Municipal Solid Waste (MSW) Collection Process Model Overview Megan Jaunich, PE PhD Student Department of Civil, Construction and Environmental Engineering Environmental Research & Education Foundation Lonnie C. Poole Jr./Waste Industries Scholar S WOLF http://go.ncsu.edu/iswm
Overview Introduction Model overview Example equations Data development Illustrative results
INTRODUCTION
Collection process model Estimating cost and energy use Incoming Municipal Solid Waste (Mg in ) User Inputs Waste composition Waste generation Collection schedule and services Collection times and distances Capital, labor, O&M, fuel costs Fuel type and efficiency Garage and office electricity use Waste storage containers, quantity and cost Collection Process Model Direct Emissions (kg/mg in ) Electricity Use (kwh/mg in ) Capital Cost ($/Mg-yr -1 ) Operating Cost ($/Mg in )
Process Flow and System Boundary 1 ton MSW for collection Collection Transit Unloading 1 ton MSW delivered to treatment, disposal, or transfer facility Energy Emissions System Boundary Mixed waste or residual waste collection Single stream recycling Dual stream recycling Pre-sorted recycling, drop-off Pre-sorted recycling, crew-sort Leaf vacuum Yard waste/source-separated organics Wet/Dry (co-collected) Yard waste, drop-off Single Stream Material Recovery Facility Dual stream MRF Pre-sorted MRF Mixed waste MRF Thermal waste to energy (WtE) Anaerobic digestion (AD) Composting Transfer station
MODEL OVERVIEW
Collection Sector, Services, and Destinations Three types of collection sectors: Single-family residential (SF) Multi-family residential (MF) Commercial (COM) User creates any number of collection sectors, and defines the following inputs for each sector: Sector type Population and number of stops (e.g. houses, buildings) Waste generation rate and composition Collection services offered Waste destinations (treatment or disposal facility)
Collection process Residual Sample Collection Scheme Single-Family Sector Single Family SS Recyclables Collection service Yard Waste Collection area Commercial Sector Commercial SS MRF Multi-Family Sector Multi Family Compost Residual MW MRF PS Recyclables PS MRF Yard Waste Compost Residual DS Recyclables DS MRF Yard Waste MRF types: SS Single-stream DS Dual-stream PS Pre-sorted
Sample Collection Scheme Collection process Single-Family Sector Single Family Collection service Collection area Collection Sector Residual SS Recyclables Yard Waste Collection Services SS MRF Compost Disposal and treatment facilities Multi-Family Sector Residual Multi Family DS Recyclables DS MRF Yard Waste Commercial Sector Collection process Residual MW MRF PS Recyclables PS MRF Commercial Yard Waste Compost MRF types: SS Single-stream DS Dual-stream PS Pre-sorted
Collection process Residual Sample Collection Scheme Single-Family Sector Single Family SS Recyclables Collection service Yard Waste Collection area Commercial Sector Commercial SS MRF Multi-Family Sector Multi Family Compost Residual MW MRF PS Recyclables PS MRF Yard Waste Compost Residual DS Recyclables DS MRF Yard Waste The waste stream collected by each collection service can be sent to one or more destinations
Sample SWM System Material Reprocessing Comingled Recyclable Collection Commingled MRF Thermal WtE Ash Each collection service can unload at one or more disposal or treatment facilities Mixed Waste/ Residual Collection Organics Collection Mixed Waste MRF Anaerobic Digestion Soil Amendment Mixed waste and recyclables can be sent to transfer station prior to disposal or treatment facility Composting Mixed Waste Recyclables Combustibles Organics Ash
Waste sent to landfill or thermal WtE or mixed-waste MRF Process and waste stream description All materials collected (except hazardous or prohibited items). No other collection services offered (e.g., recyclables) All materials collected after recyclables and/or organics have been separated Sector type Single-family (SF) Multi-family (MF) Commercial (COM) SF, MF, COM Collection Service Mixed waste Residual waste Disposal or Treatment Facility Mixed waste MRF Waste to energy
Waste sent to single-stream, dual-stream, or pre-sorted MRF Process and waste stream description Sector type Collection Service Disposal or Treatment Facility Commingled recyclables collected from same bin(s) Paper, aluminum, plastic, and un-soiled, dry waste collected in one compartment; wet waste in separate compartment SF, MF, COM SF, MF Single-stream recyclables Dry waste Single-stream MRF Pre-sorted recyclables collected in a single truck with multiple compartments SF, MF, COM Dual-stream recyclables Dual-stream MRF Commingled recyclables sorted at the point of collection SF, MF, COM Pre-sorted recyclables Pre-sorted MRF
