Tetsuo Mukai

Ultrafiltration behaviour of extracellular and metabolic products in activated sludge system with UF separation process

Ultrafiltrations were conducted using a stirred batch cell for the batch culture supernatants containing extracellular and metabolic products released into culture medium from activated sludge bacteria mixture and Sphaerotilus natans strains responsible for aerobic bulking of the conventional activated sludge process. There existed differences in time-dependent relative permeate flux among growth phases for the same organisms and among the organisms grown to the same stationary growth phases, respectively. The retained ratio of protein to sugar during filtration may be one of the factors affecting the magnitude of time-dependent relative permeate flux decline, suggesting different degrees of interactive effect of both protein and sugar dependent on organism species and their growth phases on permeate flux decline characteristics of culture solutions.

Limiting nutrients of phytoplankton community in Hiroshima Bay, Japan

Abstract Ratios of DIN:DIP, indigenous algal assay and nitrogen fixation by phytoplankton were determined to estimate the limiting nutrient for phytoplankton growth in Hiroshima Bay, Seto Inland Sea, Japan. The algal assay was performed using indigenous pico-, nano- and microphytoplankton assemblages fractionated by filtration. Nitrogen fixation was determined using an acetylene reduction method. The DIN:DIP ratio in the study area was above 16:1 (Redfield ratio) in August 1993 and May 1994. However, in other months, the ratio was below 16:1. These values suggest that the growth of phytoplankton community is limited by nitrogen, with an exceptional phosphorus limitation in August 1993 and May 1994. Nutrient enrichment algal assay of size-fractionated phytoplankton community also supported these findings. The growth of picophytoplankton fraction was stimulated by phosphorus addition in August 1993 and May 1994, while nano- and microphytoplankton fractions were stimulated by nitrogen addition in almost all months during the study period. No nitrogen fixation by phytoplankton was detected during the study period. The results suggest that nitrogen rather than phosphorus is the limiting nutrient for the growth of the whole phytoplankton community, but picophytoplankton by itself, tends to be limited by phosphorus compared to other large-size phytoplankton when high DIN:DIP ratio was observed.

Source and transport of tricresyl phosphate (TCP) isomers in Kurose river basin

Atmospheric tricresyl phosphate (TCP) isomers in Kurose river basin were determined. The concentrations of o-TCP and m-TCP were 0.13 and 0.09 ng m−3, respectively, while p-TCP was scarcely detected. Exhaust gases from motorcycles and automobiles were main sources for TCP isomers in the atmosphere. Exhaust gas from incinerator also contributes to atmospheric concentration of TCP isomers. Most of the TCP isomers could be estimated to be sorbed to particles, due to their low vapor pressures. The concentrations of TCP isomers were relatively high in soils collected from an open storage yard of waste PVC and near the highway and greenhouse of agricultural film. On the other hand, the concentrations were negligibly small in soil collected from the forest except for the silt-clay fraction in the soil. Dry deposition fluxes of o-TCP and m-TCP from the atmosphere was 0.2 and 0.04 μg m−2 d−1, respectively. Wet deposition flux of TCP isomers during one rainfall exceeded occasionally the dry deposition flux for two weeks. TCP isomers accumulated in soil were discharged into river by precipitation event. Their concentrations increased with an increase in river flow, characteristic of a non-point source of TCP isomers.

Origin and stormwater runoff of TCP (tricresyl phosphate) isomers

TCP concentration in the Kurose River, Higashi-Hiroshima, increases after rainy days, suggesting that typical contamination originates from non-point sources. Our study was focused on a greenhouse as an important source of TCP isomers. The amounts of TCP released from agricultural plastic films were studied. Field surveys during rainy days were also carried out to clarify the processes which release TCP isomers from the greenhouse with rainfall, and its accumulation and degradation processes in soil. The runoff processes of TCP from greenhouse to ditch and river was also investigated. Concentration of TCP isomers in rainfall drop from a greenhouse were significantly higher than those in rainwater and river water, indicating that agricultural plastic films were the probable source of TCP. The ratio of o-TCP concentration in rainfall drop from greenhouse decreased with time, whereas that of m-TCP increased. These results suggest that more o-TCP was released from plastic film than m-TCP. TCP released from plastic film by rainfall was preferentially adsorbed on the silt-clay fraction of the soil. The m-TCP isomer concentration in soil around the greenhouse increased if cumulative precipitation for 3 consecutive days before sampling was less than 20 mm, but decreased if it was more than 20 mm. TCP concentration in the soil was highest in the surface (0–1 cm) and decreased below the surface. The significant decrease with depth is probably affected by adsorption and biodegradation. TCP concentrations in surface soil and water decreased along the flow of surface water from greenhouse to ditch. It is probable that TCP released from the greenhouse was transported to the ditch with adsorption on top soil.

Effects of environmental gradients concerning water qualities on the structure of the phytoplankton community in the coastal sea

Abstract The effects on the structure of the phytoplankton community of in situ environmental gradients concerning water qualities, formed during the mixing process of coastal with oceanic waters, were investigated on macro scale over a wide area of the Seto Inland Sea, Japan. The community structure of the phytoplankton varied almost constantly along the in situ environmental gradients in the community, which was shown by use of the diversity index rather than a mere listing of the phytoplankton community. These observations were considered to be the result of the direct or indirect response of the phytoplankton community to environmental gradients which occur in situ , which mean a series of variations of the habitat of the phytoplankton community. Their effects were reflected not in biomass but in the structure of the phytoplankton community. It was difficult to establish quantitatively the extent of their effects because of the variability in the degree of the environmental gradients which occur in situ .

Effects of micro-scale in situ environmental gradients concering water qualities on the structure of the phytoplankton community in a coastal embayment

Abstract An attempt was made to clarify the effects of micro-scale in situ environmental gradients concerning water qualities on the structure of the phytoplankton community in Hiroshima Bay, Japan. The differentiation in the phytoplankton community structure over an environmentally heterogeneous area, much of which is related to fluctuations in the physical and chemical environments, was well documented for micro-scale in situ environmental gradients using the diversity index. The effects of salinity, water temperature and nutrients are not always equal in magnitude on the structure of the phytoplankton community as the degree of locally dominant in situ environmental gradients is variable over both time and space. However, physical factors, such as salinity and water temperature, appeared to play a more important role in determining the structure of the phytoplankton community in a semi-enclosed coastal embayment.

Simulation study of eutrophication in Hiroshima Bay: Simulation of particulate and dissolved organic matter using cyclic transformation of carbon

Abstract A phytoplankton model, which includes a carbon cycle combined with a constant current obtained by the computation of tidal currents, was applied to the coastal region (Hiroshima Bay, Japan). The transformation rate constants for the carbon cycle were experimentally evaluated. The seasonal variations of particulate and dissolved organic matter by the simulation model were reasonably consistent with the field data. Carbon concentration increased by primary production in the upper layer was approx. 10 times that augmented by loading of carbon from land at the shore in summer. Sinking plays an important role in the elimination of particulate organic matter. On the other hand, horizontal advection and turbulent diffusion are important factors for the diminution of dissolved organic matter.