Suguru Okunishi

Effect of salinity on denitrification under limited single carbon source by Marinobacter sp. isolated from marine sediment.

Marinobacter comprises Gram‐negative, aerobic, motile, and rod‐shaped bacteria within the γ‐subclass of the Proteobacteria and is known to be halophilic or halotolerant, heterotrophic neutrophile. Two strains classified as belonging to Marinobacter, named PAD‐2 and SeT‐1, were isolated from marine sediment. The most closely related species of PAD‐2 and SeT‐1 are M. alkaliphilus and M. guinea, respectively. The strain PAD‐2 exhibited remarkably higher denitrification at concentrations of 0.5 to 1 M NaCl (3–6% w/w) than at other salinities (2 and 3 M NaCl, 12–18% w/w), and optimal denitrification was observed in media with 0.5 M NaCl. The effect of pH on denitrification by strain PAD‐2 was also examined, and the optimum denitrification occurred at neutral pH rather than under alkaline conditions. Overall, strain PAD‐2 appears to be a novel halotolerant species belonging to the genus Marinobacter that shares many characteristics, such as substrate utilization profile and optimum NaCl concentration for growth with M. alkaliphilus. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Transformation of microflora during degradation of gaseous toluene in a biofilter detected using PCR-DGGE.

A laboratory-scale biofiltration system, the rotatory-switching biofilter (RSB), was operated for 199 days using toluene as a model pollutant. The target gaseous pollutant for the biofiltration experiment was ∼300 ppmv of toluene. Toluene removal efficiency (RE, %) was initially approximately 20% with a 247-ppmv concentration (0.9 g m−3) of toluene during the first 10 days. Although the RE decreased several times whenever nitrogen was consumed, it again reached almost 100% when the nitrogen source was in sufficient supply. Denaturing gradient gel electrophoresis (DGGE) analysis was employed to assess the transformation of microflora during operation of the biofilter. The results based on a 16S rRNA gene profile showed that the microbial community structure changed with operation time. Although the microflora changed during the initial period (before day 40), transformation of the bacterial component was hardly observed after day 51. Statistical analyses of the DGGE profiles indicated that the bacterial community was almost unaffected by the environmental factors, such as adding ozone, high-level nitrogen supply, increase of loading toluene, and the shutdown of the RSB. The DGGE profile using tmoA-like genes, which encode proteins belonging to the hydroxylase component mono-oxygenases involved in the initial attack of aerobic benzene, toluene, ethylbenzene, and xylene degradation, confirmed the existence of toluene-degrading bacteria. There were at least four kinds of toluene-degradable bacteria having tmoA-like genes up to day 36, which decreased to two species after day 40. Sequence analysis after DGGE profiling revealed that Burkholderia cepacia, Sphingobacterium multivorum, and Pseudomonas putida were present in the biofilter. Only Alicycliphilus denitrificans was present throughout the whole operation period. In the initial stage of operating the RSB, many types of bacteria may have tried to adapt to the conditions, and subsequently, only selected bacteria were able to grow and to degrade toluene. Implications: Biofiltration technology, which is more cost-effective and environmentally friendly than any other physicochemical method, has been applied to the treatment of volatile organic compounds (VOCs). It was difficult to maintain a high level of activity because the performance of the biofilter depends on microbial degradation of pollutants. However, there is little knowledge about the transformation of bacteria during long-term biofiltration operations. This study revealed the transformation of microflora in a biofilter using a molecular biological method, PCR-DGGE.

Optimizing nutrient supply in a rotatory-switching biofilter for toluene vapor treatment

The influence of nutrient conditions on the degradation of toluene vapor in a rotatory-switching biofilter (RSB) was investigated. The biofilter consists of four segments connected in series, each with a packing layer made of polyvinyl formal. The influent airstreams including toluene vapors were passed through segments 1–3 as up-flow with a toluene concentration of 0.9–1.2 g m−3 and with an empty-bed retention time of 26–52 sec. Nutrient solutions were fed to all packed segments once a day by means of immersion. The nutrient solution was used repeatedly and replenished by the addition of (NH4)2SO4. The result at 155 days showed nitrogen depletion was particularly obvious and the lack of nitrogen affected toluene removal. By adding 161 g of nitrogen solution per volumetric cubic meter of reactor, toluene removal efficiency was immediately increased to greater than 99%. With long-term biofilter operation, 21%–32% of ammonium was utilized for nitrification because of the growth of nitrifying bacteria such as Nitrosomonas sp. Based on the carbon-nitrogen balance, the daily nitrogen demand for toluene removal was estimated 2.1 g day−1 at a toluene load of 70 g m-3 hr−1. Implications: Biofilters are considered as an alternative technology to control waste volatile organic compound (VOC) gases from various industries. In recent years, a major challenge has been to update the designs of biofilter systems and achieve their operational optimization (e.g., biomass control, nutrient supply). This paper describes the application of a newly designed biofilter, the rotatory-switching biofilter (RSB), which involves repeated use of nutrient solution. The results demonstrate how performance of biofiltration processes can be improved by the supply of nitrogen, and provide key knowledge for improving the performance of biofiltration processes by optimizing nutrient supply.