An attractive alternative to the use of fossil fuels is biodiesel, which can be obtained from a variety of feedstock through different transesterification systems such as ultrasound, microwave, biological, chemical, among others. The efficient and cost-effective biodiesel production depends on several parameters such as free fatty acid content in the feedstock, transesterification reaction efficiency, alcohol:oil ratio, catalysts type, and several parameters during the production process. However, biodiesel production from vegetable oils is under development, causing the final price of biodiesel to be higher than diesel derived from petroleum. An alternative to decrease the production costs will be the use of economical feedstocks and simple production processes. Castor oil is an excellent raw material in terms of price and quality, but especially this non-edible vegetable oil does not have any issues or compromise food security. Recently, the use of castor oil has attracted attention for producing and optimizing biodiesel production, due to high content of ricinoleic fatty acid and the possibility to esterify with only methanol, which assures low production costs. Additionally, biodiesel from castor oil has different advantages over conventional diesel. Some of them are biodegradable, non-toxic, renewable, they can be used alone, low greenhouse gas emission, among others. This review discusses and analyzes different transesterification processes, technologies, as well as different technical aspects during biodiesel production using castor oil as a feedstock.

Aromatic hydrocarbons like benzene, toluene, xylene, and ethylbenzene (BTEX) can escape into the environment from oil and gas operations and manufacturing industries posing significant health risks to humans and wildlife. Unlike conventional clean-up methods used, biological approaches such as bioremediation can provide a more energy and labour-efficient and environmentally friendly option for sensitive areas such as nature reserves and cities, protecting biodiversity and public health. BTEX contamination is often concentrated in the subsurface of these locations where oxygen is rapidly depleted, and biodegradation relies on anaerobic processes. Thus, it is critical to understand the anaerobic biodegradation characteristics as it has not been explored to a major extent. This review presents novel insights into the degradation mechanisms under anaerobic conditions and presents a detailed description and interconnection between them. BTEX degradation can follow four activation mechanisms: hydroxylation, carboxylation, methylation, and fumarate addition. Hydroxylation is one of the mechanisms that explains the transformation of benzene into phenol, toluene into benzyl alcohol or p-cresol, and ethylbenzene into 1-phenylethanol. Carboxylation to benzoate is thought to be the primary mechanism of degradation for benzene. Despite being poorly understood, benzene methylation has been also reported. Moreover, fumarate addition is the most widely reported mechanism, present in toluene, ethylbenzene, and xylene degradation. Further research efforts are required to better elucidate new and current alternative catabolic pathways. Likewise, a comprehensive analysis of the enzymes involved as well as the development of advance tools such as omic tools can reveal bottlenecks degradation steps and create more effective on-site strategies to address BTEX pollution.

Agro-industrial residues such as bagasse, pomace, municipal residues, vinasse and cheese whey are an environmental problem around the world, mainly due to the huge volumes that are generated because of the food production to satisfy the nutritional needs of the growing world population. Among the above residues, cheese whey has gained special attention because of its high production with a worldwide production of 160 million tons per year. Most of it is discarded in water bodies and land causing damage to the environment due to the high biological oxygen demand caused by its organic matter load. The environmental regulations in developing countries have motivated the development of new processes to treat transform cheese whey into added-value products such as food supplements, cattle feed and food additives. In addition, during the last decade, several processes and technologies have been developed to produce bioenergy through the biotechnological process using cheese whey as a potential feedstock. This review discusses the production of bioethanol, biohydrogen, biomethane and microbial lipid-biodiesel production using cheese whey as a potential substrate.