English abstract
This study focuses on characterizing the quality of domestic and industrial sludge in selected three regions in the Sultanate of Oman: Muscat, Sohar and Salalah. The wastewater sludge samples were collected from three industrial treatment plants and six domestic treatment plants. Three samples were collected from each treatment plant: retained activated sludge (RAS), waste activated sludge (WAS) and primary sludge. The sampling program continued over a period of approximately one year starting from February 2009. The tested parameter included pH, electrical conductivity (EC), cations (Cadmium (Cd), Chromium (Cr), Cupper (Cu), Lead (Pb), Molybdenum (Mo), Nickel (Ni) and Zinc (Zn)), anions (Fluoride, Chloride, Nitrite, Bromide, Nitrate, Phosphate and Sulfate) and volatile content (VC). For the industrial STPs the overall range of pH in RAS and WAS samples were 5.8 to 8.0. Most of ĘC results were below 1000 uS/cm. The range of VC percentage in RAS samples was 44 to 86% and 41 to 77% for WAS samples. Fluoride concentrations were the lowest concentrations compared with the other anions. The range of Bromide in RAS samples were narrow but in WAS samples it was wide in both Rusayl Industrial Estate STP and Sohar Industrial Estate STP. The range of Chloride concentration in Raysut Industrial Estate STP was wider than the other STPs and the maximum concentration was 51891 mg/kg for RAS samples. Phosphate concentration ranged between 19 and 18250 mg/kg in Sohar Industrial Estate STP RAS samples which was wider than the other STPs. The range of overall average of Sulfate concentration was 1684 to 16681 mg/kg in RAS samples while the range in WAS samples was 2656 to 5233 mg/kg. Nitrite concentration range in Sohar Industrial Estate STP was wider than the other STPs for RAS samples. The ranges of Nitrate for RAS and WAS samples were narrow except for RAS samples in Rayşut Industrial Estate STP. The average obtained values of the cations in both RAS and WAS samples were within the Omani Standard for the re-use of sludge in agriculture except for Cd in Rusayl Industrial Estate STP. For the domestic STPs the value of pH for RAS samples was in the range of 6.08 to 7.8. The range of pH values of WAS in Darsait STP samples was wider than the other STPs. The overall EC average for RAS, WAS and Primary Sludge samples were 9334S/cm, 702uS/cm and 404uS/cm, respectively. The range of VC percentage in RAS samples was 49.5 to 84.3% compared to 32.2 to 83% for WAS samples. Fluoride concentrations were the lowest concentrations compared with the other anions. The range of Chloride concentration in Rusayl STP was wider than the other STPs and the maximum concentration is 35910 mg/kg for RAS samples. Nitrite concentration range in Darsait STP and Sohar STP was much wider than the other STPs for RAS samples. The Nitrite ranges of WAS values were small in all STPs except for Sohar STP. The ranges of Nitrate in RAS samples were narrow except for Sohar STP and Salalah STP. For WAS samples, the Nitrate ranges were narrow except for Sohar STP. The concentration of Phosphate compared to other anions was relatively high and the highest range in RAS samples was for Salalah STP (26 to 33861 mg/kg). On the other hand, the range in Rusayl STP for WAS samples was wider than the other STPs (the highest value was 32745mg/kg). The range of overall average of Sulfate concentration in RAS and WAS samples were 832 to 37998 mg/kg and 550 to 48649 mg/kg, respectively. The average obtained values of the cations in both RAS and WAS samples were within the Omani Standards for the re use of sludge in agriculture except for Zn in WAS sample in Sohar STP.
