Nobuo Chiba

A comparison of zeta potentials and coagulation behaviors of cyanobacteria and algae

Abstract In this study, the zeta potential of Microcystis aeruginosa (cyanobacteria), Synechococcus sp. (picocyanobacteria) and Chlorella vulgaris (algae) was investigated in order to determine the zeta potential range for optimum cell removal. Algae and cyanobacteria species were treated by coagulation–sedimentation using 0–500 mg/l polyaluminum chloride (PACl). Analyses included zeta potential measurement, cell counts and turbidity removal. The role of pH on the zeta potential also investigated in this study. The pH of coagulation system was adjusted to pH 6.5 and 7.0. At pH 6.5, the optimum zeta potential bands were between –2.1 mV and +20.45 mV for Microcystis aeruginosa, +3.45 mV and +8.71 mV for Chlorella vulgaris and +7.41 mV and +13.33 mV for Synechococcus sp. The ranges were much narrower at pH 7 than at pH 6.5. The cell removal efficiencies were 98.9%, 90.6% and 55.7% for Microcystis aeruginosa, Chlorella vulgaris and Synechococcus sp, respectively. The implications of such findings are that the...

Differences in adsorption mechanisms of heavy metal by two different plant biomasses: reed and brown seaweed

The adsorption of Pb(II) by two different biomaterials, reed (Phragmites australis) and brown seaweed (Sargassum horneri) biomass pretreated with CaCl(2), were compared in an attempt to explain the differences in adsorption performance between the two biosorbents. A very interesting characteristic was found in their individual adsorption performances; the Pb(II) adsorption capacity of brown seaweed (Q(max)=0.45 mmol/g) was much higher than that of reed (Q(max)=0.05 mmol/g), but its adsorption affinity (b=112 L/mmol) was much lower compared with that of reed (b=471 L/mmol). To elucidate the mechanism, the elemental components, ion exchange phenomenon and roles of functional groups of these two biosorbents were compared. The higher Pb(II) adsorption by brown seaweed could be due to its richness in total functional groups and calcium contents on its surface. In contrast, the functional complexity, higher zeta potential and pK(a) value (deprotonation state) of reed are believed to lead to its high adsorption affinity.

Evaluation of extremely shallow vertical subsurface flow constructed wetland for nutrient removal

Mesocosm-scale vertical subsurface flow constructed wetlands (SSF, 0.5 m length, 0.3 m width) with different reed-bed thickness, including standard SSF (SD, 0.6 m deep), shallow SSF (S, 0.3 m deep) and extremely shallow SSF (ES, 0.075 m deep) were set up at sewage treatment plant and their nutrient removal efficiencies from the sewage plant effluent were compared under three hydraulic loading rate (HLR) conditions of 0.15, 0.45 and 0.75 m(3) m(-2) d(-1). A very interesting characteristics was found for the extremely shallow SSF, in which a high nitrogen removal efficiency was obtained despite the effective hydraulic retention time was only 1/8 times as long as the standard SSF. The results of kinetic analysis confirmed that the high volumetric nitrogen removal efficiency observed in the extremely shallow SSF did not depend on high response against the water temperature but on much higher basic nitrogen removal activity compared with other SSF. The phosphorus removal depending on the adsorption to sand in the reed-bed filter was, however, the lowest in the extremely shallow SSF although the volumetric removal efficiency was much higher compared with other SSF. Results of morphological analysis of rhizosphere collected from respective reed-bed suggested that the extremely shallow SSF lead to a very high-density rhizosphere, resulting in a high basic nitrogen removal activity and volumetric phosphorus removal efficiency.

Marine macroalga Sargassum horneri as biosorbent for heavy metal removal: roles of calcium in ion exchange mechanism

Brown seaweed Sargassum horneri, a troublesome biomass scattered along the seashore, was utilized as a biosorbent for Pb(II) removal from aqueous solutions. The Pb(II) adsorption by brown seaweed was enhanced by pretreatment with CaCl(2), and the Langmuir adsorption isotherm equation showed a maximum capacity of a Q(max) of 0.696 mmol/g and a b value of 94.33 L/mmol. Results obtained from the mass-balance equation derived from the simulation model of the Langmuir adsorption isotherm suggested that the adsorption performance of brown seaweed biosorbent was sufficient to reduce the concentration of Pb(II) to meet the range of WHO guideline. The mechanism, as elucidated using pH monitoring, adsorption rate and ion exchange model, involved the rapid pH change of metal solutions that led to high reaction rate and Pb(II) uptake in the first 30 min of the biosorption process. The energy X-ray analysiss result confirmed the sharp reduction of calcium content in the biosorbent after Pb(II) adsorption. The amount of calcium ions released from the biosorbent was about 1.5 times the amount of Pb(II) adsorbed and proved the role of calcium in the ion exchange mechanism. These adsorption equilibrium and mechanistic studies provide useful information for system design and performance prediction of biosorption processes.

EVALUATION FOR THE CREATION OF REED FIELDS WITH SEEDLINGS ON DREDGED SEDIMENTS

本研究では, 浚渫したへドロ上へのヨシ原の創出手法を確立するために, ヨシ種子の発芽特性及び「種子苗植栽手法」による凌深へドロ上での生育特性を把握し, ヨシ原創出の可能性について検討した. その結果, 発芽実験では, 発芽前に浸水状態で5℃5日間保存する「前低温処理」により塩分阻害を克服し得ること, 汽水産種子は淡水産種子より塩分耐性が高いことが確認された. 種子苗の生育実験では浚渫へドロ上に約80～90%の苗が植栽後定着し, 植栽場に砂を用いた系では, 土壌中の塩分濃度が1.3～2.0%でも自生しているヨシと生育, 生活環が植栽2年目で同程度となった. これらの結果より, 種子への工夫及び苗からの環境条件への馴化を行うことで, 種子苗植栽手法は浚渫へドロ上にもヨシ原の創出が可能であることが示唆された.