Influence of electron acceptors on hexanoic acid production by Clostridium kluyveri

Clostridium kluyveri was used for chain elongation of C2C4 fatty acids in stirred tank bioreactors. The influence of different electron acceptors (acetic acid, butyric acid and the mixture of both) on C6 fatty acid production was evaluated in presence of ethanol using similar molar alcohol/acid ratios around 3.5. Bottle batch assays without pH regulation and with only acetic acid as electron acceptor yielded a final C6 fatty acid concentration of 6.8 ± 0.6 g L^-1. Then, pH-regulated bioreactors were operated at constant pH of 6.8. Under such conditions, the maximum growth rate was 0.039 h^-1 obtained using acetic acid and butyric acid as electron acceptors, whereas the lowest growth rate was 0.010 h^-1 with only butyric acid as electron acceptor. The maximum growth rate with acetic acid only, was similar, though slightly lower, as with the mixture of C2C4 fatty acids. Besides, the maximum productions of hexanoic acid were 11.8 g L^-1, 13.1 g L^-1 and 21.2 g L^-1 using, respectively, acetic acid, butyric acid and the mixture of both acids as electron acceptors. Thus, the use of a mixture of acetic acid and butyric acid in presence of ethanol for chain elongation, at constant pH, proved to be efficient for hexanoic acid production.

Organic loading rate effect on the acidogenesis of cheese whey: a comparison between UASB and SBR reactors

Volatile fatty acids (VFA) production and degree of acidification (DA) were investigated in the anaerobic treatment of cheese whey by comparison of two processes: a continuous process using a laboratory upflow anaerobic sludge blanket (UASB) reactor and a discontinuous process using a sequencing batch reactor (SBR). The main purpose of this work was to study the organic loading rate (OLR) effect on the yield of VFA in two kinds of reactors. The predominant products in the acidogenic process in both reactors were: acetate, propionate, butyrate and valerate. The maximum DA obtained was 98% in an SBR at OLR of 2.7 g COD L^-1 d^-1, and 97% in the UASB at OLR at 15.1 g COD L^-1 d^-1. The results revealed that the UASB reactor was more efficient at a medium OLR with a higher VFA yield, while with the SBR reactor, the maximum acidification was obtained at a lower OLR with changes in the VFA profile at different OLRs applied.

Optimization of the performance of a thermophilic biotrickling filter for alpha-pinene removal from polluted air

Biodegradation of alpha-pinene was investigated in a biological thermophilic trickling filter, using a lava rock and polymer beads mixture as packing material. Partition coefficient (PC) between alpha-pinene and the polymeric material (Hytrel G3548 L) was measured at 50 degrees C. PCs of 57 and 846 were obtained between the polymer and either the water or the gas phase, respectively. BTF experiments were conducted under continuous load feeding. The effect of yeast extract (YE) addition in the recirculating nutrient medium was evaluated. There was a positive relationship between alpha-pinene biodegradation, CO2 production and YE addition. A maximum elimination capacity (ECmax) of 98.9 g m(-3) h(-1) was obtained for an alpha-pinene loading rate of about 121 g m(-3) h(-1) in the presence of 1 g L(-1) YE. The ECmax was reduced by half in the absence of YE. It was also found that a decrease in the liquid flow rate enhances alpha-pinene biodegradation by increasing the ECmax up to 103 gm(-3) h(-1) with a removal efficiency close to 90%. The impact of short-term shock-loads (6 h) was tested under different process conditions. Increasing the pollutant load either 10- or 20-fold resulted in a sudden drop in the BTF's removal capacity, although this effect was attenuated in the presence of YE.

Evaluation of the biomethane potential of solid fish waste

Manufacturing processes in fish canning industries generate a considerable amount of solid waste that can be digested anaerobically. The aim of this research was to study the biochemical methane potential of different solid fish waste. For tuna, sardine and needle fish waste, around 0.47g COD-CH(4)/g COD(added) was obtained in batch experiments with 1%TS; whereas for mackerel waste, the methane production attained 0.59g COD-CH(4)/g COD(added). The increase in the waste/inoculum ratio, from 1.1-1.3 to 2.8-3.3g VS(waste)/g VS(inoculum), led to overload due to VFA and LCFA accumulation. Afterward, co-digestion assays of fish waste with gorse were undertaken but the biochemical methane potential did not improve.

