Study On Composting Of Dehydrated Slaughtering Sludge And Its Improvement Effect On Green Saline-alkali Soil

With the development of livestock and poultry industry in China,the production amount of slaughter wastewater have also increased greatly,and a large amount of slaughter sludge is produced along with the treatment of slaughter wastewater.Due to the huge output and complex composition of slaughter sludge,if not properly treated in time,it will cause serious impact on the surrounding environment and even pose a threat to human health.Slaughter sludge has high nutrient content and can be applied to soil as fertilizer or amendment after harmless treatment.With the release and implementation of the new standard NY525-2021 Organic Fertilizer,sludge has been prohibited as a raw material for agricultural organic fertilizer.However,the14th Five-Year Development Plan for Urban Sewage Treatment and Resource Utilization issued by the National Development and Reform Commission clarified that sludge harmless treatment can be used in landscaping and land improvement after meeting the relevant standards.Saline-alkali land is an important reserve land resource in China.Due to its high soluble salt content and high alkalinity,which is not conducive to the growth and development of plants,nearly 70%of saline-alkali land has not been exploited and utilized,and the large area of saline-alkali land with bad soil properties has seriously hindered the exploitation and utilization of reserve land resources and the sustainable development of ecological industry.In view of the above problems,this paper takes the sludge(hereinafter referred to as dehydrated slaughter sludge)produced in the treatment process of slaughter wastewater with different dehydrating agents as the research object,optimizes the aerobic composting technology.Compost products combined with aluminum sulfate were applied to green saline-alkali soil to explore the improvement mechanism and effect of different dehydrated slaughter sludge compost on green saline-alkali soil,and takes ryegrass as the test plant.The physiological indexes and plant nutrient content differences of ryegrass in saline-alkali soil under different improvement schemes were studied to verify the feasibility and effectiveness of the improvement schemes,in order to provide technical support for sludge resource utilization and improvement of saline-alkali soil greening.The main research achievements of this study are as follows:(1)Effects of initial C/N and dehydrating agent on the compost quality of dehydrated slaughter sludgeDehydrated slaughter sludge and corn straw without dehydrating agent were used as raw materials.By adjusting the ratio of raw materials,the initial C/N of the sludge was controlled as25:1,30:1 and 35:1,and aerobic composting was carried out respectively.The days when the temperature of the sludge was higher than 55℃during the whole composting process were 7d,9d and 5d,respectively.At the end of the composting process,the seed germination index of the three sludge composts were 91.6%,106.6%and 95.7%,respectively.All the three sludge composts could reach the standard of maturation,but the quality of the sludge composts with the initial C/N of 30:1 was significantly higher than that of the other two composts.The dehydrated slaughter sludge without dehydrating agent,the dehydrating agent polyacrylamide(PAM)and the dehydrating agent polyaluminum chloride(PAC)were used as raw materials.According to the initial C/N ratio of 30:1,the dehydrated slaughter sludge with dehydrating agent PAC was compared with the compost with dehydrated slaughter sludge with dehydrating agent PAC as raw materials.The p H and seed germination index of the three sludge compost were slightly lower,and the conductivity was slightly higher,but all the indexes of the three sludge compost met the standards of mature compost.(2)Improvement mechanism of dehydrated slaughter sludge composting on saline-alkali soil and technical optimizationWhen three kinds of sludge compost were applied to saline-alkali soil according to the application amount of 3.0kg/m2,soil colloid cohesibility was enhanced and soil p H decreased by 0.58～0.65.Soil bulk density,exchangeable Na~+,alkalinity and soluble salt content decreased by 9.2%～13.8%,15.1%～21.4%,9.5%～10.5%and 5.7%～8.8%,respectively.The physical and chemical properties of saline-alkali soil were effectively improved.The contents of organic matter,alkali-hydrolyzed nitrogen,available phosphorus and available potassium increased by 11.2%～13.6%,168.8～178.7%,131.9%～142.4%and 38.6%～43.0%,respectively.The soil nutrient content of saline-alkali soil increased significantly.The results showed that the compost with dehydrated slaughter sludge PAC as raw material improved the physical and chemical properties of saline-alkali soil better than the compost with dehydrated slaughter sludge without dehydrated agent and dehydrated sludge with dehydrated agent PAM.Compared with the single application of sludge compost,soil colloid cohesion was further enhanced and soil p H decreased by 0.46～0.75 after applying 0.3kg/m2 aluminum sulfate.Soil bulk density,exchangeable Na~+,alkalinity and soluble salt content decreased by 7.0%～7.1%,8.8%～10.1%,6.9%～10.5%and 16.8%～19.8%,respectively.Soil physical and chemical properties were further improved.Soil organic matter,alkali-hydrolyzed nitrogen,available phosphorus,available potassium and other nutrient indexes had no significant difference.When the compost made from dehydrated slaughter sludge with dehydrating agent PAC was combined with aluminum sulfate,the improvement effect of salt-alkali soil was the best.Compared with the salt-alkali soil without any improvement measures,the p H decreased by 1.34.Soil bulk density,exchangeable Na~+,alkalinity and soluble salt content decreased by 16.9%,28.3%,21.3%and 26.1%,respectively,and soil nutrient content increased significantly.(3)Study on the effect of dewatering slaughter sludge composting to improve saline-alkali soil on plant growthBy comparing the physiological indexes and plant nutrient content of ryegrass planted in saline-alkali soil with different treatments,it was found that when the compost of dehydrated slaughter sludge with dehydrating agent PAC was combined with aluminum sulfate on saline-alkali soil,the growth form of ryegrass was the best,and the contents of total nitrogen,total phosphorus and total potassium of the plants were the highest.Compared with the saline-alkali soil without any improvement measures,The emergence rate,plant height,root length and biomass of ryegrass were increased by 91.7%,72.4%,105.4%and 128.0%,respectively.The contents of total nitrogen,total phosphorus and total potassium were increased by 20.9%,60.2%and 22.8%,respectively,which fully verified the feasibility and effectiveness of the improvement scheme.It provides technical support for sludge resource utilization and saline-alkali soil improvement.