Indian Journal of Biotechnology Vol 12, April 2013, pp 246-253 Role of calcium (II) in anaerobic sludge granulation and UASB reactor operation: A method to develop calcium-fortified sludge outside the UASB reactors R Sanjeevi, Tasneem Abbasi* and S A Abbasi Centre for Pollution Control and Environmental Engineering, Pondicherry (Central) University, Pondicherry 605 014, India Received 17 March 2012; revised 10 June 2012; accepted 2 August 2012 Calcium is essential to the growth of several strains of microorganisms involved in anaerobic digestion. It has also been found to be effective in speeding up granulation of anaerobic sludges. But there are reports that the metal can exert a harmful effect on the performance of upflow anaerobic sludge blanket (UASB) reactor by causing the ‘cementing’ of some of the active sludge in the reactor, leading to loss of mobility and/or microbial activity of the sludge. In the present work, calcium-assisted granule formation was done outside the UASB reactor to foreclose this possibility. The granules were then used to run UASB reactors without any further fortification of the feed with Ca 2+ . The work has led to an option whereby granular seed sludge of good settling characteristics can be generated outside UASB reactor through Ca 2+ fortification without any possibility of endangering the UASB reactor performance. This route also helps in much quicker UASB start-up. Keywords: Biogas, calcium, granulation, methane capture, UASB, wastewater Introduction The upflow anaerobic sludge blanket (UASB) reactor, introduced by Lettinga 1 and developed subsequently by Lettinga and others 2 has found wide application across the world for the treatment of biodegradable wastewaters 3-4 . In recent years, a new dimension has been added to the usefulness of UASB due to its ability to generate ‘captive’ methane, thereby reducing the global warming potential of wastewaters, which otherwise produce methane that goes unharnessed 5-8 . A UASB reactor is essentially a variant of the classical expanded bed reactor. In it, wastewater flows upward through a column of a sludge bed, followed by a column of less dense sludge blanket. The sludge, in turn, consists of minute biosolids or ‘granules’, each of which sports a bacterial film 9 . The constantly expanding, settling and resuspending sludge granules bring the bacterial films in contact with the upflowing wastewater, resulting in the anaerobic digestion of the latter. Even as the liquid upflow velocity, organic loading rate, hydraulic retention time, etc play important roles in the performance of a UASB reactor, the heart of the reactor is the sludge. It should support an active biofilm, and should have good settling characteristics so that it does not wash out with the inflowing liquid. It also should not be so heavy that the upflowing liquid fails to expand it. These attributes are achieved if the sludge is granular 9 . Due to these reasons, development of grannular sludge to start a UASB reactor, and management of the sludge after the reactor goes in operation, are integral to the success of UASB reactors 10 . It must be mentioned that several attempts have been made to do away with the necessity of having a granular sludge for the UASB reactors by running the reactors with non-granular materials 11 . There are also reports that even non-granular sludge can be effective in certain situations, for example, in the treatment of domestic sewage 12 , but granular sludge has proved indispensable in most other situations as it contains higher concentration of microorganisms per particle, which, therefore, possess greater ability per unit microbial film area for substrate utilization 9 . This directly enhances process efficiency. The substrate- microorganism contact is also better with granular sludge due to the latter’s perpetual setting- resuspension dynamics. Moreover, granular sludge does not wash out easily; it, therefore, enhances the biosolids retention in the UASB reactor 9 . Past attempts to find ways of developing appropriate sludge for UASB reactors include the manipulation of upflow velocity and hydraulic ____________ *Author for corresponding: Mobile: +91-9751468491 E-mail: tasneem.abbasi@gmail.com