Effect of shear stress and growth conditions on detachment and physical properties of biofilms.

Detachment is one of the major processes determining the physical structure and microbial functionalities of biofilms. To predict detachment, it is necessary to take the mechanical properties of the biofilm and the effect of both hydrodynamic and growth conditions into account. In this work, experiments were conducted with biofilms developed under various shear stresses and with various substrate natures. In addition, two cases were considered in order to differentiate between the effect of hydrodynamic factors and growth factors: the biofilms were directly grown under the targeted shear stress (τ) condition or they were precultivated under very low shear stress (0.01 Pa) and then exposed to high shear stress in the range of 0.1-13 Pa. An exponential and asymptotic decrease of the biofilm thickness and mass with increasing τ was observed in both cases. On contrary density, expressed as the biofilm dry mass on a known substratum divided by the average thickness increased with τ. Denitrifying biofilms always showed greater thickness and density than oxic biofilms. These results showed the presence of a compact basal layer that resisted shear stresses as high as 13 Pa whatever the culture conditions. Above this basal layer, the cohesion was lower and depended on the shear stress applied during biofilm development. The application of shear stress to the biofilms resulted in both detachment and compression, but detachment prevailed for the upper part of the biofilms and compression prevailed for the basal layers. A model of biofilm structure underlying the stratified character of this aggregate is given in terms of density and cohesion.

Recycled and virgin plastic carriers in hybrid reactors for wastewater treatment.

The reduction of organic and nitrogen pollution of wastewater was investigated in two hybrid reactors and compared with the reduction obtained by using a conventional activated sludge reactor (ASR) run as a control. Both HR-1 and HR-2 were activated sludge systems where a low-density carrier, P1 (polyethylene) for HR-1 and P2 (recycled plastics) for HR-2, was added. Firstly, the three reactors were operated at 10 days Suspended Solid Retention Time (SRT(SS)), leading to a complete nitrification. Secondly, the SRT(SS) for each reactor was lowered to 3 days. Nitrification was lost for the ASR but remained complete for HR's. Respirometric techniques were used to measure fixed or suspended biomass activities for heterotrophic and autotrophic biomass. More than 90% of the autotrophic activity was found on the supports whatever the SRT(SS) used. The results may underline the role of the carrier geometry or surface characteristics on the autotrophic/heterotrophic microorganism distribution.

Nitrification in hybrid reactor with a recycled plastic support material

This work investigated the nitrification in a hybrid moving bed pilot scale reactor, which used a low density recycled plastic support material for biomass growth. The filling rate was 20 percent of its working volume (22L). The feeding and recirculation outflow was 45L/day. The reactor operated at a temperature of 16°C, in two phases, according to the sludge retention time (SRT): A phase was 10 days and B phase was 3 days (average values). The applied average volumetric nitrogen and organic loads were 0.16KgTKN/m3.day and 1kgCOD/m³.day, respectively. The results showed an average nitrogen removal of 95 percent and average COD removal of 89 percent, in both A and B phases. Nitrogen removal rates were independents of the SRT.

Resultados funcionales de la inestabilidad radiocubital distal mediante la transposición de la mitad cubital del músculo cubital posterior / Functional results of diastal radio-ulnar instability by transposition of the medial half of the extensor carpi ulnaris tendon

Se trataron 11 pacientes con inestabilidad radiocubital distal, mediante la transposición de la mitad interna del tendón del cubital posterior, pasado del cúbito al radio y protegido con un tornillo AO cortical de 3.5 mm tricortical del cúbito al radio. Fueron 8 del sexo masculino y 3 del femenino. La edad varió de 19 a 38 años con promedio de 30. Los resultados mostraron una recuperación de los arcos de movimiento prácticamente a lo normal en todos los casos. La fuerza mejoró en 9 casos (81 por ciento). Sin embargo el dolor sólo desapareció en 3 casos (27 por ciento), disminuyó en 7 (73 por ciento) y desapareció sólo en 3 (27 por ciento). Regresaron a sus actividades originales 7 individuos, se requirió un cambio temporal de actividades en 3 y uno tuvo que se retirado del trabajo