The challenges and perspectives for anaerobic digestion of animal waste and fertilizer application of the digestate

The increase in livestock production creates a serious problem of managing animal waste and by-products. Among the wide range of waste valorization methods available, anaerobic digestion is very promising. It is a form of material recycling that also produces renewable energy in the form of biogas, which is reminiscent of energy recycling. The effluent and digestate from the anaerobic digestion process need to be processed further. These materials are widely used in agriculture due to their composition. Both the liquid and solid fractions of digestate are high in nitrogen, making them a valuable source for plants. Before soil or foliar application, conditioning (e.g., with inorganic acids) and neutralization (e.g., with potassium hydroxide) is required to eliminate odorous compounds and microorganisms. Various methods of conducting the process by anaerobic digestion (use of additives increasing activity of microorganisms, co-digestion, multiple techniques of substrate preparation) and the possibility of controlling process parameters such as optimal C/N ratio (15-30), optimal temperature (psychrophilic (<20 C), mesophilic (35-37 degrees C) and thermophilic (55 degrees C) for microorganism activity ensure high efficiency of the process. Literature data describing tests of various digestates on different plants prove high efficiency, determined by yield increase (even by 28%), nitrogen uptake (by 20%) or phosphorus recovery rate (by 43%) or increase of biometric parameters (e.g., leaf area).

Automated summary

The increase in livestock production creates challenges in managing animal waste and by-products. Anaerobic digestion is a promising waste valorization method that not only recycles materials but also produces renewable energy in the form of biogas. Effluent and digestate from this process can be used in agriculture after further processing. Various methods and controls ensure the efficiency of the anaerobic digestion process, as evidenced by literature data showing increased yield, nitrogen uptake, phosphorus recovery rate, and biometric parameters of plants.