Shinichi KUSANO
Evaluation of retained sludge property and processingĦĦcharacteristicsĦĦin a UASB reactor treating domestic sewage
Takashi YAMAGUCHI
UASB (Upflow Anaerobic Sludge Blanket) reactor maybe suitable option for municipal wastewater treatment. operation maintenance of UASB under the low temperature is still unstable and it has not been established yet. To manage the stable running, knowledge about the SS is essential. However, the demonstration data of processing characteristics of UASB treating sewage are biased to tropical and sub-tropical regions. Moreover, the quantitative information of retained sludge fluctuation and property in UASB reactor are less. Therefore, in this study, the objective is to investigate of treating characteristics, SS accumulation and retained sludge property in UASB treating domestic sewage in moderate climate conditions including winter period.
This study was conducted during over 500 day continuously in the moderate temperatures (average 20.3, low temperature period below 15 during 80 days ). Settleability of retained sludge possessed less than 50 mL/gVSS of SVI in the whole part of reactor. In addition, the particle size distribution did not fluctuate and the weight ratio of the particle size of retained sludge in a UASB reactor was steady state 0.43-2.00 mm whole full year. Therefore it was confirmed that the granules could be formed and kept form digested sludge whole year-round.
The concentrations of SS, cellulose increased in the middle part of UASB in the winter. A amount of SS accumulation kept up 7.1-17% for cumulative SS influent. Average of SS accumulation increasing rate was 0.081 gSS/L-reactor/day in the winter, and ?0.029 gSS/L-reactor/day in the summer. At the same time, methane production rate was 360 gCOD-CH4/day in the winter, and 455 gCOD-CH4/day in the summer. Then, it was considered that the autoproteolysis of retained sludge progress attendant increasing temperature.
A amount of SS accumulation has been increasing and it is not reached to steady state still thought over 500 days. It indicated UASB has a more capacity of retained sludge, and the dangerousness to cause of washout. Therefore, it was showed centrality to discharge accumulated sludge. Since it gat a this result (1) Granules retained in the bottom part or UASB whole year-round, (2) the concentrations of MLSS, cellulose increased in the middle part of UASB, (3) A Amount of SS accumulation increased in the winter season. It was concluded from that result that it is availableness to discharge accumulated sludge from middle part of UASB in winter season for measure against washout.
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