Primary treatment: Particle separation by rotating belt sieves
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Fine mesh rotating belt sieves (RBSs) offer a compact solution for removal of particles in primary treatment of wastewater. This chapter shows examples from lab-scale, pilot-scale and full-scale testing of primary treatment and chemically enhanced primary treatment (CEPT). In a Norwegian full-scale survey, the use of a 350 µm belt showed more than 40% removal of total suspended solids (TSS) and 30% removal of chemical oxygen demand (COD) at sieve rates as high as 160 m3 ⋅ m−2 ⋅ h−1 . Maximum sieve rate tested was 288 m3 ⋅ m−2 ⋅ h−1 and maximum particle load was 80 kg TSS ⋅ m−2 ⋅ h−1 . When the sludge mat on the belt increased from 10 to 55 g TSS ⋅ m−2, the removal efficiency for TSS increased from about 35 to 60%. CEPT is a simple and effective way of increasing the removal efficiency of an RBS. When adding about 0.7–1.0 g ⋅ m−3 of cationic polymer and using about 2 min of flocculation time, the removal of TSS typically increased from 40–50% without polymer to 60–75% with polymer. The particulate organic matter that was removed in the RBS had little or no effect on the denitrifying capacity of the wastewater. The high volatile solids (VS) content of the RBS sludge as compared to primary clarifier sludge, gave a higher methane potential in anaerobic digesters for the RBS sludge. The high caloric value of RBS sludge makes it attractive for incineration.