Bioplastic production using wood mill effluents as feedstock

Fibreboard production is one of the most important industrial activities in Galicia (Spain). Great amounts of wastewater are generated, with properties depending on the type of wood, treatment process, final product and water reusing, among others. These effluents are characterized by a high chemical oxygen demand, low pH and nutrients limitation. Although anaerobic digestion is one of the most suitable processes for the treatment, lately bioplastics production (mainly polyhydroxyalkanoates) from wastewaters with mixed cultures is being evaluated. Substrate requirements for these processes consist of high organic matter content and low nutrient concentration. Therefore, wood mill effluents could be a suitable feedstock. In this work, the possibility of producing bioplastics from to wood mill effluents is evaluated. First, wood mill effluent was converted to volatile fatty acids in an acidogenic reactor operated at two different hydraulic retention times of 1 and 1.5 d. The acidification percentage obtained was 37% and 42%, respectively. Then, aerobic batch assays were performed using fermented wood mill effluents obtained at different hydraulic retention times. Assays were developed using different cultures as inoculums. The maximum storage yield of 0.57 Cmmol/Cmmol was obtained when when the culture was enriched on a synthetic media.

Composition and role of extracellular polymers in methanogenic granules

Methanobacterium formicicum and Methanosarcina mazeii are two prevalent species isolated from an anaerobic granular consortium grown on a fatty acid mixture. The extracellular polysaccharides (EPS) were extracted from Methanobacterium formicicum and Methanosarcina mazeii and from the methanogenic granules to examine their role in granular development. The EPS made up approximately 20 to 14% of the extracellular polymer extracted from the granules, Methanobacterium formicicum, and Methanosarcina mazeii. The EPS produced by Methanobacterium formicicum was composed mainly of rhamnose, mannose, galactose, glucose, and amino sugars, while that produced by Methanosarcina mazeii contained ribose, galactose, glucose, and glucosamine. The same sugars were also present in the EPS produced by the granules. These results indicate that the two methanogens, especially Methanobacterium formicicum, contributed significantly to the production of the extracellular polymer of the anaerobic granules. Growth temperature, substrates (formate and H(inf2)-CO(inf2)), and the key nutrients (nitrogen and phosphate concentrations) affected polymer production by Methanobacterium formicicum.

Valuable product production from wood mill effluents

Fibreboard production is one of the most important industrial activities in Galicia (Spain). Great amounts of wastewater are generated, with properties depending on the type of wood, treatment process, final product and water reusing, among others. These effluents are characterized by a high chemical oxygen demand (COD), low pH and nutrients limitation. Aerobic and anaerobic processes have been used for their treatment. Presently, bioplastics production (mainly polyhydroxyalkanoates or PHA) from wastewaters with mixed cultures is being studied. Substrate requirements for these processes are a high organic matter content and low nutrient concentration. Therefore, wood mill effluents could be a suitable feedstock. PHA production from wastewaters is carried out in three steps. First, complex organic matter is converted into volatile fatty acids (VFA) through acidogenic fermentation. Then, VFA are used as substrate in an aerobic sequencing batch reactor (SBR), in which the enrichement of PHA producing bacteria from a mixed culture is favoured. Finally, the sludge from the SBR is fed with a pulse containing high VFA concentrations, resulting in PHA accumulation inside the cells. In this work, the possibility of applying this process to wood mill effluents is proposed. An acidification percentage of 37% and a storage yield (Y(STO)) of 0.23 Cmmol/Cmmol were obtained.

The SHARON process in the treatment of landfill leachate

The purpose of this paper was to study the partial nitrification of the nitrogen present in a landfill leachate applying the SHARON process in order to obtain a suitable effluent to the ANAMMOX process. As a first step, the SHARON reactor was fed anaerobically pre-treated leachate at an ammonium concentration of 2,000 mg N/L (1.1 kg N/m(3) d). In such conditions, the average ammonium and nitrite concentrations in the effluent were 775 mg N/L and 1,225 mg N/L, respectively. During this period the COD removal was very low since most of the biodegradable organic matter was removed in the anaerobic pre-treatment. Afterwards, the SHARON reactor was fed leachate without a previous treatment and the efficiency of the partial nitritation diminished. As well, the COD removal increased, achieving a percentage around 28%.

