Kenji Fujita

Study on fouling materials in the membrane treatment process for potable water

Studies were made on a water treatment process which used hollow fiber microfiltration membranes for potable water. The influent, which was from a eutrophic lake named Kasumigaura, was provided directly into the treatment system, and no pre-treatment such as coagulation was done. Dead-end filtration was carried out under constant rate permeation, and membranes were washed by air-scrubbing. The trans-membrane pressure (TMP) had increased to 100 kPa, and the color of the membranes turned brown after 19 days of operation. X-ray microanalyzer (XMA) revealed that the brown material on the membrane surface was manganese. Furthermore, the amount of total organic carbon (TOC) and manganese in the fouling materials were one order of magnitude higher than that of other inorganic elements. TOC and manganese were dominant fouling materials. By correlating the amount of extracted fouling materials and the recovery of membrane permeability, it was concluded that the decline in membrane permeability was mainly caused by organic matter.

Manganese removal by hollow fiber micro-filter. Membrane separation for drinking water

Manganese (Mn) removal is one of the many problems of using ground water since Mn is a common element in ground water. Mn cannot be removed by membrane filtration without being oxidized to manganese dioxide. To find an applicable and clean oxidation method, advanced oxidize processes (AOPs) and Mn sand self-catalytic oxidization were evaluated in this study. Oxidization speed of manganese by hydrogen peroxide was found to be proportional to the concentration of hydrogen peroxide and pH. When pH was adjusted to 9.0 and concentration of H2O2 to 170 mg/L, it took about 100h of contact hours to obtain a removal of 70%. When pH was adjusted to 9.3, it took no more than 50h to achieve a 95% removal rate. Mn sand showed a promising effect compared to H2O2. In certain pH and contact time, the removal of Mn is proportional to an increasing in Mn sand contact area, however the effect has limitations, which depend on pH and contact time. As a result of comparing continuous filtration, the Mn sand not only removed over 95% of Mn(II), but also decreased the membrane fouling, and prolonged the operational life of the membrane.

Factors affecting nitrogen removal from domestic wastewater using immobilized bacteria

The parameters affecting the nitrogen removal process by the immobilized bacteria in the anoxic-oxic process have been studied by investigating two bench scale Runs A and B. The hollow polypropylene pellets have been dosed into the anoxic reactor in Run A and into the oxic reactors of both Runs up to 24% of volume. Run B was operated with no pellets in the anoxic reactor as a control. The maximum nitrification rate of 0.4 kg NH 4 -N/m 3 d was achieved in sufficient DO (6.5 mg/l) at 15°C in the reactor with both activated sludge and immobilized micro-organisms. The volumetric nitrification rate was found to be greatly dependent on bulk oxygen concentration especially when the DO was maintained below 4 mg/l. A mathematical model developed successfully simulated the experimental results showing the variation of nitrification rate with DO. In the case of denitrification, the contribution of immobilized bacteria was prominent when lesser concentration of MLSS was present in the activated sludge in the combined immobilized and activated sludge system. The presence of immobilized bacteria in the anoxic reactor will be effective when higher nitrate nitrogen loadings are expected and the maintenance of higher MLSS than 2 g/l in an activated sludge facility is not feasible.

Membrane fouling decrease by microfiltration with ozone scrubbing

Abstract In order to control membrane fouling in the microfiltration process for drinking water production, a hollow-fiber membrane module was scrubbed with ozone gas (0.0435 mgO3/l) for 20 s every 1 h. In comparison with a control experiment, it was proved that membrane fouling can be significantly subdued by ozone scrubbing. Pre-ozonation of raw water also had the same effect of decreasing membrane fouling.

On the crystalline structures of iron oxides formed during the removal process of iron in water

The samples collected from two reactors are analyzed by X-ray diffraction and Mssbauer spectroscopy in this study. It is concluded that the iron oxide crystal attached on anthracite media which possesses catalytic ability is identified to be Ferrihydrite, regardless of the value of pH from the analysis of the iron oxide. Iron oxide in Batch reactor is identified to be Microcrystalline goethite.

BIOLOGICAL DENITRIFICATION IN GRANULAR FILTERS

ABSTRACT Experiments were conducted to describe the performance of laboratory scale biological denitrification in granular fiters. A first-order model could be Used to express deoxygenation rate in the fiter. The concentration of methanol and nitrate nitrogen in raw water did not effect deoxygenation rate. A model of denitrification rate considered to depend on methanol concentration in the filter was acceptable. It was found that the effect of dissolved oxygen on denitrification rate was not significant. A filter with smaller media size produced higher deoxygenation rate and denitrification rate than a filter with bigger media size.