Life Cycle Assessment of municipal solid waste management - Cost by wii13090

VIEWS: 9 PAGES: 6

									Proceedings of International Symposium and Workshop on Environmental Pollution Control ans Waste Management
7-10 January 2002, Tunis (EPCOWM’2002), p.243-248.




Life Cycle Assessment of municipal solid waste management
- Cost, energy consumption, & CO2 emission -

Toshihiko Matsuto
Department of Environmental Engineering, Hokkaido University, Japan
Fax +81 11 707 6585
E-mail matsuto@eng.hokudai.ac.jp


ABSTRACT
In recent years, solid waste management system beccame very complicated system with many alternative
treatment/disposal options. To realize “Recycling Based Society”, the best scenario of waste management should be
selected. In this paper, two typical zero-emission scenarios are proposed. The one is a scenario to minimize landfill by
incineration, and the other scenario maximize material/energy recovery to minimize incineration. They are evaluated by
the decision making tool developed by the author in terms of cost, energy consumption, and carbon dioxide emission.


KEYWORDS
LCA, MSW management, Zero-emission


1. Introduction
After “Basic law for establishing RBS” was enacted together with related recycling laws in 2000,              “Recycling-based
society(RBS)” which minimizes both environmental impact and natural resource consumption came to the most
important national target in Japan. The country had highly depended on incineration for MSW(municipal solid waste)
treatment, and landfilled mainly incineration residue and noncombustible fraction. Such a simple choice of disposal
methods should be replaced by recycle-oriented technologies. However, there are many alternatives to be selected. We
need a scientific basis to choose the best or better combination of disposal or recycling options. In this paper, two
typical disposal scenarios for zero-emission are compared with present scenario in terms cost, energy consumption, and
carbon dioxide emission, using LCA methodology.


Selected Zero-emission scenario
    Three waste disposal scenarios were selected. The first one is the most typical scenario at present: burn
combustibles including light fraction of shredded bulky waste, and landfill noncombustibles and incineration residues
(Figure 1(a)). It is called Present-scenario, which is served as the reference for the following two Zero-emission
scenarios.
    Because of the difficulty to find new landfill site and because of the fear for hazardous chemical emission from
incinerators, the reduction of waste amount to be incinerated or landfilled is a big challenge for local governments.
Above all the lack of landfill space is seious probledm in urban areas. So the second scenario was selected to minimize
landfilling. This goal can be realized by melting incineration residues, then by using the product slag as construction
materials. This is called Zero-emission scenario with incineration, or ZE-w-inc scenario(Figure 1(b)). In this scenario,
noncombustible waste, bulky waste, and residues from a material recovery facility as well as combustible waste are
                                                                  243
                                                                                      Matsuto

incinerated. Gasification-melting facility, which is the Advanced technology of incineration with the combination of
pyrolysis and melting of residue, is assumed. The third scenario doesn’t use incineration by maximize recycling, so it is
called Zero-emission scenario without incineration, or ZE-w/o-inc scenario(Figure 1(c)). In this scenario food waste is
anaerobically digested to produce methane gas, followed by composting of solid residue; plastics are pyrolyzed to
produce oil; combustible fraction is pelletized as RDF (refuse derived fuel) and used for power generation.

              Recyclables                     Recyclables                                                         Recyclables                Recovery
              (glass bottle,                   25654              Unit:t/y                                        (glass bottle,             25654
                                Material                                                                                                                                 Unit:t/y
              steel can                                                                                           steel can
              PET bottles)
                                Recovery       Residues                                                           PET bottles)               Residues
                 27004          Facility       1350                                                                                           1350             Electricity 52.7GWh
                                                                                                                     27004
            Noncombustibles                                                                                                                                    Slag            Construction
                                                                                                                                   Incineration
             70559                                                                                                                                              46178          material
                                         Noncombustible                                                                            592027
                                                                                                                  Combustible
Household                                residue                                      Household                                         Gasification/          Ferrous metal /Aluminum
                                                                        Business/                                 waste
waste                                            2927                                 waste                        360789               melting                 3197
                         Shredding/                                     commercial
            Bulky                      Ferrous metal
                         separation             6688                          15412                                                                            Fly ash         Landfill
            waste                                       Electricity                                               Business/
                                       Combustible      31.3GWh                                                                                                  21313
              19513                                                                                               commercial
                                                                             Landfill
                                       residue            Bottom    Landfill 154980
                                        9899                                                                          154116
                                                          ash 39965
            Combustible                Incineration                                                                                                                       Residue
                                                                                                                  Noncomb. &                      Shredding/
            waste 360789                                  Fly ash   Stabilization                                                                                          75772
                                                                                                                  bulky waste                     separation              Ferrous metal
                                      Business/            11367                                                     90071
                                                                                                                                                                          14300
                                      commercial 138705

