Biomedical subjects

D Patureau

Publications and source records attributed to D Patureau.

7 recordsLinked to original sources

PubMed2006

Impact of anaerobic and aerobic processes on polychlorobiphenyl removal in contaminated sewage sludge.

Aerobic and anaerobic biodegradation of six priority PCBs was investigated in continuous stirred tank reactors fed with naturally contaminated sewage sludge. Anaerobic and aerobic abiotic losses were higher for the lightly chlorinated PCBs but remained for all PCBs below 20%. Under strict methanogenic conditions, PCB removals were about 40% whatever PCB molecular weight or their degree of chlorination. However, considering abiotic losses, the heaviest PCBs were more efficiently anaerobically biodegraded probably because of higher dechlorination rates. The aerating sludge process enhanced removal of the lightest chlorinated PCBs from 40% up to 100%, while removal rates of the heaviest PCBs remained around 40%. Although the mesophilic aerobic process exhibits better removal efficiencies because of operating conditions, the results suggest that PCB biodegradation was strongly limited by their bioavailability in naturally contaminated sludge, under both redox conditions. Indeed, since PCB removal was closely linked to the solid reduction rates, PCB bioavailability was likely the limiting factor for biodegradation. As a consequence, the raw PCB concentrations (in mg kg(-1) (dry weight)) which are concerned by legislative procedures did not decrease sufficiently in both processes to reach a limit value fulfilling the current French/European regulation about PCB contents in sewage sludge before spreading on agricultural land.

Aerobiosis↗

PubMed2003

Enhancement of polycyclic aromatic hydrocarbons removal during anaerobic treatment of urban sludge.

Anaerobically stabilized sewage sludge has potential to partially substitute synthetic fertilizers. The main risk with the recycling of urban sludge on agricultural soils is the accumulation of unwanted products, such as trace metals and organic micropollutants. In this context, the polycyclic aromatic hydrocarbons (PAHs) are particularly monitored because of their toxic properties at low concentrations and their high resistance to biological degradation. The aim of the present study was to optimize PAHs removal during anaerobic digestion of contaminated sewage sludge. Thirteen PAHs were monitored in laboratory-scale anaerobic bioreactors under mesophilic (35 degrees C) and thermophilic (55 degrees C) methanogenic conditions. Abiotic losses were statistically significant for the lightest PAHs, such as fluorene, phenanthrene and anthracene. It was shown that PAH removal was due to a specific biological activity. Biological PAHs removal was significantly enhanced by an increase of the temperature from 35 degrees C to 55 degrees C, especially for the heaviest PAHs. Bioaugmentation experiment was also performed by addition of a PAH-adapted bacterial consortium to a non-acclimated reactor. Significant enhancement of PAHs removal was observed. It was finally shown that PAH removal efficiencies and methanogenic performances were closely linked. The rate of biogas production may be used as an indicator of bacterial activity on PAH removal.

Bacteria, Anaerobic↗

PubMed2001

Combined phosphate and nitrogen removal in a sequencing batch reactor using the aerobic denitrifier, Microvirgula aerodenitrificans.

A phosphate removal sludge was bioaugmented with the aerobic denitrifier, Microvirgula aerodenitrificans in order to reduce the nitrate produced during the aerobic nitrifying-phosphate uptake phase. Fluorescent in situ hybridization (FISH) was used to follow the fate of the added strain. In order to maintain the pure strain in the complex ecosystem, diverse physiological and kinetic based strategies of bioaugmentation were tested under the sequencing batch reactor (SBR) type culture. The nature of the M. aerodenitrificans inoculum (adapted to nitrate-aerobic conditions or to anoxic one) had no influence on the SBR performances and did not enhance aerobic denitrifying performances. The optimum quantity of the added strain (10% of the total biomass) seemed to have much more positive influence on the long term maintenance of the pure strain than on the SBR performances. A small but daily supply of M. aerodenitrificans gave exactly the same result than a massive and 1-day supply, i.e. no enhancement of performances and no amelioration of the length of maintenance. A continuous supply of carbon during the first hour of the aerobic phase combined to a 10% supply of M. aerodenitrificans gave the best compromise in terms of phosphate removal, nitrification and aerobic denitrification performances. It was accompanied too by a decreased number of the ammonia and nitrite-oxidizing bacteria and a modification of the nitrite-oxidizing floc structure. FISH on M. aerodenitrificans revealed that (i) before bioaugmentation, the strain was already present in the phosphate removal sludge and (ii) the added bacteria almost disappeared from the reactor after 16 HRT. In a last experiment, M. aerodenitrificans embedded in alginate beads allowed enhancement of both aerobic denitrifying performances and length of strain maintenance.

Aerobiosis↗

PubMed2000

Aerobic Denitrifiers Isolated from Diverse Natural and Managed Ecosystems.