Waste sent to landfill, AD, thermal WtE, or compost Process and waste stream description Sector type Collection Service Disposal or Treatment Facility Specially-fitted collection vehicle that seasonally vacuums curbside leaves SF, MF, COM Leaf vacuum Yard waste and/or source separated organics (SSO) collected curbside (or dropped off) Food waste, soiled paper, etc. collected in one compartment; dry waste in separate compartment SF, MF, COM (SF) SF, MF Yard waste/ SSO Wet waste Anaerobic digestion Waste to energy Compost facility
Collection process Residual Sample Collection Scheme Single-Family Sector Single Family SS Recyclables Collection service Yard Waste Collection area Commercial Sector Commercial SS MRF Multi-Family Sector Multi Family Compost Residual MW MRF PS Recyclables PS MRF Yard Waste Compost Residual DS Recyclables Yard Waste DS MRF For each collection process, the user defines a set of input parameters
Sample Collection Input Parameters Description Unit Participation rate % Collection frequency at each stop Times/week Number of working days per week Days/week Distance between garage, collection route, and destination Miles Travel time between garage, collection route, and destination Minutes Distance between collection stops Miles Loading time at one service stop Seconds Time to unload Minutes Break time Minutes Collection vehicle volume yd 3 Waste density by waste stream lbs/yd 3 Utilization factor % Fuel efficiency MPG Vehicle capital and O&M costs $ Labor cost $
Collection Model Outputs User reviews default input parameters and changes values as appropriate for each collection scheme (collection sector-process-destination) Model computes four primary outputs: Number of collection vehicles, Nt Cost per waste mass collected, C ($/Mg) Fuel use by collection vehicles per quantity MSW, Fuel (L/Mg) Support facility electricity per quantity MSW, Elec (kwh/mg) Sample calculations
EXAMPLE EQUATIONS
Number of Trucks Nt = stops F r ( Cd Ht Rd Calculated values: Ht stops per trip Rd trips per day per vehicle stops number of participating collection stops per sector Inputs: Fr Cd collection frequency (1/week) number of working days per week
Number of Trucks Nt = stops F r ( Cd Ht Rd Calculated values: stops number of participating collection stops per sector Inputs: Pr stops total stops = Pr stops total participation rate (% stops setting out waste per collection day) total collection stops per sector
Number of Trucks Nt = stops F r ( Cd Ht Rd Calculated values: Rd trips per day per vehicle WV F + Tgr + Tfg 0.5 (Trf + S Rd = Tc Inputs: Trf travel time between collection route and facility Tgr travel time from garage to first collection route Tfg travel time from disposal facility to garage Tc time per trip (time to fill truck + Trf + S) F total break time S time to unload at transfer, treatment, or disposal facility WV working hours per day
Calculated values: Ht Inputs: gen stop Number of Trucks Nt = stops F r ( Cd Ht Rd stops per trip Ht = waste generation per stop per week (ton/stop-collection) cap total truck capacity (yd 3 ) Ut truck utilization factor (%) den waste density (ton/yd 3 ) 1 gen stop cap Ut den
Energy Consumption Fuel used per ton of waste collected Fuel = Fuel D Ref D Ref D is the total mass waste collected per collection vehicle-day Ref D = Ht Rd gen stop where: Ht Rd gen stop houses per trip trips per day/vehicle waste per stop (tons/stop) Fuel D is the total fuel used per vehicle per day
Energy Consumption Fuel used per ton of waste collected Fuel = Fuel D Ref D Fuel D is the total fuel used per vehicle-day Fuel D = where: Ref D Drf Dgr Dfg Db Drf MPG Drf + Dgr MPG Drgr + Dfg MPG Dfg + total tons waste collected per collection vehicle-day distance between collection route and facility distance from garage to first collection route distance from disposal facility to garage total distance between collection stops Db MPG Db + T idle gal/hr idle
DATA DEVELOPMENT
MSW Collection Data Study Data obtained from several municipalities and private waste management organizations transit times time/distance between each collection stop time at each collection stop unloading time at processing/disposal/transfer facility fuel consumption (mpg and gallons/ton waste) Local collection activities observed
City Type(s) of Disposal Facility Location and Data Summary Appx. Area mi 2 Population Density cap./mi 2 City A, MRF <100 2500 Data Provided or Observed Fuel consumption and tonnages; collection route data (distances, times, tonnages) City B, Transfer Station 400-500 2900 GPS tracking data (distances, times, tonnages) City C N/A <100 9900 Fuel consumption and tonnages City D N/A 400-500 2900 Engine control module records for collection vehicles (e.g. fuel efficiency, total distance travelled) City E Private MRF 100-200 2900 Tip times City E Municipality landfill and transfer station 100-200 2900 Tip times
