Removal of dichloromethane from waste gases in one- and two-liquid-phase stirred tank bioreactors and biotrickling filters

The removal of dichloromethane (DCM) from polluted air was studied both in biotrickling filters and in continuous stirred tank bioreactors, using either a single-liquid aqueous phase or a combination of an aqueous-organic liquid phase. The presence of the organic phase, i.e. silicone oil, at a volume ratio of 10% of the liquid phase, increased the maximum EC by about 25% in the BTF, reaching 200 g m³/h, and by as much as 300% in the CSTB, reaching 350 g m³/h. Based on data of chloride release in the aqueous phase and carbon dioxide production in the gas phase, complete dechlorination and mineralization of the pollutant could be confirmed. When applying shock loads, a more stable behaviour was observed in the presence of the organic phase. Generally, the completely mixed reactors were also more stable than the plug-flow biotrickling filters, irrespective of the presence of the organic phase. The use of molecular techniques allowed showing that the originally inoculated DCM-degrading Hyphomicrobium strains remained present, although not dominant, after long-term bioreactor operation. Different new bacterial populations did also appear in the systems, some of which were unable to degrade DCM.     

Degradation of organic matter from black shales and charcoal by the wood-rotting fungus Schizophyllum commune and release of DOC and heavy metals in the aqueous phase

We investigated the degradation of refractory organic matter (OM) by the basidiomycete fungus Schizophyllum commune to understand the release of dissolved organic compounds, heavy metals and sulfur. The investigated OM consisted of: charcoal, the short time end product of high temperature wood alteration in the absence of oxygen and composed mainly of pure OM; and black shales composed of clay minerals, quartz, sulfides and OM formed geogenically in an abiotic long-term process. In both cases, the OM fraction contains mainly polyaromatic hydrocarbons. We investigated the degradation of these fractions by a wood-rotting basidiomycete, which is able to produce exoenzymes like peroxidases and laccases. These enzymes can perform radical reactions to oxidize OM (like lignin) and therefore hypothetically are able to degrade OM from charcoal and/or low grade metamorphic black shales. Release of new components into dissolved organic carbon (DOC) could be detected in both cases. The attack on OM in the case of black shales coincided with the release of the heavy metals Fe, Mn and Ni. By following sulfur concentrations throughout the experiment, it was shown that heavy metal release is not due to pyrite oxidation. Ground black shale and charcoal samples were inoculated with S. commune in a diluted minimal medium containing aspartic acid and glucose. The aqueous and solid phases were sampled after 1, 7, 28 and 84 days. DOC was measured as non purgeable carbon and characterized by size exclusion chromatography and UV detection. Carbon concentrations of the solid phase were determined by element analyses. After initial decrease of the DOC concentrations due to the degradation of the carbon source provided with the medium, DOC increased up to 80 mg/l after 84 days. Carbon decreased in the solid fraction confirming that this carbon was released as DOC by the fungus. The newly generated DOC formed larger agglomerations than the DOC of the growth medium. The investigation proved that the degradation of persistent carbon sources, such as charcoal and black shale, is accelerated by fungal activity. Consequently, the associated release of heavy metals is also accelerated by the fungus. Main products of the biological degradation processes were organic heavy metal complexes which can enter the environment.     

Mercury contamination in fish from gold mining areas in Indonesia and human health risk assessment

This study investigates the effects on fish and assesses human health hazards from mercury released in two gold mining areas in Indonesia: Tatelu (North Sulawesi Province) and Galangan (Katingan District, Central Kalimatan Province). In Tatelu, 154 fish specimens of 10 freshwater species were collected, as well as five marine species from the fish market. The mean concentration of total mercury in muscles of freshwater fish from this area was 0.58+/-0.44 microg/g, with more than 45% of fish having Hg levels above the WHO guideline for human consumption of 0.5 microg/g. In Galangan, where 263 fish specimens of 25 species were collected, the total mercury in muscles averaged 0.25+/-0.69 microg/g. Excluding data from flooded open pits in sub-area P4, mean Hg levels in fish from Galangan were 2 to 4 times lower than 0.5 microg/g, while fewer than 10% of fish from Galangan exceeded WHO guidelines. The Hazard Quotient (HQ) was applied to both areas to determine the threat of MeHg exposure for communities in both areas. The HQ is a risk assessment indicator which defines the ratio of exposure level to a single substance in relation to a reference dose. Samples from Tatelu (excluding marine species) had an HQ above one, while those from Galangan resulted in values of 2.4 for the whole area and 9.9 for sub-area P4, pointing to potentially harmful fish consumption for the local population. By using the single-compartment model to estimate mercury levels in blood and hair from daily intake dose, sub-area P4 showed the highest levels, higher than the upper limit guideline for pregnant women, but still lower than threshold levels associated with observed clinical effects.