154
Clean Biocide Project: Halophilic plant extracts for prevention
155 Results and discussion
The experiments show a significant reduction in H2S, indicating a reduction of SRB species; the effect becoming more pronounced as concentration increases (Figure 10). Visual degradation of the biofilm was observed during the experiment after addition of extracts and Biofilm formation on carbon steel coupons from a bioreactor was reduced by two-thirds.
Figure 10: Serum bottle H2S concentration in bottles with 5% (a) and 20% (b) (v/v%) extract. Black line is concentration observed in controls without added halophyte extracts Note that the Control (black) are the same, but the Y-scale is changed.
Furthermore, next generation 16S rRNA amplicon sequencing of DNA from Bacteria and Archaea, proved a significant shift away from SRBs (
Control sample Halophyte sp. 1
Halophyte sp. 2
Halophyte sp. 3
Halophyte sp. 4
0 200 400 600 800 1000 1200 1400
0 10 20 30 40
[H2S] µmol/L
Days
H
2S - 5% extract
0 10 20 30 40 50 60 70 80 90 100
0 10 20 30 40
[H2S] µmol/L
Days
H
2S - 20% extract
156 Table 2) in the microbial composition when compared to samples not treated with extracts. Lastly, visual and measurable reduction in corrosion was observed with 3D surface scanning. Long-term solutions to prevent MIC using natural antimicrobial compounds from halophyte plants are discussed and proposed in this study.
157
Table 2: 16S rRNA amplicon sequencing results comparing the most common species in two samples. Highlighted in bold are species identified as causes for MIC. Arrows indicate an increase or decrease in relative abundance in the sample. Note that a relative increase could be caused by a decrease in overall bacteria concentration.
BACTERIA GENERA CONTROL 20%
EXTRACT
Clostridium sensu stricto 13 18% 5%
Methanosarcina 8% 0%
Photobacterium 8% 6%
Terrisporobacter 7% 1%
Fusobacteriaceae 6% 1%
Vibrio 6% 23%
Desulfosporosinus 6% 0%
Clostridium sensu stricto 1 4% 6%
(FAMILY) Lachnospiraceae Spp. 4% 0%
Paraclostridium 3% 4%
(ORDER) Clostridiales Spp 3% 1%
Shewanella 3% 2%
Epulopiscium 2% 2%
Bacillus 1% 1%
Clostridium sensu stricto 7 1% 38%
OTHER 18% 10%
In just a few days a biofilm had formed in both bioreactors. After two weeks when the extracts were added it was clear that adding the extracts continuously (Figure 11-B: right) was the superior method of the two and proved very effective at removing the established biofilm. H2S readings were taken continuously and showed low SRB activity in the bioreactor (Figure 11-B: right) Atempts at measuring the other reactor was made, but readings results were distorted by a thick biofilm layer covering the sensor.
Figure 11: (A) Bioreactor which was continuously treated with the halophyte extracts in growth medium for after 1 week (B) Comparison between bioreactors after experiment concluded and bioreactors were emptied. From left, bioreactor treated with halophyte extracts for 4 hours twice per week, and a bioreactor with halophyte extract added to growth medium. The first exhibit no disernable difference from before extracts were added.
158 References
Cybulska, I. et al. (2014) ‘Phytochemical composition of some common coastal halophytes of the United Arab Emirates’, Emirates Journal of Food and Agriculture, 26(12), pp. 1046–1056. doi: 10.9755/EJFA.V26I12.19104.
DSMZ GmbH (2017) ‘Desulfovibrio (Postgate) Medium’. DSMZ GmbH, p. 1. Available at:
https://www.dsmz.de/microorganisms/medium/pdf/DSMZ_Medium63.pdf.
Skovhus, T. L., Enning, D. and Lee, J. S. (2017) Microbiologically Influenced Corrosion in the Upstream Oil and Gas Industry. CRC Press. Available at: https://www.crcpress.com/Microbiologically-Influenced-Corrosion-in-the-Upstream-Oil-and-Gas-Industry/Skovhus-Enning-Lee/p/book/9781498726566.
