Anaerobic Treatment of HTC Waste Water

B. Wirtha,b, J. Mummea, B. Erlachb

a) Leibniz Institute for Agricultural Engineering, APECS Junior Research Groupb) Technische Universität Berlin, Institute for Energy Engineering

Supported by

The APECS Concept

Introducing APECS

Anaerobic Pathways to Renewable Energies and Carbon SinksMember of IBIJunior 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 feasibilityProcess performanceCOD (chemical oxygen demand) and TOC (total organic carbon) removal efficiencyComparison of two reactor typesEconomic impact on an industrial-scale HTC plant

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State-of-the-Art IHydrothermal Carbonization

Products of HTC:Solid phase – hydrocharGaseous phase – 90 % CO2

Liquid phase

HTC liquor:Contains volatile fatty acids, phenols, sugars, etc.Contains up to 20 % of initial carbonNeeds treatment before released to the environment

-> An anaerobic treatment of waste water yields methane and can gain further energy!

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State-of-the-Art IIAnaerobic Digestion

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Flow Diagram of Anaerobic Digestion

4 major steps

Hydrolysis is the speed-limiting step

AD of HTC liquor should be dominated by immediate methanogenesis

Materials & Methods IExperimental Set-Up

Experimental Set-up @ ATB

Biofilm Carriers

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Materials & Methods IISubstrate Properties and Reactor Operation

Property Unit Value

pH-Value [-] ~ 4.00

Dry Matter Content (DM) [%wt] ~ 3.00

Chemical Oxygen Demand (COD) [g L-1] 41.35

Total Organic Carbon (TOC) [g L-1] 15.66

Acetic Acid [g L-1] 5.26

Propionic Acid [g L-1] 0.34

Phenol Sum Parameter [mg L-1] ~ 250.00

HTC liquorHTC of corn silage 220 °C – 6 hrs

Reactor operation37 °C – mesophilicDaily feeding of HTC liquorOrganic loading rate (OLR) of 1 gCOD L-1 d-1

Weekly removal of (liquid) digestate13 weeks continuous operation

Monitoring of pH, reactor temperature, gas production rate, and gas compositionRegular 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 waste11.15 MWHHV biomass input @ 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 UnitHTC Plant Design

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

m3 h-1 45.0 59.4

kJ MJchar-1 69.0 92.9

Produced Hydrochar tTS a-1 9797 12947

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Economic AssessmentResults

Parameter Unit 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

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 anaerobicallyMethane yield of up to 0.65 L gTOC

-1

COD removal as high as 80 %AF was more stable compared to the CSTRLasting inhibition by process intermediates was not observedFurther experiments (higher OLRs, thermophilic conditions, etc.) are in preparation

60-75 % of natural gas could be replaced at 80 % COD degradationHigher OLRs increase economicsSavings for the aerobic treatment may further improve economics

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Thank you for your attention!

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