Denitrification in the Presence of Chlorophenols: Progress and Prospects

Diverse industrial effluents may contain recalcitrant compounds such as chlorophenols. Besides, excessive use of pesticides in agriculture is a major cause of the appearance of chlorophenols in surface and groundwater. To mitigate and control the effects of chlorophenols in the environment, various methods have been developed for their elimination. Biological processes represent a sustainable and economical alternative that can lead to the mineralization of chlorophenols and be effective for the removal of these pollutants from different water bodies, such as rivers, groundwater, and wastewater. Some studies have reported that chlorophenols mineralization and nitrate reduction may simultaneously be performed. Other works have suggested that a reductive dechlorination occurs such as the first step and later, the phenol formed is subsequently mineralized by denitrification. However, the published information can be confusing as the denitrifying process is often associated with the sole nitrate consumption without corroborating the total reduction of nitrate to N2. Additionally, there are alternative systems that combine biological process with a chemical or electrochemical process for chlorophenols removal. This chapter focuses on the advances accomplished in the study of the removal of chlorophenols under denitrifying conditions with the aim of having a clearer panorama of the treatment alternatives that can be applied for treatment of this type of effluents

Diversidad y flexibilidad metabólica de consorcios nitrificantes y desnitrificantes usados en el tratamiento de aguas residuales

Background. Nitrification and denitrification processes are part of the biogeochemical nitrogen cycle. The microorganisms that carry them out are used in wastewater treatment systems to remove a very common pollutant; ammonium (NH4 +) and release molecular nitrogen (N2 ). Objective. Show the diversity and metabolic flexibility of nitrifying and denitrifying consortia used in the elimination of nitrogen from wastewater. Results. Among these taxonomically diverse microorganisms, bacteria are the best studied. They are divided and named according to the main process they carry out. Although thanks to the genes they share, their diversity and metabolic flexibility can enable them to survive under changing conditions and through functions different from the process that is canonically attributed to them. The characteristic genes of these processes are used as molecular markers in community studies. However, taxa known canonically as nitrifying may have functional genes of the denitrifying process. Microorganisms classified as typically denitrifying may have functional genes of the nitrifying process. The consortia (flocules, granules and biofilms) used in the elimination of NH4 + are an example of communities that can have superior or different capacities than those of their individual members. Conclusions. This review compiles physiological, genetical, and ecological information that contributes to a better understanding of the great diversity and metabolic flexibility of nitrifying and denitrifying consortia. It stands out that in artificial systems, a better knowledge of the participating taxa and their trophic, metabolic and communication relationships, would allow a better control of the nitrifying and denitrifying processes for making them more efficient and stable.Antecedentes. Los procesos de la nitrificación y desnitrificación forman parte del ciclo biogeoquímico del nitrógeno. Los microorganismos que los llevan a cabo son empleados en los sistemas dedicados al tratamiento de aguas residuales para eliminar un contaminante muy común; el amonio (NH4 +), y liberar nitrógeno molecular (N2 ). Objetivo. Mostrar la diversidad y flexibilidad metabólica de consorcios nitrificantes y desnitrificantes usados en la eliminación de nitrógeno de aguas residuales. Resultados. En estos microorganismos taxonómicamente diversos, las bacterias son las mejor estudiadas. Se las divide y nombra según el proceso principal que realizan. Aunque en realidad gracias a los genes que comparten, pueden presentar una diversidad y flexibilidad metabólica, que las capacita para sobrevivir en condiciones cambiantes y con funciones distintas del proceso que canónicamente se les atribuye. Los genes característicos de estos procesos son empleados como marcadores moleculares en estudios de comunidades. Sin embargo, taxones conocidos canónicamente como nitrificantes pueden tener genes funcionales propios del proceso desnitrificante. Microorganismos catalogados como típicamente desnitrificantes pueden tener genes funcionales del proceso nitrificante. Los consorcios (flóculos, gránulos y biopelículas) empleados en la eliminación de NH4 + son un ejemplo de comunidades que pueden tener capacidades superiores o distintas de las que tienen sus integrantes individualmente. Conclusiones. La presente revisión conjunta información fisiológica, genética y ecológica que contribuye a entender mejor la gran diversidad y flexibilidad metabólica de los consorcios nitrificantes y desnitrificantes. Se destaca que, en los sistemas artificiales, un mayor conocimiento de los taxones participantes, así como de sus relaciones tróficas, metabólicas y de comunicación posibilitaría un mejor control de los procesos nitrificante y desnitrificante para que estos sean más eficientes y estables

Selective biosorption of lanthanide (La, Eu, Yb) ions by an immobilized bacterial biomass

International audienceThe removal of metallic ions La3+, Eu3+ and Yb3+ from aqueous solution by immobilized biomass of Pseudomonas aeruginosa was investigated in batch and column reactors. Batch studies consisted in kinetic measurements for lanthanum adsorption by biomass-chitosan beads. Results did not show a significant effect of the presence of bacteria into chitosan matrix on the lanthanum uptake. Then, laboratory scale fixed-bed column experiments were carried out using biomass-entrapped polyacrylamide gel beads, which contained approximately 48% (dry weight basis) of biomass. The lanthanum sorption was dependent on the superficial liquid velocity based on empty column in the range 0.76-2.29 m.h(-1). The removal of lanthan decations (2 mM) at pH 5.0 and 0.76 m/h was 198 mu mol.g(-1) (dry biomass) for lanthanum, 167 mu mol.g(-1) for europium and 192 mu mol.g(-1) for ytterbium (+/-10%). These results are of the order of 1.7-2 times lower than those observed in batch systems with free bacterial cells. Column experiments with mixed-cation solutions showed the following sequence of preferential biosorption: Eu3+ > Yb3+ > La3+

