Publications by authors named "Piet N L Lens"

204 Publications

Biofilm carrier type affects biogenic sulfur-driven denitrification performance and microbial community dynamics in moving-bed biofilm reactors.

Chemosphere 2021 Aug 20;287(Pt 1):131975. Epub 2021 Aug 20.

Department of Civil, Architectural and Environmental Engineering, University of Naples Federico II, via Claudio 21, 80125, Naples, Italy.

Autotrophic denitrification with biosulfur (ADBIOS) provides a sustainable technological solution for biological nitrogen removal from wastewater driven by biogenic S, derived from biogas desulfurization. In this study, the effect of different biofilm carriers (conventional AnoxK™ 1 and Z-200 with a pre-defined maximum biofilm thickness) on ADBIOS performance and microbiomics was investigated in duplicate moving bed-biofilm reactors (MBBRs). The MBBRs were operated parallelly in continuous mode for 309 days, whilst gradually decreasing the hydraulic retention time (HRT) from 72 to 21 h, and biosulfur was either pumped in suspension (days 92-223) or supplied in powder form. Highest nitrate removal rates were approximately 225 (±11) mg/L·d and 180 (±7) mg NO-N/L·d in the MBBRs operated with K1 and Z-200 carriers, respectively. Despite having the same protected surface area for biofilm development in each MBBR, the biomass attached onto the K1 carrier was 4.8-fold more than that on the Z-200 carrier, with part of the biogenic S kept in the biofilm. The microbial communities of K1 and Z-200 biofilms could also be considered similar at cDNA level in terms of abundance (R = 0.953 with p = 0.042). A relatively stable microbial community was formed on K1 carriers, while the active portion of the microbial community varied significantly over time in the MBBRs using Z-200 carriers.
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http://dx.doi.org/10.1016/j.chemosphere.2021.131975DOI Listing
August 2021

Simultaneous removal of lead and selenium through biomineralization as lead selenide by anaerobic granular sludge.

J Hazard Mater 2021 Jul 16;420:126663. Epub 2021 Jul 16.

National University of Ireland Galway, University Road, H91 TK33 Galway, Ireland.

This study demonstrated the simultaneous removal of lead (Pb) and selenium (Se) as lead selenide biomineralization using anaerobic granular sludge. The microbial community of the granular sludge was first enriched for 140 days in the presence of Pb(II) only, selenate and selenite only, Pb(II)+selenate, and Pb(II)+selenite. In the absence of Se, removal of Pb(II) mainly occurred via biosorption and deposited on the biomass as lead oxide and lead carbonate. The Pb removal efficiency (94% of initial 50 mg L) was reduced to 90% and 86% in the presence of selenate and selenite, respectively, due to biosorption. Addition of Pb(II) didn't exert any toxic effect on the Se-reducing microbial community, on the contrary: Pb(II) addition improved the Se removal efficiency for selenate from 85% to 90%, but did not affect selenite removal after 14 d of incubation. The bioreduction of the Se-oxyanions produced elemental Se (Se(0)) and selenide, which later interacted with Pb(II) to produce lead selenide (PbSe). Adsorption of Pb(II) onto the Se(0) nanoparticles and precipitation as the Se(0)-Pb complex might also have contributed to the simultaneous removal of Pb and Se. XPS and XRD analysis further confirmed the immobilization of Pb as PbSe, PbO and PbCO in the biomass.
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http://dx.doi.org/10.1016/j.jhazmat.2021.126663DOI Listing
July 2021

Valorization of selenium-enriched sludge and duckweed generated from wastewater as micronutrient biofertilizer.

Chemosphere 2021 Oct 3;281:130767. Epub 2021 May 3.

Laboratory of Analytical Chemistry and Applied Ecochemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium.

Selenium (Se) is an essential trace element for humans and animals with a narrow window between deficiency and toxicity levels. Application of conventional chemical Se fertilizers to increase the Se content of crops in Se deficient areas could result in environmental contamination due to the fast leaching of inorganic Se. Slow-release Se-enriched biofertilizers produced from wastewater treatment may therefore be beneficial. In this study, the potential of Se-enriched biomaterials (sludge and duckweed) as slow-release Se biofertilizers was evaluated through pot experiments with and without planted green beans (Phaseolus vulgaris). The Se concentration in the bean tissues was 1.1-3.1 times higher when soils were amended with Se-enriched sludge as compared to Se-enriched duckweed. The results proved that the Se released from Se-enriched biomaterials was efficiently transformed to health-beneficial selenoamino acids (e.g., Se-methionine, 76-89%) after being taken up by beans. The Se-enriched sludge, containing mainly elemental Se, is considered as the preferred slow-release Se biofertilizer and an effective Se source to produce Se-enriched crops for Se-deficient populations, as shown by the higher Se bioavailability and lower organic carbon content. This study could offer a theoretical reference to choose an environmental-friendly and sustainable alternative to conventional mineral Se fertilizers for biofortification, avoiding the problem of Se losses by leaching from chemical Se fertilizers while recovering resources from wastewater. This could contribute to the driver for a future circular economy.
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http://dx.doi.org/10.1016/j.chemosphere.2021.130767DOI Listing
October 2021

Production of selenium-enriched microalgae as potential feed supplement in high-rate algae ponds treating domestic wastewater.

Bioresour Technol 2021 Aug 28;333:125239. Epub 2021 Apr 28.

GEMMA-Group of Environmental Engineering and Microbiology, Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya·BarcelonaTech, Jordi Girona 1-3, Building D1, 08034 Barcelona, Spain.

