Bioaugmentation of UASB reactors with immobilized Sulfurospirillum barnesii for simultaneous selenate and nitrate removal
Lenz, M. ; Enright, A.M. ; O’Flaherty, V. ; Aelst, A.C. van; Lens, P.N.L. - \ 2009
Applied Microbiology and Biotechnology 83 (2009)2. - ISSN 0175-7598 - p. 377 - 388.
anaerobic granular sludge - waste-water treatment - respiring bacteria - elemental selenium - sulfate reduction - precipitation - remediation - bioreactors - chain - se
Whole-cell immobilization of selenate-respiring Sulfurospirillum barnesii in polyacrylamide gels was investigated to allow the treatment of selenate contaminated (790¿µg Se¿×¿L-1) synthetic wastewater with a high molar excess of nitrate (1,500 times) and sulfate (200 times). Gel-immobilized S. barnesii cells were used to inoculate a mesophilic (30°C) bioreactor fed with lactate as electron donor at an organic loading rate of 5 g chemical oxygen demand (COD)¿×¿L-1 day-1. Selenate was reduced efficiently (>97%) in the nitrate and sulfate fed bioreactor, and a minimal effluent concentration of 39¿µg Se¿×¿L-1 was obtained. Scanning electron microscopy with energy dispersive X-ray (SEM–EDX) analysis revealed spherical bioprecipitates of =2¿µm diameter mostly on the gel surface, consisting of selenium with a minor contribution of sulfur. To validate the bioaugmentation success under microbial competition, gel cubes with immobilized S. barnesii cells were added to an Upflow Anaerobic Sludge Bed (UASB) reactor, resulting in earlier selenate (24 hydraulic retention times (HRTs)) and sulfate (44 HRTs) removal and higher nitrate/nitrite removal efficiencies compared to a non-bioaugmented control reactor. S. barnesii was efficiently immobilized inside the UASB bioreactors as the selenate-reducing activity was maintained during long-term operation (58 days), and molecular analysis showed that S. barnesii was present in both the sludge bed and the effluent. This demonstrates that gel immobilization of specialized bacterial strains can supersede wash-out and out-competition of newly introduced strains in continuous bioaugmented systems. Eventually, proliferation of a selenium-respiring specialist occurred in the non-bioaugmented control reactor, resulting in simultaneous nitrate and selenate removal during a later phase of operation
Selenate removal in methanogenic and sulfate-reducing upflow anaerobic sludge bed reactors
Lenz, M. ; Hullebusch, E.D. van; Hommes, G. ; Corvini, P.F.X. ; Lens, P.N.L. - \ 2008
Water Research 42 (2008)8-9. - ISSN 0043-1354 - p. 2184 - 2194.
afvalwaterbehandeling - bioreactoren - slib - selenium - verwijdering - efficiëntie - biologische filtratie - slibzuivering - sulfaatreductie - waste water treatment - bioreactors - sludges - selenium - removal - efficiency - biological filtration - sludge treatment - sulfate reduction - acid-mine drainage - granular sludge - elemental selenium - respiring bacteria - waste-water - se - reduction - sediments - coal - particulate
This paper evaluates the use of upflow anaerobic sludge bed (UASB) bioreactors (30 degrees C, pH = 7.0) to remove selenium oxyanions from contaminated waters (790 mu g Se L-1) under methanogenic and sulfate-reducing conditions using lactate as electron donor. One UASB reactor received sulfate at different sulfate to selenate ratios, while another UASB was operated under methanogenic conditions for 132 days without sulfate in the influent. The selenate effluent concentrations in the sulfate-reducing and methanogenic reactor were 24 and 8 mu gSeL(-1), corresponding to removal efficiencies of 97% and 99%, respectively. X-ray diffraction (XRD) analysis and sequential extractions showed that selenium was mainly retained as elemental selenium in the biomass. However, the total dissolved selenium effluent concentrations amounted to 73 and 80 mu gSeL(-1), respectively, suggesting that selenate was partly converted to another selenium compound, most likely colloidally dispersed Sea nanoparticles. Possible intermediates of selenium reduction (selenite, dimethylselenide, dimethyldiselenide, H2Se) could not be detected. Sulfate reducers removed selenate at molar excess of sulfate to selenate (up to a factor of 2600) and elevated dissolved sulfide concentrations (up to 168mgL(-1)), but selenium removal efficiencies were limited by the applied sulfate-loading rate. in the methanogenic bioreactor, selenate and dissolved selenium removal were independent of the sulfate load, but inhibited by sulfide (101 mg L-1). The selenium removal efficiency of the methanogenic UASB abruptly improved after 58 days of operation, suggesting that a specialized selenium-converting population developed in the reactor. This paper demonstrates that both sulfate-reducing and methanogenic UASB reactors can be applied to remove selenate from contaminated natural waters and anthropogenic waste streams, e.g. agricultural drainage waters, acid mine drainage and flue gas desulfurization bleeds.
