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Biosolids Composting Impacts on PFAS

Todd O. Williams, P.E., BCEE

todd.williams3@jacobs.com

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Presented at USCC Annual Conference

January 27, 2021

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Biosolids Composting Impacts on PFAS Outline

  • Overview of PFAS sources
  • PFAS in Biosolids Products – Why should we care?
  • Regulations related to PFAS in biosolids and soils?
  • Biosolids Composting Impact on PFAS
  • Summary thoughts

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What Are PFAS?

  • Per- and poly-FluoroAlkyl Substances
  • Thousands of man-made compounds, no natural occurrence
  • Used since the 1950s in many products
    • Heat resistant
    • Flame retardant
    • Oil resistant
    • Water resistant
    • Found in blood of people, animals, and fish worldwide
  • Properties which make these compounds useful also result in their persistence in the environment

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©Jacobs 2020

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firefighting foam

paints and stains

stain – resistant carpets

water – repelling fabrics

nonstick cookware

food packaging

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Uses/Sources

  • Aqueous Film-Forming Foam (AFFF)
    • Airports
    • Railroads
    • Fire Departments
    • Oil & Gas
  • Manufacturing
    • Metal Plating
    • Automotive
    • Chemicals
    • Coatings
    • Pulp & Paper
  • Commercial
    • Car Wash Waxes
    • Electronics
    • Landfill Leachates

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©Jacobs 2020

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PFAS in Biosolids – Why should we care?

  • Land application makes up 60% of the global biosolids market
  • In the US, half of the 7.2 M dry tons per year of WWTP biosolids are land applied.
  • The US biosolids land application market is valued at $600M/year and growing 4% per year or more

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  • Problems with landfills is forcing even more biosolids to land application
  • What are the concerns?
    • Surface water, ground water, plant uptake
  • What do farmers and compost users think?

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Biosolids Market – Growth Rate by Region, 2019-2024

Biosolids Market, Volume (%), by Application, Global 2018

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PFAS regulations in soil/biosolids with values protective of groundwater

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Entity

µg/Kg (ppb)

PFOA

PFOS

PFBS

US EPA (Soil Screening Level)

0.017

0.038

13

State values *

0.6 – 350

0.22 - 25

53 – 910

Maine (Biosolids Specific Screening)

2.5

5.2

1900

* Current states: AK, MI, NE, NC, TX. Enforceable value in AK.

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PFAS Concentrations Within Wastewater Facilities is Highly Variable (ng/l)

  • Measured PFAS pass through WWTP with limited/no reduction
  • Precursors discharged to WWTP cause detectable PFAS to increase across aeration
  • PFAS also leaves plant through biosolids

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Plant

Location

PFHxA

PFHpA

PFOA

PFHxS

PFOS

Total

A

Influent

59

13

206

24

134

444

Effluent

60

13

200

28

240

560

B

Influent

9.7

2.2

3.1

6.6

12

35

Effluent

31

3.7

14

48

22

120

Source: Gallen et. al., 2018, Chemosphere

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A Conventional �Wastewater Facility�PFAS Concentrations (ng/L)

  • Low concentrations of PFAS detected
  • Often see detectable concentrations due to wastewater source:
    • Domestic products
    • Landfill leachate
    • Human excretion
  • Does not appear to have “significant” industrial contribution
  • Increase across aeration commonly observed from “precursor” conversion

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Sample

Location

PFHxA

PFOA

PFBS

PFHxS

PFOS

Total

7/6 Inf

7/8 Eff

Influent

ND

1.3

2.0

1.3

3.2

7.8

Effluent

15

4.4

2.7

ND

3.3

26.4

7/7 Inf

7/9 Eff

Influent

ND

2.3

3.3

ND

3.2

8.8

Effluent

20

4.2

3.1

ND

2.9

30.2

7/8 Inf

7/10 Eff

Influent

ND

2.0

1.6

ND

4.4

8.0

Effluent

17

4.6

2.9

1.3

2.9

28.7

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A Conventional Wastewater Facility Biosolids PFAS Concentrations (ng/g)

  • 100% WAS treated through ATAD system
  • PFBS and PFHxS not detected
  • Increase across digestion from aerobic “precursor” conversion and/or changes in % solids

