Performance And Succession Of Microbial Community Of A Hybrid Anaerobic Baffled Reactor

Hybrid anaerobic baffled reactor (HABR), which is a novel reactor based on anaerobic baffled reactor (ABR) design concept, is required to investigate for start-up manner optimization, operation performance and microorganism characteristics in high-strength industrial wastewater treatment. Therefore, a five-compartment HABR was used to treat synthetic brewery wastewater at stable hydraulic residence time (HRT) of 20h and 15h in start-up period and stable operation period, respectively. The reactor was fed under an average organic loading rates (OLRs) at about 1.2,2.4,4.8 and 5.6kgCOD/(m3·d) for 33,36,21 and 19 d respectively.Operating results during start-up period showed that granulation could be encouraged after the HABR was seeded with anaerobic granular sludge with a low initial loading rate and a long HRT.In a 33d's acclimation of activated sludge, the reactor completed start-up succesfully. The buffering capacity to the decrease of pH resulted by the accumulation of the total VFAs was notably enhanced, which could be owing to pH adjustment of the influent by alkali materials. Thus the systerm could maintain the acidity in terms of pH and VFAs concentration at a level that allowed effective anaerobic digestion to proceed.It should be practical to judge whether there was a balance between acidification and methanization according to the VFAs variation. The VFAs concentreations in the 2nd,3rd, and 4th compartments were maintained at a constant level due to the effective consumption of VFAs, which indicated that the homeostasis between the formation in foremost compartments and the degradation in subsequent compartments. A negative correlation was found between total gas production rate and VFAs in effluent, which showed that acidogenesis preceded methanogenesis to the new environment, and the biogas production would increase soon after the acclimation of methanogenesis.Shock loading caused by frequently fluctuation of OLR did not influence the stable running of HABR, thus effluent water quality was satisfactory. A decrease in pH was observed in the front compartments due to the VFAs accumulation with the increasing OLR, which indicated an irreversible state of the digester going sour, even the failure of the operation. Nonetheless, to some extent, a slight temporary fluctuation in influent pH may not affect the performance significantly if it could recover to the optimum pH range soon. The gradual increase in COD concentration in the effluent throughout the experiments was due to the accumulation of the total VFAs, which showed a similar response as well. The result that the total VFAs concentrations decreased longitudally down the reactor from the 2nd compartment was consistent with the sequential degradation of fatty acids. The total gas production rate increased with increasing OLRs, whereas the methane content in biogas increased gradually from the 1 st compartment to the 5th. The packing modification has shown beneficial effects on sludge retention, and preventability of solids washout caused by high gas production. Furthermore, bioflocs, which became buoyant due to a reduction in density caused by high gas production, were hastened the separation with bubbles by packing layers, thus satisfying the essential requirements of granulation.The operation perdormance reveals that an obvious separation of phases occurred within the HABRs. The first two compartments was mainly acidogenic fermentation bacteria, the 3rd compartment was mainly hydrogen-producing acetogenic bacteria and the fourth, fifth compartment mainly contained the methanogens with high biomass activity and competitive capacities in niches.During the start-up period, VSS in 1st compartment decreased from the very beginning, despite a steady increase after acidogenic fermentation bacteria acclimated. The 3rd compartment generally produced marked rise in the growth rate of biomass than the other compartments, where optimal conditions for the growth of various microorganisms were maintained. Owing to the buffering function of the initial compartments, the solids concentration in 4th and 5th compartments increased slowly but steadily all along that the OLR was increased. At stable operation period the solids concentration increased in all compartments as the OLR was increased, indicating the excellent capacity of the HABR structure to modify the physical characteristics of the sludge. At each OLR, the increases in biomass in the front compartments were greater than these in the rear compartments, which appeared to coincide with the results in terms of COD removal rates.At the end of the experiment, sludge samples from each compartment were examined with scanning electron microscopy (SEM) and confirmed that all the compartments contained granules of different shapes and sizes. The pronounced differences between the granules appearance could be attributable to different loads, mixed speeds and intensifications among compartments. In hydrolytic acidification compartments, the color of granular sludge turned from black to cream white or yellowish brown. Since the mass transfer resistance was strong in these compartments, granules seeded previously disintegrated gradually and slurry like sludge was observed. However, as the concentration gradient requireds are less due to the smaller granule sludge in size in the methanogenesis compartments, proper states were easy to reach for the methanogenic bacteria.There existed a variation tendency of bacteria shape that was transformation from rod-shaped to coccoid, and then filamentous, which disclosed the regulation of microbial community succession in HABR system. The methanogenic bacteria predominate gradually along the length of the reactor, in palce of acidogenic bacteria. Methanosarcina coexisted with Methanosaeta in the 4th compartment, while the dominant microflora of 5th compartment was Methanosaeta.