Selenium Speciation Assessed by X-Ray Absorption Spectroscopy of Sequentially Extracted Anaerobic Biofilms
Lenz, M. ; Hullebusch, E.D. van; Farges, F. ; Nikitenko, S. ; Borca, C.N. ; Grolimund, D. ; Lens, P.N.L. - \ 2008
Environmental Science and Technology 42 (2008)20. - ISSN 0013-936X - p. 7587 - 7593.
granular sludge - elemental selenium - anoxic sediments - selenate - reduction - sulfate - fractionation - bacteria - soils - forms
Wet chemical methods such as sequential extraction procedures are commonly used to assess selenium fractionation in anoxic environments, allowing an estimation of the mobility and bioavailability of selenium. However, the interpretation can be biased by unselective extraction of targeted species and artifacts introduced during the extraction. Here,the selectivity of the single extraction steps to gain reliable selenium speciation information are scrutinized for the first time by direct nondestructive X-ray absorption near edge structure (XANES) spectroscopy at the selenium K-edge. The sequential extraction procedures seriously overestimated the elemental selenium fraction, as major parts (58%) of the total selenium were present as metal selenides and organic selenium compounds, although extracted in the elemental fraction. Spectral fitting of the XANES spectra by the least-squares linear combinations utilizing a large set of model compounds, including previously neglected Se(-I) selenides, showed a novel degree of complexity in the speciation of selenium treating anaerobic biofilms, with up to 4 modeled selenium species contributing to the speciation, i.e., different elemental, organic, and metal-bound selenium species. Furthermore, a short exposure (10 min) to ambient air during the sequential extraction procedure induced the oxidation of organic selenium compounds, revealing the fragility of selenium speciation in anaerobic biofilms.
Selenium oxyanion inhibition of hydrogenotrophic and acetoclastic methanogenesis
Lenz, M. ; Janzen, N. ; Lens, P.N.L. - \ 2008
Chemosphere 73 (2008)3. - ISSN 0045-6535 - p. 383 - 388.
anaerobic granular sludge - agricultural drainage sediment - escherichia-coli - thauera-selenatis - waste-water - elemental selenium - sulfate reduction - bed reactors - bioremediation - removal
Inhibitory effects of selenite and selenate towards hydrogenotrophic and acetoclastic methanogenesis were evaluated in anaerobic toxicity assays. The 50% inhibitory concentration (IC50) of both selenium oxyanions was below 6.1 X 10(-5) M in hydrogenotrophic assays, whereas acetoclastic methanogens were less inhibited: IC50 = 8.3 x 10(-5) M and 5.5 x 10(-4) M for selenite and selenate, respectively. Selenite completely inhibits methanogenesis from both substrates tested at concentrations >= 10(-3) M selenite, while only marginal methanogenic activities occur at equimolar concentrations of selenate. Selenite becomes irreversibly inhibitory upon a single exposure, whereas selenate inhibits methanogens upon repeated exposure. Consequently, methane recovery can be seriously hampered or even impossible during anaerobic treatment of highly selenium contaminated waste streams.
