Responses of earthworm to the electric stimulation and the parameter quantification of its stress separation from earthworm dung

Abstract: Earthworm composting can serve as one type of agricultural waste treatment to combine with conventional composting with biological digestion. The earthworms can be selected to decompose the organic matter. The 'ecological interface' of earthworm composting has been utilized to optimize the earthworm culture using the large-scale breeding equipment, particularly for the harmless, reduction and recycling of agricultural wastes. However, a perfect balance needs to be gained between the short mature period of earthworms, and the large output of earthworm and earthworm dung. The separation can be the key link to harvesting the earthworm products and earthworm dung organic fertilizer. Electric stimulation can be used to separate using the instinctive reaction of earthworms with less harm. Once the electric stimulation is directly applied to the material carrier where earthworms are, the earthworms can be actively driven to leave the growing environment. There was no harm to the health of earthworms, and no secondary pollution to the environment, synergistically coupled with the breeding equipment in practice. Therefore, it is a high demand to clarify the separation process for the rapid design of the separation facility. In this study, a systematic investigation was conducted to determine the response of the separation rate of earthworms to the mode, intensity, and duration of electric stimulation, the water content of the carrier, and the material thickness. An evaluation was made to clarify the effects of electric stimulation on physiological and biochemical indexes of earthworms. The results show that electrical stimulation promoted the separation of earthworm and dung, where the intermittent electrical stimulation presented a better separation performance than the continuous. The earthworm separation rate was significantly correlated with the intensity of electrical stimulation under the intermittent mode, the circulation cycle time of power-on and power-off, as well as the times of power-on. The optimal moisture content of the material carrier was 52.6% for the earthworm growth. The smaller the material carrier thickness was, the better the earthworm separation rate was. Electrostimulation treatment had no significant effect on the contents of catalase, superoxide dismutase, acetylcholinesterase, cellulase and soluble protein in earthworms, but significantly increased the content of malondialdehyde. After 5 days of recovery domestication, the content of malondialdehyde could be restored to the level of control treatment. Consequently, the earthworm can be separated by intermittent electrical stimulation, in terms of the separation rate and the technical parameters. An optimal combination was achieved, where the intensity of electrical stimulation was 2mA, the on-off cycle time was 30 s, and the power-on time was 1s. The earthworm separation efficiency reached about 85% after 30 minutes of electrical stimulation, where the water content of the material carrier was about 50%, the material thickness was 20-25 cm, and the auxiliary 210 lx white light. The finding can provide strong support to the equipment application for the rapid and efficient separation of earthworm and earthworm dung during agricultural waste treatment