                                (a) Present scenario                                                    (b) Zero-Emission with incineration scenario
                                                                                                            (ZE-w-inc scenario)
                                                                                                      HCl 732
                                                                                                                           Unit:t/y
                                                                            Pyrolysis                Oil 2050
                                                                   Plastics
                                                                   except PET 14645                   Residue
                                                    Recyclables
                                                                                                      4247
                                                       41649         Material             Recovery
                                                                     Recovery              25654
                                                                     Facility             Residue
                                                                                           1350
                                                      Noncomb. &                                     Recyclables
                                                                             Shredding/              14300
                                                      bulky waste
                                                       87082                 separation               Residue
                                      Household                                                        72758            Electricity
                                                      Combustibles                                                                            Landfill
                                                                                           RDF       Power             231.5GW
                                      waste                                                                                                   214354
                                                      except food                         150852     generation
                                                                        RDF                                              Ash
                                                       waste                                                            11540
                                                                                   Residue
                                                      199039                        21071                                              Landfill
                                                      Business/commercial       Methane gas
                                                      55939                     3271000m3
                                                      Food waste        Methane fermentation              Residue
                                                      141862            & composting                      23590 Business/commercial
                                                   Business/commercial                                            79798
                                                                                               Compost 10144
                                                   26637

                                                            (c) Zero-Emission without incineration scenario
                                                                (ZE-w/o-inc scenario)
                                           Figure 1 Selected scenario of solid waste management


Procedures of system evaluation
    System evaluation was done by using a computer program which the author developed to simulate waste
management in a municipality. Once recycling rates of individual waste component and waste separation categories for
collection are given by a user, the material flow of solid waste is calculated. A user can choose waste disposal method
for each collection category and key system parameters for each treatment/disposal facility, then the integrated solid
waste management system is evaluated in terms of life-cycle cost, energy consumption, and carbon dioxide emission.
The calculation includes overall design of facilities. Since all system variables but a few site-specific variables like a
population are predetermined as defaults, which were collected by extensive questionnaire surveys or by surveys of
literature, a user is only requested to give a few input.
    Major assumptions for the calculation are as follows.
 1) The city of Sapporo, having a population of 1.8 million, is used as a model city. The amount of
    business/commercial waste is assumed 30 percents of those of household waste.
 2) For Present scenario, 10 percents of business/commercial waste are directly landfilled.

                                                                                          244
                                                                   LCA

 3) For ZE-w-inc scenario, 100 percents of business/commercial waste are incinerated.
 4) For ZE-w/o-inc scenario, 90 percents of food waste from households are separated for composting. Of
   business/commercial waste, 70 percents of food waste are recovered for composting, and 70 percents of
   combustible fraction (paper and plastics) are collected for RDF. The rest of business/commercial waste is landfilled.
   From households, 30 percents of plastics excluding PET bottles are collected and pyrolyzed.


   The numbers of facilities and their process capacities were supposed as shown in Table 1. Material balances which
were calculated under the condition mentioned above have been provided in Figure 1. The amount of fuel, water,
chemicals, and other input materials are also calculated, though they are not shown here because of limited space. At
last, by multiplying those amounts with unit values in Table 2, cost, energy consumption, and carbon dioxide emission
were calculated. Unit values in Table 3 were used to calculate the reduction of energy and carbon dioxide by material
and energy recovery.


                Table 1 Number of facilities and capacity for selected three scenario
                Waste treatement            Present                  ZE-w-Inc                 ZE-w/o-Inc
                 /disposal facility         Cap     No ΣCap Cap               No       ΣCap Cap      No ΣCap
                Material recovery               42      3       126        42        3    126     42     3  126
                Shredding                       90      1        90      139         3    417    134     3  402
                CH4 fermentation/Composting                                                      130     6  780
                Pyrolysis of plastics                                                             68     1   68
                Incinerator                    512      5      2560
                Gasification/melting                                     595         5   2975
                RDF production                                                                   235     5 1175
                RDF power generation                                                             496     1  496
                Landfill                      1200      1      1200        93        1      93 1070      2 2140
                                            Unit of Capacity: t/day except landfill (m3/day)