Twenty-eight bacterial strains were isolated from an ecosystem adapted to fluctuating oxic-anoxic conditions. This ecosystem comprised a mixture of different natural and wastewater treatment environments. Among the 28 strains isolated, 10 exhibited aerobic denitrifying activity, i.e., co-respiration of oxygen and nitrate and simultaneous production of nitrite by 4 of them and of nitrogen gas by the remaining 6. Comparisons between the 16S rDNA sequences of the 10 strains showed that 3 of them were identical to M. aerodenitrificans, whereas RAPD profiles showed that the 3 strains were identical to each other but that they were different from M. aerodenitrificans. This implies that alternating aerobic-anoxic conditions allowed the isolation of a new strain of this aerobic denitrifier. Moreover, other denitrifying bacteria belonging to the genera Paracoccus, Thiobacillus, Enterobacter, Comamonas, and Sphingomonas were isolated in this way. These data imply that a wide variety of bacteria are able to carry out this type of metabolism. M. aerodenitrificans was also detected in methanogenic, denitrifying, nitrifying, phosphate removal, and activated sludge ecosystems by two-step PCR amplification. After 4 months of acclimation to oxic-anoxic phases, the strain was also detected in a canal and in a pond. This suggests that there is no specific natural ecological niche for aerobic denitrifiers but, as soon as selective pressure such as alternating aeration conditions is applied, this metabolism is amplified.

Journal Article↗

PubMed2000

Effect of dissolved oxygen and carbon-nitrogen loads on denitrification by an aerobic consortium.

Four samples of natural ecosystems and one sample from an activated sludge treatment plant were mixed together and progressively adapted to alternating aerobic/anoxic phases in the presence of nitrate in order to enrich the microflora in aerobic denitrifiers. Aerobic denitrifying performances of this mixed ecosystem at various dissolved oxygen concentrations and various carbon-nitrogen loads were evaluated and compared to those obtained with the aerobic denitrifier Microvirgula aerodenitrificans. The consortium and the pure strain exhibited an aerobic denitrifying activity at air saturation conditions (7 mg dissolved oxygen 1(-1)), i.e. there was co-respiration of the two electron acceptors with significant specific nitrate reduction rates. Dissolved oxygen concentrations had no influence on denitrifying performances above a defined threshold: 0.35 mg l(-1) for the consortium and 4.5 mg l(-1) for M. aerodenitrificans respectively. Under these thresholds, decreasing the dissolved oxygen concentrations enhanced the denitrifying activity of each culture. The higher the carbon and nitrogen loads, the higher the performance of the aerobic denitrifying ecosystem. However, for M. aerodenitrificans, the nitrate reduction percentage was affected more by variations in nitrogen load than in carbon load.

Aerobiosis↗

PubMed2000

Ecological study of a bioaugmentation failure.

A nitrifying sequencing batch reactor was inoculated twice with the aerobic denitrifying bacterium Microvirgula aerodenitrificans and fed with acetate. No improvement was obtained on nitrogen removal. The second more massive inoculation was even followed by a nitrification breakdown, while at the same time, nitrification remained stable in a second reactor operated under the same conditions without bioaugmentation. Fluorescent in situ hybridization with rRNA-targeted probes revealed that the added bacteria almost disappeared from the reactor within 2 days, and that digestive vacuoles of protozoa gave strong hybridization signals with the M. aerodenitrificans-specific probe. An overgrowth of protozoa, coincident with the disappearance of free-living bacteria, was monitored by radioactive dot-blot hybridization only in the bioaugmented reactor. Population dynamics were analysed with a newly developed in situ quantification procedure of the probe-targeted bacteria. The nitrifying groups of bacteria decreased in a similar way in the bioaugmented and non-bioaugmented reactors. Other bacterial groups evolved differently. The involvement of different ecological parameters are discussed separately for each reactor. These results underline the importance of predator-prey interaction and illustrate the undesirable effects of massive bioaugmentation.

Animals↗

PubMed1998

Microvirgula aerodenitrificans gen. nov., sp. nov., a new gram-negative bacterium exhibiting co-respiration of oxygen and nitrogen oxides up to oxygen-saturated conditions.

A denitrifier micro-organism was isolated from an upflow denitrifying filter inoculated with an activated sludge. The cells were Gram-negative, catalase- and oxidase-positive curved rods and very motile. They were aerobic as well as anoxic heterotrophs that had an atypical respiratory type of metabolism in which oxygen and nitrogen oxides were used simultaneously as terminal electron acceptors. The G&C content was 65 mol%. Our isolate was phenotypically similar to Comamonas testosteroni, according to classical systematic classification systems. However, a phylogenetic analysis based on the 165 rRNA sequence showed that the aerobic denitrifier could not be assigned to any currently recognized genus. For these reasons a new genus and species, Microvirgula aerodenitrificans gen. nov., sp. nov., is proposed, for which SGLY2T is the type strain.

Base Sequence↗