Membrane and Desalination Technologies - TCE Moodle Website

Membrane Processes for Reclamation of Municipal Wastewater 463
organics. Sodium hypochlorite and antiscalant PermaTreat 191 were dosed to the RO feed
line to prevent biofouling and scaling to RO membranes (47). A 5-mm pore-size cartridge
filter was installed prior to RO membranes to protect them from foreign materials. Both the
product water from the RO unit and the concentrate stream were sent back to the outfall sump
during the study.
7.2.2. UF and RO Units
The UF unit contained four HF66–45-XM50P modules installed in parallel from Koch
Membrane Systems, Inc. The membranes were polyacrylonitrile hollow fibers with a molecular
weight cut-off of 50,000 Da. The UF unit was designed to operate at high velocity of feed
water by recirculation pump, periodic reversal of the feed flow direction and periodic backwashing
sequences to reduce fouling of UF membranes. A Clean-In-Place (CIP) system was
provided for manual chemical cleaning to UF membranes. Kochkleen ® Liquid Detergent was
used for cleaning at pH 10.0 and 2% citric acid was used for cleaning at pH 2.0.
The RO unit was constructed with three pressure vessels in 2:1 configuration. Each
pressure vessel held two LFC1-4040 spiral-wound modules that were made of thin film
polyamide composite membranes. A solenoid valve was installed in parallel with the throttled
SS glove valve on the concentrate line and was automatically controlled by PLC to periodically
flush the RO membrane surface under high feed flow and low pressure. Pressure, flow,
temperature, pH, and conductivity indicators and online instruments were installed at the RO
unit. There was also a CIP system attached with the RO unit. Two percent citric acid was used
for cleaning at pH 2.0 over 3 h. Then, 1% EDTA was used at pH 12.0 over 1 h operation
followed by 16 h soaking and 0.5 h operation (31).
7.2.3. Trial Runs
Preliminary investigation was conducted to monitor the raw feed quality and understand
the characteristics of the raw feed from March to August 2003 prior to the plant operation.
Samples were collected on hourly basis with an automatic sampler from the discharge outfall
sump for 24 h. pH, conductivity, turbidity, and TOC of hourly samples were measured and
analyses of daily composite samples were conducted.
The study was conducted from September 2003 to February 2004, over 6 months. The
conductivity probing was conducted after RO membranes were loaded into the pressure
vessels to ensure no leakage between the interconnections of membrane elements. The plant
was disinfected thoroughly.
In order to increase RO operating pressure while the RO feed flow remained the same, the
number of RO elements was cut down from previously running with 6–4. One pressure vessel
in RO train was isolated, and the RO unit was operated with four elements in series from
November 2003. The operating pressure of RO unit was increased to 100 psi. The operating
conditions of the pilot plant during the study are summarized in Table 10.19.