| In recent years, ecological engineering construction has intensified, and its main measure and key is vegetation restoration. The lands used for ecological restoration and reforestation usually are four types of wastelands, dried rivers, abandoned mines, deserted lands and so on, whose site condition is poor and soil lacks nutrients. The sludge contains nitrogen, phosphorus, potassium and organic matter, which are just nutrients necessary for plant growth. Therefore, the municipal sewage sludge could be widely used for forestation and ecological restoration in the future.Using sludge for ecological restoration is also one of the land use types. Now sludge land use is an efficient way of changing sludge into resources. But a large quantity of pollutants in the sludge limits its safety use, and how to use sludge safely is now a hotspot. For the secondary pollution question in the current sludge resource and sludge land use, we tested and laboratory anglicized the sludge's main components from sewage treatment plants in Beijing to systematic understand the physical and chemical properties of Beijing sewage sludge and heavy metals and other contaminants in it. Based on that, we used the sludge and compost from Gaobeidian sewage treatment plant and Panggezhuang composting plant for the field test of sludge application. We choose two types of soil in the experiment, sand soil and loam soil. The experiment contains three treatments and a control (ck). By leaching experiment, we can study the PH, nutrients, heavy metals change in the soil leaching filtrate after the application of fresh sludge and compost. By box plant experiment, we can study the plant growth characteristics and the impacts of nutrients and heavy metals on the plant, soil and water environment after the use of fresh sludge and compost. By pot experiment, we can study the impacts of the use of fresh sludge and compost on the trees growth, such as Amorpha fruticosa Linn, and the forest soil enzyme activities. The results can provide theoretical basis for the harmless use of municipal sewage sludge as resources and for ecological restoration. The main conclusions are:(1) The results of analyzing the characteristic of the nutrients, heavy metals, toxic substances and hazardous substances in the sludge from 18 sewage treatment plant and compost from 2 compost plant in Beijing show:Because wastewater sources and treatment processes differ among different sewage treatment plants, the content of nutrients and heavy metals and use value of sludge of different plants are different. The PH of Beijing sewage sludge is weak alkaline (6.71-7.51); the sludge has a high level of nutrient and the contents of organic matter, TN, TP and so on; the contents of heavy metals in sludge are generally lower than the national standards of both China and western countries; the contents of heavy metals in downtown sludge show a decreasing trend from 2001 to 2010, but the contents of heavy metals in suburbs sludge show seasonal differences, and the content of Cu, Zn and Ni is over standard.(2) For examining the possibility that take the sewage and sewage sludge as the matrix of soil improvement, the raw sludge and sludge compost were mixed with the topsoil (loam) and sand in different proportions (dry weight), respectively in 0%,2%,4%,6%. The results indicated that: after mixing the raw sludge and sludge compost with the topsoil and sand, the indicators of the pH, total nitrogen (TN), total phosphorus (TP), total Potassium (TK) of the soil leachate are more stabilized than the control treatment. So appropriately adding the raw sludge and sludge compost is helpful to maintain the soil nutrient. The N, P of the sludge are retained in the soil to replenish the N, P of soil and improve the fertility, which is good for the crop growth. Early the TK of the soil leachate is lower than the control experiment and later it is higher than the control experiment, but it meets the standard. The density of the heavy metal of soil leachate such as Pb, As, Hg, Cr and Cd were increased, which need our concern. But the risk of proper application of the sewage and sewage sludge to cause groundwater pollution is smaller.(3) Taking the indoor cultivation experiment of Spinacia oleracea Linn. with different application of compost in sandy loam soil, the result showed that: compost have significant promoting effect on Spinacia oleracea Linn, growth and the effect vary. The content of Cu, Zn and Cr of edible parts of vegetable has significant increase, but all were within the national food hygiene standards. The application of sewage had significant effect on the soil, that part was several times than the controlled, but it had no significant effect on the heavy metal of the groundwater. However, the application of sewage sludge and compost is different for different soil, which must be controlled in an appropriate range for the best soil nutrient status and the lowest effect to the soil heavy metal content. While the sewage sludge and compost have some advantages such as reducing the amount of sewage, reducing the amount of heavy metal and so on. And the transportation and application are very convenience which provides a new way to solve the municipal sewage.(4) Taking the experiment of trees potted under different proportion application of sludge and compost in loam and sand. The result indicated that: raw sledge and compost is advantage to the plant growth. The specific performance is that when the application of sewage is 10%-15%, it has significant effect on the tree height, crown width and diameter. Different soil has different adaptability to sewage and compost. When afforesting in land, the application of sewage within 20% will enhance the soil catalase activity and alkaline phosphates activity. While the application beyond 20%, it will inhibit the alkaline phosphates activity. When afforesting in loam,10%-15% application of sewage doesn't affect the catalase activity, and beyond 20% it will inhibit the hydrogen peroxide activity.
|
PDF Full Text Request