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
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
The APECS Concept
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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 I
Hydrothermal 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
-> An anaerobic treatment of waste water yields
methane and can gain further energy!
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State-of-the-Art II
Anaerobic Digestion
4 major steps
Hydrolysis is the speed-limiting
step
AD of HTC liquor should be
dominated by immediate
methanogenesis
Flow Diagram of Anaerobic Digestion
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Materials & Methods I
Experimental Set-Up
Biofilm Carriers
Experimental Set-up @ ATB
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Materials & Methods II
Substrate Properties and Reactor Operation
HTC liquor
HTC of corn silage
220 °C – 6 hrs
Reactor operation
Property
pH-Value
Unit
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
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
[mg
L-1]
~ 250.00
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 Results
Gas 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 Results
COD and TOC Removal Efficiency
Maximum COD removal as high as 80 %
TOC removal always ~ 20 percentage points lower
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Economic Assessment
Basic 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 @ 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
Waste Water
HTC Plant Design
Wood Chips
Organic Waste
kg h-1
2141
6706
TOC
g L-1
20.4
10.0
COD
g L-1
54.0
26.4
kW
965
1272
m3 h-1
45.0
59.4
kJ MJchar-1
69.0
92.9
tTS a-1
9797
12947
Natural Gas Demand
Produced Hydrochar
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Economic Assessment
Results
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
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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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