



				Dr.Hiroki ITOKAWA
				Research and Technology Development,
				Japan Sewege Works


				In Membrane Bioreactor System, final settling tanks are not
				necessary, because solid liquid separation is performed by
				filtration through the MF/UF membranes, which are placed
				directly into the bioreactor.
				As filtrate is extracted by imposing a vacuum on the MF/UF
				membranes,excellent treated wastewater quality can be obtained
				without any sand filtration, and MBR has more advantages.

				Membrane bioreactor (MBR) is a wastewater treatment system in
				which biologically treated wastewater is separated from biomass
				by means of membrane separation with very small pore size
				typically, 0.1-0.4μm). Thus secondary clarifier in
				conventional activated sludge (CAS) processes is replaced
				with membrane modules placed either internally (submerged in
				bioreactor) or externally (with circulation pump). The
				schematics of these configurations are shown in Figure 1.









				The membrane separation ensures virtually complete retention
				of solid matters under high solid concentration condition in
				the bioreactor.

				The advantages of MBR over CAS processes include:
				(i)	improved effluent quality without solid matters
					including pathogenic bacteria,
				(ii)	smaller reactor volume due to higher biomass
					concentration,
				(iii)	smaller sludge production due to longer solids
					reration time (SRT), and
				(iv)	easy operation and maintenance since less attention
					is necessary on sludge condition (e.g. bulking).

				Although MBR is rather "expensive" process in terms of both
				construction and operating costs, it is getting more and
				more economically competitive, especially in cases where
				(i)	stringent effluent regulation is applied,
				(ii)	land area is not large enough, or
				(iii)	reuse of the effluent is required.

				MBR has been installed in full-scale municipal wastewater
				treatment plants (WWTPs) since late 90s, especially in
				Europe and North America. Figure 2 shows an example for
				Europe.



				Since the first full-scale installation in 1998 at Porlock
				WWTP in UK with the capacity of 1,900 m³/d, the number of
				MBR plants has been increased year by year, especially
				after 2001.

				As of the end of 2005, 79 plants were operated with the total
				capacity of 300,000 m³/d. In all the world, more than 2,000
				full-scale MBRs, including small-scale on-site treatment
				facilities, are operated at the moment.

				Although the majority of the above mentioned installations are
				for relatively small-scale municipal WWTPs (median capacity in
				Europe : 1,300 m³/d), larger-scale installations are also the
				recent trend. More than 15 plants with the capacities of more
				than 30,000m³/d are operated or under construction worldwide.

					Aerobic reactor with submerged membrane modules at Nordkanal WWTP, the largest MBR in Germany with the capacity of 80,000 PE.




				In Japan, MBR installations in private sectors (e.g. industrial
				WWTPs, individual building WWTPs) and public nightsoil
				treament plants preceded. As for municipal WWTPs, the first
				intensive pilot-plant study was carried out by Japan Sewage
				Works Agency (JS) in cooperation with private companies from
				1998 to 2001, followed by preparation of standardized design
				recommendations in 2003.

				JS also conducted 2nd phase pilot-plant study with private
				companies from 2001 to 2004, aiming at reducing operating
				costs. Following these studies, the first full-scale municipal
				MBR plant was commissioned in 2005.

					Fukusaki WWTP, the first full-scale MBR in Japan for municipal WWTP.

					Aerobic reactor with submerged membrane modules at Fukusaki WWTP.

				At the moment, three more plants are operated, and more than
				ten plants are under construction or planning.

				In addition, around 500 small-scale MBRs have been installed
				for on-site household wastewater treatment system
				(JOHKASOU system). The principal issue at the moment is
				larger-scale installations,and JS Started 3rd phase
				pilot-plant study for the subject.

				Thanks to a lot of pilot-scale studies and full-scale
				installations, a stable treatment performance of MBR has been
				realized by more and more engineers in the world. Further
				reduction of costs for construction, especially concerning
				membrane inself, and operation would be an important subject
				of research and development.