This study assessed the selenium (Se) removal efficiency of two pilot-scale high-rate algae ponds (HRAPs) treating domestic wastewater and investigated the production of Se-enriched microalgae as potential feed supplement. The HRAP-Se had an average Se, NH-N, total phosphorus and COD removal efficiency of, respectively, 43%, 93%, 77%, and 70%. Inorganic Se taken up by the microalgae was mainly (91%) transformed to selenoamino acids, and 49-63% of Se in the Se-enriched microalgae was bioaccessible for animals. The crude protein content (48%) of the microalgae was higher than that of soybeans, whereas the essential amino acid content was comparable. Selenium may induce the production of the polyunsaturated fatty acids omega-3 and omega-6 in microalgae. Overall, the production of Se-enriched microalgae in HRAPs may offer a promising alternative for upgrading low-value resources into high-value feed supplements, supporting the drive to a circular economy.
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http://dx.doi.org/10.1016/j.biortech.2021.125239DOI Listing
August 2021

Kinetic modeling of hydrogen and L-lactic acid production by Thermotoga neapolitana via capnophilic lactic fermentation of starch.

Bioresour Technol 2021 Jul 6;332:125127. Epub 2021 Apr 6.

Institute of Biomolecular Chemistry, National Research Council, Via Campi Flegrei 34, 80078 Pozzuoli, Napoli, Italy; Department of Biology, University of Napoli "Federico II", Via Cupa Nuova Cinthia 21, 80126 Napoli, Italy. Electronic address:

This study investigated the feasibility of hydrogen (H) and L-lactic acid production from starch under capnophilic lactic fermentation (CLF) conditions by using Thermotoga neapolitana. Batch experiments were performed in 120 mL serum bottles and a 3 L pH-controlled continuous stirred-tank reactors (CSTR) system with potato and wheat starch as the substrates. A H yield of 3.34 (±0.17) and 2.79 (±0.17) mol H/mol of glucose eq. was achieved with, respectively, potato and wheat starch. In the presence of CO, L-lactic acid production by the acetyl-CoA carboxylation was significantly higher for the potato starch (0.88 ± 0.39 mol lactic acid/mol glucose eq.) than wheat starch (0.33 ± 0.11 mol lactic acid/mol glucose eq.). A kinetic model was applied to simulate and predict the T. neapolitana metabolic profile and bioreactor performance under CLF conditions. The CLF-based starch fermentation suggests a new direction to biotransform agri-food waste into biofuels and valuable biochemicals.
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http://dx.doi.org/10.1016/j.biortech.2021.125127DOI Listing
July 2021

Bioethanol Production From H/CO by Solventogenesis Using Anaerobic Granular Sludge: Effect of Process Parameters.

Front Microbiol 2021 10;12:647370. Epub 2021 Mar 10.

National University of Ireland Galway, Galway, Ireland.

CO fermentation by biocatalysis is a promising route for the sustainable production of valuable chemicals and fuels, such as acetic acid and ethanol. Considering the important role of environmental parameters on fermentation processes, granular sludge from an industrial anaerobic wastewater treatment system was tested as inoculum for ethanol production from H/CO at psychrophilic (18°C), submesophilic (25°C), and mesophilic (30°C) temperatures. The highest acetic acid and ethanol production was obtained at 25°C with a final concentration of 29.7 and 8.8 mM, respectively. The presence of bicarbonate enhanced acetic acid production 3.0 ∼ 4.1-fold, while inhibiting ethanol production. The addition of 0.3 g/L glucose induced butyric acid production (3.7 mM), while 5.7 mM ethanol was produced at the end of the incubation at pH 4 with glucose. The addition of 10 μM W enhanced ethanol production up to 3.8 and 7.0-fold compared to, respectively, 2 μM W addition and the control. The addition of 2 μM Mo enhanced ethanol production up to 8.1- and 5.4-fold compared to, respectively, 10 μM Mo and the control. This study showed that ethanol production from H/CO conversion using granular sludge as the inoculum can be optimized by selecting the operational temperature and by trace metal addition.
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http://dx.doi.org/10.3389/fmicb.2021.647370DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8006448PMC
March 2021

Methanogenic granule growth and development is a continual process characterized by distinct morphological features.

J Environ Manage 2021 May 3;286:112229. Epub 2021 Mar 3.

Microbial Communities Laboratory, School of Natural Sciences, National University of Ireland Galway, University Road, Galway, H91 TK33, Ireland; Infrastructure and Environment, School of Engineering, The University of Glasgow, Oakfield Avenue, Glasgow G12 8LT, United Kingdom; Ryan Institute, National University of Ireland Galway, University Road, Galway, H91 TK33, Ireland. Electronic address:

Up-flow anaerobic bioreactors are widely applied for high-rate digestion of industrial wastewaters and rely on formation, and retention, of methanogenic granules, comprising of dense, fast-settling, microbial aggregates (approx. 0.5-4.0 mm in diameter). Granule formation (granulation) mechanisms have been reasonably well hypothesized and documented. However, this study used laboratory-scale bioreactors, inoculated with size-separated granular sludge to follow new granule formation, maturation, disintegration and re-formation. Temporal size profiles, volatile solids content, settling velocity, and ultrastructure of granules were determined from each of four bioreactors inoculated only with small granules, four with only large granules, and four with a full complement of naturally-size-distributed granules. Constrained granule size profiles shifted toward the natural distribution, which was associated with maximal bioreactor performance. Distinct morphological features characterized different granule sizes and biofilm development stages, including 'young', 'juvenile', 'mature' and 'old'. The findings offer opportunities toward optimizing management of high-rate, anaerobic digesters by shedding light on the rates of granule growth, the role of flocculent sludge in granulation and how shifting size distributions should be considered when setting upflow velocities.
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http://dx.doi.org/10.1016/j.jenvman.2021.112229DOI Listing
May 2021

Dynamic modeling of anaerobic methane oxidation coupled to sulfate reduction: role of elemental sulfur as intermediate.

Bioprocess Biosyst Eng 2021 Apr 10;44(4):855-874. Epub 2021 Feb 10.

Department of Environmental Engineering and Water Technology, UNESCO-ΙΗΕ, Westvest 7, 2611-AX, Delft, The Netherlands.

