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## 3.3.4.31 Sludge Drying Units 

Thermal sludge drying plant shall be designed, constructed and equipped to increase the dry solid content, to further sterilize the sludge and to enhance storage capability before final disposal. Thermal sludge drying plant shall be designed, constructed, supplied and installed in turn-key to meet the required sludge output characteristics. Further requirements are given in Section 7.8.44. Foul air shall be collected from the building and shall be sent to the odor control unit. The dry solid shall be transferred from the sludge drying plant to the sludge cake storage area with conveyors (air shall not be used for transferring of dry sludge).The dewatered sludge shall be dried to get minimum outlet sludge dry solids content of 90%. Please note that dewatered sludge prior to drying process shall be taken as 22% DS as specified in Table 2.5. 

## 3.3.4.32 Sludge Cake Storage 

Individual or common sludge cake storage area for dewatered and dried sludge shall be constructed. Each cake storage area shall have at least 2 days storage capacity. The sludge storage area shall be roofed top with metal sheds made from galvanized steel, aluminum or equivalent material. Floor shall be reinforced concrete suitable for driving over with a front-end loader or similar machine and surrounded by concrete walls. Adequate drainage system and lightening system shall be designed and constructed. The service water supply system and sufficient connection port shall be supplied for the cleaning of sludge cake storage areas. 

## 3.3.4.33 Supernatant Pumping Station 

Supernatant from dewatering and thickening process(es) shall be delivered back to the system by gravity as possible. However, in case gravitational flow is not possible, a supernatant pumping station shall be provided. 

All supernatant water shall be collected to the supernatant pumping station. The pumps for supernatant shall be submersible pumps. The actual capacity of the pumps shall be calculated by taking the maximum amount of supernatant water into account. The backwash water of mechanical thickener and decanter shall also take into account in determination of maximum capacity. Ultrasonic level sensors shall be used in pump tanks for pump operation. Supernatant water flow rate shall be measured in accordance with “Measurement and Instrumentation” section of this document. 

The mixture of supernatant with drainage water and sewerage generated in the WWTP buildings is not permitted. 

