Conditionnement et déshydratation de boues d'étangs aérés facultatifs à l'aide du gel – dégel naturel: résultats d'essais

Abstract

This article presents the results of tests investigating the conditioning and dewatering of biological and chemical sludge (alum dephosphatation sludge) from facultative aerated lagoons using natural freeze–thaw. The results presented here highlight the excellent efficiency of this conditioning method used with drying beds. Following freeze–thaw, immediately after drainage, sludge presents little odor and has lost its liquid state since dry solid contents of more than 30% can be obtained with ease. Freeze–thaw also eliminates the gelatinous consistency of chemical sludge. The filtrates are clear and contain low levels of suspended solids but may have relatively high chemical oxygen demand. To maximize the depth of sludge that can be frozen, it is necessary to freeze the sludge in thin layers. This requires the pumping of sludge from a separate storage basin to a freezing bed for the duration of winter (separate basin–bed method). The storage basin may however be combined with the freezing bed provided the depth of the sole sludge layer does not exceed the maximum depth of sludge that can be frozen during the winter season (combined basin–bed method). Freeze–thaw is not affected by the initial dry solid content of the sludge. The grain size of the sludge can however have some influence, although quite marginal, and freeze–thaw is efficient for all types of aqueous sludge. Key words: conditioning, dewatering, sludge, facultative aerated lagoons, natural freeze–thaw, trials.