Characteristics of methanogenic granules grown on glucose in an upflow anaerobic sludge blanket reactor

The development of granular sludge is the key factor for successful operation of the upflow anaerobic sludge blanket (UASB) reactors. This paper deals with the changes in physico-chemical and microbial characteristics while transforming anaerobically digested sludge to granular sludge grown on glucose in an UASB reactor. The bench scale reactor was operated at 35 ± 2 °C for a period of 120 days at an organic loading rates (OLR) varying from 1.5 to 15 kg [COD] m−3 d−1. Results demonstrated that a good quality, well settling granular sludge was cultivated and retained in the reactor. The specific methanogenic activity (SMA) of sludge granules increased linearly with the increasing age of the sludge as well as OLR. X-ray diffraction (XRD), Energy dispersive X-ray analysis (EDXA) and Inductive coupled plasma mass spectrometer (ICP-MS) analysis showed that considerable constitutional change occurred during the operation period. The results indicated that silicon and aluminium may have played a crucial role in the formation of the aggregates of sludge. Na, Mg, K and Ca were the major constituents in the sludge and the changes in concentration may be ascribed to the formation of compounds with minor concentrations of P, Co and Fe, which is thought to be responsible for the formation of stable granules. Fourier transform infra-red spectroscopy (FTIR) spectral analysis confirmed accumulation of volatile fatty acids, mineral matter and other aliphatic components in the granular sludge. Scanning electron microscope microphotographs demonstrated that granulation can be accomplished successfully by gradually increasing the OLR.

► Anaerobic digested sludge can be granulated within a period of about 120 days.
► SMA of granules increased linearly with the increasing age of the sludge.
► Na, Mg, K and Ca were the major constituents in the sludge.
► Silicon and aluminium may have played a crucial role during operation period.
► FTIR spectral analysis confirmed accumulation of volatile fatty acids.