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Heavy Metals in Sewage Sludge

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					Implications of Heavy Metals in
        Sewage Sludge
  Where Do We Stand on Regulations?
                  Regulation?
• Why? - Authorization or mandate
• How? - Concepts, goals, assumptions, and
  approaches
• What?
    – Contents
    – Implement-able package



•
        Regulate? Not Regulate?
• Opponent
   – Potentially hazardous substances are present
   – Assuming practice will be harmful until proven safe
   – Ban or strict limitation
• Advocate
   – Practiced for a long time without “documented” harmful effects
   – Assuming practice is safe until proven otherwise
   – Promotion, no need to regulate, or general guidelines
• Framework of mind
   – Decision of regulate may be different
               Cumulative Loading
Cumulative      USA     Canada France Holland
  Rate
Cd (kg ha-1)
                  39      4     3.75    1.25
Cu (kg ha-1)
                1,500    150    200      75
Ni (kg ha-1)
                 420     36     62.5     38
Pb (kg ha-1)
                 300     100    125     225
Zn (kg ha-1)
                2,800    370    550     300
Hg (kg ha-1)
                  17      1      2.3    0.75
            Annual Loading
 Annual    Cd        Pb        Zn          Hg
  Input (kg/ha-1) (kg/ha-1) (kg/ha-1)   (kg/ha-1)
USA        1.9       15       140         0.85
Germany   0.15        6        15         0.125
Sweden    0.015      0.3       10         0.008
Holland  0.0025     0.45       0.6       0.0015
Finland   0.12       4.8       20          0.1
Denmark 0.015       0.06        -           -
          Discrepancies, Why?
• Rule making process
  –   Mandates
  –   Concepts
  –   Goals
  –   Assumptions
  –   Approaches
           Rule Making Process
• Objective
   – goals regulation must accomplish
• Assumptions
   – domain within which proposed rules apply
• Approach
   – strategy to accomplish objective
• Final rule
   – Reasonable?
   – Implement-able?
• Acceptance? Public, stakeholders
                Approaches
• Ecological Balance
  – Prevent pollutant accumulation in soils
• Capacity utilization
  – Maximize pollutant attenuation capacity
     of soils
 Prevent Pollutant Accumulation
                    Assumptions


• Soil - foundation of terrestrial ecosystem
  and irreplaceable natural resource
• Use without undue restrictions, if soil is free
  of pollutants
• Experience increasing difficulty to support
  uses, if pollutants are allowed to accumulate
• Unknown ecological consequences
 Prevent Pollutant Accumulation
                     Goal



• No pollutant accumulation in the sewage
  sludge-receiving soils
 Prevent Pollutant Accumulation
                  Regulatory Approach



• Pollutant-free sewage sludge
• Pollutant input = Pollutant output
 Prevent Pollutant Accumulation
                   Advantages



• In agreement with ecology - sustainable
  practice
• Numerical limits - obtain from simple mass
  balance calculations
• Detailed knowledge on fate and transport of
  pollutants not needed
• One set of standards fits all situations
• Easy to implement
 Prevent Pollutant Accumulation
                   Disadvantages



• Require rigorous pretreatment for
  wastewater discharge
• Phase out incompatible industrial raw
  material and household products
• Performance and reliability of wastewater
  treatment processes
• Little agronomic benefit
 Maximize Attenuation Capacity
                    Assumptions



• Soil assimilates, attenuates, and detoxifies
  pollutants
• Capacity should be utilized - realize
  benefits of resource conservation
• Land application, environmentally, is equal
  if not a better option
• Stringent limits discourage resource
  conservation and recovery
 Maximize Attenuation Capacity
                      Goal



• Realize agronomic benefits of applying
  sludge on land
• Keep pollutants in the soil at a safe level -
  public health and environment
• Beneficial use without compromising public
  health and environment
 Maximize Attenuation Capacity
                 Regulatory Approach



• Identify safe/unsafe sludge for land
  application
• Determine maximum tolerable pollutant
  input
• Set maximum tolerable pollutant levels in
  soil or products
 Maximize Attenuation Capacity
                    Advantages



• Resource conservation - appreciation of
  agronomic benefits
• Flexibility of developing safe and site-
  specific land application operations
• Cost effective - competitive with other
  options
 Maximize Attenuation Capacity
                   Disadvantages I



• Upper limits for each pollutant must be
  evaluated separately
• Technical information is not always
  available - uncertainties in setting numerical
  limits
• Pollutant levels in receiving soil will
  increase - under long-term use and high
  rates
 Maximize Attenuation Capacity
                  Disadvantages II




• Margin of safety “may be” narrower
• Site may require long-term monitoring
            U.S. vs Europe
• U.S. - maximizing pollutant attenuation
  capacity of soils
• European countries - preventing pollutant
  accumulation in soils
   Will Sludge Ever Be Free of
             Metals?
• Not likely
• Metals will always be used in industrial
  processing and consumer goods
• They will find their ways into the
  wastewater collection systems
• Source control is essential
Heavy Metals in Sewage Sludge
                    Trends



• Metal concentration of sludge continued to
  decrease - implementation of industrial
  waste pre-treatment program
• Pollutant input decreases when “agronomic
  rate” is followed
USEPA Sewage Sludge Survey
 Element     1979   1988   Change

Cd (mg/kg)    69     7     - 90%
Cr (mg/kg)   429    119    - 72%
Cu (mg/kg)   602    741    + 23%
Pb (mg/kg)   369    134    - 63%
Ni (mg/kg)   135     43    - 68%
Zn (mg/kg)   1594   1202   -24%
AMSA Sewage Sludge Survey
 Element     1987   1996   Change

Cd (mg/kg)    26     6     - 75%
Cr (mg/kg)    430   103    - 76%
Cu (mg/kg)    711   506    - 28%
Pb (mg/kg)    307   111    - 64%
Ni (mg/kg)    167   57     - 66%
Zn (mg/kg)   1540   830    - 46%
     Estimated Pollutant Inputs
           (1000 t ha-1)
• Reasonable application: <10 t ha-1y-1 for
  <100 y, therefore <1000t ha-1
• Use Sewage Sludge from San Jose as an
  example
• Estimated pollutant inputs are considerably
  less than pollutant loading rates specified in
  Part 503 regulation
 San Jose Sewage Sludge
Element    Conc.     Input@     CPLR
                    1000 t ha-1
          (mg kg-1) (kg ha-1) (kg ha-1)

  As        5.8        5.8       41
  Cd        9.6        9.6       39
  Cr        400        400      1,200
  Pb        150        150       300
  Hg        1.5        1.5       17
San Jose Sewage Sludge
Element    Conc.        Input      CPLR
          (mg kg-1)   (kg ha-1)   (kg ha-1)

  Mo        4.9         4.9           -

  Ni        100         100         420

  Se        2.8         2.8          36

  Zn       1,100       1,100       2,800
            Implementation
• No rule is and will be perfect
• Fulfill its mandate and accomplish its goals
• If not implementable, regulation = no
  regulation
• Regulations are better than no regulation
• Technological issues
• Costs issues
          Possible Approaches
• Match benefits
   – Waste disposal
   – Plant nutrients
• Sharing and distribution of cost and risk
• Urban-rural alliance
   – Special district
   – Cooperative
   – Collective planning and implementation
• Long-lasting institutional entities

				
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