Presentation on theme: "Separation , Processing and Transformation of Solid Waste"— Presentation transcript:
1 Separation , Processing and Transformation of Solid Waste Chapter 9
2 Presentation Outline Introduction Reuse and Recycling Opportunities For Waste MaterialsMaterials Recovered At Drop – Off and Buy Back CentersOperations For the Separation Of Waste MaterialsIntroduction to the Unite Operation Used For the Separation and Processing of Waste MaterialsFacilities for Handling, Moving, and Storing Waste MaterialsDevelopment and Implementation of MRFWaste Transformation Through CombustionImpacts of Source Reduction and Waste Recycling on Waste Transformation Process
3 IntroductionSeparation, Processing and Transformation make up the fourth of the functional elements of solid waste management systemthe methods now used to recover source separated wastes materials include curb side collection and home owner delivery of separated materials to drop off and buy back centers.The further separation and processing of waste that have been source separated occur at MRF or at large integrated MR-TF.Chemical & biological transformation process are used to reduce the volume and weight of waste requiring disposal and to recover conversion products and energy in the form of heat.The most commonly used chemical transformation process is combustion which is used in conjunction with the recovery of energy in the form of heat.The most commonly used biological transformation process is aerobic composting.
4 Reuse & Recycling Opportunities for Waste Materials Materials separated from MSW can be used directly as:raw material for remanufacturing and reprocessingfeedstock for production of biological and chemical conversion productsfuel source for the production of energyland reclamationReuse opportunities for the materials separated from MSW are reported in Table 9-1.In assessing the opportunities for recycling, the available options for separation and processing of waste materials, the economics of material recovery and material specifications are critical
5 Reuse & Recycling Opportunities for Waste Materials
6 Reuse & Recycling Opportunities for Waste Materials
7 Materials Recovered at Drop- off & Buy Back Center Drop- off Centersa drop-off program requires residents or business to separate recyclable materials at the source & bring them to a specified drop-off or collection center.Low participation can be a problem in achieving the diversion rated desired from these programs.Drop-off centers also requires residents and business to store the materials until sufficient material is collected to warrant a trip to the drop-off center.To encourage participation, most successful programs have made drop-off centers as convenient to use as possible (e.g., drop off points at shopping centers are common, in many communities combination drop –off and buy back centers are located at MRF, mobile collection centers which can be moved to a new locations periodically.
8 Materials Recovered at Drop- off & Buy Back Center
9 Materials Recovered at Drop- off & Buy Back Center
10 Materials Recovered at Drop- off & Buy Back Center Buy – Back CentersBuy – Back refers to a drop-off program that provides a monetary incentive to participateIn type of this program, the residents are paid for their recyclable either directly or indirectly through a reduction in monthly collection and disposal fees. Other incentive systems include contests t or lotteries
11 Options for the separation of waste materials Separation is a necessary operation in the recovery of reusable materials from municipal solid waste. Separation can be accomplished either at the source of the generation or at MRFs.Waste separations at the source is usually accomplished by manual means, the number & types of components separated will depend on the waste diversion program. Additional separation and processing will be usually required before these materials can be reused or recycled.MRFs & MR-TFs are used for :the further processing of source separated wastethe separation & recovery of reusable & recyclable materials from commingled MSWimprovement inequality ( specification)in the simplest term, AMRF can function as centralized facilities for the separations, cleaning & shipping of large volume of materials recovered from municipal solid waste
12 Options for the separation of waste materials The separation of waste materials from MSW can be accomplished manually or mechanically.Manual separation is used almost exclusively for the separation of waste at the source of generation. Many of the early MRFs built in 1970 s were designed to separate the waste components mechanically. Unfortunately, none of these early facilities is currently in operation, primarily because of mechanical problem.The currant trend is to design MRFs based on the integration of both manual and mechanical separation functions
