Isolation and Characterization of Surface-Active Fractions Responsible for Foam Formation During Anaerobic Digestion of Municipal Wastes

A simple and rapid method to isolate surfactant-like fractions responsible for foaming production during anaerobic digestion (AD) is proposed. Alkaline extraction of organic matter and subsequent fractionation of extracts into alkali-soluble/acid-insoluble (humic acid, HA) and alkali-soluble/acid-soluble fractions (fulvic acid, FA) were performed on samples directly taken from a full-scale plant operating anaerobic digestion. Lab-tests performed to measure foaming ability of the isolated organic fractions, allowed the separation of the fraction responsible for foam production, fulvic acid. Fraction isolation and subsequent chemical characterization revealed its specific chemical nature, i.e. high hydrophobicity, due to low carboxylic group content, and the presence of high N-containing molecules. These characteristics agreed with those reported in the literature for molecules responsible for foam formation during anaerobic digestion, confirming the ability of this simple fractionation procedure to isolate the fraction responsible for foam formation. Foam formation during anaerobic digestion (AD) represents a problem for AD plants, reducing process efficiency, and increasing operational costs. The proposal of a simple and rapid procedure to isolate the fraction responsible for foam production is useful because it allows better characterizing this fraction from a chemical point of view. Knowledge of the chemical nature of the foaming agent is an important factor contributing towards developing successful antifoaming strategies.