Characterisation of the granulation process during UASB start-up

The granulation process was quantitatively examined through continuous measurement of granular growth in a 5-1 upflow anaerobic sludge blanket (UASB) reactor. A synthetic feed composed of glucose, peptone and meat extract was used as a substrate with the chemical oxygen demand (COD) concentration of 2000 mg/l. Anaerobic digested sludge was used as a seed. During start-up, the sludge loading rate (SLR) was increased, based on the specific methanogenic activity (SMA) measured of the sludge, with the SLR value maintained consistently at 80% of the SMA. The results show that the SMA of the sludge was increasing rapidly immediately after start-up and approaching stabilisation after just 2 months. Granulation was initiated slowly during the first month, then the initiated granules grew rapidly for 3 months with specific granular growth rate by diameter (v ) of 0.02–0.10 d−1, and finally accompanied by the fast decline of v , the granules matured. Based on the granular growth course, the granulation process is characterised by three phases: acclimation; granulation; and maturation. The granular sludge, consisting mainly of Methanothrix-like species, was highly active and well settleable with a median diameter of 2.6 mm, specific methanogenic activity of 1.72 g CH4-COD/gVSS•d and sludge volume index of 9.5 ml/gSS.