Problem definition and objectives: Wastewater treatment from the paper industry is one of the key aspects in environmental management and achieving industrial sustainability. Membrane filtration is one of the new and efficient methods in wastewater treatment, which is known as an effective solution, especially in industries with specific pollution. Membrane fouling is one of the basic issues in the wastewater treatment process using membrane filtration technologies which has negative effects such as reducing efficiency, increasing treatment costs, and reducing the useful life of the membranes. In this research, two methods of coagulation and ozonation were used to solve the problem of membrane fouling for papermaking wastewater treatment. Coagulation method was used as an effective solution to remove most of the large suspended particles, while ozonation method was used to remove color and destroy complex compounds.
Methodology: The raw wastewater with a chemical oxygen demand (COD) of 62,000 mg/liter was obtained from the Sepid Damavand Paper Industry Company in Tabriz, which is located in East Azarbaijan province. In this process, NaOH was used to increase the pH and Poly Aluminium Chloride (PAC) was used as a coagulant, and after coagulation and sedimentation of heavy particles, the pre-treated wastewater was transferred to another tank using a pump. In the next embedded process, the effect of ozonation before and after coagulation, as well as the effect of the amount of ozone injected into the effluent on the COD of the effluent was investigated. In this regard, ozonation was done with three amounts of 0.4, 0.8, and 1.2 g/liter, and the appropriate amount of ozone was selected to reduce COD. Finally, the two methods of coagulation and ozonation were used in a combination as the pre-treatment steps of membrane filtration in order to improve the flux passing through the membrane and reduce COD of the effluent.
Results: Based on the obtained results, the presence of coagulation before the ozonation stage improved the performance of this stage and the amount of 1.2 mg/liter of ozone had the greatest impact on the effluent compared to other amounts. The results of wastewater COD measurement showed that each of the three treatment steps used contributed to the reduction of COD, so that the COD of the wastewater after the coagulation, ozonation and membrane filtration stages was reduced by 37, 48, and 68%, respectively, compared to the raw wastewater COD. The amount of wastewater color was also reduced by 95% using the treatment process. In addition, the flux passing through the membrane increased by 16 times compared to the state without pre-treatment which is equivalent to a 16-fold reduction of the required membrane surface in the purification process and makes the purification process more economical.
Conclusion: Each of these steps played a key role in wastewater treatment; So that the coagulation stage was effective in removing a large volume of large suspended particles, the ozonation stage played a role in removing color and destroying complex compounds, and the membrane filtration stage as the final stage in removing very fine suspended particles provided a special performance. In addition, the two stages of coagulation and ozonation played a significant role in reducing membrane fouling and improving the flux passing through the membrane.