Maintenance is directly related to the quantity of solids applied to the surface of the filter which is related to the concentration of solids in the influent to the filter and the hydraulic loading rate. Filters with low hydraulic loading rates tend to operate for extended periods as shown in the above references and Table 5.8. With such extended operating periods, maintenance consists of routine inspection of the filter, removing weeds, and an occasional cleaning by removing the top 5 to 8 cm of sand after allowing the filter to dry out. A summary of reported annual maintenance for three field-scale, lagoon-intermittent sand filter facilities is shown in Table 5.9.
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