Post-anoxic denifitrication process can remove nitrogen from wastewater at a lower cost than pre-anoxic denitrification process since the nitrified water is not circulated during this process unless exogenous carbon addition is required. However, the denitrification rate is generally lower than that of a pre-anoxic process because endogenous carbon sources within the denitrifying bacteria are used as electron donors. The objective of this study was to develop a better understanding of this endogenous denitrification rate. A sequencing batch reactor fed with propionate was operated under variable anaerobic-aerobic conditions for 26 days to allow the biomass to accumulate polyhydroxyalkanoate (PHA) and glycogen stores. Sludge samples were collected from the reactor periodically, and nitrate removal rates were measured in the absence of any external carbon sources. Nitrate reduction rates ranged from 1.20 to 2.74 mgN/gMLSS/h. Meanwhile, PHA consumption (1.04 - 8.01 mgC/gMLSS/h) and glycogen synthesis (0 - 4.74 mgC/gMLSS/h) and consumption (0 - 1.54 mgC/gMLSS/h) were observed. The PHA consumption correlated positively with the nitrate reduction rate. Furthermore, glycogen consumption seemed to reduce both PHA consumption and nitrate reduction.
1,4-Dioxane is a cyclic ether mainly utilized in various chemical and pharmaceutical industries as solvent and reactant. Due to its toxic and persistent nature, 1,4-dioxane is a serious pollutant in the aquatic environment. Although 1,4-dioxane is quite recalcitrant to biodegradation, recent researches have shown 1,4-dioxane biodegradation as a sole carbon and energy source or by co-metabolism with tetrahydrofuran (THF). This study isolated and characterized THF-degrading bacteria to develop a biological process of 1,4-dioxane-containing wastewater treatment. Among five THF-degrading bacteria that were isolated, strain T1 from landfill soil and strains T3 and T5 from activated sludge showed stable co-metabolic degradation of 100 mg/L of 1,4-dioxane when coexisting with 100 mg/L of THF. Strains T1 and T5, identified as Rhodococcus ruber, were further characterized. Both strains could utilize a wide range of carbon sources, and grow at 15 - 35°C and pH 6 - 8. They demonstrated to have inducible THF degrading enzymes, and degraded up to 400 mg/L of THF as a growth substrate although they could not mineralize it. The optimum THF/1,4-dioxane ratios for the co-metabolic 1,4-dioxane degradation by strains T1 and T5 were determined to be 2 to 4. Our results would be useful for the development of biological 1,4-dioxane-containing wastewater treatment system.
Iron-based advanced oxidation technologies, such as the Fenton process, are widely used for industrial wastewater treatment. However, wastewater sometimes contains chelating agents such as detergents, stabilizers, and masking agents for metallic ions, which have a potential to inhibit the iron-based advanced oxidation process through the masking of iron. In this research, we investigated the influence of chelating agents on Fenton-type reaction using ferrous ion (Fe2+) and hypochlorous acid (HOCl). Chelating agents tested were oxalic acid, ethylenediaminetetraacetic acid (EDTA) and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). Hydroxyl radicals generated were determined by 1,4-dioxane degradation. When HOCl was reacted with Fe2+ at pH 6.0, oxalic acid and EDTA strongly inhibited the 1,4-dioxane degradation. However, the inhibition effect declined at acidic pH because of the protonation of carboxyl groups in the chelating agents. The HEDP differed from the other chelating agents in the inhibition effect. It showed the inhibition effect only under the low dose at pH 6.0. On the contrary, the higher dose and acidic pH enhanced the 1,4-dioxane degradation efficiency. The regeneration of Fe2+ from ferric ion (Fe3+) by the degradation of Fe3+-HEDP complex was inferred to be responsible for the enhancement effect.
Bacterial diversity of the microbial consortia in a biological filtration plant for the elimination of iron (Fe) and manganese (Mn) from groundwater in Joyo City, Kyoto, Japan, was studied. PCR-based denaturing gradient gel electrophoresis (DGGE) analysis of bacterial 16S ribosomal RNA (rRNA) genes represented at least 15 signals, and nucleotide sequences of the dominant fragments showed similarities to Gallionella and Nitrospira. Phylogenetic analysis using the obtained nucleotide sequences of the 16S rRNA gene clone library showed the presence of the bacteria related to Hyphomicrobium, Gallionella, and Sideroxydans, which are supposed to be involved in Fe and Mn removal. In contrast, no 16S rRNA gene clone affiliated with the genus Leptothrix, which have been regarded as a major Fe- and Mn-oxidizer in biological filtration system, was observed. Though a large number of 16S rRNA gene clones closely related to Nitrospira was obtained, no clone showed high sequence similarity to known ammonium oxidizing bacteria (AOB). However, PCR-amplification of the ammonia monooxigenase gene (amoA) of AOB and ammonia oxidizing archaea (AOA) indicated the presence of both AOB and AOA in this biological filtration plant.
This study investigated the influence of cultural conditions on the cellular biovolume (VC) and gelatinous sheath volume (VG) of Staurastrum arctiscon (Charophyceae) and its growth characteristics during laboratory culturing. A unialgal culture isolated from Lake Biwa was incubated in modified M11 medium containing various concentrations of nitrogen and phosphorous in the form of nitrate and phosphate (0.01 or 0.1 mg P/L). The N/P mass ratio of the medium and incubation temperature ranges were 5 - 100 and 5 - 35°C, respectively. VC was lower at higher incubation temperature and higher nitrate concentrations, whereas VG increased with temperature. As VC and VG changed, the size of the gelatinous sheath increased relative to the cellular biovolume (VR) with the water temperature and nitrate concentration. The enhanced growth rate and net production rate with a rising temperature were considered to contribute to the decreased VC and increased VG. The positive effect of nitrate concentration on VG was believed to be attributable to the enhanced net production rate with higher nitrate concentrations.