13 Options for the separation of waste materials Two types of MRF:MRF for Source – Separated WasteMRF for commingled MSWThe sophistication of the MRF will depend onthe number and types of the components to be separatedthe waste diversion goals established for the waste recovery programthe specifications to which the separated products must conform
14 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials Unit operations used for the separation and processing of separated and commingled wastes are designed toModify the physical characteristics of the wastes so that the waste components can be removed easilyRemove specific components and contaminants from the waste streamprocess and prepare the separated materials for subsequent usesCommonly used unit operations for processing of MSW are summarized in Table 9-3
15 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials
16 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials Size ReductionSize reduction is the unit operation in which as collected waste material are mechanically reduced in sizeThe objective of size reduction is to obtain a final product that is reasonably uniform and considerably reduced in size in comparison with its original form.Note that size reduction does not necessarily imply volume reduction. In some situations, the total volume of the material after the size reduction may be greater than that of the original volume.Size reduction equipment used for the processing of wastes includesShreddersGlass crushersWood grinders
17 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials Shreddersthe three most common types of shredding devices used to reduce the size of MSW areHammer millFlail millShear shredder
18 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials Glass Crushersglass crushers are used to crush glass container and other glass products found in MSWglass is often crushed after it has been separated to reduce storage and shipping costscrushed glass can also be separated optically by color. However, because the equipment of the optical sorting of glass is expensive and on-line reliability of such equipment has not been good, optical sorting is not used commonly at presentWood GrindersTypically, most wood grinders are wood chippers, used to shred large pieces of wood into chips, which can be used as a fuel and finer material which can be composted
19 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials ScreeningScreening is used to separate mixtures of materials of different sizesThe principal applications of screening devices in the processing of MSW include:removal of oversized materialsremoval of undersized materialsseparation of waste into light combustible and heavy combustiblerecovery of paper, plastic and other light materials from glass and metalSeparation of glass, girt and sand from combustible materialsSeparation of rocks and oversized debris from soil excavated at construction sitesremoval of oversized materials from combustion ash
20 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials ScreeningThe types of screen used most commonly for the separation of solid waste materials areVibrating screensRotary screensDisc screensself cleaningadjustability with respect to the spacing of the discs on the drive shaftsInsert Figure 9-8
21 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials
22 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials Density Separation (Air Classification)Air classification is used to separate light materials from heavier material, based on the weight difference of the material in an air stream.
23 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials Magnetic SeparationMagnetic separation is a unit whereby ferrous metals are separated from waste materials (Source – separated, commingled and shredded MSW) by utilizing their magnetic propertiesThe specific location (s) where ferrous materials are recovered will depend onThe objectives to be achieved such as the reduction of wear and tear on processing and separation equipmentThe degree of product purity to be achievedThe required recovery efficiencyDensification (compaction)Densification is a unit operation that increases the density of waste materials so that can be stored and transported more efficientlySeveral technologies are available for the densification of solid wastes and recovered materials including baling, cubing and pelleting.
24 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials Balersbalers reduces the volume of waste for storage , prepare the waste for marketing and increase the density of the waste thereby reducing the shipping coststhe materials most commonly baled include paper, cardboard, plastics, aluminum and tin cans and large metal component
25 Introduction to the Unit Operation Used for the Separation and Processing of Waste Materials Can CrushersCan Crushers are used to crush aluminum and tin cans, thus increasing their density and reducing handling and shipping costs.Typically, aluminum cans are crushed and blown into large transport trailers for shipping.
