Susana Rossi

Degradation and detoxification of cresols in synthetic and industrial wastewater by an indigenous strain of Pseudomonas putida in aerobic reactors

We studied the degradation of mixtures of o‐cresol, m‐cresol, and p‐cresol, by Pseudomonas putida isolated from natural sources, and the application of this degradation to the depuration and detoxification of synthetic and industrial wastewater. Biodegradation assays were performed in batch and continuous‐flow fixed‐bed aerobic reactors. Biodegradation was evaluated by cresol determination using micellar electrokinetic capillary chromatography, UV spectrophotometry, and chemical oxygen demand (COD). Mineralization of cresols was assessed by gas chromatography performed both at the end of the batch process and in the continuous flow reactor effluent. Microbial growth was measured by the plate count method. Scanning electronic microscopy was employed to observe bacterial cells adsorbed on polyvinyl chloride cylinders in the reactor. Detoxification was evaluated by Vibrio fischeri, Pseudokirchneriella subcapitata, and Daphnia magna toxicity tests. Results obtained show that under batch conditions the strain grew exponentially with 100, 200, and 300 mg/L of each of the isomers in synthetic minimal medium within 48 h; in industrial wastewater with 540 mg/L of cresols similar results were obtained. Removal of cresols and COD was higher than 99.9% and 95.0%, respectively. When assays were performed in continuous flow reactor in synthetic wastewater under operating conditions a removal of total cresols and COD of 99.9% and 96.4%, respectively, was achieved. Results of capillary electrophoresis may suggest a concurrent isomers utilization and simultaneous growth on the substrates. Toxicity was neither detected at the end of the batch process nor in the continuous flow reactor effluent.

Case Method in the Teaching of Food Safety

One of the fundamental aims of education is the integration of theory and practice. The case method is a teaching strategy in which students must apply their knowledge to solve real-life situations. They have to analyze the case described and propose the best possible solution. Although the case may be written, the use of new information and communication technologies can develop the case plan in ways that would achieve greater realism and widen the possibilities for discussion. This paper describes our experience in implementing the case method to teach food safety in the Chair of Hygiene. At first this methodology was used to improve the teaching of good practices in food preparation, later practical work was implemented where small groups of students designed and carried out the microbiological analysis of suspected food. This practical work was presented online as a multimedia activity; students were given face-to-face and on-line tutoring. Evaluation was based both on students’ performance and on a survey they had to answer. More than 92% of students regarded the methodology used for the understanding of the unit as sound. Professors collaboration on providing guidance and multimedia presentation were also positively assessed. The bringing together of face-to-face and virtual tasks and small-group discussion of cases under professors guidance contributed to making good use of the positive aspects of this methodology in order to improve the understanding of problems which do not always have a single answer.