Treatment Of Nitrate In Water By Sulfur Autotrophic Denitrification

In recent years,nitrate,as the main source of water environmental pollution,has become a dangerous factor affecting environmental quality and human health.Therefore,it is urgent to remove nitrate nitrogen from water.How to safely and efficiently remove nitrogen has become a hot research topic in modern water treatment technology.At present,the main methods of nitrate removal are physical method,chemical method and biological method.Among them,sulfur autotrophic denitrification system with sulfur as electronic donor has gradually become a research hotspot of scholars all over the world because of its low sludge yield,no additional carbon source,simple operation and low operating and management costs.The fillers used in traditional sulfur autotrophic denitrification process are composed of elementary sulfur particles and limestone particles in accordance with a certain volume ratio.The diameter of the particles is small and different.The diameter of the fillers can not be controlled and the volume ratio of the fillers can not be used as an accurate standard to measure the total amount of materials.In order to solve this problem,many new methods of filler fabrication have been tried,and the mass ratio has been taken as a new mixing standard.The hydrogen ion produced in the process of sulfur autotrophic denitrification reduces the pH of the system and results in a slow denitrification rate.Therefore,the suitable alkaline buffer material was also discussed in this study,and the shell powder and limestone with good buffer performance were used as the comparison.On this basis,the effects of various factors on the reactor efficiency were explored,and the sulfur autotrophic denitrification process was further improved.In this paper,a new idea is put forward for the production of fillers.The first one is to directly add alkaline materials as fillers,the second one is to mix sulfur and alkaline materials evenly in advance as fillers,and determine the best production method of fillers by comparing the denitrification effect through experiments.Then,the simulated wastewater was used to inoculate and acclimate the sludge.After the reactor was started successfully,the effect of sulfur limestone and sulfur shell powder on the treatment effect of the reactor was explored according to the principle of control experiment.Through the experiments,we can find that the filler made by mixing sulfur and alkaline materials in advance has better experimental effect.By comparing the experimental results of sulfur limestone and sulfur shell powder,we can get better experimental results of sulfur shell powder.The shell,as a solid waste,can be used as an alkaline material for sulfur autotrophic denitrification.Its effect is better than that of the traditional alkaline material limestone.It can provide reference for the development of sulfur autotrophic denitrification and help to reduce environmental pollution.The main factors affecting the process of sulfur autotrophic denitrification are filler diameter,dissolved oxygen,temperature,HRT,pH and influent NO3-N concentration.In this study,the six factors mentioned above were investigated and analyzed by using control variable method one by one.It was found that proper reduction of filler diameter and dissolved oxygen was conducive to denitrification process,and the reduction of HRT would lead to the decrease of reactor treatment effect.At the same time,the optimum denitrification temperature and denitrification pH of the system were determined to be 35℃ and 7.On this basis,response surface methodology was used to optimize the analysis of many factors,BBD test model was established,and the peak removal rate of NO3-N in the effluent of the reactor was predicted.The interaction of influent concentration,temperature,HRT and pH was deeply explored through 2D contour map and 3D surface map,and the optimal process parameters were obtained.The microbial community structure of sludge in different stages of the reactor was analyzed.The results showed that the distribution of microbial species in the reactor was different.In addition to Thiobacillus,which has been found to be involved in the process of sulfur autotrophic denitrification,several microbial species were found to be able to participate in the process,but Thiobacillus accounts for a high proportion of 8.4%in the system,which plays a major role in sulfur autotrophic denitrification.The suitable living conditions of functional bacteria in the system are different,and Thiobacillus is suitable for higher NO3-N concentration and more stable.Thiothrix and Sulfurimonas can survive under lower nitrogen concentration and faster water flow.