Time (sec) Collection route time inputs 80 Stop Duration (sec) 70 60 2.7σ ( 99%) 50 40 30 20 10 0 City A Residual City B Residual City A Recycling City B Recycling City A Yard Waste A, Residual Waste B, Residual Waste A, Recycling B, Recycling A, Yard Waste Automated Automated Municipality Automated and Route Automated Semi-Auto/Manual 75 th percentile Median 25 th %ile 2.7σ
Time (sec) 80 Collection route time inputs Transit Time(sec) 70 60 2.7σ ( 99) 50 40 30 20 10 0 City A, Residual A Residual Waste City B, Residual B Residual Waste City A, A Recycling City B, B Recycling City A, A Yard Yard Waste Automated Automated Municipality Automated and Route Automated Semi-Auto/Manual 75 th percentile Median 25 th %ile 2.7σ
mpg Total average diesel fuel economy 3 2 1.8 2.1 2.3 2.5 2.4 1.9 2.3 1 0 A, City RWA B, City RWB C, City RWC D, City RWD A, City Rec A B, City Rec B C, City Rec C Residual Waste Recyclables City (A-C) and Collection Type (Residual Waste or Recyclables)
City D: Fraction driving vs. idling Fuel Used Time Driving (>2.8 (>1.8 km/hr) mph) Idling (<2.8 (<1.8 km/hr) mph) 23% 42% 58% 79% Total fuel use: 1,707,973 451,198 gallons L Total time: 112,564 hours
Frequency Frequency Frequency Frequency 100 90 80 70 60 50 40 30 20 10 0 7 Material Recovery Facility Tip Durations Tip durations for City E 1 56 10 11 15 16 20 21 2526 30 31 35 36 40 41 45 46 50 51 556 Minutes MRF Tip Durations (Observed) 40 35 30 25 20 15 10 25 5 0 Tip Durations 1 56 1011 15 16 20 21 2526 30 31 35 36 40 41 45 46 50 51 55 56 Minutes Transfer Station Tip Durations 6 5 4 20 15 3 2 1 10 5 0 1 56 1011 15 16 2021 2526 3031 3536 4041 4546 5051 5556 Minutes 0 1 56 10 11 16 15 21 20 25 26 31 30 36 35 41 40 46 45 51 50 56 55 Minutes
ILLUSTRATIVE RESULTS
gallons/ton Sample Results and Model Validation Model-calculated fuel use was compared with operational fuel use value reported by participating municipalities Results demonstrate model functionality; highlight importance of user-defined input parameters 6 5 4 3 2 1 0 3.1 3.2 2.6 2.2 4.7 4.4 5.4 5.1 City A, RW A B, City RWB A, City Rec A B, City Rec B Residual Waste Recyclables City (A-B) and Collection Type (Residual Waste or Recyclables) Operational, diesel Model-predicted, diesel
Environmental Impacts Sample Analysis The collection process model sums life-cycle emissions resulting from collection vehicle fossil fuel use (diesel or CNG) and from garage electricity use A 15% energy penalty assumed for CNG, i.e. fuel economy in miles per diesel gallon equivalent is 15% lower for CNG* Emissions factors developed from EcoInvent 2.2 database were employed along with IPCC 2007 100-year Direct Global Warming Potential (GWP) values *NREL studies report ~10-30% energy reduction per BTU of CNG with respect to diesel
GWP per ton waste Environmental Impacts Sample Analysis For the representative municipalities (Cities A and B), fuel type was changed to compare emissions from diesel vs. CNG vehicles based on user-defined emissions profiles Model results can be used to determine lifecycle impacts, such as carbon dioxide equivalent emissions 140 120 100 80 60 40 20 0 A, City RWA B, City RWB A, City Rec A B, City Rec B Residual Waste Operational, diesel Model-precicted, CNG Recyclables City (A-B) and Collection Type (Residual Waste, Recycling) Model-predicted, diesel
Global Warmiing Potential GWP: Illustrative sensitivity to inputs 250 Tons per trip (Mg/trip) 0 5 10 15 20 25 30 200 150 100 50 0 0 5 10 15 20 25 30 35 40 45 50 55 60 Distance (miles) Time at facility (min) Collection time (sec) Time at facility, (min) Metric tons per trip (Mg/trip) Distance route to facility (miles) Time at stop (sec)
Discussion Bottom-up collection model can predict cost, fuel consumption, energy use, associated emissions, and selected environmental impacts (e.g., global warming potential) Model-predicted fuel use for representative cities within 5-45% of operational values Different collection scenarios can be created to compare environmental implications of changing inputs
Summary A linear process model was developed to compute the total fuel use, electricity use, and cost per Mg waste collected for a defined collection area, and number of trucks required to service each user-defined collection area. Bottom-up analysis allows user to adjust input parameters and enables what if analyses of future collection scenarios, and integrated analyses using SWOLF. Default data set developed from operational data. Collection model results for fuel and electricity use are paired with appropriate emissions coefficients to compute emissions and enable impact assessment.
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