On-site treatment of pesticide waste is necessary to prevent surface and ground water from being polluted. A treatment method using photocatalyst (titanium dioxide) is proposed. In the study, kinetics of photocatalytic decomposition of herbicide 2, 4-D-butyl under solar-simulated irradiation was investigated. The following results were obtained.
(1) The rates of photocatalytic decomposition are described by a simple Langmuir form, r=kKC/ (1+KC) and the rate equation can be approximated by first-order kinetics with respect to the concentration of 2, 4-D-butyl below 2.1×10^-6 mol·l^-1 (0.58 ppm).
(2) The rate constants k are proportional to both the square root of the concentration of titanium dioxide and that of light-intensity.
(3) The equilibrium constants of adsorption K are constant under the experimental conditions examined.
(4) Above 300 mg·l^-1 of the concentration of titanium dioxide, more than 90 % decomposition occurs within the depth of 0.5 cm in the reactor.

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The Aerobic Upflow Sludge Blanket (AUSB) Process is a new biological wastewater treatment process applying the concept of the self-immobilization to aerobic activated sludge. The system consists mainly of two devices : an oxygen dissolving device and a biological reactor. The sludge produced in the AUSB process formed granules (diameter : 2-8 mm), showing excellent settability.
Extracellular polymer from AUSB sludge was examined to characterize the sludges which have self-immobilizing ability. As the sludge granulation progressed in the AUSB experimental apparatus supplied with domestic sewage, the amount of extracellular polymer increased and the activity to aggregate kaoline also increased. The AUSB sludge derived from the AUSB reactor supplied with municipal sewage produced more extracellular polymer, having high activity to aggregate kaoline, than standard activated sludge derived from apparatus supplied with the same sewage. Multivalued metallic ions were necessary for aggregation. The ability was lost after protein denaturating treatment.
These results suggest that extracellular polymer plays an important role in self-immobilization of activated sludge in the AUSB process. Therefore, AUSB process could be considered as the efficient process applying the special function of the extracellular material, such as aggregating activity, to wastewater treatment.

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The wetland systems with emergent plants such as reeds and cattails are classified into free water surface systems and subsurface flow systems. In order to estimate the natural purification potential of the natural wetlands with free water surface systems, we investigated the natural wetland for four years which had been recieving the gray water from the residential area which consits of 45 households for twelve years. The removal rate of organic matter in the wetland ranged from 80% (COD) to 95% (BOD) throughout four years. However, the removal rate of nitrogen was lower than that of organic matter. NH₄-N release from the bottom sediment and repression of nitrification in the wetland system seem to be responsible for the low removal rate of nitrogen in winter.

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Various batch and continuous experiments were carried out in order to investigate the starch wastewater treatment using pellets formed by Aspergillus niger. The results obtained from this study were summarized as follows :
(1) Pellets formed by A. niger were effective for wastewater treatment and had good ability of starch decomposition and TOC removal.
(2) Optimum pH ranges for 2-stage starch decomposition were determined by batch culture experiments.
(3) During the continuous culture period, it was confirmed that the form and high intensity of pellet were maintained under aeration and/or agitation, and that its diameter became larger gradually.
(4) From the results of continuous experiment using the 2-reactor, it was shown that over 90% of starch was decomposed and 75% of TOC was removed.

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The various organic matters of sewage are to be devided into dissolved matters and suspended matters. It is well-known that the dissolved organic matters can be removed by biological treatment within a short period of time, compared with suspended organic matters. Therefore, an advanced removal of suspended organic matters will contribute to the improvement of the biological treatment process.
An innovative sewage treatment with a Non-Coagulant Flotation-Filtration System followed by a biological treatment was studied in some pilot scale experiments.
The results of these experiments at the pilot plant obtained the following sufficient results ; for example the average SS and BOD removal at the pilot plants was 85% and 70%, respectively.
The effluent of this system was treated by biological treatment, these were the following results :
1) Almost equal BOD removal for the conventional activated sludge process was obtained within one to two hours retention time.
2) Nitrogen removal was obtained by the anaerobic-aerobic activated sludge process within six hours retention time.

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Photographic processing wastewater was continuously treated with an aerobic fixed-bed reactor filled with the granular activated carbon on which microorganisms were fixed, with 24 hours of hydraulic retention time. The pH values of all the effuluents began to decrease abruptly after the experiment was started, and 7 of the initial pH value went down to about 3 in 7days finally. The conversion of thiosulfate to sulfate by sulfer bacterium was attributed to the decrease of pH. The COD removal ratio decreased with increase of the COD load, i.e., when the loads were 1.7, 3.5, 4.9 and 13g·kg^-1 GAC·d^-1, the removal ratios were 75, 59, 55 and 45% respectively.
Two-stage system with the aerobic fixed-bed reactor above-mentioned was applied to the waste water treatment. On the basis of the material balance of COD and sulfate in the reactor, it was estimated that 63% of the removed COD was attributed to the oxidation of thiosulfate to sulfate in the first stage. On the other hand, the formation of sulfate was little detected in the effuluent of the second stage. The application of the system to the wastewater treatment led to such high removal efficiency that the removal ratios of COD and BOD were 83 and 99%, respectively.
The short period acclimation and high removal efficiency were found in the reactor filled with the granular activated carbon in comparison with that of the porous ceramics.

