Pulp and Paper Mill Effluent Treated by Combining Coagulation-Flocculation-Sedimentation and Fenton Processes

Pulp and paper industries face serious environmental challenges, especially with regard to the conservation of water resources. Chemical thermal mechanical pulping (CTMP) is a process of pulping that combines chemical and mechanical pulping. This reduces the volume of water used in the process. But on the other hand, CTMP generates an effluent with high concentration of organic matter and is difficult to treat. This study evaluated the efficiency in the combination of physicochemical pretreatment by coagulation-flocculation-sedimentation (CFS) process and advanced oxidation process (AOP) by Fenton in sequence to treat CTMP effluent of a Brazilian industry. At first, the best treatment conditions for this type of effluent were determined. To evaluate the efficiency, pH, chemical oxygen demand, biochemical oxygen demand, total organic carbon, lignin contents, color, total phenolic contents, turbidity, and solids were measured before and after treatment. The acute toxicity on Daphnia magna was also determined. The treatment with CFS showed better results in the removal of solids and Fenton in the removal of recalcitrant compounds, such as lignin, demonstrating the need to use them in sequence. Combining CFS and Fenton to treat CTMP effluent allowed to achieve a removal efficiency of 95% for TOC, 61% for COD, and 76% for lignin contents.