| For earthworms have the trait of accumulating heavy metals, this experiment treated sewage sludge by earthworms in order to study whether earthworms can absorb and accumulate certain heavy metals and whether they can affect the conformations of heavy metals in sewage sludge. What's more, to afford methods of using treated sewage sludge in agriculture, potted plant was studied whether it could validate the effect of sewage sludge treated by earthworms. The results are as follows:1. After earthworms living in sewage sludge for 60 days, the total weight of earthworms increased. But the increment of earthworms in sewage sludge with high heavy metals is little. The domino effect equation between the increase rate of earthworm weight and the concentrations of Cu, Pb, Cd and Zn in sewage sludge is that f=38.883-0.471Cd+0.001Cd2-5.022Zn+0.005Zn2+3.918Pb-0.003Pb2-0.346Cu (R=0.94, f=8.97*) . Comparing the partial correlation coefficient of the weight increase rate of earthworms and the concentrations of Cu, Pb, Cd and Zn in sewage sludge, the results show that the minus effect of four heavy metals in sewage sludge on weight increase rate of earthworms is Pb>Cu>Zn>Cd.2. The earthworms could live in the sewage sludge of high contents of Cu, Zn, Mn, Mo and Fe, could absorb but not accumulate these heavy metals in sewage sludge. When the contents of Pb, As, Cr and Cd in a certain value, the earthworms could accumulate them. The correlation between the concentrations of Cu, Cd, Mn, Cr, Mo and Fe in earthworms and sewage sludge is not remarkable, while the correlation coefficients between the concentrations of Pb, Zn and As and in sewage sludge are 0.967, 0.989and 0.891 respectively, and the correlation is remarkable.3. The tested sewage sludge is acid. The research indicated that the earthworm treatment could increase pH value of sewage sludge relatively. The earthworm treatment could accelerate the process of decomposing the organic matter and increase the transform of total nitrogen in sewage sludge, and as time went on, the concentration of organic matter and total nitrogen decreased, while the concentration of available nitrogen and available phosphor increased. Earthworm treatment had no remarkable effect on total potassium, total phosphor and available potassium in sewage sludge. As a result, earthworm treatment can increase the fertility of sewage sludge.4. With the concentrations of heavy metals in sewage sludge increasing, the concentrations of all form metals increased. While the percents of exchangeable leaddecreased and the percents of unavailability lead increased. The percents of exchangeable copper, zinc and cadmium increased, while the percents of unavailability copper, zinc and cadmium decreased. As time went on, the concentrations of exchangeable zinc, lead, chromium, manganese and arsenic decreased and the concentrations of unavailability zinc, lead, chromium, manganese and arsenic increased. While the concentrations of exchangeable copper increased and the concentrations of unavailability copper decreased. Time of treatment had no remarkable effect on the concentrations of different forms of copper. Earthworm treatment could decreased the concentrations of exchangeable copper, cadmium, zinc, lead, chromium, manganese and arsenic, and increased the concentrations of unavailability copper, cadmium, zinc, lead, chromium, manganese and arsenic.5. The effect of sewage sludge application on the yields of cabbage is related to the concentrations of heavy metals in sewage sludge. Applying sewage sludge with high concentrations of heavy metals decreased the yields of cabbage. Applying sewage sludge treated by earthworms increased the yields of cabbage more than that applying sewage sludge untreated by earthworms. The concentrations of nitrate-nitrogen in cabbage applying sewage sludge were more than the controls. Except the concentrations of nitrate-nitrogen applying sewage sludge with highest concentrations of heavy metals were more' than the regulation, the others were less than the regula...
|
PDF Full Text Request