Preliminary Study On The Simultaneous Removal Of Nitrate And Arsenic From Water With Nature Pyrrhotite

The pollution of arsenic and nitrate in groundwater is becoming increasingly severe with the progress and development of the human society,which have drawn a widely public attention.In this research,the feasibility and efficiency of arsenic and nitrate removal in groundwater was investigated by natural pyrrhotite based on their physicochemical properties,which established a theoretical foundation for the technology of arsenic and nitrate removal simultaneously by natural pyrrhotite.Natural pyrrhotite exhibited excellent performance for As(V)via the adsorption experiments.Under the condition of 30 ℃,pH=4,30 mg/L,0.5g pyrrhotite obtained an adsorption efficiency as high as 99%of As(V)within 24 h.Higher temperature and particle size could promote As(V)removal.The Langmuir adsorption Isotherm model and pseudo-second-order model was more favorable to describe the process of As(V)uptake onto the adsorbents,and the maximum adsorption(qmax)was reached to 2.46 mg/g at the temperature of 30℃.The adsorption of As(V)by Pyrrhotite was an endothermic process through ligand exchange,with some chemical precipitation reactions at the same time.The batch experiment results showed pyrrhotite could be used for the coinstantaneous removal of nitrate and As(V)belonging to the prefabricate sewage by utilization of sulfur autotrophic denitrification bacteria.Under the condition of 30℃(bacteria inoculation quantity 5%,total volume 40mL),35 mg/L N03-N,30 mg/L As(Ⅴ),10g pyrrhotite,the removal efficiency of nitrate and As(Ⅴ)almost researched to 100%both by a combintion of pyrrhotite and sulfur autotrophic denitrification bacteria within 13 d.The smaller particle size of synchronous magnetic pyrite,the better the efficiency of As(Ⅴ)removal;The initial concentration of As(Ⅴ)showed no influence on denitrification.As(Ⅴ)removal performance increased with the increasing of temperature,while the denitrification efficiency reached the maximal level at 30℃.Ferric sulfate were generated as oxidation production by microorganism.Sulfurimonas as the dominant bacteria of mixed bacteria belonged to the sulfur-based autotrophic denitrification bacteria.Arsenic removal effect could be estimated by the removal rate of phosphate via the small filter experiments.With the inflow average concentrations of 6.36 mg/L,1.48 mg/L,0.39 mg/L,16.24 mg/L,respectively,the NO3-N,PO4-P,NH4-N,COD removal rate of P-CW and L-CW was 81.9%,93.8%,33.8%,49.5%and 62.2%,3.2%,38.4%,41.4%,respectively.So,the effects of nutrient and phosphorus removal by constructed wetland based on Pyrrhotite were higher than that based on limestone,while the treatment efficiency of ammonia nitrogen and COD were basically kept the same.P-CW obtained an excellent efficiency of PO4-P,so a similar performance for As could be speculated.The analysis of soil biological community in the both artificial wetland showed that the content of autotrophic and heterotrophic denitrifying bacteria content in Pyrrhotite artificial wetland were significantly higher than that of limestone artificial wetlands.