عنوان مقاله [English]
Background and objectives: One of the major problems in the industrial wastewater treatment plant is sludge volume, which requires to providing economic and environmental solutions. The use of natural compounds is preferable to the chemical compounds in the sludge treatment process, environmentally. For this reason, experts are trying to find a suitable material for replacement. Yousefi et al (2012) evaluated the efficacy of chitosan natural polyelectrolyte as a coagulant to elimination of water opacity. The results showed that chitosan has little effect on water pH and its efficiency is better in elimination of high opacity.
The chitosan is one of the natural materials. The purpose of this study was determine of optimal pH and concentration of the alum, chitosan and early preparations for simultaneous use in a pilot-scale to improve dewatering sludge. Also, the effect of these treatments was measured on turbidity, color, COD of water sludge Filtration.
Materials and methods: For this purpose, from determine of filtering time and measuring of moisture content was used for assay of dewatered sludge capabilities. In this regard, 10 percent alum solution were prepared by dissolving 10 g from aluminum sulfate in one liter of distilled water. To prepare of the chitosan solution, 100 mg from chitosan powder is carefully weighed and dissolved by 10ml chloric acid 0.1 M and then its volume was bring up to 100 ml. acidity of aqueous sludge adjustment by sodium hydroxide and sulfuric acid in the range of 4 to 9. Afterward the constant concentration of alum, chitosan and chitosan-chitosan was added. Ml 50 dewatering time was determined by Buchner funnel, filter paper and vacuum device and water content was determined by oven-dry.
Results: The results indicated that the optimal pH for alum, chitosan and alum-chitosan is 5, 7 and optimal concentrations 800, 90 and 600-70 ppm, respectively. By applying this treatment in optimal conditions the best treatment to achieve the minimum dewatering time is alum-chitosan treated with pH 7 and 70-600 ppm consumption. Also, the best treatment for reducing color, turbidity and COD of sludge filtered water is treated alum with concentration of 800ppm and pH 5.
Conclusion: Dewatering time of the control and treated with alum increased with increase in pH from 4 to 9. Dewatering time in about the samples treated with chitosan, especially alum – chitosan showed less sensitive to pH. So, the alum treatment little effect on the color and COD at pH =7, whereas the opacity decreased to 24 percent. The chitosan had highest effect on COD and then turbidity and color. Alum-chitosan treatment has a significant impact on turbidity and COD.