Enhanced Phenol Removal by Aerobic Granules

Aerobic granules are typically cultivated by using activated sludge as a starting inoculum. However, activated sludge might not be suitable for direct inoculation into a reactor that has a high input of chemical toxicity. One solution might be to use a better inoculum. Because the microbial community in the granules contains a high diversity of microorganisms, the granules themselves should possess enough physiological traits and a reservoir of functional responses to make them ideal candidates for use as a starting seed to rapidly produce stable granules that can efficiently degrade toxic chemicals such as phenol. In addition, the strong and compact structure of the acetate-fed granules should provide adequate protection against exposure to chemical toxicity.

Fig. 9.2. An ethidium bromide-stained 10% polyacrylamide denaturing gradient gel (30-70%) with DGGE profiles of 16S rRNAgene fragments after PCR amplification of nucleic acids derived from acclimated activated sludge, from aerobic granules and from individual isolates. Lanes 1, activated sludge; 2, aerobic granules; 3, PG-01; 4, PG-02; 5, PG-08; 6, PG-03; 7, PG-04; 8, PG-05; 9, PG-06; 10, PG-07; 11, PG-09; 12, PG-10; 13, PG-01; 14, aerobic granules. Bands from lanes 3, 4, and 5 (strains PG-01, PG-02, and PG-08) co-migrated with bands from lane 2 (aerobic granules).

Fig. 9.2. An ethidium bromide-stained 10% polyacrylamide denaturing gradient gel (30-70%) with DGGE profiles of 16S rRNAgene fragments after PCR amplification of nucleic acids derived from acclimated activated sludge, from aerobic granules and from individual isolates. Lanes 1, activated sludge; 2, aerobic granules; 3, PG-01; 4, PG-02; 5, PG-08; 6, PG-03; 7, PG-04; 8, PG-05; 9, PG-06; 10, PG-07; 11, PG-09; 12, PG-10; 13, PG-01; 14, aerobic granules. Bands from lanes 3, 4, and 5 (strains PG-01, PG-02, and PG-08) co-migrated with bands from lane 2 (aerobic granules).

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Fig. 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). (See Color Plate Section before the Index.)

A recent study (Tay et al., 2005) investigated the feasibility of using aerobic acetate-fed granules as a starting seed material to rapidly develop stable aerobic phenol-degrading granules. In this study, aerobic granules were first cultivated in four sequencing batch reactors with acetate as sole carbon source at a loading rate of 3.8 g l-1 d-1. Phenol was then added to the four reactors at loading rates of 0, 0.6, 1.2, and 2.4 gl-1 d-1, respectively. The granules acclimated quickly to the phenol loading, and stabilized only one week after phenol was introduced. The granules exhibited good settling ability with good biomass retention and good metabolic activity, as evidenced by the low SVI values, stable biomass concentrations and good removal of acetate and phenol. No significant inhibitory effects from phenol toxicity were observed at the intermediate loadings of 0.6 and 1.2 g phenol l-1 d-1. At the highest loading of 2.4 g phenol l-1 d-1, a sharp buildup of phenol was observed in the reactor but this quickly dissipated as the granules adapted rapidly to the high phenol concentrations. The compact structure of the acetate-fed granules likely protected the microorganisms against phenol toxicity and facilitated microbial acclimation towards faster phenol degradation rates. This concept of using granules to produce different granules can be extended to granule-based applications involving other toxic chemicals and other types of high-strength industrial wastewaters, where rapid reactor start-up and system stability are key considerations.

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