Practical Application of Aerobic Microbial Granules

The biodegradation activity of microbial cells in granules is smaller than in microbial flocs of activated sludge and significantly smaller than that of suspended cells. It was shown in many experiments and generally it just follows the ratio of surface of mass transfer from medium into particle to volume of this particle. Other disadvantages of the treatment of waste-water with microbial granules can be considered their potential instability, long-time formation, and risk of accumulation of pathogens. Therefore, application of aerobic microbial granules can be useful for all cases, but only for case-specific wastewater treatments, for example:

1. Land is a premium, so absence of settling stage in the wastewa-ter treatment using microbial granules can give significant economic advantages in comparison with conventional activated sludge process;

2. Electrical energy is cheap, so intensive aeration in granulation process cannot be an obstacle in application of microbial granules;

3. There are substances in wastewater that are toxic for microbial cells; due to the presence of protective outer layer the granules are more resistant to toxicants than microbial flocs or suspended cells;

4. Granules are effective in the treatment of ammonia-containing wastewater and simultaneous removal of organic matter and nitrogen from wastewater due to the retention of nitrifiers in the granules.

Currently, there are few known cases of recently started pilot and industrial-scale applications of aerobic granules in wastewater treatment and it is impossible to analyze efficiency of practical applications from this limited experience. However, there is no doubt that new applications of granulation technology will demonstrate more cases, when the aerobic microbial granules will be more effective than commonly used microbial activated sludge.

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Plate 4.4. Cross section view of aerobic granules; (a) fresh granule; (b) granule stained by calcofluor white. Bar: 100 ^m; (c) profile of the dye fluorescence intensity distribution along the granule radius from the surface to the center (arrow) (Wang et al., 2005b).

Plate 6.1. Shape of the aerobically grown microbial granules (a) spherical and ellipsoid granules; (b) granules of irregular shape; (c) super-elongated granules produced at high upflow air velocity (photo from Dr. Liu Yongqiang); (d) granules produced by filamentous microorganisms (fungi, actinomycetes, filamentous bacteria).

Plate 7.2. Four stages of aerobic granules development: (a) young granules; (b) mature granules; (c) old granules with black cores; and (d) disintegrated granules.

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Plate 9.3. FISH-CLSM image of outer section of the granule. Red area represents cells hybridized with an eubacterial probe and green area represents cells hybridized with a probe specific for strain PG-01 (Jiang et al., 2004b).

Plate 10.12. Light microscopy image of sheath bacteria on surface of phenol-degrading granule. Scale bar is 10 ^m long.

Plate 10.13. DGGE profiles of R1 and R2 using partial bacterial 16S rRNAgene fragments. Lanes: 1, migration standards; 2, R1 biomass on day 0; 3, R1 biomass on day 3; 4, R2 biomass on day 0; 5, R2 biomass on day 3; 6, R2 biomass on day 15; 7, R2 biomass on day 30; 8, migration standards.

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