Continuous 3-year outdoor operation of a flat-panel membrane photobioreactor to treat effluent from an anaerobic membrane bioreactor

A membrane photobioreactor (MPBR) plant was operated continuously for 3 years to evaluate the separate effects of different factors, including: biomass and hydraulic retention times (BRT, HRT), light path (Lp), nitrification rate (NOxR) and nutrient loading rates (NLR, PLR). The overall effect of all these parameters, which influence MPBR performance had not previously been assessed. The multivariate projection approach chosen for this study provided a good description of the collected data and facilitated their visualization and interpretation. Forty variables used to control and assess MPBR performance were evaluated during three years of continuous outdoor operation by means of principal component analysis (PCA) and partial least squares (PLS) analysis. The PCA identified the photobioreactor light path as the factor with the largest influence on data variability. Other important factors were: air flow rate (Fair), nitrogen and phosphorus recovery rates (NRR, PRR), biomass productivity (BP),optical density at 680 nm (OD680), ammonium and phosphorus effluent concentration (NH4, P), HRT, BRT, and nitrogen and phosphorus loading rates (NLR and PLR). The MPBR performance could be adequately estimated by a PLS model based on all the recorded variables, but this estimation worsened appreciably when only the controllable variables (Lp, Fair, HRT and BRT) were used as predictors, which underlines the importance of the non-controlled variables on MPBR performance. The microalgae cultivation process could thus only be partially controlled by the design and operating variables. As effluent nitrate concentration was shown to be the key factor in the nitrification rate, it can be used as an indirect measurement of nitrifying bacteria activity. A high nitrification rate was found to be inadvisable, since it showed an inverse correlation with NRR. In this respect, temperature appeared to be the main ambient/controlling factor in nitrifying bacteria activity

Production of microalgal external organic matter in a Chlorella-dominated culture: influence of temperature and stress factors

Although microalgae are recognised to release external organic matter (EOM), little is known about this phenomenon in microalgae cultivation systems, especially on a large scale. A study on the effect of microalgae-stressing factors such as temperature, nutrient limitation and ammonium oxidising bacteria (AOB) competition in EOM production by microalgae was carried out. The results showed non-statistically significant differences in EOM production at constant temperatures of 25, 30 and 35 °C. However, when the temperature was raised from 25 to 35 °C for 4 h a day, polysaccharide production increased significantly, indicating microalgae stress. Nutrient limitation also seemed to increase EOM production. No significant differences were found in EOM production under lab conditions when the microalgae competed with AOB for ammonium uptake. However, when the EOM concentration was monitored during continuous outdoor operation of a membrane photobioreactor (MPBR) plant, nitrifying bacteria activity was likely to be responsible for the increase in EOM concentration in the culture. Other factors such as high temperatures, ammonium-depletion and low light intensities could also have induced cell deterioration and thus have influenced EOM production in the outdoor MPBR plant. Membrane fouling seemed to depend on the biomass concentration of the culture. However, under the operating conditions tested, the behaviour of fouling rate with respect to the EOM concentration was different depending on the initial membrane state

Nitrite inhibition of microalgae induced by the competition between microalgae and nitrifying bacteria

Outdoor microalgae cultivation systems treating anaerobic membrane bioreactor (AnMBR) effluents usually present ammonium oxidising bacteria (AOB) competition with microalgae for ammonium uptake, which can cause nitrite accumulation. In literature, nitrite effects over microalgae have shown controversial results. The present study evaluates the nitrite inhibition role in a microalgae-nitrifying bacteria culture. For this purpose, pilot- and lab-scale assays were carried out. During the continuous outdoor operation of the membrane photobioreactor (MPBR) plant, biomass retention time (BRT) of 2 d favoured AOB activity, which caused nitrite accumulation. This nitrite was confirmed to inhibit microalgae performance. Specifically, continuous 5-d lab-scale assays showed a reduction in the nitrogen recovery efficiency by 32, 42 and 80% when nitrite concentration in the culture accounted for 5, 10 and 20 mg N·L−1, respectively. On the contrary, short 30-min exposure to nitrite showed no significant differences in the photosynthetic activity of microalgae under nitrite concentrations of 0, 5, 10 and 20 mg N·L−1. On the other hand, when the MPBR plant was operated at 2.5-d BRT, the nitrite concentration was reduced to negligible values due to increasing activity of microalgae and nitrite oxidising bacteria (NOB). This allowed obtaining maximum MPBR performance; i.e. nitrogen recovery rate (NRR) and biomass productivity of 19.7 ± 3.3 mg N·L−1·d−1 and 139 ± 35 mg VSS·L−1·d−1, respectively; while nitrification rate (NOxR) reached the lowest value (13.5 ± 3.4 mg N·L−1·d−1). Long BRT of 4.5 d favoured NOB growth, avoiding nitrite inhibition. However, it implied a decrease in microalgae growth and the accumulation of nitrate in the MPBR effluent. Hence, it seems that optimum BRT has to be within the range 2-4.5 d in order to favour microalgae growth with respect to AOB and NOB