The process dynamics of anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR), and the potential role of elemental sulfur as intermediate are presented in this paper. Thermodynamic screening and experimental evidence from the literature conclude that a prominent model to describe AOM-SR is based on the concept that anaerobic methane oxidation proceeds through the production of the intermediate elemental sulfur. Two microbial groups are involved in the process: (a) anaerobic methanotrophs (ANME-2) and (b) Desulfosarcina/Desulfococcus sulfur reducers cluster (DSS). In this work, a dynamic model was developed to explore the interactions between biotic and abiotic processes to simulate the microbial activity, the chemical composition and speciation of the liquid phase, and the gas phase composition in the reactor headspace. The model includes the microbial kinetics for the symbiotic growth of ANME-2 and DSS, mass transfer phenomena between the gas and liquid phase for methane, hydrogen sulfide, and carbon dioxide and acid-base reactions for bicarbonate, sulfide, and ammonium. A data set from batch experiments, running for 250 days in artificial seawater inoculated with sediment from Marine Lake Grevelingen (The Netherlands) was used to calibrate the model. The inherent characteristics of AOM-SR make the identification of the kinetic parameters difficult due to the high correlation between them. However, by meaningfully selecting a set of kinetic parameters, the model simulates successfully the experimental data for sulfate reduction and sulfide production. The model can be considered as the basic structure for simulating continuous flow three-phase engineered systems based on AOM-SR.
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http://dx.doi.org/10.1007/s00449-020-02495-2DOI Listing
April 2021

Effect of voltage intensity on the nutrient removal performance and microbial community in the iron electrolysis-integrated aerobic granular sludge system.

Environ Pollut 2021 Apr 27;274:116604. Epub 2021 Jan 27.

UNESCO-IHE, Institute for Water Education, Westvest 7, 2601, DA Delft, the Netherlands.

The effects of voltage intensity on the nutrient removal performance and microbial community in the iron electrolysis-integrated aerobic granular sludge (AGS) system were investigated over a period of 15 weeks. Results revealed that the application outcomes of iron electrolysis for AGS systems relied on voltage intensity. When a constant voltage of 1.5 V was applied, the sludge granulation was most obviously accelerated with a specific growth rate of the sludge diameter of 0.078 day, and the removal efficiencies of total nitrogen (TN) and total phosphorus (TP) increased by 14.1% and 20.2%, respectively, compared to the control reactor (without the iron electrolysis-integration). Moreover, the AGS developed at different voltages included different microbial communities, whose shifts were driven by the Fe content and the average diameter of AGS. Both heterotrophic nitrifiers and mixotrophic denitrifiers were significantly enriched in the AGS developed at 1.5 V, which effectively enhanced TN removal. Together with the response of the functional genes involved in Fe, N, and P metabolism, the electrolytic iron-driven nutrient degradation pathway was further elaborated. Overall, this study clarified the optimum voltage condition when iron electrolysis was integrated into the AGS system, and revealed the enhancement mechanism of this coupling technology on nutrient removal during the treatment of low-strength municipal wastewater.
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http://dx.doi.org/10.1016/j.envpol.2021.116604DOI Listing
April 2021

Performance of AnMBR in Treatment of Post-consumer Food Waste: Effect of Hydraulic Retention Time and Organic Loading Rate on Biogas Production and Membrane Fouling.

Front Bioeng Biotechnol 2020 18;8:594936. Epub 2021 Jan 18.

Department of Civil and Environmental Engineering, University of South Florida, Tampa, FL, United States.

Anaerobic digestion of food waste (FW) is typically limited to large reactors due to high hydraulic retention times (HRTs). Technologies such as anaerobic membrane reactors (AnMBRs) can perform anaerobic digestion at lower HRTs while maintaining high chemical oxygen demand (COD) removal efficiencies. This study evaluated the effect of HRT and organic loading rate (OLR) on the stability and performance of a side-stream AnMBR in treating diluted fresh food waste (FW). The reactor was fed with synthetic FW at an influent concentration of 8.24 (± 0.12) g COD/L. The OLR was increased by reducing the HRT from 20 to 1 d. The AnMBR obtained an overall removal efficiency of >97 and >98% of the influent COD and total suspended solids (TSS), respectively, throughout the course of operation. The biological process was able to convert 76% of the influent COD into biogas with 70% methane content, while the cake layer formed on the membrane gave an additional COD removal of 7%. Total ammoniacal nitrogen (TAN) and total nitrogen (TN) concentrations were found to be higher in the bioreactor than in the influent, and average overall removal efficiencies of 17.3 (± 5) and 61.5 (± 3)% of TAN and TN, respectively, were observed with respect to the bioreactor concentrations after 2 weeks. Total phosphorus (TP) had an average removal efficiency of 40.39 (± 5)% with respect to the influent. Membrane fouling was observed when the HRT was decreased from 7 to 5 d and was alleviated through backwashing. This study suggests that the side-stream AnMBR can be used to successfully reduce the typical HRT of wet anaerobic food waste (solids content 7%) digesters from 20 days to 1 day, while maintaining a high COD removal efficiency and biogas production.
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http://dx.doi.org/10.3389/fbioe.2020.594936DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7848113PMC
January 2021

Propionate Production by Bioelectrochemically-Assisted Lactate Fermentation and Simultaneous CO Recycling.

Front Microbiol 2020 15;11:599438. Epub 2020 Dec 15.

Microbiology, School of Natural Sciences and Ryan Institute, National University of Ireland Galway, Galway, Ireland.

Production of volatile fatty acids (VFAs), fundamental building blocks for the chemical industry, depends on fossil fuels but organic waste is an emerging alternative substrate. Lactate produced from sugar-containing waste streams can be further processed to VFAs. In this study, electrofermentation (EF) in a two-chamber cell is proposed to enhance propionate production lactate fermentation. At an initial pH of 5, an applied potential of -1 V vs. Ag/AgCl favored propionate production over butyrate from 20 mM lactate (with respect to non-electrochemical control incubations), due to the pH buffering effect of the cathode electrode, with production rates up to 5.9 mM d (0.44 g L d). Microbial community analysis confirmed the enrichment of propionate-producing microorganisms, such as sp. and sp. Organisms commonly found in microbial electrosynthesis reactors, such as sp. and sp., were also abundant at the cathode, indicating their involvement in recycling CO produced by lactate fermentation into acetate, as confirmed by stoichiometric calculations. Propionate was the main product of lactate fermentation at substrate concentrations up to 150 mM, with a highest production rate of 12.9 mM d (0.96 g L d) and a yield of 0.48 mol mol lactate consumed. Furthermore, as high as 81% of the lactate consumed (in terms of carbon) was recovered as soluble product, highlighting the potential for EF application with high-carbon waste streams, such as cheese whey or other food wastes. In summary, EF can be applied to control lactate fermentation toward propionate production and to recycle the resulting CO into acetate, increasing the VFA yield and avoiding carbon emissions and addition of chemicals for pH control.
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http://dx.doi.org/10.3389/fmicb.2020.599438DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7769879PMC
December 2020

Biohythane production from food waste in a two-stage process: assessing the energy recovery potential.

