Biodegradation of Recalictrant Components of Organic Mixtures

Biodegradation of two recalcitrant compounds, dichloromethane and methyl tert-butyl ether was investigated individually and in combination with toluene and benzene. A vapor phase biofilter operating at an air flux of 1 m³/m²·min and an empty bed residence time of 1 minute was used as the reaction system. Inlet recalcitrant contaminant concentrations were typically 35 ppm on a volume basis while the aromatic compound concentrations were varied from 8 ppm to 150 ppm. Dichloromethane removals were not impacted by the introduction of toluene. However, a rapid decrease in methyl tert-butyl ether removal resulted from the initial introduction of toluene. Complete removal of both methyl tert-butyl ether and toluene was achieved within a week of operation.     

Potential and limitations of ozone for the removal of ammonia, nitrite, and yellow substances in marine recirculating aquaculture systems

The high levels of water-reuse in intensive recirculating aquaculture systems (RAS) require an effective water treatment in order to maintain good water quality. In order to reveal the potential and limitations of ozonation for water quality improvement in marine RAS, we tested ozone's ability to remove nitrite, ammonia, yellow substances and total bacterial biomass in seawater, considering aspects such as efficiency, pH-dependency as well as the formation of toxic ozone-produced oxidants (OPO). Our results demonstrate that ozone can be efficiently utilized to simultaneously remove nitrite and yellow substances from process water in RAS without risking the formation of toxic OPO concentrations. Contemporaneously, an effective reduction of bacterial biomass was achieved by ozonation in combination with foam fractionation. In contrast, ammonia is not oxidized by ozone so long as nitrite and yellow substances are present in the water, as the dominant reaction of the ozone-based ammonia-oxidation in seawater requires the previous formation of OPO as intermediates. The oxidation of ammonia in seawater by ozone is basically a bromide-catalyzed reaction with nitrogen gas as end product, enabling an almost complete removal of ammonia-nitrogen from the aquaculture system. Results further show that pH has no effect on the ozone-based ammonia oxidation in seawater. Unlike in freshwater, an effective removal of ammonia even at pH-values as low as 6.5 has been shown to be feasible in seawater. However, as the predominant reaction pathway involves an initial accumulation of OPO to toxic amounts, we consider the ozone-based removal of ammonia in marine RAS as risky for animal health and economically unviable.     

Newcomers in the Baltic Sea: an attempt to trace the origins and whereabouts of thicklip grey mullet <Emphasis Type="Italic">Chelon labrosus</Emphasis>

In recent years, thicklip grey mullet Chelon labrosus has shown increasing expansion of its native habitats in the north-eastern Atlantic into northerly adjacent areas including the North Sea and the brackish Baltic Sea. Despite the regular annual and seasonal occurrence of C. labrosus in the western Baltic during the warm months, nothing is known of the origin or whereabouts of the mullet during the cold season. As different possible migration scenarios can be considered, we performed otolith microchemistry analyses on specimens from the western Baltic Sea to identify the origin of this nonindigenous species. Comparison with North Sea samples revealed common habitat preferences and underlined the highly euryhaline nature of C. labrosus in different recently occupied habitats. Occasional fluctuations of Sr/Ca ratio along the growth axis suggest periodical migration between waters of different salinities but did not reveal distinct migration pathways.