Membrane and Desalination Technologies - TCE Moodle Website

616 P. Kajitvichyanukul et al.
Fig. 14.4. Direction and
magnitude of water flux
as a function of applied
pressure in FO, PRO, and
RO (adapted from Lee
et al. (56)).
Fig. 14.5. Water across
the membrane from
dilute to the concentrated
solution in osmosis
(adapted from Kneen
et al. (30)).
Reverse
osmosis
(ΔP>Δπ)
Fig. 14.5 (30). To make the RO process work, the hydraulic pressure (DP) is applied to the
contaminated water in the opposite direction of the osmotic pressure gradient (Dp), where
the hydraulic pressure is higher than the osmotic pressure (DP > Dp). Under this circumstance,
pure water is “squeezed” through the membrane from the concentrated to the dilute
side as shown in Fig. 14.6 (30). Since contaminants do not move with the water as it moves
across the membrane, pure water collects on the other side of the membrane. The purified
water that accumulates on one side of the membrane can then be used or stored. This purified
water is cleaner and healthier drinking water. The rejected impurities on the concentrated side
of the membrane are washed away in a stream of wastewater and not accumulated as on a
traditional filter.
Water flux
0
Flux reversal
point
(ΔP=Δπ)
Forward
osmosis
(ΔP=0)
Diluted
Semipermeable membrane
Δπ
Concentrated
Water flow
ΔP
Pressureretarded
osmosis
(Δπ>ΔP)