Presenting Author
Jakob Lykke Stein, Research Assistant
Aalborg University - Department of Energy, Esbjerg, Denmark
Is the presenting author an IWA Young Water Professional? Y/N (i.e. an IWA member under 35 years of age)
Bio: Jakob Lykke Stein, M.Sc. in Chemical Engineering from Aalborg University Esbjerg in 2019. For the past year I have been working in a biorefining-focused research group. My focus is environmentally friendly biocides from halophytes (salt-tolerant plants) for the oil and gas industry, but our findings extend to other fields where biocorrosion happens. Starting November, I will be continuing my research as part of my Ph.D.
159
Emerging Technologies Session I
Flash presentations
160
Influence of mass transfer characteristics on nitrogen removal in sponge-bed trickling filters
T. Bressani-Ribeiro 1,2, C. A. L. Chernicharo 2, E.I.P. Volcke 1
1 BioCo Research Group, Department of Green Chemistry and Technology, Coupure links 653, 9000 Gent, Ghent University, Belgium
2 Department of Sanitary and Environmental Engineering, Av. Antônio Carlos 6627, 31270-901 Belo Horizonte/MG, Federal University of Minas Gerais, Brazil
* Corresponding author: Eveline.Volcke@ugent.be
Summary: Efficient nitrogen removal following anaerobic sewage treatment is generally accomplished in mechanically aerated systems, which are energy-intensive compared to naturally ventilated process, such as sponge-bed trickling filters (SBTFs). Promising configurations have been presented for total nitrogen removal in SBTFs treating anaerobic effluents. Nevertheless, there is a remaining knowledge gap on the main factors influencing process performance. This contribution mechanistically assesses the effect of key reactor and kinetic parameters controlling nitrogen conversions in SBTFs. The results support that the interplay between the oxygen transfer coefficient, external mass transfer resistance and biofilm thickness influences the optimum oxygen concentration to sustain AOB activity without compromising anammox growth.
Keywords: biofilm thickness; external mass transfer resistance; oxygen transfer coefficient
Introduction
As a proved technology in warm climate regions, anaerobic reactors (i.e. UASB reactors) for sewage treatment contribute towards an energy-positive facility. Nevertheless, total nitrogen removal efficiency at the post-treatment step of anaerobic reactors is typically modest (less than 80%) and currently only achieved by energy-intensive aerated systems (i.e. activated sludge process) (von sperling et al., 2019). Latin American countries generally lack discharge limits for nitrogen, but there has been growing momentum to set at least a 20 mg L-1 effluent target. Based on the typical characteristics of anaerobic effluents (approximately 45 mg N L-1), such a goal would therefore be achieved considering a minimum of 60% total nitrogen removal efficiency.
Sponge-bed trickling filters (SBTFs) constitute a biofilm reactor originally designed to remove residual carbon and ammonium from anaerobic effluents (Tandukar et al., 2005). Total nitrogen removal in those reactors is reported ranging from 20 to 95% (Bressani-Ribeiro et al., 2018) and a knowledge gap still remains on the main operational factors driving process performance. Therefore, a model was developed, calibrated, and validated (Bressani-Ribeiro et al., 2021) based on a demo-scale SBTF following a UASB reactor. The present contribution used such a model to mechanistically assess the interplay of key reactor and kinetic parameters controlling nitrogen conversions at steady-state conditions in SBTFs treating anaerobic effluents.
Materials and methods
A previous developed SBTF one-dimensional model (Bressani-Ribeiro et al., 2021) was applied to simulate different scenarios for long-term operation following anaerobic sewage treatment, as summarized in Table 1.1. The SBTF reactor was described using a sequence of four completely mixed biofilm reactor compartments of the AQUASIM software (Reichert, 1995), in which the biological conversions were implemented.