Biological alkylation and colloid formation of selenium in methanogenic UASB reactors
Lenz, M. ; Smit, M.P.J. ; Binder, P. ; Aelst, A.C. van; Lens, P.N.L. - \ 2008
Journal of Environmental Quality 37 (2008)5. - ISSN 0047-2425 - p. 1691 - 1700.
enterobacter-cloacae sld1a-1 - anaerobic granular sludge - agricultural drainage sediment - selenate-reducing bacterium - bacillus sp sf-1 - elemental selenium - dimethyl selenone - bed reactors - waste-water - toxicity
Bioalkylation and colloid formation of selenium during selenate removal in upflow anaerobic sludge bed (UASB) bioreactors was investigated, The mesophilic (30 degrees C) UASB reactor (pH = 7.0) was operated for 175 d with lactate as electron donor at an organic loading rate of 2 g COD L-1 d(-1) and a selenium loading rate of 3.16 mg Se L-1 d(-1). Combining sequential filtration with ion chromatographic analysis for selenium oxyanions and solid phase micro extraction gas chromatography mass spectrometry (SPME-GC-MS) for alkylated selenium compounds allowed to entirely close the selenium mass balance in the liquid phase for most of the UASB operational runtime. Although selenate was removed to more than 98.6% from the liquid phase, a less efficient removal of dissolved selenium was observed due to the presence of dissolved alkylated selenium species (dimethylselenide and dimethyldiselenide) and colloidal selenium particles in the effluent. The alkylated and the colloidal fractions contributed LIP to 15 and 31%, respectively, to the dissolved selenium concentration. The size fractions Of the colloidal dispersion were: 4 to 0.45 mu m: up to 21%, 0.45 to 0.2 mu m: up to 11%, and particles smaller than 0.2 mu m: up to 8%. Particles of 4 to 0.45 pin were formed in the external settler, but did not settle. SEM-EDX analysis showed that microorganisms form these Selenium containing colloidal particles extracellularly on their Surface. Lowering the temperature by 10 degrees C for 6 h resulted in drastically reduced selenare removal efficiencies (after a delay of 1.5 d), accompanied by the temporary formation of all unknown, soluble, organic selenium species. This study shows that a careful process control is a prerequisite for selenium treatment in UASB bioreactors, as disturbances in the operational conditions induce elevated selenium effluent concentrations by alkylation and colloid formation.
Bioconversion of Selenate in Methanogenic Anaerobic Granular Sludge
Astratinei, V. ; Hullebusch, E.D. van; Lens, P.N.L. - \ 2006
Journal of Environmental Quality 35 (2006). - ISSN 0047-2425 - p. 1873 - 1883.
soluble selenium removal - bacillus sp sf-1 - elemental selenium - sequential extraction - reducing bacterium - toxic metals - reduction - speciation - oxyanions - reactor
The capacity of anaerobic granular sludge to remove selenate from contaminated wastewater was investigated. The potential of different types of granular sludge to remove selenate from the liquid phase was compared to that of suspended sludge and contaminated soil and sediment samples. The selenate removal rates ranged from 400 to 1500 µg g VSS¿1 h¿1, depending on the source of biomass, electron donor, and the initial selenate concentration. The granular structure protects the microorganisms when exposed to high selenate concentrations (0.1 to 1 mM). Anaerobic granular sludge "Eerbeek," originating from a UASB reactor treating paper mill wastewater, removed about 90, 50, and 36% of 0.1, 0.5, and 1 mM of Se, respectively, from the liquid phase when incubated with 20 mM lactate at 30°C and pH 7.5. Selenite, elemental Se (Seo), and metal selenide precipitates were the conversion products. Enrichments from the anaerobic granular sludge "Eerbeek" were able to convert 90% of the 10-mM selenate to Seo at a rate of 1505 µg Se(VI) g cells¿1 h¿1, a specific growth rate of 0.0125 g cells h¿1, and a yield of 0.083 g cells mg Se¿1. Both microbial metabolic processes (e.g dissimilatory reduction) as well as microbially mediated physicochemical mechanisms (adsorption and precipitation) contribute to the removal of selenate from the Se-containing medium