Changes

Studies have shown that the HRT is the most important design parameter influencing filter performance. An HRT of 0.5 to 1.5 days is a typical and recommended. A maximum surface-loading (i.e. flow per area) rate of 2.8m/d has proven to be suitable. Suspended solids and BOD removal can be as high as 85% to 90% but is typically between 50% and 80%. Nitrogen removal is limited and normally does not exceed 15% in terms of total nitrogen (TN).

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- Resistant to organic and hydraulic shock loads. <br> - No electrical energy required. <br> - Can be built and repaired with locally available materials. <br> - Long service life. <br> - Moderate capital costs, moderate operating costs depending on emptying; can be lowered depending on number of users. <br> - High reduction of BOD and solids. | con=