Experimental Study On Denitrification Performance Of Sulfur Autotrophic Denitrification Filte

At present,the tailwater of conventional sewage treatment facilities contains a considerable concentration of nitrogen,and most sewage treatment plants still face the need for further nitrogen removal.Traditional biological denitrification relies on the addition of external carbon sources,and the cost cannot be ignored.Sulfur autotrophic denitrification uses sulfur as an electron donor,and under the action of sulfur autotrophic denitrifying bacteria,nitrate nitrogen can be converted into nitrogen to achieve nitrogen removal.However,at present,the sulfur autotrophic denitrification process technology is not mature,some reaction mechanisms are not clear,and the technical parameters are not clear.Therefore,in this experiment,a sulfur autotrophic denitrification filter was constructed,with sulfur elemental as electron donor,activated carbon,activated carbon and limestone as the packing materials of the two reactors,which played a role in improving the operating efficiency,and the effects of nitrate nitrogen concentration and hydraulic residence time on nitrate nitrogen removal,nitrogen and ammonia nitrogen accumulation and pH value were studied and analyzed,and the denitrification efficiency of different packing reactors was compared,and scanning electron microscopy and high-throughput sequencing were used to study from a microscopic perspective.Therefore,the operating efficiency of sulfur autotrophic denitrification filter was investigated.The main findings are:（1）Sludge domestication was carried out under environmental conditions of 30±2℃,the original granular sludge,culture liquid and sulfur particles were added to the 5 L beaker,and after 30 days,sulfur autotrophic denitrifying sludge was successfully domesticated,and the nitrate nitrogen removal rate could reach 80-90%.（2）The sludge,sulfur element and filler completed by domestication are mixed evenly,and the two reactors are added to enter the reactor start-up stage,the formation of biofilm in the activated carbon reactor takes about 25 d,and the formation of biofilm in the activated carbon-limestone reactor is relatively fast,about 20 d,and the removal rate of more than 95%can be reached by both reactors after about 40 days.The concentration of nitrous nitrogen effluent of the two reactors is maintained at a low level at this stage,among which the concentration of nitrous nitrogen effluent of the activated carbon-limestone reactor is higher than that of the activated carbon reactor,which is due to the high pH value of the activated carbon-limestone reactor,the activity of nitrite reductase is affected,and the removal rate of nitrite is reduced.（3）During the operation stage of the reactor,the nitrate nitrogen removal effect of the activated carbon-limestone reactor is more stable,the optimal influent water concentration is about 20-40 mg/L,and the optimal hydraulic residence time is 4 h and above.The nitrate nitrogen removal rate of the activated carbon reactor is greatly affected by the nitrate nitrogen concentration and hydraulic residence time of the influent water,the optimal influent concentration is about 20 mg/L,and the optimal hydraulic residence time is 8 h.The accumulation of nitrous nitrogen in both reactors was less affected by the concentration of nitrate nitrogen in the influent water,and the concentration was below 1 mg/L.At the same time,when the concentration of nitrate nitrogen in the influent is too high and the hydraulic residence time is too long,the occurrence of DNRA reaction will cause the ammonia nitrogen concentration of the effluent of the two reactors to be too high,which will not meet the effluent standard.The nitrous nitrogen concentration and ammonia nitrogen concentration in the effluent of the activated carbon-limestone reactor are higher than those in the activated carbon reactor,the reason is that sulfur autotrophic denitrification is an acid-producing reaction,and the addition of limestone as a filler neutralizes the H⁺generated by the reaction,so that the pH value in the reactor is maintained at about 7.5,which is higher than the pH value in the activated carbon reactor,although the removal rate of nitrate nitrogen is improved,making the removal effect more stable,but it also leads to the accumulation of nitrous nitrogen and the DNRA reaction is more likely to occur.SO₄^2-was generated by sulfur autotrophic denitrification at the same time,and the actual amount of SO₄^2-was lower than the theoretical generation due to the presence of some heterotrophic denitrifying bacteria,but when the nitrate nitrogen removal was high,the amount of SO₄^2-was also higher,which could not achieve a good effluent effect.（4）Through scanning electron microscopy,the microbial morphology inside the reactor of the two filters can be observed,mainly bacillus breve and coccus,the length of bacillus breve is about 1μm,the body is without flagella,and the growth condition in the two reactors is good and the number is large.Using high-throughput sequencing for microbial community analysis,from the Alpha diversity index and the number of OTUs,it can be known that the community diversity in the two reactors is good,and has certain similarity,the abundance of Proteobacteria in the phylum level is the highest,and its abundance in activated carbon reactor and activated carbon-limestone reactor is 20.24%and 25.80%,respectively.The abundance of Sulfurimonas,among which the abundances of Thiobacillus in activated carbon reactor and activated carbon-limestone reactor were 19.69%and 14.05%,respectively,and the abundance of Thiomoons was 5.52%and 12.76%,respectively,and the above communities played an important role in the denitrification process.