Research Paper Characteristics of methanogenic granules grown on glucose in an upflow anaerobic sludge blanket reactor Revanuru Subramanyam a, *, Indra Mani Mishra b a Department of Civil Engineering, Jaypee University of Engineering & Technology, Guna-473 226, Madhya Pradesh, India b Department of Chemical Engineering, Indian Institute of Technology, Roorkee, Roorkee-247 667, Uttarakhand, India article info Article history: Received 3 April 2012 Received in revised form 9 November 2012 Accepted 20 November 2012 Published online 23 December 2012 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 accom- plished successfully by gradually increasing the OLR. ª 2012 IAgrE. Published by Elsevier Ltd. All rights reserved. 1. Introduction Upflow anaerobic sludge blanket (UASB) reactors have been successfully used to treat a wide variety of domestic and industrial wastewaters. In this system, support material is not required for the immobilisation of microorganisms and the formation of granular sludge. Granular sludge has superior settling characteristics and rich microbial diversity which helps in rapid degradation of organic wastes. The natural turbulence caused by influent flow and the biogas released by the granules keeps adequate contact between substrate and biomass. Granulation in UASB reactors is favoured by a combination of high liquid upflow velocity and short hydraulic retention time (Alphenaar, Sleyster, Reuver, Ligthart, & Lettinga, 1993). The successful operation of an UASB reactor mainly depends on the formation of larger size of granules with * Corresponding author. Tel.: þ91 7544 267051; fax: þ91 7544 267011. E-mail addresses: revanuru@rediffmail.com (R. Subramanyam), imishfch@iitr.ernet.in (I.M. Mishra). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/issn/15375110 biosystems engineering 114 (2013) 113 e123 1537-5110/$ e see front matter ª 2012 IAgrE. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biosystemseng.2012.11.010