NIRAS VOLUME 2 [2.7] 52
Rotary drum vacuum filter in operation
Operational considerations •
Conditioned sludge should be filtered as quickly as possible after the addifion of the chemicals and adequate mixing.
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Continuous feeding is preferable to batch conditioning. In raw sludge filtration, fresh sewage solids and sludge filter more readily than stale or septic sludge.
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Completely digested sludge usually filters more readily than partially digested sludge.
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The concentration of sludge to be filtered is critical as sludge with the higher solid content usually filters more readily than that with a lower solid content.
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The presence of mineral oils and wastes from dry cleaning establishments makes sludge filtration difficult. Such wastes should, therefore, be kept out of the sewer system and disposed of separately.
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After every use the vacuum filter should be cleaned, and all sludge drained from the unit. This sludge and wash water should not be returned to the sludge storage tank but to the raw sewage channel or to a digester.
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Sludge dewatered using vacuum filtration is normally chemically conditioned just prior to filtration. Sludge conditioning increases the percentage of solids captured by the filter and