Seasonal and basinal variations of mutagenicity of Sagami River water were investigated for one and half year with blue cotton, which is a selective adsorbent for Salmonella typhimurium TA98 sensitive mutagens, and the variations were compared with those of known water pollution indicators.
Adsorbates on blue cotton from Sagami River water showed mutagenicity toward TA98 strain in the presence of S9 mix, suggesting the occurence of indirect mutagens in water tested. The mutagenicity depended on season and basin of sampling. Adsorbates in the upper stream showed relatively high mutagenicity in winter but not in summer, while those in the lower stream showed less mutagenicity in all season.
No significant correlation was found between variations of mutagenicity and those of water pollution indicators, such as coliform group, potassium permanganate consumed, BOD, electric conductivity and anionic surfactant. These facts suggest that mutagenicity of river water cannot be predicted with known water pollution indicators. New type of pollution indicator with bio-system such as mutagenicity test may need to monitor the safety of water.

View full abstract

Kinetic study on overall reaction rate for thermophilic (54°C) anaerobic degradation of boiled soybean wastewater with fixed bed reactor containing porous ceramic filling has been conducted through analysis of experimental data.
At steady state, biofilm accumlation rate was negligible and biomass attached to surface of the filling was 0.220 kg·m^-2, which was equivalent to 32.1 kg VSS·m^-3 in terms of volumetric concentration of biomass. Considering soluble COD as the rate-limiting substrate (S), the overall reaction rate could be described by Moser equation within the range of S<20.2 kg COD·m·^-3. Kinetic constants were obtained from Powell non-linear regression as follow : the maximum specific growth rate, 0.823 d^-1; the half rate constant, 20.2 kg COD·m^-3; the biomass yield, 0.076 kg VSS·kg^-1 COD ; and the decay rate, 0.00960 d^-1.
These results offered the relationship between HRT and the overall reaction rate. The rate increased with decrease of HRT, and minimum HRT to keep the reaction ratio up to 90% and the maximum rate was estimated to be 1.61 d and 36.2 kg COD·m^-3·d^-1, respectively. These values showed an excellent performance of the reactor.

View full abstract

A method of determining the oxygenation rates of Fe(II) to Fe(III) was developed in relation to the mechanism of phosphate release from sediments because it is related to the redox reaction of Fe(II)-Fe(III).
The method uses observed redox potential (Eh_obs) to determine Fe(II) concentration in high pH region, because it is too low to be determined by spectrophotometry.
The redox potential is based on the redox reaction Fe³⁺+e^-_??_Fe²⁺ and expressed by Eh=Eh⁰-0.059 log([Fe²⁺]/[Fe³⁺])(25°C). On condition that produced ferric hydroxide is in solution equilibrium, the change of Fe²⁺ concentration with time was expressed as log([Fe²⁺]_t=t/[Fe²⁺] _t=0)={(Eh_obs)_t=0-(Eh_obs)_t=t}/0.059(25°C). Here, the solution equilibrium of Fe³⁺ and OH^- was found to be in an apparent equilibrium [Fe³⁺][OH^-]^2.68=10^-35.8.
The redox potential in the test solutions was found to be also affected with the redox equilibrium between NO₂^- and NO₃^-, formed from the absorbed NO₂ gas. Therefore, it is necessary to use the initial part of the observed redox potential changes to determine the oxygenation rates of Fe(II).

View full abstract

[in Japanese]

View full abstract