methane removal from anaerobic digestion liquor 450
The anaerobic digestion liquor is commonly inoculated into the inflow of the 451
WWTP and mixed with the influent wastewater, which results in a net increase of the 452
TN loading of up to 30% (Beylier et al. 2011). Therefore, a specific treatment for the 453
anaerobic digestion liquor can improve the biological nitrogen removal efficiency 454
(Beylier et al. 2011). The combination of partial nitritation and Anammox processes 455
was previously proposed to be implemented at full scale to treat the anaerobic 456
digestion liquor (Joss et al. 2009, Lackner et al. 2014, van der Star et al. 2007).
457
However, the theoretically maximum TN removal efficiency is limited to 89% due to 458
the nitrate production by Anammox bacteria (Khin and Annachhatre 2004, Strous et 459
al. 1998). In addition, the Anammox process requires a specific molar 460
nitrite/ammonium ratio of 1.32 (Khin and Annachhatre 2004), which entails an 461
effective control over the partial nitritation process. More importantly, the dissolved 462
methane in the anaerobic digestion liquor would be stripped due to the aeration in the 463
partial nitritation process. The stripping of dissolved methane into the environment 464
not only represents a loss of energy, but also contributes to the carbon footprint of the 465
treatment plant (Daelman et al. 2012). From a global perspective, wastewater 466
treatment was estimated to account for 4 – 5% of the total methane emission (Conrad 467
2009, El-Fadel and Massoud 2001). So far, few efforts have been dedicated to 468
investigating the removal of dissolved methane from the anaerobic digestion liquor.
469
Membrane-based degasification (Bandara et al. 2012, Bandara et al. 2011) has been 470
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found to be effective in recovering dissolved methane. However, in addition to the 471
extra construction investment in such a membrane degasification module, the creation 472
of the vacuum environment will greatly increase the plant energy consumption.
473
Biological oxidation of dissolved methane using aerobic methanotrophs in the down-474
flow hanging sponge (DHS) reactors is able to oxidize methane and release soluble 475
organic compounds, which was proposed to remove dissolved methane from the 476
anaerobic digestion liquor (Hatamoto et al. 2010, Matsuura et al. 2010). However, in 477
addition to the dissolved methane removal, other treatment processes need to be 478
coupled to the aerobic methane oxidation to remove ammonium from the anaerobic 479
digestion liquor. Moreover, a significant amount of dissolved methane would still be 480
stripped during aeration when using aerobic methanotrophs for methane oxidation.
481
In this work, a new approach to simultaneous ammonium and dissolved methane 482
removal from the anaerobic digestion liquor is proposed. To the best of our 483
knowledge, this novel technology through integrating partial nitritation-Anammox-484
DAMO process in a single MBfR is developed for the first time and its feasibility for 485
achieving simultaneous ammonium and methane removal is assessed using 486
mathematical modeling. The separation and counter-diffusion of gaseous and liquid 487
fluxes of the MBfR not only render the controlled redox stratification of the biofilm, 488
but also avoid the stripping of dissolved methane, which represents a significant 489
advantage over the previous treatment processes. Such stratified activity as well as the 490
cooperation between AOB and Anammox bacteria in the biofilm is essentially 491
responsible for the high-level TN removal in membrane aerated biofilm systems, 492
which is consistent with the findings of Terada et al. (2007) and Pellicer-Nacher et al.
493
(2010). The results of this work reveal that the simultaneous removal of TN and 494
dissolved methane is highly dependent on the relative abundance of Anammox and 495
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DAMO bacteria in the biofilm, which was also confirmed in a granule-based system 496
by Winkler et al. (2015). Their competition for intermediate nitrite produced by AOB 497
would substantially determine the relative abundance. Our results (Figures 3 and 4) 498
demonstrate that both a too high influent surface loading (e.g., >0.00075 m d-1) and a 499
too low oxygen surface loading (e.g., <1.64 g m-2 d-1) would result in limited nitrite 500
availability, and consequently DAMO bacteria would be mostly outcompeted by 501
Anammox bacteria. Thus, appropriate control strategies derived from this work would 502
benefit the operation of this novel MBfR system. By adjusting the HRT (i.e., influent 503
surface loading) and oxygen surface loading whilst maintaining a sufficient and 504
suitable biofilm thickness (e.g., Scenario 4 in Table S4), the maximum simultaneous 505
removal efficiencies of TN and dissolved methane can reach up to 96% and 98% (as 506
shown in Figure 4), respectively. With this new technology, the TN removal 507
efficiency of the previously applied partial nitritation-Anammox process (89%) could 508
be improved (e.g., up to 96%) due to the additional contribution from the DAMO 509
microorganisms, together with a high-rate dissolved methane removal (e.g., 98%) 510
simultaneously.
511
We further assessed the concept feasibility by using a lower dissolved methane 512
concentration (e.g., 30 g COD m-3) as it might vary in real application. The results 513
show that a similar high dissolved methane removal efficiency (>90%) could be 514
achieved, which is comparable with that at a high dissolved methane concentration 515
condition (as shown in Figure S5 in the SI), suggesting the validity and applicability 516
of the proposed approach to a wide range of dissolved methane concentrations 517
possibly from different anaerobic digestion liquors. It should be noted that salinity or 518
suspended solids are not specifically considered in this work, which might also play 519
roles in real anaerobic digestion liquor. Further work on these relevant process 520
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parameters would be useful for a more comprehensive understanding of the proposed 521
system.
