Fate of aerobic bacterial granules with fungal contamination under different organic loading conditions

Abstract

Aerobic sludge granulation is an attractive new technology for biological wastewater treatment. However, the instability of aerobic granules caused by fungal growth is still one of the main problems encountered in granular bioreactors. In this study, laboratory experiments were conducted to investigate the fate and transformation of aerobic granules under different organic loading conditions. Bacterial granules (2-3mm) in a poor condition with fungi-like black filamentous growth were seeded into two 1L batch reactors. After more than 100d of cultivation, the small seed granules in the two reactors had grown into two different types of large granules (>20mm) with different and unique morphological features. In reactor R1 with a high organic loading rate of 2.0g COD L(-1)d(-1), the black filaments mostly disappeared from the granules, and the dominance of rod-shaped bacteria was recovered. In contrast, at a low loading of 0.5g COD L(-1)d(-1) in reactor R2, the filaments eventually became dominant in the black fungal granules. The bacteria in R1 granules had a unique web-like structure with large pores of a few hundred microm in size, which would allow for effective substrate and oxygen transport into the interior of the granules. DNA-based molecular analysis indicated the evolution of the bacterial population in R1 and that of the eukaryal community in R2. The experimental results suggest that a high loading rate can be an effective means of helping to control fungal bloom, recover bacterial domination and restore the stability of aerobic granules that suffer from fungal contamination.

Granular activated carbon for aerobic sludge granulation in a bioreactor with a low-strength wastewater influent

“…Meanwhile, the SVI 5 decreased from 250 to 100 ml/g in R1 and from 200 to 40 ml/g in R2. However, the SVI 5 remained about twice as large as SVI 30 for the R1 sludge throughout the rest of the SBR test. This agreed with the microscopic observation that the sludge in R1 remained in the form of suspended flocs.…”

“…Thus, as demonstrated in Phase 1, it is apparently impossible for granules to grow and become dominant in a reactor without selective discharge. Discharge of suspended small and loose sludge flocs removes these competitors from the system and makes the substrates more available for the biomass in attached-growth form, which leads to granulation [30].…”

Effect of the food-to-microorganism (F/M) ratio on the formation and size of aerobic sludge granules

“…However, although large granules can be formed more quickly at a higher F/M, the large sizes of granules are not desirable for the wastewater treatment purpose. It has been found that large granules usually are less stable and have more problems in long-term operation, such as breakage, erosion, floating, and fungal contamination [30,31]. image; bottom: schematic).…”

Characterization of the bacterial communities of aerobic granules in a 2-fluorophenol degrading process

“…Sequences belonging to this group have previously been retrieved from aerobic granules degrading chloroanilines, methyl tert -butyl ether, tert -butyl alcohol and simple carbon sources such as glucose, acetate and propionate [6], [16], [23], [24], [43], [47], [50], [51], [52]. Particularly, Pseudoxanthomonas sp., Xanthomonas sp., Rhizobales sp., Acidovorax sp., and Nitrospira sp., which were the closest relatives of the sequences from bands S1, S3, S4, S6, and S8, respectively, have been previously found in aerobic granules [3], [16], [24], [46], [47], [48], [52]. Interestingly, these species were identified in the aerobic granules as being involved on volatile fatty acids and amino acids uptake, on exopolysaccharides production and on the nitrification and denitrification processes [3], [47].…”