Earthworm photophobic movement under different light conditions and quantitative analysis of mechanical separating vermicompost parameters

Abstract: The vermicomposting has shown to be efficient in processing the organic solid waste like crop straw, dump of poultry and municipal sludge. It is of necessity to separate the earthworm from vermicompost before resulting product is marketed and further developed. But the problems of labor and time intensity, which induce poor earthworm separating efficiency, are urgent to be solved in the stage of vermicomposting. The light separation method has been widely recognized and applied to separate vermicompost. After the earthworm disappeared in the vermicompost pile under the simulated light, there is fixed thickness of vermicompost near the pile surface that can be scraped out. In this way the pure vermicompost can be collected without hurting earthworm. Nowadays, for lacking mechanization and relevant quantitative parameters, the task of earthworm separation is still done by manual labor, which had a higher cost. In this study, the mature earthworms were evenly distributed on the surface of fixed mirco-vermicompost pile. Different monochromatic lights including white light, yellow light, green light, red light, and incandescent light, and the light intensity from 10 to 270 lx, were applied to investigate the earthworm photophobic movement. In order to compare the effect between natural light environment and artificial light, the controlled experiments of indoor light, outdoor light, and direct sunlight were conducted in real environment. The time all earthworms disappeared from the surface of mirco-vermicompost pile was measured and the layer without earthworm was collected. Typically, the study discussed the reason of forming the layer without earthworm through analyzing the pattern of illumination attenuation in the vermicompost. The result indicated that no matter what light qualities were, when the light intensity was less than 10 lx, the earthworm showed almost no reaction; when the light intensity changed from 10 to 30 lx, the earthworm showed weak photophobic reaction; when the light intensity changed from 30 to 210 lx, the extent of earthworm photophobic reaction got increased with the increase of light strength; when the light intensity was over 210 lx, the extent of earthworm photophobic reaction reached the maximum. The white light and direct sunlight had the most significant influence compared with the other light environments, and the disappearing time was 6.5 and 5 min, respectively. After disappearing for 5 min the thickness of the layer without earthworm reached 15 mm, showing no significant difference with other time gaps (10, 15 and 20 min) after disappearing. The red light exerted the weakest impact on earthworm, and the disappearing time was over 20 min in the experiment replicates under different light intensities. With the light intensity increasing, the disappearing time of earthworm dropped logarithmically. When it came to the application for the white light and sunlight with light intensity over 210 lx, 10-15 mm layer without earthworm could be formed. The study calculated the earthworm reaction and responding time under different illumination conditions, which can offer reference for earthworm cultivation. The results of disappearing time, light environment and the thickness of layer without earthworm can be treated as process parameters to provide reference for designing the separating machine.