•High rate, high efficiency autotrophic denitrification was demonstrated in a FBR.•Complete nitrate and nitrite removal was achieved at HRTs as low as 10min.•The nitrate and nitrite loading rates ...reached 600 and 228mgL−1h−1, respectively.•The biofilms were dominated by T. denitrificans and tolerated pHs as low as 5.8.•The optimal temperature for nitrate removal was 26.6°C based on Ratkowsky modeling.
High rate, high efficiency thiosulfate-driven autotrophic denitrification and denitritation with Thiobacillus denitrificans dominated biofilms were achieved in fluidized-bed reactors (FBRs) operated at 20.0±2.0 and 30.0±0.2°C. Complete nitrate removal was obtained even at nitrate loading rate and hydraulic retention time (HRT) of 600mgL−1h−1 and 10min, respectively. Further decrease of HRT to 5min resulted in 50% of nitrate removal efficiency. Nitrite did not accumulate when nitrate was used as electron acceptor unless HRT was decreased to 5min. Effluent pH remained at 5.8 during denitrification. When nitrite was supplemented as the electron acceptor, denitritation effectively proceeded with the highest nitrite loading rate of 228mgL−1h−1. Similar denitrification and denitritation performances were obtained at 20.0±2.0 and 30.0±0.2°C. Batch assays conducted at temperature range from 1 to 46°C, however, showed a significant impact of temperature on autotrophic denitrification. Ratkowsky model was used to estimate the minimum, optimal and maximum growth temperatures of T. denitrificans dominated culture that were below 1, 26.6 and 50.8°C, respectively.
Lipids in wastewaters are potential raw material for renewable diesel, but may complicate biological treatment of wastewaters. The lipid composition of palm oil mill effluent (POME), ...chemithermomechanical pulp mill (CTMP) wastewater and municipal wastewater (MWW) was studied with a combination of thin-layer chromatography and nuclear magnetic resonance. Gravimetrically determined content of extracted lipids from the solids of POME and CTMP wastewater were 8.4 ± 1.2 g/L (19.6 ± 0.8% of dry weight) and 0.17-0.23 g/L (12.4-18.5%), respectively, while MWW contained 0.021 ± 0.002 g/L (9.3 ± 1.4%) of lipids. All lipid extracts contained mono-, di- and triacylglycerols (TAGs) and free fatty acids (FFAs). In POME, lipids were mostly TAGs (11.5 ± 0.2 μmol/10 mg of lipid extract). In CTMP and MWW lipid composition was more diverse than in POME containing also sterol derivatives and fatty acid methyl esters and the main lipids were FFAs.
Anaerobic microflora enriched for dark fermentative H2 production from a mixture of glucose and xylose was used in batch cultivations to determine the effects of sudden short-term temperature ...fluctuations on H2 yield and microbial community composition. Batch cultures initially cultivated at 55 °C (control) were subjected to downward (from 55 °C to 35 °C or 45 °C) or upward (from 55 °C to 65 °C or 75 °C) temperature shifts for 48 h after which, each culture was transferred to a fresh medium and cultivated again at 55 °C for two consecutive batch cycles. The average H2 yield obtained during the first cultivation at 55 °C was 2.1 ± 0.14 mol H2 mol−1 hexose equivalent. During the temperature shifts, the obtained H2 yields were 1.8 ± 0.15, 1.6 ± 0.27 and 1.9 ± 0.00 mol H2 mol−1 hexose equivalent at 35 °C, 45 °C and 65 °C, respectively, while no metabolic activity was observed at 75 °C. The sugars were completely utilized during the 48 h temperature shift to 35 °C but not at 65 °C and 45 °C. At the end of the second cycle after the different temperature shifts, the H2 yield obtained was 96.5, 91.6, 79.9 and 54.1% (second cycle after temperature shift to 35 °C, 45 °C, 65 °C and 75 °C, respectively) when compared to the average H2 yield produced in the control at 55 °C. Characterization of the microbial communities present in the control culture at 55 °C showed the predominance of Thermoanaerobacteriales, Clostridiales and Bacilliales. The microbial community composition differed based on the fluctuation temperature with Thermoanaerobacteriales being most dominant during the upward temperature fluctuations and Clostridiales being the most dominant during the downward temperature fluctuations.
•Optimum H2 production depends on the resilience of the microbial community.•H2 production at 35 and 45 °C decreased but rapidly recovered at 55 °C.•H2 production decreased at 65 °C and stopped completely during 75 °C shift.•H2 production recovered better after 65 °C than after 75 °C temperature shift.•The major microbial genera were Clostridium spp. and Thermoanaerobacterium spp.