Environ Technol 2021 Jan 6:1-7. Epub 2021 Jan 6.

Department of Civil, Architectural and Environmental Engineering, University of Naples Federico II, Naples, Italy.

Biohythane (hydrogen + methane) production in a two stage dark fermentation (DF) and anaerobic digestion (AD) process from food waste (FW) has been studied. This paper investigated the effect of operation temperature, i.e. mesophilic (34 °C) and thermophilic (55 °C) , on biohythane yield and total energy recovery carried out at the initial culture pH 5.5 and pH 7, respectively for DF and AD batch tests. The mesophilic DF tests gave a higher hydrogen yield of 53.5 (4) mL H/g VS added compared to thermophilic DF tests, i.e. 37.6 (1) mL H/g VS added. However, higher methane yields, i.e. 307.5 ( 10) mL CH/g VS, were obtained at thermophilic AD tests compared to mesophilic AD, i.e. 276.5 (4.3) mL CH/g VS. The total energy recovery from thermophilic DF + AD was higher (11.4 MJ/kg VS) than the mesophilic (10.4 MJ/kg VS) combined process. Interestingly, the analysis of kinetic parameters of mesophilic tests, determined from the Modified Gompertz equation, showed that mesophilic DF had faster H production kinetics, which can be attributed to a faster adaptation of the heat-shocked inoculum used in the tests to the incubation temperature. However, thermophilic AD tests exhibited faster kinetics for methane production.
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http://dx.doi.org/10.1080/09593330.2020.1869319DOI Listing
January 2021

Photocatalytic degradation of Congo Red by zinc sulfide quantum dots produced by anaerobic granular sludge.

Environ Technol 2020 Dec 16:1-10. Epub 2020 Dec 16.

National University of Ireland Galway, University Road, Galway, Ireland.

Sulfate reducing bacteria present in anaerobic granular sludge mediate the metabolic conversion of sulfate to sulfide. In the presence of heavy metals, sulfides precipitate as metal sulfides. In this study, dissimilatory sulfate reduction was coupled to the precipitation of zinc as ZnS quantum dots (QDs) at ambient conditions. The biogenic ZnS QDs had average sizes of 5-7 nm and were formed within 2-4 days of incubation. X-ray diffraction analysis indicated that the biosynthesised ZnS QDs possessed a crystalline cubic lattice structure. The organics present during ZnS biosynthesis were characterized using 3D-fluorescence excitation-emission measurements (FEEM) and the presence of an organic coating on the biogenic ZnS QDs was affirmed using FTIR analysis. The UV-visible absorption spectra of the samples exhibited a prominent absorption peak below 325 nm, which is the characteristic of the surface plasmon resonance of ZnS QDs. The band gap energy of the biogenic ZnS QDs was estimated to be 3.84 eV, comparable to the values reported for chemically synthesised ZnS QDs. The direct band gap energy indicates a large redox potential and carrier mobility, which capacitate the application of these QDs as effective photocatalysts for the photo-assisted decolourization of dyes, as illustrated for the dye congo red.
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http://dx.doi.org/10.1080/09593330.2020.1856940DOI Listing
December 2020

Cadmium Selenide Formation Influences the Production and Characteristics of Extracellular Polymeric Substances of Anaerobic Granular Sludge.

Appl Biochem Biotechnol 2021 Apr 20;193(4):965-980. Epub 2020 Nov 20.

UNESCO-IHE Delft Institute for Water Education, 2611 AX, Delft, The Netherlands.

Feeding cadmium (II) and selenium (IV) simultaneously to anaerobic granular sludge with the aim of synthesizing cadmium selenide (CdSe) nanoparticles induces compositional changes in the extracellular polymeric substances (EPS) matrix of this sludge. A methanogenic anaerobic granular sludge was repeatedly exposed to Cd(II) (10-50 mg L) and selenite (79 mg L) for 300 days at pH 7.3 and 30 °C in a fed-batch feeding regime for enrichment of Se-reducing bacteria and synthesis of CdSe nanoparticles. EPS fingerprints of the granular sludge, obtained by size exclusion chromatography coupled to a fluorescence detector, showed a significant increase in the intensity of protein-like substances with > 100 kDa apparent molecular weight (aMW) upon repeated exposure to Cd(II) and Se(VI). This was accompanied by a prominent decrease in protein-like substances of aMW < 10 kDa. The fingerprint of the humic-like substances showed emergence of a new peak with aMW of 13 to 300 kDa in the EPS extracted from the Cd/Se fed granular sludge. Experiments on metal(loid)-EPS interactions showed that the CdSe nanoparticles interact mainly with loosely bound EPS (LB-EPS). This study showed that the formation of Se(0) and CdSe nanoparticles occurs in the LB-EPS fraction of the granular sludge and repeated exposure to Cd and Se induces compositional changes in the EPS matrix.
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http://dx.doi.org/10.1007/s12010-020-03464-xDOI Listing
April 2021

Long Chain Fatty Acid Degradation Coupled to Biological Sulfidogenesis: A Prospect for Enhanced Metal Recovery.

Front Bioeng Biotechnol 2020 23;8:550253. Epub 2020 Oct 23.

Department of Microbiology, School of Natural Sciences and Ryan Institute, National University of Ireland Galway, Galway, Ireland.

