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The purpose of this work was to present original monthly mean values of the removal efficiencies related to the quality specific indicators for each stage of wastewater treatment processes of a plant, obtained over 20 years of operation. Studies were performed on the most modern wastewater treatment plant in Romania, located on the Black Sea Coast, which processes about 500 l s[sup -1] of effluent from an important petrochemical complex. The average removal efficiencies for oil products, total suspended solids, H[sub 2]S and sulphides, chemical oxygen demand (CODCr), biochemical oxygen demand (BOD[sub 5]) and phenols, for each particular stage and overall, are shown. The analytical control used, demonstrated that the primary treatment was the most important stage for the removal of oil products and total suspended solids, due to sedimentation. In the case of H[sub 2]S and sulphides removal, the most efficient stages were the chemical and biochemical processes, because of precipitation and oxidation. CODCr was reduced most efficiently in the biochemical stage due to microbial activity of the active sludge. [ABSTRACT FROM AUTHOR]

This paper presents the determination of the total concentration of cadmium (Cd), copper (Cu), chromium (Cr), lead (Pb), zinc (Zn) and nickel (Ni) in the biotop (sandy sediment and water) and biocenose (mature and young plants of Phragmites sp.) for a tertiary biological treatment stage of a petrochemical effluent. Analyses were performed using the ICP-AES technique after the chemical mineralisation of the samples with a Digestahl device. The metal (cadmium, copper, lead, zinc and chromium) concentrations in mature plants were higher than those in the sediments. At the same time, the young plants contained higher quantities of nickel, lead and zinc than the mature ones, and also lower quantities of cadmium, chromium and copper. [ABSTRACT FROM AUTHOR]