No abstract

The following heavy metal levels were found in plankton of the Gulf of Riga and of the open Baltic Sea: 0.89-10.20 mg Cu/kg; �0.89-106.96 mg Zn/kg; 2.31-199.9 mg Mn/kg 0.19-0.85 mg Cd/kg; and 0.35-9.35 mg Pb/kg wet weight. Heavy metal accumulation in the plankton was found to depend on species composition of the community and on deve• lopment stage of a species. Heavy metal contents in bottom sediments increase �ear densely populated coastal areas. Levels of lead, copper, and zinc depend on the season, increasing in spring in areas affected by river runoff. Maximum concentrations of the metals studied were found in 0.05-0.063 mm sediment fractions. Accumulation patterns of each metal exhibited their own respective peculia• rities.

The catalytic hydrotreatment of sunflower (SO), linseed (LO), coconut (CO), rapeseed (RO), and its soapstock derived acid oil (RS) over commercial Ni65%/SiO2-Al2O3 catalyst was investigated to evaluate utilization feasibility of various vegetable oil feedstocks with different fatty acid content, composition, and saturation for marketable hydrocarbon production. The active metal loading of catalyst was characterized by XRF and its textural properties by N2 sorption analysis. The hydrotreatment tests of different vegetable oils were carried out in solvent free medium, under initial H2 pressure 10 MPa, at operating temperature 340 oC, and residence time 15 min using catalyst amount 5%. GC-FID and GC-MS analysis were used for estimation of dominant n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, and other hydrocarbon contents in obtained samples. Under studied hydrotreatment conditions complete conversion of different vegetable oils into marketable liquid renewable hydrocarbons without presence of oxygen containing substances was achieved. Highly active Ni65%/SiO2-Al2O3 has remarkable selectivity to hydrocarbons produced by reaction pathways, where elimination of carbonyl groups occurs. The saturation of fatty acids in feedstock determines H2 consumption, but influence on produced hydrocarbon production is insignificant. Depending on the fatty acid composition different saturated linear hydrocarbons with wide range of carbon chain length C5-C19 and similar calorific value 47.16-47.34 MJ/kg were produced in process. Overall liquid hydrocarbon yields were from 44.6 % to 78.1 %. The highest overall liquid saturated linear hydrocarbon yield was observed for feedstock with high amount of long chain fatty acids – SO, LO, RO and RS. Pure hydrocarbons obtained from vegetable oils depending on hydrocarbon composition can be used in various areas.