Use of Enrichment Culture for Facilitated Granule Formation

By the analogy with other wastewater treatment systems, formation of the granules can be enhanced by selected microbial cultures (Beun et al., 1999). For example, Limbergen et al. (1998) proposed that selection and

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Particle diameter (^m)

Fig. 10.2. The size distribution of three kinds of different cells from disrupted granules. Selected cells with high settleability (•); high hydrophobicity (A); cells before selection (■) are shown.

Particle diameter (^m)

Fig. 10.2. The size distribution of three kinds of different cells from disrupted granules. Selected cells with high settleability (•); high hydrophobicity (A); cells before selection (■) are shown.

application of floc-forming bacteria are important for good flocculation in activated sludge system. When the inoculated microorganisms are incorporated into activated sludge, they can stay in this aggregate for a longer time, thus helps to form floc and maintain the degradative capacity of the flocs. Addition of selected strains or enrichment culture with specific function was also helpful in wastewater treatment (Dabert et al., 2005).

Ivanov et al. (2005) applied enrichment culture with increased cell surface hydrophobicity for faster formation of the granules. Mechanically stronger granules, which were suitable for the reactors with mechanical stirring, were formed for several days after the start of the cultivation. The strains of aerobic bacteria with aggregation index (AI) higher than 6080% or with cell hydrophobicity, measured by hydrocarbon adherence test, higher than 80%, were selected and isolated from the microbial granules using the repeated cycles of adhesion, settling, and cultivation. There were sporogenic gram-positive rods, gram-negative rods, and gliding bacteria.

The duration of the lifetime of the granules is close to the time of granule formation from activated sludge which is usually from 8 to 14 days (Fig. 10.3). This duration can be reduced if selected microbial cultures with high self-aggregation ability are added to the SBR. The granules with mean diameter 1 mm were formed after 2 days when cells with high cell surface hydrophobicity were used as inoculum (seeds) for granulation

Time of cultivation, day

Fig. 10.3. Formation of the granules from selected cells with high cell surface hydrophobicity (1) and from the flocs of activated sludge (2).

Time of cultivation, day

Fig. 10.3. Formation of the granules from selected cells with high cell surface hydrophobicity (1) and from the flocs of activated sludge (2).

(Fig. 10.3). Formation of the granules with mean diameter 1 mm from the flocs of activated sludge required 8 days.

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