Biomedical subjects

J M Audic

Publications and source records attributed to J M Audic.

13 recordsLinked to original sources

PubMed2005

Oxidative and thermo-oxidative co-treatment with anaerobic digestion of excess municipal sludge.

The effect of oxidative and thermo-oxidative co-treatment of excess municipal sludge was investigated. A mixture of primary and waste activated sludge was anaerobically treated using two different configurations: i) two stages and ii) a single stage with recycling. Oxidative or thermo-oxidative co-treatment placed in between the reactor or in the recycle line was studied. A two-stage configuration with no co-treatment served as a control and resulted in 50.1% overall solids removal. Compared to the control, an increase in solids removal of 10.8 and 2.7% was observed when oxidative co-treatment was placed between reactors and in the recycle line respectively. When thermo-oxidative co-treatment was placed between the two stages or in the recycle line an increase in solids removal of 25.1 and 26.9% respectively was observed. The performances of the different configurations were also evaluated with parameters such as COD, TKN, ammonia, and fecal coliform concentration.

Bacteria, Anaerobic↗

PubMed2005

Leachate pre-treatment strategies before recirculation in landfill bioreactors.

Nitrified leachate recirculation represents a promising strategy for a more sustainable landfill management. Our objective was to determine the reactions involved in nitrate reduction in municipal solid waste batch biodegradation tests. Anaerobic digestion of waste in the three control reactors showed a good reproducibility. In two test reactors, nitrate was added at various moments of the waste degradation process. We observed that: (1) H2S concentration controlled the nitrate reduction pathway: above a certain threshold of H2S, dissimilatory nitrate reduction to ammonium (DNRA) replaced denitrification. (2) N2O/N2 ratio varied with the organic carbon concentration: the lower the easily biodegradable carbon concentration, the higher the N2O/N2 ratio. (3) N2 was consumed after denitrification. The possibility of a nitrogen fixation reaction in the presence of NH4 is discussed. Nitrified leachate recirculation during acidogenesis should be avoided because of higher H2S production which could induce DNRA.

Bacteria, Anaerobic↗

PubMed2004

Measurement of glutathione in activated sludges.

Thermal, electric, mechanical or oxidative stress seem a promising way to reduce the production of excess activated sludge during biological wastewater treatment. However, the adaptation and the resistance of the sludge microbial ecosystem to stress conditions is a major question as it may definitively limit the effect of some treatments. Defence mechanisms developed by aerobic organisms, in particular, in response to oxidative stress involve various antioxidant activities and compounds such as glutathione. An HPLC method was developed for measuring reduced and total glutathione (GSH and GSHt) in perchloric acid sludge extracts. The method was sensitive, highly specific and validated for linearity, precision and recovery. Considering the extraction yield and the oxidation of GSH during extract storage, the measured GSH concentration was estimated to represent 60% of the GSH content from activated sludges. GSHt ranged from 0.32 to 3.34micromolg(-1) volatile solids and the GSH/GSHt ratio ranged from 32% to 91%. Measurements performed on sludges stressed in precise conditions selected to reach a reduction of sludge production showed a decrease of GSH and GSHt concentrations with thermal, mechanical, electric and ozone stress.

Bacteria, Aerobic↗

PubMed2003

Impact of soluble organic compounds on permeate flux in an aerobic membrane bioreactor.

The relative impact of mixed liquor suspended solids and soluble organic compounds on the permeate flux in an aerobic membrane bioreactor (MBR) were investigated during long-term operation. A statistical correlation analysis performed on data obtained over an approximately 700 day operational period revealed that permeate flux was strongly correlated to soluble organic compounds such as soluble sugars and proteins and was not correlated to total mixed liquor COD. Organic compounds with sizes less than 0.10 microm exhibited the strongest correlation to permeate flux. Specific filtration tests conducted on the MBR showed that the effect of soluble COD was most pronounced in the range of 110-210 mg 1(-1). A critical level of soluble COD was established at 500 mg 1(-1) after which point no correlation was present. The effluent quality remained high throughout the study at below 5 mg 1(-1) total COD, indicating that the membrane was able to retain most organic compounds regardless of mixed liquor soluble COD content. It was concluded that MBR permeate fluxes are enhanced when operating at conditions where bio-degradation is improved and soluble organic compounds are reduced.

Bacteria, Aerobic↗

PubMed2002

Operating conditions for the determination of the biochemical acidogenic potential of wastewater.

The aim of this work was to study the test conditions for the determination of the biochemical acidogenic potential (BAP) of wastewater, which should be useful to predict the performance of enhanced biological phosphorus removal (EBPR). Proposed operating conditions for a simple and reproducible BAP test in 250 ml serum bottles (equipped with black butyl stoppers and magnetic bars) are: use of either frozen or fresh water, no inoculum addition, fermentation carried out in the dark during 15 days, addition of 1 mM bromo-ethane sulfonate (BES) and 2 mM barium chloride (BaCl2), stirring speed strong enough to maintain vortex conditions, no pH control and controlled temperature of 20 degrees C.