Effect of phenol on the biological treatment of wastewaters from a resin producing industry

The effect of phenol on the biological treatment of wastewaters from a resin producing industry was analyzed in a pre-denitrification system. First, the effect of phenol overloads on the removal of organic matter and nitrogen compounds was studied. During the overloads (from 250 to 4000 mg/L), phenol was detected in the effluent of the anoxic reactor but the system recovered fast after stopping the overloads. The total organic carbon (TOC) removal remained unchanged during phenol addition (91.9% at 0.20 kg TOC/m3 d), except for the highest overload. With regard to total Kjeldahl nitrogen (TKN), its mean removal (87.9% at 0.08 kg TKN/m3 d) was not affected by the phenol overloads. Afterwards, the effect of different phenol concentrations on the biological treatment of these wastewaters was analyzed. Phenol concentrations from 250 to 4000 mg/L were added to the feed. Phenol was completely removed despite the presence of other carbon sources in the wastewater. In spite of the presence of phenol, a TOC removal around 91.3% was achieved at an average organic loading rate of 0.11 kg TOC/m3 d. The mean applied nitrogen loading rates were 0.05 and 0.08 kg TKN/m3 d, obtaining TKN removals around 85.8% and 87.1%, respectively. Therefore, the biological treatment of wastewaters from a resin producing industry in a pre-denitrification system was not affected by the presence of phenol.

Removal of formaldehyde, methanol, dimethylether and carbon monoxide from waste gases of synthetic resin-producing industries

The removal of mixtures of gas-phase pollutants released from formaldehyde- and formaldehyde resin-producing industries was studied in different bioreactor systems. The waste gases contained formaldehyde, methanol, dimethylether and carbon monoxide. The use of a hybrid two-stage bioreactor, composed of a biotrickling filter and a conventional biofilter connected in series, led to very high elimination capacities and removal efficiencies close to 100% for overall pollutant loads exceeding 600g m(-3)h(-1). The presence of low concentrations of dimethylether in the gaseous mixture did not have a significant effect on the removal of formaldehyde or methanol under our operating conditions, although moderate concentrations of these compounds did negatively affect the biodegradation of dimethylether. When a mixture of all four compounds, at concentrations around 100, 100, 50 and 50mg m(-3) for formaldehyde, methanol, carbon monoxide and dimethylether, respectively, was fed to a conventional biofilter, removal efficiencies higher than 80% were obtained for the first three pollutants at empty bed retention time values above 30s. On the other hand, dimethylether was removed to a lower extent, although its reduced environmental impact allows to conclude that these results were satisfactory.

Formaldehyde biodegradation and its effect on the denitrification process

Simultaneous formaldehyde biodegradation and denitrification in batch assays and in a continuous lab-scale reactor were studied. In batch assays, initial biodegradation rates between 0.7 and 3.3 g CKH2O g VSS(-1) d(-1) were obtained at formaldehyde concentrations between 300 and 2150 mg l(-1). The denitrification process was affected by the presence of formaldehyde. The nitrite accumulation increased with the initial formaldehyde concentration. In the continuous reactor, removal efficiencies above 98.5% were obtained at formaldehyde loading rates between 0.37 and 2.96 kg COD m(-3) d(-1) (625-5000 mg CH2O l(-1)). Formaldehyde removal led to the appearance of methanol and formic acid in the medium. Denitrification process was almost complete (around 99.7%) at nitrogen loading rates up to 0.44 kg N-NO3- m(-3) d(-1). Nitrite occasionally appeared in the effluent at concentrations less than 2.9 mg l(-1). The composition of the biogas indicated that denitrification and methanogenesis occurred simultaneously in the same unit.

Combined post-ozonation and biological treatment of recalcitrant wastewater from a resin-producing factory

In this study, effluent from the biological treatment of wastewater from a resin-producing factory containing recalcitrant compounds was ozonated under different conditions. Afterwards, the biodegradability of the ozonated effluent was studied under anoxic conditions. The post-ozonation of the industrial effluent was performed using a wide range of ozone doses, from 1.8 to 29.5 mg L(-1)min(-1). After the biological treatment of the ozonated effluent, organic carbon and nitrogen removals from 27 to 97% and from 27 to 80%, respectively, were achieved. The effect of the contact time was studied at a constant ozone dose of 13.0+/-1.2 mg L(-1)min(-1) and contact times ranging from 30 to 180 min. In this case, organic carbon removals from 55 to 100% and organic nitrogen removals from 41 to 77% were obtained after biological treatment.

