Steady-state and transient-state performance of a biotrickling filter treating chlorobenzene-containing waste gas.

Biotrickling filter (BTF) technology was applied for the treatment of waste gas containing a mixture of chlorobenzene and 1,2-dichlorobenzene. An adapted microbial community was immobilised on a structured packing material. The strategy followed was to reach high removal efficiencies at initially low mass loading rates followed by an increase of the latter. This procedure was successful and resulted in a short start-up period of only 2 weeks. A 3-month operation under steady-state conditions showed good performance, with >95% removal efficiency at a mass loading rate of 1,800 g m(-3) day(-1). Dimensionless concentration profiles showed that the chlorobenzenes were simultaneously degraded. Low dissolved organic carbon of 15 mg l(-1) and stoichiometric chloride concentrations in the trickling liquid indicated complete mineralisation of the pollutant. Transient-state experiments with five times higher mass loading rates caused a decrease in the removal efficiency that recovered rapidly once the mass loading rate returned to its original steady-state level. A progressive increase of the mass loading rate in a long-term performance experiment showed that the removal efficiency could be kept stable between 95 and 99% at loads of up to 5,200 g m(-3) day(-1) over several days. Above this mass loading rate, the elimination capacity did not increase any further. These results demonstrated that with a well-adapted inoculum and optimal operation parameters, a BTF system with excellent performance and stability that efficiently removes a mixture of chlorobenzene vapours from air can be obtained.

Improvement of acetate production from lactose by growing Clostridium thermolacticum in mixed batch culture.

AIMS: The objective of this study was to increase the acetate production by Clostridium thermolacticum growing on lactose, available as a renewable resource in the milk and whey permeate from the cheese industry. METHODS AND RESULTS: Experiments for increased acetate productivity by thermophilic anaerobes grown on lactose were carried out in batch cultures. Lactose at concentration of 30 mmol l(-1) (10 g l(-1)) was completely degraded by Cl. thermolacticum and growth rate was maximal. High concentrations of by-products, ethanol, lactate, hydrogen and carbon dioxide were generated. By using an efficient hydrogenotroph, Methanothermobacter thermoautotrophicus, in a defined thermophilic anaerobic consortium (58 degrees C) with Cl. thermolacticum and the acetogenic Moorella thermoautotrophica, the hydrogen partial pressure was dramatically lowered. As a consequence, by-products concentrations were significantly reduced and acetate production was increased. CONCLUSION: Through efficient in situ hydrogen scavenging in the consortium, the metabolic pattern was modified in favour of acetate production, at the expense of reduced by-products like ethanol. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of this thermophilic anaerobic consortium opens new opportunities for the efficient valorization of lactose, the main waste from the cheese industry, and production of calcium-magnesium acetate, an environmentally friendly road de-icer.

BOD5 measurements of water presenting inhibitory Cu2+. Implications in using of BOD to evaluate biodegradability of industrial wastewaters.

In industrial effluents, the presence of an infinite number of possible mixtures of substances and the high variability of chemical conditions ask for an evaluation of biodegradability by a global and simple method. Biological oxygen demand after five days (BOD5) using synthetic wastewater was studied by two different ways: dilution and manometric methods. It can therefore be established that BOD5 obtained by adding manufactured inocula to the synthetic medium (effluent containing known and easily biodegradable substances) is close to the values obtained with inocula taken from the treated effluent of an urban and a rural purification plant. It was found that BOD5 measurement of effluents presenting factors affecting biodegradation, similar of those found in industrial effluents, is very questionable. The BOD is in this case influenced by the synergic and antagonist interactions between numerous and variable parameters like as pH, nature and concentration of inoculum, concentration of nutriments, amount and nature of assimilable substances, presence of toxicants, and presence of nitrification inhibitors, which are typical of real industrial wastewaters.

Concentrating versus non-concentrating reactors for solar photocatalytic degradation of p-nitrotoluene-o-sulfonic acid.

