through the pores. The operational range of membrane bioreactors is much higher
compared to conventional activated sludge process. The solid retention time for
membrane bioreactor can be up to a month compared to about a few days for
conventional processes. Membrane bioreactors can operate at high suspended
loads usually known as mixed liquor suspended solids unlike conventional systems.
The configuration of the membranes in membrane bioreactor can be flat sheet,
tubular, or hollow fiber, depending on the design constraints. Ceramic membranes
with multiple tubes can also be used. There are two ways by which membrane
bioreactors can be deployed, namely, wet (submerged or immersed) installation and
dry side stream (outside the activation tank). In wet installation, membrane module is
directly submerged into the activation tank, while in dry installation, membrane
module is installed outside the tank. Aeration is done for wet installation from the
bottom toward the membrane, while for the side-stream design, air is injected along
with wastewater. Both of them have their merits and demerits (Dohare and Trivedi
2014). Side-stream installation requires higher power but can be easily cleaned and
can handle variations in the feed conditions. On the other hand, the power consumption is less for submerged membrane bioreactor, but cleaning in the membrane is
difficult and time-consuming (Gupta et al. 2008). Nowadays more installation
follows side-stream installation. The advantages of membrane bioreactor include
low footprint area, low hydraulic retention time, and high solid retention time
besides high-quality treated water. Membrane bioreactors have been used in the
treatment of many industrial effluents having high organic loading such as in food
and beverage, petroleum, pharmaceutical, pulp and paper, textiles (Dohare and
Trivedi 2014; Mutamim et al. 2012), and municipal wastes. The major challenges
include fouling, membrane life, energy consumption, and the overall cost of treatment, particularly due to limited membrane life and energy consumption.
Solvent Extraction Using Membranes
There are two types of membrane contactors used for liquid–liquid extraction,
namely, supported liquid membranes and membrane solvent extraction.
Supported Liquid Membrane
Supported liquid membrane technique provides for simultaneous extraction and
stripping, less inventory of solvent, and high selectivity. Hollow fiber ultrafiltration
membranes are the preferred configuration as it offers high interfacial surface area. In
supported liquid membrane, a solvent is immobilized within the pores of the
membrane. The feed and the strip solutions are passed through either side of the
membranes (tube/shell), and the contact between them is established by the solvent
immobilized in the pores. The species, which is being separated, gets transported
through the solvent, diffuses through it, and gets stripped by the strip solution. The
advantage of this process is its high selectivity and the possibility of uphill transport.
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A. Kapoor et al.
compared to conventional activated sludge process. The solid retention time for
membrane bioreactor can be up to a month compared to about a few days for
conventional processes. Membrane bioreactors can operate at high suspended
loads usually known as mixed liquor suspended solids unlike conventional systems.
The configuration of the membranes in membrane bioreactor can be flat sheet,
tubular, or hollow fiber, depending on the design constraints. Ceramic membranes
with multiple tubes can also be used. There are two ways by which membrane
bioreactors can be deployed, namely, wet (submerged or immersed) installation and
dry side stream (outside the activation tank). In wet installation, membrane module is
directly submerged into the activation tank, while in dry installation, membrane
module is installed outside the tank. Aeration is done for wet installation from the
bottom toward the membrane, while for the side-stream design, air is injected along
with wastewater. Both of them have their merits and demerits (Dohare and Trivedi
2014). Side-stream installation requires higher power but can be easily cleaned and
can handle variations in the feed conditions. On the other hand, the power consumption is less for submerged membrane bioreactor, but cleaning in the membrane is
difficult and time-consuming (Gupta et al. 2008). Nowadays more installation
follows side-stream installation. The advantages of membrane bioreactor include
low footprint area, low hydraulic retention time, and high solid retention time
besides high-quality treated water. Membrane bioreactors have been used in the
treatment of many industrial effluents having high organic loading such as in food
and beverage, petroleum, pharmaceutical, pulp and paper, textiles (Dohare and
Trivedi 2014; Mutamim et al. 2012), and municipal wastes. The major challenges
include fouling, membrane life, energy consumption, and the overall cost of treatment, particularly due to limited membrane life and energy consumption.
Solvent Extraction Using Membranes
There are two types of membrane contactors used for liquid–liquid extraction,
namely, supported liquid membranes and membrane solvent extraction.
Supported Liquid Membrane
Supported liquid membrane technique provides for simultaneous extraction and
stripping, less inventory of solvent, and high selectivity. Hollow fiber ultrafiltration
membranes are the preferred configuration as it offers high interfacial surface area. In
supported liquid membrane, a solvent is immobilized within the pores of the
membrane. The feed and the strip solutions are passed through either side of the
membranes (tube/shell), and the contact between them is established by the solvent
immobilized in the pores. The species, which is being separated, gets transported
through the solvent, diffuses through it, and gets stripped by the strip solution. The
advantage of this process is its high selectivity and the possibility of uphill transport.
270
A. Kapoor et al.