Sludge volume index etc.
cipal wastewaters with an alkalinity over 5 eqv /m 3 will not cause problems in
connection with nitrification, denitrification and simultaneous precipitation, whereas
lower alkalinity may cause a drop in the pH and low efficiency of the processes. In
the event of preprecipitation and post precipitation, low alkalinity will, on the other
hand, often be an advantage as smaller quantities of chemicals will then be required
to obtain the desired pH-value.
2.6. Sludge volume index etc.
The sludge volume tells something about the flocculation and settling characteristics of the activated sludge. The sludge volume index is the reciprocal sludge
concentration in the sludge phase after 0.5 hour's settling in a cylinder glass:
SVI = Xl (unit normally ml/g SS)
0.5
where Xo.s is the sludge concentration in the sludge phase after 0.5 hour's settling.
The lower the sludge volume index is, the better flocculation and settling characteristics. By stirring in the cylinder glass during settling, the stirred sludge volume
index may be determined which is smaller than than the "conventional" one.
The German word for "the sludge volume index" is "Schlammindex" or "Mollmans
Index".
SVI values of 100 ml/ g are usually considered to be satisfactory to ensure a good
functioning of activated sludge plants. In this way it will be possible to maintain a
satisfactory return sludge concentration and have a well-functioning settling.
The sludge density index (SDI) states the sludge concentration in the slugde phase
after 30 min. settling(= Xo.s).
The sludge percentage states the percentage which is taken up by the sludge phase
volume (compared to the start volume) after 30 min. settling.
50
Example2.3
A sample of activated sludge is taken from an aeration tank and is filled into a 1 I
standard cylinder glass. The sludge concentration is 5 g SS/1 (5 kg SS/m 3 )
After 30 min. settling the sludge phase takes up 400 ml, the water above is clear. What
is the sludge volume index, the sludge density index and the sludge percentage?
Sludge volume index: 5 g sludge takes up 400 mi.
SVI = 400 ml/5 g = 80 ml/g
Sludge density: 5 g sludge takes up 400 ml
SOl= 5 g/400 ml = 5 g/0.41 = 12.5 g/1
Sludge percentage: (400 ml/1 000 ml) · 1 00% = 40%
cipal wastewaters with an alkalinity over 5 eqv /m 3 will not cause problems in
connection with nitrification, denitrification and simultaneous precipitation, whereas
lower alkalinity may cause a drop in the pH and low efficiency of the processes. In
the event of preprecipitation and post precipitation, low alkalinity will, on the other
hand, often be an advantage as smaller quantities of chemicals will then be required
to obtain the desired pH-value.
2.6. Sludge volume index etc.
The sludge volume tells something about the flocculation and settling characteristics of the activated sludge. The sludge volume index is the reciprocal sludge
concentration in the sludge phase after 0.5 hour's settling in a cylinder glass:
SVI = Xl (unit normally ml/g SS)
0.5
where Xo.s is the sludge concentration in the sludge phase after 0.5 hour's settling.
The lower the sludge volume index is, the better flocculation and settling characteristics. By stirring in the cylinder glass during settling, the stirred sludge volume
index may be determined which is smaller than than the "conventional" one.
The German word for "the sludge volume index" is "Schlammindex" or "Mollmans
Index".
SVI values of 100 ml/ g are usually considered to be satisfactory to ensure a good
functioning of activated sludge plants. In this way it will be possible to maintain a
satisfactory return sludge concentration and have a well-functioning settling.
The sludge density index (SDI) states the sludge concentration in the slugde phase
after 30 min. settling(= Xo.s).
The sludge percentage states the percentage which is taken up by the sludge phase
volume (compared to the start volume) after 30 min. settling.
50
Example2.3
A sample of activated sludge is taken from an aeration tank and is filled into a 1 I
standard cylinder glass. The sludge concentration is 5 g SS/1 (5 kg SS/m 3 )
After 30 min. settling the sludge phase takes up 400 ml, the water above is clear. What
is the sludge volume index, the sludge density index and the sludge percentage?
Sludge volume index: 5 g sludge takes up 400 mi.
SVI = 400 ml/5 g = 80 ml/g
Sludge density: 5 g sludge takes up 400 ml
SOl= 5 g/400 ml = 5 g/0.41 = 12.5 g/1
Sludge percentage: (400 ml/1 000 ml) · 1 00% = 40%