Characterization of domestic wastewater sludge in Oman from three different regions and recommendations for alternative reuse applications

Background: There are more than 350 wastewater treatment plants distributed across different parts of Oman. Some of them produce large quantities of domestic sewage sludge, particularly this study focused on characterizing domestic sludge of six treatment plants that may contain various pollutants, therefore the proper management of domestic sewage sludge is essential. Methods: Samples of domestic sewage sludge were collected for each month over a period of one year in 2010.Samples of retained/ recycled activated sludge (RAS) and waste activated sludge (WAS) were analyzed for electrical conductivity (EC), potential of hydrogen (pH), cations, anions and volatile content. All tests were conducted according to the Standard Method for the Examination of Water and Wastewater. Results: Monitoring ofelectrical conductivity, nitrite and nitrate, the presence of chloride, sulfate and phosphate were higher than the other anions, the phosphate was found very high in all domestic STPs. The average obtained values of the cations in both domestic RAS and WAS samples were within the Omani Standards. Conclusion: The study showed the very high concentration of phosphate, it might be worth to further investigate on the sources of phosphate. Cations in both domestic RAS and WAS samples were low and suggest that the domestic sludge can be re used in agriculture. A regular maintenance should be performed to prevent any accumulation of some harmful substances which may affect the sludge quality and the sludge drying beds should be large enough to handle the produced sludge for better management.