Variation and correlation of content and leachability of hazardous metals in MSW molten slag

To increase the amount of accessible municipal solid waste molten slag (MSWS) for its use in aggregates such as sand, MSWS must be deemed environmentally safe. Municipal solid waste (MSW) is a heterogeneous waste source used in MSWS and varies in chemical composition. Due to its nature, there is great concern about hazardous metal contamination among users of MSWS. In this study, MSWS samples were obtained weekly for 1 year from a typical incineration ash melting facility for municipal solid waste in Japan. Variation in heavy metal contents and the leachability of MSWS were investigated using two content analysis methods and two leaching tests, respectively. There is a weak correlation between metal content and concentration, and the leachability of metals in slag could not be reduced by decreasing its metal content. No measured values of hazardous metal concentration and metal content exceed the regulation levels stipulated in Japanese Industrial Standards A5031 and A5032, respectively, thereby demonstrating that the slag can be safely utilized as road and concrete aggregates. However, metal concentrations varied widely and differed by greater than 1 order of magnitude and Pb concentrations of several MSWS samples approach the regulation level. Therefore, frequent monitoring of lead leachability of MSWS and storing MSWS for several weeks to obtain a high quality that is more homogeneous in chemical composition are demanded. This study provides fundamental information for controlling the quality of MSWS and the contributing factors for achieving a safe slag recycling system.

Characteristics of element distributions in an MSW ash melting treatment system

Thermal treatment of municipal solid waste (MSW) has become a common practice in waste volume reduction and resource recovery. For the utilization of molten slag for construction materials and metal recovery, it is important to understand the behavior of heavy metals in the melting process. In this study, the correlation between the contents of elements in feed materials and MSW molten slag and their distributions in the ash melting process, including metal residues, are investigated. The hazardous metal contents in the molten slag were significantly related to the contents of metals in the feed materials. Therefore, the separation of products containing these metals in waste materials could be an effective means of producing environmentally safe molten slag with a low hazardous metals content. The distribution ratios of elements in the ash melting process were also determined. The elements Zn and Pb were found to have a distribution ratio of over 60% in fly ash from the melting furnace and the contents of these metals were also high; therefore, Zn and Pb could be potential target metals for recycling from fly ash from the melting furnace. Meanwhile, Cu, Ni, Mo, Sn, and Sb were found to have distribution ratios of over 60% in the metal residue. Therefore, metal residue could be a good resource for these metals, as the contents of Cu, Ni, Mo, Sn, and Sb in metal residue are higher than those in other output materials.

Residual of 17beta-estradiol in digestion liquid generated from a biogas plant using livestock waste

A biogas plant using livestock waste in which a methane fermentation process is applied is a useful facility for generating energy. The digestion liquid generated from the biogas plant as a residue has high potential for use as a crop fertilizer. However, high-density estrogens such as 17beta-estradiol (E2) are included in livestock waste, and there is little information on the behavior of E2 in the digestion liquid. In this study, a survey of E2 concentration at each process in a biogas plant using livestock waste was carried out. In addition, the efficiencies of E2 removal from the digestion liquid by activated carbon adsorption and soil infiltration were examined. The total concentration of E2 in raw livestock waste was reduced to 2 microg/l after treatment, and the removal efficiency of E2 was about 80% for the plant. The methane fermentation process is important not only for the generation of methane but also for the removal of E2. The proportion of E2 conjugates comprising the total E2 concentration was 10% or less in all treated samples. In the plant, there is no likelihood of an increase in estrogen activity by the cleaving of E2 conjugates. By carrying out activated carbon adsorption to remove E2 from the digestion liquid, a large portion of E2 was removed from the digestion liquid, but an E2 concentration of 0.5 microg/l still remained in the treated digestion liquid. In contrast, it was possible to purify the digestion liquid to an E2 concentration of less than 0.002-0.011 microg/l by soil infiltration. It is thus possible to utilize the digestion liquid as a fertilizer without causing aquatic environmental pollution, but factors such as application rate, soil characteristics, and the E2 concentration of digestion liquid should be considered first.

Application of a gas-solid fluidized bed separator for shredded municipal bulky solid waste separation

A laboratory-scale gas-solid fluidized bed separator able to separate fractions of 5.6-50mm was used for separation of shredded municipal bulky waste (SBW) into combustibles and incombustibles. In batch-scale tests, it was found that accumulation of SBW in the bottom of the bed significantly reduced the separation efficiency. In this study, stirring was shown to be effective in preventing this accumulation. Flexible sheet materials such as paper and film plastics also significantly decreased the separation efficiency. In batch-scale tests, an overall efficiency of 90% was obtained when flexible materials such as film plastics and paper were excluded from the feed SBW. In continuous feeding tests, purities of the float and sink fractions attained 95% and 86% efficiencies, respectively, with an overall efficiency of 79%. The effect of feedstock shape on separation efficiency was also investigated. This study revealed that large particles can be properly separated on the basis of density, while the shape of the material significantly influenced behavior in the fluidizing bed.

Autophagy in yeast: a TOR-mediated response to nutrient starvation

TOR plays a key role in cell growth and cell-cycle progression, but in addition recent studies have shown that TOR is also involved in the regulation of a number of molecular processes associated with nutrient deprivation, such as autophagy. In budding yeast, TOR negatively regulates activation of Apg1 protein kinase, which is essential for the induction of autophagy. This review describes recent research in this field and the mechanism by which TOR mediates induction of autophagy.

