The Primary Exploration For Dried Sludge Improvement And Plant Growth In Saline Alkali Soil

The environmental pollution problem is getting worse as the fast development of economic.A large number of countries construct sewage treatment plants, but the sewage treatmentprocess will generate much sludge which fails properly dispose. The sludge will result thesecondary pollution problem. The dispose of sludge faces the dehydration technologyproblems because it has high water content. Existing drying process has many issues such ashigh input and energy consumption, etc. The spray drying process with less investment, lowenergy consumption, high evaporation rates, etc., has become one of the hottest researches.The experimental sludge is living sludge from the Huaming sewage treatment plant ofJinghai. Studying the properties of sludge dried by the spray drying process showed: theindicators were in line with the results of urban sewage treatment plant mud GB/T24188-2009, municipal wastewater treatment plant sludge disposal farm mud-B class CJ/T309-2009and municipal wastewater treatment plant sludge disposal land improvement muddyGB/T24600-200; The pH of sludge was7.66, and it maintained the nutritional content of theoriginal mud. The moisture content of sludge was40.55%. Therefore, the improvement ofsaline-alkali soil by the dried sludge could reduce soil pH and increase nutrient content. Thisis a more economically and viable way. In this study, the dried sludge was added to alkali soilin different proportions. The experiment included the leaching, pot and field experimentswhich needed to measure leaching, soil indicators and plant growth conditions to find thesludge application range. In this range, the sludge could meet standards, and it could improvesoil and promote plant growth.The leaching experiments showed: The pH of these processes which were mixed thedried sludge was lower than the control. The application rate of the dried sludge should notmore than1:5(the content of sludge is16.67%), because the content of the salt andphosphorus were in line with the irrigation water quality standards; the content of nitratenitrogen was in line with the class Ⅲ of ground water standards; The comprehensivepollution index of heavy metals(As、Cd、Cr、Cu、Ni、Pb、Zn and Hg) were less than1, andthe factors on the risk of potential contamination of environment was small.The pot experiment showed: With the increase of dry sludge application, the pH of soildecreased and the nutrient content of soil were significantly increased; The ratio of1:3in saltcontent increased to0.47%, it belonged to a severe saline soil. The salt content of the otherswas between0.2~0.4%, it belonged to a medium saline soil. The pollution levels of heavymetal were mild in the sludge-soil of1:3, the content of other treatments had no pollution andgrowth of the plant was higher than the blank. And plants were growing well in thesludge-soil of1:9. In this processing, the plant height and root diameter of Euonymushamitonianus was31.71%and42.29%higher than the control, The plant height and rootdiameter of Koelreuteria paniculata Laxm was36.23%and33.86%higher than the control.The fitting curve of height and root diameter growth about different plants showed that theratio around1:9could promote the growth of different plants to the greatest degree.The field tests showed that the dried sludge could significantly improve the properties ofsaline soil. With the increasing application rate of the dried sludge, the soil bulk density wasdecreased and the capillary, non-capillary porosity and field capacity of the soil wereincreased. During sampling, the pH of the soil mixed with the dried sludge was always lowerthan the blank, and the concentration of various heavy metals declined in varying degrees. Inthe sampling of november, the content of salt in the treatments which were mixed the driedsludge was only0.01to0.06percent higher than the control. The content of the organic matter,available nitrogen and rapid available phosphorus were at least5.05g/kg,138.94mg/kg and 23.73mg/kg higher than the blank. The survivals of plants in the mixed sludge treatmentplants were20%higher than the blank. In the early application of sewage sludge, the growthof plants was inversely proportional to the amount of sludge. With the nutrients in sludgereleased, the longest branch of three plants in the treatment of1:8was slightly longer than therest of the application of sewage sludge treatment. Lagerstroemia indica, Euonymushamitonianus and Koelreuteria paniculata Laxm’s root diameter and plant height were91.04%、35.24%，68.45%、62.31%，54.88%、71.04%higher than the blank. The fitting curveof height and root diameter about different plants showed that the ratio of1:8~1:10couldpromote the growth of different plants to the greatest degree.