Propostas de métodos de mitigação de espuma na produção de biogás em biodigestores industriais: um estudo sobre o estado da arte

Abstract

The anaerobic biodigestion process of organic materials from different sources can produce a mixture of gases, most of which is methane, called biogas. The process consists of 4 complex reactions categorized as hydrolysis, acidogenesis, acetogenesis and methanogenesis, which makes its operational control difficult. Due to the instability in the process caused by several factors, the stages of biogas formation can be harmed and interrupted, generating an accumulation of intermediate by-products, such as volatile acids and nitrogenous gases, increasing the surface tension of the digestate, confining the biogas produced and causing the formation of bubbles with consequent generation of foam. Excessive foam generation is a recurrent problem and harms process equipment, causing blockage of safety valves and even rupture of the biodigester, which can affect biogas production by up to 40%. This study aims to find possible causes through a study of the state of the art, and then propose action plans to identify ways to mitigate foam formation. In evaluating the state of the art, it was identified that the topic is recent in the academic community, with studies on foam only starting in the 21st century. Most articles focus on identifying the influence of digestate composition and key operating parameters such as temperature and agitation. Based on this information, seven actions were proposed using the 5W2H methodology, in which each operational parameter of the biogas plant will be evaluated. In preliminary tests, a direct relationship was identified between the ammoniacal nitrogen concentration in the digestate and the nitrogen in the biogas. Furthermore, in experimental tests it was observed that the temperature and conditions of the digestate have a high influence on the height and consistency of the foam, obtaining a height of 1.7 and 0.7 cm in the blank tests without nitrogen, carried out on the day and in the morning following the collection of the digestate sample, respectively.