suspended solids ( SS ) in liquid sludge

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When sludge is not very concentrated, the dry weight must not include the level of dissolved substances contained in sludge interstitial water. There are two possible systems.

the centrifugation method

This system uses a laboratory centrifuge equipped with 100 mL graduated scoops. Each scoop is filled with 80 mL of sludge and centrifuged at 4 000-5 000 rpm–1 for 10 minutes. At the end of this operation, the supernatant liquor is removed and all sludge pellets are carefully collected and allowed to dry out at 105°C in an oven until a constant mass is achieved (this usually takes at least 12 hours).

Comment: Preliminary flocculation of the sludge using a few mg· L-1 of polymer (flocculation carried out in situ in the scoop) will produce homogenous pellets of sludge that can very easily be collected without losing any matter. Let M(g) be the mass of residual dry solids obtained and V (mL) the volume of sludge centrifuged (V = 160 or 320 mL).

Formula: SS liquid sludge - centrifugation method

filtration method

This method tends to be reserved for very low concentration sludge (e.g. 2 to 10 g · L-1).

Precisely calibrate a filter paper (extra rapid ash-free filter type _ 150, Durieux for example) and filter the sludge (25 to 100 mL depending on concentration) over a glass funnel. This may be a somewhat protracted method in some cases when the sludge has a poor filtering capacity. Then dry the filter in an oven at 105°C until a constant mass is achieved.

Formula: SS liquid sludge - filtration method

M: dry mass of the filter and of the cake (g),
F: mass of the filter only (g),
V: volume of sludge filtered (mL).