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Table 11

Summary of harvesting methods (Chen et al. 2011)

Method	Energy demand	Achievable solid concentration	Advantages	Disadvantages	Household Applicability rating
Flocculation	Low 1.3 kWh/m³ of medium, depending on plant size	1.5–5%	- Suitable for large scale application - Less cell damages - Applied to vast range of species - Less energy requirements	- Metal contamination (by inorganic flocculants) - Chemicals may be expensive - Highly pH dependent - Difficult to separate the coagulant from harvested biomass - Culture medium recycling is limited	High (for autoflocculation) Medium (for electroflocculation) Low (for bio/chemicalflocculation)
Flotation	Low	4–8%	- Short operation time - Low space requirement - Large scale harvesting - Low initial cost (surfactants are required) - Suitable for large scale application	- Needs surfactants - Presence of contaminants on final products	Low
Filtration	Low Primary step –0.32 kWh/m³ Secondary step – 1 kWh/m³^a	Primary harvester – Approx 3% of total suspended solids (TSS) Secondary dewatering – 15–25% TSS	- High recovery efficiency - Cost effective - No chemical required - Low shear stress - Water recycles - No contamination	- Slow, requires pressure or vacuum, which would consume high energy - Not suitable for small algae - Membrane fouling/clogging take place and replacement increases - Operational and maintenance costs	High
Centrifugation	Very high 0.85–0.95 kWh/m³	15–30%	- Fast and effective technique - High recovery efficiency (>90)	- Expensive technique with high energy requirement - High operation and maintenance costs - Time consuming and too expensive for large scale - Risk of cell destruction - AOM^a and EOM^b released - cause toxicity	Low

Method	Energy demand	Achievable solid concentration	Advantages	Disadvantages	Household Applicability rating
Flocculation	Low 1.3 kWh/m³ of medium, depending on plant size	1.5–5%	- Suitable for large scale application - Less cell damages - Applied to vast range of species - Less energy requirements	- Metal contamination (by inorganic flocculants) - Chemicals may be expensive - Highly pH dependent - Difficult to separate the coagulant from harvested biomass - Culture medium recycling is limited	High (for autoflocculation) Medium (for electroflocculation) Low (for bio/chemicalflocculation)
Flotation	Low	4–8%	- Short operation time - Low space requirement - Large scale harvesting - Low initial cost (surfactants are required) - Suitable for large scale application	- Needs surfactants - Presence of contaminants on final products	Low
Filtration	Low Primary step –0.32 kWh/m³ Secondary step – 1 kWh/m³^a	Primary harvester – Approx 3% of total suspended solids (TSS) Secondary dewatering – 15–25% TSS	- High recovery efficiency - Cost effective - No chemical required - Low shear stress - Water recycles - No contamination	- Slow, requires pressure or vacuum, which would consume high energy - Not suitable for small algae - Membrane fouling/clogging take place and replacement increases - Operational and maintenance costs	High
Centrifugation	Very high 0.85–0.95 kWh/m³	15–30%	- Fast and effective technique - High recovery efficiency (>90)	- Expensive technique with high energy requirement - High operation and maintenance costs - Time consuming and too expensive for large scale - Risk of cell destruction - AOM^a and EOM^b released - cause toxicity	Low

^aAlgae Organic Matter, ^bExtracellular Organic Matter.