4
1 Introduction
biofilm attached media into the aeration tank for maintaining the proper biomass in
the reactor can reasonably be thought for the treatment of municipal wastewater.
1.3 Brief Overview on Past Experience
It has been found from the past experience that the hybrid bioreactor process has
significantly improved the efficiency of biological treatment of slowly biodegradable substance and has been widely applied to municipal wastewater treatment in
recent years. In the past, the hybrid bioreactor technology has been incorporated into
municipal wastewater treatment as a new plant installation as well as for upgradation/retrofitting of the overloaded plants in many variations. In case of new plant
installation, the reactor volume gets reduced due to additional attached biomass.
For the plant upgradation, enhanced treatment capacity can be obtained without
increasing the volume of the existing tank. Hybrid bioreactor was used for studying
the nutrients removal from municipal wastewater [19]. It was found that the hybrid
bioreactor ensured a better removal than the purely attached biofilm system. IFAS
process was also installed at Maryland municipal wastewater reclamation facility,
where rope like ringlace IFAS media of 30,000 m were installed in a volume of
475 cum. Nitrification in the IFAS section was found more than three times that
in the control section without media [9]. A sponge type IFAS media was used at
Moundsville wastewater treatment plant, USA in 3 years of full-scale operation.
This is a combined suspended- and attached-growth process, where polyurethane
foam media was incorporated into ASP process increasing the equivalent MLSS
concentration level. The attached and suspended MLSS were maintained between
6500–12,000 mg/l and 900–1700 mg/l, respectively.
The efficiency in removal of BOD, nitrification and denitrification was found
95%, 70–90% and 40–60%, respectively, at a HRT 50–90 min [20].
A study was conducted to see the effect of attached biomass on the filamentous
growth of suspended biomass in the nitrification process and found that nitrification became independent of SRT of suspended biomass, since nitrifying bacteria
are predominantly attached to the support materials. In this case, dispersed plastic
foam particles and fully submersed plastic disks were used as a supporting media
for attached biomass [21]. In a cold region, treatment of domestic wastewater was
done by a hybrid activated sludge biofilm process, which contained both suspended
biomass and biofilm, usually referred as integrated fixed-film activated sludge (IFAS)
process, created by introducing plastic elements as biofilm carrier media into a
conventional activated sludge reactor. Pilot-scale study was carried out at the Department of Hydraulic and Environmental Engineering at the Norwegian University of
Science and Technology in Trondheim. The results revealed that this kind of reactor
can efficiently be used for the upgrading of conventional activated sludge plant for
achieving a good quality of effluent [22]. Sriwiriyarat et al., [23] also made his
research study treating a weak municipal wastewater with IFAS using sponge media
at different aerobic mean cell residence times for evaluating his model performance
1 Introduction
biofilm attached media into the aeration tank for maintaining the proper biomass in
the reactor can reasonably be thought for the treatment of municipal wastewater.
1.3 Brief Overview on Past Experience
It has been found from the past experience that the hybrid bioreactor process has
significantly improved the efficiency of biological treatment of slowly biodegradable substance and has been widely applied to municipal wastewater treatment in
recent years. In the past, the hybrid bioreactor technology has been incorporated into
municipal wastewater treatment as a new plant installation as well as for upgradation/retrofitting of the overloaded plants in many variations. In case of new plant
installation, the reactor volume gets reduced due to additional attached biomass.
For the plant upgradation, enhanced treatment capacity can be obtained without
increasing the volume of the existing tank. Hybrid bioreactor was used for studying
the nutrients removal from municipal wastewater [19]. It was found that the hybrid
bioreactor ensured a better removal than the purely attached biofilm system. IFAS
process was also installed at Maryland municipal wastewater reclamation facility,
where rope like ringlace IFAS media of 30,000 m were installed in a volume of
475 cum. Nitrification in the IFAS section was found more than three times that
in the control section without media [9]. A sponge type IFAS media was used at
Moundsville wastewater treatment plant, USA in 3 years of full-scale operation.
This is a combined suspended- and attached-growth process, where polyurethane
foam media was incorporated into ASP process increasing the equivalent MLSS
concentration level. The attached and suspended MLSS were maintained between
6500–12,000 mg/l and 900–1700 mg/l, respectively.
The efficiency in removal of BOD, nitrification and denitrification was found
95%, 70–90% and 40–60%, respectively, at a HRT 50–90 min [20].
A study was conducted to see the effect of attached biomass on the filamentous
growth of suspended biomass in the nitrification process and found that nitrification became independent of SRT of suspended biomass, since nitrifying bacteria
are predominantly attached to the support materials. In this case, dispersed plastic
foam particles and fully submersed plastic disks were used as a supporting media
for attached biomass [21]. In a cold region, treatment of domestic wastewater was
done by a hybrid activated sludge biofilm process, which contained both suspended
biomass and biofilm, usually referred as integrated fixed-film activated sludge (IFAS)
process, created by introducing plastic elements as biofilm carrier media into a
conventional activated sludge reactor. Pilot-scale study was carried out at the Department of Hydraulic and Environmental Engineering at the Norwegian University of
Science and Technology in Trondheim. The results revealed that this kind of reactor
can efficiently be used for the upgrading of conventional activated sludge plant for
achieving a good quality of effluent [22]. Sriwiriyarat et al., [23] also made his
research study treating a weak municipal wastewater with IFAS using sponge media
at different aerobic mean cell residence times for evaluating his model performance