dryer beds on sand layers

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These systems are still used (with polymer if necessary for accelerating the drainage phase) in low rainfall regions. On average, however, it takes 3 to 4 weeks before a 30-40 cm deep layer of liquid sludge dries out.

This process is far less widespread because of the extensive areas involved and because dry cake removal is very labour-intensive.

There are a few rare examples in mechanised drying bed applications (20 m wide x 1 km long elements where sludge is pumped in and dispersed and after drying, is collected by an automatically controlled scraper).