Page 446 - Industrial Wastewater Treatment, Recycling and Reuse

Application of Anaerobic Membrane Bioreactor 417

10.4.2.1 Optimization of OLR
The average COD maintained in the feed tank during the study was about
385 mg/L. Initially, the AnMBR was started with an OLR of 0.62 kg
3
COD/m /day. In the first 120 days operation of the bioreactor, the
OLR was increased in a stepwise manner, i.e., 0.62, 0.77, 0.92, and
3
1.32 kg COD/m /day with corresponding hydraulic retention time
(HRT) of 15, 12, 10, and 7 h, respectively. The bioreactor temperature

was constant and maintained at 37 C for the complete study. Depending
upon the OLR, the calculated quantity of sludge from the bioreactor was
withdrawn on a daily basis to keep the MLVSS in the range of 7500–
8000 mg/L. The treated water from the bioreactor was pumped through
two tubular membrane modules arranged in a series for filtration of treated
water. The reject from the membrane module was recycled back to the bio-
reactor. The treated water was recirculated through the membrane unit at a
3
constant flow rate of 10 m /h to maintain sufficient cross-flow velocity on
the membrane surface. To keep a constant HRT in the bioreactor, the per-
meate flow rate from the external membrane was always set a little higher
than the feed flow rate, recycling the excess permeate because it was difficult
to precisely keep a constant flux. Feed, bioreactor effluent, and permeate
samples were tested on a daily basis for pH, TSS, VSS, soluble COD,
BOD 5 , and TOC. The generated biogas was measured on daily basis during
the study. All analyses were performed according to Standard Methods for
the Examination of Water and Wastewater (APHA, 1992). A standard prac-
tice of membrane cleaning was adopted after every two months of operation
as per the membrane cleaning protocols.
The experimental operating conditions maintained during the investiga-
tion are given in Table 10.6.

10.4.2.2 Membrane-Cleaning Protocols
The membrane filtration unit was disconnected from the bioreactor before
starting the chemical cleaning of the membranes. Prior to this cleaning exer-
cise, the membrane modules were rinsed two to three times with tap water
for the removal of the sludge layer and solid particles deposited on the mem-
brane surface. One hundred liters of 1.5% citric acid solution was prepared in
the cleaning tank and recirculated through the membrane for 30 min at a
3
constant flow of 10 m /h. After stopping the recirculation flow, the module
was allowed to soak in the acid solution for 60 min. This acid solution was
discharged from the tank, and the membranes were flushed with tap water