Effect of key parameters on the removal of formaldehyde and methanol in gas-phase biotrickling filters

The effect of some important operation parameters, as pH, pollutant load and composition of the nutrient media, on the biodegradation of a mixture of formaldehyde and methanol in a gas-phase biotrickling filter was studied. pH proved to affect the degradation of both compounds at moderately acidic values. Replacing ammonium with nitrate as nitrogen source in the liquid solution led to a slight decrease in performance, though this difference was not really significant. A slight decrease in the elimination rate was also observed when reducing the N-NO(3)(-) concentration to 60% of its original value. No interactions between the two pollutants were found under our working conditions.

Development of a novel monolith-bioreactor for the treatment of VOC-polluted air

A novel bioreactor packed with ceramic monolith colonized by a toluene-degrading culture was investigated in order to assess its suitability for waste gas treatment. Operational parameters that were considered included start-up of the bioreactor, toluene loading rate, changes in gas flow rate, liquid feed mode, and steady-state operation. This is the first report on the treatment of toluene-polluted air in such a biological monolith reactor. Data on performance and stability have been obtained showing that this system is suitable for waste gas treatment. Removal efficiencies around 90% could be maintained at different gas flow rates, although this value gradually dropped when increasing the load above 30 g m(-3) h(-1). Interestingly, omitting the continuous feed of a liquid trickling phase improved the reactor's performance. One potential drawback that needs to be minimized is related to clogging after long term operation. Further studies aimed at optimizing this novel application would allow reaching a high performance under long-term, stable conditions.

Simultaneous nitrification and formaldehyde biodegradation in an activated sludge unit

The simultaneous removal of formaldehyde and ammonium in a lab-scale activated sludge unit was investigated. The unit was operated at a hydraulic retention time of 2.4 days with an ammonium concentration in the influent of 350 mg NH4+-N/L, maintaining the ammonium loading rate at 0.15 g NH4+-N/Ld during the operation time. However, the applied organic loading rate was increased stepwise by increasing the formaldehyde concentration from 26 up to 3168 mg/L, corresponding to 0.01-1.40 g COD/Ld. High formaldehyde removal efficiencies, around 99.5% (+/-0.38), were maintained at all the formaldehyde concentrations. Ammonium removal was also very high during the operation period, around 99.9% (+/-0.01). The ammonium concentration in the effluent was lower than 0.1 mg NH4+-N/L at all applied organic loading rates, indicating that there was no inhibition of nitrification by formaldehyde.

Phenol biodegradation and its effect on the nitrification process

Phenol biodegradation under aerobic conditions and its effect on the nitrification process were studied, first in batch assays and then in an activated sludge reactor. In batch assays, phenol was completely biodegraded at concentrations ranging from 100 to 2500 mg l(-1). Phenol was inhibitory to the nitrification process, showing more inhibition at higher initial phenol concentrations. At initial phenol concentrations above 1000 mg l(-1), the level of nitrification decreased. In the activated sludge reactor, the applied ammonium loading rate was maintained at 140 mg N-NH(4)(+)l(-1)d(-1) (350 mg N-NH(4)(+)l(-1)) during the operation time. However, the applied organic loading rate was increased stepwise from 30 to 2700 mg COD l(-1)d(-1) by increasing the phenol concentration from 35 up to 2800 mg l(-1). High phenol removal efficiencies, above 99.9%, were maintained at all the applied organic loading rates. Ammonium removal was also very high during the operation period, around 99.8%, indicating that there was no inhibition of nitrification by phenol.

Partial nitrification of wastewater from an aminoplastic resin producing factory

Nitrification via nitrite was studied in two aerobic reactors treating wastewater from an aminoplastic resin producing factory at HRT varying between 1.37-1.89 and 2.45-3.63 days. Both eactors were fed with concentrations of 366, 450, 1099 and 1899 mg N-NH4+/L. In general in the reactor operated at a lower HRT, the nitritation percentage decreased from 87.2 to 21.6%, while the nitratation percentage remained always lower than 2.5% (except in the last period) when the ammonium concentration was increased. This behaviour could be due to the inhibition of the ammonium and nitrite oxidation produced by high free ammonia concentrations up to 179.3 mg N-NH3/L. In the reactor operated at a higher HRT, the nitritation percentage decreased and the nitratation percentage increased from 88.6 to 39.6% and from 0.65 to 35.7%, respectively, due to an increase of the dissolved oxygen concentration from 0.76 to 1.02 mg O2/L. However, when ammonium was fed at a concentration of 1898.7 mg N-NH4+/L, the nitritation increased and the nitratation decreased, probably as a result of the accumulation of free ammonia up to 2.04 mg N-NH3/L, meaning that nitrite oxidizers were inhibited. Nitrite build-up was observed after each modification of ammonium concentration in the feed.

