Preparation Of Coffee Pectin Hydrolysate And Its Experimental Study As Denitrification Carbon Source

Nitrate nitrogen is a great threat to human health and ecological environment.In order to improve the denitrification effect in sewage treatment,it is often necessary to add carbon source,but the traditional carbon source has the problem of high cost.Pectin in coffee primary processing wastewater is a complex polysaccharide,and the hydrolysate containing monosaccharide produced by hydrolysis can be used as denitrification carbon source,which reduces the operating cost of sewage treatment plant and realizes the treatment of waste with waste.In this study,the pectin in coffee primary processing wastewater is taken as the research object.On the basis of exploring the hydrolysis conditions and mechanism of coffee pectin,the coffee pectin hydrolysate is used as the additional carbon source in denitrifying biological filter(DNBF)reactor to carry out continuous denitrification experiments,evaluate its feasibility as a denitrification carbon source,and analyze the microbial community structure in the system.The main results are as follows:(1)The optimum conditions of acid hydrolysis combined with enzymatic hydrolysis of coffee pectin are studied by single factor experiment and orthogonal experiment.The results shows that the optimum conditions of acid hydrolysis are hydrochloric acid concentration of 1 mol/L,hydrolysis temperature of 90℃ and hydrolysis time of 2 h.The optimum conditions of enzymatic hydrolysis are as follows:enzyme dosage of 250 U/mL,hydrolysis time of 3 h,hydrolysis temperature of 50℃and hydrolysis pH of 5.Under these conditions,the reducing sugar content in coffee pectin hydrolysate is 2620±23 mg/L.By analyzing the infrared spectrum,monosaccharide composition and relative molecular weight of hydrolysis products at different stages,it is concluded that the acid method mainly breaks the intermolecular glycosidic bonds on the pectin side chain,and the enzyme method mainly breaks the intermolecular glycosidic bonds on the pectin main chain.(2)Continuous denitrification experiments are carried out with coffee pectin hydrolysate as additional carbon source in DNBF,and the denitrification effect under different process conditions is analyzed and compared with sodium acetate.The optimal HRT of coffee pectin hydrolysate and sodium acetate as denitrification carbon sources are 1 h and the optimal C/N are 6 and 5 respectively.Under the optimum technological conditions,the biological denitrification effect of coffee pectin hydrolysate as denitrification carbon source is equivalent to that of sodium acetate,and the NO3--N in the effluent is stable below 1 mg/L and the removal rate is 97.13%.There is no obvious accumulation of NO2--N,and the denitrification capacity is 0.22 gN/gCOD.Using coffee pectin hydrolysate as supplementary carbon source to treat actual sewage,the TN in the effluent is stable below 1 mg/L,and the removal rate is 85.58%.All discharge indicators meet the national first-level A discharge.(3)The diversity and difference of microbial community structure between coffee pectin hydrolysate system and sodium acetate system show that the microbial richness and diversity in coffee pectin hydrolysate system are higher than those in sodium acetate system,and the similarity of microbial community structure between them is high.Comparing the differences of microorganisms in coffee pectin hydrolysate system and sodium acetate system at phylum level,class level and genus level,it is found that the microbial community structures in coffee pectin hydrolysate system and sodium acetate system are similar at phylum level and class level,with Proteobacteria,Bacteroidetes and Chloroflexi as the main components at phylum level,Betaprotebacteriaceae and Anaerolineae as the main components at class level.At the genus level,in addition to Thauera and unclassified_Anaerolineaceae,there are a large number of organic degradation microorganisms and denitrification microorganisms in the coffee pectin hydrolysate system such as Zoogloea,Ignavibacterium,unclassified_prolixibacitraceae and Longilinea,which ensure the denitrification effect of coffee pectin hydrolysate as a carbon source.