Project Al Khumra WWTP Rehabilitation

    Set of HUBER Disc filter RoDisc® installed on site

    The treatment of industrial and municipal wastewaters on sewage treatment plants in most cases consists of a mechanical and biological stage (primary and secondary) as seen with a typical conventional activated sludge (CAS) process. Nowadays tertiary treatment after the secondary clarifier is more and more required to fulfil regulatory standards for discharge or reuse of the TSE (treated sewage effluent). Such third treatment stage usually consists of a micro screening or granular media filtration system, primarily with the aim to improve the TSE quality related to carbon, nitrogen and phosphorus concentration. On many plants a disinfection stage of the wastewater follows after the third treatment stage. UV disinfection for example removes up to 99.9% of all pathogenic germs contained in the wastewater. The WWTP Al Khumra is located about 30 km south of Jeddah City in the Al Khumra district, which is an industrial area. Sewage treatment on site presently consists of four phases. The plant operators (National Water Company - JCBU) started to refurbish phase two and three in 2014 to meet the latest standards and laws for effluent parameters so that "unrestricted water reuse" is possible. AK2, commissioned in 1998, is designed for 60,000 m³/d (peak: 1,042 l/s) and AK3, commissioned in 2004, is designed for 140,000 m³/d (peak: 2,430 l/s). The new legislation demands not only the reduction of dissolved substances, such as BOD, phosphorus or nitrogen, moreover the total suspended solids (TSS) in the effluent must not exceed 10 mg/l. To achieve this, the HUBER Disc Filter RoDisc® is used as micro screen to treat a total peak flow of 375,000 m³/d after the secondary clarifier and prior to UV disinfection. The removal of activated sludge flocks (TSS) and fine distributed suspended matter is the basic requirement for an efficient and trouble-free operation of the UV disinfection plant. The virtually solids-free effluent from the disc filter system reduces current consumption and increases not only the efficiency but also the lifetime of the UV disinfection plant. HUBER has installed 18 Disc Filters RoDisc® with 24 discs each, mounted within stainless steel tanks, at the WWTP Al Khumra. The disc filter operates on the basis of the well-proven system of drum filters. The disc filter consist of 24 horizontally arranged rotating filter discs installed on a central shaft and are submerged by up to 65% while in operation. According to the design the maximum inlet concentration of TSS is 40 mg/l; these remain in a “rest position” inside the discs during the filtration process. The suspended solids settle by gravity on the inner disc surface which leads to a gradual blinding of the mesh with the retained solids as the filtration process continues. That is resulting in an increasing differential water level between the inside of the disc towards the outside of the disc (surrounding filtered effluent). When the maximum internal / operational head loss has been reached, the solids are washed off from the filter surfaces by a spray bar whilst the filter disc is rotating slowly. The back wash water used is directly taken from the filtered effluent and provided via integrated multi-stage pumps fixed to the disc filter. An external wash water supply is not required. The removed solids are washed into a trough situated below the segment openings prior to being discharged back to the WWTP. The system installed at Al Khumra guarantees a TSE quality of ≤10 mg/l TSS. One filter disc consists of 12 single filter segments made of high-quality polypropylene. The filter mesh itself is made a stainless steel mesh following the end-users request. Polyester mesh is also available. A very special and unique thermal embedding process is applied to fix the mesh onto the filter segment frame. Thermal embedding achieves a form-locked connection of the mesh with the filter segment frame so that the mesh is permanently protected and safely fixed to the segment frame.