Different membrane operations can be utilized for water treatment
and reuse, such as MBR, FO and MD. MBRs are already applied
for wastewater treatment at industrial level around the World.
Fertilizer driven FO is an interesting combination of producing irrigation
water and fertilizer solutions. In this case the additional
treatment of the draw solution can be neglected and the produced
water/fertilizers can be applied directly on the field. If other types of
draw solutions should prove to be more effective for water production,
FO can also be combined withMD for re-concentrating the drawsolution
and producing fresh water. Moreover, membrane operations such as FO
and MD have fewer fouling problems compared to pressure driven
membrane operations. Biofouling can be minimized by implementing
quorumquenching.Hybrid RO–MD–MCr systems can increase the overall
water production, decrease energy consumption and recover valuable
salts from the brine [113] (Fig. 10). Theoretical and experimental data of
MD/MCr treating RO brine have shown that NaCl can be recovered from
the solution at a concentration factor around 4.5 with respect to the RO
brine [114], therefore if the MCr process is stopped after NaCl recovery,
the other components in the RO brine can be retained in the solution
and eventually blended with fresh water to reach a concentration appropriate
for irrigation purposes. MCr can also be utilized for the production
of fertilizers as high quality crystals.
In conclusion, membrane processes are promising technologies for
approaching water solutions in the agricultural industry. The various
techniques both as stand-alone units and in integration can address
the different water qualities required by the agricultural industry according
to crop selection, soil and existing water resources. Moreover,
the possibility of having small and large scale plants together with centralized
and decentralized systems according to the specific requirements
in the given area makes membranes an interesting answer for
water production in agriculture.
RO
MD
MCr
Seawater
Fresh water
Fresh water
Fresh water
Irrigation
water
RO Brine
MD Brine
MCr Brine
Salts
e.g NaCl
Fig. 10. Flow sheet of the hybrid RO–MD–MCr system for potable water, irrigation water and salt production.Many studies highlight the effect of water quality with respect to
crop yield, to the hazardous components that can accumulate in the
soil and on fruit or vegetables or other crops consumed by humans
due to their potential negative health effects. Wastewater treatment
by membrane operations can also address the removal of substances
harmful to human health (such as pathogens or other contaminants
from, e.g., drug degradations).
Improved membrane engineering, better membranes and enhanced
integrated membrane systems are necessary to reduce production costs,
increase efficiency and obtain water with quality adequate for the specific
crops and with a better vision of the future in terms of sustainable
food production.