The Study On Survival Characteristics Of Earthworm In Sludge Composting Environment And Its Effect On Sludge Degradation Efficiency

Sludge is an organic waste produced in the process of sewage treatment.Due to the complex composition of sludge,but at the same time sludge contains more nutrients and toxic substances,in order to reduce its impact on the environment and reduce the waste of resources,it is necessary to reduce the sludge harmless treatment.Earthworm composting is one of the best treatment methods in the harmless treatment of sludge in recent years.In this study,a sewage treatment plant sludge in Anhui Province was taken as an example to carry out earthworm survival experiment and sludge degradation experiment.In the experiment of earthworm survival,2%,4%,6%,8%and 10%biochar(rice husk carbon,straw charcoal,bamboo charcoal)were added to the sludge.The earthworm avoidance behavior experiment was used to explore the effect of biochar addition on the survival characteristics of earthworms.The physicochemical properties,TN and TP of sludge after adding biochar were determined to explore the environmental factors affecting the survival of earthworms In the experiment of sludge degradation,rice husk was used as additive,Eisenia foetida was used as earthworm,rice husk with different proportion(0%,10%,20%)and density(0 g/kg,13 g/kg,26 g/kg,52 g/kg,78 g/kg)were added into the sludge After the experiment,the physical and chemical properties,nutrient elements and heavy metals of the sludge were measured to compare the effects of different earthworm feeding densities on the sludge degradation performance.The conclusions are as follows:(1)In the experiment of earthworm survival,biochar alone increased sludge pH and organic matter,decreased sludge EC,TN and TP content;earthworm alone increased sludge EC and TN,decreased pH,organic matter and TP content;earthworm and biochar combined action reduced sludge EC,pH,organic matter and TP,and further increased TN content.It can be seen that the addition of three biochars further improved the effect of Earthworm on pH,organic matter,TN and TP,and changed the effect of Earthworm on sludge EC.(2)In the survival experiment of earthworm,the adaptability coefficient of earthworm first increased and then decreased with the increase of the proportion of three biochar.When the proportion of rice husk carbon,straw charcoal and bamboo charcoal were 6%,4%and 6%,respectively,the adaptability coefficient of earthworm reached the maximum value.And the earthworm adaptation coefficient was rice husk carbon>bamboo charcoal.Through stepwise regression analysis,it was found that straw charcoal could improve the adaptability of earthworms only by changing the pH of sludge,while rice husk carbon could improve the adaptability of earthworms in sludge by comprehensively improving sludge pH,EC and organic matter,so rice husk carbon might be more suitable for sludge composting with earthworms.(3)In the experiment of sludge degradation,the average weight gain of earthworm first increased and then decreased with the increase of rice husk addition ratio,and 10%rice husk addition ratio was the most suitable for earthworm growth.With the increase of earthworm dosage density,the average weight gain of earthworm first increased and then decreased.When the earthworm dosage density was 26 g/kg,the average weight gain of earthworm was the largest and the growth condition was the best.Under the same earthworm density,the contents of pH,EC,TN,TP and TK(total potassium)in sludge decreased gradually with the increase of rice husk addition ratio,while the content of organic matter increased gradually.Under the same rice husk addition ratio,with the increase of earthworm density,the contents of pH,organic matter,TN and TP in sludge decreased at first and then increased,the contents of EC in sludge increased gradually,and the content of TK increased at first and then decreased(4)With the increase of earthworm density,the total and available concentrations of the four heavy metals decreased at the same rice husk addition ratio.With the increase of rice husk addition ratio,the total amount of heavy metals in sludge decreased gradually,the available contents of Cu,Zn and CD decreased gradually,and the available contents of Pb decreased first and then increased.The results showed that the earthworm had the best passivation effect on Cu and CD with 20%rice husk,the earthworm had the best passivation effect on Pb with 10%rice husk,and the earthworm had the best passivation effect on Zn without rice husk.(5)In the sludge degradation experiment,with the increase of earthworm dosage density,the proportion of stable state content of Cu,Zn and Cd increased first and then decreased.Earthworm had the best passivation effect at the dosage density of 26 g/kg(20 earthworms);for Pb,the proportion of inactive form increased gradually with the increase of earthworm dosage density,The best passivation effect of Pb was obtained at the earthworm density of 78g/kg(60 earthworms).At the same earthworm density,with the increase of rice husk addition ratio,the activities of Cu and CD decreased,and the activities of Pb decreased first and then increased.However,the passivation effect of Earthworm on Zn was reduced,and the proportion of exchangeable Zn increased,while the proportion of residual Zn decreased.Figure[17]table[8]reference[121]...