| Sewage sludge contains organic matter, nitrogen, phosphorus, potassium and trace elements. It can be used as fertilizer or soil conditioner to achieve the resource utilization. Meanwhile, desertification not only causes the degradation of the soil quality and the decline of productivity, but also restricts the construction and development of the local eco-environment. It would be a new way to combine the utilization of municipal sludge with the improvement of the degrading sandy soil. However, the contained heavy metal and organic contaminants in the sewage sludge are the factors limiting land improvement. Therefore, it is really necessary to research the risk of pollution during the utilization of sewage sludge. Korqin Sandy soil was chosen as study objects and the sewage sludge was collected from wastewater treatment plant of Shenyang. The major objective of this work was to investigate the impact of the dewatered sludge on soil and plants during the process of improvement. And combined with the comprehensive benefit analysis, was to provide the reference information for resource utilization of sewage sludge and improvement of degrading sandy soil.The results showed that the pH of the sewage sludge was weak alkaline and high level in moisture contents and dissolved salts. The contents of organism, total nitrogen, total phosphorus and total potassium were400-531g/kg,14.86-17.58g/kg,13.15-28.54g/kg and6.51-9.13g/kg, respectively. These data showed that it was significantly higher than manure (swine manure and cow dung), with high potential in land-use. The content of heavy metal in sludge in different wastewater treatment plants are variety because the source of the sewage, the capacity of wastewater treatment plant and the treatment processes. The highest content in the sewage sludge was Zn, varying from4285mg/kg to7154mg/kg which are all higher than the limits of standard. Moreover, in all the sewage sludge samples of three sewage treatment plants, tetracycline, sulfonamides, macrolides and quinolones were detected. The contents of norfloxacin and ofloxacin are the highest, with7.20-9.27mg/kg and0.18-0.85mg/kg respectively. Followed by tetracycline antibiotics, the content of oxytetracycline is0.40-0.85mg/kg. Combined all characteristics of the sewage sludge in all wastewater treatment plants, municipal sludge was taken as the material to improvement soil.A soil column leaching experiment showed that the different addition rates of the sewage sludge to soil significantly increased the content of nitrogen and phosphorus in topsoil and improved the sandy soil quality. The sewage sludge application rates had a significant effect on nitrogen and phosphorus concentrations in leacheate, but the leaching risk of nitrogen to groundwater was higher than that of phosphorus. The concentrations of total nitrogen (TN) and total phosphorus (TP) in leacheate after applying sewage sludge with30t/hm2had no significant difference compared with the control treatment. The nitrate concentrations were enhanced by11%-33%compared to the control treatment and there was not significant difference between them (P>0.05). The concentrations of nitrogen and phosphorus in leacheate after applied60t/hm2and90t/hm2were significantly increased (P<0.01). The nitrate concentrations were greater than the threshold values for Environmental Quality Standards for Ground Water in China after the third leaching, increasing a potential contamination risk to groundwater.And the application of sludge had an impact on the pH value, eventually stabilized at8.24-8.54. The Cu, Zn, Pb concentrations in leachate decreased as leaching times, it may not pose a risk to groundwater contamination. The soil column leaching experiment results showed that the pH in leachate was opposited to conductivity, and that the pH initially increased and then stabilized with the different addition rates of the sewage sludge to soil. The concentrations of Cd applied sewage sludge60t/hm2and90t/hm2increased with the fifth leaching times, the maximum concentration of Cd in leachate was3times than the control treatment. With the increase of rainfall, Cd accumulated in the top soil was a risk of migration to the subsoil. The results indicated that Cd had contamination risk during soil improvement.The heavy mental of Cd could decrease the concentration of nitrate nitrogen, ammonium nitrogen and nitrite nitrogen in the soil in1-3days. The influence of Cd in three days was the most obvious. And the changes of the concentration of the three forms of nitrogen trend toward a moderation. Oxytetracycline inhibited to the soil ammonification and the level of inhibition is related to the concentration of the oxytetracycline. The condition of10and25mg/kg ofloxacin could promote the nitrification and ammonification. The interaction between oxytetracycline, ofloxacin and Cd would influence on inorganic nitrogen transformation in the soil in a significant way.Application of sewage sludge significantly promoted the growth of Pennisetum alopecuroides. When the application rate was30t/hm2, the fresh weight and leaf area index of P. alopecuroides were3.07and2.33times compared to the control treatment, and then decreased with increased application rate. The concentrations of nitrogen and phosphorus in soil after applied sewage sludge were enhanced by1.23,2.13,7.10times and11.94%,44.78%,91.94%, compared to the control treatment. The uptake ability of P. alopecuroides to heavy metals was promoted, especially Cd, which was significantly different among treatments (P<0.05), while the Cu, Pb, Zn contents in P. alopecuroides were not significant. The transfer coefficient of Cu, Cd, Pb, Zn was less than1, indicating that the roots have the enrichment of heavy metals. Hence, the application rate of30t/hm2can effectively improve soil fertility and increase P. alopecuroides biomass.Analyses on the organic matter, N, P, K and other nutrient ingredients of sewage sludge, and the energy and economy showed that sewage sludge could be widely used in the future. The sludge application to the degraded soil improvement would be a good method. From the economic aspect, application of sewage sludge to degraded sandy soil was feasible, and it could achieve better economic efficiency and improve the ecological environment through scientific guidance and management. |
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