Effect Of Oyster Shell Powder On Reducing Nitrogen Loss During Aerobic Fermentation Of Municipal Sludge

Using additives in aerobic fermentation of municipal sludge to improve the quality of fermentation products is a research hotspot in recent years.As a cheap and easily available additive,oyster shell powder has been shown to effectively reduce nitrogen loss in aerobic fermentation of municipal sludge,but the mechanism of reducing nitrogen loss is not clear.In this experiment,oyster shell powder in different proportions was added to the aerobic fermentation reactor.By analyzing the changes of physical and chemical properties,nitrogen form transformation and enzyme activity,the effect of environmental factors on nitrogen loss in the process of aerobic fermentation of municipal sludge was explained.Then,based on16S r RNA high-throughput sequencing technology,the change law of bacterial community structure in fermentation reactor was deeply explored,and the main microorganisms that significantly affect nitrogen form conversion and nitrogen loss were identified through the correlation analysis of microbial community,enzyme activity and environmental factors.Finally,the nitrogen retention mechanism of aerobic fermentation of municipal sludge with oyster shell powder was revealed.The main conclusions are as follows:（1）Based on headspace gas chromatography,a new method for rapid and accurate determination of denitrifying enzyme activity（NR）in sludge was established,which greatly improved the experimental efficiency.After the samples were cultured at constant temperature for 12 hours,the denitrifying enzyme activity was indirectly expressed by detecting the peak area of NO₂ gas in the headspace bottle.The final results show that the method has good reproducibility and high accuracy,and the relative standard deviation is less than 5%.（2）The temperature of the four groups of materials in the aerobic fermentation process reached the requirements of harmless standard.The addition of oyster shell powder can effectively promote the degradation of organic matter,and the loss of TOC and TC in the pile after adding oyster shell powder is less,indicating that the addition of oyster shell powder can effectively retain the organic carbon in the sludge.Compared with CK group,OS group contains more humus,which can maintain the nutrient and structure of products,promote the decomposition of minerals and the release of nutrients in the reactor.（3）In the final fermentation products,OS group contains more TN,NO₃^-and Son,more available nitrogen and higher quality of fermentation products.Adding oyster shell powder can effectively reduce the ammonia emission rate and reduce nitrogen loss.The effect of OS15 group is the best,and the ammonia emission is reduced by 36.13%。Meanwhile,Spearman correlation analysis showed that the reduction of TN after adding oyster shell powder was greatly affected by T,TC and C/N.Moreover,the change of NO₂^-can be significantly affected by affecting the nitrification and denitrification intensity of the reactor.（4）The analysis of bacterial community structure based on 16S r RNA high-throughput sequencing technology showed that the addition of oyster shell powder created a good fermentation environment for the reactor,promoted the activity of aerobic bacteria,made microbial activities more intense,and significantly improved the species abundance and community diversity of aerobic fermentation products.In the early stage of aerobic fermentation,Actinobacteria and Firmicutes were the main species,while the species abundance of OS group was significantly higher than that of CK group;At the genus level,the main species Brevibacillus and Symbiobacterium are the branches of Firmicutes,while Actinobacteria,Brevibacillus and Symbiobacterium have good ammonia assimilation ability and can absorb ammonia.Thermobispora,Brevibacillus and Symbiobacterium were positively correlated with TN,indicating that these microbial communities had a significant impact on total nitrogen loss;At the same time,Brevibacillus,a branch of Firmicutes,has a significant correlation with NS,which can reduce nitrogen loss by enhancing the nitrification of reactor.Based on the study of the basic physical and chemical properties of fermentation reactor,this study defines the main environmental factors and microorganisms affecting the transformation of nitrogen forms in the aerobic fermentation process of municipal sludge with oyster shell powder,and defines the action mechanism of reducing nitrogen loss after adding oyster shell powder,which further confirms the feasibility of oyster shell powder,a cheap and easily available solid waste,as an additive in the aerobic fermentation of municipal sludge,It provides theoretical and practical reference data for the resource utilization of municipal sludge and oyster shell.