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The thickened primary sludge shall be pumped directly to the anaerobic digesters or to the digested sludge storage tank. Quantity of primary sludge transferred to anaerobic digester or digested sludge storage tank shall be measured. The pumps shall be speed controlled by means of frequency- converters. Adequate space within the unit shall be left for proper operation and maintenance of all equipment. Access to the pumps and components (such as valves and local control panels) shall be secure and unhindered. A permanent crane or lifting system shall be provided to carry out the maintenance works for thickened primary sludge pumps. 

Washing water shall be connected to both the suction and discharge lines of the sludge pumps. This washing system will engage automatically when the pumps are not operated. In addition, the service water line shall be installed to the appropriate places of the thickened primary sludge pumping station and sufficient number of connection points shall be supplied. The treated water should be used for this purpose. 

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## 3.3.4.26 Anaerobic sludge digester 

The Anaerobic sludge digester tanks shall be designed, constructed and equipped regarding the requirements set in Table 2-1. 

The organic material in primary settled sludge and excess sludge are biologically converted in the anaerobic digestion process. The preferred anaerobic process used for the treatment of sludge is mesophilic, fully mixed digestion where the sludge is heated to approximately 35°C because it is widely used in Turkey. 

The digesters shall be constructed as insulated cylindrical concrete tanks. Epoxy coating shall be applied to anaerobic digester tank that come into contact with the biogas so that the coating protects concrete against the effects of H$_{2}$S gas and a threat of sulphuric acid formation. Epoxy product to be used for coating is subject to Engineer’s approval. 

To create optimum process conditions for the methane bacteria in the digesters, effective mixing shall be provided. The mixing system shall be designed for complete mixing so that floating sludge layers and sedimentation of sludge at the bottom are avoided. All parts in contact with the sludge shall be stainless steel. The effective mixing may be performed by using top mounted agitators or may be using gas compressors and gas injection pipes. The tenderer shall provide details of mixing calculation with his proposal. 

If the Contractor intended to use a patented process like thermal hydrolysis and ultrasound disintegration in combination with anaerobic sludge digestion process, the Contractor shall provide all relevant information, data and calculation related with this system to the Employer during the tender period. The proposed system should be technically and operationally proved by on-site data from three wastewater treatment plant with the proposed alternative process like thermal hydrolysis process and ultrasound disintegration. 

