Nitrate Driven Sulfide And Ferrous Oxidation And Their Effect On Phosphorus Immobilization In Black-odorous River Sediment

The black color and odor problem phenomenon is a common polluted problem of river sediments in the South China cities.Moreover,the release of pollutants from the sediments into the overlying waters is the key reason of poor water quality.Researches had shown that the accumulation of sulfide and ferrous iron was the main cause of black color and odor problem in the sediments,and phosphorus was the key factor attributing to overlying water eutrophication.It had been repored that the addition of nitrate could effectively oxidize the sulfide and ferrous iron in the sediment and inhibit the release of phosphorus in the sediment.Therefore,nitrate addition was considered to be an effective apparoach for sediments odor control and for eutrophication inhibition of the river water body.However,it was generally agreed that the effect of nitrate(such as calcium nitrate)on phosphorus fixation could be attribute to the conbination of Ca2+ and phosphate producing Ca-P,while the effect of nitrate-reduction-driven iron and sulfur oxidation on shift of phosphorus form was less of studied.In order to further study the influence of iron-sulfur oxidation on the changes of phosphorus form in the treatment of black and odorour sediment,and verify the possibility of reuse of the oxidized sediments as a phosphorus sorbent for the wastewater,relavant experiments was conducted in this work.This study selected urban river black-odorour sediments as the research object.Then quantified sodium nitrate(with ratio R=N/(1.6*S+0.2*Fe))was added to separate the ferrous oxidation and sulfide oxidation in the sediments,and the effects of different oxidation stages on the change of phosphorus forms and microbial communited structure in the sediment were clarified,by which the mechanism of phosphorus fixation in the oxidized sediment was explained.The results of this study showed that:1)After the first batch of sodium nitrate addition with a ratio of R=0.5,sulfides oxidation was the main process during the sediment treatment.The oxidation rate of sulfide was about 75%,and the oxidation rate of ferrous iron was about 30%,indicating that when the nitrate was insufficient,the sulfide in the sediment was preferentially oxidized to the ferrous iron.In the second stage,the sodium nitrate was added at the ratio of R=2.0,nitrate was reduced mainly couplling with ferrous iron oxidation,with the ferrous oxidation rate of 86%.Both the sulfur-oxidation driven by nitrate reduction and the ferrous oxide oxidation process could change the sediment from a reduced state to an oxidized state.In addition,from the perspective of sediment color changed,while the color change of sediment was related to ferrous iron oxidation.Furthermore,there were significant differences in the microbial community structure between the sulfide oxidation process and the iron oxidation process,among which the Proteobacteria displayed the most obvious changes.2)The concentration of dissolved phosphorus in initial sediments was in the range of 2.9mg/L-3.7mg/L,while total phosphorus ranged from 2.9 mg/L to 3.8 mg/L,indicating that the main form of phosphorus in interstitial water was existed as dissolved phosphorus.After adding nitrate,the soluble phosphorous and total phosphorus in the interstitial water decreased to the range of 0.1mg/L-0.5mg/L,which suggested that both the sulfide oxidation and the ferrous oxidation process could remarkly reduce SRP and TP concentration in interstitial water.Moreover,inorganic phosphorus was the mainly compositions in inital sediments,in which Fe-P was the mian form.During the process of sulfide oxidation,the phosphorus form showed no obvious change,while for ferrous iron oxidation,the content of Fe-P and Na OH-P increased significantly.This revealed that the fixation of phosphorus during the nitrate reduction process was closely related to the ferrous oxidation process.3)The fitting of phosphorus adsorption during ferrous oxidation process and sulfide oxidation process could be described by the pseudo-second-order kinetics.While the adsorption isotherm could be fitted by the Langmuir isotherm.The adsorption rates of ferrous iron oxided sediments at 5g20°C,5g30°C,and 5g30°C were 128,714,and 175 g/(mg·min),respectively,and the saturated adsorption capacities were 82,104,and 78 mg/g,respectively.The adsorption rates of the sediment after sulfide oxidation at 5g 20°C,5g 30°C,and 5g 30°C were 6,26,8g/(mg·min),and the saturated adsorption capacities were 14,61,and 21 mg/g,respectively.Compared by the adsorption rate and saturated adsorption capacity,it could be found that sediment after ferrous iron oxidation showed a higher adsorption efficiency and temperature impact load.It indicated that the ferrous iron oxidized sediments was more suitable for the adsorption of phosphorus in wastewater..From the above results,it could be conclued that the immobilization effect of oxidized sediment on phosphorus was mainly related to the oxidation process of ferrous iron.At the same time,from the results of adsorption kinetics and isotherm,the oxidized sediments had the high potential of recycling use as an adsorbent to remove phosphorus from wastewater or overlying water in river.