Effects Of Earthworms Activity On Heavy Metal Uptake And Bioavailability In Municipal Sewage Sludge

The excessive heavy metal has all along been the sticking point in soil application of municipal sewage sludge. The specific ecological functions of earthworm together with behaviours of its yellow cell uptaking heavy metals render the treatment and disposal of sewage sludge by earthworm not just conceivable but also viable. To begin with, Orthogonal test L16(45) of tetrad factors and tetrad horizontals in this paper was designed to identify the optimal combination of environmental conditions for the two earthworm treatment of sewage sludge(Eisenia andrei and Eisenia fetida). The best sawdust amendment rate, matrix humidity, ambient temperature, inoculation density for Eisenia andrei were20%,75%,21℃,24mg/g, respectively; as for Eisenia fetida, the case were30%,75%,14℃,32mg/g, respectively.Sewage sludge was artificially spiked with copper and zinc (in the fashion of chloride salts) in the second episode to investigate the foregoing two earthworms affinity for heavy metals as well as metal regulation in earthworms in the context of varying contamination scales. Results revealed that the surviving rate, growth rate and substrate consumption per day of both Eisenia andrei and Eisenia fetida tended to dwindle with the increasing of Cu/Zn concentrations in sewage sludge; And Cu/Zn concentrations in the two earthworms climbed to the peak when the introducing Cu/Zn concentrations stood at300/400mg/kg, afterwards gradually ebbing away, which unravelled Cu/Zn tolerance and regulation occurred in earthworms. In addition, Cu accumulation capacity of Eisenia andrei’ was better than Eisenia fetida, whileas with Zn, the converse was true.It is becoming more and more apparant that heavy metals’ bioavailability critically hinges on the chemical forms of heavy metals, or rather the labile fraction. The third part of experiments was geared to examine effects of different inoculation time scales(0、30.45、60、90d) on the bioavailability of Cu and Zn in sewage sludge. Results indicated that both Eisenia andrei and Eisenia fetida treatment lowered water-extractable and CaCl2-extractable fractions of Cu/Zn in the sludge as inoculation interval was45days; whereas these fractions were lifted when earthworm inoculation interval was90days. There was no significant alteration for exchangeable fractions of Cu/Zn in the sludge followed30days treatment by Eisenia andrei and Eisenia fetida, A decrease in the exchangeable fractions of Cu/Zn was found when earthworm inoculation interval stretch into45days; while the exchangeable fractions of Cu/Zn were significantly elevated in the wake of60and90days treatment.Lettuce that was seasonal vegetable and had comparatively large aerial biomass was adopted to carry out pot experiment in an effort to further examine the impact of earthworm activity on the bioavailability of Cu and Zn in sewage sludge by dint of the bioassay and penetrate the potential of soil application of slduge subjected to earthworms treatment, therby determining the best Eisenia andrei and Eisenia fetida inoculation time for the treatment of sludge. Results unfolded that the biomass of shoot and root in lettuce was markedly boosted by the application of sludge subjected to earthworms treatment, and the growing rate of shoot oupaced that of root; Cu/Zn concentrations in the root and shoot of lettuce overall gradually mounted as the extending of inoculation time; And the optimum inoculation time for sludge treatment by Eisenia andrei and Eisenia fetida was45days through the lens of heavy metals minimization and safety soil application of sludge.