Morphology and physiology of anaerobic granular sludge exposed to organic solvents

Abstract

The use of quantitative image analysis techniques, together with physiological information might be used to monitor and detect operational problems in advance to reactor performance failure. Industrial organic solvents such as white spirit are potentially harmful to granular sludge. In preliminary batch assays, 33 mg.Lˉ¹ of solvent caused 50% relative biomass activity loss. In an Expanded Granular Sludge Blanket reactor fed with 40 mg.Lˉ¹ of solvent, during 222 h, the reactor performance seemed to be unaffected, presenting COD removal efficiency constantly above 95 %. However, in the first hours of exposure the specific acetoclastic and the specific hydrogenotrophic methanogenic activities decreased by 29 and 21 %, respectively. The % of projected aggregates area with equivalent diameter (Deq) higher than 1 mm decreased from 81 to 53 % and consequently the % of projected area of small aggregates increased. The average equivalent diameter of the aggregates larger than 2 mm decreased as well as the settling velocity, showed that the granules experienced fragmentation phenomenon caused by the solvent shock load. The ratio between total filaments length and total aggregates projected area (LfA) increased 2 days before effluent volatile suspended solids, suggesting that LfA could be an early-warning indicator of washout events.