Water Recovery and Recycle
Reclamation and reuse of water have become quite popular with the advent of
membrane technologies because of its cost-effectiveness. Reverse osmosis has
been used for the reclamation of water from effluents (Shang et al. 2011). Integrated
use of reverse osmosis along with ultrafiltration and microfiltration is common for
the tertiary treatment of municipal wastewater to augment water sources as exemplified by 270 MLD plant at the Orange County Water District in Southern California and many other plants in Singapore (Wong 2012). Similar systems have been
used in petrochemical industries such as China American Petrochemical Company
for recovering 9000 m
3 /day at Taiwan and 26,000 m
3 /d zero liquid discharge system
at PEMEX refinery in Minatitlan, Veracruz, Mexico. Recovery of water from
sewage has been in practice in India since the late 19280s, and a number of reverse
plants have been established. Currently most of the industries and small residential
communities in water stress regions are recovering water for recycle. Virtually all
industrial effluent streams including leather (Cassano et al. 1999), paper (Zhang et al.
2009), and textiles (Bottino et al. 2001) can be treated with membrane processes to
reclaim water for reuse through reverse osmosis. In all these processes, reclamation
of water for reuse is obtained through reverse osmosis, while other membrane
processes could be used as a pretreatment or in some cases recovery of valuables.
Reverse osmosis plant follows the primary and secondary treatment in all the
effluent treatment systems. One may have to ensure that during the postsecondary
treatment, neither chlorine nor microorganisms enter the reverse osmosis system by
appropriate treatment. Since the dissolved solid contents are likely to be less, mostly
below 3000 ppm, one can achieve high recoveries of about 70–80%. The product
water can be further polished or posttreated to suit the end-use quality requirements.
Reverse osmosis has been used for the concentration of aqueous radioactive effluents
to reduce the volume for further treatment. When cellulose acetate membranes were
used, reverse osmosis gave a poor rejection of nitrate species as the concentration
increased. This factor was exploited in isolating uranyl species from ammonium
nitrate solution (Prabhakar et al. 1992, 1994, 1996).
In general, the role of reverse osmosis process in wastewater treatment is to
recover water and concentrate the contaminants to a small volume for further
treatment. The recovery is limited by the scaling threat and the osmotic pressure of
the concentrating feed due to the continuous removal of water through the membrane. The concentrated streams would contain all the contaminants and salts, and
their disposal would be a challenge environmentally. For zero liquid discharge, one
more unit operation such as evaporator or crystallizers may have to be used. As the
water demand and value are in the ascending trend, it is imperative to recover water
from any spent stream and in that reverse osmosis has a major role to play.
8 Role of Membranes in Wastewater Treatment
265
Reclamation and reuse of water have become quite popular with the advent of
membrane technologies because of its cost-effectiveness. Reverse osmosis has
been used for the reclamation of water from effluents (Shang et al. 2011). Integrated
use of reverse osmosis along with ultrafiltration and microfiltration is common for
the tertiary treatment of municipal wastewater to augment water sources as exemplified by 270 MLD plant at the Orange County Water District in Southern California and many other plants in Singapore (Wong 2012). Similar systems have been
used in petrochemical industries such as China American Petrochemical Company
for recovering 9000 m
3 /day at Taiwan and 26,000 m
3 /d zero liquid discharge system
at PEMEX refinery in Minatitlan, Veracruz, Mexico. Recovery of water from
sewage has been in practice in India since the late 19280s, and a number of reverse
plants have been established. Currently most of the industries and small residential
communities in water stress regions are recovering water for recycle. Virtually all
industrial effluent streams including leather (Cassano et al. 1999), paper (Zhang et al.
2009), and textiles (Bottino et al. 2001) can be treated with membrane processes to
reclaim water for reuse through reverse osmosis. In all these processes, reclamation
of water for reuse is obtained through reverse osmosis, while other membrane
processes could be used as a pretreatment or in some cases recovery of valuables.
Reverse osmosis plant follows the primary and secondary treatment in all the
effluent treatment systems. One may have to ensure that during the postsecondary
treatment, neither chlorine nor microorganisms enter the reverse osmosis system by
appropriate treatment. Since the dissolved solid contents are likely to be less, mostly
below 3000 ppm, one can achieve high recoveries of about 70–80%. The product
water can be further polished or posttreated to suit the end-use quality requirements.
Reverse osmosis has been used for the concentration of aqueous radioactive effluents
to reduce the volume for further treatment. When cellulose acetate membranes were
used, reverse osmosis gave a poor rejection of nitrate species as the concentration
increased. This factor was exploited in isolating uranyl species from ammonium
nitrate solution (Prabhakar et al. 1992, 1994, 1996).
In general, the role of reverse osmosis process in wastewater treatment is to
recover water and concentrate the contaminants to a small volume for further
treatment. The recovery is limited by the scaling threat and the osmotic pressure of
the concentrating feed due to the continuous removal of water through the membrane. The concentrated streams would contain all the contaminants and salts, and
their disposal would be a challenge environmentally. For zero liquid discharge, one
more unit operation such as evaporator or crystallizers may have to be used. As the
water demand and value are in the ascending trend, it is imperative to recover water
from any spent stream and in that reverse osmosis has a major role to play.
8 Role of Membranes in Wastewater Treatment
265