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Experiments were carried out to treat synthetic Bismarck Brown dye effluent using electro coagulation covering a wide range in operating conditions. The influence of operating parameters on efficiency of the process has been critically examined. The batch experimental results showed that the dye effluent can be effectively treated using electro coagulation. The overall COD removal efficiencies has been obtained 99%, under optimum operating condition. Further it is attempted to fit the experimental data with popular adsorption isotherms Langmuir and Temkin models. The predictions of Langmuir adsorption isotherm model are in good agreement with the experimental data.

The use of Carica papaya seeds as an adsorbent for decontamination of toxic metal ions like Ni (II) and Cr (VI) in solution was investigated. The maximum biosorption capacities of Cr (VI) and Ni (II) were observed at pH 2 and pH 6 respectively. The experimental isotherm data were analyzed using the Langmuir, Freundlich, Dubinin–Radushkevich and Temkin equations. In order to determine the best fit isotherm, five error analysis methods were used, namely the sum-of-squared errors (SSE), the composite functional error (HYBRID), the Marquardt’s percent standard deviation (MPSD), the average relative error (ARE) and the sum of absolute error (EABS). The error values demonstrated that the Langmuir isotherm model provided the best fit to the experimental data for Cr (VI) and the Freundlich model for Ni (II). Adsorption kinetics data were tested using pseudo-first-order and pseudo-second-order models. Kinetic studies showed that the adsorption followed a pseudo-second-order model. Thermodynamic parameters such as changes of standard free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were determined. The maximum metal uptake of 5.85 mgg–1 for Cr (VI) and 5.58 mgg–1 for Ni (II) from Langmuir model demonstrates the ability of Carica papaya seed to absorb heavy metals. Fourier transform infrared spectroscopy analysis was used to evaluate the binding characteristics of Carica papaya seed with metals.

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