Cleotilde Juárez-Ramírez

Batch and fed-batch cultures for the treatment of whey with mixed yeast cultures

Abstract ‘Lactic yeasts’ produce some extracellular metabolites, as well as biomass, when cultivated in whey. Mixed cultures are able to use several sources of carbon simultaneously and therefore the use of mixed yeast cultures is proposed in order to reduce the whey COD and increase the biomass yield. Of the mixed yeast cultures tested, the highest biomass yield was obtained with Torulopsis cremoris and Candida utilis . C. utilis consumed some metabolic by products generated by T. cremoris . Repeated fed-batch culture of T. cremoris and C. utilis , carried out in an airlift bioreactor designed to operate variable volume processes, is a potential alternative for the treatment of whey, since it produces a high yield of biomass (0.75 g of biomass/g of lactose) and a greater COD removal efficiency (95.8%) than those reported in the literature.

Degradation kinetics of phenol by immobilized cells of Candida tropicalis in a fluidized bed reactor

Degradation kinetics of phenol by free and agar-entrapped cells of Candida tropicalis was studied in batch cultures. The initial phenol degradation rate achieved with free cells was higher than that obtained with immobilized cells, when phenol concentrations up to 1000 mg l−1 were used. However, at higher phenol concentrations, the behaviour was quite different. The initial degradation rate of the immobilized yeast cells was about 10 times higher than that of the free cells, at a phenol concentration of 3500 mg l−1. The semicontinuous and continuous degradation of phenol by immobilized yeast cells was also investigated in a multi-stage fluidized bed reactor. The highest phenol removal efficiencies and degradation rates as well as the lowest values of residual phenol and chemical oxygen demand were obtained in the semicontinuous culture when phenol concentrations up to 1560 mg l−1 were used.

Biodegradation of a mixture of the herbicides ametryn, and 2,4-dichlorophenoxyacetic acid (2,4-D) in a compartmentalized biofilm reactor.

In this work, an efficient degradation process for the removal of 2,4-D and ametryn, together with organic and inorganic adjuvants used in the commercial formulations of both herbicides, was developed. Although both compounds are toxic for microbial communities, ametryn is markedly more toxic than 2,4-D. In spite of this, the microbial consortium used could resist loading rates up to 31.5 mg L(-1) d(-1) of ametryn, with removal efficiencies up to 97% for both herbicides. Thus, an alternative use of this consortium could be bioaugmentation, as a tool to protect the structure and function of an activated-sludge biota against ametryn or 2,4-D shock loads. The process was carried out in a lab-scale prototype of aerobic biobarrier constructed as a compartmentalized fixed film reactor with airlift recirculation of oxygenated liquid.

Lactic acid bacteria production from whey

The main purpose of this work was to isolate and characterize lactic acid bacteria (LAB) strains to be used for biomass production using a whey-based medium supplemented with an ammonium salt and with very low levels of yeast extract (0.25 g/L). Five strains of LAB were isolated from naturally soured milk after enrichment in whey-based medium. One bacterial isolate, designated MNM2, exhibited a remarkable capability to utilize whey lactose and give a high biomass yield on lactose. This strain was identified as Lactobacillus casei by its 16S rDNA sequence. A kinetic study of cell growth, lactose consumption, and titratable acidity production of this bacterial strain was performed in a bioreactor. The biomass yield on lactose, the percentage of lactose consumption, and the maximum increase in cell mass obtained in the bioreactor were 0.165 g of biomass/g of lactose, 100%, and 2.0 g/L, respectively, which were 1.44,1.11, and 2.35 times higher than those found in flask cultures. The results suggest that it is possible to produce LAB biomass from a whey-based medium supplemented with minimal amounts of yeast extract.

Aerobic biodegradation of a mixture of sulfonated azo dyes by a bacterial consortium immobilized in a two‐stage sparged packed‐bed biofilm reactor

The biodegradation of the sulfonated azo dyes, Acid Orange 7 (AO7) and Acid Red 88 (AR88), by a bacterial consortium isolated from water and soil samples obtained from sites receiving discharges from textile industries, was evaluated. For a better removal of azo dyes and their biodegradation byproducts, an aerobically operated two‐stage rectangular packed‐bed biofilm reactor (2S‐RPBR) was constructed. Because the consortiums metabolic activity is affected by oxygen, the effect of the interstitial air flow rate QGI on 2S‐RPBRs zonal values of the oxygen mass transfer coefficient kLa was estimated. In the operational conditions probed in the bioreactor, the kLa values varied from 3 to 60 h−1, which roughly correspond to volumetric oxygen transfer rates, dcL/dt, ranging from 20 to 375 mg O2 L−1h−1. Complete biodegradation of azo dyes was attained at loading rates BV,AZ up to 40 mg L−1d−1. At higher BV,AZ values (80 mg L−1 d−1), dye decolorization and biodegradation of the intermediaries 4‐amino‐naphthalenesulphonic acid (4‐ANS) and 1‐amino‐2‐naphthol (1‐A2N) was almost complete. However, a diminution in COD and TOC removal efficiencies was observed in correspondence to the 4‐aminobenzenesulfonic acid (4‐ABS) accumulation in the bioreactor. Although the oxygen transport rate improved the azo dye mineralization, the results suggest that the removal efficiency of azo dyes was affected by biofilm detachment at relatively high QGI and BV,AZ values. After 225 days of continuous operation of the 2S‐RFBR, eight bacterial strains were isolated from the biofilm attached to the porous support. The identified genera were: Arthrobacter, Variovorax, Agrococcus, Sphingomonas, Sphingopyxis, Methylobacterium, Mesorhizobium, and Microbacterium.

