The effects of NH₄－N loading and temperature on nitrification rates were investigated using biofilm from activated sludge attached to PVA carriers. Continuous treatment of nitrification was operated using influent NH₄－N of 400 mg/l. Influent NH₄－N was removed to below 1.0 mg/l at a loading of 0.56–1.20 kg－N/m³/day under nitrite type. A high nitrification rate of 1.95 kg－N/m³/day was obtained under a mixture of nitrite and nitrate type. The activation energy of nitrification was 77.9 kJ/mol using batch tests. This value was almost the same as that of immobilized activated sludge. Real-time PCR of the amoA genes and the norB genes was performed to estimate the abundance of ammonia oxidizers and Nitrobacter. The copy number of amoA in PVA carriers was 2.08 × 10¹¹ copy/g-carrier and that for norB was 6.04 × 10¹⁰ copy/g-carrier at nitrification rate of 1.61 kg－N/m³/day. Molecular analysis of bacterial community structure was applied to the carrier using a next-generation sequencer. A quarter of 23,848 reads was Nitrosomonadaceae.

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Biological 1,4－dioxane removal process using gel carrier entrapped Pseudonocardia sp. strain D17, which can utilize 1,4－dioxane as the sole carbon source, is developed. In the present study, effect of immobilized biomass on the 1,4－dioxane removal performance was investigated. Three types of gel carriers which entrapped different culture volume of Pseudonocardia sp. strain D17 on the range from 10 to 30％ （1.2 × 10⁵ to 3.6 × 10⁵ CFU/ml） were used in the continuous feeding tests. Consequently, high 1,4－dioxanre removal performance was observed on the reactor using gel carrier entrapped 30％ of Pseudonocardia sp. strain D17 culture compared to that of 10 and 20％. On all of three bioreactors, 20 mg/l of influent 1,4－dioxane was treated to lower than 0.5 mg/l, the Japanese effluent standard, within two weeks. Effect of storage time of the culture and gel carriers on the start up of the biological 1,4－dioxane removal reactors were also investigated. As a result, there are no significant negative effects for 1 month storage of the culture at 7℃. Moreover, it was clearly shown that the gel carrier can be stored for 1 month without any deactivation.

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The purpose of this study is to evaluate a biological effect of influent, secondary and final effluent obtained by conventional activated sludge process on aquatic organisms. Biological tests were conducted using 3 kinds of aquatic organisms （Pseudokirchneriella subcapitata, Daphnia magna and Danio rerio） referring to the draft Japanese Whole Effluent Toxicity test guidelines. These tests were repeated twice for D. magna, three times for P. subcapitata and D. rerio. As a result, some influents had some effects on all of the organisms, but secondary and final effluents had no effect. These results suggested that biological impacts by sewage water were improved by the process, and that chlorination in this study （maximum total chloride concentration: 0.87mg/l for P. subcapitata, 0.37mg/l for D. magna and 0.55mg/l for D. rerio） had no harmful effect on the organisms.

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Lake Biwa has an increase of recalcitrant dissolved organic matter in the water. We examined acute toxicity of fulvic acid extracted from the lake by algal growth inhibition, crustacean immobilization, and reproduction tests to evaluate impact of recalcitrant dissolved organic matter on aquatic organisms. The results of these tests showed that present concentration of fulvic acid （FA） in Lake Biwa water did not inhibit growth of Pseudokirchneriella subcapitata, did not immobilize two Daphnia spp. and did not limit reproduction of Ceriodaphnia dubia.

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This paper describes the seasonal changes of water quality and environmental factors influencing the occurrence of cyanobacterial blooms in an eutrophic pond in an urban park. Water quality parameters in the pond were measured once monthly from May, 2009 to September, 2014. And, phytoplankton and zooplankton density and species compositions from May, 2011 to September, 2014 were also investigated in addition to other water quality parameters. In the summer of 2014, the difference between surface and bottom temperature was about 4℃ due to the formation of the thermocline in the park pond. Furthermore, Microcystis spp. were the dominance of bloom-forming cyanobacteria in the pond, and their density reached the maximum values in July or September. On the other hand, the density of competitors （Diatom, Chlorophyta） tended to increase with increasing temperature during the early summer period, and these spices were the dominance during May and June. Moreover, the predators （Branchiopoda, Copepoda, Rotifera） tended to increase with increasing temperature during the early summer period, and their density reached the maximum values during July and August. These results suggested that the growth of Microcystis spp. were inhibited by phytoplankton competition and zooplankton grazing in an eutrophic pond in parks.

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The effectiveness of suspended solid (SS), total coliforms (TC), and Escherichia coli (E. coli) removal from pond waters in a rural area of Bangladesh by a filtration unit using simple ceramic filter (SCF) was investigated. The SCF was manufactured using Bangladesh local clay soil and rice bran, and the filter unit was made by attaching the SFC to a 15 l clay flower pot. Laboratory testing with artificial pond water was performed in Japan followed by a field test with actual pond water in Bangladesh. The log removal of TC and E. coli by the filtration unit in the laboratory test was 2 to 3 log or more, and in the field test, it was 1 to 2 log or more during the wet season and approximately 1.5 log during the dry season. The filter unit also had good removal efficiency for SS (primarily algae) from the raw pond water. The effect of additional devices (iron net, rice husk charcoal and immobilized rice husk charcoal) was not apparent, but the addition of an iron net decreased dissolved phosphorus (D－P). The filter unit can be applied to actual pond water and is an alternative treatment system for pond water.

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