RESUMEN

Various methods used to assess the biodegradability of chemicals often employ activated sludge as an inoculum since chemicals that ultimately enter the environment are often discharged through wastewater. Differences in the structure and function of activated sludge microbial communities that may complicate interpretation of biodegradation tests could arise from differences in wastewater composition, wastewater treatment plant (WWTP) operation, or manipulations done after collection of the activated sludge. In this study, various methods were used to characterize the structure of microbial communities found in freshly collected activated sludge from WWTPs in Japan, Europe, and the United States, as well as sludge that had been continuously fed either sewage or a glucose-peptone mixture for several weeks after collection. Comparisons of biomass levels, whole-community substrate utilization (determined using Biolog GN and GP plates), and phospholipid fatty acid (PLFA) profiles indicated there were both geographical and temporal differences among freshly collected activated sludge samples. Moreover, marked shifts in the structure of activated sludge microbial communities occurred upon continuous cultivation in the laboratory for 5 weeks using a glucose-peptone feed. These shifts were evident from whole-community substrate utilization and PLFA profiles as well as differences in the profiles of 16S rDNA genes from numerically dominant populations obtained by denaturing gradient gel electrophoresis and terminal restriction fragment analyses. Further studies are needed to better define the variability within and between activated sludge from wastewater treatment plants and laboratory reactors and to assess the impact of such differences on the outcome of biodegradability tests.

Asunto(s)

Bacterias , Contaminantes Ambientales/metabolismo , Aguas del Alcantarillado/microbiología , Eliminación de Residuos Líquidos/métodos , Biodegradación Ambiental , Biomasa , ADN Bacteriano/análisis , Monitoreo del Ambiente/métodos , Ácidos Grasos/análisis , Glucosa/metabolismo , Fosfolípidos/análisis , Reacción en Cadena de la Polimerasa , Dinámica Poblacional , ARN Ribosómico 16S/análisis

RESUMEN

A bisubstrate secondary utilization model is based on the concept that an individual substrate can be utilized not only by the biomass by its utilization but also by the biomass made from the utilization of the other substrate. When substrate concentrations are low, a key factor is having sufficient substrate to initiate biofilm growth. Modeling results for three characteristic cases demonstrate that satisfying a total S(min) concentration for a bisubstrate system is the necessary condition for initiating biofilm growth and simultaneous utilization of both substrates. Because having more than one substrate supporting biofilm growth enhances the removal of each compound, the utilization rate of a specific compound can be increased by the concentration of other compounds, and the total S(min) concentration can be less than the weighted average of individual S(min) values.

RESUMEN

A bisubstrate system having S(s1) > S(min 1) was tested with phenol and acetate as model compounds in completely mixed biofilm reactors. Two series of experiments compared the kinetics of phenol removal as a single substrate and as part of a bisubstrate system having a fixed total feed COD. Experimental results showed that, although the rate of utilization of either substrate was almost the same in a bisubstrate system as in a single substrate system, the utilization rate of either compound always was slightly greater in a bisubstrate system than in a single-substrate system. This slight enhanced removal of an individual compound in a bisubstrate system was attributed to the extra biomass accumulated from the utilization of the other substrate. As the fraction of the feed COD contributed by an individual compound decreased in a bisubstrate system, the effluent concentration of that compound decreased and its fractional removal efficiency increased. The bisubstrate secondary-utilization model successfully described the experimental results and explained the differences that occurred as phenol became a smaller fraction of the fixed total feed COD.

RESUMEN

This article develops and utilizes an in situ technique to estimate the Monod half-maximum rate concentration, K(s) and the maximum specific utilization rate constant, k, for biofilms. The technique employs a curve-matching method with kinetic results from several short-term experiments with completely mixed biofilm reactors. Use of the in situ method eliminates the two drawbacks of using conventional suspended-growth measurements to characterize biofilm: possible alteration of cell physiology and a major investment to run the suspended-growth tests. Results with five cultures of biofilm-forming oligotrophs demonstrated the in situ technique and supported the hypothesis that K(s) values were lower for the biofilm oligotrophs than for typical copiotrophs.