Anaerobic Treatment of HTC Waste Water

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Anaerobic Treatment of HTC Waste Water

• B. Wirtha,b, J. Mummea, B. Erlachb
• a) Leibniz Institute for Agricultural
  Engineering, APECS Junior Research Group
• b) Technische Universität Berlin, Institute for
  Energy Engineering

Supported by
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Introducing APECS

• Anaerobic Pathways to Renewable Energies and
  Carbon Sinks
• Member of IBI
• Junior research group focusing on the combination
  of anaerobic digestion (AD) and carbonization
  technologies

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Aim of this Study

• Investigation of anaerobic digestion as a
  treatment for waste water from hydrothermal
  carbonization (HTC)
• General feasibility
• Process performance
• COD (chemical oxygen demand) and TOC (total
  organic carbon) removal efficiency
• Comparison of two reactor types
• Economic impact on an industrial-scale HTC plant

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State-of-the-Art IHydrothermal Carbonization

• Products of HTC
• Solid phase hydrochar
• Gaseous phase 90 CO2
• Liquid phase
• HTC liquor
• Contains volatile fatty acids, phenols, sugars,
  etc.
• Contains up to 20 of initial carbon
• Needs treatment before released to the
  environment
• -gt An anaerobic treatment of waste water yields
  methane and can gain further energy!

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State-of-the-Art IIAnaerobic Digestion

• 4 major steps
• Hydrolysis is the speed-limiting step
• AD of HTC liquor should be dominated by immediate
  methanogenesis

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Materials Methods IExperimental Set-Up
Experimental Set-up _at_ ATB
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Materials Methods IISubstrate Properties and
Reactor Operation

• HTC liquor
• HTC of corn silage
• 220 C 6 hrs
• Reactor operation
• 37 C mesophilic
• Daily feeding of HTC liquor
• Organic loading rate (OLR) of 1 gCOD L-1 d-1
• Weekly removal of (liquid) digestate
• 13 weeks continuous operation
• Monitoring of pH, reactor temperature, gas
  production rate, and gas composition
• Regular analysis of the chemical properties of
  the digestate

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Experimental ResultsGas Production during
Continuous Operation

• Methane fraction 50-65
• Methane yield 0.25 L gCOD-1 and 0.65 L gTOC-1

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Experimental ResultsCOD and TOC Removal
Efficiency

• Maximum COD removal as high as 80
• TOC removal always 20 percentage points lower

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Economic AssessmentBasic Parameters

• Based on previous HTC plant design (Erlach et
  al., 2010) and previous economic assessment
  (Wirth et al., 2011)
• HTC of SRF wood chips and municipal organic waste
• 11.15 MWHHV biomass input _at_ 7000 h a-1
• Amounts of waste water and demand of natural gas
  (for raising steam for the HTC process) extracted
  as referring values

Parameter Unit HTC Plant Design HTC Plant Design
Parameter Unit Wood Chips Organic Waste
Waste Water kg h-1 2141 6706
TOC g L-1 20.4 10.0
COD g L-1 54.0 26.4
Natural Gas Demand kW 965 1272
Natural Gas Demand m3 h-1 45.0 59.4
Natural Gas Demand kJ MJchar-1 69.0 92.9
Produced Hydrochar tTS a-1 9797 12947
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Economic AssessmentResults
Parameter Unit Wood Chips Wood Chips
COD Degradation 80 100
Natural Gas Replaced 58.2 74.4
Share on the Feedstock 2.6 3.3
Share on the Char 2.9 3.7
Organic Waste Organic Waste
COD Degradation 80 100
Natural Gas Replaced 75.2 94.0
Share on the Feedstock 4.4 5.6
Share on the Char 5.0 6.3
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Conclusions

• HTC liquor can be treated anaerobically
• Methane yield of up to 0.65 L gTOC-1
• COD removal as high as 80
• AF was more stable compared to the CSTR
• Lasting inhibition by process intermediates was
  not observed
• Further experiments (higher OLRs, thermophilic
  conditions, etc.) are in preparation
• 60-75 of natural gas could be replaced at 80
  COD degradation
• Higher OLRs increase economics
• Savings for the aerobic treatment may further
  improve economics

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Thank you for your attention!
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