A New, Environmentally Acceptable Method For Reducing Production of Excess Biosolids From Biological

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CIWEM MEETING, WRc 7 December 2006

• A New, Environmentally Acceptable Method For
  Reducing Production of Excess Biosolids From
  Biological Wastewater Treatment Processes

Stephanie Edmunds, Kirstie Hearn, Luc Louvel,
Yves Mottot, Rod Palfrey, Howard Richmond
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Summary

• History
• The Uncoupling Process
• Tetrakishydroxymethylphosphonium Sulphate (THPS)
• Feasibility
• Process assessments
• Conclusions
• Future work programme

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Potential Benefits of Uncoupling
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Energy Generating Mechanism
Oxidation and ATP synthesis are coupled by
trans-membrane proton fluxes
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Uncoupling - Modifying Cell Energetics
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Examples of Classical Uncouplers

• Para-nitrophenol
• 2,4-dinitrophenol
• 2,4,5-trichlorophenol
• Tetrachlorosalicylanilide
• Meta-chlorophenol

Said to operate by capturing protons,
transporting them through the membrane and
releasing them inside the bacterial cell
These uncouplers can achieve useful reductions in
sludge growth but are too environmentally toxic
for general use
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THPS Uncoupler Candidate
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THPS History
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Effect of THPS on Bacterial Membranes
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THPS Environmental Profile

• Relatively low fish toxicity
• Readily biodegradable
• Breaks down rapidly to inert compounds in aerobic
  conditions
• Degrades to THPO
• Does not bioaccumulate

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Research Project
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Oxitop Method
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Oxitop Method

• THPS is clearly an uncoupling agent
• Up to 70 uncoupling was observed at a treatment
  level of 25 mg/l
• Significant uncoupling (32) was achieved at only
  2.5 mg/l
• Initial results were very encouraging but the
  test was rather artificial
• Needed to move to a more realistic test method

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Chemostat Method
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Chemostat Method

• Chemostat charged with activated sludge from
  Courly (Lyon)
• Synthetic sewage fed continuously
• Each weekday, mixed liquor was removed to give a
  7.5 day SRT
• One chemostat retained as untreated control
• Other chemostats treated with THPS via flash
  mixing
• Biosolids growth monitored by measuring MLSS
• Chemostat tests achieved up to 37 decrease in
  biosolids growth at 4 mg/l/day dose

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Porous Pot Method

• Sewage at WRc is continuously abstracted from a
  local sewer carrying sewage from a housing estate
• Screened to remove large solids
• Settled to remove most suspended solids and piped
  to the laboratory
• THPS dosed using a recirculating line coupled to
  the pots

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Porous Pot Method
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Porous Pot Method

• Peak biosolids reduction observed was 55
• No adverse effects on the quality of the treated
  water
• E.g. BOD, COD, Ammonia, Nitrate
• No evidence of acclimatisation in fact the
  effect (biosolids reduction) was increasing
  throughout the test period

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Pilot Scale Work
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Pilot Scale Work
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Analytical Specifications
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Settled Sewage Feed Concentrations
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Average Influent Sewage Quality
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THPS Dosing
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Pilot Plant Cumulative Sludge Production
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Pilot Plant Sludge Growth Reduction
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Sludge Growth

• During the period January May a cumulative
  reduction in sludge production of up to 32 was
  observed.
• The MLSS (mg/l) values for control and treated
  plants indicate on a daily basis there is a clear
  and maintained reduction in sludge volumes.

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Pilot Plant Effluent Qualities
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Pilot Plant Effluent Qualities
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Effluent Qualities

• No significant effect on treated water quality.
• COD removal, generally good.
• Slight increase in soluble COD in some dosing
  periods
• Nitrification problems identified on one occasion
  however system recovered without intervention.

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Daphnia Test Results

• EC50 is the concentration which immobilises 50
  of neonates over 48 hours.

• No effect was observed in any samples.

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Sludge Digestion
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Phytotoxicity

• Tests Carried out using Tomato and Barley
• There was no inhibition by the dosed sludge of
  germination or early development of either barley
  or tomato plants, at the concentrations tested.
• The THPS (or products) within the dosed sludge
  were either insufficient to cause adverse effects
  in the test, or are not phytotoxic to tomatoes or
  barley at typical land application rates.

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Conclusions

• THPS can be used to reduce the mass of sludge
  produced from a simulated activated sludge plant.
• The measured reduction in biosolids during the
  five month period was between 14 and 32.
• No significant adverse effects on the quality of
  the treated water were observed.

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Future Work

• Trial Work
• Trials throughout Europe are sought.
• Preparations already in progress for 2 trials.
• Operational parameters need to be closely
  monitored.
• Research Work
• Research program is continuing
• University collaborations

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Acknowledgements
The authors would like to thank CIWEM for the
opportunity to present this technical
paper. Also, we would like to thank Rhodia and
WRc plc for permission to publish this work.