specifications given in Section 7.8.27. It shall be possible to dismantle the diffusers and remove them for repair. 

The blowers for grit removal shall be located in a separate building located adjacent to the grit and grease removal tanks. The blowers shall be speed controlled by means of frequency-converters. One stand-by blower unit shall be provided in the system. 

The grit pumps shall be supplied and installed in accordance with Section 7.8.19 and 7.8.26. 

Each grit and grease removal tank shall have a separate bridge moving independently. The submersible grit pumps shall be connected to the bridge and move together with the bridge. The pump can be lowered and removed by chains on 1.4404 stainless steel guide rails. The pump shall transfer the grit to the grit accumulation channel by means of stainless steel pipelines installed on the grit removal bridge. The grit discharged to this channel shall reach to grit classifier then separated from water and the settled grit shall be transported to containers. On the other hand, the retained grease shall be scraped off into a grease collector pit. 

The capacity of the grit pump should be selected twice of the calculated requirement. The classifier proposed by the Contractor shall be in accordance with the specifications given in Section 7.8.28. The capacity of the grit classifier shall be 20% higher than the total capacity of the grit pumps. The grit classifier equipment shall be with clean water washing. The efficiency of the grit classifier shall be over 90 % for the particles of 0.2 mm and bigger grit size. The grit classifier will have the bottom drainage and the valve and installed in a suitable location in the building. A screw conveyor will transport the settled grit from the grit classifier to a container with a capacity for approximately one week's grit production. Grit classifier, screw conveyor and grit container shall be located in the same building where the fine screens are installed. 

The surface scum and floated grease shall be scrapped by a scraper system mounted on the moving bridge that provides collection and transported into a grease collector pit, and then directed to the drum sieve by means of air lifting. Pipework for air lift system shall be stainless steel. The air requiring for air lift application shall be provided from grit and grease removal blowers. When determining the capacity of these blowers, this additional amount should be considered. After the drum sieve, the scum and floating materials shall be transported to screen press and then collected in the containers. 

The limiting criteria for surface load in grease removal part is 25 m$^{3}$/m$^{2 }$h on the max allowed. The width of grease section shall be min 30% of width of grit section. 1/3 of the wastewater flow rate shall be taken account for the hydraulic load of the grease channel. 

The grease scrapers and grit pumps shall be autonomously, locally timer controlled. 

In order to keep water in certain level in grit and grease removal tank, the ultrasonic level sensor shall be installed in each grease and grit removal tank. Each grease and grit removal tank shall be isolated by means of the electrical actuated penstocks installed at downstream of each unit. This penstock shall be adjustable according to water level. These outlet penstocks shall be weir type with double spindle and fully watertight. The operation status of the penstocks should be monitored and controlled by the SCADA system. 

