Role of calcium (II) in anaerobic sludge granulation and UASB reactor operation: A method to develop calcium-fortified sludge outside the UASB reactors

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. The work has led to an option whereby granular seed sludge of good settling characteristics can be generated outside UASB reactor through Ca fortification without any possibility of endangering the UASB reactor performance. This route also helps in much quicker UASB start-up.