Mitochondria-to-nuclear signaling is regulated by the subcellular localization of the transcription factors Rtg1p and Rtg3p

Cells modulate the expression of nuclear genes in response to changes in the functional state of mitochondria, an interorganelle communication pathway called retrograde regulation. In yeast, expression of the CIT2 gene shows a typical retrograde response in that its expression is dramatically increased in cells with dysfunctional mitochondria, such as in rho(o) petites. Three genes control this signaling pathway: RTG1 and RTG3, which encode basic helix-loop-helix leucine zipper transcription factors that bind as heterodimer to the CIT2 upstream activation site, and RTG2, which encodes a protein of unknown function. We show that in respiratory-competent (rho(+)) cells in which CIT2 expression is low, Rtg1p and Rtg3p exist as a complex largely in the cytoplasm, and in rho(o) petites in which CIT2 expression is high, they exist as a complex predominantly localized in the nucleus. Cytoplasmic Rtg3p is multiply phosphorylated and becomes partially dephosphorylated when localized in the nucleus. Rtg2p, which is cytoplasmic in both rho(+) and rho(o) cells, is required for the dephosphorylation and nuclear localization of Rtg3p. Interaction of Rtg3p with Rtg1p is required to retain Rtg3p in the cytoplasm of rho(+) cells; in the absence of such interaction, nuclear localization and dephosphorylation of Rtg3p is independent of Rtg2p. Our data show that Rtg1p acts as both a positive and negative regulator of the retrograde response and that Rtg2p acts to transduce mitochondrial signals affecting the phosphorylation state and subcellular localization of Rtg3p.

The secondary structure and phylogenetic relationship deduced from complete nucleotide sequence of mitochondrial small subunit rRNA in yeast Hansenula wingei

We have accomplished the nucleotide sequence of the 1537 bp mitochondrial gene coding for small subunit (SSU) rRNA of yeast Hansenula wingei, and also determined the 5'- and 3'-termini by S1 nuclease mapping. Eight universally conserved (U) elements of the SSU rRNA were identified. Comparison of U regions among five fungal mitochondrial SSU rRNA shows the striking similarity between H. wingei and Saccharomyces cerevisiae. The construction of the secondary structure revealed a core structure similar to the counterpart of Escherichia coli 16S rRNA. The secondary structure also enabled us the specify seven variable (V) regions differing from those of other mitochondrial SSU rRNAs in size, sequence and possible secondary structure. Molecular phylogenetic evaluation based on U regions of five fungi indicates that mitochondria of H. wingei and S. cerevisiae diverged from the same lineage. This suggests that the evolution of mitochondria-encoded genes does not directly correlate with the alteration of mitochondrial genetic system: genome size, gene organization and codon usage.

Clone bank of the mitochondrial genome of yeast Hansenula wingei

For sequencing, mitochondrial DNA from Hansenula wingei yeast was digested with various restriction enzymes and the resultant DNA fragments were cloned into a pEMBL phasmid vector. Our clone bank consists of 39 overlapping clones which cover the entire 27,694 bp region of the H. wingei mitochondrial genome.

The complete mitochondrial DNA sequence of Hansenula wingei reveals new characteristics of yeast mitochondria

The complete 27,694-bp mitochondrial (mt) DNA sequence of Hansenula wingei, which is a typical budding yeast and contains circular mitochondrial DNA, has been determined. The mt sequence contains genes encoding large and small ribosomal RNAs, 25 tRNAs, three subunits of cytochrome c oxidase (subunits 1, 2 and 3), three subunits of ATPase (subunits 6, 8 and 9), apocytochrome b, seven subunits of NADH dehydrogenase (subunits 1, 2, 3, 4, 4L, 5 and 6), and a ribosomal protein, VAR1. The VAR1 gene is considered to be a typical yeast type. This is consistent with data on DNA and the deduced amino-acid sequence homology comparisons of genes ubiquitous in yeast and fungi. However, we have identified seven genes encoding NADH dehydrogenase subunits, which are not found in other yeast mitochondrial genomes, thus placing the H. wingei mitochondrial genome in a unique position. In addition the H. wingei mitochondrial genome also encodes one tRNA pseudogene and one short unidentified ORF. The genome is compact with only two introns both of which contain an ORF. One intron lies in the large rRNA gene while the other is situated in the cytochrome c oxidase subunit-1 gene. The conserved nonanucleotide motif (A/T)TATAAG (T/A)(A/T), which is a transcription start signal in Saccharomyces cerevisiae mitochondria, has also been found in the H. wingei mitochondrial genome. The codon assignments for ATA and CTN in H. wingei mitochondria are different from those in S. cerevisiae mitochondria. These results indicate a unique and novel structure for the H. wingei mitochondrial genome in terms of characteristics which are typical for both yeast and for filamentous fungi. This is the first complete mt DNA sequence report in yeast.

The mitochondrial genome of yeast Hansenula wingei encodes NADH dehydrogenase subunit genes ND4L and ND5

Genes homologous to those encoding mitochondrial NADH dehydrogenase subunits ND4L and ND5 in filamentous fungi were identified in the mitochondrial genome of a budding yeast, Hansenula wingei. The structure and expression of these genes were investigated. The H. wingei ND4L gene is 282 bp long, and potentially codes for a polypeptide of 94 amino acids. The putative ND4L protein sequence shares about 46% homology with the analogous mitochondrial proteins of filamentous fungi. The H. wingei ND5 gene is 1935 bp long, and encodes a 645-residue polypeptide. The derived ND5 protein shares about 38% sequence homology with the analogue in filamentous fungi. The ND4L and ND5 genes have no intervening sequence, and form a gene cluster in the order of 5'-ND4L-ND5-3'. A presumptive mature dicistronic or polycistronic transcript of these genes was detected by Northern blot hybridization. These results strongly indicate that these ND4L and ND5 genes are active. As far as we are aware, this is the first report on the identification of mitochondrially encoded ND genes in yeast.