Formation of Granules

The maximum of biomass (MLVSS) was 3.8 g L-1 in control and 2.9 g L-1 in experiment. The SVI values in control (reactor R1) were always higher than in experiment (reactor R2). After three days of cultivation, SVI in experiment (reactor R2) was 80 mL g-1, which is close to typical SVI of matured granules (Fig. 10.6).

200 i

200 i

Time (day)

Fig. 10.6. SVI changes during cultivation. (A): control reactor (R1); (■): experimental reactor (R2).

At the same time, SVI in control was 150 mL g-1. Lowest SVI in experiment was 36 mL g-1 and lowest SVI in control was 110 mL g-1, which is almost three times higher than the minimum for the experiment.

Aggregates in experiment (reactor R2) were mainly the granules (Fig. 10.7). The aggregates in control were the mixture of flocs, granules of regular structure, fluffy granules, bulking sludge, and filamentous bacteria (Fig. 10.7). There was no statically significant difference in the particle sizes in the two bioreactors. The presence of filamentous bacteria in control could be the major reason for the high SVI value.

Granules started to form in the experiment after three days of cultivation, while only microbial flocs can be seen at that time in control. It is showed that addition of strains B and F with higher aggregation abilities than that of activate sludge, reduced the duration of granulation process from several weeks to 8 days. This evaluation is based on maximum of biomass accumulation and value of SVI, which was lower than 70 mL g-1 of the typical value of matured granules (Fig. 10.6). F/M ratio in the experimental and control reactor was 1.46 g COD g VSS-1 day-1,

R1 R2

Day 1

Day 1

Day 2

Day 2

w T

Day 3

Day 3

A • * •

Day 5

- T t •

- m_'k 4 »1 ^

■4 • *■

Fig. 10.7. Morphological changes during the cultivation in control (reactor R1) and experiment (reactor R2).

Day 7

* J

.f * " 4 f^'v^ i. r

4 » «i i r* *

i Day 9

♦ .

i* ~ a

i

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k i ■ « »

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* ■ -v^'Vt-

^ vftr v r;* » • ♦<

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and 1.12 g CODg VSS-1 day-1, respectively. Mean cell residence times were 15 and 4.7 days for experimental and control reactors, respectively. The COD removal efficiencies for both control and experiment reactors were stable at 95% after 8 days of cultivation (Fig. 10.6). The granules were formed and dominated a bioreactor after 8 days of cultivation in an experimental reactor and the COD removal efficiency was stable after 8 days of cultivation.

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