EFFECTS OF NI(II) ON RESPIROMETRIC OXYGEN-UPTAKE

The effects of Ni(II), substrate and initial biomass concentrations on biochemical oxygen demand (BOD) were studied by using an electrolytic respirometer. The effects of Ni(II) (2.5, 5.0, 10.0, 25.0 mg/l) and s ubstrate (325, 650, 1300 mg/l as chemical oxygen demand) in a syntheti c wastewater with differing initial biomass concentrations (1, 10, 100 mg/l) were investigated. The biomass-to-metal ratio was found to be t he most important parameter affecting the measured BOD values. The max imum specific growth rates were calculated and the results of batch re spirometric experiments were analysed both by graphical and statistica l methods. In statistical analyses, a factorial experimental design ap proach was followed and results were treated by multiple regression te chniques. A mathematical model was developed to express the maximum ox ygen uptake in terms of nickel, substrate and initial biomass concentr ations and their magnitudes of their effects were compared. The biomas s-to-metal ratio was found to be very significant so that another mode l that expresses oxygen uptake in relation to the biomass-to-metal rat io and also to substrate concentration was developed. Finally, the eff ect of Ni(II) was demonstrated to depend on both substrate and initial biomass concentrations. This effect was stimulatory at low concentrat ions of Ni(II). and complete inhibition was never observed even at the highest concentration of Ni(II) studied, which was 25.0 mg/l.