Treatment Of High Concentration Nitrate Wastewater By Sulfur Autotrophic Denitrification Under Carbon Source Enhancement

At present,chlor-alkali wastewater,electroplating wastewater,coking wastewater and other industrial wastewater and landfill leachate contain a large number of ammonia nitrogen,nitrate nitrogen and other nitrogen pollutants,easy to cause water eutrophication and other problems.The traditional heterotrophic denitrification process requires the consumption of organic matter,so it is necessary to add additional organic carbon sources to the reaction system,and the reaction will produce a large amount of sludge,which increases the treatment cost.The sulfur autotrophic denitrification process does not require adding a carbon source.The CO₂emission of the reaction is less and the operating cost is low,but the reaction will produce acid and sulfate.If the two processes are combined,the alkalinity produced by heterotrophic denitrification can neutralize the acid produced by sulfur autotrophic denitrification and reduce the amount of sulfate production.At the same time,higher denitrification efficiency can be obtained.In this study,the sulfur autotrophic denitrification reactor is activated by elemental sulfur,the appropriate reaction stage is selected by controlling the concentration of HRT and inlet nitrate,and then the strengthening of carbon sources on the system’s denitrification ability is studied by adding different concentrations of organic carbon sources to the sulfur autotrophic reactor.The strengthening mechanism of the carbon source is preliminarily explored by comparing the operation efficiency of the reaction system before and after the addition of the carbon source and the changes in the community and abundance of microorganisms in the system.（1）When the water intake of the reactor NO₃^--N is 80 mg/L and HRT is reduced from 10 h to 4 h,the nitrate removal rate of the reactor is reduced from 99%to 92.31%.When HRT is 6 h,the control water inlet NO₃^--N is increased from 80 mg/L to 200mg/L,the removal rate of the reactor NO₃^--N is reduced to 78.51%,and the effluent NO₃^--N concentration is about 43 mg/L.At this time,the reactor NO₃^--N removal load is 0.63kg.NO₃^--N/（m³·d）.Add the theoretical carbon source of 2/5,3/5 and 4/5 to the reactor to remove the residual TN of sulfur self-contained effluent.The NO₃^--N removal rate increased from 86.16%to 98.95%,and the NO₃^--N removal load increased to 0.796kg NO₃^--N/（m³·d）.The added carbon source improves the denitrification ability of the system.（2）By comparing the ratio and amount of nitrogen removal of sulfur autotrophic denitrification and heterotrophic denitrification,we can see that the carbon source can not only strengthen the system,but also make heterotrophic denitrification take place,more importantly,the carbon source enhances the denitrification capability of autotrophic denitrification.With the increase of carbon source addition,the NO₃^--N removal amount of autotrophic denitrification increased from 157.01 mg/L to 176.24mg/L,the NO₃^--N removal amount of heterotrophic denitrification increased from12.51 mg/L to 21.65 mg/L,and the half-stage reaction rate constant of the reactor increased from 2.84 mg^1/2/(L^1/2·h)to 4.81 mg^1/2/(L^1/2·h),from the decrease of NO₂^--N peak value along the course of co-denitrification,it can be concluded that the addition of carbon source may accelerate the conversion rate of NO₂^--N in the reactor.Compared with heterotrophic denitrification,synergistic denitrification can effectively reduce the cost of wastewater treatment.（3）The analysis of the microbes in the system shows that adding carbon source can eliminate some of the non-essential inferior flora in the system,and reduce the diversity of microbes.Relative to sulfur autotrophic denitrification,at 4/5 theoretical carbon source dosage,the relative abundance of the denitrification dominant family Proteobacteria increased from 50%to 72%,and the sum of the abundance of autotrophic denitrifying dominant bacteria Thiobacillus and Sulfurmonas increased from 23.27%to 29.50%,the relative abundance of the dominant genus Thauera in heterotrophic denitrification was also increased,but autotrophic denitrifying bacteria dominated the total.