26 Facilities for Handling, Moving and Storing Waste Material To handle, move and store at MRFs, the following are used:ConveyorsConveyor facilities (picking belts) in conjunction with the manual separation of wastePneumatic conveyorMovable and fixed waste-handling equipmentScalesStorage facilities
27 Facilities for Handling, Moving and Storing Waste Material ConveyorsConveyors transfer wastes from one location to anotherThe principal types may be classified as hinge, bucket, belt drag, vibrating and pneumaticThe conveyance of unprocessed commingled wastes with conveyors has not been trouble freeconveyors have been damaged by solid wastes dropped onto them, especially those containing some of the heavier components often found in the waste. Problems have also developed at transfer points (e.g., where the waste are discharged from one conveyor to another)waste spillage and overflows are common
28 Facilities for Handling, Moving and Storing Waste Material Conveyor Facilities Used in Conjunction with the Manual Sorting of WasteThe manual separation of wastes at a MRF is usually accomplished by removing the individual waste components from the waste streamTo improve the separation of waste components from commingled MSW, plastic bags used for on-site storage must be open and the contents spread out on the belt.The design of facilities for sorting waste components depends to a large extent on thecharacteristics of the wastenumber of commingled recyclable items that are to be separatedthroughput capacity of the facilitywidth of the beltspeed of the beltthe average thickness of the waste materials on the belt
29 Facilities for Handling, Moving and Storing Waste Material Conveyor Facilities Used in Conjunction with the Manual Sorting of WasteThe manual separation of wastes at a MRF is usually accomplished by removing the individual waste components from the waste streamTo improve the separation of waste components from commingled MSW, plastic bags used for on-site storage must be open and the contents spread out on the belt.The design of facilities for sorting waste components depends to a large extent on thecharacteristics of the wastenumber of commingled recyclable items that are to be separatedthroughput capacity of the facilitywidth of the beltspeed of the beltthe average thickness of the waste materials on the belt
30 Facilities for Handling, Moving and Storing Waste Material
31 Facilities for Handling, Moving and Storing Waste Material Pneumatic Conveyorspneumatic conveying can be defined as materials transport using air as the transport medium.Two types of pneumatic transport system (positive pressure and vacuum)Velocities needed for the pneumatic transport of unprocessed solid waste are in the range of 4800 to 6000 ft/min.Facilities for Weighingweighing facilities are an important and necessary part of any MRFthe types of weighing facilities used at MRFs vary from the small scales used to weigh the amounts of wastes brought in by individuals to the platform scales used for weighing collection vehicles
32 Facilities for Handling, Moving and Storing Waste Material Storage facilitiesMaterials that have been separated and processed must be stored until a buyer picks them up.In some facilities, space is provided for materials to be displayed for viewing by purchasersKey considerations are these:will the buyer provide storage containers for recovered materialswith what frequency will the buyer pick up and remove prepared materials from MRFis it possible to rent temporary storage facilities for the processed materials away from the MRF
35 Development and Implementation of MRFs Development of Separation Process Flow DiagramsA process flow diagram is defined as the assemblage of unit operations, facilities and manual operations to achieve a specified waste separation goal or goals.The following factors must be considered in the development of the process flow diagrams:identification of the characteristics of the waste materials to be processedconsideration of the specifications for the recovered materials now and in the futurethe available types of equipment and facilitesFor example, specific waste materials cannot be separated effectively from commingled MSW unless bulky items are first removed.A typical process flow diagram for the separation of source – separated paper and cardboard is shown in Fig. 9-20a
37 Development and Implementation of MRFs Material Balances and Loading RatesOnce the process flow diagram has been developed, the next step in the design of MRF is to estimate the quantities of materials that can be recovered and the appropriate design loading rates.the expected process loading rates must be known in order to select and size equipment properly. Loading rate for a given process are based on a mass balanceLoading rates for most processes are expressed in tons per hour. In determining the design loading rates, one should make careful analysis to determine the number of hours per day and the year equipment will be operated.Based on 1820 operating hours per year, the base hourly loading rate is given by the following expression:Loading rate, ton/h = (Number of ton/year / 1820 processing h/yr)
38 Development and Implementation of MRFs System Layout and Designthe layout and design of the physical facilities that make up the processing facilities will depend on the types and amounts of materials to be processed.Important factors in the layout and design of such system includethe methods and means by which the waste will be delivered to the facilityestimates of material delivery ratesdefinition of the materials loading ratesdevelopment of materials flows and handling patterns within MRFDevelopment of performance criteria for the selection of equipment
39 Development and Implementation of MRFs Typical Materials Recovery Facilities for Source – Separated Wastesin this text book, there are two types of MRFSMRF designed to process source – separated wastesMRF designed to process garden trimmings and wood wastes
