11.08.2015   BIOFUELS FROM ALGAE

Cultivation of Microalgae

13.1.1.1 Cultivation System and Growth Medium

Microalgae cultivation is generally realized in two kinds of systems: open raceways (ORW) or photobioreactors (PBR). ORWs are shallow ponds (between 10 and 50 cm depth). They can be built in concrete (Lardon et al., 2009) or simply carved from the ground (Campbell et al., 2011) and can be recovered by a plastic liner made of high-density polyethylene (HDPE) (Collet et al., 2011) or polyvinylchloride (PVC). Ponds are generally open but can be sheltered under a greenhouse. This kind of system is commonly used in the industry to produce

TABLE 13.3 Various Sources of Nutrients Used for Microalgae Cultivation.

Nitrogen

Phosphorus

Potassium

Ref

Mineral

Organic and Recycled

NC

Mineral

Organic and Recycled

NC

Mineral

Organic and Recycled

NC

Kad

Ammonia

—

—

Single

superphosphate

—

—

Potassium

sulphate

—

—

Lar

Calcium

nitrate

—

—

Single

superphosphate

—

—

Chloride

potassium

—

—

Bal

—

—

X

—

—

X

—

—

—

Bat

—

—

X

—

—

X

—

—

—

Cla10

—

Urea,

wastewater

—

Single

superphosphate

Wastewater

—

—

—

Jor

—

—

—

—

—

—

—

—

—

San

—

Wastewater

—

—

Wastewater

—

—

—

—

Ste

Ammonium

nitrate

—

—

Triple

superphosphate

—

—

—

—

—

Bre

Ammonium

nitrate

—

—

Calcium

phosphate

—

—

—

—

—

Cam

—

—

X

—

—

X

—

—

—

Cla11

Ammonium

phosphate

Digestates

—

Ammonium

phosphate

Digestates

—

—

—

—

Col

Ammonium

sulphate

Digestates

—

Single

superphosphate

Digestates

—

Chloride

potassium

Digestates

—

Hou

—

—

X

—

—

X

—

—

—

Kho

Sodium

nitrate

—

—

Sodium

phosphate

—

—

—

—

—

Yan

—

—

X

—

—

X

—

—

X

NC = Not communicated.

microalgae used as foodstuffs (Shimamatsu, 2004; Del Campo et al., 2007). PBRs are closed systems that allow the intensification of the culture. There are numerous types and very dif­ferent designs of PBR. They can be tubular (TPBR) or made of flat panels (FPBR) (Jorquera et al., 2010) or more rustically made of simple polyethylene bags soaked in a thermostatic wa­ter bath (Batan et al., 2010).

The choice of growth medium can be made independently of the cultivation system. Depending on the chosen species, algae can be cultivated in fresh water, brackish water, or seawater. The use of wastewater has also been suggested by several authors (Clarens et al., 2010,2011; Sander and Murthy, 2010), offering the double advantage of an unreclaimed source of water and nutrients. However, it should be acknowledged that microalgae grown in wastewater could not be used afterward as feedstock for fish or cattle. Water consumption has

Climate change Human health Ecosystems Resources

FIGURE 13.4 Climate change and endpoint impacts of various fertilizers (percentage of the worst case by impact category).

been identified as one of the main environmental concerns of bioenergy production from microalgae. Consequently, some authors suggest growing algae in seawater in order to have an unlimited resource (Batan et al., 2010; Khoo et al., 2011). Brackish water from groundwater is also used in some systems (Clarens et al., 2011). It should be noted that fresh water is still required in these systems in order to stabilize the salinity.

Table 13.4 lists cultivation systems, growth media, and cultivated species mentioned in the selected studies.