Carmen Arnaiz

Anaerobic digestion of dairy wastewater by inverse fluidization: The inverse fluidized bed and the inverse turbulent bed reactors

Abstract This paper describes the application of the inverse fluidization technology to the anaerobic digestion of dairy wastewater. Two reactors were investigated: the inverse fluidized bed reactor and the inverse turbulent reactor. In these reactors, a granular floating solid is expanded by a down‐flow current of effluent or an up‐flow current of gas, respectively. The carrier particles (Extendospheres(™)) were chosen for their large specific surface area (20,000 m2m−3) and their low energy requirements for fluidization (gas velocity of 1.5 mm s−1, 5.4 m h−1). Organic load was increased stepwise by reducing hydraulic retention time from more than 60 days to 3 days, while maintaining constant the feed COD concentration. Both reactors achieved more than 90% of COD removal, at an organic loading rate of 10–12 kgCOD m−3d−1, respectively. The performances observed were similar or even higher than that of other previously tested fluidized bed technologies treating the same wastewater. It was found that the main advantages of this system are: low energy requirement, because of the low fluidization velocities required; there is no need of a settling device, because solids accumulate at the bottom of the reactor, so they can be easily drawn out and particles with high‐biomass content can be easily recovered. Lipid phosphate concentration has been revealed as a good method for biomass estimation in biofilms since it only includes living biomass.

Influence of different anoxic time exposures on active biomass, protozoa and filamentous bacteria in activated sludge

Medium-sized wastewater treatment plants are considered too small to implement anaerobic digestion technologies and too large for extensive treatments. A promising option as a sewage sludge reduction method is the inclusion of anoxic time exposures. In the present study, three different anoxic time exposures of 12, 6 and 4 hours have been studied to reduce sewage sludge production. The best anoxic time exposure was observed under anoxic/oxic cycles of 6 hours, which reduced 29.63% of the biomass production compared with the oxic control conditions. The sludge under different anoxic time exposures, even with a lower active biomass concentration than the oxic control conditions, showed a much higher metabolic activity than the oxic control conditions. Microbiological results suggested that both protozoa density and abundance of filamentous bacteria decrease under anoxic time exposures compared to oxic control conditions. The anoxic time exposures 6/6 showed the highest reduction in both protozoa density, 37.5%, and abundance of filamentous bacteria, 41.1%, in comparison to the oxic control conditions. The groups of crawling ciliates, carnivorous ciliates and filamentous bacteria were highly influenced by the anoxic time exposures. Protozoa density and abundance of filamentous bacteria have been shown as promising bioindicators of biomass production reduction.

CONECTANDO LA TEORÍA CON LA PRÁCTICA EN ASIGNATURAS DE INGENIERÍA QUÍMICA

This paper presents the design of a virtual undergraduate course of Unit Operations in Chemical Engineering and its implementation in the WebCT platform. The opinion, use and impact on the academic performance of a group of students are analyzed through a questionnaire. This information allowed determining the positive perception of the students about the visual contents as an important complement of learning. However, the students did not actively use the visual tool while studying the course subjects, but this did not significantly impact the academic performance of the students. It seems that too many face-toface classes, too much homework, and the medium-high level of the group of students would explain these results.