Selective biosorption of lanthanide (La, Eu, Yb) ions by Pseudomonas aeruginosa

International audienceThe ability of Pseudomonas aeruginosa to adsorb selectively La3+, Eu3+, and Yb3+ from aqueous solution was investigated. The lanthanide biosorption equilibrium obeyed the Brunauer-Emmett-Teller isotherm model, indicating multilayer adsorption. Determined levels of maximum adsorption capacities were 397 mu mol/g far lanthanum, 290 mu mol/g for europium and 326 mu mol/g for ytterbium (+/-10%). The results indicated that there were about 100 preferential sites for lanthanum per g of dry biomass. Experiments with mixed-cation solutions showed that the sequence of preferential biosorption was Eu3+ = Yb3+ > La3+. Biomasses dried at 37 and 70 degrees C showed the same selective behavior as wet biomass. Inert microbial biomass dried at 37 degrees C appeared to be the most efficient farm for experimental use. The uptake of lanthanide by P. aeruginosa cells was not affected by the presence of sodium, potassium, calcium, chloride, sulfate and nitrate ions. Aluminum was a strong inhibitor of lanthanide ions biosorption. 87% of the total Al3+ was removed from the 3 mM solution, whereas only 8%, 20% and 3% of the total La3+, Eu3+, and Yb3+, respectively, were sorbed from 3 mM solutions. The results suggested that cells of Pseudomonas aeruginosa may find promising applications for removal and separation of lanthanide ions from aqueous effluents

Selective biosorption of lanthanide (La, Eu) ions by Mycobacterium smegmatis

International audienceThe ability of Mycobacterium smegmatis to adsorb lanthanide (lanthanum (La), europium (Eu)) cations from aqueous solutions was studied. Adsorption isotherms of lanthanum ions showed that the adsorption capacity was higher for wet biomass than for dry biomasses (37 degrees C and 70 degrees C). The biosorption capacity on cells dried at 70 degrees C is reduced. Potentiometric titrations revealed the existence of at least two types of acidic functions in the cell wall, with strong and weak affinity. The weak acidic groups became inaccessible at a drying temperature of 70 degrees C. Lanthanum and europium adsorption by Mycobacterium smegmatis obeyed the Freundlich and Langmuir isotherm relations. Eu3+ was preferentially adsorbed with respect to the lanthanum cations. The extended Langmuir equation enabled a preliminary theoretical approach of the multicomponent adsorption phenomenon

Rare earth elements removal by microbial biosorption: A review

International audienceThis paper reviews published work on the sorption of rare earth elements by microbial biomass. In a first part, the biosorption capacities and the various experimental conditions performed in batch reactor experiments are compared. Secondly, sorption modelling generally used in biosorption studies are described. Thirdly, the microbial cell wall characteristics of the metallic ion binding sites are considered. From these observations it seems that the important functional groups for metallic ion fixation are the carboxyl and the phosphate moieties. Moreover, the competing effect of various ions like aluminium, iron, glutamate, sulphate etc. is described. Finally, some adsorption results of the rare earth elements in dynamic reactors are presented

Characterization of lanthanide ions binding sites in the cell wall of Pseudomonas aeruginosa

International audienceEarlier studies have shown that Pseudomonas aeruginosa can adsorb selectively La3+, Eu3+, and Yb3+ from aqueous solution. These bacterial cells may find promising applications for removal and separation of lanthanide ions from contaminated effluents. In this work, potentiometric titrations and time-resolved laser-induced fluorescence spectroscopy were used to determine the binding sites of the biomass and, consequently, to elucidate the underlying mechanisms involved in the biosorption of lanthanide ions. Around 90 +/- 5% of the adsorbed lanthanum was easily desorbed with an EDTA 0.1 M solution. In most instances, lanthanides seemed to concentrate extracellularly. The diversity of potential metal-binding groups was revealed by potentiometric titrations of the biomass. The amount of strong and weaker acidic functional groups in the wet biomass was estimated at 0.24 +/- 0.04 acid 0.86 +/- 0.02 mequiv/g, respectively. Time-resolved laser-induced fluorescence spectroscopy on europium-loaded P. aeruginosa biomass suggests that europium binding occurs mostly through carboxyl and phosphate groups

Fixed-bed study for lanthanide (La, Eu, Yb) ions removal from aqueous solutions by immobilized Pseudomonas aeruginosa: experimental data and modelization

International audienceA fixed-bed study was carried out by using cells of Pseudomonas aeruginosa immobilized in polyacrylamide gel as a biosorbent for the removal of lanthanide (La, Eu, Yb) ions from aqueous solutions. The effects of superficial liquid velocity based on empty column, particle size, influent concentration and bed depth on the lanthanum breakthrough curves were investigated. Immobilized biomass effectively removed lanthanum from a 6 mM solution with a maximum adsorption capacity of 342 mumolg(-1) (+/-10%) corresponding closely to that observed in earlier batch studies with free bacterial cells. The Bohart and Adams sorption model was employed to determine characteristic parameters useful for process design. Results indicated that the immobilized cells of P. aeruginosa enable removal of lanthanum, europium and ytterbium ions from aqueous effluents with significant and similar maximum adsorption capacities. Experiments with a mixed cation solution showed that the sequence of preferential biosorption was Eu3+ greater than or equal to Yb3+ > La3+. Around 96 +/- 4% of the bound lanthanum was desorbed from the column and concentrated by eluting with a 0.1 M EDTA solution. The feasibility of regenerating and reusing the biomass through three adsorption/desorption cycles was suggested. Neural networks were used to model breakthrough curves performed in the dynamic process. The ability of this statistical tool to predict the breakthrough times was discussed. (C) 2002 Elsevier Science Ltd. All rights reserved