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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.

A detailed system identification procedure and self-tuning generalized minimum variance (STGMV) control of glucose concentration during the aerobic fed-batch yeast growth were realized. In order to determine the best values of the forgetting factor (λ), initial value of the covariance matrix (α), and order of the Auto-Regressive Moving Average with eXogenous (ARMAX) model (n a, n b), transient response data obtained from the real process wereutilized. Glucose flow rate was adjusted according to the STGMV control algorithm coded in Visual Basic in an online computer connected to the system. Conventional PID algorithm was also implemented for the control of the glucose concentration in aerobic fed-batch yeast cultivation. Controller performances were examined by evaluating the integrals of squared errors (ISEs) at constant and random set point profiles. Also, batch cultivation was performed, and microorganism concentration at the end of the batch run was compared with the fed-batch cultivation case. From the system identification step, the best parameter estimation was accomplished with the values λ = 0.9, α = 1,000 and n a = 3, n b = 2. Theoretical control studies show that the STGMV control system was successful at both constant and random glucose concentration set profiles. In addition, random effects given to the set point, STGMV control algorithm were performed successfully in experimental study.

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.

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