The photocatalytic oxidation of the non-biodegradable p-nitrotoluene-o-sulfonic acid (p-NTS) in homogeneous (photo-Fenton reactions) and heterogeneous (with TiO2) solutions has been studied at a pilot-scale under solar irradiation at the Plataforma Solar de Almeria (PSA). In this study two different reactors were tested: a medium concentrating radiation system (Heliomans, HM) and a non-concentrating radiation system (CPC). Their advantages and disadvantages for p-NTS degradation have been compared and discussed. The degradation rates obtained in the CPC collector are around three times more efficient than in the HM collectors. However, in both systems, 100% of the initial concentration of p-NTS was removed. Kinetic experiments were performed in both systems using TiO2 suspensions. During the photodegradation, the disappearance of p-NTS was followed by HPLC, the mineralization of the solution by the TOC technique, the evolution of NO3-, NO2-, and SO4(2-) concentration by ionic chromatography, the toxicity by the standard Microtox test, and the biodegradability by BOD5 and COD measurements. The obtained results demonstrated the utility of the heterogeneous catalysis (using TiO2 as catalyst) as a pretreatment method that can be followed by a biological process.

Photochemical-biological treatment of a real industrial biorecalcitrant wastewater containing 5-amino-6-methyl-2-benzimidazolone.

5-amino-6-methyl-2-benzimidazolone (AMBI), used in the manufacture of dyes, was characterised as a biorecalcitrant compound by means of different biodegradability tests. In order to enhance the biodegradability of this important pollutant, the application of Advanced Oxidation Process (AOPs) as a pretreatment was explored. Some experiments were addressed to find the most efficient AOP. The systems H2O2/hv, TiO2/H2O2/hv, Fe3+/hv, Fe3+/H2O2 and Fe3+/H2O2/hv were compared. The photo-Fenton system was the most efficient and the optimal conditions (AMBI, Fe3+, H2O2 concentrations) for the degradation of AMBI were found. During the photo-Fenton degradation, experiments were also made to obtain information concerning the evolution of: (a) organic carbon and initial compound concentration; (b) the oxidation state; (c) the toxicity; (d) the biodegradability; and (e) the chemical nature of the intermediates. These analyses show that the solution resulting from the treatment of AMBI is biologically compatible and complete mineralisation can be performed by biological means. A combined photochemical (Fenton) and biological flow reactor for the degradation of AMBI was successfully operated in continuous mode at laboratory scale. 100% of the initial concentration of AMBI and 80.3% of Dissolved Organic Carbon (DOC) were removed in 3.5 hours of total residence time. Finally, some field experiments under direct sunlight carried out at the Plataforma Solar de Almeria, Spain, demonstrated that this solar catalytic system is an effective treatment for this kind of industrial wastewater.

A procedure for production of adapted bacteria to degrade chlorinated aromatics.

Production of biomass adapted to the degradation of a mixture of chlorobenzene (CB) and 1,2-dichlorobenzene (DCB) was investigated in a batch culture with substrates supplied by pulses. CB and o-DCB concentrations which gave the best adapted biomass productivity were determined and found to be 150 and 30 microl l(-1), respectively. The biomass productivity was 51 mg l(-1) h(-1). The biomass yield was 0.38 g of biomass dry weight per gram of substrate. The pulses of 200 microl CB and 40 microl o-DCB, were inhibitory to the bacterial culture. Among the metabolites, muconic acid was found in large quantities in the medium and in the cells. At a time between two pulses of 60 min, adding 150 microl CB and 30 microl o-DCB per each pulse, 7.6g l(-1) of biomass was obtained. The produced biomass served as an inoculum for the biotrickling filter which treated industrial waste gases contaminated by CBs. The method of adapted biomass production was described using CBs, but the degradation of any other toxic volatile pollutant can be improved using this technique.

Observation of a P/M interconversion of a gold-phosphine helicate via 31P NMR.

Ligands containing P-CH2-CH2-P elements have been shown to form double-stranded helicates whose axis consists of gold atoms with Au...Au contacts; the interconversion of the P and M forms of the helicate [Au3(mu-pp2)2](OTf)3 (pp2 = PhP(CH2CH2PPh2)2) is monitored via 31P NMR.

Acetic acid production from lactose by an anaerobic thermophilic coculture immobilized in a fibrous-bed bioreactor.

