Investigation of treatment of paper recycling wastewater by electrochemical oxidation process

The importance of finding the best environmental and economic methods for the management of wastewater generated in a facility using waste paper in paper production and improving existing methods will increase even more, considering the increasing need for the paper manufacturing sector and the trend towards reusing raw material resources for waste paper. In this sector, depending on many variables such as raw material source, content, and applied production method, the wastewater generated has a different composition on a country and facility basis. In this thesis, the applicability of the electrochemical oxidation process in the treatment of wastewater generated in a facility producing paper-cardboard from waste paper was investigated. In the electrochemical oxidation process, lower cost and easily available stainless steel and graphite electrodes were used, and the effects of ambient conditions (reaction time, potential applied to the electrodes, distance between the electrodes), initial pH level, electrolyte addition and the application of the classical coagulation-flocculation process as a pre-treatment on the treatment efficiency were also investigated experimentally. The efficiency of the electrochemical treatment process was monitored with COD and color parameters. Compared to the graphite electrode pair, higher color and COD removal was achieved with the stainless steel electrode pair. By using stainless steel electrodes, at the original pH value of the wastewater (6.86), at the end of 240 min reaction time, at the distance between the electrodes of 2.5 cm and for the potential applied to the electrodes of 10 V, COD and color removal were determined as 57% and 99.7%, respectively. Under the same conditions, the specific energy consumption was determined as 17.4 kW.h/kg COD. When the initial pH value was adjusted to 5.5, at the end of 180 min reaction time, COD removal increased to 66.3% and color removal was determined as 99%. The addition of electrolyte decreased the specific energy consumption value to 11.8 and 12.3 kW.h/kg COD for 0.01 M Na2SO4 and NaCl, respectively. It has been observed that the conventional coagulation-flocculation pre-treatment does not provide a positive contribution to the electrochemical oxidation process in the case of commercial iron (III) chloride and aluminium chloride hydroxide. It has been concluded that the electrochemical oxidation process using steel electrodes can be used as an alternative treatment method in the treatment of paper recycling wastewater, either alone or as a pre-treatment step, depending on the receiving environment to which the effluent will be discharged.