Thesis - faculty.ait.ac.th - Asian Institute of Technology

optimization of the filtration cycle, improvement of aerator reliability and improved
cleaning strategies on a rotational basis.
The development of membrane module, improved anti-trash screening and cyclic
aeration and standardised design which are the recent advancements. This allowed for the
systems to be handled at peak loads and prolonged membrane life to at least 5 years and
reduced membrane costs.
The first full-scale plant was located in South West England, where the MBR was
designed to treat municipal wastewater in a site with area restrictions and located close to a
beach and residential area. The plant was able to treat 13,000 m 3 /d and enclosed in a
building 105 m long. The system was effective in removing bacteria and ammonia. The
second plant was built in the open and used for dairy effluent treatment. The plant was
simple in design and unsophisticated yet was able to treat an effluent load of 16 ton/d on
BOD and was able to discharge effluent directly into a river. The MBR units were located
in 10 tanks, each with a flow of 1,000 m 3 /d of screened effluent prior to discharge into an
existing oxidation ditch. Though, initially it had been used for treating domestic
wastewater, later its application widened.
2.11.2 Application of Membrane Bioreactors
Bressi and Favari (1997) conducted studies on a MBR system consisting of an
activated sludge process coupled with an external hollow fibre ceramic MF unit. The
system was aerated by means of diffusers and the mixed liquor passed through the lumen
of membrane and was recycled to the activated sludge whilst permeate was extracted on
the shell side. The continuous recycle aided in maintaining homogeneous conditions within
the aerobic reactor.
Hall, et al. (1995) investigated the system for removal of adsorbable organic halogen
(AOX). It gained 61% AOX removal during the operation at HRT of 24 h. It was operated
under condition of MLSS from 10,000 to 20,000 mg/L and with an initial AOX from 21 to
50 mg/L. Lubbecke, et al. (1995) experimented the pilot scale for landfill leachate
treatment by MBR process. Concentration of raw leachate contains 2,700 to 4,300 mg/L
COD, 200 to 350 mg/L BOD, and 1.5 to 4.4 mg/L AOX. This system was operated at HRT
from 15 to 25 hours and pressure from 2.5 to 4.5 bars. It achieved 75% to 80% COD
removal and 30% to 60% AOX reduction under the average permeate flux 15 L/m 2 -h for
the NF membrane. While, for an average permeate flux of 40 L/m 2 -h for UF membrane, it
could eliminate 65% and 25% to 30% of COD and AOX, respectively. Jensen, et al. (2001)
investigated MBR for leachate treatment. This process was conducted at pH range from 6.5
to 6.8 with HRT of 2.7 days the performance achieved a COD removal efficiency of more
than 90%.
Results from the study indicated that the membrane bioreactor processes have great
potential with respect to biomass retention and their treatment efficiency. The study
showed that the incorporation of membranes in the system retains active biological bacteria
population and produces a high quality effluent. The system also showed that it was
probably capable of higher loading rates and has yet to achieve its maximum treatment
capacity. This was made possible with good control of bacteria population in the reactor
provided by the membranes. Throughout the study, there was negligible biomass loss
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