Effect of Vermibed Height on Excess Sludge Treatment in Vermifilter

The height of vermibed is considered as an important factor in vermifilter. Parallel vermifilters with vermibed height of 30, 50, 70, 100 and 150 cm (defined as H30, H50, H70, H100, H150, respectively) were operated to determine the impact on excess sludge treatment. The physiological response of earthworms was also studied. H30, H50, H70 could run steadily, while H100 and H150 appeared phenomenon of sludge accumulated in vermibeds and could not function. A little decrease of protein in earthworm with the vermibed height increase from 70 to 100 cm and followed a significant decrease with the height increase to 150 cm were observed. The activity patterns observed for antioxidant enzymes of earthworm, characterized by a gradually little increase along the increase of vemibed height from 30 to 100 cm and subsequent a sharp increase with the height increase to 150 cm. For earthworm, the vermibed height 100 cm and 150 cm had bad effect on the growth of organism. Increasing the vermibed height from 30 to 70 cm, SS and VSS reduction rate and quantity increased remarkably. With a higher vermibed height, H70 were marked with SS and VSS reduction rate of 55.4-61.4%, and 69.87-73.56% respectively. Moreover, TCOD (total chemical oxygen demand) removal rate of vermifilters and the proportion of SCOD (soluble chemical oxygen demand) to TCOD in effluent took on an obvious increase with the increasing vermibed height from 30 to 70 cm, which was favored for hydrolysis effect and promote of microorganism activity.