This research assessed the microbiological suitability of oleate degradation coupled to sulfidogenesis by enriching communities from anaerobic sludge treating dairy products with S, , , and S as electron acceptors. The limiting factor hampering highly efficient oleate degradation was investigated in batch reactors. The best sulfidogenic performance coupled to specialization of the enriched bacterial community was obtained for S- and S -reducing enrichments, with 15.6 (± 0.2) and 9.0 (± 0.0) mM of sulfide production, respectively. Microbial community analyses revealed predominance of (50.6 ± 5.7%), (23.1 ± 0.1%), (7.5 ± 1.5%) and (6.9 ± 1.1%) in S-reducing cultures. In S -reducing enrichments, the genus predominated (49.2 ± 1.2%), followed by the order (20.9 ± 2.3%). S-reducing cultures were not affected by oleate concentrations up to 5 mM, while S -reducing cultures could degrade oleate in concentrations up to 10 mM, with no significant impact on sulfidogenesis. In sequencing batch reactors operated with sulfide stripping, the S-reducing enrichment produced 145.8 mM sulfide, precipitating Zn as ZnS in a separate tank. The S fed bioreactor only produced 23.4 mM of sulfide precipitated as ZnS. The lower sulfide production likely happened due to sulfite toxicity, an intermediate of thiosulfate reduction. Therefore, elemental sulfur reduction represents an excellent alternative to the currently adopted approaches for LCFA degradation. To the best of our knowledge, this is the first report of oleate degradation with the flux of electrons totally diverted toward sulfide production for metal precipitation, showing great efficiency of LCFA degradation coupled to high levels of metals precipitated as metal sulfide.
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http://dx.doi.org/10.3389/fbioe.2020.550253DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7644789PMC
October 2020

Carboxylic acids production and electrosynthetic microbial community evolution under different CO feeding regimens.

Bioelectrochemistry 2021 Feb 15;137:107686. Epub 2020 Oct 15.

Microbiology, School of Natural Sciences and Ryan Institute, National University of Ireland Galway, University Road, Galway H91 TK33, Ireland.

Microbial electrosynthesis (MES) is a potential technology for CO recycling, but insufficient information is available on the microbial interactions underpinning electrochemically-assisted reactions. In this study, a MES reactor was operated for 225 days alternately with bicarbonate or CO as carbon source, under batch or continuous feeding regimens, to evaluate the response of the microbial communities, and their productivity, to dynamic operating conditions. A stable acetic acid production rate of 9.68 g m d, and coulombic efficiency up to 40%, was achieved with continuous CO sparging, higher than the rates obtained with bicarbonate (0.94 g m d) and CO under fed-batch conditions (2.54 g m d). However, the highest butyric acid production rate (0.39 g m d) was achieved with intermittent CO sparging. The microbial community analyses focused on differential amplicon sequence variants (ASVs), allowing detection of ASVs significantly different across consecutive samples. This analysis, combined with co-occurence network analysis, and cyclic voltammetry, indicated that hydrogen-mediated acetogenesis was carried out by Clostridium, Eubacterium and Acetobacterium, whereas Oscillibacter and Caproiciproducens were involved in butyric acid production. The cathodic community was spatially inhomogeneous, with potential electrotrophs, such as Sulfurospirillum and Desulfovibrio, most prevalent near the current collector. The abundance of Sulfurospirillum positively correlated with that of Acetobacterium, supporting the syntrophic metabolism of both organisms.
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http://dx.doi.org/10.1016/j.bioelechem.2020.107686DOI Listing
February 2021

Homoacetogenesis and solventogenesis from H/CO by granular sludge at 25, 37 and 55 °C.

Chemosphere 2021 Feb 16;265:128649. Epub 2020 Oct 16.

National University of Ireland Galway, H91 TK33, Galway, Ireland.

CO fermentation is a promising process to produce biofuels like ethanol. It can be integrated in third generation biofuel production processes to substitute traditional sugar fermentation when supplied with cheap electron donors, e.g. hydrogen derived from wind energy or as surplus gas in electrolysis. In this study, granular sludge from an industrial wastewater treatment plant was tested as inoculum for ethanol production from H/CO via non-phototropic fermentation at submesophilic (25 °C), mesophilic (37 °C) and thermophilic (55 °C) conditions. The highest ethanol concentration (17.11 mM) was obtained at 25 °C and was 5-fold higher than at 37 °C (3.36 mM), which was attributed to the fact that the undissociated acid (non-ionized acetic acid) accumulation rate constant (0.145 h) was 1.39 fold higher than at 25 °C (0.104 h). Methane was mainly produced at 55 °C, while neither acetic acid nor ethanol were formed. Ethanol production was linked to acetic acid production with the highest ethanol to acetic acid ratio of 0.514 at 25 °C. The carbon recovery was 115.7%, 131.2% and 117.1%, while the electron balance was almost closed (97.1%, 110.1% and 109.1%) at 25 °C, 37 °C and 55 °C, respectively. The addition of bicarbonate inhibited ethanol production both at 25 °C and 37 °C. Clostridium sp. were the prevalent species at both 25 and 37 °C at the end of the incubation, which possibly contributed to the ethanol production.
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http://dx.doi.org/10.1016/j.chemosphere.2020.128649DOI Listing
February 2021

The dairy biorefinery: Integrating treatment processes for cheese whey valorisation.

J Environ Manage 2020 Dec 28;276:111240. Epub 2020 Aug 28.

DICAAR - Department of Civil and Environmental Engineering and Architecture, University of Cagliari, Piazza D'Armi 1, 09123, Cagliari, Italy.

