The effect of anoxic/anaerobic condition on filamentous bulking of activated sludge is studied experimentally using completely mixed reactor and sequencing batch reactor activated sludge process. These laboratory scale processes were fed with synthetic wastewater by modifying operational schedule with timer. And aeration was performed after feeding substrate in a cycle. As result the following conclusions can be made from this study.
1) In completely mixed reactor process, the anoxic/anaerobic condition has no effect on controlling growth of Sphaerotilus natans. Regardless of anoxic/anaerobic and aerobic conditions, starvation period ratio defined by the auther (1981) has effect on growth of filamentous microorganisms. And filamentous bulking is proved to be controlled in the case in which its ratio is held over 6.
2) In sequencing batch reactor process, Sphaerotilus natans is found in the case of low COD-SS loading and over pH 6, and Type 1863 or free bacteria is found in the case of high COD-SS loading because of accumulation of metabolic substances such as organic acids in anaerobic stage, but growth of these are not influenced by pH value.

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To satisfy the current reguration by laws, most of night soil treatment plants are making effort to rearrange existing plants into more effective systems, or reinforce the conventional systems by adding various advanced treatment processed.
In this article, therefore, we analyzed the existing states of the plants, especially those which are needed improvements or more suitable operation at the present or in future.
1. Capacities and type of treatment processes of plants have diverse characteristics influenced by regional circumstances, such as climates and regional regulation.
2. Though about a half of the plants have the capacity of 50 150kl day^-1, the differences of capacity are independent to treatment procedures.
3. Since demands for the annual planned amounts of treatment are increasing, eighty institution will be added for every year after 1984 fiscal year. Even though, a third of the total demands at the time must be treated by old ones which have been used more than fifteen year.
4. Instead of tendency to decrease of anaerobic digestion process and chemical treatment systems, biological denitrification process or hight rate aerobic biological treatment are increasing as an effective new systems.
5. The most of the plants are operated with a reasonable treatment-rate. After introduce the regulation by total mass organic discharge, however, advanced treatment plants in the particular area regulated by new law are operated more intense than the plants outside of the area.
After finding-out the problems summerized above we also attempted to find the ways of improvement of the plants or the points to operate the plants efficiently.

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Effects of COD loading and temperature on COD removal rate, sludge growth, nitrification and nitrogen removal rate in the aerobic submerged loop fiber biological contactor which is twisted round aluminous wire were investigated, operating the pilot plants applied to synthetic organic wastewater.
COD loading change in the range of 0.22 to 0.85 g COD ·l^-1·d^-1 has no effect on soluble COD removal rate, but total COD removal rate decreases a little at the higher COD loading because of an increase of suspended solids. Variation of COD concentration of influent has no effect on effluent COD concentration. Sludge growth weight is proportional to COD loading, regardless of continuous and intermittent feeding process. Nitrification does not proceed in the case that COD loading is over 0.48 g COD ·l^-1·d^-1. And in the intermittent feeding process nitrification proceeds in the aeration period and nitrogen removal is performed in the feeding period.
Compared with operations at 25°C, 16°C, and 9°C, COD removal rate is a little higher in the lower temperature, and Fungi grow under 20°C. But temperature does not influence on nitrification in the case that nitrification has been fixed.

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