161
Table 1.1 – Overview of the performed scenario analysis considering key reactor and kinetic parameters kLa (d-1) LL (µm) LF (µm)
Reference scenario
Reference scenario 330 1500 65
Interaction of key parameters influencing total nitrogen removal in SBTFS Scenario analysis 50 – 1000 20 – 1500 65 – 100 kLa: oxygen transfer coefficient; LL: external mass transfer boundary layer thickness; LF: biofilm thickness
Results and discussion
Figure 1.1 shows the total nitrogen removal efficiency in SBTFs considering the interaction between the oxygen transfer coefficient (kLa) and the external mass transfer resistance (LL), for two different biofilm thicknesses (LF = 65 µm (Figure 1.1a) and 100 µm (Figure 1.1b)). As for thin biofilms (LF
= 65 µm), an operational window for total nitrogen removal efficiency higher than 60% is identified, considering kLa ranging from 100 d-1 to 660 d-1, regardless of the imposed LL. Higher kLa (> 660 d-1) imply decreased total nitrogen removal unless a higher LL (1500 µm) is assured. Conversely, kLa lower than 100 d-1 impair total nitrogen removal irrespective of the adopted LL. A maximum removal efficiency of 95% was achieved considering the simulation at a kLa and LL of 330 d-1 and 1500 µm, respectively. This refers to steady-state condition considering the default parameters (i.e., the reference scenario). Overall, for thin biofilms, the higher the LL the better the total nitrogen removal performance.
As for thick biofilms (LF = 100 µm (Figure 1.1b)), a broader operational window takes place for total nitrogen removal efficiency higher than 60%, considering kLa ranging from approximately 200 d-1 up to 1000 d-1. A maximum removal efficiency of approximately 95% was achieved considering simulations at a kLa of 330 d-1 and LL at 500 or 1500 µm. Moreover, efficiencies higher than 87%
were reached under higher kLa (1000 d-1 ), except for the simulation at LL 1500 µm. Overall, the beneficial effects of operation under higher LL observed for thin biofilms are less relevant for thicker biofilms, especially for high kLa (> 600 d-1) conditions.
Figure 1.1 Total nitrogen removal considering the interaction between oxygen transfer coefficient (kLa) and external mass transfer resistance (LL) at a fixed biofilm thickness (LF) of (a) 65 and (b) 100 µm
(a) (b)
LL=20 µm LL=100 µm
LL=500 µm LL=1500 µm
AOB repression
Anammox inhibition
AOB repression
LF = 65 µm LF = 100 µm
162 The higher the LL the lower the oxygen concentration at the biofilm-liquid interface at the top compartment of the SBTF, as shown in Figure 1.2a. The oxygen gradient as a function of LL is even more evident for thin biofilms. This explains why anammox, which is the prevailing nitrogen removal process at steady-state, is inhibited under high kLa (> 660 d-1) and low LL (< 1500 µm) for thin biofilms. In such conditions, the oxygen inhibition term in the annamox growth reaction equation (K_O2/(K_O2+S_O2)) imposes rate limitations from 31% (LL 500 µm) to 63% (LL 20 µm) compared to the operation under high LL (1500 µm). On the other hand, the oxygen concentration at the biofilm-liquid interface is less affected by LL for thick biofilms, which assures a biofilm niche for anammox even under high kLa. Therefore, the effect of a higher LL protecting against oxygen inhibition is counteracted by biofilm thickness, which was simply assumed less relevant for other biofilm reactors such as MBBR (Pérez et al., 2020).
For all the performed simulations, low kLa (< 100 d-1 and < 200 d-1, for thin and thick biofilms, respectively) hampered ammonium conversion. This is due to the lack of oxygen in the bulk liquid (and consequently at biofilm-liquid interface) compared to the operation under high kLa (e.g., 1000 d-1), as shown in Figure 1.2b. As no nitrite accumulation was noticed and nitrate was completely removed, hence nitrification was the limiting process for enhanced total nitrogen removal.
Figure 1.2. Dissolved oxygen concentrations at the top compartment of the SBTF for thin and thick biofilms (a) at the biofilm-liquid interface (LBi) for a kLa of 1000 d-1, and (b) at the bulk liquid for a kLa of 100 and 1000 d-1
Increasing biofilm thickness (LF) also directly impacts the amount of biomass retained in the SBTF, which affects the oxygen consumption at the top compartment of the reactor due to the conversion of biomass decay products. Hence, the proportional oxygen penetration depth for a thicker biofilm (LF = 100 µm) is approximately halved for concentrations higher than 0.06 mg O2 L-1, as shown in Figure 1.3. Reduced oxygen penetration as a function of biofilm size was also suggested by Pérez et al. (2005). This benefits anammox bacteria growth, especially when operation under high kLa (> 660 d-1) is considered. These results support that the interplay between kLa, LL and LF in SBTFs ultimately dictates optimum oxygen levels in the biofilm to sustain AOB activity without compromising anammox bacteria growth.
