Design Of Fermentation Tank And Improvement Of Hyperthermophilic Pretreatment Composting Of Agricultural Waste

China is the 3^rd largest agricultural country in the world with 8.8%of the arable land.It has become the world’s largest agricultural waste producer due to its rapid increase in agriculture production scale.There is a huge amount of organic matter in agricultural waste,but if this resourceful waste is not treated timely,it causes severe pollution to the environment.Unfortunately,the utilization rate of domestic waste resources is relatively low in China.The sustainable agricultural development and agricultural circular economy depend on promoting recycling and industrial development of agricultural waste.The traditional composting method of agricultural waste is an effective way of treatment with low cost and simple mechanisms,but it is limited in wide application.According to analysis of existing literature,thermal pretreatment-assisted fermentation tank composting of agricultural waste could be a promising technique to overcome disadvantages of traditional composting.This research project was mainly aimed at the resource utilization of the increasing agricultural waste.The primary objective of this research project was to develop a rapid fermentation technique for the production of quality enhanced compost.This research study includes the design of a well-controlled fermentation tank,study and improvement of hyperthermophilic pretreatment composting of agricultural waste.The main contents of this project are discussed below.The fermentation tank is designed based on research and analysis of aerobic fermentation technology and equipment at home and abroad.The fermentation tank structure consists of an agitation system,aeration system,heating system,insulation material,and control systems.Such systems provide the composting process with a semi-closed environment by monitoring various variables at values of needed levels.The main structure is designed,calculated,and checked according to requirements of use.The whole fermentation systems were modeled in UG19.0,and two-dimensional diagrams were drawn by using AUTOCAD-2020.The fermentation tank was manufactured in the university mechanical workshop.The designed fermentation tank is suitable for composting various agricultural solid wastes with strong universality.Recently,an innovating technology of hyperthermophilic pretreatment composting（HPC）of agricultural waste（mixture of poultry manure and corn straw）was studied and improved to overcome traditional composting shortcomings.The first study was completed by optimizing the HPC process with the help of the Taguchi technique and analyzing the effects of HPC on physio-chemical characteristics,heavy metals,material loss,macroscopic properties,and bacterial communities.The novelty in results/findings and the significance of the results are outlined as follows:（i）The most suitable HPC process conditions were 65°C temperature and 18 h time（E5）based on Taguchi analysis to obtain a stabilized compost in terms of physicochemical characteristics.（ii）Overall,HPC increased the C/N ratio in compost and decreased the moisture content as compared to feedstock.（iii）All physio-chemical characteristics and heavy metals of optimal compost（E5）were within the limits of the Chinese Standards of Organic Fertilizer（NY525-2012）.（iv）Elimination rates of volatile fatty acid and NH₄⁺-N were observed at 98%and79%,respectively.（v）Optimal conditions of HPC reduced the mass of feedstock,dry matter,moisture contents,TN,and TP by 78%,50%,93%,23%,and 41%of initial masses,respectively.（vi）Overall medium size particle distribution of E5 compost was observed under the macroscopic analysis.（vi）Deeper analysis of bacterial communities by Mi Seq illumine sequencing technique revealed that abundance of Bacillus and Sinibacillus enhanced in E8（75°C&18 hr）compost as compared feedstock from 22%to 28%and from 5%to&7%respectively,whereas the abundance of Galbibacter reduced from 11%to 0.7%.（vii）This research encouraged the thermal pretreatment process of agricultural waste composting and provided the base for its further improvement.To further improve thermal pretreatment of agricultural waste composting,hyperthermophile microbial agent was inoculated with feedstock during HPC and named this novel process as“Ultra-High Temperature Aerobic Fermentation（UHT-AF）pretreatment process.”In this second study,the process of UHT-AF pretreatment was optimized,and its mechanisms were illustrated by analyzing its effects on physio-chemical characteristics,changes in chemical composition,and physical structure.The novelty in results/findings and the significance of the results are outlined as follows:（i）The optimal UHT-AF process conditions were 75°C,15 hr,40 g/kg of feedstock（R5）based on Taguchi analysis with C/N ratio as target factor.（ii）Based on the spectroscopic indicator of Fourier-transform infrared（FTIR）and Scanning electron microscope（SEM）,differences in chemical composition and physical structure between feedstock and pretreated-product were characterized.Variations in different FTIR analysis peaks of feedstock and pretreated-product suggested an increase in aromatic components,a decrease in polysaccharide,and the degradation of lignocellulose and aliphatic structures.SEM analysis indicated a relatively looser structure with holes and location of apparent microbial communities of pretreated-product compared feedstock.（iii）Together,these results of FTIR spectral and SEM morphological characterizations and physio-chemical parameters suggested that UHT-AF could stimulate the subsequent composting process.Results of the previous study indicated that the UHT-AF pretreatment process is superior to HPC.In this study,the comparative experiments between UHT-AF-assisted subsequent high-temperature tank composting（HTC）and traditional aerobic tank composting（CCT）were performed to investigate differences in composting process by studying physio-chemical and biological compost maturity parameters,which would provide theoretical basis and technical support for HTC technology.The novelty in results/findings and the significance of the results are outlined as follows:（i）HTC produced mature compost 24 days from agricultural waste,whereas CCT was still ongoing.（ii）HTC could run at the hyperthermophilic phase of≥80°C,maintained for 10 days with a maximum value of 96.02°C on the 3^rd day,and thermophilic phase of≥60°C lasted for 20 days,which could promote degradation of organic matter and enhance compost maturity.（iii）At the end of 24 days composting process,TOC and TN in HTC were decreased by27%and 8%,respectively,while they were decreased by 23%and 17%in CCT,respectively.In the case of HTC,C/N decreased to 15.13,adjusted-moisture content decreased from～60%to35.5%,p H increased from 7.80 to 8.17,and GI reached 95%,whereas,for the CCT process,C/N reached only 18.34,moisture content reduced to 47.3%,p H increased from 7.32 to 8.75,and GI reached only 60%.（iv）These observations revealed that UHT-AF assisted fermentation tank composting is superior to traditional composting as HTC could improve the composting temperature,speed up the degradation of organic matter and enhance the compost quality and maturity,which resulted in higher composting efficiency and shorten the composting period compared to CCT,showing incomparable techno-economic advantages and great application potential for recycling agricultural waste.