Biodegradation and effect of formaldehyde and phenol on the denitrification process

Formaldehyde and phenol biodegradation during the denitrification process was studied at lab-scale, first in anoxic batch assays and then in a continuous anoxic reactor. The biodegradation of formaldehyde (260 mgl(-1)) as single carbon source and at phenol concentrations ranging from 30 to 580 mgl(-1) was investigated in batch assays, obtaining an initial biodegradation rate around 0.5g CH(2)OgVSS(-1)d(-1). With regard to phenol, its complete biodegradation was only observed at initial concentrations of 30 and 180 mgl(-1). The denitrification process was inhibited at phenol concentrations higher than 360 mgl(-1). Studies were also done using a continuous anoxic upflow sludge blanket reactor in which formaldehyde removal efficiencies above 99.5% were obtained at all the applied formaldehyde loading rates, between 0.89 and 0.14g COD (CH(2)O)l(-1)d(-1). The phenol loading rate was increased from 0.03 to 1.3g COD (C(6)H(6)O)l(-1)d(-1). Phenol removal efficiencies above 90.6% were obtained at phenol concentrations in the influent between 27 and 755 mgl(-1). However, when the phenol concentration was increased to 1010 mgl(-1), its removal efficiency decreased. Denitrification percentages around 98.4% were obtained with phenol concentrations in the influent up to 755 mgl(-1). After increasing phenol concentration to 1010 mgl(-1), the denitrification percentage decreased because of the inhibition caused by phenol.

Formaldehyde and urea removal in a denitrifying granular sludge blanket reactor

Simultaneous formaldehyde biodegradation, urea hydrolysis and denitrification in anoxic batch assays and in a continuous laboratory anoxic reactor were investigated. In batch assays, the initial formaldehyde biodegradation rate was around 0.7 g CH(2)Og VSS(-1)d(-1) and independent of the urea concentration (90- 370 mg N-NH(2)CONH(2)l(-1)). Urea was completely hydrolyzed to ammonium in the presence of 430 mg l(-1) formaldehyde and complete denitrification took place in all cases (125 mg N-NO(-)(3)l(-1)). Formaldehyde removal efficiencies above 99.5% were obtained in a lab-scale denitrifying upflow sludge blanket reactor at organic loading rates between 0.37 and 2.96 kg CODm(-3)d(-1) (625-5000 mg CH(2)Ol(-1)). The urea loading rate was increased from 0.06 to 0.44 kg Nm(-3)d(-1) (100-800 mg N-NH(2)CONH(2)l(-1)) and hydrolysis to ammonium was around 77.5% at all loading rates. The denitrification process was always almost complete (100-800 mg N-NO(3)(-)l(-1)), due to the high COD/N ratio of 6.7 in the influent. A minimum value of 3.5 was found to be required for full denitrification. The composition of the biogas indicated that denitrification and methanogenesis occurred simultaneously in the same unit. A good granulation of the sludge was observed.

Hydrodynamic behaviour and comparison of technologies for the removal of excess biomass in gas-phase biofilters

The hydrodynamic behaviour of a biofilter fed toluene and packed with an inert carrier was evaluated on start-up and after long-term operation, using both methane and styrene as tracers in Residence Time Distribution experiments. Results indicated some deviation from ideal plug flow behaviour after 2-year operation. It was also observed that the retention time of VOCs gradually increased with time and was significantly longer than the average residence time of the bulk gas phase. Non-ideal hydrodynamic behaviour in packed beds may be due to excess biomass accumulation and affects both reactor modeling and performance. Therefore, several methods were studied for the removal of biomass after long-term biofilter operation: filling with water and draining, backwashing, and air sparging. Several flow rates and temperatures (20-60 degrees C) were applied using either water or different chemicals (NaOH, NaOCl, HTAB) in aqueous solution. Usually, higher flow rates and higher temperatures allowed the removal of more biomass, but the efficiency of biomass removal was highly dependent on the pressure drop reached before the treatment. The filling/draining method was the least efficient for biomass removal, although the treatment did basically not generate any biological inhibition. The efficiency of backwashing and air sparging was relatively similar and was more effective when adding chemicals. However, treatments with chemicals resulted in a significant decrease of the biofilter's performance immediately after applying the treatment, needing periods of several days to recover the original performance. The effect of manually mixing the packing material was also evaluated in duplicate experiments. Quite large amounts of biomass were removed but disruption of the filter bed was observed. Batch assays were performed simultaneously in order to support and quantify the observed inhibitory effects of the different chemicals and temperatures used during the treatments.