44 Development and Implementation of MRFs Planning and Design Process for MRFsThe planning and design of MRFs involve three basic stepsFeasibility analysisthe purpose of the feasibility analysis is to decide whether the MRF should be builtthe feasibility study should provide the decision makers with clear recommendations on the technical and economic meritsA typical feasibility analysis may contain sections dealing with integrated waste management plan, conceptual design, economics, ownership and operation, and procurementPreliminary designthe preliminary design includes development of the process flow diagramdevelopment of material mass balances and loading rates for the unit operations that make up the MRF and the layout of the physical facilitiesthe cost estimate developed in the feasibility study is refined in the preliminary design report using actual price quotations from venders
45 Development and Implementation of MRFs Planning and Design Process for MRFsFinal designfinal design includes preparation of final plans and specifications that will be used for constructionA detailed engineers cost estimate is made based on materials take offs and vender quotesthe cost estimate will be used for the evaluation of contractor bids if the traditional procurement process is used
46 Development and Implementation of MRFs Issues in the Implementation and Operation of MRFsthe principal non-engineering issues associated with the implementation of the MRFs are related toSitingEnvironmental emissionstraffic, noise, odor, dust, airborne debris, liquid discharge, visual unsightliness and vector controlPublic health and safetyEconomics
48 Waste Transformation Trough Combustion Transformation processes are used to reduce the volume and weight of waste requiring disposal and to recover and to recover conversion products and energyThe organic fraction of MSW can be transformed by a variety of chemical and biological processes.The most commonly used chemical transformation process is combustion, which can be used to reduce the original volume of the combustible fraction of MSW by 85 to 95 percent. In addition, the recovery of energy in the form of heat is another attractive feature of the combustion processAlthough combustion technology has advanced in the past two decades, air pollution control remains a major concern in the implementation
50 Waste Transformation Trough Combustion The principal elements of solid wastes are carbon, hydrogen, oxygen, nitrogen and sulfur.Under ideal conditions, the gaseous products derived from the combustion of MSW with stoichiometric amount of air would include CO2, H2O, N2, SO2.the basic reactions for the oxidation of the carbon, hydrogen and sulfur contained in the organic fraction of MSW are as followsFor carbon,C + O2CO2For Hydrogen,2H2+O22H2OFor Sulfur,S+O2SO2
52 Waste Transformation Trough Combustion Types of CombustorsSolid waste combustors can be designed to operate with two types of solid waste fuelMass-Fired CombustorRefuse – Derived Fuel – Fired CombustorsEnergy RecoveryEnergy can be recovered from the hot flue gases generated by combusting processed MSW or from unprocessed MSWEither hot water or steam can be generated.Hot water can be used for low-temperature industrial or space heating applicationsSteam is more versatile, as it can be used for both heating and generating electricity.
53 Waste Transformation Trough Combustion Volume ReductionAmong the factors that must be considered in assessing the combustion process for MSW are the amount of residue remaining after combustion and whether auxiliary fuel will be required when heat recovery is not of primary concernThe amounts of residue depends on the nature of the wastes to be combusted
56 Waste Transformation Trough Combustion Issues in the Implementation of Combustion FacilitiesSitingin many communities, combustion facilities are located in remote locations within the city limits or at the landfill sitesAir Emissionsthe operation of combustion facilities results in the production of a variety of gaseous and particulate emissions, many of which are thought to have a serious health impactsIn some cases, the cost and complexity of the environmental control systems are equal or even greater than the cost of the combustion facilitiesDisposal of ResidueBottom ashfly ashscrubber productManagement of these soild residuals is an integral part of the design and operation of a combustion facility ( ash is now disposed of in lined MSW landfill or in double lined monofills devoted solely to the disposal of ash
57 Waste Transformation Trough Combustion Liquid Emissionsliquid emissions from combustion facilities can arise from one or more of the following sourceswastewater from the ash removal facilitiseffluent from wet scrubbersWastewater from pump seals, cleaning, flushing, and general housekeeping activitiesWastewater from treatment systems used to produce high quality boiler waterCooling tower blowdownThe proper handling and disposal of these liquid emissions is also an important part of the design of combustion facilitiesEconomicsthe best way to compare alternatives is by the use of life cycle coasting, which accounts for operating and maintenance costs over the lifetime of the system
58 Waste Transformation Trough Aerobic Composting With the exception of plastic, rubber components, the organic fraction of most MSW can be considered to be composed of proteins, amino acids, lipids, carbohydrates, cellulose and ash
59 Waste Transformation Trough Aerobic Composting The general objectives of composting areto transform the biodegradable organic materials into a biologically stable material and in the process reduce the original volume of wasteto destroy pathogens, insect eggs and other unwanted organisms and weed seeds that may present in MSWto retain the maximum nutrients ( nitrogen, phosphorus and potassium content)To produce a product that can be used to support plant growth and as soil amendmentIn general, the chemical and physical characteristics of compost vary according to the nature of starting material , the condition under which the composting operation was carried out and the extent of the decomposition.
