Extracellular polymeric substances (EPS) in upflow anaerobic sludge blanket (UASB) reactors operated under high salinity conditions

Abstract

Considering the importance of stable and well-functioning granular sludge in anaerobic high-rate reactors, a series of experiments were conducted to determine the production and composition of EPS in high sodium concentration wastewaters pertaining to anaerobic granule properties. The UASB reactors were fed with either fully acidified substrate (FAS) consisting of an acetate medium (reactor R1) or partly acidified substrate (PAS) consisting of acetate, gelatine and starch medium (reactors R2, R3, and R4). For EPS extraction, the cation exchange resin (CER) method was used. Strength and particle size distribution were determined by assessing the formation of fines sludge under conditions of high shear rate and by laser diffraction, respectively. Batch tests were performed in 0.25 L bottles to study Ca 2+ leaching from anaerobic granular sludge when incubated in 20 g Na +/L in the absence of feeding for 30 days. Results show a steady increase in the bulk liquid Ca 2+ concentration during the incubation period. UASB reactor results show that the amounts of extracted proteins were higher from reactors R2 and R3, fed with PAS compared to the sludge samples from reactor R1, fed with FAS. Strikingly, the amount of extracted proteins also increased for all reactor sludges, irrespective of the Na + concentration applied in the feed, i.e. 10 or 20 gNa +/L. PAS grown granular sludges showed an important increase in particle size during the operation of the UASB reactors. Results also show that, addition of 1 gCa 2+/L to the high salinity wastewater increases the granules' strength.