Continuous Co-Digestion of Agro-Industrial Mixtures in Laboratory Scale Expanded Granular Sludge Bed Reactors
"> Figure 1
<p>Schematic diagram of the reactor. The parts are (1) feed tank, (2) three-way sampling valve, (3) eccentric screw pumps, (4) mixer for influent and recirculation, (5) bioreactor, (6) recirculation, (7) bell separator, (8) biogas outlet, (9) foam trap, (10) gas flow-meter, (11) three-phase separator or settling zone, (12) transition zone, (13) digestion zone, (14) effluent, (15) siphon, and (16) digestate storage.</p> "> Figure 2
<p>Summary of the main response variables for reactor 1. •: averaga values;<span class="html-fig-inline" id="applsci-12-02295-i003"> <img alt="Applsci 12 02295 i003" src="/applsci/applsci-12-02295/article_deploy/html/images/applsci-12-02295-i003.png"/></span>: outliers.</p> "> Figure 3
<p>Volatile organic acids to total inorganic carbon ratio (VOA/TIC), organic loading rate (OLR), and hydraulic retention time (HRT) in reactor 1.</p> "> Figure 4
<p>Volatile fatty acids and chemical oxygen demand (COD) in the feed of reactor 1.</p> "> Figure 5
<p>PCA overview of the averaged data. (<b>a</b>) Score plot, (<b>b</b>) bi-plot, and (<b>c</b>) correlation loading.</p> "> Figure 6
<p>Stover–Kincannon model fitting for the datasets of R1, R2, and R3.</p> "> Figure 7
<p>Comparison of the Stover–Kincannon model against measured data for EGSB reactors (R2 and R3). Blue and green lines corresponded to the model and confidence limits of the model at 95%, respectively.</p> "> Figure 8
<p>Graphical optimizations of the optimum MPR and MY of R2 and R3 using the OLR.</p> ">
Abstract
:1. Introduction
2. Materials and Methods
2.1. Mixtures and Inoculum Characterization
2.2. Bioreactor Setup and Operation
2.3. Data Cleaning and Analysis
- The HRT is ≤30 day.
- The MY < biomethane potential of the mixture at HRT∞ (BMP∞), which was taken from Regalado et al. [24].
- The chemical oxygen demand removal is ≥0.
2.3.1. Overview of Each Reactor’s Operation
2.3.2. Principal Component Analysis
2.4. SRT/HRT
2.5. Characterization of Synergistic Effects
2.6. Characterization of Hydraulic Behaviors
2.7. Modeling of Reactors
Stover–Kincannon Model
2.8. Reactor’s Optimization
3. Results
3.1. Reactors’ Operation Overview
3.2. PCA
3.3. SRT/HRT
3.4. Characterization of Synergistic Effects
3.5. Hydraulic Analysis
3.6. Modeling of Reactors
3.7. Optimization of a Reactor
4. Discussion
- The synergistic effects described by the batch model in [24] were also found in the continuous operation.
- The maximum methane yields in the continuous operation of any mixture of these four substrates were predicted using the batch model and multiplying the BMP∞ by a coefficient between 0.7 and 0.8.
- The employment of the Stover–Kincannon model showed that all three mixtures had a different kinetical behavior, which could even be noticed among the two triple mixtures.
5. Conclusions
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
Abbreviations
AD | Anaerobic digestion |
HRT | Hydraulic retention time |
AcoD | Anaerobic co-digestion |
SRT | Solids retention times |
UASB | Up-flow anaerobic sludge blanket |
CSTR | Continuous stirred tank reactor |
EGSB | Expanded granular sludge bed |
PM | Piglet manure |
CWM | Cow manure |
SBT | Sugar beet |
SWW | Starch wastewater |
COD | Chemical oxygen demand |
d | day |
OLR | Organic loading rate |
MPR | Methane productivity |
MY | Methane yield |
ŋCOD | Removal efficiencies of chemical oxygen demand |
ŋBOD5 | Biological oxygen demand on the fifth day |
PCA | Principal component analysis |
Peaxial | Axial Peclet number |
Re | Reynolds number |
RMSE | Root-mean-square error |
RTD | Residence time distribution |
CFD | Computer flow dynamics |
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Reactor | Substrates | Dry Matter (wt.%) | Organic Dry Matter (wt.%) | Carbon-to-Nitrogen Ratio (%) |
---|---|---|---|---|
1 | Pellets 1 | 7.79 ± 0.16 | 87.59 ± 0.06 | |
PM+CWM | 2.92 ± 1.40 | 60.08 ± 9.32 | 13.70 | |
