Analysis of the filtration time and interception characteristics of tandem mesh filters

Easy clogging and short service life of mesh filters have posed great challenges in the irrigation water system. In this study, the pre- and post-pump mesh filters in series were combined to determine the interception of sediment and organic impurities at both pre- and post-pump filters. The indoor prototype tests were also carried out. The results showed that the distribution of the filter interception of sediment and organic impurities was related to the aperture of the mesh at pre- and post-pump filters. The smaller the aperture of the post-pump filter was, the shorter the filtration time was. There was basically unchanged in the distribution of sawdust and sediment that was intercepted at pre- and post-pump filters. The smaller the aperture of the pre-pump filter was, the longer the filtration time was, and the smaller the percentage of sawdust intercepted by the filter. The percentage of sawdust intercepted by the pre-pump filter increased under the condition of the same screen aperture, with the increase of inlet water flow rate. It was recommended that the pre-pump filter with the screen aperture of 0.32 mm and the post-pump filter with the screen aperture of 0.20 mm were used for filtration when the content of organic impurities was high. Furthermore, the 0.32 and 0.20 mm mesh apertures of the pre- and post-pump filters were for filtration, when the mass ratio of organic impurities and sediment in the irrigation water source was less than 2. The 0.25-0.32 mm screen aperture of pre-pump filter prolonged the filtration time. There was a variation in the head loss with the filtration time, in order to clarify the influence of water conditions and screen aperture on the filtration time. Combined with the range analysis and multivariate analysis of variance (MANOVA), the initial and peak head loss were concentrated in the 2.43-5.87 and 13.92-28.92 m, respectively, under different inlet flow conditions. The impurity ratio posed a smaller influence on the head loss. Additionally, the larger the inlet water flow rate was, the shorter the filtration time was. The empirical formula of head loss was established to fit the filtration time. The error between the fitting and the test was less than 7%, indicating the better suitable for the filtration time of tandem mesh filters under actual irrigation water. The best combination of the factor level for the orthogonal test was screened as the aperture D₁（pre-pump is 0.32 mm, post-pump is 0.20 mm）, the sawdust to sediment mass ratio 1:1, sand content 0.12 g/L, and inlet flow 120 m³/h. The influence of each factor on the filtration time was ranked in descending order: the impurity ratio, the screen aperture, the sand content, and the rate of inlet water flow. MLP neural network model was used to predict the filtration time. The error between the predicted and measured values was basically within 10%. The mean square error and the average relative error were 0.32% and 5.85%, respectively, suitable for the prediction of the filtration time under the complex water sources. The finding can also provide a strong reference to configuring the screen aperture of the pre- and post-pump filters in the tandem mesh filters for the irrigation projects.