Granulation is an important characteristic of sludges used in upflow anaerobic sludge blanket (UASB) reactors. As the UASB technology is rapidly spreading, there is a need of granular sludge for inoculation of new reactors, particularly in those countries where anaerobic technologies have been just recently accepted.

Alternative sources of inocula are digested sludge, digested manure, septic tank sludges and pond sediments. Raw waste activated sludges have also been identified as a convenient material for reactor seeding, with previous treatment.

In this work, anaerobic flocculant sludge obtained from raw waste activated sludge has been granulated with hydraulic stress, in a lab-scale column under different upflow velocities (1 to 50 m h−1). A methodology is proposed for enhancing the quality of non granular anaerobic sludges in batch treatments of less than 8 hours. The granular sludge produced was used as inoculum for a UASB lab scale reactor. The seed sludge improved all its characteristics and maintained the granulation, in spite of the low velocity (0.08 m h−1) applied.

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