Research On The Process Of S/Fe-co-dependent Autotrophic Denitrification By Paracoccus Denitrificans ZGL1

The nitrate pollution of water is an increasingly serious issue that is in dire need to be soveld.The denitrification process has been considered to be the most cost-effective way of water denitrification.Heterotrophic denitrification is not favored for high running costs result of high consumption of organic matter.Autotrophic denitrification processes,especially ferric-iron co-substrate?ie,ferro-sulphur as an electron donor?autotrophic denitrification,become more promising choices in industrial conditions for low operating costs,as the elimination of nitrate pollution is free of carbon source.In view of this,to elucidate the transformation laws and influencing factors of elements such as sulfur,iron and nitrogen involved in the co-substrate autotrophic denitrification process of ferro-sulfur,a strain named Paracoccus denitrificans ZGL1,which has the ability of sulphur autotrophic denitrification and iron autotrophic denitrification,was applied in this experiments.The pyrite and ferrous sulfide were used as co-substrate main electron donors to reduce nitrates.The main research contents and conclusions are as follows:With pyrite as the electron donor,the nitrate was completely reduced and the nitrite reached the maximum at 24 h.Subsequently,the nitrite decreased slowly,and was reduced completely at 900 h.The ferrous ion reached the maximum at 24 h and then descended slowly.The total iron increased rapidly during the first 200 hours and remained almost constant then.When using pyrite as electron donor,whether with EDTA or not,the increase of initial amount of bacteria would promote the reduce of nitrate and nitrite,when adding more pyrite,the reduction rate of nitrate varied only with little extent,while the reduction rate of nitrite increased significantly when 500 mM pyrite was added.When with EDTA,nitrate was completely reduced with the initial pH as 7 or 8,and the reduction rate of nitrite increased with the initial pH as 6;when without EDTA,the reduction rate of nitrate was relatively higher with the initial pH as 7 or 8,and the reduction comlpeted in 36 h,while the reduction did not complete with the initial pH as 5 or 9.Whether with EDTA or not,when with higher concentration of Fe²⁺,the reduction rates of nitrate and nitrite were higher.When with EDTA,when the concentration of sulfur ion increased from 0.2 mM to 0.8 m M,the reduction rate of nitrate and nitrite increased;when without EDTA,when the concentration of sulfur ion increased from 0.2 mM to 0.4 mM,the reduction rate of nitrate increased,and with the increased initial concentration of sulfur ion in the solution,the reduction rate of nitrite in the system became lower on the contrary.When with EDTA,the 2 mM NO₃^-in the system was reduced completely at 4 h when adding glucose,while it took 30 hours for the NO₃^-to be completely reduced in the the system without glucose.With the increased amount of glucose added,the reduction rate of nitrite also increased.When ferrous sulfide was used as electron donor,when with EDTA,nitrate was completely reduced and nitrite reached the maximum at 24 h.Subsequently,the nitrite decreased slowly,and was completely reduced at the 780 h.The concentration of ferrous ions and total iron increased with time.Their increments were almost the same,and their concentrations remained almost the same after 200 hours.When using ferrous sulfide as electron donor,the addition of EDTA had little influence on the reduction of nitrate,and had significant inhibiting effect on the reduction of nitrite.Whether with EDTA or not,the increase of initial amount of bacteria and ferrous sulfide would promote the reducing of nitrate and nitrite.When with EDTA,nitrate was completely reduced at 80 h with the initial pH as 7,and the accumulation of nitrite was relatively lower under acidic conditions;when without EDTA,nitrate was completely reduced at 50 h with the initial pH as 7,and the reduction of nitrate could be completed when the initial pH was between 5 and 8.When with EDTA,with higher concentration of added Fe²⁺,the reduction rate of nitrate was higher,and the concentration of nitrite in the system was lower;when without EDTA,when the added concentration of Fe²⁺in the system was respectively 20,30,40 mM,nitrate can be reduced at 12 h,and no nitrite was accumulated.When with EDTA,with higher amount of sulfur ion added,the reduction of nitrate became faster.When without EDTA,when adding 0.8 mM sulfur ion and 1.2 mM sulfur ion respectively,the complete reduction of nitrate took 48 hours,and the reduction of nitrite did not complete even after 250hours,but the concentration of sulfur ion was raised and the concentration of accumulated nitrite was lowered.When with EDTA,if compared with sodium acetate and trisodium citrate,glucose can promote the reduction of nitrate and nitrite by considerably larger amplitude.Sodium acetate and trisodium citrate can promote the reduction of nitrate significantly,but can hardly influence the reduction of nitrite.