With an estimated worldwide production of 190 billion kg per year, and due to its high organic load, cheese whey represents a huge opportunity for bioenergy and biochemicals production. Several physical, chemical and biological processes have been proposed to valorise cheese whey by producing biofuels (methane, hydrogen, and ethanol), electric energy, and/or chemical commodities (carboxylic acids, proteins, and biopolymers). A biorefinery concept, in which several value-added products are obtained from cheese whey through a cascade of biotechnological processes, is an opportunity for increasing the product spectrum of dairy industries while allowing for sustainable management of the residual streams and reducing disposal costs for the final residues. This review critically analyses the different treatment options available for energy and materials recovery from cheese whey, their combinations and perspectives for implementation. Thus, instead of focusing on a specific valorisation platform, in the present review the most relevant aspects of each strategy are analysed to support the integration of different routes, in order to identify the most appropriate treatment train.
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http://dx.doi.org/10.1016/j.jenvman.2020.111240DOI Listing
December 2020

Pre-treatment and temperature effects on the use of slow release electron donor for biological sulfate reduction.

J Environ Manage 2020 Dec 25;275:111216. Epub 2020 Aug 25.

National University of Ireland, University Road, H91 TK33, Galway, Ireland.

Lignocellulosic materials can be used as slow release electron donor (SRED) for biological sulfate reduction, potentially enhancing the subsequent metal sulfide precipitation. Lignocellulosic materials require a pre-treatment step in other biotechnological applications, but pre-treatment strategies for its use as a SRED for biological sulfate reduction have not yet been tested. Three pre-treatments strategies (mechanical, acid, and mechanical followed by acid pre-treatment) were tested to enhance electron donor release from brewery spent grain (BSG), and compared to a non-pre-treated control. Mechanical pre-treatment provided the highest sulfate removal rate (82.8 ± 8.8 mg SO.(g TVS.day)), as well as the highest final sulfide concentration (441.0 ± 34.4 mg.L) at mesophilic conditions. BSG submitted to mechanical pre-treatment was also assessed under psychrophilic and thermophilic conditions. Under mesophilic and psychrophilic conditions, both sulfate reduction and methane production occurred. Under psychrophilic conditions, the sulfate reduction rate was lower (25 ± 2.0 mg SO.(g TVS.day)), and the sulfide formation depended on lactate addition. A metal precipitation assay was conducted to assess whether the use of SRED enhances metal recovery. Zinc precipitation and recovery with chemical or biogenic sulfide from the BSG batches were tested. Sulfide was provided in a single spike or slowly added, mimicking the effect of SRED. ZnS was formed in all conditions, but better settling particles were obtained when sulfide was slowly added, regardless of the sulfide source.
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http://dx.doi.org/10.1016/j.jenvman.2020.111216DOI Listing
December 2020

Organic waste biorefineries: Looking towards implementation.

Waste Manag 2020 Aug 16;114:274-286. Epub 2020 Jul 16.

Department of Civil and Environmental Engineering and Architecture, University of Cagliari, Piazza d'Armi, 09123 Cagliari, Italy. Electronic address:

The concept of biorefinery expands the possibilities to extract value from organic matter in form of either bespoke crops or organic waste. The viability of biorefinery schemes depends on the recovery of higher-value chemicals with potential for a wide distribution and an untapped marketability. The feasibility of biorefining organic waste is enhanced by the fact that the biorefinery will typically receive a waste management fee for accepting organic waste. The development and implementation of waste biorefinery concepts can open up a wide array of possibilities to shift waste management towards higher sustainability. However, barriers encompassing environmental, technical, economic, logistic, social and legislative aspects need to be overcome. For instance, waste biorefineries are likely to be complex systems due to the variability, heterogeneity and low purity of waste materials as opposed to dedicated biomasses. This article discusses the drivers that can make the biorefinery concept applicable to waste management and the possibilities for its development to full scale. Technological, strategic and market constraints affect the successful implementations of these systems. Fluctuations in waste characteristics, the level of contamination in the organic waste fraction, the proximity of the organic waste resource, the markets for the biorefinery products, the potential for integration with other industrial processes and disposal of final residues are all critical aspects requiring detailed analysis. Furthermore, interventions from policy makers are necessary to foster sustainable bio-based solutions for waste management.
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http://dx.doi.org/10.1016/j.wasman.2020.07.010DOI Listing
August 2020

Selenate and selenite uptake, accumulation and toxicity in Lemna minuta.

Water Sci Technol 2020 May;81(9):1852-1862

IHE Institute for Water Education, 2601 DA Delft, The Netherlands.

The kinetics of Se uptake and toxicity to Lemna were studied over a period of 14 days of exposure to Se(IV) or Se(VI). The growth of Lemna stopped immediately after exposure to 5.0 mg/L of Se(IV) or Se(VI). The content of chlorophyll and phaeopigments of Lemna exposed to 5.0 mg/L of Se(IV) was two to three times less than in the control after 3 d exposure. Lemna took up Se rapidly within the first 3 d. The Se content in Lemna along with the exposure time fitted well the two-compartment and the hyperbolic model, which demonstrates that the mechanism of Se(IV) and Se(VI) uptake in Lemna is not only through passive diffusion, but also through other processes such as ion channel proteins or transporters. The kinetic bioconcentration factors (BCFs) were 231 and 42 for 0.5 mg/L Se(IV) and Se(VI) exposure, respectively. The uptake rate of Lemna reached 263 mg/kg/d and 28 mg/kg/d in the Se(IV) and Se(VI) treatments, respectively. This study showed that Se(IV) has a faster accumulation rate than Se(VI), but a higher toxicity, indicating Lemna could be a good candidate to remove Se(IV) from water, producing Se-enriched biomass which may eventually also be considered for use as Se-enriched feed supplement or fertilizer.
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http://dx.doi.org/10.2166/wst.2020.214DOI Listing
May 2020

Recycling of European plastic is a pathway for plastic debris in the ocean.

Environ Int 2020 09 27;142:105893. Epub 2020 Jun 27.

Ryan Institute, National University of Ireland, University Road, Galway H91 REW4, Ireland.