               Table 2 Unit value used in calculation
                                                                      Energy          CO2 emission Cost
               Item                                        *          consumption
                                                                      [Mcal/*]        [kg-C*]        [yen /*]
               Electricity                                 kWh                  2.25          0.129                     20
               Heavy oil                                   L                      9.3         0.705                     34
               Light oil                                   L                      9.2          0.74                     57
               Caustic soda                                t                   2348             150                70,800
               Sulfuric acid                               t                     476             28                23,800
               Hypochlorous acid soda                      t                     899             52               266,700
               Chelate agent                               t                 24469              725               450,000
               Chemicals for gas scrubber                  t                   2329             136               359,700
               Ammonia water                               t                   2380             185               230,000
               Cement                                      t                     908            225                12,000
               Calcium hydroxide                           t                     530            299                20,000
               Water                                       m3                    3.2          0.175                    300
               Chemicals for leachate treatment            m3                 0.514           0.029                     18
               Civil engineering work                      1000yen              18.6           1.54           -
               Construction work                           1000yen              15.1             1.2          -
               Maintenance                                 1000yen              11.5           0.84           -
               Bulldozer                                   1000yen              11.4          0.818        32mil yen/truck
               Ladfill compactor                           1000yen              11.4          0.818        50mil yen/truck
               Refuse collection truck(2t)                 1000yen              11.4          0.859         5mil yen/truck
               Truck (4t)                                  1000yen             11.4           0.859         6mil yen/truck
               Truck for refuse transfer(6t)               1000yen              11.4          0.859        10mil yen/truck
               Acetic acid soda                            t                     899              52              266,700
               Iron chloride, coagulant                    t                   2329             136               359,700
               Hydrochloric acid                           t                   2348             150                23,800
               Limestone                                   t                     177            100                  6700
               Utility gas                                 m3                     10           0.58                     2.5

                                                                   245
                                                                                                  Matsuto



                                    Table 3 Unit values for material/energy recovery

                                                                                             Energy           CO2 emission Cost
                                                                            *                consumption
                                                                                             [Mcal/*]         [kg-C*]         [yen /*]
                                    Paper                                   t                          2,300              307           4,000
                                    Textile                                 t                            530               40               0
                                    PET bottle                              t                           2820              438               0
                                    Glass bottle                            t                          1950                 8               0
                                    Steel can                               t                          2,930              444               0
                                    Aluminum can                            t                        50,200             1524           60,000
                                    Compost                                 t                            330               12           7,000
                                    RDF                                     t                           4500              341           4,000
                                    Electricity                             kWh                          2.25          0.129                8
                                    Heat(steam, water)                      Mcal                            1          0.076                4
                                    Slag (melted)                           t                              22             1.6               0
                                    Lead, Zinc                              t                           3239           224.2                0
                                    Oil                                     L                             9.3          0.705               34
                                    Methane gas                             m3                             10            0.58             2.5
                                    Hydrochloric acid                       L                          2.348             0.15            23.8




Results and Discussion
   The results of system evaluations for the three scenarios are shown in Figure 2 to 4. "Initial" is the amount which
were consumed or emitted when the facility was constructed. It was calculated by multiplying construction cost with
the unit value in Table 2, and by dividing by durable years of the facility. In the figures, bar graphs in positive side
(right-hand side) are consumption or emission, meanwhile negative values are the reduction by energy or material
recovery. “Total” in each figure is the sum of all facilities; the top counts only positive values, the bottom in a
parenthesis includes the reduction.
1) Present scenario (Figure 2): Incineration has the biggest contribution to all three indicators. Some fraction of
  electricity generated by incineration is consumed in the facilities, and they are excluded in the figure. When these
  self-consumed energy is included, the energy consumption in incineration increases by 120 percents (in positive
  side) in Figure 2, and the ratio of “Initial” is 30 percents. “Initial” accounts small percentage in all three indicators
  for every facility. For carbon dioxide emission, incineration produces 80 percents of the total, of which 60 percents
  are originated from biomass source.
                                                       Initial    Labor     Electricity/chemicals        Maintenance    Material/energy recovery
                                                                          Collection

                                                                             Landfill

                                                                          Incinerator
                                                                                                       Total 15855
                                                                          Shredding                    (15520:Net including reduction)

                                                                  Material Recovery

                                                  -5000             -2500               0              2500          5000            7500            10000
                                                                                            Cost[Million yen/year]
                                                                                                              Initial                       Electricity/chemicals      Direct emission
           Initial    Electricity/chemicals   Maintenance         Material/energy recovery
                                                                                                              Maintenance                   Material/energy recovery
                                                Collection                                                                         Collection

                Total 150.4                        Landfill                                                                           Landfill
                (-77.5)
                                                Incinerator                                                                        Incinerator
                                                Shredding                                                                          Shredding             Total 137.9
                                        Material Recovery                                                                                                (122.3)
                                                                                                                            Material Recovery
         -750             -500           -250                 0               250                500
                                                                                                          -100               -50                 0            50             100         150
                                 Energy consumption[Tcal/year]
                                                                                                                        Carbon dioxide emission [Thousand ton-C/year]

                                                                            Figure 2 Present scenario
2) ZE-w-inc scenario(Figure 3): An increased cost by having sophisticated gasification-melting facility and larger
                                                                                                       246
                                                                                                                         LCA

  shredding facilities is almost comparable with cost reduction by smaller landfill. So there is little merit/demerit in
  cost when compared with Present scenario. For energy, a considerable reduction is obtained by an increase of power
  generation in gasification melting facility, while reduction by material recovery is rather small. Emission of carbon
  dioxide increases because the increased amount waste is incinerated.

