Recently, a space of landfill for disposing excess sludge for activated sludge processes is decreasing. Therefore, a development of a new technique of a low excess sludge production system will be necessary.
In this study, effects of the addition of humus or the extract of field horsetail on decrease in the excess amount of sludge were investigated. Measurement of the cumulative sludge amount and an analysis of kinetic parameters of the activated sludge process were conducted.
Experimental results are summarized as follows:
(1) The sludge amount which was produced a day in the treatment system with the humus addition and the control (conventional activated sludge process) were 1.45g and 1.74g respectively.
(2) According to kinetic parameters, it was effective with the humus in decreasing in 40% of excess sludge as compared with the control.
(3) Effects of the addition of humus and the extract of field horsetail on decrease in excess sludge were significant.

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The anaerobic digestion of sewage sludge was earned out. The sludge used was the mixed sludge of centrifugally thickened excess sludge (TS about 4%) and gravitationally thickened sludge (TS about 5%) from treatment plant of separate sewerage system, and the bio-active regent (saponin 5ppm) was dosed in the anaerobic digestion tank. The temperature of tank was 35°C in the mesophlic digestion. The retention time of sludge was 20, or 7 days. The volume of produced gas was about 20 times compared with that of feed sludge. The produced gas volume per feed organic substace was 0.4-0.55 [l/g-VTS] . The concentration of H₂S and CH₃SH in the gas was remarkably decreased by dosing saponin.

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Recently, the biological deodorization method by packed tower has been proved to be economical and efficient. The filter materials are the key components of the biological deodorization method. In this study, we have investigated the biological deodorization of hydrogen sulfide and methyl mercaptane using the porous glass and other inorganic filter materials or organic filter material. As a result, we have selected the inorganic filter material, a small size column contains carbonized sludge from the paper industry sewage, on the removal efficiency of hydrogen sulfide.

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