The dispersion of nitrogenous compounds and heavy metals into the environment is frequent during mining activities. The effects of nickel (Ni) and cobalt (Co) on denitrification of simulated mine ...waters were investigated in batch bioassays and fluidized-bed reactors (FBRs). At pH 7, batch tests revealed that Co did not exhibit inhibition on denitrification even at 86.6 mg/L. Ni showed to be inhibitory at 50 and 100 mg/L by decreasing nitrate removal efficiencies of 18 and 65 %, respectively. In two FBRs, operated at 7–8 and 22 °C, 5.5 mg/L Ni did not affect nitrate and nitrite removals because of FBR potential of diluting soluble Ni feed concentration. On the contrary, the effluent pH clearly decreased in both FBR1 and FBR2 because of nickel sulfide precipitation and Ni inhibition of the last two steps of denitrification. When Ni injection was stopped, the process recovered more slowly at 22 than 7–8 °C. This is the first study reporting the effect of Ni on denitrification in biological FBRs.
Since the discovery of microbiological metal dissolution, numerous biohydrometallurgical approaches have been developed to use microbially assisted aqueous extractive metallurgy for the recovery of ...metals from ores, concentrates, and recycled or residual materials. Biohydrometallurgy has helped to alleviate the challenges related to continually declining ore grades by transforming uneconomic ore resources to reserves. Engineering techniques used for biohydrometallurgy span from above ground reactor, vat, pond, heap and dump leaching to underground in situ leaching. Traditionally biohydrometallurgy has been applied to the bioleaching of base metals and uranium from sulfides and the biooxidation of sulfidic refractory gold ores and concentrates before cyanidation. More recently the interest in using bioleaching for oxide ore and waste processing, as well as extracting other commodities such as rare earth elements has been growing. Bioprospecting, adaptation, engineering and storing of microorganisms has increased the availability of suitable biocatalysts for biohydrometallurgical applications. Moreover, the advancement of microbial characterisation methods has increased the understanding of microbial communities and their capabilities in the processes. This paper reviews recent progress in biohydrometallurgy and microbial characterisation.
•Biohydrometallurgy has been mostly used for sulfidic gold, base metal and uranium ores.•Interest in waste bioleaching and extracting other commodities is increasing.•In situ and vat bioleaching are gaining interest along with heaps and bioreactors.•Bioprospecting, adaptation, engineering increase the availability of novel strains.•Microbial characterisation increases the understanding on biocatalysts.
Microbial electrochemical technologies have gained much attention in the recent years during which basic research has been carried out to provide proof of concept by utilizing microorganisms for ...generating bioenergy in an electro redox active environment. However, these bio-electrocatalyzed systems pose significant challenges towards up-scaling and practical applications. Various parameters viz., electrodes, materials, configuration, biocatalyst, reaction kinetics, fabrication and operational costs, resistance for electron transfer etc. will critically govern the performance of microbial catalyzed electrochemical systems. Majorly, the surface area of electrode materials, biofilm coverage on the electrode surface, enrichment of electrochemically active electrode respiring bacteria and reduction reactions at cathode will aid in increasing the reaction kinetics towards the upscaling of microbial electrochemical technologies. Enrichment of electroactive microbial community on anode electrode can be promoted with electrode pretreatment, controlled anode potential or electrical current, external resistance, optimal operation temperature, chemical additions and bioaugmentation . Inhibition of the growth of methanogens also increases the columbic efficiency, an essential parameter that determines the efficacy of bioelectricity generation. Considering the practical implementation of these microbial electrochemical technologies, the current review addresses the challenges and strategies to improve the performance of bio-electrocatalyzed systems with respect to the operational, physico-chemical and biological factors towards scale up. Besides, the feasibility for long term operation, the scope for future research along with the operational and maintenance costs are discussed to provide a broad spectrum on the role of the system components for the implementation of these bio-electrochemical technologies for practical utility.