A technique using a membrane flow cell to determine average mass transfer coefficients and tortuosity factors in biofilms

Average mass transfer coefficients of an inert compound (LiCI) within denitrifying biofilms were monitored during biofilm growth in a membrane flow cell under different flow conditions, until the biofilm reached (pseudo-) steady state. Average effective diffusivities were found to increase with the decrease tortuosity factors of the biofilm matrix. The lowest tortuosity factor corresponded the highest liquid velocity.

Optimization of nutrient supply in a downflow gas-phase biofilter packed with an inert carrier

Several methodologies were tested to supply nutrients to a downflow biofilter packed with perlite and used to treat toluene-polluted air. Despite the presence of an inorganic carrier, elimination capacities of up to around 60 g/m(3) per hour could be maintained when a basal medium, containing nitrogen, phosphorus and potassium, was supplied once every fortnight or even once a month rather than once a week. Experimental results also indicated that the addition of vitamins or trace minerals to the basal aqueous medium hardly improved biofilter performance. Furthermore, the nutrient supply could be combined with a biomass control strategy, using air sparging, without any adverse effect on biofilter performance compared to supplying nutrients alone, and limiting the accumulation of excess biomass on the packing material. The performance of the biofilter was not significantly affected by temperature fluctuations between 25 and 33 degrees C.

Kinetics of inhibition in the biodegradation of monoaromatic hydrocarbons in presence of heavy metals

The toxicity and inhibitory effects of heavy metals such as cadmium, nickel and zinc on alkylbenzene removal were evaluated with a Bacillus strain. The kinetics of alkylbenzene biodegradation with the different heavy metals at various concentrations were modeled using the Andrews equation which yielded a good fit between model and experimental data. Additional experiments undertaken with a Pseudomonas sp. in presence of nickel confirmed a good fit between experimental data and the Andrews model for this strain as well. The heavy metals inhibition constants (Ki) were calculated for different combinations of volatile organic compounds (VOC) and heavy metals. The present approach provides a method for evaluating and quantifying the inhibition effect of heavy metals on the biodegradtion of pollutants by specific microbial strains.

Parameters affecting performance and modeling of biofilters treating alkylbenzene-polluted air

Both short-term and long-term biofiltration experiments were undertaken with a biofilter inoculated with a defined microbial consortium and treating an alkylbenzene mixture. The results obtained with such a biofilter in short-term experiments were very similar to those obtained with a biofilter inoculated with a non-defined mixed culture, in terms of maximum elimination capacities (70-72 g m(-3) h(-1)) and the corresponding removal efficiencies (>95%). However, in long-term experiments, a better performance was reached, with a maximum elimination capacity of 120 g m(-3) h(-1), corresponding to a removal efficiency >99% after 2 years of operation. Inoculation proved to be useful for shortening the start-up period. In the long term, it appeared that biomass distribution was not homogenous along the biofilter, which in some cases resulted in a bad fit between simple model equations and experimental data.

Start-up and long-term performance of a gas phase biofilter packed with an inert carrier

Several parameters affecting the performance and characteristics of alkylbenzene fed biofilters were checked when using perlite as inert carrier material. The influence of the inoculum on startup and long term performance was studied using both non defined as well as defined cultures. The inoculated pure cultures, which were still detected in the biofilter after several months operation, allowed shortening the start-up period Qualitative and quantitative biomass distribution appeared to be uneven along the biofilter bed in long term operation studies. The biofilter could withstand a drying period of several weeks although such operating condition led to a shift in dominant microbial populations in the biofilm which was followed by an increase of the biofilter performance. Although a water content of 55-60% appeared to be optimal with perlite, peformance data were still satisfactory down to a water content around 35-40%.

