Background and objective: Paper, pulp and cardboard manufacturing industries discharge large amounts of waste which contain a variety of pollutants and paints. These wastes are believed to generate the most environmentally hazardous industrial wastewaters. Biological procedures alone may not suffice the treatment of such wastes due to having a high BOD5/COD ratio. On the other hand, applying costly chemical  approaches to remove all these pollutants in a short time often results in the production of large quantities of sludge. Therefore, these industries are obliged to combine both these methods in order to optimize wastewater treatment.

Methods: In this experimental study, the sample wastewater was provided from the discharge channel of Pazh cardboard factory located in Tous Industrial Zone of Mashhad, Iran. The wastewater samples were collected from this factory by composite sampling. Coagulation of these samples was accomplished by clay soil as the single coagulant. The optimum pH of the treatment was determined by Jar tests in various pHs (from 4 to 9). Afterwards, the optimum concentration of the coagulant was also verified at the optimum pH
of 8 by Jar tests.

Results: The optimum dosage and pH of treatment by clay soil wasdetermined to be 75 g/L and 8, respectively. Under optimized conditions, the removal efficiency of COD, BOD5 and TSS was calculated as 47%, 26% and 57%, respectively. In addition, the pH adjustment at 8 resulted in a 60% reduction of clay consumption.

Conclusion: According to the results of this study, the coagulation of cardboard wastes by clay soil could be a suitable pretreatment method. This particular material makes it possible to improve the quality of wastewater in subsequent bio treatments in a much less costly way compared to other conventional coagulants or adsorbents. It was also observed that the ratio of BOD5/COD reduced from 4.5 to about 3. Although the clay dosage required for the wastewater treatment is relatively high, this approach could still
be recommended for the pretreatment of this type of wastewater as well as the wastes produced by similar industries mainly because the overall cost of this treatment is insignificant.

Paper Type: Research Article