Polyethylene (PE) is one of the most common types of plastic. Whilst an increasing share of post-consumer plastic waste from Europe is collected for recycling, 46% of separated PE waste is exported outside of the source country (including intra-EU trade). The fate of this exported European plastic is not well known. This study integrated data on PE waste flows in 2017 from UN Comtrade, an open repository providing detailed international trade data, with best available information on waste management in destination countries, to model the fate of PE exported for recycling from Europe (EU-28, Norway and Switzerland) into: recycled high-density PE (HDPE) and low-density PE (LDPE) resins, "landfill", incineration and ocean debris. Data uncertainty was reflected in three scenarios representing high, low and average recovery efficiency factors in material recovery facilities and reprocessing facilities, and different ocean debris fate factors. The fates of exported PE were then linked back to the individual European countries of export. Our study estimated that 83,187 Mg (tonnes) (range: 32,115-180,558 Mg), or 3% (1-7%) of exported European PE in 2017 ended up in the ocean, indicating an important and hitherto undocumented pathway of plastic debris entering the oceans. The countries with the greatest percentage of exported PE ending up as recycled HDPE or LDPE were Luxembourg and Switzerland (90% recycled for all scenarios), whilst the country with the lowest share of exported PE being recycled was the United Kingdom (59-80%, average 69% recycled). The results showed strong, significant positive relationships between the percentage of PE exported out of Europe and the percentage of exports which potentially end up as ocean debris. Export countries may not be the ultimate countries of origin owing to complex intra-EU trade in PE waste. Although somewhat uncertain, these mass flows provide pertinent new evidence on the efficacy and risks of current plastic waste management practices pertinent to emerging regulations around trade in plastic waste, and to the development of a more circular economy.
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http://dx.doi.org/10.1016/j.envint.2020.105893DOI Listing
September 2020

Draft Genome Sequence and Annotation of Paracoccus versutus MAL 1HM19, a Nitrate-Reducing, Sulfide-Oxidizing Bacterium.

Microbiol Resour Announc 2020 Mar 5;9(10). Epub 2020 Mar 5.

Department of Botany, Faculty of Science, Chulalongkorn University, Bangkok, Thailand

MAL 1HM19 is a mixotrophic nitrate-reducing sulfide-oxidizing bacterium which plays a crucial role in hydrogen sulfide (HS) and nitrate (NO ) removal. In this study, we report the draft genome sequence of MAL 1HM19.
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http://dx.doi.org/10.1128/MRA.01419-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7171218PMC
March 2020

Effect of tungsten and selenium on C gas bioconversion by an enriched anaerobic sludge and microbial community analysis.

Chemosphere 2020 Jul 14;250:126105. Epub 2020 Feb 14.

Chemical Engineering Laboratory (BIOENGIN Group), Faculty of Sciences and Center for Advanced Scientific Research (CICA), University of La Coruña (UDC), E-15008, La Coruña, Spain. Electronic address:

The effect of trace metals, namely tungsten and selenium, on the production of acids and alcohols through gas fermentation by a CO-enriched anaerobic sludge in a continuous gas-fed bioreactor was investigated. The CO-enriched sludge was first supplied with a tungsten-deficient medium (containing selenium) and in a next assay, a selenium-deficient medium (containing tungsten) was fed to the bioreactor, at a CO gas flow rate of 10 mL/min. In the absence of tungsten (tungstate), an initial pH of 6.2 followed by a pH decrease to 4.9 yielded 7.34 g/L acetic acid as the major acid during the high pH period. Subsequently, bioconversion of the acids at a lower pH of 4.9 yielded only 1.85 g/L ethanol and 1.2 g/L butanol in the absence of tungsten (tungstate). A similar follow up assay in the same bioreactor with two consecutive periods at different pH values (i.e., 6.2 and 4.9) with a selenium deficient medium yielded 6.6 g/L acetic acid at pH 6.2 and 4 g/L ethanol as well as 1.88 g/L butanol at pH 4.9. The results from the microbial community analysis showed that the only known CO fixing microorganism able to produce alcohols detected in the bioreactor was Clostridium autoethanogenum, both in the tungsten and the selenium deprived media, although that species has so far not been reported to be able to produce butanol. No other solventogenic acetogen was detected.
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http://dx.doi.org/10.1016/j.chemosphere.2020.126105DOI Listing
July 2020

Production of selenium- and zinc-enriched Lemna and Azolla as potential micronutrient-enriched bioproducts.

Water Res 2020 Apr 22;172:115522. Epub 2020 Jan 22.

Laboratory of Analytical Chemistry and Applied Ecochemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium.

Selenium (Se) and zinc (Zn) are essential micronutrients that are often lacking in the diet of humans and animals, leading to deficiency diseases. Lemna and Azolla are two aquatic plants with a substantial protein content, which offer the possibility of utilizing them to remove Se and Zn from (waste)water while producing micronutrient-enriched dietary proteins and fertilizers. In this study, we explored interaction effects occurring between Se and Zn when these micronutrients are taken up by Azolla and Lemna. The two aquatic plants were grown on hydroponic cultures containing 0-5.0 mg/L of Se (Se(IV) or Se(VI)) and Zn. The Se and Zn content of the plants, growth indicators, bioconcentration factor (BCF) and Se/Zn removal efficiency from the water phase were evaluated. The results demonstrated that Se(IV) is more toxic than Se(VI) for both plant species, as evidenced by the remarkable decrease of biomass content and root length when exposed to Se(IV). Both aquatic plants took up around 10 times more Se(IV) than Se(VI) from the medium. Moreover, the Se accumulation and removal efficiency increased by 66-99% for Se(IV) and by 34-59% for Se(VI) in Lemna when increasing Zn dosage from 0 to 5.0 mg/L in the medium, whereas it declined by 13-26% for Se(IV) and 21-35% for Se(VI) in Azolla, suggesting a synergetic effect in Lemna, but an antagonistic effect in Azolla. The maximum BCF of Se in Lemna and Azolla were 507 and 667, respectively. The protein content in freeze-dried Lemna and Azolla was approximately 17%. The high tolerance and accumulation of Se and Zn in Lemna and Azolla, combined with their rapid growth, high protein content and transformation of inorganic to organic Se species upon Se(IV) exposure make Lemna and Azolla potential candidates for the production of Se(IV)- and Zn-enriched biomass that can be used as crop fertilizers or protein-rich food/feed supplements or ingredients. Accordingly, by growing the Azolla and Lemna on wastewater, a high-value product can be produced from wastewater while recovering resources.
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http://dx.doi.org/10.1016/j.watres.2020.115522DOI Listing
April 2020

Effect of selenate and thiosulfate on anaerobic methanol degradation using activated sludge.