Biofilter performance and characterization of a biocatalyst degrading alkylbenzene gases

A biofilter treating alkylbenzene vapors was characterized for its optimal running conditions and kinetic parameters. Kinetics of the continuous biofilter were compared to batch kinetic data obtained with biofilm samples as well as with defined microbial consortia and with pure culture isolates from the biofilter. Both bacteria and fungi were present in the bioreactor. Five strains were isolated. Two bacteria, Bacillus and Pseudomonas, were shown to be dominant, as well as a Trichosporon strain which could, however, hardly grow on alkylbenzenes in pure culture. The remaining two strains were most often overgrown by the other three organisms in liquid phase batch cultures. mu max, KS, KI values and biodegradation rates were calculated and compared for the different mixed and pure cultures. Since filter bed acidification was observed during biofiltration studies reaching a pH of about 4, experiments were also undertaken to study the influence of pH on performance of the different cultures. Biodegradation and growth were possible in all cases, over the pH range 3.5-7.0 at appreciable rates, both with mixed cultures and with pure bacterial cultures. Under certain conditions, microbial activity was even observed in the presence of alkylbenzenes down to pH 2.5 with mixed cultures, which is quite unusual and explains the ability of the present biocatalyst to remove alkylbenzenes with high efficiency in biofilters under acidic conditions.

Methanogenic and perchloroethylene-dechlorinating activity of anaerobic granular sludge

The biodegradation and toxicity of tetrachlorethylene (C2Cl4) and trichloroethylene (C2HCl3) were studied with different anaerobic enrichment cultures using the following electron donors: acetate, propionate, butyrate, methanol, formate and hydrogen. All of them sustained dechlorination except propionate, for which C2Cl4 biodegradation rates were not significant. The best results were obtained with butyrate. Hydrogen appeared to be a relevant electron donor for dechlorination with the present cultures. In the presence of specific inhibitors such as bromoethanesulphonate or molybdate, a slight inhibition of dechlorination was observed. According to dechlorination kinetics, Monod-type behaviour was observed up to 120 microM C2Cl4 or 200 microM C2HCl3 with Ks values around 7 microM for both compounds. Dechlorination was partially inhibited at higher concentrations. In contrast, methanogens, or at least methane production, were more sensitive to the presence of chlorinated ethylenes and inhibitions of methanogenesis was observed to different extents over all the C2Cl4/C2HCl3 concentration range tested, even at the lowest concentrations.

[Effect of dietary protein levels on the genesis of repair tissue in rats]

The objective of this study was to verify if the diet protein level affects the genesis of the repair tissue in rats submitted to a poly-chloro-vinyl (PVC) sponge implantation, as well as to analyse the possible alterations in the synthesis of the mucopolysaccharides acids (glucosaminoglycans) by the histophotometry technique. Forty five Wistar weanling male rats, at 21 days of age, were divided into three experimental groups; the groups were fed diets al 6%, 15% and 40% protein level from casein source, during at 69 days period. The animals which received the low protein diet (6%) presented an inhibition in the evolution and maturation of the granulation tissue mainly in the 4th, 7th and 10th days after the sponge PVC implantation. It was also observed that there was less infiltration of the inflammatory cells, less fibroblasts proliferation, reduction of the collagen fibers synthesis, neovascularization decreased and an inhibition of the mucopolysaccharide acids synthesis.

Trophic relationships between Saccharomyces cerevisiae and Lactobacillus plantarum and their metabolism of glucose and citrate

Glucose and citrate are two major carbon sources in fruits or fruit juices such as orange juice. Their metabolism and the microorganisms involved in their degradation were studied by inoculating with an aliquot of fermented orange juice a synthetic model medium containing glucose and citrate. At pH 3.6, their degradation led, first, to the formation of ethanol due to the activity of yeasts fermenting glucose and, eventually, to the formation of acetate resulting from the activity of lactobacilli. The yeast population always outcompeted the lactobacilli even when the fermented orange juice used as inoculum was mixed with fermented beet leaves containing a wider variety of lactic acid bacteria. The evolution of the medium remained similar between pH 3.3 and 5.0. At pH 3.0 or below, the fermentation of citrate was totally inhibited. Saccharomyces cerevisiae and Lactobacillus plantarum were identified as the only dominant microorganisms. The evolution of the model medium with the complex microbial community was successfully reconstituted with a defined coculture of S. cerevisiae and L. plantarum. The study of the fermentation of the defined model medium with a reconstituted microbial community allows us to better understand the behavior not only of fermented orange juice but also of many other fruit fermentations utilized for the production of alcoholic beverages.