| With the development of science and technology,and the growth of population,the problem of land and energy shortage is becoming more and more serious.The demands of how to decrease the energy consumption,reduce the area of treatment facilities,and improve the efficiency during wastewater treatment process become more and more urgent.Compared with traditional biological nitrogen removal,simultaneous nitrification and denitrification(SND)has the advantages of shortening denitrification process,saving carbon source,reducing power consumption,decreasing the area of facilities,improving the processing capacity and simplifying the daily operation process.The key step to achieve SND is making aerobic denitrification stable and highefficiency.On the other hand,iron,as a necessary element for microbial metabolism,is one of the essential elements in the biological removal of nitrogen in sewage.Adding zero-valent iron or ironcompound matter to sewage treatment system to improve microbial metabolism and treatment performance is a new biological treatment method.This study explored the phenomenon and mechanism of enhancing biological nitrogen removal through rapid initiation of aerobic denitrification by zero-valent iron(ZVI).By adding ZVI into the aerobic nitrification system,it was verified that ZVI could rapidly enhance the nitrogen removal.Taking quick enhancement of nitrogen removal as a key point,it was demonstrated that ZVI played a major role in the initiation of aerobic denitrification.By exploring the influence of ZVI dosages on biological denitrification efficiency,the optimal dosage was get.Based on this,the contributions of the iron as electron donor,iron microbiologically influenced corrosion and siderophile bacteria community structure to the denitrification was investigated.At the same time,the mechanism of aerobic denitrification rapidly initiated by ZVI was further explored by metagenomics.Finally,the sequential batch biological membrane reactor enhanced by ZVI was used to treat the printing and dyeing wastewater produced in a printing and dyeing factory in Jiangsu province after mixing with artificial wastewater,so as to investigate whether the removal efficiency in this system can be enhanced by ZVI.The main conclusions are as follows:(1)The addition of ZVI could rapidly enhance the nitrogen removal efficiency,and the aerobic denitrification was initiated in 1-2 days.The nitrogen removal efficiency was kept at around 60%.(2)The optimal dosage iron scrap is 80 g/L.Compared with the addition of iron compound with other valence states of iron,the introduction of ZVI was the main reason for rapid nitrogen removal improvement.Besides,ZVI had a maintenance effect on the enhancement of biological nitrogen removal.(3)With microbiologically influenced corrosion,some denitrifying bacteria could use ZVI as electron donor,and nitrate as the final electron acceptor was reduced.Meanwhile,the new iron ion produced by corrosion could quickly stimulate microbial enzyme activity and bacteria metabolism,thus promoting the aerobic denitrification and improving the biological nitrogen removal.(4)The introduction of ZVI led to some sludge microflora migration in the spatial location,so that ferrophilic bacteria with higher denitrificaiton capacity could selectively be gathered in the iron-rich environment,which benefited the nitrogen removal.(5)Sequential batch biological membrane reactors introducing ZVI was used to treat printing and dyeing wastewater produced in a printing and dyeing factory in Jiangsu province after mixing with artificial wastewater.The results showed that the COD of effluent was stable at 60±10 mg/L.The total nitrogen in effluent of the ZVI-added system was lower,maintained at 15±5 mg/L.The biofilm system enhanced by ZVI still showed good removal of nitrogen.Therefore,ZVI is expected to enhance the biological nitrogen removal in printing and dyeing wastewater treatment. |
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