An anaerobic thermophilic coculture consisting of a heterofermentative bacterium (Clostridium thermolacticum) and a homoacetogen (Moorella thermoautotrophica) was developed for acetic acid production from lactose and milk permeate. The fermentation kinetics with free cells in conventional fermentors and immobilized cells in a recycle batch fibrous-bed bioreactor were studied. The optimal conditions for the cocultured fermentation were found to be 58 degrees C and pH 6.4. In the free-cell fermentation, C. thermolacticum converted lactose to acetate, ethanol, lactate, H(2) and CO(2), and the homoacetogen then converted lactate, H(2), and CO(2) to acetate. The overall acetate yield from lactose ranged from 0.46 to 0.65 g/g lactose fermented, depending on the fermentation conditions. In contrast, no ethanol was produced in the immobilized-cell fermentation, and the overall acetate yield from lactose increased to 0.8-0.96 g/g lactose fermented. The fibrous-bed bioreactor also gave a higher final acetate concentration (up to 25. 5 g/L) and reactor productivity (0.18-0.54 g/L/h) as compared to those from the free-cell fermentation (final acetate concentration, 15 g/L; productivity, 0.06-0.08 g/L/h). The superior performance of the fibrous-bed bioreactor was attributed to the high cell density (20 g/L) immobilized in the fibrous-bed and adaptation of C. thermolacticum cells to tolerate a higher acetate concentration. The effects of yeast extract and trypticase as nutrient supplements on the fermentation were also studied. For the free-cell fermentation, nutrient supplementation was necessary for the bacteria to grow in milk permeate. For the immobilized-cell fermentation, plain milk permeate gave a high acetate yield (0.96 g/g), although the reactor productivity was lower than those with nutrient supplementation. Balanced growth and fermentation activities between the two bacteria in the coculture are important to the quantitative conversion of lactose to acetic acid. Lactate and hydrogen produced by C. thermolacticum must be timely converted to acetic acid by the homoacetogen to avoid inhibition by these metabolites.

Anaerobic thermophilic fermentation for acetic acid production from milk permeate.

Fermentation of milk permeate to produce acetic acid under anaerobic thermophilic conditions (approximately 60 degrees C) was studied. Although none of the known thermophilic acetogenic bacteria can ferment lactose, it has been found that one strain can use galactose and two strains can use lactate. Moorella thermoautotrophica DSM 7417 and M. thermoacetica DSM 2955 were able to convert lactate to acetate at thermophilic temperatures with a yield of approximately 0.93 g g(-1). Among the strains screened for their abilities to produce acetate and lactate from lactose, Clostridium thermolacticum DSM 2910 was found precisely to produce large amounts of lactate and acetate. However, it also produced significant amounts of ethanol, CO2 and H2. The lactate yield was affected by cell growth. During the exponential phase, acetate, ethanol, CO2 and H2 were the main products of fermentation with an equimolar acetate/ethanol ratio, whereas during the stationary phase, only lactic acid was produced with a yield of 4 mol per mol lactose, thus reaching the maximal theoretical value. When this bacterium was co-cultured with M. thermoautotrophica, lactose was first converted mainly to lactic acid, then to acetic acid, with a zero residual lactic acid concentration and an overall yield of acetate around 80%. Under such conditions, only 13% of the fermented lactose was converted to ethanol by C. thermolacticum.

Escherichia hermanii--a new bacterial strain for chlorobenzene degradation.

A new bacterial strain capable of chlorobenzene degradation has been isolated from sludge of an industrial wastewater treatment plant. The micro-organism is short, rod-shaped, Gram-negative, yellow-pigmented and has been identified as Escherichia hermanii. It was observed that high chlorobenzene concentrations (up to 394 mg l-1) had low toxic effects towards this strain, which was able to degrade chlorobenzene without any previous adaptation.

Growth inhibition of biomass adapted to the degradation of toluene and xylenes in mixture in a batch reactor with substrates supplied by pulses.

A biomass adapted to degrade toluene and xylenes in mixture was grown in a batch reactor with substrates supplied by pulses. The inhibition of biomass growth in the course of substrate degradation was investigated. The maximal biomass concentration of 7 g l-1 was obtained using 150 microliters of toluene and 15 microliters of a mixture of xylenes in one litre of liquid medium, and the maximal biomass productivity and yield were 53 mg l-1 h-1 and 0.32 gDW gs-1, respectively. Higher quantities of substrate added by pulses, that is 200 microliters of toluene with 20 microliters of xylenes and 300 microliters of toluene with 30 microliters of xylenes, caused an accumulation of metabolites. These higher quantities of substrates caused inhibition of microbial growth. Among the metabolites produced, 4-methyl catechol was found in large quantities in the culture medium and in the cells.