2 | Pellets 2 | 8.84 ± 1.75 | 89.47 ± 1.45 | |
PM+CWM+SWW | 1.76 ± 0.94 | 58.33 ± 9.07 | 16.32 | |
3 | Pellets 3 | 7.93 ± 0.29 | 87.56 ± 0.10 | |
PM+CWM+SBT | 3.14 ± 0.99 | 64.55 ± 8.52 | 18.87 |
Variable | Input | Inside the Reactor | Output |
---|---|---|---|
Temperature (°C) | x | ||
Dry matter (%) | x | x | x |
Organic dry matter (%) | x | x | x |
C/N (%) | x | ||
Chemical oxygen demand (mgO2/L) | x | x | |
Biochemical oxygen demand at 5th day (mgO2/L) | x | x | |
Loading rate per unit volume (kgCOD/m3·d) | x | ||
Hydraulic residence time (d) | x | ||
pH value (-) | x | ||
Gas composition in volume fractions (%, ppm) | x | ||
Ratio of volatile organic acids to total inorganic carbon (-) | x |
Operating Points | Mean Values COD Removal Efficiency (%) | Mean Values of Methane Yield (LCH4/kgVS) | Mean Values of Methane Productivity (LCH4/Lreact/d) | Mean Values BOD5 Removal Efficiency (%) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
R1 | R2 | R3 | R1 | R2 | R3 | R1 | R2 | R3 | R1 | R2 | R3 | |
Operating Point 1 (15 d) | 52.7 | 49 | 59.5 | 265.7 | 295.6 | 217.6 | 0.23 | 0.15 | 0.29 | 88.13 | 84.98 | 76.84 |
Operating Point 2 (10 d) | 53.6 | 58.6 | 76.2 | 180.2 | 261.6 | 382.5 | 0.41 | 0.21 | 0.83 | 68.77 | 83.64 | 85.34 |
Operating Point 3 (7 d) | 45.3 | 82.5 | 63.7 | 189.2 | 395.8 | 317 | 0.64 | 0.46 | 0.96 | 90.16 | 95.22 | 97.69 |
Operating Point 4 (5 d) | 34.2 | 73.9 | 53.8 | 61.1 | 158 | 158.8 | 0.19 | 0.42 | 0.6 | 73.03 | 90.93 | 81.23 |
Operating Point 5 (3 d) | 53.2 | 77.3 | 55.7 | 78.1 | 200.3 | 193.9 | 0.34 | 0.91 | 0.79 | 78.21 | 91.09 | 77.47 |
Operating Point 6 (1 d) | 42.6 | 64.1 | 43.7 | 41.4 | 77.6 | 89.4 | 0.64 | 1.2 | 1.21 | 84.56 | 92.77 | 84.56 |
Operating Points | Solid Retention Time to Hydraulic Retention Time Ratio | ||
---|---|---|---|
R1 | R2 | R3 | |
Start-up (15 d) | 1.10 | 1.29 | 1.24 |
Operating Point 1 (15 d) | 1.72 | 1.41 | 1.59 |
Operating Point 1 (15 d) | 0.82 | 0.83 | 1.16 |
Operating Point 4 (5 d) | 1.22 | 1.33 | 1.15 |
Reactor recovery (5 d) | 1.30 | 1.68 | 1.18 |
Operating Point 4 (5 d) | 1.20 | 1.42 | 0.99 |
Operating Point 5 (3 d) | 1.22 | 1.28 | 1.11 |
Average value | 1.23 | 1.32 | 1.20 |
Mixture | Maximum Methane Yield in Continuous Tests (LCH4/kgVS) | Methane Yield Ratios in Continuous Tests | Methane Yield Predicted by the Model in Batch Tests (LCH4/kgVS) | Methane Yield Ratios in Batch Tests | Continuous to Batch Methane Yield Ratio |
---|---|---|---|---|---|
PM+CWM | 265.70 | 1.00 | 342.83 | 1.00 | 0.78 |
PM+CWM+SWW | 395.80 | 1.49 | 513.07 | 1.50 | 0.77 |
PM+CWM+SBT | 382.50 | 1.44 | 530.76 | 1.55 | 0.72 |
Parameter | Influent | Reactor Tube | Separation Zone |
---|---|---|---|
Re | 295.42 | 295.42 | 295.42 |
Peaxial | 1.10 | 9.33 | 38.87 |
Data Set | RMSE (LCH4/Lreact/d)(-) | Mmax (LCH4/Lreact/d) | MB (gCOD/L/d) |
---|---|---|---|
(R1, R2, R3) | 0.214 | 1.29 | 6.08 |
(R1, R2) | 0.188 | 1.25 | 8.21 |
(R1, R3) | 0.245 | 1.07 | 4.20 |
(R2, R3) | 0.118 | 1.48 | 5.07 |
(R1) | 0.132 | 0.68 | 3.59 |
(R2) | 0.031 | 1.76 | 9.99 |
(R3) | 0.132 | 1.52 | 5.12 |
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Hernández Regalado, R.E.; Häner, J.; Baumkötter, D.; Wettwer, L.; Brügging, E.; Tränckner, J. Continuous Co-Digestion of Agro-Industrial Mixtures in Laboratory Scale Expanded Granular Sludge Bed Reactors. Appl. Sci. 2022, 12, 2295. https://doi.org/10.3390/app12052295
Hernández Regalado RE, Häner J, Baumkötter D, Wettwer L, Brügging E, Tränckner J. Continuous Co-Digestion of Agro-Industrial Mixtures in Laboratory Scale Expanded Granular Sludge Bed Reactors. Applied Sciences. 2022; 12(5):2295. https://doi.org/10.3390/app12052295
Chicago/Turabian StyleHernández Regalado, Roberto Eloy, Jurek Häner, Daniel Baumkötter, Lukas Wettwer, Elmar Brügging, and Jens Tränckner. 2022. "Continuous Co-Digestion of Agro-Industrial Mixtures in Laboratory Scale Expanded Granular Sludge Bed Reactors" Applied Sciences 12, no. 5: 2295. https://doi.org/10.3390/app12052295