Optimising an outdoor membrane photobioreactor for tertiary sewage treatment

The operation of an outdoor membrane photobioreactor plant which treated the effluent of an anaerobic membrane bioreactor was optimised. Biomass retention times of 4.5, 6, and 9 days were tested. At a biomass retention time of 4.5 days, maximum nitrogen recovery rate:light irradiance ratios, photosynthetic efficiencies and carbon biofixations of 51.7 ± 14.3 mg N·mol−1, 4.4 ± 1.6% and 0.50 ± 0.05 kg CO2·m3influent, respectively, were attained. Minimum membrane fouling rates were achieved when operating at the shortest biomass retention time because of the lower solid concentration and the negligible amount of cyanobacteria and protozoa. Hydraulic retention times of 3.5, 2, and 1.5 days were tested at the optimum biomass retention times of 4.5 days under non-nutrient limited conditions, showing no significant differences in the nutrient recovery rates, photosynthetic efficiencies and membrane fouling rates. However, nitrogen recovery rate:light irradiance ratios and photosynthetic efficiency significantly decreased when hydraulic retention time was further shortened to 1 day, probably due to a rise in the substrate turbidity which reduced the light availability in the culture. Optimal carbon biofixations and theoretical energy recoveries from the biomass were obtained at hydraulic retention time of 3.5 days, which accounted for 0.55 ± 0.05 kg CO2·m−3influent and 0.443 ± 0.103 kWh·m−3influent, respectively

Improving membrane photobioreactor performance by reducing light path: operating conditions and key performance indicators

Microalgae cultivation has been receiving increasing interest in wastewater remediation due to their ability to assimilate nutrients present in wastewater streams. In this respect, cultivating microalgae in membrane photobioreactors (MPBRs) allows decoupling the solid retention time (SRT) from the hydraulic retention time (HRT), which enables to increase the nutrient load to the photobioreactors (PBRs) while avoiding the wash out of the microalgae biomass. The reduction of the PBR light path from 25 to 10 cm increased the nitrogen and phosphorus recovery rates, microalgae biomass productivity and photosynthetic efficiency by 150, 103, 194 and 67%, respectively. The areal biomass productivity (aBP) also increased when the light path was reduced, reflecting the better use of light in the 10-cm MPBR plant. The capital and operating operational expenditures (CAPEX and OPEX) of the 10-cm MPBR plant were also reduced by 27 and 49%, respectively. Discharge limits were met when the 10-cm MPBR plant was operated at SRTs of 3-4.5 d and HRTs of 1.25-1.5 d. At these SRT/HRT ranges, the process could be operated without a high fouling propensity with gross permeate flux (J20) of 15 LMH and specific gas demand (SGDp) between 16 and 20 Nm3air·m−3permeate, which highlights the potential of membrane filtration in MPBRs. When the continuous operation of the MPBR plant was evaluated, an optical density of 680 nm (OD680) and soluble chemical oxygen demand (sCOD) were found to be good indicators of microalgae cell and algal organic matter (AOM) concentrations, while dissolved oxygen appeared to be directly related to MPBR performance. Nitrite and nitrate (NOx) concentration and the soluble chemical oxygen demand:volatile suspended solids ratio (sCOD:VSS) were used as indicators of nitrifying bacteria activity and the stress on the culture, respectively. These parameters were inversely related to nitrogen recovery rates and biomass productivity and could thus help to prevent possible culture deterioration

