# The Perspective of Large-Scale Production of Algae Biodiesel
## 3 Production of Algal Biodiesel
### The Environmental Impact of Algal Biodesel Production  
#### 3.4.1 GHG Emission  
From an environmental point of view, algae-produced biofuels must comply with international sustainability regulations like the EU Renewable Energy Directive, which provides guidelines for reducing GHG emissions. In this sense, biofuels from algae can contribute to reducing GHG emissions [80]. [PERSON] et al. [83] analyzed the CO\({}_{2}\) footprint of different algae farming systems. The results show that the lowest quantity of greenhouse gases in the amount of 67 \(\mathrm{g}\) CO\({}_{2}\) eq/MJ of energy produced is associated with an open-pond system that uses wastewater. The reason is the use of solar energy for lighting and drying in an open pond. Heterotrophic culture (PBR) produces 89 \(\mathrm{g}\) CO\({}_{2}\) eq./MJ. During heterotrophic farming, a continuous supply of CO\({}_{2}\) has been eliminated that reduced GHG emissions. ORP system with water recycling has 95 \(\mathrm{g}\) CO\({}_{2}\) eq./MJ, and the ORP system utilizing fresh water has 149 \(\mathrm{g}\) CO\({}_{2}\) eq./MJ. In the life cycle analysis (LCA) of biodiesel production, there are relatively large discrepancies in estimates of CO\({}_{2}\) eq/MJ emissions of biofuel produced, with many results exceeding fossil diesel emissions [29]. The differences in the analysis are mainly due to the choice of diverse models and accompanied by considerable variations of microalgae treatment as well as the harvesting methods and fuel extraction. The results of these studies indicate the need to develop more effective and efficient farming and harvesting technologies to reduce GHG emissions in the LCA of algae biodiesel production. Figure 4: Prices of algae biodiesel obtained from different farming systems. GHG emissions of advanced biofuel are depicted in Figure 5. The dashed lines show a 50% to 60% reduction of GHG emissions to a reference value of fossil fuel of 87.1 g CO\({}_{2}\) eq/MJ [84]. Better conversion efficiency is the cause of the reduction in GHG emissions. The transesterification of micro-algae currently produces the highest emissions above 60 gCO\({}_{2}\) eq/MJ fuel. If the intake of energy and nutrients is high, the CO\({}_{2}\) emission for biodiesel production from open ponds may be comparable to the CO\({}_{2}\) emission of conventional diesel. CO\({}_{2}\) emission for biodiesel production from PBRs algae may exceed emission from oil shale feedstocks. The production of 1 kg of dry algae biomass requires at least 1.83 kg of CO\({}_{2}\), assuming a 50% carbon content of the algae. In reality, the amount of CO\({}_{2}\) should be several times greater than the specified. The theoretical efficiency of CO\({}_{2}\) absorption is in the range of 20% to 90%, depending on operating conditions, while in actual conditions in open ponds, the efficiency is about 35%. In PBRs, the CO\({}_{2}\) absorption efficiency is higher, at about 75% [85]. The need for a CO\({}_{2}\) source (as well as the need for fresh water) influences the choice of algae farming sites. If CO\({}_{2}\) from fine gas is to be applied, the algae farming location should be relatively close to the power plant or another significant source of CO\({}_{2}\). Flue gases with a temperature between 20 and 35 \({}^{\circ}\)C, containing 15-20% CO\({}_{2}\) by volume, can be used for optimal algae growth. Since the temperature of flue gases from conventional power plants is close to 95 \({}^{\circ}\)C, they have to be cooled before use [86]. A large-scale algae farming can cause extensive environmental impacts. These impacts can limit the design and operation of the system. Water recirculation can reduce freshwater and nutrient consumption, but the risk of infection increases. Recycled water contains bacteria, viruses, and fungi in higher concentrations, as well as inanimate ingredients like organic and inorganic chemicals and the remains of algae cells. Algae farming can pose a potential threat to local and regional ecosystems.