                                                       Initial         Labor        Electricity/chemicals        Maintenance          Material/energy recovery

                                                                               Collection

                                                                                    Landfill

                                                                 Gasification/melting

                                                                               Shredding                  Total 15687
                                                                                                          (15168:Net including reduction)
                                                                   Material recovery

                                                   -5000               -2500                   0              2500             5000            7500              10000
                                                                                                   Cost[Million yen/year]

               Initial   Electricity/chemicals     Maintenance          Material/energy recovery                        Initial   Electricity/chemicals     Direct emission    Maintenance   Material/energy recovery


                   Total 151.2                          Collection                                                                                Collection
                   (-203.0)
                                                            Landfill                                                                                  Landfill

                                            Gasification/melting                                                                        Gasification/melting

                                                        Shredding                                                                                 Shredding                     計146.3
                                                                                                                                                                                (122.0)
                                                 Material recovery                                                                        Material recovery

        -750                -500             -250                       0                      250               500-100                 -50                     0              50              100              150
                                       Energy consumption[Tcal/year]                                                                     Carbon dioxide emission [Thousand ton-C/year]

                                                                                    Figure 3 ZE-w-inc scenario

3) ZE-w/o-inc scenario(Figure 4): By having a variety of treatment facilities, the cost increases substantially. Especially
  multiple number of small RDF production facilities result in                                                                                     the considerable increase of construction and
  operation cost. Collection cost also increases due to the increased number of waste separation categories. For energy
  consumption, while RDF production facilities consume a lot of energy for drying waste, the reduction by power
  generation (efficiency of 32 % is assumed) can exceed the increase. The contribution of methane production from
  food waste and recovery of oil is much smaller than power generation. For carbon dioxide emission, the reduction by
  methane fermentation is unexpectedly small because food waste from households accounts for only 13 percent of
  carbon in the entire waste stream.

                                                             Initial        Labor      Electricity/chemicals           Maintenance      Material/energy recovery

                                                                                          Collection
                                                                                               Landfill
                                                                           RDF power generation
                                                                                    RDF production
                                                                                           Pyrolysis                              Total 21011
                                                                        CH4 ferm/Composting                                       (18626:Net including
                                                                                                                                  reduction)
                                                                                          Shredding
                                                                               Material recovery

                                                            -5000                -2500                    0             2500             5000              7500            10000
                                                                                                              Cost[Million yen/year]

                                                                                                                           Initial                               Electricity/chemicals       Direct emission
               Initial   Electricity/chemicals         Maintenance             Material/energy recovery
                                                                                                                           Maintenance                           Material/energy recovery
                                                      Collection                                                                                      Collection
                                                           Landfill                                                                                       Landfill
                                       RDF power generation                                                                            RDF power generation
                                                 RDF production                                                                                 RDF production                       Total 127.2
                                                       Pyrolysis                        Total 525.0                                                    Pyrolysis                     (78.9)
                                                                                        (-233.9)
                                      CH4 ferm/Composting                                                                              CH4 ferm/Composting
                                                      Shredding                                                                                       Shredding
                                            Material recovery                                                                               Material recovery
      -750               -500              -250                        0                       250                   500-100                -50                      0               50               100               150
                                   Energy consumption[Tcal/year]                                                                            Carbon dioxide emission [Thousand ton-C/year]]

                                                                                    Figure 4 ZE-w/o-inc scenario

                                                                                                                         247
                                                           Matsuto



Conclusion
   Excluding the reduction shown by negative values in Figures 2 to 4, ZE-w/o-inc scenario can reduce carbon dioxide
emission, but energy consumption and cost increase substantially. ZE-w-inc scenario, on the other hand, shows any
significant difference from Present scenario, and the minimization of landfill is quite attractive.
   In terms of net values including the reductions, ZE-w/o-inc scenario shows the same level of energy consumption
and lower carbon dioxide emission than Present scenario. Increased cost is disadvantageous, and establishing recycle
route and market, securing users of recovered material/energy is big challenge for this scenario. However, this scenario
seems to be an appropriate choice for the concept of Recycling-based society.


REFERENCES
Matsuto,T., Tanaka,N.: Computer modeling to assess cost, energy consumption and carbon dioxide emission from
  municipal solid waste disposal system, Journal of Envionmental Systems and Engineering, 685(7-20), 49-60, 2001
  (in Japanese)
Lab of Solid Waste Disposal Engineering, Hokkaido University: Decision-making tool for System evaluation program
  on the integrated solid waste management, 1998 (in Japanese)




                                                            248

								
To top