**6.2 Closed photobiorector**

As name suggest, growing of algae in closed system. Closed photobioreactor can produce higher biomass than closed system, but it is not cost effective. The most common cultivation technology in closed system is the photobioreactor (PBR) (**Figure 5**). Typically, closed reactors include tubular and flat bioreactors. The system consists of glass or plastic, although glass PBR is frequently used for large scale production [58]. In closed system, glass tubes are arranged normally in vertical, helical of in horizontal

**Figure 4.** *Open pond system for algae biomass production.*

#### **Figure 5.**

*Tubular photobioreactor with parallel tubes.*


#### **Table 4.**

*Comparison between open and closed photobioreactor system.*

manner and mechanical pumps fixed to allow CO2 and O2 exchange. Closed PBR has advantage over open system as it harnesses more sunlight and hence enhance productivity (from 20 to 40 g/m /d) in short span of time, although it is costly due to complexity in structure [59]. The advantages and disadvantages between open pond and closed bioreactor is given in **Table 4**.