60 Waste Transformation Trough Aerobic Composting When added to soil, compost has been found to lighten heavy soils, to improve the texture of light sandy soil, and to increase the water retention capacity of most soil.Process DescriptionMost modern composting operations consists of three basic stepspreprocessing of the MSWdecomposition of the organic fraction of the MSWpreparation and marketing of the final compost product
62 Waste Transformation Trough Aerobic Composting Process Design and ControlAlthough the composting process is easy to grasp conceptually, the actual design and control of the process are quite complexImportant process variables that must be considered in the design and operation of composting facilities includeParticle sizeparticle size distribution of the materials to be compostedSeeding and mixing requirementsThe required mixing/turning schedulesTotal oxygen requirementsmoisture contentstemperature and temperature controlcarbon – nitrogen ratio of the waste to be compostedpHdegree of decompositionrespiratory quotientcontrol of pathogens
67 Waste Transformation Trough Aerobic Composting Process ApplicationComposting is an increasingly popular waste management option as communities look for ways to divert portions of the local waste stream from landfills.The principal applications of composting are forYard wastesOrganic fraction of MSWpartially processes commingled MSWco-composting of the organic fraction of MSW with wastewater sludge
68 Waste Transformation Trough Aerobic Composting Issues in the Implementation of Composting Facilitiesthe principal issues associated with the use of compost process arethe production of odorsthe presence of pathogensthe presence of heavy metalsthe definition of what constitutes and acceptable compostunless the questions related to these issues are resolved, composting may never be a viable technology
69 Waste Transformation Trough Aerobic Composting Production of Odorsit is fair to say that every existing composting facility has had an odor event and in some numerous events. As a consequence, facility siting, process design and biological odor management are of critical importanceFacility Sitingimportant issues in siting as related to the production and movement of odors include proper attention to local microclimates as they affect the dispersion of odors, distance to odor receptors, the use of adequate buffer zones and the use of split facilities ( use of different locations for composting and maturation operations)
70 Waste Transformation Trough Aerobic Composting Proper Process Design and Operationif composting operations are to be successful, special attention must be devoted to the following itemspreprocessingaeration requirementstemperature controlturning and mixing requirementsBiological Odor ManagementCause of odors in composting operations includelaw carbon to nitrogen ratiopoor temperature controlexcessive moisturepoor mixingin enclosed facilities, odor control facilities such as packed towers, spray towers, activated carbon contactors , biological filters have been used for odor management
71 Waste Transformation Trough Aerobic Composting Public Health Issues:the absence of pathogenic organisms is critical if the product is to be marketed for use in application where the public health may be exposed to the compostIn general, most of pathogenic organisms found in MSW and other organic materials to be composted will be destroyed at the temperature and exposure times used in controlled composting operations ( typically 55C for daysProduct QualityProduct quality can be defined in terms ofnutrient contentorganic contentpHtextureparticle size distribution, moisture content, the presence of foreign material , the presence of pathogenic organisms and the concentration of heavy metals
72 Impact of Source Reduction And Waste Recycling on Waste Transformation Processes As more state adopt legislation mandating the development of waste diversion and recycling progrms, the quantities and composition of the wastes collected will change.The impact of change in composition will vary depending on the other types of waste management programs that are in place.
73 Impact of Source Reduction And Waste Recycling on Waste Transformation Processes