A bacterial test method was developed for detecting various DNA damaging agents by using the promoter-operator region of Escherichia coli SOS gene fused to the Vibrio harveyi luxAB genes. A E. coli strain containing the recA promoter-operator region (recApo)-luxAB fusion gene emitted light in a dose-dependent manner for the well-known DNA damaging agents mitomycin C (MMC), methyl methanesulfonate (MMS), and 4-nitroquinoline-1-oxide (4NQO). To make the response more sensitive, 4 base pairs of the recA operator sequence were changed, resulting in new promoter-operator sequence (po34) which had the consensus sequence for the LexA repressor binding. The E. coli strain containing po34-luxAB fusion gene showed 2-20 times higher sensitivity than the strain containing recApo-luxAB gene in the response to MMC, MMS, and 4NQO, because of its low background luminescence. As a comparison of the results of this method and the umu test for various compounds, the former had high sensitivity in 8 of the 14 samples compared with the latter.

View full abstract

Chemical denitrification of NO₂-N conducted with amido sulfonic acid was studied to treat NO₂-N in both bench and in situ experiments. In bench experiments, following optium conditions for NO₂-N removal were obtained. The dosage of amide sulfate was 6.9 times equivalent to NO₂-N load, pH value and stirring rate were 2.5 and 50 r.p.m., respectively in the bench reactor, and the period for reaction was more than 60 minutes. Nitrogenous gases like NO_x and N₂O, which are causative materials for air pollution and global warming, were not detected in the gas exhaust.
In situ experiment was made with wastewater containing NO₂-N discharged from a factory and with its operating parameters same as the optimum conditions obtained in the bench experiment. It ran in batch style and was controlled automatically. Results showed that efficient chemical dentrification could be conducted through continuously striring during treated wastewater discharging, and through covering nitrite sensor to keep it from the nitrogenous gases generated in the reaction.

View full abstract

A novel wastewater treatment process with thermophilic aerobic sludge digestor (TAD) was developed to reduce excess sludge generated from an activated sludge (AS) process. The TAD was operated at 65°C with hydraulic retention time 1day. The SS solubilization and VM removal in the TAD were 35% and 20%, respectively. A 40l-scale conventional AS and new processes with appropriate volume of the TAD were operated under BOD-SS loading of 0.3kg·kg^-1·d^-1 and MLSS of 2,000mg·l^-1 using artificial wastewater over 100d. As a result, the amount of excess sludge was 4.9gSS·d^-1 in the conventional AS process. On the other hand, excess sludge in the new process was reduced to nearly zero when 16.2gSS·d^-1 was recirculated to the TAD. Effluent BOD was the same level in the both processes, however, effluent S-TOC was 25% higher in the new process than that of the conventional AS process. Furthermore, similar results were obtained from a treatment test with a petrochemical wastewater. The calculated operating cost of the new process was about one third or one half compared to dewatering and landfill processes.

View full abstract

The vertical zonation of 0₂ respiration, NO₃^- respiration, H₂S oxidation and SO₄^2- reduction in microaerobic biofilms grown on rotating biological contactors (RBCs) of treating domestic wastewater was studied by measuring concentration profiles in the biofilms with microelectodes for 0₂, NO₃^-, H₂S and pH. From those profiles, in situ specific reaction rates and substrate fluxes were calculated by using a simple one-dimensional deffusion reaction model and were related to population densities of sulfate-reducing bacteria (SRB) and potential sulfate reduction rates determined by standard batch experiments. The maximum population densities and the highest potential sulfate reduction rates were found in the outermost biofilm. On the contrary, the in situ sulfate reduction rates were restricted in a narrow zone located in the middle biofilm incubated DO=100 μmol·l^-1. An increase in the O₂ and/or NO₃^- penetration depth in the biofilm induced a shift of sulfate reduction zone to the deeper biofilm and a decrease in the specific sulfate reduction rate. This is probably because that the potential sulfate reduction rate decreased toward the depth and addition of nitrate enhanced oxidation of the produced sulfide or increased competition for electron donor with denitrifiers, or both. The microelectrode measurements with the high spatial resolution enable us to quantitatively measure in situ SO₄^2- reduction rate in microaerobic biofilms, which could not be detected measureing sulfide or sulfate flux across the water-biofilm interface.

View full abstract

A small scale model of sandy beach, constructed of alumina columns and a bath with the ebb and flow of sea-water was developed and used for screening of microorganisms with cleaning activity of the oiled column. The cleaning activity was evaluated by three analytical methods after one month incubation in the column. The first method was a computer aided picture analysis of black oil stain of the column, the second was OD_660nm analysis of chloroform extract of the black oil and the third was analysis of whole oil content of the extract by TLC-FID. Among 124 strains of oil-degrading microorganisms, the only one possessing distinct cleaning activity of oiled column in the model was an oil-degrading yeast, Candida sp. M23-2, which we isolated from sea water of Mizushima Bay.

View full abstract