Biofertilizer production systems: Industrial insights

Abstract Anaerobic digestion (AD) is a biological process that converts complex substrates into biogas and digestate under microbial activity in the absence of oxygen through four main steps: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. It is one of the well-studied technologies for stabilizing organic wastes. Among the treatment technologies available for organic solid wastes, AD is quite suitable because of its environmental friendliness and high potential for energy recovery and production of quality and nutrient-rich digestates, which can in turn be processed to biofertilizers. Such positive aspects coupled with recent concerns about rapid population growth, increasing food demand, and global warming have promoted further research on the biofertilizer production process development and improvement in order to enhance the quality of biofertilizers and by extension enhance their abilities to influence crop growth and well-being and soil nutrient improvement. AD is equally known to be famous in both developed and developing countries where mostly the produced gas is used as fuel for cooking and other purposes while the digestate is used as fertilizers or soil conditioners. However, agronomic characteristics of digestates can produce harmful effects due to digestate quality in terms of pH, organic matter imbalance, and especially heavy metal content. There is therefore the need to evaluate the differences and similarities in agronomic characteristics and the values of anaerobic digestates taking cognizance of their production materials, type of biogas plant that treated it, and the prevailing environmental factors. It is important to study the chemical analyses and the availability of nutrients before applying biofertilizers. Also, crop growth and soil mineralization experiments with biofertilizers should be controlled. Lastly, lifecycle assessments must be carried out with a circular economy approach.