Emissions of N₂O from main waste management processes are reviewed in this paper. Microbiological activities as the main processes for N₂O production during the time of waste management are principally discussed with particular emphasis placed on the controlling factors of N₂O generation from a standpoint of that these factors are noteworthy for the development of technologies to reduce N₂O emission. A summary of the available data from both laboratory and field studies shows considerable spatial and temporal variability in N₂O emissions because of its high susceptibility to environmental factors like waste composition, nitrogen and oxygen availabilities, water content and temperature. To overcome the uncertainty of N₂O emission from waste management and reduce its emission, more detailed studies on effects of environmental factors are needed to simulate the procedures responsible for N₂O production, consumption and transport in various treatment systems and establish specific models for each of the management system. Thorough understanding of the influencing mechanisms may enable us to optimize the operation parameters of waste management systems to control N₂O emission.

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The water absorption quantity of the aquatic plant (Zizania latifolia) was experimentally evaluated. The weekly water absorption quantity per unit wet weight of aquatic plant was the largest in from July to August. The changes of the water absorption quantity for a long time and for a short time were affected by the temperature and the duration of sunshine, respectively. The growth rate of aquatic plant per unit water absorption weight was about 20 g (wet weight) /kg (water absorption weight) .

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A comprehensive study was carried out to examine the possibilities of separating phases by rapid recycle of the leachate from the solid state acidification reactor to the methanation reactor at 55°C with dried sorghum feed.
As a control reactor of phase separation system, a plug flow reactor in which solids pass through the reactor and are wasted in the same sequence in which they enter, begin to fail at organic loading rates of greater than 4.0 TVS/l-d. The maximum methane production rate inthis single stage plug flow reactor, approached 1.45 v/v-d and 83.1% TVS removal effciency at a solid retention time of 68 days.
The production of 20% of the total system methane in the acidification reactor at organic rates of 30g TVS/l-d indicates that separation of phase was unsuccessfully by a rapid leachate removal. Even though the solids retention time was only 4.6 days, the methanogenes were percent in the acidification reactor to produce a singificant quantity of methane. As organic loading rates increased (5g TVS/l-d to 30g TVS/l-d) the methane production rates of acidification reactor were suppressed from 0.82 v/v-d to 0.72 v/v-d, while the methane production rates of methanation reactor were increased from 0.88 v/v-d to 2.87 v/v-d. The TVS removal efficiencies decreased substantially from 82.1% to 28.8%, as the organic loading rates increased.
The average volatile fatty acids concentration of acidification reactor varied from 245 to 175mg/l as acetic acid concentration. The half saturation velocity constant of Monod equation, Ks, for methanogenesis is likely much lower than the substrate concentrations achieved in these studies, approximately 200 mg/las acetic acid.

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At the COP3 conference held in Kyoto in December 1997, reduction targets were set not only for carbon dioxide (CO₂), but also methane (CH₄) and nitrous oxide (N₂O) . As processes that treat relatively large quantities of organic material and nitrogen, wastewater treatment processes are huge potential sources of these gasses. It is feared that in the years to come the quantities of CH₄ and N₂O produced will both rise as a result of an increase in the use of treatment that combines an anaerobic process with the conventional aerobic only treatment process to encourage nitrification and denitrification as a measure to prevent the eutrophication of closed water areas. This study, which has been carried out to clarify differences in the treated water quality and CH₄ and H₂O discharge properties of aerobic only treatment and a treatment method combining aerobic and anaerobic processes, was a comparative analysis of two treatment methods: the conventional activated sludge process and the A₂O process that is a biological nitrogen and phosphorus removal method. The quantity of CH₄ discharged by the A₂O process was found to be about 1/3 of that discharged by the conventional process, presumably because CH₄ was consumed as the hydrogen donor in the denitrification reaction. The quantity of N₂O discharged from the A₂O process was found to be about 1/8 of that discharged by the conventional process, presumably because the degree of accumulation of NO₃^- in the nitrification reaction has a big effect on the quantity of N₂O produced. Based on these results, it was concluded that by appropriately combining anaerobic conditions with aerobic treatment, it is possible to link N₂O reduction measures and eutrophication prevention measures in the sewage treatment.

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Upflow anaerobic sludge blanket (UASB) process is one of the potential biological processes for the treatment of dairy waste especially in the developing countries. One of the factors of major concern in anaerobic systems is their long start-up periods. In this study, start-up of UASB reactors with activated and methanogenic granular sludges was examined. The results showed that volumetric loading rates that could be achieved at 80% COD removal efficiencies were 3.7 and 8.5 g-COD/l⋅d while time taken to establish these rates were 60 and 30 days, respectively for reactors started-up with activated and granular sludges. A solids loading rate of 1.25 to 1.5 g-COD/g-VSS⋅d was found to be a guide value for UASB reactor seeded with activated sludge. The results of this study indicated that the UASB reactors can successfully be started-up with granular or activated sludges but use of granular sludge is advantageous.

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To achieve high removal of both organic matter and nitrogen, the advanced management of activated sludge process was required. We studied on the simple methods for the determination of organic matter oxidizing and nitrifying activities by measuring oxygen uptake rate (OUR), dehydrogenase activity and ATP (adenosine 5'-triphosphate) activity using specific inhibitors for ammonia and nitrite oxidizing bacteria. The methods were mainly applied to a sequential batch activated sludge process with intermittent aeration treating swine wastewater. The results obtained were summarized as follows: It was possible to determine both organic matter oxidizing and nitrifying activities by measuring OUR, dehydrogenase activity and ATP activity according to our methods. Linear correlations among OUR, dehydrogenase activity and ATP activity related to organic matter oxidation were observed in spite of the origin of activated sludge. Ammonia oxidizing and nitrite oxidizing activities also had similar correlations. It became clear that the relationship between organic matter oxidizing and nitrifying activities was characterized by the supply of oxygen and substrates to activated sludge. Rational management of activated sludge process for the removal of both organic matter and ammonia was considered to be possible by keeping the maximum nitrifying activity.

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