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The aim of this study is to evaluate the performance of coagulation and flocculation (C/F) process and economic analysis for the advanced primary treatment in order to obtain a semi-closed water circuit in the pulp mills in the cardboard recycling industry. Since the high water quality level is not required in the pulpers, the dosages in this research were determined without pH changes or adjustment to decrease the capital and operational expenditures. The results showed that FeCl3 with the concentration of 2000 mg/L gave the best quality when coagulants were used solely. Moreover, using alum with the concentration of 1500 mg/L provided acceptable quality for the effluent re-circulation and the removal/reduction percentages of 42, 82, 71 and 97 were achieved for chemical oxygen demand (COD), total suspended solids (TSS), turbidity and colour, respectively. It was also found that the combination of coagulants did not improve the process performance significantly. The best combination was ferric chloride (500 mg/L) and alum (2000 mg/L) with the efficiency of 47% and 98% in terms of COD and colour removal/reduction, respectively, while the best couple in TSS removal was FeCl3 (500 mg/L) and CaCO3 (500 mg/L) with the efficiency of 88%. The chemicals coupled with cationic polyacrylamide (C-PAM) did not enhance the quality of pre-treated solutions when the settling time reduced up to 15 minutes. The cost analysis also showed that alum is the most cost-effective coagulant with the costs in the range of 0.06–0.12 $/kg removed TSS, 0.06 to 0.11 $/kg removed COD and 0.06–0.1 $/m3·reduced NTU whereas calcium carbonate is the economic coagulant regarding colour reduction with the cost of 0.003 $/m3·reduced unit and more than the reduction efficiency of 90%. [ABSTRACT FROM AUTHOR]

In this study three modeling approaches consisting Modified Stover-Kincannon, multilayer perceptron neural network (MLPANN) and B-Spline quasi interpolation were applied in order to predict effluent of up-flow anaerobic sludge blanket (UASB) reactor and also to find the reaction kinetics. At first run, the average total chemical oxygen demand (TCOD) removal efficiency was 48.3% with hydraulic retention time (HRT) of 26 h and 63.8% with HRT of 37 h, at OLR of 0.77–1.66 kg TCOD/m3 d. At the second run, UASB reactor operated with OLR of 1.94–3.1 kg TCOD/m3 d and achieved the average TCOD removal efficiency of 64.74 and 72.48% with HRT of 26 and 37 h, respectively. The Modified Stover-Kincannon performed well in terms of kinetic determination with a high value of regression coefficient over 0.98. The B-Spline quasi interpolation and MLPANN indicated a great fit for effluent prediction with average R of 0.9984 and 0.9986, and MSE of 157.6050 and 129.7796, respectively; however, they gave no information about reactions occurred in the system. [ABSTRACT FROM AUTHOR]