advantage in possible replacing conventional sedimentation for the separation of the
treated water from the sludge [48]. The use of submerged membranes has reduced
the power consumption of membrane bioreactors and hence increased their potential
for the application of membranes in wastewater treatment. Moreover, ultra- or
micro-filtration membranes with a pore size of 0.2 μm or less retain not only bacteria
but also viruses [49]. The complete retention of sludge allows operation at much
higher biomass concentrations. The higher the concentration, the lower the F/M ratio
becomes, with the effect that the microorganisms utilize a growing portion of the
carbon content of the feed for maintenance.
Urbain et al. [50] and Rosenberger et al. [51] demonstrated the good performance
of aerobic treatment of municipal wastewater using a membrane bioreactor.
Rosenberger et al. [51] pilot plant comprised an anoxic zone to enable denitrification. The hydraulic retention time (HRT) varied between 10.4 and 15.6 h.; accordingly, the volumetric loading rate was between 1.1 and 1.7 kg COD/m
3 /d. The mixed
liquor suspended solid concentration gradually increased to 18–20 g MLSS/L. The
F/M ratio varied according to the operation conditions but decreased to a value of
0.07 kg COD/kg MLSS/d. Treatment performance was very stable and on a high
level. The COD was reduced by 95%. Nitrification was complete and up to 82% of
the total nitrogen could be denitrified [52–58].
4 Trickling Filter
4.1 Process Description of Attached-Growth Systems
A contact bed, contact aerator, trickling filter, rotating disks, or other attachedgrowth systems consist of a bed of coarse contact media such as crushed trap rock,
granite, limestone, clinkers, wood slats, plastic tubes, corrugated plastic sections,
hard coal, or other material over which wastewater is distributed or contacted
[14, 36, 58–64]. Wastewater flows over the contact media on which a biological
slime layer (i.e., zoogleal slime) develops. Dissolved organic pollutants in the
wastewater are transported into the slime layer, where biological oxidation takes
place. Organic pollutants are removed by the biological slime film, which consists of
various microorganisms, as shown in Fig. 3.12. In the outer portions of the film,
organic pollutants (C a H b O c N d P e S f ) are degraded by aerobic and facultative bacteria
under aerobic conditions according to a biochemical reaction approximately
expressed by Eq. (3.22).
4 C a H b O c N d P e S f þ 4a þ b À 2c À 3d þ 5e þ 6f
ð
Þ O 2 !
4a CO 2 þ 2b À 6d À 6e À 4f
ð
Þ H 2 O þ 4d NH 3 þ 4e PO 4
3À
þ4f SO 4
2À
þ 12e þ 8f
ð
ÞH
þ
ð3:22Þ
110
L. K. Wang et al.
treated water from the sludge [48]. The use of submerged membranes has reduced
the power consumption of membrane bioreactors and hence increased their potential
for the application of membranes in wastewater treatment. Moreover, ultra- or
micro-filtration membranes with a pore size of 0.2 μm or less retain not only bacteria
but also viruses [49]. The complete retention of sludge allows operation at much
higher biomass concentrations. The higher the concentration, the lower the F/M ratio
becomes, with the effect that the microorganisms utilize a growing portion of the
carbon content of the feed for maintenance.
Urbain et al. [50] and Rosenberger et al. [51] demonstrated the good performance
of aerobic treatment of municipal wastewater using a membrane bioreactor.
Rosenberger et al. [51] pilot plant comprised an anoxic zone to enable denitrification. The hydraulic retention time (HRT) varied between 10.4 and 15.6 h.; accordingly, the volumetric loading rate was between 1.1 and 1.7 kg COD/m
3 /d. The mixed
liquor suspended solid concentration gradually increased to 18–20 g MLSS/L. The
F/M ratio varied according to the operation conditions but decreased to a value of
0.07 kg COD/kg MLSS/d. Treatment performance was very stable and on a high
level. The COD was reduced by 95%. Nitrification was complete and up to 82% of
the total nitrogen could be denitrified [52–58].
4 Trickling Filter
4.1 Process Description of Attached-Growth Systems
A contact bed, contact aerator, trickling filter, rotating disks, or other attachedgrowth systems consist of a bed of coarse contact media such as crushed trap rock,
granite, limestone, clinkers, wood slats, plastic tubes, corrugated plastic sections,
hard coal, or other material over which wastewater is distributed or contacted
[14, 36, 58–64]. Wastewater flows over the contact media on which a biological
slime layer (i.e., zoogleal slime) develops. Dissolved organic pollutants in the
wastewater are transported into the slime layer, where biological oxidation takes
place. Organic pollutants are removed by the biological slime film, which consists of
various microorganisms, as shown in Fig. 3.12. In the outer portions of the film,
organic pollutants (C a H b O c N d P e S f ) are degraded by aerobic and facultative bacteria
under aerobic conditions according to a biochemical reaction approximately
expressed by Eq. (3.22).
4 C a H b O c N d P e S f þ 4a þ b À 2c À 3d þ 5e þ 6f
ð
Þ O 2 !
4a CO 2 þ 2b À 6d À 6e À 4f
ð
Þ H 2 O þ 4d NH 3 þ 4e PO 4
3À
þ4f SO 4
2À
þ 12e þ 8f
ð
ÞH
þ
ð3:22Þ
110
L. K. Wang et al.