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Multi-Soil-Layering method (MSLM) was applied to install high performance, N & P removable on-site domestic waste water treatment system. The MSLM unit is composed from soil layer containing 1025% of 10 mesh metal iron and pelletized jute. The MSLM units were piled a brick pattern at 5cm vertical and 10cm horizontal distance, which were surrounded by layers of Zeolite particles of 15mm diameter. Air can be supplied through porous pipes.
The systems were tested one year. The domestic waste waters which were pretreated by septic tank to the level of SS 1489 (mean 50), BOD 20205 (mean 53), COD 2972 (mean 42), T-N 20106 (mean 65) and T-P 518 (mean 8) mg·l^-1 could be treated at the rate of 100850 l·m^-2·d^-1 without significant clogging. The ranges of qualities of treated waters were SS 036 (mean 11), BOD 113 (mean 5), COD 89 (mean 11), T-N 314 (mean 5), and T-P 0.12.5 (mean 0.8) mg·l^-1 respectively.
Zeolite layer and brick pattern of the MSLM units may contribute to prevent clogging. BOD decomposition and nitrification occur at aerobic parts of MSLM units and Zeolite layers. Metal iron particles are oxidized to Fe²⁺, which is transfered, oxidized, and deposited on the Zeolite particles which can fix phosphate ion. The pelletized jute was used for denitrification in the anaerobic parts of MSLM units. Oxidation of jute and metal iron contributes to produce anaerobic condition. The life of the jute pellets and iron particles was estimated 611 years.
Intensive aeration assists the decomposition of BOD, COD, and SS components and the nitrification, but decreases the denitrification and dissolution of metal iron, and hence decrease phosphate fixation. The level of purification could be controlled by setting adequate aeration which is varied depending on seasons : Summer needs longer aeration, whereas winter needs shorter aeration.

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Characteristics and performance of solid-liquid separation of raw sewage using floating media and multiple inlets were studied in bench-scale and pilot-scale equipments.
The results are summarized as follows : Particles over 7μm, representing approximately 80% of SS and 50% of BOD in raw sewage were efficiently removed. There was little difference in SS removal ratio (SSRR) between floating media and glass beads. The maximum SSRR and SS quantity removed per unit filter surface (SSR) was achieved using a particle size of 5.5mm and a filtration rate of 150m·d^-1. Inlet switching to lower position of the filter column promised to prolong the filter run significantly and to increase total SS removed in filter. Using 5.5mm filter particles, 80-89% of SS was removed, 38-42kg of SS was removed per unit filter sectional area, and filter runs were 54-64 hours at a filtration rate of 150m·d^-1. The backwash-filtrate ratio was around 2%. The space requirement of this system will be significantly smaller than the ordinary primary treatment system judging from the trial design of a practical scale plant.

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A pilot-scale three-phase fluidized bed was employed for the biological treatment of actual restaurant kitchen wastewater. In the experiments, the complete mixing type was used to deal with the changeful condition of wastewater. Cement ball (CB ball) was used as media. The evaluation method of the characteristics of biological treatment, which the authors had already proposed, was applied to the treatment of the restaurant kitchen wastewater.
This system obtained a high performance for the purification of kitchen wastewater and it is concluded that ;
(1) It was confirmed that the three-phase fluidized bed was effectual in the removal of BOD, TOC and other pollutants.
(2) The volumetric BOD removal became 2, 050g·m^-3·d^-1, and that of TOC became 230g·m^-3·d^-1.
(3) The characteristics value of TOC removal for the first-order reaction was obtained as K/K_m=0.0164d·m^-1.

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A hollow fiber microfiltration (HMF) membrane featured a unique air-backwashing and a high filtration rate under a low pressure and a low cross flow rate was successfully incorporated with aerobic submerged biofilters for the advanced treatment of domestic wastewater. The average filtrate flux around 1.3×10^-5 m s^-1 with organic removal of 70-85% was obtained for direct filtration of domestic wastewater under the working pressure of 50-100 kPa and the cross flow rate of 0.2-0.3 m s^-1 with the periodical chemical cleaning at every 3-4 weeks. The filtrate was successfully treated by using a packed bed biofilter (PBF) at low SS discharge rate in the effluent.
The biological wastewater treatment system consists of a moving bed aerobic biofilter followed by HMF was found to be extremely effective to treat the domestic wastewater for the reuse of treated water. The filtrate flux in this system was over 2.5×10^-5 m s^-1 with the effluent BOD of 1-5 mg·l^-1. The power consumption to treat 1 m³ of domestic wastewater in this system was estimated to be 0.3-0.4 kWh, which is comparable to that in municipal treatment plants.

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The denitrification process in a soil column (60 cm in depth) was studied by use of an ultrafiltrated secondary effluent from a wastewater treatment plant. At the steady-state of the denitrification, more than 90% of NO₃-N was removed from the secondary effluent within the depth of 0-5 cm in the soil column. The material-balance study showed that 1) 30-50% of TN fed was collected as N₂ gas, 2) 38-39% of TN was accumulated in the soil, probably as organic nitrogen, and 3) 4% of TN was escaped from the column as N₂ gas dissolved in the effluent.
The rate of the denitrification were determined by use of finite-difference procedure as an inverse problem for a convection-dispersion equation including a reaction term.

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The effects of temperature and pH on characteristic of immobilized microorganisms and the removal of ammonium nitrogen were investigated. The activated sludge was entrapped in polyethylene glycol gel, and elastic pellets containing activated sludge were obtained. The life of the pellets in terms of compressive strength was estimated with Arrhenius equation. The result indicated that the life of the pellets was at least 5 years at a pH from 6 to 9, and at a temperature under 40 °C. Wastewater contained 95260mg·l^-1 of ammonium nitrogen was treated with pilot plant by immobilized microorganisms over a retention time of 6 h. Influent NH₄-N could be removed and the removal was 98%. Practical plant with 140 m³ of aeration tank was operated and the wastewater could be treated at the retention time of 7 h.

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