The MBR Book: Principles and Applications of Membrane

246 The MBR Book
Early examples (from the mid-1990s) of installations for industrial effluent treatment
include the JA (Japan Agricultural Cooperative) facility for processing milk and
ume plums and a livestock wastewater recycling plant (Mitsubishi Rayon, 2000).
The effluents involved in these early examples are particularly challenging, leading
to very low membrane permeabilities.
The food processing effluent had BOD and SS levels of 810 and 710 mg/L, respectively,
from a 0.02 MLD flow combined with a 0.007 m 3 /day flow from ume plum
processing wastewater with BOD and SS levels of 4600 and 32 mg/L, respectively.
The company had voluntary discharge concentration limits of 25 mg/L BOD and
5 mg/L SS, with discharge to a nearby stream. The treatment scheme consisted of a
holding tank followed by aerated equalisation upstream of the MBR unit, with the
waste sludge being concentrated using the same immersed membrane technology.
The MBR itself was fitted with two tiers of two 64 m 2 units (256 m 2 total), thus operating
at a mean flux of �4 LMH. The sludge concentration unit comprised 4 � 4m 2
units. For both the MBR and the sludge processes, permeate was removed by suction.
The plant operated at an MLSS of 8–12 g/L and 1.5 h HRT with chemical cleaning
carried out twice yearly by a 16 h soak in 0.1 wt% NaOCl/4 wt% NaOH. No membrane
replacement was required in the first 4 years of operation.
The 0.06 MLD livestock wastewater recycling plant was designed for zero liquid
discharge and comprised two holding tanks, screening, equalisation, sedimentation
(with the sludge fed to a drying unit, the condensate from which was returned to the
equalisation tank) and an anoxic tank (with sludge recycled from MBR tank), all
upstream of the MBR. The MBR permeate was treated by reverse osmosis, operating
at 80% conversion, with the concentrate being used for composting. This plant used
two tiers of five units (640 m 2 total) and operated at a mean flux of �4 LMH with a
TMP between 0.25 and 0.4 bar and hence a mean permeability of �12 LMH/bar.
The MLSS was maintained at 8–12 g/L and chemical cleaning applied every 8
months according to the same protocol as the dairy effluent treatment plant. No
membrane replacement was needed in the first 3 years of operation.
5.3.2.2 US installations
The USA licence for the Mitsubishi Rayon technology is held by Ionics, now part of
GE Water and Process Technologies. Between 2000 and end of 2005, 18 contracts
were secured by the company for MBR installations, ranging in capacity from 0.1 to
1.9 MLD and 15 of these being in the USA or Caribbean regions. For all plants, a
standard aeration rate of 68 Nm 3 per module is employed, regardless of the number
of tiers (between one and three). Thus, the SAD m can vary from 0.65 Nm 3 /h air per m 2
for a single-tier, 70-element module (105 m 2 ) to 0.22 for a triple-tier module.
Moreover, the newer elements provide double the membrane area of the old ones
(3 m 2 vs. 1.5 m 2 ), reducing the aeration demand to as low as 0.11 Nm 3 /m 2 h for a
triple-tier module.
The oldest of these installations is the Governor Dummer Academy plant in Byfield,
Massachusetts. This plant, 0.38 MLD capacity, is fed with moderate strength sewage
(200–300 mg/L BOD, 100–150 mg/L TSS, 40 mg/L TN) and produces high-quality
effluent (�2 mg/L BOD, �2 mg/L TSS, �1 mg/L ammonia, �10 FCU/100ml sample).
The plant operates at a mean MLSS of around 12 g/L. The design flux of the plant is