Table 1.

Advantages and disadvantages of current cell disruption techniques for microalgal biotechnology.

Method	Operates at Industrial Scale	Suitability for Commercial Application	Advantages	Disadvantages	Ref.
High pressure homogeniser	✓	-	Destruction of cell walls at room temperature, effective for neutral lipid extraction	High energy input, not effective for extraction of high molecular weight proteins	[15,19]
Mechanical cell press	✓	-	Industry standard for oil recovery from oilseeds	Inefficient cell disruption, high energy input	[20]
Hydrodynamic cavitation	✓	-	Relatively low energy input	Cavitation area limited	[21]
Horn sonication	✓	++	Effective cell wall disruption, low maintenance cost, relatively rapid process, hazardous chemicals are not required	Multiple units required, cavitation area limited, high operational costs and energy input	[15]
Bath sonication	x	+++	Effective cell wall disruption, minimal maintenance cost, relatively rapid, no hazardous substances required	High operational costs and energy input	[15]
Microwaves	x	++++	Effective cell wall disruption and excellent recovery of bioactives, relatively low energy input, fast heating and short reaction time, reduced solvent usage	Generates heat, high maintenance cost	[15]
Bead milling/beat beating	✓	++	Effective cell wall disruption, rapid extraction	Varied efficiency across species, additional step required to remove beads, high maintenance costs and energy input	[15]
Osmotic shock	x	-	Low energy input, easier to scale-up	Inefficient cell disruption, generation of waste saltwater, time consuming	[22]
Acid/alkali	✓	-	Low energy input	Requires disposal of acid/alkali after extraction, carotenoid degradation	[22]
Enzymatic hydrolysis	✓	++	Effective cell wall hydrolysis, high selectivity, mild treatment, carotenoid bioactivity not affected	High cost of enzymes, longer treatment time, enzymes must be disposed of after use	[15]
Autoclave	x	+	Low maintenance cost	High energy input, not suitable for pigments	[11,23]
Steam explosion	✓	+++++	Effective cell wall disruption, low maintenance costs, relatively low energy input	Varied efficiency across species	[15]
Freeze drying	✓	+	Mild operating conditions, drying and extraction can be incorporated in one step, does not affect cellular components	Cell disruption variable and often the integrity of the cell wall is weakened but not disrupted, cost associated with pump maintenance, time consuming, expensive, high energy input	[15]
Nanoparticles	x	-	Non-toxic	Expensive, additional step required to remove nanoparticles, technology in its infancy	[24]
Supercritical fluid extraction	✓	+	Polarity of solvent is tunable, fast process, uses non-toxic solvents such CO2, effective for carotenoid extraction	Expensive, not suitable for scale-up	[13,25]
Grinding (with/without cryogens)	x	-	Quick and efficient at a laboratory-scale	Time consuming, degradation of some of the bioactives	[26]
Pulse electric field	✓	+	High selectivity, mild treatment, carotenoid bioactivity not affected, relatively low energy input	Still in its infancy	[27]
Hydrothermal liquefaction	x	-	Uses a wet feedstock	High variability in recovery, high energy input and temperature, requires expensive catalyst	[28,29]
Ionic liquids	x	-	Low cost	Still in their infancy, issues over toxicity	[30]
Soxhlet extraction	✓	+	Cost-effective, easy to scale-up	Long extraction time, uses large amounts of solvents (often toxic)	[12]

✓: Yes; x: No; -: Not suitable; +: Weak; ++: Moderate; +++: High; ++++: Higher; +++++: Very high.