Environmental Engineering Reference
In-Depth Information
taBle 32.18
expected solids concentrations from various treatment operations and Processes
solids concentration
(% dry solids)
operation or Process application
range
typical
Primary settling tank
Primary sludge
5-9
6
Primary sludge to a cyclone degritter
0.5-3
1.5
Primary sludge and waste activated sludge
3-8
4
Primary sludge and trickling filter sludge
4-10
5
Primary sludge with iron salt addition for phosphorous removal
0.5-3
2
Primary sludge with low lime addition for phosphorous removal
2-8
4
Primary sludge with high lime addition for phosphorous removal
4-16
10
Scum
3-10
5
Secondary settling tank
Waste activated sludge with primary settling
0.5-1.5
0.8
Waste activated sludge without primary settling
0.8-2.5
1.3
High purity oxygen with primary settling
1.3-3
2
High purity oxygen without primary settling
1.4-4
2.5
Trickling filter sludge
1-3
1.5
Rotating biological contactor sludge
1-3
1.5
Gravity thickener
Primary sludge
5-10
8
Primary sludge and waste activated sludge
2-8
4
Primary sludge and trickling filter sludge
4-9
5
Dissolved air flotation thickener:
Waste activated sludge with polymer addition
4-6
5
Waste activated sludge without polymer addition
3-5
4
Centrifuge thickener (waste activated sludge only)
4-8
5
Gravity belt thickener (waste activated sludge with polymer addition)
4-8
5
Anaerobic digester
Primary sludge
2-5
4
Primary sludge and waste activated sludge
1.5-4
2.5
Primary sludge and trickling filter sludge
2-4
3
Aerobic digester
Primary sludge
2.5-7
3.5
Primary sludge and waste activated sludge
1.5-4
2.5
Primary sludge and trickling filter sludge
0.8-2.5
1.3
pretreatment causes solubilization and thermal decomposition of lignocellulosic material to more
simple molecules and therefore makes the sludge more easily digestible. In some cases sludge can be
so solubilized that it can be treated in UASB reactors (under certain conditions) massively reducing
digester size (D'abbieri et al. 2008). Pretreatments of sludge usually do not require more than 20%
of parasitic energy.
The technology used for anaerobic digestion is usually a simple, single-stage process; rarely in
practice are two-stage processes used, although they do offer a reduction in digester size. However,
the control of the process is more demanding; therefore WWTP operators usually choose simpler
technology. The vast majority of digesters are mesophilic, although in recent years thermophilic
digesters are surfacing more often. It was believed for quite some time that mesophilic digesters
use too much parasitic energy for operation and that was the reason for much larger application
