Influence of substrate concentration on microbial selection and granulation during start‐up of upflow anaerobic sludge blanket reactors

Abstract

Microbial granulation was examined in four lab-scale upAow anaerobic sludge blanket (UASB) reactors at 35°C. The reactors had working volumes of 3.2,5.0,7.6, and 9.4 L. A synthetic wastewater of glucose, peptone, and meat extract was used as substrate and anaerobic digested sludge as seed. The reactors were fed I 000, 2 000, 5 000, and 10 000 mg CODIL. The start-up was followed by maintaining a high microbial load index (the ratio of sludge loading rate applied to specific methanogenic activity measured) of -0.8 in each reactor. Microbial granulation was initiated within I month and matured within 4 rna despite different influent substrate concentrations. The granulation process was characterized by acclimation, granulation, and maturation. However, the growth rates and the granules cultivated differed significantly. Large Methanothrix-like species (thrix granules) were cultivated with I 000 to 5 000 mg CODIL inAuents, and small Methanosarcinalike species (sarcina granules) were cultivated with 10 000 mg CODIL influent. The thrix granules with median diameters of 2.5-3.4 mm exhibited better settleability, higher substrate affinity, and slightly higher bioactivity than the 0.54-mm sarcina granules. With thrix granules, the reactors operated efficiently and stably at a volumetric loading rate (VLR) of 30-40 g CODIL' d and/or a hydraulic retention time (HRT) of 1-2 h. However, the sarcina granules proved too small to be retained effectively in the reaction zone. At a moderate VLR of 10-20 g CODI L . d, the sludge granules expanded into the settling zone and accumulated there; at 25 g CODIL' d, the sludge granules were lost excessively with effluent, and the reactor was unstable. Influent with concentrations of I 000-5 000 mg CODIL is desirable for cultivation of Methanothrixdominated, well-settling, large granules.

Treatment of poultry slaughterhouse wastewater in upflow anaerobic filter under low upflow velocity

“…Granules were observed in anaerobic filters, and the formation of granules is the result of microbial and hydraulic selection pressure. Microbial selection depends on substrate concentration, substrate type and various environmental factors (Hulshoff Pol et al, 1983;Grotenhuis et al, 1991;Tay and Yan, 1996). Hydraulic selection involves the physical separation of dispersed microorganisms using shear forces and differences in mixing characteristics (Hulshoff pol et al, 1983).…”

A full-scale UASB reactor for treatment of pig and cattle slaughterhouse wastewater with a high oil and grease content

“…However, fats, oil and grease, especially long-chain fatty acids (LCFAs), cause operational problems when continuously discharged at high concentrations, inhibiting several bacteria involved in the process (Koster & Cramer, 1987;Sayed et al, 1988;Tay & Yan, 1996;Thiele et al, 1988), thus requiring a pretreatment phase. Hanaki et al (1981) conducted an extensive study of the inhibitory effect of LCFA on anaerobic digestion.…”

“…This is in accordance with theories that relate LCFA inhibition to physical interactions between the acids and the microbial membranes. The main result is a difficulty in anaerobic biomass granulation and granule flotation (Menju et al, 1997) and impaired syntrophic interaction between microbial groups (Tay & Yan, 1996).…”

Review of Upflow Anaerobic Sludge Blanket Reactor Technology: Effect of Different Parameters and Developments for Domestic Wastewater Treatment

“…The high performance of the UASB reactor is based on the formation of an active sludge in the lower part of the reactor. The development of sludge bed occurs by the accumulation of incoming suspended solids and bacterial growth under specific conditions, due to the natural aggregation of bacteria in flocs and evolution of granules in the form of layered structure [29,115]. These granules are not washed out from the reactor during operation of UASB.…”