**8. Technology for growing algae**

There are two algae cultivation technologies currently in use for commercial microalgae production and proposed for algal biofuel production (viz. extensive or open ponds, intensive or raceway ponds or closed photobioreactors in many designs and closed fermenter systems).

### **8.1. Open pond system**

Large extensive or open pond systems are currently in use for wastewater treatment and *Dunaliella salina* production. Oxidation ponds in wastewater treatment systems are not in the true sense for algae production as no algae are harvested. Cognis Australia Pty Ltd produce β-carotene from *D. salina* harvested from hypersaline extensive ponds in Hutt Lagoon and Whyalla. The halotolerant *D. salina* dominates naturally in brine at salt concentrations >100 g L-1 but grows relatively slowly (producing perhaps not much more than 2.2 t ha-1 yr-1). *Hutt Lagoon* has a total pond surface area of ca. 520 ha and Whyalla is ca. 440 ha. In terms of pond surface area, *Hutt Lagoon* and *Whyalla* are among the largest algal production systems in the world. These extensive pond algae production systems have limited mixing, and rely on natural selection and the bounty of nature with minimal intervention.

Open pond system used big shallow pond which is open. This type of pond is easy to construct and operate than close pond system. Shallow pond is constructed to provide large area to algae for exposed to sunlight. Open pond system is use for cultivation of algae especially having high oil content. Both natural and artificial water pond can be used to algae biomass produc‐ tion. Main advantages of open pond system are low operating cost and their simple structure.

**Figure 5.** Spirulina farms on Hainan Island China & Circular chlorella ponds at Yaeyama on Okinawa Island, Southern Japan [121]

Similarly their many disadvantage are also associated with open pond system are poor productivity, little control over algae production, large evaporative losses, large area required, diffusion of carbon dioxide to the atmosphere and expensive harvesting etc [93].

### **8.2. Closed ponds**

and polyunsaturated fats have an ability to retain their fluidity at lower temperature during

**Microalgae species Carbohydrates (%) Proteins (%) Lipids (%)**

There are two algae cultivation technologies currently in use for commercial microalgae production and proposed for algal biofuel production (viz. extensive or open ponds, intensive or raceway ponds or closed photobioreactors in many designs and closed fermenter systems).

Large extensive or open pond systems are currently in use for wastewater treatment and *Dunaliella salina* production. Oxidation ponds in wastewater treatment systems are not in the true sense for algae production as no algae are harvested. Cognis Australia Pty Ltd produce β-carotene from *D. salina* harvested from hypersaline extensive ponds in Hutt Lagoon and Whyalla. The halotolerant *D. salina* dominates naturally in brine at salt concentrations >100 g L-1 but grows relatively slowly (producing perhaps not much more than 2.2 t ha-1 yr-1). *Hutt Lagoon* has a total pond surface area of ca. 520 ha and Whyalla is ca. 440 ha. In terms of pond surface area, *Hutt Lagoon* and *Whyalla* are among the largest algal production systems in the world. These extensive pond algae production systems have limited mixing, and rely on

Open pond system used big shallow pond which is open. This type of pond is easy to construct and operate than close pond system. Shallow pond is constructed to provide large area to algae for exposed to sunlight. Open pond system is use for cultivation of algae especially having high oil content. Both natural and artificial water pond can be used to algae biomass produc‐ tion. Main advantages of open pond system are low operating cost and their simple structure.

natural selection and the bounty of nature with minimal intervention.

winter but it will have also lower stability during regular seasonal temperature.

**Table 10.** Chemical composition of biofuel source microalgae

**8. Technology for growing algae**

**8.1. Open pond system**

120 Biofuels - Status and Perspective

**Chaetoceros muelleri** 11–19 44–65 22–44 **Chaetoceros calcitrans** 10 58 30 **Isochrysis galbana** 7–25 30–45 23–30 **Chlorella protothecoides** 10.62–15.43 10.28–52.64 14.57–55.20 **Chlorella sp.** 38–40 12–18 28–32 **Nannochloropsis sp.** - - 31–68 **Neochloris oleoabundans** - - 35–54 **Schizochytrium sp.** - - 50–77 **Scenedesmus– obliquus** 10–17 50–56 12–14 **Quadricauda de Scenedesmus** - 47 1.9

> Closed pond system mean which is not open to expose in the air. Control over environment is much better much better than open pond system and it allows more species to grown than other. It is not only more expensive system than open pond system, but also low productivity of biomass.

### *8.2.1. Photo bioreactor*

Photobioreactors are closed systems of transparent tubes, plates, bags or hemispherical domes. Photobioreactors improve yields by protecting productive strains to some extent from contamination, pathogens, and predators, offer the benefits of some temperature control and eliminate climate related impacts of open ponds (viz. rainfall, evaporation, and diurnal and seasonal temperature fluctuations). While better mixing in photobioreactors may provide slight area productivity gains, claims of productivity, which refer to the area or footprint of the growth vessel, can be extremely high when the reactors are configured vertically and are misleading. Vertical photobioreactors must be situated far enough from each other so as to not shade, and consequently the basic limitation on productivity remains the same for both open ponds and closed photobioreactors.

Surface fouling due to bacteria, other organisms, and, in particular, algae, is a major problem with photobioreactors, and cleaning can be a major design and operational problem. Where CO2 input and O2 evolution must be optimized for maximum productivity, gas transfer, which is restricted to the surface area of gas liquid interfaces, can limit scalability of photobioreactor designs.

Commercial photobioreactors as shown in figure 6 are in operation at different facilities including the production of *H. pluvialis* in Israel and Hawaii and C. vulgaris in Germany. Typical plant gate selling prices/production costs are well above \$100/kg from such systems. Consequently, biofuels production based entirely on photobioreactor systems is generally considered unlikely to be commercially viable.

Algae pumped with nutrient rich water through plastic and borosilicate tube, exposed to sunlight called photobioreactor (PBR). Algae biomass produces using carbon dioxide and light by the process of photosynthesis and nutrient from wastewater in artificial environment not in natural environment. Using photobioreactor, algae easily grow on the land which is not arable such as desert and even ocean surface also. PBR is more productive and controlled but more costly and difficult than open pond system.

Table 10 makes a comparison between PBR and ponds for several culture conditions and growth parameters. Comparison of performances achieved by PBRs and open ponds may not be easy, as the evaluation depends on several factors, among which the algal species cultivated and the method adopted to compute productivity. There are three parameters commonly used to evaluate productivity in algae production units: Volumetric productivity (VP): productivity per unit reactor volume (expressed as g/L d).Areal productivity (AP): productivity per unit of ground area occupied by the reactor (expressed as g/m2 d). Illuminated surface productivity (ISP): productivity per unit of reactor illuminated surface area (expressed as g/m2 d).

**Figure 6.** Photobioreactor for large scale algae production [122]

As stated by Richmond [96] despite closed systems offer no advantage in terms of areal productivity, they largely surpass ponds in terms of volumetric productivity (8 times higher) and cell concentration (about 16 times higher). In conclusion, PBR and open ponds should not be viewed as competing technologies, but the real competing technology will be genetic engineering [96].
