Kiyoshi Minami

Continuous anaerobic treatment of wastewater from a kraft pulp mill

Abstract A pilot-scale study of the thermophilic anaerobic digestion of high-strength wastewater (evaporator condensate, EC) discharged from a kraft pulp production process was performed. The system consisted of a microfiltration (MF) membrane module for oily substances removal, a stripping system using evolved gas from the digester for sulfur compounds removal, an anaerobic fixed-bed bioreactor for methane fermentation, and an ultrafiltration (UF) membrane module for retention of a high density of bacterial cells. The bioreactor had a fixed-bed with an effective volume of 5 m 3 packed with pumice stone. In a continuous run with only the MF membrane module for oily substances removal, the digester efficiency declined because of methanogenic inhibition by sulfur compounds. After fitting of the stripping system which used evolved gas from the digester, the inhibitive sulfur compounds in the EC were removed more than 80%, and high-loading and high-efficiency operation could be attained. The BOD loading and BOD removal of 35.5 kg BOD/m 3 /d and 93%, respectively were attained. By anaerobic treatment of the evaporator condensate waste before the conventional aerobic activated sludge method, the total costs would be reduced to ¥3.31/m 3 wastewater compared with ¥4.53/m 3 -wastewater by the aerobic activated sludge method only. The stability of digester performance against interruption by feed stoppage was also examined.

Diffusion of tritiated water in cement materials

Abstract The diffusion of airborne tritiated water into cement materials is discussed in terms of unsteady state adsorption and depth profile experiments. Consistent apparent diffusion coefficients of tritiated water in cement materials were obtained from different experiments. From the comparison between experimental results, Raoults law was found to be applicable to the vapor-liquid equilibrium between tritiated water vapor and liquid water at the surface. The results of depth profile experiments suggested that there were two different diffusion processes in cement materials; one is a fast diffusion process of a relatively small portion, and the other is a slow process having higher capacity. From the permeation experiments, in which liquid water was used, the intrinsic diffusion coefficient was observed to be a function of the porosity and found to increase from 3.19×10 −12 to 11.3×10 −12 m 2 /s with a porosity increase from 0.07 to 0.28.

Methane production using a bio-reactor packed with pumice stone on an evaporator condensate of a kraft pulp mill

Abstract When an evaporator condensate stream from a kraft pulp mill was treated by anaerobic methane fermentation, the stream could not ferment continuously. Therefore, after the raw evaporator condensate was treated by various procedures, the treated samples were tested in a batch fermentation system. There seemed to be an inhibitor, an oily material, and the evaporator condensate could be fermented easily, after removal of the oily material, in a bio-reactor packed with pumice stone. In continuous operation, the minimum hydraulic retention time was 0.64 days, the maximum volumetric BOD removal rate was 11.47 kg/m3/d, and the maximum gas production rate for the theoretical volume was 97%. The efficiency of a bio-reactor using pumice stone was studied. The pumice stone has a large number of connected pores. The major pore sizes are 20–100 μm. The cell density of the pumice stone used in the bio-reactor was 18–19 g per liter.

Effects of volatile fatty acids on methanogenesis of methanol and of pregrowth with methanol on acetate utilization by methanogens

Abstract The effect of acetic acid and/or propionic acid on thermophilic methanogenesis of methanol as a sole substrate was studied using Methanosarcina species (MST-A1, CHTI-55 and MP). M. thermophila (TM-1) and two isolated strains from a thermophilic digester. All strains were resistant up to approximately 10 g/l of volatile fatty acid in a methanol medium containing yeast extract and peptone. Deletion of yeast extract and peptone from the medium, however, reduced resistivity to propionic acid by half but did not reduce it to acetic acid. Methanogenesis is affected more by pH in the presence of propionic acid than in the presence of acetic acid. Methanosarcina sp. (CHTI-55) grown on methanol could grow on acetate as the sole substrate when inoculated at the logarithmic growth phase or stationary phase within a few days after exhaustion of methanol. However, when methanol-grown cultures incubated for more than 1 week after exhaustion of methanol were inoculated to fresh methanol or acetate medium, the methanogen was able to grow with methanol but not with acetate. When methanogens which had lost their acetate-utilizing ability were inoculated to methanol-containing medium, the acetate-utilizing ability was recovered.

