Study On The Characteristics And Potential Of Aerobic Composting For Sewage Sludge Recycling In Tibet Plateau

The yield of sewage sludge（SS）of Tibet is continuously increasing in recent years,making SS disposal in plateau area become a research spot in the field of environmental engineering.Composting technology can transform SS into fertilizer and thus showing significant potentials.However,due to the low oxygen content of plateau environment and the different microbial communities of SS from the plain regions,the application of SS composting technology to the plateau is facing severe challenges.In this paper,the SS from Tibet plateau region was used as raw material,the highland barley straw（HBS）and the compost were used as conditioning agents for composting,operation and maturation processes were investigated.The influence of different aeration rates on the basic physicochemical properties and the decomposing effect of SS composting in the plateau area was preliminarily analyzed,and the aerating scheme suitable for the plateau area was determined.The microbial community of SS in plateau and plain regions composting was studied,and the rule of microbial community structure succession was explored,which provides a theoretical basis for the effect on composting process.A water-waste-nutrient nexus analysis model was established to simulate and analyzed the economic and environmental impacts of the application of land use technology of SS composting in the plateau region.The main results are as follows:（1）Through the composting experiment of SS and HBS with different gradient aeration rate,the influence of aeration rate on composting and decomposing processes under the plateau environment was investigated.The results showed that all the composting groups could be successfully heated up and maintained at high temperature to achieve harmless SS disposal.At the end of the composting,the seed germination index of each group was around 104.89%～127.44%,and the compost was beneficial to plant germination and growth,thus realizing the resource utilization of the SS disposal.In the composting heating period,the experimental group with aeration rate of 0.42 L·min^-1·kg^-1 had the best heating effect,and the maximum temperature could reach 58.4℃.In the composting maturation period,the experimental group with aeration rate of 0.69 L·min^-1·kg^-1 had the best composting effect,and the humic acid extracted from the compost had the highest aromatization degree.The comprehensive evaluation index of SS composting in plateau region was put forward by principal component analysis.After the evaluation of each experiment,it was found that the aeration rate of 0.42L·min^-1·kg^-1 in the early composting stage and 0.69 L·min^-1·kg^-1 in the middle and late composting stage had the highest comprehensive evaluation index（0.84）,which was the optimal aeration scheme of plateau SS composting.（2）SS composting was carried out with compost from Lhasa and Tianjin as composting conditioner,and the diversity and structural changes of SS microbial community in plateau and plain regions during composting were studied by high-throughput sequencing technology.The results showed that the microbial community of sludge in plain area was more abundant in the early stage of composting,which was beneficial to increase the heating rate of compost.Streptomyces is the key bacteria to improve the decomposing capacity of SS in the plateau region.In the composting process,the microbial community of SS fungi in the plateau area was more abundant than that in the plain area.Coprinopsis was the absolute dominant fungus in the composting process.（3）Taking farmland,water body and sewage and sludge treatment system in Lhasa area as the research object,a water-waste-nutrient nexus analysis mathematical model was established,and the influence of SS composting with land use technology application in Lhasa area was simulated and analyzed with a simulation period of 20 years.The results showed that in the simulated period,compared with straw returning technology,SS composting with land use technology could effectively alleviate 61.11%of soil nitrogen loss,save 8016.32 t of nitrogen fertilizer application,and cost 4.4090 million yuan,with considerable economic benefits.However,the application of land use technology of sludge composting will lead to the increase of nitrogen discharged into local water bodies.In order to avoid eutrophication of water bodies,corresponding measures should be taken to reduce the nitrogen content in farmland overflow water.To sum up,this study explores the application of SS aerobic composting in the Tibetan plateau region and its potential for resource utilization,and provides scientific basis and data support.The research results can provide a new way for harmless disposal and resource utilization of SS in the plateau region.