types of incoming waste, i.e.
bio-waste and gardenwaste. One way to do this is to have two separatetreatment lines for each category of waste. However, G21 it is more appropriate to choosethis technique when the plant is treating a higher quantity of garden waste.
Inthis case, daily peak flow of garden waste is about 1.48% of overall peak dailywaste (4.04 tons out of 272.
26 tons) and it makes much more sense to firsttreat 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 ofincoming waste is chosen. This has quite a few advantages over two linetreatment system. For example, space, power consumption and extra investment onequipment 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-linepre-treatment processes are depicted in Figure 1. Bio-waste and garden wasteare treated in batches one after the other using same conveyor belt systems andequipment. Waste from the storage unit is loaded using wheel loaders into G25 feeders which feed the waste onto conveyorstransporting waste to the processing unitG26 .
Thedescription of equipment involved in carrying out above mentioned operations isdiscussed in section 2.2 in detail.G27 G28 G29 G30 The processing unit comprises ofthe following processes – 1. Bagopening 2. Magneticseparation3.
Screening4. Airseparation5. Fineshredding 2.2 Pre-treatment EquipmentG31 This section comprises ofdescriptions and specifications of all technical equipment involved in thepre-treatment process.
G32 2.2.1 Bag OpenerThe possibility of waste comingin plastic bags facilitates the inclusion of a bag opener at the start ofpre-treatment process. Albeit manual checking is common in most of the wastetreatment plants, particularly in developing countries where cheap manpower isavailable, it is planned to eliminate this considering state-of-the-art nature G33 and location of the proposed wastetreatment plantG34 . The bag opener decided upon for thisplant is BOS 4000 which shall be supplied by a sub-vendor namely EnvironmentalMarketing Solutions Ltd. and it has the following specifications.Table 4: Bag openerspecifications 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 anopening efficiency of over 95% according to claims of the supplier and iseffective in opening both wholly as well as partially bagged waste. It consistsof special ripper knives to work upon even the smaller bags. The bags presentin the waste stream are opened and the product is conveyed to the downstreamprocesses using a chain conveyor in the discharge hopper. (EMS Turnkey Waste Recycling Solutions, 2018) 2.2.
2 Magnetic SeparatorSome of the impurities in wastestream are expected to be metals. Thus, a magnetic separator is incorporated toremove 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-streamsizing equipment, i.e. shredder, from being harmed. Out of several options, anover-head magnetic separator is chosen for this process because of itsflexibility, simple construction and overall good performance. The working principle is quitesimple and is depicted in figure 3. A permanent magnet is installed at a fixeddistance, 900 mm in this case, from the conveyor belt with waste stream having aworking width of 2 metersG35 .
All ferrous metals being conveyed along with the waste stream areattracted to the magnetic field generated by the over-head magnet and segregatefrom rest of the waste. In this plant, the permanent magnet is proposed to bepositioned over pulley instead of over belt in the conveyor system as the metaltramps are removed easily when magnets are placed over pulley because thisposition takes the aid of the natural break-up of the metal flow as it leavesthe head pulley.G36 Thus, a sG37 ignificant performance improvement isreported 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 ScreenThe next stage in pre-treatmentis size separation. A trommel is included in the processing unit to performscreening of the waste based on their particle size.G39 It is used to sort the waste as per sizerequirements and is nothing but a rotating drum.
It has been used successfullyin numerous waste recycling plants around the world and hence, is anestablished equipment to be used for pre-treatment of waste. Itsdownside of occupying more footprint, the intermittent formation of plaits anddust emissions are balanced by the advantages of decompressions, thoroughmixing, minimal risk of clogging and it is a G40 G41 rugged, heavy-duty system in general. Abasic 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 canhandle municipal waste effectively and desired size separation can be obtainedby selecting appropriate screen size with optimum tilt position. For theproposed municipal waste treatment plant, we’re procuring heavy-duty trommelscreen from Krause Manufacturing, Inc. To suit the need of the system, a screenwith 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 usedwith deflectors to increase the overall efficiency of the trommel. When gardenwaste is being pre-treated, separated smaller fractions can be taken directlyto compost after removal of lighter fractions in air classification processwhereas, the over-size fractions of garden waste are then shredded to reduceparticle size before feeding into composting unit. However, for bio-waste, itis necessary to subject G45 the smaller fractions to fine shredding asper system requirements of the fermenter.2.2.
4 Density Separator Following screening where the particle is separated based on size, afinal separation equipment is incorporated which segregates the waste into twofractG46 ions based on density. This helps inremoving any plastic, film, paper or other lighter unwanted materials that mayhave passed through up-stream pre-treatment processes. A density separatorutilizes air stream for material separation. Smaller and or denser materialsare segregated by air and drop down onto the discharge conveyor. Since air isbeing blown to perform separation, emissions of foul odor is a disadvantage. This isminimized by circulating most G47 of the aiG48 r stream. Another possible reduction inefficiency can be observed when bio-waste with high moisture content is passingthrough the density separator.
Thus, a very robust system is chosen which shallbe designed, engineered and supplied by our sub-vendor EMS Turnkey WasteRecycling 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 intoconsideration the system requirements of the plant and to match the throughputof 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 ShredderThe last unit operation includedin the proposed waste management facility is size reduction. A fine shredder isused for this process. Impurities are eliminated before feeding waste streaminto the shredder and it is vital in particular to remove metals from the wastestream owing to the fact that they have the potential to disrupt the operationof shredder by clogginG55 g the cutting blades.
This may also lead tocomplete shut-down of the equipment and subsequently bring the entire processto a halt. Shredding of sorted waste is animportant stage here because of the requirement of downstream process of dryfermentation wherein particle size is warranted to be less than 40 mm. It shall alsofacilitate enhanced microbial activity by shredding the waste results intoincrease in surface area of the particles. G56 Thus, we shall procure a shredder from oursub-vendor WEIMA Maschinenbau GmbHG57 which can carry out fine shredding ofmunicipal waste of any sort. It is made up of knife-like blades, one rotatingclockwise and the other anti-clockwise and in between the two, particles areshredded and fall underneath the blades through a screen onto a beltconveyor.
G58 The model selected is WEIMA Powerline andit is capable of shredding the waste down to 30 mm particle size. Thespecifications 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/.
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