M. Duran-Ros

Using Computational Fluid Dynamics to Predict Head Losses in the Auxiliary Elements of a Microirrigation Sand Filter

It is often assumed that total head losses in a sand filter are solely due to the filtration media and that there are analytical solutions, such as the Ergun equation, to compute them. However, total head losses are also due to auxiliary elements (inlet and outlet pipes and filter nozzles), which produce undesirable head losses because they increase energy requirements without contributing to the filtration process. In this study, ANSYS Fluent version 6.3, a commercial computational fluid dynamics (CFD) software program, was used to compute head losses in different parts of a sand filter. Six different numerical filter models of varying complexities were used to understand the hydraulic behavior of the several filter elements and their importance in total head losses. The simulation results show that 84.6% of these were caused by the sand bed and 15.4% were due to auxiliary elements (4.4% in the outlet and inlet pipes, and 11.0% in the perforated plate and nozzles). Simulation results with different models show the important role of the nozzles in the hydraulic behavior of the sand filter. The relationship between the passing area through the nozzles and the passing area through the perforated plate is an important design parameter for the reduction of total head losses. A reduced relationship caused by nozzle clogging would disproportionately increase the total head losses in the sand filter.

A new predictive model for the filtered volume and outlet parameters in micro-irrigation sand filters fed with effluents using the hybrid PSO-SVM-based approach

Prediction of sand filter outlet values allows assessing drip emitter clogging risk.A hybrid model based on SVMs with the PSO technique was used for this prediction.The developed model predicted satisfactorily sand filter outlet parameters.Performance of the PSO-SVM model was better than with other techniques. Filtration is a key operation in micro-irrigation for removing the particles carried by water that could clog drip emitters. Currently, there are not sufficiently accurate models available to predict the filtered volume and outlet parameters for the sand filters used in micro-irrigation systems. The aim of this study was to obtain a predictive model able to perform an early detection of the filtered volume and sand filter outlet values of dissolved oxygen (DO) and turbidity, both related to emitter clogging risks. This study presents a novel hybrid algorithm, based on support vector machines (SVMs) in combination with the particle swarm optimization (PSO) technique, for predicting the main filtration operation parameters from data corresponding to 769 experimental filtration cycles in a sand filter operating with effluent. This optimization technique involves kernel parameter setting in the SVM training procedure, which significantly influences the regression accuracy. To this end, the most important physical-chemical parameters of this process are monitored and analyzed: effective sand media size, head loss across the filter and filter inlet values of dissolved oxygen (DO), turbidity, electrical conductivity (Ec), pH and water temperature. The results of the present study are two-fold. In the first place, the significance of each physical-chemical variables on the filtration is presented through the model. Secondly, a model for forecasting the filtered volume and sand filter outlet parameters is obtained with success. Indeed, regression with optimal hyperparameters was performed and coefficients of determination equal to 0.74 for outlet turbidity, 0.82 for filtered volume and 0.97 for outlet dissolved oxygen were obtained when this hybrid PSO-SVM-based model was applied to the experimental dataset, respectively. The agreement between experimental data and the model confirmed the good performance of the latter.

Irrigation Performance and Water Productivity in Ornamental Plant Production in Girona (Spain)

The ornamental plant production in Girona (Spain) represents an important economic sector, being with 1200 hectares one of the first production zones in Southern Europe.

Filter and emitter performance of micro-irrigation systems using secondary and tertiary effluents.

The performance of four filtration systems (sand, screen, disc and a combination of screen and disc) and six emitter types (four pressure compensated and two non-pressure compensated), using secondary and tertiary effluents from a wastewater treatment plant, was studied for 1000 h. Only sand filtration significantly reduced turbidity and suspended solids. The best emission uniformity was obtained by the emitters placed after the sand filter and the screen filter with the secondary and tertiary effluent, respectively. On the other hand, emitters that operated with disc filters showed the worst emission uniformity for both effluents. Emitter type P2 was the only one achieving values of emission uniformity higher than 90% with all filtration systems and effluents except the screen filter and the tertiary effluent.