Wastewater Sludge Management
Sludge is generally the solid residue in suspension from the wastewater stream and can be produced in two steps during the treatment of the effluent. Primary sludge is generated during the removal of insoluble matters such as grit, grease, and scum from wastewater by screening followed by coagulation and sedimentation. The settled primary sludge contains mainly water (between 97% and 99%) and highly putrescible organic matters. The secondary sludge or waste activated sludge (WAS) is generated as a result of biological treatment of the effluent from primary treatment containing different types of dissolved organic matters, and it consists of a complex activated sludge floc structure. Generally, sludge is a mixture of organics (such as proteins, carbohydrates and lipids) or volatile matters, inorganic matters and associated water. Sludge management is one of the most difficult and challenging tasks of wastewater treatment plants due to its high water content and poor dewaterability, Sludge management can cost as high as 60% of the total cost for a wastewater treatment plant.and strict regulation for sludge reuse or disposal. One of the recent goals of wastewater sludge management is to develop more environmentally friendly processes to reduce the volume of sludge for disposal and to convert sludge into bio-energy. Energy recovery of the sludge generally includes the conversion of the organic matters of sludge into biogas, syngas and bio-oil, which can be further converted into electricity, mechanical energy and heat, and the inorganic matters into bio-char or construction materials.