HAMASAKI TATSUHIDE

下水生物学的処理水を対象として、オゾン/過酸化水素処理による有機物の分解実験を、半回分式実験装置を用いて行った。通気したオゾン濃度は50 mg/Lで、過酸化水素は初期に0、7.5、30、75または150 mg/Lを添加した。生物学的処理水の場合、初期過酸化水素濃度は30 mg/Lが最も速いTOC除去速度が得られ、反応器当たり0.08〜0.11 mg C/L/minであるのに対し、生物学的処理水の後段の急速砂ろ過塔でろ過した処理水の場合、初期に添加する過酸化水素濃度は7.5 mg/Lが最も速いTOC除去速度が得られ、0.19〜0.21 mg C/L/minであった。各々で単位TOC除去当たりの消費オゾン量は、26〜36 mg O3/mg Cおよび14〜15 mg O3/mg Cであった。また、生物学的処理水と生物学的処理水をガラス繊維ろ紙でSSを除去した処理水を用いた実験でも、SSを除去した処理水が速い除去速度が得られた。このことから、TOC除去速度はSSの存在が影響することがわかった。ろ過水では、1 mg/L程度までTOCが除去された。

Two modified SBRs, specially configured to consist of both oxic and anoxic zones, and be operated with only a single simultaneous oxic/anoxic phase in each treatment batch, were tested to evaluate their applicability in the treatment of RLP wastewater. The effects of COD to TN ratio and their loading rates on the performance of the modified SBRs in the simultaneous removal of organic matter and nitrogen from RLP wastewater were investigated. It was observed that the performance of the two reactors in removal of COD and ammonium-N was similar, and did not remarkably change when varying the COD/TN ratio, as well as COD and TN loading rates in the ranges of 3.4-6.0 gCOD/gN, 0.8-1.7 kgCOD⋅m-3⋅d-1 and 0.15-0.34 kgN⋅m-3⋅d-1, respectively.

An O3/H2O2 advanced oxidation process was experimentally examined for leaching radioactive cesium from contaminated sewage sludge since the excessive oxalic acid from the conventional method of coprecipitation with ferrocyanide complex salts disturbs the process of radioactive cesium removal. The most suitable condition for leaching radioactive cesium was a pH of 3, which subsequently mineralized the oxalic acid effectively. According to this study, 30 mg/L of hydrogen peroxide was an appropriate concentration. TOC was reduced from 100 mg/L to 40 mg/L within 40 minutes. The ozone requirement per TOC removal was 1.9 mgO3/mgC. Therefore, it proved that one molecule of ozone was needed to mineralize one molecule of oxalic acid. Oxalic acid was effectively decomposed at a pH of 3. Therefore, an O3/H2O2 dvanced oxidation process using a multistage reactor with 30 mg/L of hydrogen peroxide was recommended.

Pilot tests of a cubic-lattice-based rotating biological contactor were implemented to remove organic matter from wastewater from a milk factory and a hospital in Vietnam. In the milk factory wastewater, the BOD removal ratio was stable between 60% and 90% using this method, with a BOD surface load of 0.002–0.020 kg•m-2•day-1. The average nutrient ratio of the raw wastewater was 0.13 of total nitrogen and 0.015 of T-P compared with 1.0 of BOD. The BOD of treated water was less than 50 mg•L-1, achieving category B of the industrial wastewater standard of Vietnam. For the hospital wastewater, the BOD removal ratio was stable between 60% and 90%, with a BOD surface load of 0.005–0.022 kg•m-2•day-1. The average nutrient ratio of the raw wastewater was 0.25 of total nitrogen and 0.018 of total phosphorus compared with 1.0 of BOD. The BOD of treated water was less than 50 mg•L-1, satisfying category B of the medical wastewater standard of Vietnam . The electric power consumption was 0.73 KWh•m-3 of wastewater. The sludge conversion ratio from BOD was 0.51 kg TSS•kg BOD-1 based on the excess sludge and suspended solids in raw wastewater and treated water.

地下水源には鉄とマンガンが主たる除去対象として含まれており、それらの除去には生物濾過法が適している。金属イオンに富む水源にはしばしばヒ素が含まれているが、生物濾過法においては、ヒ素酸化細菌による直接的除去と鉄・マンガンの除去で生じた酸化物の作用による間接的除去の両方が関与していると考えられている。微生物の寄与の度合いを推し量るため遺伝子の解析を行い、微生物の寄与を確認した。

Application of methanogenic digestate of livestock excrements as a fertilizer to paddy fields may lead to pollution of the surrounding aquatic ecosystems due to estrogens in the digestate. To evaluate the potential environmental impacts of estrogens, the rate of degradability of the estrogens in the field is important. In this study, we investigated degradation of estradiol and estron in the digestate and paddy field surface water by using incubation tests and a fractionation test. Results show that the estrogens were degraded rapidly in the paddy field surface water but not in the digestate, possibly due to adsorption of the estrogens by organic matter in the digestate. It is suggested that the main factor in the degradation of the estrogen is the microbial reaction, and that the principal species of microbes in paddy field soil have a higher degradation ability than those in the digestate.

In the overland flow wastewater treatments and the constructed wetlands, the purification by soil infiltration units is enhanced using vegetation. However, wetland plants (i.e. cattail (Typha latifolia)) and trees, rather than agronomic crops, have been used in conventional systems. We carried out laboratory-scale soil infiltration experiments using two forage crops, tall fescue (Festuca araundinacea) and white clover (Trifolium repens) while using livestock wastewater for irrigation. The purpose of the study was to clarify the amount of accumulation of available phosphorus and exchangeable cations in the soil and its effect on the plant growth. The application of livestock wastewater increased available phosphorus, and exchangeable potassium and sodium in the upper soil. The soil sodification, examined based on exchangeable sodium ratio and plant growth, was not very significant after 10 months of livestock wastewater application. Growing forage crops on the soil infiltration system may be a promising technology to improve crop production and treatment efficacy.

Anaerobic digestion is one of the key technologies to produce renewable energy. Municipal solid waste (MSW) anaerobic digesters usually decompose 70% of charged MSW (generate 30% residue) and discharge ammonia-rich waste water. We found that thermal anaerobic digester (55°C) sludge hydrolyzed MSW biologically at higher efficiency under the condition of 80°C than 55°C. A continuous feed bench-scale digester study revealed that pretreatment of MSW at 80°C with mixing thermal anaerobic digester sludge reduced the amount of residue by 57% and increased the amount of biogas by 27%. A Sludge dewatering test revealed no difference in the amount of coagulation chemical needed between the two cases. An ammonia stripping test suggested that the electricity needed for ammonia stripping was small enough compared to incremental electricity by adoption of hyperthermal hydrolysis of MSW.

河川底質について2000μmから1μm以下の粒子を対象としていくつかに分画し、それぞれの粒径へのダイオキシン類の分配について毒性を有する2,3,7,8置換体のみならず1～8塩素全ての異性体の定量を行い、それを基に同族体分布についても見当を行った。また、実際の底質の沈降実験を行い、有機物の挙動とダイオキシン類について検討を行い、微粒子中のダイオキシン類の挙動について明らかにした。

活性汚泥法などの下水処理では、余剰汚泥を分離・濃縮しているが、活性汚泥の曝気槽や沈殿槽に直接、濃縮することができる円筒型ろ布ろ過法の基礎実験を紹介した。簡単な布を円筒型にし、圧送ポンプと凝集剤添加だけで、含水率が90%を下回る結果となった。