Factors Affecting Sludge Culking in the Activated Sludge Process

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The results of the environmental influences on the sludge characteristics can be summarized as follows.1)The respective values of the minimum nitrogen and phosphorus requirements of activated sludege were more than ten and one per cent of the COD_<Cr>(COD_<Cr> : N : P=100 : 10 : 1) for preventing the growth of filamentous organisms.2)The poor settleability caused by the low concentration of dissoloved oxygen was due to small fragments of the flocs being broken up with a consequent reduction in specific gravity. When the DO level in the mixed liquor was less than 1.5 mg/l, the organisms in the interior of flocs seemed to suffer from a deficiency of oxygen.3)Although the minimum value of SVI was observed at 25℃ for any organic loading, filamentous sludge bulking never occurred in the temperature range of 15-35℃ when the sludge loading was less than 1.0 kg COD_<Cr>/kg MLSS・day.4)When shocks, consisting of step decreases in the influent pH from 7.0,were applied to the system, the SVI values did not change, but the step increase stimulated the growth of filamentous organisms with a consequent increase of SVI values.The effect of various organic loading on the sludge characteristics were evalluated using two continuous activated sludge systems with different flow patterns, one of them was a complete mixing reactor and the other a reactor with a dispersed plug flow pattern.In the complete mixing system, microbial flocs with good settleability were produced at sludge loadings below 1.0 kg COD_<Cr>/kg MLSS・day, but above that value, the sudden development of filamentous organisms caused a rapid increase of the SVI values. In the dispersed plug flow systems, the critical sludge loading to prevent the growth of filamentous organisms was approximately two times higher than tin the complete mixing systems. Also, when the same sludge loading was applied to the system, the intermittent shock load caused the tendency toward prevention of filamentous bulking as opposed to the system to which the constant sludge loading was applied. These experimental findings could be explained by the fact that both the dispersed plug flow and intermittent shock load systems possessed two contradictory characteristics, i.e. the high removal ability of organic substances which was observed in the log growth culture and the formation of a flocculant biomass which took place inherently in the endogenous phase. Furthermore, the dispersed plug flow system brought about improvement in the removal of suspended bacteria and led to superior water quality of the effluent compared with the complete mixing system under the normal operating conditions.
公益社団法人日本生物工学会の論文
1980-06-25

Factors Affecting Sludge Culking in the Activated Sludge Process

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