Physicochemical characterization of UASB sludge with different size distributions

Upflow anaerobic sludge blanket (UASB) sludges developed in UASB system are used to treat various wastewaters. Methanogenic microbial consortia in UASB sludges convert organic compounds to methane under anaerobic conditions. Sludge granules are developed by self-granulation of microorganisms and dynamic balance between granule growth and decay results in coexistence of UASB sludges with different sizes in the reactor. In this study, UASB sludges taken from a laboratory-scale UASB reactor were classified into 4 groups based on their diameters and their physicochemical characteristics were investigated. Each group was analyzed for settling ability, specific methanogenic activity (SMA), and elemental content. Settling ability was proportional to diameter of UASB sludges, suggesting effective detainment of larger granular sludges in the reactor. When acetate or glucose was used as a substrate all groups showed a relatively slight difference in MA. However SMA with a volatile fatty acid mixture showed a significant increase with sludge diameter, suggesting better establishment of syntrophic relationship in larger granular sludges. Larger granular sludges showed a higher value of SMA upon environmental changes (i.e., pH, temperature, or toxicant concentration). Comparative analysis of elemental contents showed that content (dry weight %) of most tested elements (Fe, Ca, P, Zn, Ni, and Mn) decreased with sludge diameter, suggesting that the elements could be important for initial granulation. Taken together, tiffs study verified experimentally that physicochemical properties of UASB sludges are related to UASB sludge size distributions. Overall results of physicochemical characterization supports that larger granular sludges are better applicable to UASB systems