Effect of Aeration Applied During Different Phases of Anaerobic Digestion

Aerobic treatment has been investigated as a method to enhance putrescible substrate degradation and biogas production through anaerobic digestion (AD). A series of aeration methods has been studied in different phases of anaerobic digestion (before, during, or at a late stage of AD). Several research groups have applied aeration together with anaerobic digestion to improve hydrolysis and increase substrate conversion efficiencies. Aeration has been proven to reduce volatile fatty acids (VFA) accumulation during AD, reducing pH inhibition for methanogens, and thus increasing process yields. Aeration may represent an effective method to reduce substrates’ toxicity (e.g. sulphur compounds), particularly when digestate, resulting from their anaerobic digestion, is destined for use on the land. However, a potential drawback is represented by decreased methane production observed as a consequence of excessive soluble COD consumption prior to the AD phase. Duration and intensity of aeration, substrate type, aeration method, temperature during aeration, and air application phase are deemed important factors capable of affecting the efficiency of this treatment. The present review aims to provide a comprehensive insight into research studies performed over the past decades to test the combination of aerobic treatment and anaerobic digestion of organic substrates.