Wastewater nutrient removal in a mixed microalgae bacteria culture: effect of light and temperature on the microalgae bacteria competition

[EN] The aim of this study was to evaluate the effect of light intensity and temperature on nutrient removal and biomass productivity in a microalgae¿bacteria culture and their effects on the microalgae¿bacteria competition. Three experiments were carried out at constant temperature and various light intensities: 40, 85 and 125¿µE¿m¿2¿s¿1. Other two experiments were carried out at variable temperatures: 23¿±¿2°C and 28¿±¿2°C at light intensity of 85 and 125¿µE¿m¿2¿s¿1, respectively. The photobioreactor was fed by the effluent from an anaerobic membrane bioreactor. High nitrogen and phosphorus removal efficiencies (about 99%) were achieved under the following operating conditions: 85¿125¿µE¿m¿2¿s¿1 and 22¿±¿1°C. In the microalgae¿bacteria culture studied, increasing light intensity favoured microalgae growth and limited the nitrification process. However, a non-graduated temperature increase (up to 32°C) under the light intensities studied caused the proliferation of nitrifying bacteria and the nitrite and nitrate accumulation. Hence, light intensity and temperature are key parameters in the control of the microalgae¿bacteria competition. Biomass productivity significantly increased with light intensity, reaching 50.5¿±¿9.6, 80.3¿±¿6.5 and 94.3¿±¿7.9¿mgVSS¿L¿1¿d¿1 for a light intensity of 40, 85 and 125¿µE¿m¿2¿s¿1, respectivelyThis research work was possible because of Projects CTM2011-28595-C02-01 and CTM2011-28595-C02-02 [funded by the Spanish Ministry of Economy and Competitiveness jointly with the European Regional Development Fund and the Generalitat Valenciana GVA-ACOMP2013/203]. 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Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV

Two-particle angular correlations between unidentified charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum range 0.7 $< p_{\rm{T}, assoc} < p_{\rm{T}, trig} <$ 5.0 GeV/$c$ is examined, to include correlations induced by jets originating from low momen\-tum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range $|\eta|<0.9$. The near-side long-range pseudorapidity correlations observed in high-multiplicity p-Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton--parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p-Pb collisions. Further, the number scales in the intermediate multiplicity region with the number of binary nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/161

Multi-particle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider

Measurements of multi-particle azimuthal correlations (cumulants) for charged particles in p-Pb and Pb-Pb collisions are presented. They help address the question of whether there is evidence for global, flow-like, azimuthal correlations in the p-Pb system. Comparisons are made to measurements from the larger Pb-Pb system, where such evidence is established. In particular, the second harmonic two-particle cumulants are found to decrease with multiplicity, characteristic of a dominance of few-particle correlations in p-Pb collisions. However, when a $|\Delta \eta|$ gap is placed to suppress such correlations, the two-particle cumulants begin to rise at high-multiplicity, indicating the presence of global azimuthal correlations. The Pb-Pb values are higher than the p-Pb values at similar multiplicities. In both systems, the second harmonic four-particle cumulants exhibit a transition from positive to negative values when the multiplicity increases. The negative values allow for a measurement of $v_{2}\{4\}$ to be made, which is found to be higher in Pb-Pb collisions at similar multiplicities. The second harmonic six-particle cumulants are also found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find $v_{2}\{4\} \simeq v_{2}\{6\}\neq 0$ which is indicative of a Bessel-Gaussian function for the $v_{2}$ distribution. For very high-multiplicity Pb-Pb collisions, we observe that the four- and six-particle cumulants become consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and Pb-Pb are measured. These are found to be similar for overlapping multiplicities, when a $|\Delta\eta| > 1.4$ gap is placed.Comment: 25 pages, 11 captioned figures, 3 tables, authors from page 20, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/87

Analyzing factors that influence the folk use and phytonomy of 18 medicinal plants in Navarra