Bioreactors↗

PubMed2002

Nitrogen removal in a SBR using the OGAR process control system.

OGAR is an industrial process control system that utilises on-line redox measurements to control the aeration sequence in an activated sludge process. Compared to conventional process control systems that use dissolved oxygen, OGAR makes use of redox as a control parameter during both aerobic and anoxic conditions. This paper reports on its first application in a sequencing batch reactor. The principal aim of this project is to demonstrate the capability of OGAR to achieve concentrations of total nitrogen in the treated effluent of less than 10 mg/L, which are typically stipulated by Queensland's Environmental Protection Agency (EPA). In this study the use of the control system resulted in the following SBR performance: consistent effluent total nitrogen less than 5.0 mg/L; ammonia concentration reduced from 31.6 mg/L to 0.32 mg/L, effluent nitrate 2.8 mg/L; DO setpoint 1.5 mg/L had 10% higher effluent total nitrogen compared to DO setpoint 4.0 mg/L and redox end-points for nitrification 400 mV, denitrification 150 mV.

Ammonia↗

PubMed2002

Comparison of aerobic and anoxic phosphorus uptake in NDBEPR systems (UCT and ENBNRAS).

Two Nitrification-Denitrification Biological Excess Phosphorus Removal (NDBEPR) systems have been operated for 8.5 months in order to compare their Biological Excess Phosphorus Removal (BEPR) performance. One of these systems, i.e. the University of Cape Town (UCT) system, exhibits mainly aerobic P uptake while the External Nitrification Biological Nutrient Removal Activated Sludge (ENBNRAS) system is characterised by high anoxic P uptake. It was observed that when operating with predominantly aerobic P uptake, the UCT system released more P than the ENBNRAS system, even though it had a lower anaerobic mass fraction. However, when the influent TKN/COD was high, i.e. > 0.1, anoxic P uptake also occurred in the UCT system and P release dropped to lower levels than in the ENBNRAS. Accordingly, P uptake of the UCT system was 5 mg P/l influent higher than that of the ENBNRAS system, when it was predominantly aerobic, but 9 mg P/l influent lower when anoxic P uptake occurred. As a result, the UCT system achieved superior P removal when aerobic P uptake was predominant (23% higher), but when high influent TKN/COD promoted anoxic P uptake the P removal of the UCT system was poorer than that of the ENBNRAS system. This study clearly showed that anoxic P uptake is not beneficial to NDBEPR systems.

Bacteria, Aerobic↗

PubMed2001

Prediction of mean circulation velocity in oxidation ditch.

In wastewater treatment, oxidation ditches are used for the removal of carbon and nitrogen of activated sludge. The control of the single-phase flow is essential to the optimisation of the whole process. Among the two global functioning parameters (mean liquid velocity Uc, power dissipated per unit of volume P/V), the mean circulation velocity can be recommended. Indeed, the values of the power dissipated per unit of volume P/V obtained in different scale plant show that the industrial criterion on P/V leads to an overdesign of channel. Therefore a mean liquid circulation velocity Uc created by horizontal impellers must be maintained inside the ditch. In order to predict the velocity Uc, a model has been proposed based on the Equations of the continuity and motion and using a few simple parameters. Experiments were carried out on pilot plant (1 m3) and full scale ditches (860, 1400 and 2800 m3) in which the characteristics of the mixing system and the dimensions of channels were varied. A good agreement was observed between the model predictions and experimental data for the mean circulation velocity Uc.

Models, Theoretical↗

PubMed2001

Changes in the organic composition of wastewater during biological treatment as studied by NMR and IR spectroscopies.

Despite its importance, relatively little is known about the composition and fate of wastewater organic matter (OM) in treatment plants. Monitoring the chemical changes in OM during activated sludge treatment can improve our knowledge of the processes involved in the biological elimination of OM. Direct chemical analyses of treated water OM typically account for about 20% of the OM, and structural information was obtained in this study using Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FTIR) spectroscopic techniques. Distinct changes in the OM during wastewater biological treatment were underlined. 13C and 1H NMR showed that aromatic carbons were minor constituents of the samples. Alkyl chains exhibited a more highly branched character in treated water, as compared to long chain aliphatic carbons present in wastewater. Carboxyl signals in the 13C NMR spectrum of wastewater could be due to peptide bonds in proteins, whereas in the treated water spectrum, this signal could be related to the presence of non-proteinaceous nitrogen. Besides the non-degraded compounds, treated water OM could contain recondensation products of simple molecules. Their refractory character probably derives from their complex structures rather than from particular chemical functions, as suggested by the lack of fundamental differences in the chemical structures of wastewater and treated water OM.

Biodegradation, Environmental↗

PubMed2001

Hydrolysis of wastewater colloidal organic matter by extracellular enzymes extracted from activated sludge flocs.

