Investigation of Sewage Sludge Stabilization in Vermifilters with Ceramic Pellets of Different Diameter

The filter media dimensions are the key design parameter in filter system. In this study, the ceramic pellets with diameter of 3-5 mm, 6-9 mm and 10-13 mm were employed in the vermifilters of D1, D2 and D3, respectively, for excess sludge treatment. The aim of this study was to optimize the diameter of filter media based on the stabilization degree of excess sludge and the corresponding physiological responses of earthworms living in the vermifilters. D1 was seriously clogged due to the flooding. In contrast, D2 and D3 operated steadily. Both the stable sludge stabilization and the favorable physiological response of earthworms were achieved in the vermifilter with the ceramic pellets of 6-9 mm in diameter, with the peak value of VSS reduction 65.3% was obtained. In contrast, the ceramic pellets of 3-5 mm in diameter had negative effect on the physiological responses of earthworms, with the earthworm biomass sharply reducing to 20.8 g/L. The niche in D3 favored the ecological and physiological adaptabilities of earthworm. The highest earthworm biomass (54.4g/L) was observed in D3. And the lowest CAT and POD activities were recorded in earthworms in D3. However, the VSS reduction decreased remarkably when the ceramic pellets of 10-13 mm in diameter were applied in the vermifilter. This was probably because that the large voidage was prone to sludge penetration in filter bed. So, the effluent VSS/SS in D3 was recorded as high as 65%.