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 biochemical oxygen demand (BOD) removal ratio was stable between 60% and 90% (average 75%) 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 total phosphorus 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 (QCVN 40:2011). For the hospital wastewater, the BOD removal ratio was stable between 60% and 90% (average 78%), 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 (QCVN 28:2010/BTNMT). 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.