(a) (b)
(a) (b)
Biofilm surface Biofilm surface
34 µm 81 µm
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Figure 1.3. Biofilm-liquid interface concentrations of dissolved oxygen (DOLBi) through the biofilm depth (z) at the top compartment of the SBTF for (a) thin and (b) thick biofilms considering a kLa of 660 d-1 and LL of 500 µm
References
Bressani-Ribeiro, T., Almeida, P.G.S., Chernicharo, C.A.L., Volcke, E.I.P., 2021. Inorganic carbon limitation during nitrogen conversions in sponge-bed trickling filters for mainstream treatment of anaerobic effluent. Water Res.
201, 117337. https://doi.org/10.1016/j.watres.2021.117337
Bressani-Ribeiro, T., Almeida, P.G.S., Volcke, E.I.P., Chernicharo, C.A.L., 2018. Trickling filters following anaerobic sewage treatment: state of the art and perspectives. Environ. Sci. Water Res. Technol. 4, 1721–1738.
https://doi.org/10.1039/C8EW00330K
Pérez, J., Laureni, M., van Loosdrecht, M.C.M., Persson, F., Gustavsson, D.J.I., 2020. The role of the external mass transfer resistance in nitrite oxidizing bacteria repression in biofilm-based partial nitritation/anammox reactors.
Water Res. 186. https://doi.org/10.1016/j.watres.2020.116348
Pérez, J., Picioreanu, C., Van Loosdrecht, M., 2005. Modeling biofilm and floc diffusion processes based on analytical solution of reaction-diffusion equations. Water Res. 39, 1311–1323. https://doi.org/10.1016/j.watres.2004.12.020 Reichert, P., 1995. Design techniques of a computer program for the identification of processes and the simulation of
water quality in aquatic systems. Environ. Softw. 10, 199–210. https://doi.org/10.1016/0266-9838(95)00010-I Tandukar, M., Uemura, S., Machdar, I., Ohashi, A., Harada, H., 2005. A low-cost municipal sewage treatment system
with a combination of UASB and the “fourth-generation” downflow hanging sponge reactors. Water Sci. Technol.
52, 323–329. https://doi.org/10.2166/wst.2005.0534
von sperling, M., Almeida, P.G.S., Bressani-Ribeiro, T., Chernicharo, C.A. de L., 2019. Post-treatment of anaerobic effluents, in: Anaerobic Reactors for Sewage Treatment: Design, Construction and Operation. IWA Publishing, pp.
275–338. https://doi.org/10.2166/9781780409238_0275
Acknowledgements
The authors acknowledge the support obtained from the Ghent University Special Research Fund (BOF UGent – funding for joint doctorate: BOF DCV 2017.0012.01) and from the following Brazilian institutions: Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq;
Fundação de Amparo à Pesquisa de Minas Gerais – FAPEMIG; Instituto Nacional de Ciência e Tecnologia em Estações Sustentáveis de Tratamento de Esgoto – INCT ETEs Sustentáveis.
Presenting Author
Mr. Thiago Bressani Ribeiro PhD student
BioCo Research Group, Department of Green Chemistry and Technology, Ghent University, Belgium
Department of Sanitary and Environmental Engineering, Federal University of Minas Gerais, Brazil
Is the presenting author an IWA Young Water Professional? Y (i.e. an IWA member under 35 years of age)
Bio:Thiago Bressani Ribeiro is an environmental engineer with a M.Sc. in environment, sanitation, and water resources from the Federal University of Minas Gerais (UFMG - Brazil). He is currently a joint PhD researcher between Ghent University and the UFMG, focusing on post-treatment of anaerobic effluents.
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