A novel dead-end mode operation for filtering anaerobic suspensions was investigated. In this mode, the filtration system automatically adjusted backwashing frequency to a preselected transmembrane pressure set-point. This paper discusses the effectiveness of the backwashing conditions on membrane fouling. Anaerobic suspensions from a conventional wastewater treatment plant digester were used as model suspensions for the trials carried out at lab-scale. Gas sparging aided backwashing significantly enhanced membrane cleaning efficiency. No effect of gas sparging on internal fouling was detected. Also, the cleaning efficiency linearly decreased with permeate flux. Nevertheless, due to a high increase in the reversible fouling, a reasonable net permeate flux (7.2-6.8 L/h m(2)) can be achieved when intermediate fluxes (12-16 L/h m(2)) were imposed and the higher transmembrane pressure set-point value (50 kPa) was applied. Both backwashing duration and flux exhibited similar influence on cake fouling removal for a given volume of permeate produced.

A novel strategy for membrane fouling control based on combination of intermittent gas sparging and transmembrane pressure setpoint (TMP sp ) for backwashing initiation was assessed at laboratory scale. Ultrafiltration of anaerobic suspensions, complex and highly concentrated, was carried out at supracritical permeate fluxes and different TMP sp values. Intermittent gas sparging effectively mitigated reversible fouling mainly caused by a cake layer formed of large particles, regardless of the selected TMP sp . In fact, cycle duration increased with dimensionless gas-sparging time (Θ gs ) and TMP sp , although this trend diminished with rising permeate flux (J p ). Additionally, backwashing initiation by TMP sp demonstrated its high effectiveness in preventing residual fouling, independent of the applied conditions (Θ gs , J, and TMP sp ). As a result, high net permeate fluxes were obtained at moderate J and low Θ gs values. Therefore, the applied combined strategy is a promising option for reducing gas consumption that should contribute to a sustainable operation of anaerobic membrane bioreactors.

ResumenEl objetivo de este trabajo es evaluar los costes de producción de tomate de exportación en Canarias y compararlos con los de sus principales competidores. Se ha adoptado un enfoque de costes basados en las actividades. La información se ha obtenido a partir de las respuestas proporcionadas por una muestra de agricultores y centros de empaquetado a dos cuestionarios relativos, respectivamente, a las fases de cultivo y empaquetado desarrolladas en una campaña agrícola. Finalmente, se ha evaluado el coste de transporte y distribución hasta la venta al mayorista en el destino europeo. El resultado es que, una vez contemplados los costes financieros, un kilogramo de tomate puesto en el punto de venta en destino europeo costaría algo más de 1,05 euros en el caso canario, aproximadamente 80 céntimos de euro para el tomate peninsular y claramente menos de 70 céntimos para el marroquí.

In this study, a saline effluent from an anaerobic membrane bioreactor was treated by nanofiltration in order to allow its agricultural reuse. Short-term tests were conducted to investigate membrane fouling and selective rejection of ions and emerging organic contaminants (EOCs). The study has been conducted with a negatively charged commercial thin-film composite membrane (DK, GE Osmonics). The effect of operating pressure (5-20 bar) and cross-flow velocity (0.12-0.37 m/s) on membrane performance have been researched. Dimensional analysis of steady permeate flux indicated that the gel layer or the polarization layer can be completely removed at critical cross-flow velocity. At a subcritical velocity, membrane autopsies by scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy revealed a complex mixture of organic matter, phosphates and colloidal silica over the membranes surface. Since the rejection of monovalent cations (76-88%) was lower than that of multivalent cations (above 96%), the treated effluent was characterized by a very high levels of sodium adsorption ratio and ammonium. In addition, moderate rejection of low molecular weight EOCs (clofibric acid and caffeine) was observed. Therefore, the treated effluent did not achieve enough quality to be reused for agricultural irrigation. V C 2017 American Institute of Chemical Engineers Environ Prog, 37: 383-390, 2018 During the last decade, interest in the application of nanofiltration in wastewater treatment has grown in response to stringent water quality standards and increasing concern about the presence of emerging organic contaminants (EOCs). Nevertheless, information remains scarce about membrane fouling and EOCs rejection. The current research addresses these issues during its application to a brackish effluent from an anaerobic membrane bioreactor to be reused for agricultural irrigation. Dimensional analysis has allowed establishing the optimum operation conditions in terms fouling control. As regard of EOCs rejection, low molecular weight compounds were not completely retained by the membrane.

Agradecimientos: Los autores desean manifestar su agradecimiento a dos evaluadores anónimos cuyas sugerencias han contribuido a mejorar la versión original. Este trabajo ha sido financiado por el proyecto PI2008/126 de la Agencia Canaria de Investigación, Innovación y Sociedad de la Información. RESUMEN:Los productores canarios de plátano han optado en los últimos años por no enviar al mercado peninsular una parte significativa de su oferta exportable. Este trabajo aporta una herramienta analítica que permite aproximar los efectos marginales en el ingreso y en el beneficio derivados de estas decisiones. El elemento clave del procedimiento radica en la estimación de un modelo de determinación de precios en función de la oferta exportada. Los volúmenes óptimos de exportación deducidos deben interpretarse con la necesaria cautela debido a las limitaciones en la información estadística, pero constituyen una ayuda que podría guiar la toma de decisiones. PALABRAS CLAVE:Canarias, exportación, pica, plátano, precios.Clasificación JEL: Q11, C22. Canary banana exports. Are product withdrawal decisions rational?ABSTRACT: During the last years, Canary banana suppliers have made the decision to withdraw a significant part of their exportable supply from the Iberian Peninsula market. In this paper, an analytical tool is provided to evaluate the marginal effects of these decisions on revenues and profit. The key element is the estimation of a model to explain prices as a function of exports. The optimal export levels obtained from this procedure should be cautiously taken due to limitations on statistical information, but should be seen as a guide to the decision making process.