| Land use is an effective method of sewage sludge resource utilization. While heavy metals, PAM and other substances would be brought into soil in the process of sewage sludge land use, and these substances would remain in the soil for a long time. As a result, some environmental risks indeed exist in the soil. On one hand, soil properties might be changed, the growth of soil fauna and flora and the quality of agricultural products might be affected. All of these would ultimately damage human health through the food chain. On the other hand, the water environment would be affected when these substances migrate with the precipitation along the shower drain. In this thesis, the impacts on biological growth and the environmental risks was studied by simulating the process of municipal sewage sludge land use through the plant pot experiment, earthworms toxicological tests and leaching experiment. The main results were shown as followed.a. Heavy metals and PAM had significant impacts on the growth of plants in sewage sludge. Doping an appropriate amount of sludge could promote plant growth, while the plant growth will be inhibited if overabundant sludge is doped into the soil. For the experimental plant, festuca arundinace and brassicachinensis L., municipal sewage sludge application rate should be controlled to below 5%.b. Municipal sewage sludge had quite obvious impact on earthworm survival and reproductive capacity. For the samples of sewage sludge, the main factor affecting the survival of earthworms was heavy metal Cu, and the main factors affecting earthworm reproduction capacity were heavy metals Cr, Ni, Cu, Zn, Cd and Pb. PAM also had some influence on the propagation of earthworms. Mixed soil doped with municipal sewage sludge in an appropriate amount had not significant inhibition on earthworms' growth within a certain time. However, it showed a certain inhibitory till late in the experiment, which due to the reducing of nutrients, and the chronic poisoning accumulation of heavy and PAM.c. Plants had a strong capability of enriching heavy metals. festuca arundinace tended to enrich Cr, while brassicachinensis L. prefer to enrich Ni, Cd and Zn. Obviously, the mixed soil doped with municipal sewage sludge might pose a safety risk to human's healthy as a result of heavy metals enriched in plants entering the human body directly or indirectly.d. The content of heavy metals in the leachate was increased with the increase amount of sewage sludge incorporation, and it also related to the activity of the heavy metals. Relatively high concentrations of PAM could also be detected in the leachate, which up to 81.28 mg·L-1 at most. The long-term application of sewage sludge would inevitably lead to the increase of the content of heavy metals and PAM in soil, which likely resulted in the excessive content of heavy metals and PAM in surface water and groundwater. Then, it might be a serious security risk to surface water and groundwater.e. Controlling the amount and frequency of application of municipal sewage sludge, and selecting the appropriate plant might reduce the risks on the food chain and water environment in the process of municipal sewage sludge land use. The risk of PAM, contained in municipal sewage sludge, posed to environment, should also be concerned. |
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