Biomass growth monitoring using pressure drop in a cocurrent biofilter

The possibility of following the biomass growth by pressure drop measurement was investigated in an aerated cocurrent upflow fixed-bed bioreactor continuously fed with wastewater containing industrial organic pollutants. The experiments were carried out in a biological filtration oxygenated reactor (Biofor) pilot plant packed with expanded clay balls (Biolite) of 2.7-mm diameter, which served as biomass carriers. The column was equipped for on-line pressure drop measurements. Correlation between pressure drop measurements and Reynolds numbers of air and water were determined in experiments carried out without biomass. Under operating conditions with biomass, it was demonstrated that column clogging and the operating time between washing cycles can be predicted depending on the volumetric organic load for a given total organic carbon inlet concentration. The biological activity of the fixed biomass was estimated from the oxygen consumption rate per unit time and carrier area. The oxygen consumption rate measurements demonstrated that the biological activity depends on the inlet substrate concentration, and that the Biofor column was most efficient between 75 and 100 g m-3 of total organic carbon inlet concentration. In the course of the wastewater treatment, using pressure drop measurements, the equivalent diameter of the Biolite particles, the reduced column macroporosity, and the biofilm thickness were calculated. An expression correlating biofilm density and biofilm thickness, as determined from the pressure drop measurements, was proposed. Good agreement was found between the fixed biomass in the reactor, determined as volatile suspended solids, and the biologically active biomass, estimated by respirometry. Copyright 1998 John Wiley & Sons, Inc.

Aerobic and anaerobic biodegradability of 1-anthraquinone sulphonate.

The present work investigates 1-anthraquinone sulphonate (1-AS) biodegradation under (i) aerobic conditions using domestic activated sludge as inoculum, (ii) anaerobic conditions using sludge from an anaerobic domestic wastewater treatment digester in a sulphate-containing or methanogenic environment, (iii) a combination of anaerobic followed by aerobic conditions. The process was evaluated in terms of primary degradation, i.e. 1-AS elimination and ultimate degradation, as total dissolved organic carbon removal. It was shown that aerobic conditions lead to the complete primary and ultimate degradation, of 1-AS. By contrast, neither under sulphato-reductive nor methanogenic conditions does anaerobic digestion lead to the significant degradation of 1-AS. The use of anaerobic treatment followed by aerobic treatment did not improve degradation. Indeed aerobic post-treatment resulted in the re-appearance of pollutant in the medium even though this had been partly degraded under anaerobic conditions.

Influence of the screen material on the fouling of spin filters.

Mouse-mouse hybridomas (15 microm mean diameter) were cultivated in a simulated perfusion reactor with spin filter and external recirculation of the medium. Proteins at high concentrations, such as 10% foetal calf serum (FCS), were found to be not responsible by themselves for fouling, even at high recirculation rates. Stainless steel (10 microm pores) in contrast to polyamide (11 microm proes) led to a great accumulation of dead cells and nucleic acids on the screen, finally leading to fouling, as shown by biochemical and microscopic examinations. It is suggested that the high surface charge density of metals compared to polyamide is responsible for attachment of various residues. Stainless steel should rather be replaced by a resistant and nontoxic synthetic material, such as polyamide 66 which was successfully used. FCS should be avoided, since it seems to increased the fouling phenomenon. Moreover, the pore size of the screen should be carefully defined according to the wide size distribution of living and dead cells of the line used (33% of variation of the mean size in our case) as well as fragments. The purpose of the screen being to get rid of fragments and small dead cells, and not to wash too many new small cells, a good retention was achieved here by a 10-microm opening.

Automated HPLC monitoring of broth components on bioreactors.

Under proper operating conditions, a low dead volume continuous filtration module operated on biological broths (yeast and bacteria suspensions in stirred reactors) still fulfills the flow-rate requirements of an analytical apparatus (for example HPLC or FIA) without membrane regeneration. The filtrate stream has been successfully connected to a bioreactor in order to perform the automated HPLC analysis of broth components. The monitoring of the carbon source (lactose), and minor products (glycerol, acetate and succinate) during a yeast culture (Kluyveromyces marxianus) is shown.

[The effect of dissolved oxygen tension on the energy metabolism of yeasts]. / Influence de la tension de l'oxygène dissous sur le métabolisme énergétique des levures.

The specific ATP generation rate in yeasts was examined on the glycolytic pathway and on the respiratory chain as a function of the dissolved oxygen tension of the culture medium. Two different strains were used: Saccharomyces cerevisiae sensitive to the glucose effect and Kluyveromyces fragilis insensitive to the catabolite respression when growing on lactose. The oxidative ATP generation rate followed by these two strains a Michaelis Menten kinetics against the dissolved oxygen concentration. Dissolved oxygen tension only influenced the glycolytic ATP generation rate in Kluyveromyces fragilis. Thus glucose and Pasteur effects are two mutually exclusive regulatory mechanisms of the energy yielding metabolism of the yeasts.