Induction of Granulation by Sulphonated‐Lignin and Calcium in an Upflow Anaerobic Sludge Bed Reactor

The present study evaluates the capability of sulphonated lignin (S‐lignin) and calcium to promote anaerobic sludge granulation, which is of prime importance in the operation of upflow anaerobic sludge bed (UASB) ‐like reactors. One of two reactors fed with a synthetic sugar waste was stepwise supplemented with a spent liquor rich in S‐lignin from a neutral sulphite semi‐chemical pulping plant to reach an addition rate of 0.17 g S‐lignin per gram volatile suspended solid (VSS) per day. This resulted in biomass pre‐granulation (50–60% of the biomass aggregates had a size > 0.3 mm). No change was observed in the surface properties (hydrophobicity and zeta potential) of the bacterial aggregates. The S‐lignin‐fed sludge aggregated in an ordered and cluster‐like manner and exhibited a more compact ultrastructure than the control sludge. Moreover, the addition of S‐lignin slightly enhanced the metabolic activities of the biomass. Calcium ion addition following the S‐lignin treatment improved the size and the settleability of the aggregates and increased the solid retention time.