The present study implements a time-optimal control strategy for a discontinuous aerobic bioreactor, used to treat highly concentrated toxic wastewater present in some effluents of the chemical and petrochemical industries, using respirometric techniques. The control strategy regulates the feed rate to maintain a constant optimal substrate concentration in the reactor, which in turn minimizes the reaction time. Since this control requires on-line knowledge of unmeasurable variables, an Extended Kalman Filter is used as a nonlinear observer. The experimental setup was a 7 litre laboratory bioreactor used to treat synthetic wastewater with high concentrations of 4-chlorophenol. The controller consisted of a personal computer with data acquisition hardware and real-time software tools, peristaltic pumps and an electronic oxygen meter. Three experiments were performed: one to obtain parameters and calibrate the observer, another one to validate the time-optimal strategy and a final one to evaluate theperformance of a fully automated time-optimal operation. When well calibrated, the observer provided good enough estimates and the controller worked as expected, reducing reaction time and increasing the overall efficiency of the bioreactor, when compared with the usual SBR-type operation.

This study presents two strategies used to enhance the biological degradation of phenolic wastewaters. In the first one the operation of a sequencing batch biofilter added with granular activated carbon (SBB-AC) was studied. The second strategy presents the results of the automation of a sequencing batch reactor in order to optimize the reaction phase. In this case, the dissolved oxygen was employed to monitor and control the reactor. The results of the SBB-AC system, based on the configuration of the reactor, type and size of activated carbon and size of the packing material, are discussed. The system biodegraded efficiently (total phenol removals as high as 97%) high concentrations (600 mg/l) of a mixture of phenol, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol. Maximal eliminated loads of 4.33 kg COD/m3-d were achieved. For the second strategy, the applicability of an optimal control for a SBR using the dissolved oxygen as the measured variable was demonstrated. When the reactor was operated under the time-optimal control strategy, the degradation time of 4-chlorophenol was reduced. A very satisfactory operation of the reactor was observed, since the removal efficiencies were around 99%.

El artículo destaca la necesidad de abordar la historia de la empresa pública latinoamericana por haber cumplido un papel relevante en el desarrollo de la región durante el siglo XX, pero también por la actual re-emergencia de este tipo de organismos en el sector energético internacional, seguir cumpliendo en muchos países un papel estratégico y finalmente porque tras décadas de privatizaciones hay una débil memoria colectiva sobre estos organismos, predominando la versión neoliberal que justificó la venta del acervo público. ¿Conocemos bien la historia sobre la importancia y trayectoria de las empresas públicas en México y América Latina? ¿Qué explica su resistencia tras décadas de privatizaciones? Estas preguntas se responden en este dossier de la Revista de Gestión Pública, que reúne un grupo de trabajos que analizan los casos de Uruguay, Costa Rica, Bolivia, Brasil y Argentina entre 1912 y 2012, dando luces sobre las actividades empresariales del Estado bajo distintos modelos económicos. En esos países las empresas públicas se han ubicado en sectores básicos para el funcionamiento de las economías, como telecomunicaciones, electricidad, petróleo, transportes y, en menor medida manufacturas. En la última sección se hace una invitación no sólo a la lectura sino a iniciar una agenda de análisis que permita develar la compleja historia de estos organismos públicos.

Se presenta un artículo sobre las relaciones entre infraestructuras y sistemas sociotécnicos del transporte en los siglos XIX y XX, para comprender las bases materiales del actual proceso de globalización y la relevancia que tiene la historia de los procesos logísticos y de las cadenas de bienes. Si bien en la historia económica se le ha dado una atención mayor a la producción de materias primas exportables y bienes industriales, en este texto analizaremos en los casos de Chile y México, entre 1850 y 1970, la movilidad de factores, su distribución y la coordinación de equipos, normas, rutinas y personal que conformaron una cadena de transformación que integró desde las materias primas al bien final. Se plantea que las infraestructuras establecieron un patrón fijo y perdurable de flujos territoriales, de larga duración, de las llamadas cadenas de movimiento.

In his 1950 study, Mexico: The Struggle for Peace and Bread, historian Frank Tannenbaum remarked that “physical geography could not have been better designed to isolate Mexico from the world and Mexicans from one another.” He recognized, like others before him, that the difficulty of travel by foot, water, or wheel across the country’s troublesome landscape was an unavoidable element of its history. Its distinctive topography of endless mountains but few navigable rivers had functioned, in some sense, as a historical actor in the larger story of Mexico. In the mid-19th century, Lucas Alamán had recognized as much when he lamented that nature had denied the country “all means of interior communication,” while three centuries before that, conquistador Hernán Cortés reportedly apprised Emperor Charles V of the geography of his new dominion by presenting him with a crumpled piece of paper. Over the last half-millennium, however, technological innovation, use, and adaptation radically altered how humans moved in and through the Mexican landscape. New modes of movement—from railway travel to human flight—were incorporated into a mosaic of older practices of mobility. Along the way, these material transformations were entangled with changing economic, political, and cultural ideas that left their own imprint on the history of travel and transportation.