The fine sieve being used in the CADoS project is of the ‘rotating sieve belt’ type and is already in service for the mechanical pre-treatment of domestic wastewater. The fine sieve allows removal of the suspended matter present in the wastewater by means of filtration.
Cross-section of the fine sieve
The fine sieve consists of an endless sieve belt (sieve cloth) with a pore size of 350 or 550 micron. The pore size of the sieve cloth depends on the size of the particles and the type of wastewater. A sieve cloth of 350 micron is generally used when treating domestic waste. The influent is put on to the fine sieve (1) and then flows through the sieve cloth (5). The solid matter present in the wastewater forms a ‘bridge’ across the pores (a ‘filter cake’), thus also enabling the capture of smaller particles and their removal from the water. The filter cake is transported upwards and out of the wastewater by the sieve belt and then blown from the belt by compressed air (9). The sieve belt is regularly rinsed with hot water to prevent blockage of the pores.
The fine sieve is equipped with a regulator that anticipates the quantity of suspended matter present in the wastewater with the aim of maximising efficiency. The sieved material is moved via a screw (14) to a dewatering cylinder, after which it exits the fine sieve with a dry matter content of 15 to 25%. To dewater the sieved matter still further, it is possible to install a downstream dewatering press to obtain dry matter contents of between 35 and 50%.