Enzymatic activities associated with the exopolymeric substances (EPSs) extracted from activated sludges were tested for their ability to hydrolyse the organic colloidal fraction of wastewater. Bacteria extracted with EPS and concentrated by wastewater microfiltration were inhibited with NaN3 or KCN. The protein hydrolysis mainly resulted from the enzymatic activity of EPS, whereas the glycolytic activity was mainly present in the organic colloidal fraction of the wastewater.

Biopolymers↗

PubMed2001

Mass balance for on-line alphakLa estimation in activated sludge oxidation ditch.

The capacity of an aeration system to transfer oxygen to a given activated sludge oxidation ditch is characterised by the alphakLa parameter. This parameter is difficult to measure under normal plant working conditions. Usually this measurement involves off-gas techniques or static mass balance. Therefore an on-line technique has been developed and tested in order to evaluate alphakLa. This technique deduces alphakLa from a data analysis of low cost sensor measurement: two flow meters and one oxygen probe. It involves a dynamic mass balance applied to aeration cycles selected according to given criteria. This technique has been applied to a wastewater treatment plant during four years. Significant variations of the alphakLa values have been detected while the number of blowers changes. This technique has been applied to another plant during two months.

Environmental Monitoring↗

PubMed1998

Detection of infectious enteroviruses, enterovirus genomes, somatic coliphages, and Bacteroides fragilis phages in treated wastewater.

In this study, three types of treated wastewater were tested for infectious enteroviruses, the enterovirus genome, somatic coliphages, and Bacteroides fragilis phages. The aim of this work was to determine whether the presence of the two types of bacteriophages or of the enterovirus genome was a good indicator of infectious enterovirus contamination. The enterovirus genome was detected by reverse transcription-polymerase chain reaction. Infectious enteroviruses were quantified by cell culturing (BGM cells), and the bacteriophages were quantified by plaque formation on the host bacterium (Escherichia coli or B. fragilis) in agar medium. Forty-eight samples of treated wastewater were analyzed. Sixteen samples had been subjected to a secondary treatment for 8 to 12 h (A), 16 had been subjected to a secondary treatment for 30 h (B1), and 16 had been subjected to both secondary and tertiary treatments (B2). The mean concentrations of somatic coliphages were 4.9 x 10(4) PFU . liter-1 for treatment line A, 9.8 x 10(3) PFU . liter-1 for B1, and 1.4 x 10(3) PFU . liter-1 for B2, with all the samples testing positive (100%). The mean concentrations of B. fragilis phages were 1.7 x 10(3) PFU . liter-1 for A (100% positive samples), 17 to 24 PFU . liter-1 for B1 (44% positive samples), and 0.8 to 13 PFU . liter-1 for B2 (6% positive samples). The mean concentrations of infectious enteroviruses were 4 most probable number of cytopathogenic units (MPNCU) . liter-1 for A (31% positive samples) and <1 MPNCU . liter-1 for B1 and B2 (0% positive samples). The percentages of samples testing positive for the enterovirus genome were 100% for A, 56% for B1, and 19% for B2. The percentages of samples testing positive for the enterovirus genome were significantly higher than those for infectious enteroviruses. This finding may have been due to the presence of noninfectious enteroviruses or to the presence of infectious enteroviruses that do not multiply in BGM cell cultures. However, under our experimental conditions, nondetection of the genome implies the absence of infectious viruses. There was a significant correlation between the concentration of somatic coliphages or B. fragilis phages and the presence of infectious enteroviruses or the presence of the enterovirus genome. However, the somatic coliphage concentration did not lead to fluctuations in the infectious enterovirus concentration, whereas the B. fragilis phage concentration did.

Bacteriophages↗

PubMedDate not supplied

A comparative pilot-scale study of the performance of conventional activated sludge and membrane bioreactors under limiting operating conditions.

The behavior of the conventional activated-sludge (CAS) process was compared to that of the membrane bioreactor (MBR) process under limiting operating conditions; that is, at a low solids retention time (SRT) and hydraulic residence time (HRT). The SRT was varied from 2 to 7 days, and the HRT ranged from 5 to 18 hours. The comparison was carried out in terms of nitrification and denitrification kinetics and in terms of the carbon and nitrogen removal performance of these processes. The study involved two pilot-scale units: a CAS unit with a 9-m3 aeration tank and a 225-L MBR. Both of these units were installed and run under real process conditions at a wastewater treatment plant in Evry, France. In the case of the MBR process, the specific nitrification rates, rN, and the specific denitrification rates, rDN, increased as SRT was reduced from 6.5 days to 2 days. This trend was reversed and the rN and rDN decreased only when the HRT was reduced to 5 hours. A similar behavior was observed in the case of the CAS process, although rN and rDN increased only when the SRT was reduced to as low as 4 days; below this value, the rates dropped considerably. It seems that the presence of the membrane renders the MBR more robust by preventing the washout of nitrifiers at low SRT and HRT. Besides the structure and size distribution of the MBR, flocs are more favorable to intraparticle mass transfer than those of the CAS process and could explain the higher nitrification kinetics observed with the MBR process. In all cases, the carbon and nitrogen removal performance of the MBR process was better than that of the CAS system.

Biomass↗