Environ Sci Pollut Res Int 2020 Aug 21;27(24):29804-29811. Epub 2020 Jan 21.

UNESCO-IHE, Institute for Water Education, P. O. Box. 3015, 2601DA, Delft, The Netherlands.

Anaerobic bioconversion of methanol was tested in the presence of selenate (SeO), thiosulfate (SO), and sulfate (SO) as electron acceptors. Complete SeO reduction occurred at COD:SeO ratios of 12 and 30, whereas ~ 83% reduction occurred when the COD:SeO ratio was 6. Methane production did not occur at the three COD:SeO ratios investigated. Up to 10.1 and 30.9% of SO disproportionated to SO at COD:SO ratios of 1.2 and 2.25, respectively, and > 99% reduction was observed at both ratios. The presence of SO lowered the methane production by 73.1% at a COD:SO ratio of 1.2 compared to the control (no SO). This study showed that biogas production was not preferable for SeO and SO-rich effluents and volatile fatty acid production could be a potential resource recovery option.
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http://dx.doi.org/10.1007/s11356-020-07597-8DOI Listing
August 2020

Volatile fatty acid production from Kraft mill foul condensate in upflow anaerobic sludge blanket reactors.

Environ Technol 2021 Jun 13;42(16):2447-2460. Epub 2020 Jan 13.

UNESCO-IHE, Institute for Water Education, Delft, Netherlands.

The utilization of foul condensate (FC) collected from a Kraft pulp mill for the anaerobic production of volatile fatty acids (VFA) was tested in upflow anaerobic sludge blanket (UASB) reactors operated at 22, 37 and 55°C at a hydraulic retention time (HRT) of ∼75 h. The FC consisted mainly of 11370, 500 and 592 mg/L methanol, ethanol and acetone, respectively. 42-46% of the organic carbon (methanol, ethanol and acetone) was utilized in the UASB reactors operated at an organic loading of ∼8.6 gCOD/L.d and 52-70% of the utilized organic carbon was converted into VFA. Along with acetate, also propionate, isobutyrate, butyrate, isovalerate and valerate were produced from the FC. Prior to acetogenesis of FC, enrichment of the acetogenic biomass was carried out in the UASB reactors for 113 d by applying operational parameters that inhibit methanogenesis and induce acetogenesis. Activity tests after 158 d of reactor operation showed that the biomass from the 55°C UASB reactor exhibited the highest activity after the FC feed compared to the biomass from the reactors at 22 and 37°C. Activity tests at 37°C to compare FC utilization for CH versus VFA production showed that an organic carbon utilization >98% for CH production occurred in batch bottles, whereas the VFA production batch bottles showed 51% organic carbon utilization. Furthermore, higher concentrations of C-C VFA were produced when FC was the substrate compared to synthetic methanol rich wastewater.
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http://dx.doi.org/10.1080/09593330.2019.1703823DOI Listing
June 2021

Microbial electrochemical technologies: Electronic circuitry and characterization tools.

Biosens Bioelectron 2020 Feb 16;150:111884. Epub 2019 Nov 16.

Microbiology Department, School of Natural Sciences, National University of Ireland, Galway, University Road, Galway, Ireland.

Microbial electrochemistry merges microbiology, electrochemistry and electronics to provide a set of technologies for environmental engineering applications. Understanding the electronic concepts is crucial for effectively adopting these systems, but the importance of electronic circuitry is often overlooked by microbial electrochemistry researchers. This review provides the background on the electronics and electrochemical concepts involved in the study of microorganisms interacting with electricity, and their applications in microbial electrochemical technology (MET). The potentiostat circuitry is described along with its working principles. Electrochemical analyses are presented together with the rational and parameters employed to study MET devices and electroactive microorganisms. Finally, future directions are delineated towards the adoption of MET, and the related electronics, in environmental engineering applications.
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http://dx.doi.org/10.1016/j.bios.2019.111884DOI Listing
February 2020

A sustainable strategy for effective regulation of aerobic granulation: Augmentation of the signaling molecule content by cultivating AHL-producing strains.

Water Res 2020 Feb 16;169:115193. Epub 2019 Oct 16.

Department of Civil Engineering, University of Calgary, Calgary, T2N 1N4, Canada.

The positive roles of N-acyl homoserine lactone (AHL)-mediated quorum sensing (QS) in aerobic granular sludge (AGS) have been widely acknowledged. However, it is not feasible to manipulate granulation via direct addition of AHL chemicals or AHL-producing strains. Here, several strains with high AHL-producing capacity were successfully isolated from AGS. These QS strains were cultivated, mixed as a consortium, and then divided into two groups: AHLs supernatant and bacterial cells encapsulated in sodium alginate (CEBs). The potential of QS regulation, via doses of AHLs supernatant and CEBs, in accelerating granulation was evaluated. Results clearly indicated that short-term (days 21-70) addition of AHLs supernatant led to a rapid specific growth rate (0.08 d), compact structure without filamentous bacteria overgrowth, excellent settlement performance (SVI 37.2 mL/g), and a high integrity coefficient (4.4%) of the granules. Sustainable release of AHLs (mainly C- and C-HSL) was induced by exogenous AHLs, possibly attributed to the enrichment of the genera Aeromonas and Pseudomonas. Further, tryptophan and aromatic protein substances were produced to maintain structural stability, suggesting that short-term QS regulation had long-term positive effects on the characteristics of AGS. By comparison, the addition of CEBs posed negligible or negative impact on the granulation, as evidenced by the rupture of smaller aggregates and poor characteristics of AGS. Overall, augmentation of the signaling content via addition of AHLs supernatant from QS strains is an economical and feasible regulation strategy to accelerate granulation and sustain long-term structural stability.
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http://dx.doi.org/10.1016/j.watres.2019.115193DOI Listing
February 2020
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