Screening growth inhibitors of sulfate-reducing bacteria and their effects on methane fermentation

Abstract Growth inhibitors of sulfate-reducing bacteria (SRB) which did not significantly affect methanogenesis were screened, and their effects on methane fermentation were investigated. The screening stage was performed in vitro using two typical thermophilic anaerobic bacteria, Methanosarcina sp. (DSM 2906) as the methanogen and Desulfotomaculum nigrificans (DSM 574) as the sulfate reducer. Among eighty-eight substances tested, nine were found to be effective for inhibiting SRB growth with little or no effect on methanogenesis. Gentamicin and dodecylbenzene sulfonic acid (DBS) out of the nine effective substances were tested for their effect on the co-cultivation of two strains. These two substances were effective on co-cultivation in methane gas production. Furthermore, the effects on the methane fermentation process were investigated using a laboratory-scale membrane complex anaerobic fermentation unit with an effective volume of 20 l . In the fermentor study, DBS was found not to be effective in the suppression of sulfate reduction, whereas the addition of a small amount of gentamicin was effective for a long period.

Enzyme activity for monitoring the stability in a thermophilic anaerobic digestion of wastewater containing methanol

To maintain good conditions in a thermophilic methane bioreactor treating methanol as the main substrate, microbial enzyme activity in the reactor was investigated. In a preliminary study, seven enzymes were tested for their suitability as indicators using an acid-former, 22a originating from a digester with low efficiency, Methanosarcina sp. (CHTI-55) and Desulfotomaculum nigrificans (Delft 74). Among the tested strains, the activities of seven enzymes were the highest in 22a. Acidic phosphatase (ACP), glutamic-pyruvic transaminase (GPT) and α-amylase (AMY) were chosen as hopeful indicators for lab-scale tests and their activities were measured at the optimum temperature of 55°C. In the lab-scale test, reactor failure was induced by nitrogen deficiency or addition of dimethyl disulfide (DMDS) as an inhibitor. ACP, GPT and AMY outperformed the conventional parameters as indicators of any instability in the process.

Influence of pH on methane and sulfide production from methanol

Abstract To investigate the influence of pH on methane and sulfide production, continuous cultures were done using a bio-reactor packed with pumice stone. Sulfate (1 g SO42−·l−1) in a methanol defined medium (10 g·l−1) was almost completely reduced to sulfide at pHs between 7.0 and 7.5 in methane fermentation, but at pHs between 6.2 and 6.8, sulfate reduction to sulfide was suppressed up to 40%. In addition, methane fermentation was not inhibited by 10 g sulfate·l−1.

Production of Acetic Acid from Methanol by Thermophilic Methanosarcina sp. : Acetate Production as an Index in Abnormal Methane Fermentation

Production of approximately 80–160 μmol of acetic acid was observed in 1% (w/w) methanol culture media (10 ml) of thermophilic Methanosarcina sp. from which essential nutrients such as salts of NH4+, PO43−, K+, Ca2+ and Mg2+ were removed. Similar acetic acid production was found when methane gas formation was controlled to approximately 50% by means of inhibitors of methyl group incorporation into coenzyme M (CoM), such as 2-bromoethanesulfonic acid, 2-chloroethanesulfonic acid and 2-mercaptopropionic acid, with varying results for different doses. Among inhibitors of methane formation from methyl-CoM, only in the presence of chloroform some acetic acid production was observed. We studied the mechanism of acetic acid formation through tracing of marked methyl radicals in a culture medium containing 5 μmol of 2-bromoethanesulfonic acid, using 13C methanol and nuclear magnetic resonance (NMR).

Effect of glutamate on extracellular corrinoid production by a thermophilic, methanol-utilizing methanogen, Methanosarcina sp. CHTI 55

Abstract Addition of glutamate increased the extracellular corrinoid production by a thermophilic, methanol-utilizing methanogen, Methanosarcina sp. CHTI 55 (DSM 2906) in batch and continuous cultures. Increases in glutamate oxaloacetate transaminase (GOT) activity and the concentration of 5-aminolevulinic acid (ALA) as a result of the glutamate addition suggested that the increase in extracellular corrinoid production was caused by the stimulation of ALA biosynthesis.

Verification of dose rate calculation and selection study on low activation concrete in fusion facilities

Abstract A concrete assembly was irradiated by D-T neutrons for 10 h, and dose rate measurement one day after shutdown has been carried out in order to provide a guide line for selection studies of low activation concrete. The experimental results were analyzed by the two dimensional calculation code DOT3.5 with its related nuclear data library GICX40 based on ENDF/B-III, however disagreement between experiment and calculation was observed in the deeper detector positions. Calculations were also performed using the nuclear data library based on ENDF/B-IV, and agreement within experimental errors was obtained at all detector positions. Selection studies for low activation concrete were performed using this nuclear data library. As a result, it was found that limestone concrete exhibited excellent properties as a low activation concrete in fusion facilities.