Physicochemical properties of sewage sludge from Gaza

Abstract

This study characterized the physicochemical properties of sewage sludge collected from Gaza wastewater treatment plant. Sludge samples were collected from the drying beds, air-dried, sieved through 2 mm and stored in plastic bags at room temperature. Sludge density, particle size distribution, water holding capacity, void volume, pH, EC, total organic carbon and hydrophobicity were determined. Results showed the bulk density is about 1.18 g/cm3 whereas the real density is 2.12 g/cm3 and void volume is 50%; Particle size distribution showed that the major size of sludge is sand-like size (630-200 µm) and the minor size is silt-like size (200-20 µm) and clay-like size are less than 20 µm. Sludge has an acidic pH reaction (6.78±0.02) with an electric conductivity equal to (2.49±0.04) mS∙ cm− 1. The hydrophobicity of sludge is very high, water drop penetration time (WDPT) is 114.77±18.78 sec with a radius of 0.44±0.08 cm. In the way around, oil drop penetration time (ODPT) of sludge is 5.05±1.28 sec with a radius of 1.25±0.14 cm. The WDPT/ODPM ration is very high value 22.73 indicating extreme hydrophobicity. High value of hydrophobicity may reduce water filtration in soil when sludge applied for agriculture. These results suggest that sludge application to soil may change the physicochemical properties of soil.