Table 2.4: An overview of draw solutions considered in wastewater applications.
Draw solution type. Example. Advantages. Disadvantages. Reference.
Inorganic
substances Salts
High solubility
Low cost
High osmotic pressure potential
Salt leakage may inhibit
anaerobic digestion
Clogging/scaling/fouling
ICP
Recovery is not often
feasible
Highly soluble
zwitterionic
substances
Glycine
High flux, low leakage
Leakage beneficial to biology in
subsequent energy-generating
units
Limited storage time due to
biodegradation
High charged
compounds EDTA
High water flux
Low reverse leakage
Reconcentration via less energy
consuming processes, i.e. NF
More expensive than
common salts
pH dependency
Questionable environmental
repercussions
Nutrient-rich
substances Fertilisers Direct fertigation,
No recovery necessary
Osmotic equilibrium limits
Dilution of nutrients
available
sources
Seawater, RO
brine Abundant source
TEP fouling,
Seawater: only cost-efficient
if applied near coastal areas
Thermolytic
solutes
Ammonium
bicarbonate
High solubility in water,
Recovery by moderate heat
Toxic thermolytic product
High diffusive loss
Engineered
draw solutions
Magnetic
nanoparticles
High osmotic pressures at low
concentrations
No leakage
Overcomes scaling and
crystallisation issues in MD
Agglomeration during
magnetic separation
Ultrasonication weakens
magnetic properties
Viscosity of solution
reduces effective driving
force and flux
Figure 2.2: Draw solutions used in FO based on approximately 50% of FO publications. Results are expected to increase in
similar ratios when considering all published works.