Suspended Solids

Unfortunately, in most practical cases, colloids are not separated from suspended solids. Using a graduated Imhoff cone, a sedimentation test yields two fractions: (a) the settleable solids below and (b) the non-settleable solids above, the fraction which now contains the colloid particles.

Mostly, only the settleable solids are measured as X (in mL L-1) by reading the scale on the lower part of the Imhoff funnel. More exact data are obtained after separation of the two portions. The organic mass and inorganic mass are definable after filtration, drying, weighing, incineration at 500 °C and re-weighing the ash. Table 2.6 presents some typical data for domestic wastewater.

Table 2.6 Suspended solids as organics and minerals (Popel 1997), Q = 115 L (inh. d)-1 (Table 2.1; selected and partly converted data).

Solids

Unit

Settleable solids

Non-settleable solids

Total

Organics

g MLVSS d-1

40

20

60

g L-1 MLVSS

0.350

0.175

0.525

Minerals

g MLSS d-1

20

10

30

g L-1 MLSS

0.175

0.086

0.260

In municipal wastewater and especially in industrial effluent, the concentration of suspended solids can vary considerably from the data in Table 2.6. For more specific information about different branches of industry, see Poppinghaus et al. (1994).

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