BACKGROUND: This article analyzes whether the distribution or area of use of 18 medicinal plants is influenced by ecological and cultural factors which might account for their traditional use and/or phytonymy in Navarra. This discussion may be helpful for comparative studies, touching as it does on other ethnopharmacological issues: a) which cultural and ecological factors affect the selection of medicinal plants; b) substitutions of medicinal plants in popular medicine; c) the relation between local nomenclature and uses. To analyze these questions, this paper presents an example of a species used for digestive disorders (tea and camomile: Jasonia glutinosa, J. tuberosa, Sideritis hyssopifolia, Bidens aurea, Chamaemelum nobile, Santolina chamaecyparissus...), high blood pressure (Rhamnus alaternus, Olea europaea...) or skin diseases (Hylotelephium maximum, H. telephium, Anagallis arvensis, A. foemina). METHODS: Fieldwork began on January 2004 and continued until December 2006. During that time we interviewed 505 informants in 218 locations in Navarra. Information was collected using semi-structured ethnobotanical interviews, and we subsequently made maps using Arc-View 8.0 program to determine the area of use of each taxon. Each map was then compared with the bioclimatic and linguistic map of Navarra, using the soil and ethnographic data for the region, and with other ethnobotanical and ethnopharmacological studies carried out in Europe. RESULTS: The results clearly show that ecological and cultural factors influence the selection of medicinal plants in this region. Climate and substrate are the most important ecological factors that influence the distribution and abundance of plants, which are the biological factors that affect medicinal plant selection. CONCLUSION: The study of edaphological and climatological factors, on the one hand, and culture, on the other, can help us to understand why a plant is replaced by another one for the same purposes, either in the same or in a different area. In many cases, the cultural factor means that the use of a species is more widespread than its ecological distribution. This may also explain the presence of synonyms and polysemies which are useful for discussing ethnopharmacological data

Comparative genomics of the bacterial genus Listeria: Genome evolution is characterized by limited gene acquisition and limited gene loss

<p>Abstract</p> <p>Background</p> <p>The bacterial genus <it>Listeria </it>contains pathogenic and non-pathogenic species, including the pathogens <it>L. monocytogenes </it>and <it>L. ivanovii</it>, both of which carry homologous virulence gene clusters such as the <it>prfA </it>cluster and clusters of internalin genes. Initial evidence for multiple deletions of the <it>prfA </it>cluster during the evolution of <it>Listeria </it>indicates that this genus provides an interesting model for studying the evolution of virulence and also presents practical challenges with regard to definition of pathogenic strains.</p> <p>Results</p> <p>To better understand genome evolution and evolution of virulence characteristics in <it>Listeria</it>, we used a next generation sequencing approach to generate draft genomes for seven strains representing <it>Listeria </it>species or clades for which genome sequences were not available. Comparative analyses of these draft genomes and six publicly available genomes, which together represent the main <it>Listeria </it>species, showed evidence for (i) a pangenome with 2,032 core and 2,918 accessory genes identified to date, (ii) a critical role of gene loss events in transition of <it>Listeria </it>species from facultative pathogen to saprotroph, even though a consistent pattern of gene loss seemed to be absent, and a number of isolates representing non-pathogenic species still carried some virulence associated genes, and (iii) divergence of modern pathogenic and non-pathogenic <it>Listeria </it>species and strains, most likely circa 47 million years ago, from a pathogenic common ancestor that contained key virulence genes.</p> <p>Conclusions</p> <p>Genome evolution in <it>Listeria </it>involved limited gene loss and acquisition as supported by (i) a relatively high coverage of the predicted pan-genome by the observed pan-genome, (ii) conserved genome size (between 2.8 and 3.2 Mb), and (iii) a highly syntenic genome. Limited gene loss in <it>Listeria </it>did include loss of virulence associated genes, likely associated with multiple transitions to a saprotrophic lifestyle. The genus <it>Listeria </it>thus provides an example of a group of bacteria that appears to evolve through a loss of virulence rather than acquisition of virulence characteristics. While <it>Listeria </it>includes a number of species-like clades, many of these putative species include clades or strains with atypical virulence associated characteristics. This information will allow for the development of genetic and genomic criteria for pathogenic strains, including development of assays that specifically detect pathogenic <it>Listeria </it>strains.</p