Effectiveness of sand media filters for removing turbidity and recovering dissolved oxygen from a reclaimed effluent used for micro-irrigation

Sand media filters are among the most common filters used in micro-irrigation systems, especially for filtering waters with large amounts of organic contaminants like reclaimed effluents. An experiment was conducted for 1620 h between August 2007 and September 2008 using a reclaimed effluent to evaluate the efficiency of sand filters with sand effective diameters of 0.32, 0.47, 0.63 and 0.64 mm in decreasing turbidity and improving dissolved oxygen concentration. In addition, this study strived to determine the filter ripening period (i.e. the time after backwashing when the filtered effluent has the lowest quality) and the effect of filter backwashing on filtration efficiency. Depending on the sand effective size, the sand filter achieved turbidity reductions of between 59.6 and 85.4% and dissolved oxygen recoveries from 4.5 to 15.7%. During the experiment the filter ripening period was 15 min. Overall, the results support the idea that a daily backwashing is a good maintenance practice since it reduces inefficient backwashings and increases dissolved oxygen, which is interesting when hypoxic water is used for irrigation.