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Sample

Location

PFHxA

PFOA

PFOS

Total

7/11 DI

7/6 BS

Digester Inf

ND

2.3

10

12.3

Biosolids

35

20

38

93

7/13 DI

7/8 BS

Digester Inf

ND

ND

9.1

9.1

Biosolids

62

37

56

155

7/15 DI

7/10 Eff

Digester Inf

ND

2.4

9.2

11.6

Biosolids

33

15

45

93

Average

Digester Inf

ND

2.4

9.4

11.8

Biosolids

43.3

24

46.3

114

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PFAS Precursor Biotransformation�Background��Interpretation of AFFF degradation pathways�

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Reference:

James Hatton, Dusty Rose Berggren, Jeremy Bishop and Bill Diguiseppi. “Treatability Test: Oxidation Technologies for Destruction of PFAS Compounds”.  CH2M Hill Innovation Grant Technical Memorandum. December 2014

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Biosolids Composting and its Impact on PFAS Concentrations

  • Jacobs conducted sampling and testing of several biosolids composts in 2020 for analysis of 24 PFAS compounds using isotope dilution/LC-MS/MS method
  • Wastewater treatment systems where compost sampled have minimal industrial contribution
  • Wastewater treatment schemes prior to composting included the following:
      • Primary treatment and primary sludge only (PRI)
      • Conventional secondary treatment with nutrient removal, mixture of primary and waste activated sludge (PWAS)
      • Conventional secondary treatment with nutrient removal, waste activated sludge only (WAS)
      • Conventional secondary treatment, mixture of primary and waste activated sludge, then mesophilic anaerobic digestion (MAD)
  • All operations sampled utilized the aerated static pile method of composting

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Impact of thermal drying, blending with bulking agent, and �chemical/thermal hydrolysis treatment (not THP)

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Rotary

Drying at

480⁰C to

650⁰C

53% 🡹

20% sludge/80% wood blend prior to composting 72% 🡻

Low temperature (70⁰C) alkaline hydrolysis (Lystek)

No impact

Source: Lazcano, et.al, 2019 Water Environment Research

Expectation is that bulking agent dilution effect would reduce concentrations of PFAS in compost compared to input sludge

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PFAS Concentrations in Sludge Cakes�(ng/g dry)���

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  • In general, concentrations in sludges are not high
  • PFOS and MeFOSAA are 2 largest components in sludges
  • MeFOSAA typically degrades to PFOS

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PFAS Concentrations in Bulking Agents�(ng/g dry)���

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  • Bulking agents used included wood chips, ground pallets, ground yard waste and recycled screen overs
  • Most bulking agent concentrations are very low
  • Recycling 100% bulking agent may increase PFAS concentration

100% Recycle BA

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PFAS Concentrations in Composts�(ng/g dry)���

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  • PFOS, PFOA, PFHxA, PFBS and MeFOSAA are largest components in composts

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PFOA, PFOS and Total PFAS by Facility

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PRI and PWAS

WAS and MAD

Appears to be more precursor transformation of primary sludge vs. waste activated sludge or digested sludge

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PFSA and PFCA Compound Concentrations by Facility (note scales)

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Summary Points

  • This is a very small data set. However, there are some observations
  • PFOS is the most commonly detected compound in all materials (sludge, bulking agent and composts)
  • Primary sludge not treated aerobically first appears to be more susceptible to precursor transformation into multiple PFAS terminal compounds through composting
  • Aerobically processed sludges and anaerobically digested sludges may result in less precursor transformation during composting
  • Bulking agent recycling may increase PFAS concentration in the bulking agent and the resulting compost
  • Every sludge is different…..know what you’ve got through sampling and testing!

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Next Steps

  • Study the role of precursors in PFAS assessment in composting sludges
  • Evaluate impacts of sludge properties on PFAS transformations in composting
  • Test the leachability of PFAS in biosolids compost amended soils
  • Testing of biosolids compost products for plant uptake of PFAS
  • Continue sampling and testing more biosolids composts

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Biosolids Composting Impacts on PFAS��Thank You!

Todd O. Williams, P.E., BCEE

todd.williams3@jacobs.com

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