Effect of underdrain design, media height and filtration velocity on the performance of microirrigation sand filters using reclaimed effluents

Abstract

Sand filters are commonly used in microirrigation systems to prevent emitter clogging, especially when wastewater is used. However, little is known about the operating conditions required to guarantee a good filtration and a low energy consumption. For this reason, three sand filters with different drainage designs (collector arms, inserted domes and porous medium) using reclaimed effluents were analysed when operating with two sand media heights (0.20 and 0.30 m) and two filtration velocities (30 and 60 m h−1). Each one of these four different operating conditions (combination of two sand media heights and filtration velocities) was tested for 250 h. Filtered and backwashed volumes, energy consumption during filtration and backwashing, inlet and outlet filter pressures, and water quality parameters at filter inlet and outlet were recorded using a supervisory control and data acquisition system. Results showed that porous media underdrain design presented higher turbidity removal efficiencies for most of the tested conditions (38.53, 33.63 and 10.51% at 0.20 m/30 m h−1, 0.20 m/60 m h−1 and 0.30 m/60 m h−1, turbidity removal, with sand media height/filtration velocity, respectively) and dome underdrain only at 0.30 m/60 mh−1 (47.74%). Porous media underdrain also filtered more water volume per electrical energy unit (8.30 m3 kWh−1) than domes and arm collector underdrain (8.18 and 8.07 m3 kWh−1, respectively). In general, filtration velocities of 30 m h−1 showed higher turbidity removals and filtered more water volume per electrical energy unit than 60 m h−1. Media height did not show a clear effect, but smaller media heights did allow energy and material saving.