Biomedical subjects

J L Rols

Publications and source records attributed to J L Rols.

7 recordsLinked to original sources

PubMed2003

Activated sludge as inoculum for ready biodegradability testing: effect of source.

Results of ready biodegradability tests (RBT) are barely reproducible owing to a well-known lack of definition in inoculum source and quality. In this study, the degree of variability expected when only activated sludges are used as inoculum source was investigated. For this, the characteristics of activated sludges collected in municipal wastewater treatment plants operating at various massic loading rates (MLR; 0.1, 0.5 and 0.9 kgBOD5 kgVSS(-1) d(-1)) were compared. In order to provide suitable cellular densities for RBT, inocula were obtained after settling of activated sludges and analyzed in terms of active and cultivable cell densities, dehydrogenasic activity, BOD5 and a general profile of hydrolytic enzymes. In our analysis, biomass obtained from the High-MLR treatment plant constituted the inoculum having the highest biodegradation potential both with respect to microbial densities and to enzyme activities. This biomass also yielded the fastest biodegradation kinetics in dodecyl benzene sulfonate RBT. An attempt of biomass homogenization of inocula on the basis of cultivable cell density and dehydrogenasic activity gave negative results with this chemical compound. Since, in practice, restriction of activated sludge sources may be difficult, our results emphasize the importance of further studies aimed at homogenization of inoculum quality and quantity.

Biodegradation, Environmental↗

PubMed2001

Excess sludge reduction in activated sludge processes by integrating biomass alkaline heat treatment.

With new EC regulations, alternative treatment and disposal techniques of the excess sludge produced by activated sludge wastewater treatment plants have to be developed. To decrease activated sludge production yield, microbial cell lysis can be amplified to enhance cryptic growth (biomass growth on lysates). Cell breakage techniques (thermal, alkaline and a combination) were studied to generate Ralstonia eutropha (strain model) and waste activated sludge lysates and to evaluate their biodegradability. Gentle treatment conditions by alkaline waste treatment (20 min at 60 degrees C and pH 10 by NaOH addition) allowed waste activated sludge to be solubilized by a two step process (instantaneous and post-treatment) giving a dissolved organic carbon released by the total suspended solids treated of 267 mgDOC x g(-1)TSS. The biodegradation of the soluble fraction of the lysates by fresh sludge reached 75 and 90% after 48 and 350 hrs of incubation respectively. A validation on a laboratory scale by insertion of a liquor alkaline heat treatment loop in a biological synthetic wastewater treatment process was carried out. A reduction of 37% of the excess sludge was obtained without altering the purification yield of the process.

Biodegradation, Environmental↗

PubMed2000

Growth rate influences reductive biodegradation of the organophosphorus pesticide demeton by Corynebacterium glutamicum.

The organophosphorous pesticide, demeton-S-methyl was transformed by Corynebacterium glutamicum in co-metabolism with more readily degradable substrates. Glucose, acetate and fructose were tested as growth substrates, and the highest demeton-S-methyl biotransformation average rate (0.78 mg l(-1) h(-1)) and maximum instantaneous rate (1.4 mg l(-1) h(-1)) were achieved on fructose. This higher efficiency seems to be linked to the atypical behavior of C. glutamicum grown on fructose, characterized by a prolonged period of accelerating growth instead of a constant growth rate observed on glucose or acetate. More precisely, for growth rates in the 0.1-0.4 h(-1) range, a direct coupling between the specific demeton-S-methyl consumption rate and the growth rate was demonstrated on fructose during batch-, steady state continuous- or continuous cultures with a controlled transient growth rate (accelerostat technology). The demeton-S-methyl biotransformation was more favoured during an acceleration phase of the growth rate.

Biodegradation, Environmental↗

PubMed2000

Reductive cleavage of demeton-S-methyl by Corynebacterium glutamicum in cometabolism on more readily metabolizable substrates.

Corynebacterium glutamicum is able to biotransform demeton-S-methyl, an organophosphorus compound, during cometabolism with more readily metabolizable substrates. Among the cosubstrates used, fructose is the growth substrate that is most favorable for demeton-S-methyl biotransformation. The reaction mechanism of demeton-S-methyl biotransformation involves reductive cleavage of an S-C bond, which leads to accumulation of dimethyl thiophosphate in the culture medium.

Biodegradation, Environmental↗

PubMed1999

Towards a reduction in excess sludge production in activated sludge processes: biomass physicochemical treatment and biodegradation.

To decrease activated sludge production, microbial cell lysis can be amplified to enhance cryptic growth (biomass growth on lysates). Cell breakage techniques (thermal, alkaline, acid) were studied to generate Alcaligenes eutrophus and sludge lysates and to evaluate their biodegradability. Gentle treatment conditions produced the best results. Complete cell deactivation was obtained for temperatures higher than 55 degrees C. The release kinetics were similar for temperatures varying from 60 degrees C to 100 degrees C. A 20-min incubation was suitable for reaching 80% of the maximum releasable carbon. In thermal-chemical hydrolysis, NaOH was the most efficient for inducing cell lysis. Carbon release was a two-step process. First an immediate release occurred, which was of the same order of magnitude for A. eutrophus and sludge [100-200 mg dissolved organic C (DOC) g total suspended solids (TSS)-1], followed by a post-treatment release. The second step was virtually equivalent to the first for sludge, and weaker for A. eutrophus (< 50 mg DOC g TSS-1). The biodegradability of the soluble fraction, both the immediate and the post-treatment carbon release, was investigated. The optimal degradation yield, obtained with sludge cells, reached 55% after 48 h of incubation and 80% after 350 h. The most consistent lysis and biodegradation results occurred at pH 10 and 60 degrees C after a 20-min incubation.

Alcaligenes↗

PubMed1999

A kinetic model incorporating energy spilling for substrate removal in substrate-sufficient batch culture of activated sludge.

Batch assays are currently used to study the kinetic behavior of microbial growth. However, it has been shown that the outcome of batch experiments is greatly influenced by the initial ratio of substrate concentration (S(o)) to biomass concentration (Xo). Substrate-sufficient batch culture is known to have mechanisms of spilling energy that lead to significant nongrowth-associated substrate consumption, and the Monod equation is no longer appropriate. By incorporating substrate consumption associated with energy spilling into the balance of the substrate oxidation reaction, a kinetic model for the observed specific substrate consumption rate was developed for substrate-sufficient batch culture of activated sludge, and was further verified by experimental data. It was demonstrated that the specific substrate consumption rate increased with the increase of the S(o)/Xo ratio, and the majority of substrate was consumed through energy spilling at high S(o)/Xo ratios. It appears that the S(o)/Xo ratio is a key parameter in regulating metabolic pathways of microorganisms.

Bacteria, Aerobic↗

PubMed1989

Enhancement of oxygen transfer rates in fermentation using oxygen-vectors.

Oxygen transfer is one of the bottlenecks in conventional fermentation technology and it has so far been almost totally overlooked with regards to high cell densities and immobilized cells. This review presents some new concepts to improve oxygen supply in aerobic fermentations, especially the use of oxygen-vectors. The oxygen-vectors generally used are liquids which are insoluble in the fermentation media. Their utilization in an emulsified form can significantly increase the oxygen transfer coefficient between gas and aqueous phases. It seems that the vector acts as an active intermediate in the oxygen transport from gas bubbles to aqueous phase, but the mechanisms involved in this unconventional technique of aeration are not yet known.

Journal Article↗