Successive bioanode regenerations to maintain efficient current production from biowaste.

The long-term operation of efficient bioanodes supplied with waste-derived organics is a key challenge for using bioelectrochemical systems as a waste valorization technology. Here, we describe a simple procedure that allowed maintaining highly efficient bioanodes supplied with biowaste. Current densities up to 14.8 A/m(2) were obtained with more than 40% of the electrons introduced as biowaste being recovered in the electrical circuit. Three fed-batch reactors were started at different biowaste loading rates. A decline of coulombic efficiencies between 22 and 31% was recorded depending on the reactor over the first 3 weeks of operation. A renewal procedure of the anode was thereafter implemented, which led to a recovery of initial performances. The second and the third renewal, allowed maintaining stable high level performances with coulombic efficiency of approximately 40% over at least 3 weeks. Electroactive biofilm dynamics were monitored using 16S rRNA-gene amplicon sequencing. Retrieved sequences were dominated by Geobacter sulfurreducens-related reads (37% of total sequences), which proportion however varied along the experiment. Interestingly, sequences affiliated to various Bacteroidetes groups were also abundant, suggesting an adaptation of the anodic biofilm to the degradation of biowaste through metabolic interactions between microbial community members.

Understanding the mechanisms of thermal disintegrating treatment in the reduction of sludge production.

Among the technologies aimed at reducing sludge production, the combination of thermal treatment at 95 degrees C of sludge and the activated sludge process is a promising route. The feasibility of such a combined process is demonstrated (up to 60% sludge reduction) and the impacts of operating conditions on its efficiency are presented. Major emphasis was put on understanding the complex phenomena occurring within the thermal treatment: release and biodegradability of sludge organic matter, impact on the biological activity (decay, maintenance requirements, etc.). These effects were taken into account for the development of an ASM1-based model. Comparison between the modeling approach and experimental data (continuous and batch) showed that thermal treatment had three major issues partly explaining the reduction of sludge production: (i) a low release of organics; (ii) an immediate and reversible biological inactivation associated with additional maintenance energy requirements; and (iii) a potential inert production.

Structural Interpretations of Static Light Scattering Patterns of Fractal Aggregates.

A method based on static light scattering by fractal aggregates is introduced to extract structural information. In this study, we determine the scattered intensity by a fractal aggregate calculating the Structure and the Form factors noted, respectively, S(q) and F(q). We use the approximation of the mean field Mie scattering by fractal aggregates (R. Botet, P. Rannou, and M. Cabane, appl. opt. 36, 8791, 1997). This approximation is validated by a comparison of the scattering and extinction cross sections values calculated using, on the one hand, Mie theory with a mean optical index n) and, on the other hand, the mean field approximation. Scattering and extinction cross sections values differ by about 5%. We show that the mean environment of primary scatterers characterized by the optical index n(s) must be taken into account to interpret accurately the scattering pattern from fractal aggregates. Numerical simulations were done to evaluate the influence of the fractal dimension values (D(f)>2) and of the radius of gyration or the number of primary particles within the aggregates (N=50 to 250) on the scatterers' mean optical contrast (n(s)/n). This last parameter plays a major role in determining the Form factor F(q) which corresponds to the primary particles' scattering. In associating the mean optical index (n) to structural characteristics, this work provides a theoretical framework to be used to provide additional structural information from the scattering pattern of a fractal aggregate (cf. Part II). Copyright 2000 Academic Press.

Structural Interpretations of Static Light Scattering Patterns of Fractal Aggregates.

Information on the size and structure of aggregates is critical in predicting the formation kinetics, settling velocities, and reactivity of particle aggregates. For some systems, however, accessing this information may be very difficult. Light scattering measurements are among the most useful techniques for accessing such information. In the case of large primary particles forming aggregates, the common Rayleigh approximation is not valid. Instead, Mie scattering must be used and multiple scattering must be accounted for. Moreover, size polydispersity and structure of aggregates are combined in the scattered intensity measurements. This work presents an experimental validation of a new theoretical approach for extracting information on both aggregate structure and size when multiple scattering cannot be neglected. The chemically controlled aggregation of 0.8-µm latex particles demonstrates the following: (1) Polydispersity effects prevent the interpretation of data to obtain structural information from the Structure factor S(q). (2) The calculated optical contrast decreasing during the aggregation can be correlated with the structural changes in the growing aggregates independently of size polydispersity. We have shown that a strict correlation can be obtained between the fractal dimension D(f) and the scatterers' mean optical contrast calculated at large scattering angles. (3) The changes in the Form factor (F(q)) due to multiple scattering when particles are close together yield a predicted structure that is in agreement with expected fractal dimension values and therefore S(q) can be described in term of both structure and size polydispersity. Copyright 2000 Academic Press.

Estimation of nitrifying bacterial activities by measuring oxygen uptake in the presence of the metabolic inhibitors allylthiourea and azide

The effects of two metabolic inhibitors on an enriched nitrifying biomass during incubation for short periods of time were investigated by determining respirometric measurements. Allylthiourea (86 &mgr;M) and azide (24 &mgr;M) were shown to be strong, selective inhibitors of ammonia and nitrite oxidation, respectively. Consequently, a differential respirometry method for estimating nitrifying and heterotrophic bacterial activities within a mixed biomass is proposed.