522
523
5. Conclusions 524
A new approach is proposed for simultaneous ammonium and dissolved methane 525
removal from the anaerobic digestion liquor through integrating partial nitritation-526
Anammox and DAMO processes in a single-stage MBfR. A previously developed 527
model with appropriate extensions was applied to assess the system performance 528
under different operational conditions. The simulation results demonstrate that the 529
maximum simultaneous removal efficiencies of TN and dissolved methane can reach 530
up to 96% and 98% by adjusting the HRT (or influent surface loading) and oxygen 531
surface loading whilst maintaining a sufficient and suitable biofilm thickness (e.g., 532
750 µm). The information of this work provides first insights into this new technology 533
for simultaneous ammonium and dissolved methane removal.
534
535
Acknowledgements 536
This study was supported by the Australian Research Council (ARC) through 537
Project DP130103147. Xueming Chen acknowledges the scholarship support from 538
China Scholarship Council (CSC). Dr. Jianhua Guo acknowledges the supports of 539
ARC Discovery Early Career Researcher Award (DE130101401), Natural Science 540
Foundation of China (51208009), and Natural Science Foundation of Beijing 541
(8132008). Dr. Bing-Jie Ni acknowledges the support of ARC Discovery Early Career 542
Researcher Award (DE130100451).
543
544
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Figure Legends
Figure 1. Concept of the membrane biofilm reactor integrating partial nitritation-Anammox-DAMO process for simultaneous ammonium and dissolved methane removal with the potential microbial interactions and biochemical reactions between AOB, Anammox bacteria, DAMO archaea, and DAMO bacteria in the biofilm.
Figure 2. Model simulation results of the partial nitritation-Anammox-DAMO biofilm system from Scenario 0 in Table S4 (depth zero represents the membrane surface at the base of the biofilm): (A) Microbial population distribution; (B) substrate profiles; and (C) species-specific nitrogen turnover rates. The applied influent surface loading (ܮூே), oxygen surface loading (ܮைమ), and biofilm thickness (ܮ) are 0.00068 m d-1, 1.74 g m-2 d-1, and 750 µm, respectively.
Figure 3. Model simulation results of the partial nitritation-Anammox-DAMO biofilm system from Scenarios 1-3 in Table S4: (A) Effect of influent surface loading (ܮூே); (B) Effect of oxygen surface loading (ܮைమ); and (C) Effect of biofilm thickness (ܮ) on removal efficiencies of TN and dissolved methane and microbial community structure of the biofilm.
Figure 4. Model simulation results of the partial nitritation-Anammox-DAMO biofilm system from Scenario 4 in Table S4: the combined effect of HRT and oxygen surface loading (ܮைమ) on the TN removal efficiency in (A) 3D and (B) 2D and on the dissolved methane removal efficiency in (C) 3D and (D) 2D.
The color scale represents removal efficiency in %. The optimal region for high-rate simultaneous TN and methane removal is highlighted using dot line.
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Figure 1. Concept of the membrane biofilm reactor integrating partial nitritation-Anammox-DAMO process for simultaneous ammonium and dissolved methane removal with the potential microbial interactions and biochemical reactions between AOB, Anammox bacteria, DAMO archaea, and DAMO bacteria in the biofilm.
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Figure 2. Model simulation results of the partial nitritation-Anammox-DAMO biofilm system from Scenario 0 in Table S4 (depth zero represents the membrane surface at the base of the biofilm): (A) Microbial population distribution; (B) substrate profiles; and (C) species-specific nitrogen turnover rates. The applied influent surface loading (ܮூே), oxygen surface loading (ܮைమ), and biofilm thickness (ܮ) are 0.00068 m + concentrations (g N m-3 )
0.0
CH 4 and DO concentrations (g COD m-3 ) DO Conversion rates of AOB and Anammox (g N m-3 d-1 )
0
Conversion rates of NOB, DAMO archaea and DAMO bacteria (g N m-3 d-1 )
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Figure 3. Model simulation results of the partial nitritation-Anammox-DAMO biofilm system from Scenarios 1-3 in Table S4: (A) Effect of influent surface loading (ܮூே); (B) Effect of oxygen surface loading (ܮைమ); and (C) Effect of biofilm thickness (ܮ) on removal efficiencies of TN and dissolved methane and microbial community structure of the biofilm.
0.00045 0.00060 0.00075 0.00090 0.00105 0.0
Influent surface loading (m d-1)
Active biomass fraction
400 600 800 1000 1200 0.0
Biofilm thickness (µm)
Active biomass fraction
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Figure 4. Model simulation results of the partial nitritation-Anammox-DAMO biofilm system from Scenario 4 in Table S4: the combined effect of HRT and oxygen surface loading (ܮைమ) on the TN removal efficiency in (A) 3D and (B) 2D and on the dissolved methane removal efficiency in (C) 3D and (D) 2D. The color scale represents removal efficiency in %. The optimal region for high-rate simultaneous TN and methane removal is highlighted using dot line.
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Highlights
A new approach for simultaneous TN and dissolved methane removal is proposed.
Partial nitritation, Anammox and DAMO is integrated in one single-stage MBfR.
A model is developed to assess the system performance under different conditions.
The influent and oxygen surface loading jointly determine the overall system performance.
The substrate gradients cause stratification of AOB, Anammox and DAMO in biofilm.
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S1