Effect Of Large Wetland Plants And Tea Saponin On Excess Sludge Aerobic Composting

With the development of China’s high-speed urbanization and rural modernization,the total amount of excess sludge is increasing year by year.It is urgent to treat excess sludge safely and effectively.Aerobic composting is widely used in the treatment and disposal of excess sludge.However,in the traditional excess sludge composting process,there were often shortcomings such as low fermentation temperature,low degree of material humification,and poor nitrogen fixation effect.In order to solve these problems,it was necessary to add various compost conditioners to optimize the compost structure and improve the compost conditions,thereby improving compost efficiency and quality.In recent years,the promotion of sewage treatment technology in constructed wetlands has produced a large number of large wetland plants every year.How to solve these wetland plants has become a new problem.At the same time,the biosurfactant tea saponin has been confirmed to have certain application potential in improving microbial activity,promoting lignocellulose degradation and controlling pollutants.Therefore,the combined aerobic composting of large wetland plants and tea saponin as conditioners and excess sludge not only provides a sustainable management solution for the treatment and disposal of large wetland plants and excess sludge,but also provides a new way to further improve the efficiency and quality of excess sludge composting.In this study,two experiments were conducted to explore the effects of large wetland plants and the biosurfactant tea saponin(TS)as conditioners on excess sludge composting.To explore the effects of particle size of Triarrhena lutarioriparia on excess sludge composting,the changes of composting process parameters,material parameters and total and form of heavy metals were measured,and the humus and functional groups of the compost materials were characterized by spectral and thermal analysis.Then,the relationship between environmental parameters and heavy metal speciation was evaluated by redundancy analysis.The results showed that with the decrease of the particle size,the thermal insulation capacity of the pile increased,the maximum temperature increased,the time of thermophilic stage prolonged,and the maximum temperature area in the pile transferred to the lower layer.Meanwhile,the reduction of particle size promoted the degradation of organic matter,material maturity and nitrogen fixation effect in sludge composting process.Compost had a good effect on the passivation of heavy metals in excess sludge,especially Cd,Cu and Pb.The passivation effect of Cd and Cu was FM>CM>MM,and that of Pb was CM>FM>MM.The results of FTIR,EEMs and TGA confirmed that the content of aromatic structure and humus of FM was the highest at the end of composting.The redundancy analysis showed that MM was beneficial to improve the internal uniformity of pile.To explore the effects of tea saponin(TS)on excess sludge composting,the changes of physicochemical parameters,organic matter degradation and microbial community structure were measured.The results showed that compared with CK,the addition of TS prolonged the thermophilic stage of compost,and promoted the degradation of TOC and DOC.In terms of lignocellulosic degradation,the addition of TS significantly increased the degradation rates of hemicellulose and cellulose.The results of EEMs showed that the addition of TS improved the humification degree of compost products,and the TS addition of 5%had the best effect.In addition,the addition of TS significantly changed the community structure of bacteria and fungi during composting.In the thermophilic stage,the relative abundance of Firmicutes in TS treatments was higher than that in CK,while the relative abundance of Ascomycota was lower than that in CK.In the mature stage,Bacteroidetes were more abundant in CK,while Ascomycota were lower than those in the TS treatments.Redundancy analysis showed that adding TS significantly affected the bacterial community structure(mainly Firmicutes)in the composting process.These results suggested that the addition of TS provides a feasible strategy for improving excess sludge composting process and efficiency.