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

CumulativeRate

USA Canada France HollandCd (kg ha-1) 39 4 3.75 1.25Cu (kg ha-1) 1,500 150 200 75Ni (kg ha-1) 420 36 62.5 38Pb (kg ha-1) 300 100 125 225Zn (kg ha-1) 2,800 370 550 300Hg (kg ha-1) 17 1 2.3 0.75

Annual Loading

Annual Input

Cd (kg/ha-1)

Pb (kg/ha-1)

Zn (kg/ha-1)

Hg (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 CapacityAssumptions

• 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 CapacityGoal

• 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 CapacityRegulatory Approach

• Identify safe/unsafe sludge for land application

• Determine maximum tolerable pollutant input

• Set maximum tolerable pollutant levels in soil or products

Maximize Attenuation CapacityAdvantages

• Resource conservation - appreciation of agronomic benefits

• Flexibility of developing safe and site-specific land application operations

• Cost effective - competitive with other options

Maximize Attenuation CapacityDisadvantages 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 CapacityDisadvantages 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.

(mg kg-1)

Input@1000 t ha-1

(kg ha-1)

CPLR

(kg ha-1)

As 5.8 5.8 41Cd 9.6 9.6 39Cr 400 400 1,200Pb 150 150 300Hg 1.5 1.5 17

San Jose Sewage Sludge

Element Conc.(mg kg-1)

Input(kg ha-1)

CPLR(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