# The Perspective of Large-Scale Production of Algae Biodiesel
## 3 Production of Algal Biodiesel
### Algae Farming Systems  
When choosing an algae farming system, it is crucial to select an excellent location to obtain the wished result. Presently, there are several algae farming systems. The most widespread system of open ponds can be raceway or circular, with or without water stirring [28]. The unstirred ponds are the simplest because they have no water stirring device and, therefore, they are the cheapest [29]. From 20% to 40% of the volume of pond water can be harvested daily, depending on the season and other factors. An additional advantage of this pond type is its less demanding maintenance, the possibility of enlarging the pond area by increasing the number of ponds. The ability to integrate with wastewater treatment processes is an additional benefit. Raceway ponds consist of one or more connected canals in the shape of runways with a depth from 15 to 30 cm. The paddlewheel is commonly used to maintain the continuous flow of water through canals and the mixing of algae. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Crop**} & **Oil Yield** & **Biodiesel** & & **Oil Yield** & **Biodiesel** \\  & **(L/ha/year)** & **Productivity** & **Crop** & **(L/ha/year)** & **Productivity** \\  & **(kg/ha/year)** & & & **(kg/ha/year)** \\ \hline Rapeseed & 1190 & 862 & Sunflower & 952 & 946 \\ Oil palm & 5950 & 4747 & Jatropha & 1892 & 656 \\ Corn & 172 & 152 & Microalgae \({}^{\star}\) & 58,700 & 51,927 \\ Soybean & 446 & 562 & Microalgae \({}^{\star\star}\) & 136,900 & 121,104 \\ \hline \end{tabular}  
* 30% oil (L/wt) in algae biomass, \({}^{\star\star}\) 70% oil (L/wt) in algae biomass.  
\end{table} 
Table 1: Yield of algae and other biodiesel crops. The system is used to remain algae exposed to the sun and CO2 as much as possible and to prevent algae biomass from settling on the bottom. In the circular ponds, water is stirred by a centrally pivoted agitator. Open-pond systems typically utilize natural light, so the cost of using artificial light is avoided. Compared to photobioreactors, open ponds have disadvantages such as low biomass yield, high harvesting costs, and the possibility of attack weeds, wild algae, microorganisms, and diseases, which all further reduce algae yield [29]. A high rate of water evaporation resulting in a high water footprint [30; 31]. Two factors that enhance water loss by evaporation are temperature and wind speed. Thus, open-pond algae farming is suited only for areas with low-cost water [32]. Another algae cultivation system is based on closed glass containers called photobioreactor, as depicted in Figure 1. Different photobioreactor designs are applied, like flat panel, vertical column, tubular and hybrid systems [33]. They are made in the form of plastic or glass bags, containers, or towers. The high yield of algal biomass is obtained in bubble columns and airlift photobioreactors. The main objective of photobioreactor development is to maximize algae growth through optimal light supply through thin layers of microalgae suspension. Sometimes artificial light is used to increase yields, and some manufacturers rely solely on artificial light [8]. The use of artificial light often causes complex structures, a considerable number of surfaces with the resultant high sensitivity to pollutants, and high energy consumption for algae production. To date, commercially production in photobioreactors uses strains from only a few microalgal groups: green algae, dinoflagellates, and treatohydrides. One of the essential advantages of a closed algae farming system is the ability to create better, more controlled conditions for the growth of certain types of algae that cannot be achieved in outdoor ponds. Moreover, it can prevent or at least reduce the invasion of harmful algae and zooplankton that affect the yield of useful algae [8]. In addition to these advantages, the major disadvantage of photobioreactors is high investment cost [34; 35]. Other disadvantages include difficulties with scaling-up, overheating, oxygen accumulation, bio-fouling, and cell damage over time [9].