# Biological Methods in Biodiesel Production and Their Environmental Impact
## 1 Introduction  
In many countries, different economic crises, high pollution, and the depletion of fossil fuels are serious problems and present big challenges [1]. Given the constantly deteriorating air quality, there has been a need to find environmentally friendly solutions, including technologies of alternative fuel production. Moreover, such direction of development causes a partial move away from fossil fuels. Therefore, the development of engine fuels derived from renewable plant resources is very important. The increasing concern for environmental protection and stricter requirements in the content of harmful components in exhaust gases forces the industry to continuously develop various alternative fuels that generate less-toxic emissions. The transport sector is one of the largest greenhouse gas emitters in the world. Decarbonizing of the transport sector is a big challenge, given the dynamic development of this sector. The International Energy Agency (IEA) predicts that the demand for mobility will increase by around 60% in 2050 [2]. On the other hand, the transport sector must reduce its greenhouse gas emissions by as much as 30% by 2030. After the decrease in the period from 2007 to 2013, since 2014, the emissions generated in this sector have been constantly growing. The European Environment Agency predicts that greenhouse gas emissions from transport will remain rather stable until 2030 [3]. There are many different types of compounds which can be used as a substitute for conventional fuels. These compounds can be produced with the use of various methods and raw materials. In developed countries, research is focused on developing technologiesfor the production of advanced fuels (produced from various types of waste and non-food biomass). The level of technological advancement of individual methods is different. Developed countries are beginning to withdraw from the production of so-called first-generation biofuels (produced from food plants) and invest money in the development of advanced biofuels (produced from non-food biomass and waste). Based on the roadmap concerning biofuels in transport in the world by 2050 [4], the most technologically advanced are technologies of the following fuels' production: ethanol from lignocellulosic, methanol, fuels obtained as a result of syngas fermentation (ethanol, butanol) [5], and hydrocarbons obtained as a result of hydrotreatment of vegetable oils. There is a lack of funding for the development of new technologies in developing countries. However, global trends force the use of environmentally friendly fuels instead of fossil fuels. It means that older generation biofuels and the technology for their production are used in these countries. These fuels are most often produced from food plants (e.g., rape seed, soybean, sugar cane, and maize) and include mainly bioethanol and biodiesel. The most common method of biodiesel production is the transesterification of fats with different alcohols and in the presence of a catalyst, influencing the course of the process and its efficiency. Chemical compounds in the form of acids or bases are the most popular catalysts used in this process. The biodiesel production methods with the use of these catalysts are well-known, and commonly used in industrial conditions, but they are not free from disadvantages and negative environmental impact. It is well-known that biodiesel as a fuel has many disadvantages (it is easy to oxidize and has a high cold filter plugging point). The raw materials for its production in North America or Europe are mainly edible oil plants, which compete with food production. On the other hand, in South America, Asia, and Indonesia, the main raw material is oil palm. It is much more efficient than other oil plants and is easy to cultivate, but unfortunately, valuable natural areas, including rainforests, are adopted for its cultivation in a barbaric manner.