No abstract

a b s t r a c tIn this work, electrocoagulation (EC), electro-oxidation (EO x ), consecutive electrocoagulation electro-oxidation (EC&EO x ) and combined electrocoagulation electro-oxidation (EC/EO x ) treatment methods were executed for the pulp and paper mill wastewater. The performances of the methods were compared in terms of pollutant removal and energy consumption amounts. Batch electro-reactor was used with Al and Fe electrodes for EC stage and graphite electrodes for EO x stage. The initial process conditions were electrical conductivity in 2.10 mS/cm, pH in 5.82, temperature in 20 o C and constant current intensity in 1.22 A. The highest removal of turbidity, color and chemical oxygen demand (COD) was obtained as 99%, 100% and 90% respectively for both EC & EO x and EC/EO x processes with the utilization of Al electrodes. Although EC&EO x method was found to be more energy efficient with 26.23% less energy consumption than EC/EO x method, usage of a single reactor for EC/EO x technique has been considered as a more feasible method for treatment because of the initial investment cost and ease of application. Effects of initial pH, electrical conductivity, temperature and current intensity on pollutant removal and energy consumption by means of EC/EO x technique were also investigated and optimal operational parameters were determined as 6, 5 mS/cm, 20 o C and 1A respectively.

In this work the application of response surface methodology (RSM) to proportional-integral-derivative (PID) controller parameter tuning for electrocoagulation (EC) treatment of pulp and paper mill wastewater was researched. Dynamic data for two controlled variables (pH and electrical conductivity) were obtained under pseudo random binary sequence (PRBS) input signals applied to manipulated variables (acid and supporting electrolyte flow rates). Third order plus time delay model parameters were evaluated through System Identification Toolbox™ in MATLAB. Four level full factorial design was applied to form a design matrix for three controller tuning parameters as factors and to evaluate statistical analysis of the system in terms of integral of square error (ISE), integral of absolute error (IAE), integral of time square error (ITSE) and integral of time absolute error (ITAE) performance criteria as response. Numerical values of the responses for the runs in the design matrices were determined using closed-loop PID control system simulations designed in Simulink. Optimum proportional gain, integral action and derivative action values for electrical conductivity control were found to be 1,500 s, 0 s and 16.4636 s respectively. Accordingly, the same optimization scheme was followed for pH control and optimum controller parameters were found to be -8.6970 s, 0.0211 s and 50 s, respectively. Theoretically optimized controller parameters were applied to batch experimental studies. Chemical oxygen demand (COD) removal efficiency and energy consumption of pulp and paper mill wastewater treatment by EC under controlled action of pH at 5.5 and electrical conductivity at 2.72 mS/cm was found to be 85% and 3.87 kWh/m respectively. Results showed that multi input-multi output (MIMO) control action increased removal efficiency of COD by 15.41% and reduced energy consumption by 6.52% in comparison with treatment under uncontrolled conditions.

No abstract

Purpose – The purpose of this paper is to investigate the batch treatment of pulp and paper mill wastewater using electro-coagulation (EC). Design/methodology/approach – Statistical experimental design was used to investigate the effect of initial pH, current density and temperature. Experiments were planned to obtain the maximum amount of information in the fewest number of runs. Minimum-maximum values of current density, initial pH, temperature of medium were selected as 9-25 mA/cm2, 5-9, 25-50°C, respectively. A total number of 20 experiments including eight factorial points, six axial points and six replicates in centre points were carried out and experimental data were collected. Optimum operating parameters were determined by evaluating experimental results in MATLAB 7.9®. Findings – According to the results, the optimum values of current density, initial pH and temperature of medium are determined as 14.12 mA/cm2, 8.22 and 34.21°C, respectively. Practical implications – Many researches about different techniques including physical, chemical and biological methods have been done on the subject of pulp and paper wastewater treatment. In physical and chemical processes low molecular weight compounds are not removed efficiently, also these methods are quite expensive. Electrochemical degradation has an advantage of removing even the smallest colloidal particles compared with traditional flocculation and coagulation. Originality/value – Complete removal of pollutants, less sludge generation, simple process design and easy operation are standard features of the EC and it comes forward as one of the promising techniques.