Sustainable Treatmentof RecalcitrantCompounds – A caseStudy

Introducing Samuel is a graduate at WSP with experience in thecollection of soil and groundwater data forenvironmental assessment and remediation.He has been involved in the implementation ofvarious active treatment trials undertaken to informsite specific clean-up actions, as well as large-scaleremedial works.

Overview 1. Background2. Objective3. Process4. Findings5. Learnings

Co-authors:

Graham Smith and Shane Giliam (WSP)

Acknowledgments:

WSP acknowledges the support of the client in the successful completion of the project

Background-Issue

Following closure of a former major hazard facility:

• Site effluent treatment plan was decommissioned.

• Sludge from the decommissioned effluenttreatment plant remained onsite, contained withingeo-fabric bags on drying beds (for approx. 10years).

• Sludge required treatment/disposal in accordancewith State regulatory requirements (IWRG 631).

50 m

Background-Extent ofcontamination

Sludge is categorised as Category A under IndustrialWaste Resource Guidelines (IWRG 631).

Summary of contaminants detected in geo-fabric bags(2013):

Baseline sampling (2017) reported that 99% of remainingcontaminant mass is TRH ସܥ-ଵܥ (~9.5 t).

Contaminant Range (mg/kg) % by contaminant

TRH ସܥ-ଵܥ 12,130-103,000 85

Sum of PAHs 50-9,250 7

Styrene 0.4-8050 5

Benzene 0.35-1600 1

Bis (2-ethylhexyl) phthalate 8.2-480 0.3

Objective The challenge:

- Category A Industrial Wasteà 10yr legacy issue

- Seeking a low cost and effective solution

The approach:

- Microbial activity is a proven approach

- Composting was seen as a sustainable solution

The objective of this pilot trial was to reduceconcentrations of contaminants by stimulating naturalbiodegradation by using microbes in a large compost pile.

Mixing - Sludge,straw and compost

• Sludge from 3 geo-bags(pilot trial) of totalvolume 150 ݉ଷ.

• Commercially availablecompost (for source ofmicrobes) of totalvolume 75 ݉ଷ

• Cereal straw (forincreasing oxygencontent) of total volume75 ݉ଷ

Process

Mixing - Sludge, straw andcompost

Bio-pile

Grinding mixture tohomogenise and decreasesize of sludge lump (increasesurface area).

Fully formed and mixed“bio-pile” approximately300 ݉ଷ.

Nutrients/wateringProcess

– Adding water to preventdrying out of pile.

– Nutrients (ܱܰܭଷ) addedto promote microbialactivity

– Bunding to capture anysediment run-off andreduce erosion at toe ofpile

Monitoring– Landfill gas (ܱଶ, (ସܪܥ,ଶܱܥ

– Volatile organic compounds(VOC)s with a photo-ionisation device (PID).

– Temperature (internal andambient)

– Contaminant of concern,nutrient concentrationsand hydrocarbon utilisingbacteria (laboratory)

Process

Findings After 5-months…

Findings-Observations September November January

• Intact straw• Hard lumps• 300 ݉ଷ

Inception(August)

• Decomposed straw• Smaller/softer lumps• 225 ݉ଷ (25%

reduction)

• Progressivehomogenisation/decomposition

0.6MCFU/g

1.7MCFU/g

Findings –field data

Over the 5-month period:• Volume of the bio-pile went from an estimated 300݉ଷ to 225 ݉ଷ (25% reduction).

• Temperature in the bio-pile peaked 5 days afterformation at 72°C (one sensor).

• VOC readings were elevated in the pile (420ppm to9ppm after 21 days).

• No VOC readings above 0.1 ppm were detectedoutside the pile (VOCs contained within pile).

Findings –field data

• The average temperature (three sensors) was consistentlybetween 50-60 °C during the trial, with no indication ofcooling after 5 months.

0.00

80.00

0 5 10 15 20 25

TEM

P(C

)

WeeksAmbient Bio-pile

Findings –Field data

Over the 5-month period:• Oxygen levels peaked at 15% initially, then decreased to

0% but increased after 14 days to average ~ 4% .• Carbon dioxide levels peaked at 32% after 7 days, then

declined to around 10% at 85 days.àIndicative of aerobic respiration

0

10

20

30

40

0 5 10 15 20 25

%

Weeks

Compost monitoring data

CO2 (%) O2 (%)

Findings -Nutrients

Over 5-month period:• Presence of hydrocarbon utilising bacteria (HUB) was

confirmed.

• Nitrate levels dropped from 1,400 mg/kg to 5.9mg/kg indicates nutrients are being consumed.

• Phosphate levels remained elevated at 12 weeks(around 7,000 mg/kg total P).

Findings -Contamination

At the conclusion of the trial:• MAHs including benzene, ethyl benzene and styrene

were below laboratory detection limits.• 74% reduction in total PAH including naphthalene,

acenaphthylene and phenanthrene.• 32% reduction of bis (2-ethylhexyl) phthalate.

Overall 30% reduction in TRH - by mass,equivalent to approximately 2,800 kg of mass

…However material remains Category A under IWRG631.

Findings –Sampleheterogeneity

Initially came back extremelypositive:• TRH (Category C)

Upon reanalysis (subsample)results more conservative:• TRH (Category A)• 2 low/clean subsamples• 2 contaminated (up to 10 x

higher)

WHY?

Findings –Bio-pileheterogeneity

Virginsludgelumps(>10mm)

Finegrainedmaterial

High results from untreated sludgein lump form?

• Separated out lumps >10mm

• Found lumps to be intact withno visual change frominception

• Likelihood is that high results =lump analysed

• With high (likely lump) resultremoved, Category B achieved.

Conclusions In summary, at the conclusion of the trial:

• Mass of TRH ସܥ-ଵܥ was estimated to decrease fromapproximately 9,500 kg to 6,600 kg (32% reduction).

• Microbial degradation was still evident at the end oftrial.

• Sustainable solution in comparison to “traditional”methods.

• Time frame of treatment a significant constraint/challenge.

Learnings Key learnings of the 5-month pilot trial:

• Lab costs are significantàMinimise sampling

• Beware heterogeneity à Grinding/mixing criticalà Consider lab limitations

• Treatment time/mixing àMass calculation reliability

• Did we stimulate microbes and reducecontamination…? YES

Changingtomorrowtoday

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Should you have any questions please contact Sam atemail: sam.aldous@wsp.com

Questions?