Degradation kinetics of 4-amino naphthalene-1-sulfonic acid by a biofilm-forming bacterial consortium under carbon and nitrogen limitations

By decolorization of azo dyes, caused by reductive cleavage of the azo linkage, toxic or recalcitrant amines are generated. The present study deals with the effect of the inflowing medium composition (C:N ratio) on the kinetic behavior of a bacterial biofilm-forming consortium, able to use as carbon, nitrogen and sulfur source, the molecule of 4-aminonaphthalene-1-sulfonic acid (4ANS), which is one of the most recalcitrant byproducts generated by decolorization of azo dyes. All the experiments were carried out at room temperature in a lab-scale packed-bed biofilm reactor. Because environmental conditions affect the bioreactor performance, two mineral salts media containing 4ANS, with distinct C:N ratios; 0.68 (carbon as the limiting nutrient) and 8.57 (nitrogen as the limiting nutrient) were used to evaluate their effect on 4ANS biodegradation. By HPLC and COD measurements, the 4ANS removal rates and removal efficiencies were determined. The cultivable bacterial strains that compose the consortium were identified by their 16S rDNA gene sequence. With the enrichment technique used, a microbial consortium able to use efficiently 4ANS as the sole carbon source and energy, nitrogen and sulfur, was selected. The bacterial strains that constitute the consortium were isolated and identified. They belong to the following genera: Bacillus, Arthrobacter, Microbacterium, Nocardioides, and Oleomonas. The results obtained with this consortium showed, under nitrogen limitation, a remarkable increase in the 4ANS removal efficiency ηANS, and in the 4ANS volumetric removal rates RV,4ANS, as compared to those obtained under carbon limitation. Differences observed in bioreactor performance after changing the nutrient limitation could be caused by changes in biofilm properties and structure.

Steady-state inhibition model for the biodegradation of sulfonated amines in a packed bed reactor

Aromatic amines are important industrial products having in their molecular structure one or more aromatic rings. These are used as precursors for the synthesis of dyes, adhesives, pesticides, rubber, fertilizers and surfactants. The aromatic amines are common constituents of industrial effluents, generated mostly by the degradation of azo dyes. Several of them are a threat to human health because they can by toxic, allergenic, mutagenic or carcinogenic. The most common are benzenesulfonic amines, such as 4-ABS (4-aminobenzene sulfonic acid) and naphthalene sulfonic amines, such as 4-ANS (4-amino naphthalene sulfonic acid). Sometimes, the mixtures of toxic compounds are more toxic or inhibitory than the individual compounds, even for microorganisms capable of degrading them. Therefore, the aim of this study was to evaluate the degradation of the mixture 4-ANS plus 4-ABS by a bacterial community immobilized in fragments of volcanic stone, using a packed bed continuous reactor. In this reactor, the amines loading rates were varied from 5.5 up to 69 mg L(-1) h(-1). The removal of the amines was determined by high-performance liquid chromatography and chemical oxygen demand. With this information, we have studied the substrate inhibition of the removal rate of the aromatic amines during the degradation of the mixture of sulfonated aromatic amines by the immobilized microorganisms. Experimental results were fitted to parabolic, hyperbolic and linear inhibition models. The model that best characterizes the inhibition of the specific degradation rate in the biofilm reactor was a parabolic model with values of RXM=58.15±7.95 mg (10(9) cells h)(-1), Ks=0.73±0.31 mg L(-1), Sm=89.14±5.43 mg L(-1) and the exponent m=5. From the microbial community obtained, six cultivable bacterial strains were isolated and identified by sequencing their 16S rDNA genes. The strains belong to the genera Variovorax, Pseudomonas, Bacillus, Arthrobacter, Nocardioides and Microbacterium. This microbial consortium could use the mixture of aromatic amines as sources of carbon, nitrogen, energy and sulfur.

Simulation and experimental validation of a gradient feeding system for fast assessment of the kinetic behavior of a microbial consortium in a tubular biofilm reactor

This study deals with the mathematical simulation and experimental validation of a gradient system for the gradual change of the imidacloprid loading rate to a tubular biofilm reactor (TBR). The strategy was used for fast studies of the kinetic and stoichiometric impact caused by the increase in the pesticide loading rate in a TBR, running in plug flow regime. Seemingly, this strategy has never been used for biokinetic and stoichiometric studies in biofilm reactors. For this purpose, a mathematical model describing the substrate transient behavior Sg(t) in a concentration gradient generator system using variable volume tanks is proposed. A second model, representing the temporary variation in the loading rate of imidacloprid to an aerated equalizer tank preceding the packed zone of the TBR, is also presented. Both models were experimentally confirmed. After the treatment of the experimental data, the kinetic and stoichiometric changes occurring in the TBR, caused by the gradual increase in the imidacloprid loading rate, were readily evaluated. Although the structure of the microbial community, at the phylum level, showed similar behavior along the tubular reactor, the stress produced by the gradual increase in imidacloprid concentration had functional consequences on the mixed microbial populations which were reflected on the stoichiometric and kinetic parameters. After increasing more than five times the imidacloprid loading rate to the TBR, the imidacloprid removal efficiency decayed about 40%, and the microbial-specific removal rate of the insecticide showed a decrease of about 30%.