No abstract

The impact of tetracycline on simultaneous biological wastewater nitrogen and phosphorus removal and its fundamental mechanisms were investigated in this study. Compared with the control, a lower concentration of tetracycline (0.2 mg L À1 ) did not exert adverse effects on biological nutrient removal; however, the presence of 2 and 5 mg L À1 of tetracycline decreased the total nitrogen removal efficiency from 80.2% to 69.2% and 65.1% respectively, but they showed marginal influence on phosphorus removal. The mechanism studies showed that most of the influent tetracycline was adsorbed by sludge, which induced the release of extracellular polymeric substances (EPS) from a sludge matrix, decreased the protective role of EPS on bacterial cells, declined the viability of sludge, increased the sludge volume index, and caused the detachment of denitrifying bacteria from sludge. Thus, the denitrifiers were more easily contacted with tetracycline. Further investigation revealed that it was the denitrifiers instead of nitrifiers being negatively affected by tetracycline, and the generation of electron donor for denitrification via intracellular polyhydroxyalkanoates (PHA) decomposition was depressed. In addition, tetracycline inhibited the activities of nitrate reductase and nitrite reductase as it was a strong chelating agent which reduced the free copper ions.

Two experiments were conducted to determine the optimum level of dietary available phosphorus from monocalcium phosphate for juvenile Ussuri catfish Pseudobagrus ussuriensis. Experiment 1 was conducted to estimate phosphorus digestibility from monocalcium phosphate for juvenile Ussuri catfish. The apparent digestibility coefficient of phosphorus from monocalcium phosphate was 86.3%. In the experiment 2, triplicate groups of juvenile Ussuri catfish were fed diets containing graded levels of monocalcium phosphate (MCP: 0 g/kg, 8.2 g/kg, 16.4 g/kg, 24.6 g/kg, 32.8 g/kg and 41.0 g/kg) for 8 weeks. Fish fed the diet containing 16.4 g/kg MCP with available phosphorus of 4.8 g/kg showed the best weight gain (171.5%), feed conversion ratio (1.08) and protein efficiency ratio (2.06). No significant difference was observed in fish survival among the treatments. The best result in terms of phosphorus retention efficiency (46.10%) was observed in fish fed the diet containing 8.2 g/kg MCP with available phosphorus of 3.0 g/kg, which was not different (p > .05) from those fed the diet containing up to 24.6 g/kg MCP, and the highest vertebrae phosphorus content (58.2 g/kg) was observed in fish fed the diet containing 24.6 g/kg MCP with available P of 6.6 g/kg. The whole‐body lipid and protein, as well as phosphorus contents, were significantly affected by dietary available phosphorus (p < .05). Viscerosomatic index (VSI) and condition factor (CF) were inversely correlated with dietary phosphorus levels (p < .05). Quadratic regression analysis based on specific growth rate (SGR) against dietary available phosphorus levels indicated that the optimum available phosphorus requirement for the maximal growth of juvenile Ussuri catfish was 5.9 g/kg, and broken‐line analysis based on vertebrae phosphorus content against dietary available phosphorus levels indicated that a dietary level of 6.0 g/kg available phosphorus will provide optimum vertebrae phosphorus content.