Physicochemical and microbial aspects of anaerobic granular biopellets

Abstract

Physicochemical and microbial characteristics of anaerobic biopellets produced in a lab‐scale UASB reactor were investigated in terms of the type of waste such as sucrose waste, dairy waste and acid waste. A simple method to quantify physical characteristics such as the uniformity, the curvature and the settleability of biopellets was also introduced. In addition, models of the anaerobic pelletization mechanism and the multi‐layered structure of a biopellet were proposed. The physicochemical and microbial characteristics of anaerobic biopellets appeared to be mainly influenced by the type of waste. The biomass holding capacity and the settleability of biopellets from sucrose and dairy wastes, with carbohydrate‐ and protein‐type main ingredients, seemed to be similar, but essentially different from acid waste. The elemental compositions of biopellets appeared to be influenced by the microbial combinations and the components of peptide‐type extracellular polymers (ECPs), as well as by the type of waste. Microscopic observations including SEM revealed a lot of clusters and ECPs excretions, supposed to be due to the physiological properties of hydrogenotrophic organism, at the surface of biopellets produced from sucrose and dairy wastes. The specific methanogenic activity test revealed the role of hydrogenotrophic organisms in the anaerobic pelletization process. The settleability profile analysis could be an applicable method to define the physical characteristics, such as the uniformity and the curvature as well as the settleability, of anaerobic sludge biopellets.