The effect of slime accumulated in a long-term operating UASB using crude glycerol to treat S-rich wastewater

An up-flow anaerobic sludge blanket(UASB)reactor targeting sulfate reduction was operated under a constant TOC/S-SO2-4ratio of 1.5±0.3 g C/g S for 639 days using crude glycerol as carbon source.A filamentous and fluffy flocculant material,namely slime-like substances(SLS),was gradually accumulated in the bioreactor after the cease of methanogenic activity.The accumulation of SLS was followed by a decrease in the removal efficiencies and a deterioration in the performance.Selected characteristics of SLS were investigated to explore the causes of its formation and the effect of SLS on the UASB performance.Results showed that glycerol fermentation and sulfate reduction processes taking place in the reactor were mainly accomplished in the bottom part of the UASB reactor,as the sludge concentration in the bottom was higher.The accumulation of SLS in the UASB reactor caused sludge flotation that further led to biomass washout,which decreased the sulfate and glycerol removal efficiencies.Batch activity tests performed with granular sludge(GS),slime-covered granular sludge(SCGS)and SLS showed that there was no difference between GS and SLS in the mechanism of glycerol fermentation and sulfate reduction.However,the specific sulfate reduction rate of GS was higher than that of SLS,while SLS showed a higher glycerol fermentation rate than that of GS.The different rates in GS and SLS were attributed to the higher relative abundances of fermentative microorganisms found in SLS and higher relative abundances of sulfate reducing bacteria(SRB)found in GS.

Separation of 1,3-propanediol from glycerol-based fermentations of Klebsiella pneumoniae by alcohol precipitation and dilution crystallization

The separation of 1,3-propanediol from the glycerol-based fermentation broth of Klebsiella pneumoniae plays an important role during the microbial production of 1,3-propanediol.In this paper,the separation of 1,3-propanediol from fermentative broth by a combination of ultrafiltration and alcohol dilution crystallization was investi-gated.The broth was first filtered by ultrafiltration,and 99%of cells,89.4%of proteins and 69%of nucleic acids were removed.The obtained broth was further condensed by vacuum distillation,and then alcohol was added.The macro-molecular impurities,such as nucleic acids,polysaccharides and proteins,were precipitated,and inorganic and organic salts were crystallized.The optimal volume ratio of alcohol added to the condensed fermentation broth was determined to be 2:1.As a result,proteins,nucleic acids and electric conduc-tivity decreased by 97.4%,89.7%and 95.8%,respectively,compared with the fermentative broth.The influences of pH and water content in condensed broth on alcohol precipi-tation and dilution crystallization were also investigated.The experimental results indicated that alcohol precipitation and dilution crystallization was feasible and effective for the separation of 1,3-propanediol from actual fermentation broth.