Summary
The aim of this study was to test three flat plate photobioreactor configurations for growth of Chlorella vulgaris under non‐axenic conditions and to characterize and quantify associated ...bacterial communities. The photobioreactor cultivations were conducted using tap water‐based media to introduce background bacterial population. Growth of algae was monitored over time with three independent methods. Additionally, the quantity and quality of eukaryotes and bacteria were analysed using culture‐independent molecular tools based on denaturing gradient gel electrophoresis (PCR‐DGGE) and quantitative polymerase chain reaction (QPCR). Static mixers used in the flat plate photobioreactors did not generally enhance the growth at the low light intensities used. The maximum biomass concentration and maximum specific growth rate were 1.0 g l−1 and 2.0 day−1 respectively. Bacterial growth as determined by QPCR was associated with the growth of C. vulgaris. Based on PCR‐DGGE, bacteria in the cultures mainly originated from the tap water. Bacterial community profiles were diverse but reproducible in all flat plate cultures. Most prominent bacteria in the C. vulgaris cultures belonged to the class Alphaproteobacteria and especially to the genus Sphingomonas. Analysis of the diversity of non‐photosynthetic microorganisms in algal mass cultures can provide useful information on the public health aspects and unravel community interactions.
•Biomass and lipid production ability of three microalgal strains was studied.•High lipid content was achieved with C. vulgaris in pre-treated piggery wastewater.•C. vulgaris in piggery wastewater ...excreted xylose, mannose, and arabinose.
The aim of this study was to select a potential microalgal strain for lipid production and to examine the suitability of anaerobically treated piggery wastewater as a nutrient source for production of lipid-rich biomass with the selected microalga. Biomass and lipid productivity of three microalgal strains (Chlorella sorokiniana CY1, Chlorella vulgaris CY5 and Chlamydomonas sp. JSC-04) were compared by using different media, nitrogen sources, and nitrogen concentrations. The highest lipid content and productivity (62.5wt%, 162mg/L/d) were obtained with C. vulgaris with BG-11 with 62mgN/L. Secondly, C. vulgaris was cultivated in sterilized, diluted (1–20×), anaerobically treated piggery wastewater. Biomass production decreased and lipid content increased, when wastewater was more diluted. The highest lipid content of 54.7wt% was obtained with 20× dilution, while the highest lipid productivity of 100.7mg/L/d with 5× dilution. Piggery wastewater is a promising resource for mass production of oleaginous microalgal biomass.
Starting up a microbial fuel cell (MFC) requires often a long-term culture enrichment period, which is a challenge after process upsets. The purpose of this study was to develop low-cost storage for ...MFC enrichment culture to enable prompt process recovery after upsets. Anolyte of an operating xylose-fed MFC was stored at different temperatures and for different time periods. Storing the anolyte for 1 week or 1 month at +4°C did not significantly affect power production, but the lag time for power production was increased from 2 days to 3 or 5 days, respectively. One month storing at -20°C increased the lag time to 7 days. The average power density in these MFCs varied between 1.2 and 1.7 W/m
3
. The share of dead cells (measured by live/dead staining) increased with storing time. After 6-month storage, the power production was insignificant. However, xylose removal remained similar in all cultures (99-100%) while volatile fatty acids production varied. The results indicate that fermentative organisms tolerated the long storage better than the exoelectrogens. As storing at +4°C is less energy intensive compared to freezing, anolyte storage at +4°C for a maximum of 1 month is recommended as start-up seed for MFC after process failure to enable efficient process recovery.
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•Optimized start-up procedures are required for prompt BES start-up.•−200 mV (vs. Ag/AgCl) anode potential accelerated the current production the most.•Start-up procedures were not ...critical for long-term BES performance.•Coulombic efficiency of brewery wastewater fed air-cathode BES was 12 ± 2%.
Start-up of bioelectrochemical systems (BESs) fed with brewery wastewater was compared at different adjusted anode potentials (−200 and 0 mV vs. Ag/AgCl) and external resistances (50 and 1000 Ω). Current generation stabilized faster with the external resistances (9 ± 3 and 1.70 ± 0.04 A/m3 with 50 and 1000 Ω, respectively), whilst significantly higher current densities of 76 ± 39 and 44 ± 9 A/m3 were obtained with the adjusted anode potentials of −200 and 0 mV vs. Ag/AgCl, respectively. After start-up, when operated using 47 Ω external resistance, the current densities and Coulombic efficiencies of all BESs stabilized to 9.5 ± 2.9 A/m3 and 12 ± 2%, respectively, demonstrating that the start-up protocols were not critical for long-term BES operation in microbial fuel cell mode. With adjusted anode potentials, two times more biofilm biomass (measured as protein) was formed by the end of the experiment as compared to start-up with the fixed external resistances. After start-up, the organics in the brewery wastewater, mainly sugars and alcohols, were transformed to acetate (1360 ± 250 mg/L) and propionate (610 ± 190 mg/L). Optimized start-up is required for prompt BES recovery, for example, after process disturbances. Based on the results of this study, adjustment of anode potential to −200 mV vs. Ag/AgCl is recommended for fast BES start-up.
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