Dewatering sludge from primary and secondary clarifiers in Jabal Asfar wastewater treatment plants – case study

Dewatering is an important step in sludge treatment process; it reduces the quantity and valorize the quality of the produced sludge. This paper aims to discuss the use of screw press machine for dewatering sludge mixture from primary and secondary clarifiers in Jabal Asfar wastewater treatment plant (JAWWTP). The study was conducted using a pilot scale with capacity of 52 m3/h. Inlet and outlet samples were collected and transferred to the laboratory of JAWWTP for analysis. The speed of the screw press (rpm), the polymer dose (g) and the inlet TS% were monitored as operational parameters. Results showed that the screw press can dewater sewage sludge with lower total solids (TS) reached 0.5%. The optimum conditions for operating were regarded to the higher TS% in the outlet cake and the lower- energy and polymer consumption. Sewage sludge quantity entering the screw press fluctuated between 3.8 and 15.5 m3/h. Inlet TS ranged from 0.5% to 0.9% and the polymer consumption ranged from 2.7 to 18.6 g for each kg of dewatered sludge. Cost of dewatering processes ranged from US$ 0.009 to 0.064 for each kg of dewatered sludge depending on the polymer and energy consumption. TS outlet fluctuated between 13.12% and 21.6% depending on the TS inlet, the speed of the conveyer rotation and the polymer dose. The produced sludge will be dried and used for various purposes. It can be concluded that mechanical dewatering systems are suitable alternatives for conventional drying beds especially in highly populated cites, and screw press can dewater sludge with low TS content reached 0.5%.