Property And Efficiency Of Simultaneous Biological Removal Of Ammonium-Nitrogen And Sulfate From Wastewater

With the development of industry and agriculture, a great deal of wastewater containing either ammonium-nitrogen or sulfate and organic carbon has been discharged into nature waterbodies. The water pollution around the world is becoming serious. The removal of ammonium-nitrogen and sulfate has been one of the research hotspots in wastewater treatment. The development of the high-efficiency process for the simultaneous removal of ammonium-nitrogen and sulfate may lead to the amendment of the nature water environment, which has high theoretical value and realistic significance.The aerobic nitrification/anaerobic sulfate reduction-anaerobic desulfurization-denitrification process was introduced to the simultaneous removal of ammonium-nitrogen and sulfate in this research. Three different types of bioreactors were started up separately. Meantime, the impact factors, treatment efficiencies and reaction mechanisms to these three operating phases were discussed. And the operation of each bioreactor was optimized by adopting advantageous impact factors. Three independent bioreactors were finally connected to treat the wastewater containing either ammonium-nitrogen or sulfate and organic carbon, which actrualized the high removal of nitrogenous, sulfurous and carbonous compounds.The aerobic nitrification bioreactor of 2.26L was started up successfully by means of high-load enrichement. The dissolved oxgygen of 0.7mg/L, pH value of 8~9, temperature of 35oC, influent ammonium-nitrogen of no more than 600mg/L were beneficial to the stability of nitrification via nitrite. In order to maintain the harmonious performing of the whole process, the operation parameters were adjusted to optimize the aerobic nitrification bioreactor, while the removal efficiencies of ammonium-nitrogen and the generating efficiency of nitrite reached 98.8% and 64.2%, respectively.The anaerobic sulfate reduction biofilm reactor of 5.01L was started up successfully by means of low-load enrichment. The influent pH value of no less than 7.5, hydraulic retention time of 6.2~10.2h, sulfate of 1500~1800mg/L, mass ratio of influent organic carbon to sulfate of no less than 0.45 were advantageous to the high removals of sulfate and organic carbon with high generation of sulfide. The optimal operation of the anaerobic sulfate reduction biofilm reactor led to the sulfate and organic carbon removal efficiencies of 90.6% and 87% with the sulfide generating efficiency of 91.5%. Sufate Reducing Bacteria won in the competition for organic carbon with Methane Producing Bacteria, as it had higher affinity to organic carbon. The degradation velocity of sulfate by Sufate Reducing Bacteria was inconsistent with Monod hyperbolic saturation curve but consistent with Hill allosteric model of S-curve.The microorganisms for desulfurization-denitrification were successfully enriched in the anaerobic desulfurization-denitrification bioreactor of 3.52L at mixotrophic conditions. The influent nitrite of 20~80mgN/L, organic carbon of no more than 100mg/L, glucose as organic carbon source, sulfide of 200~300mg/L, inorganic carbon of 100~150mg/L and hydraulic retention time of 9.5~2.67h were advantageous to the oxidation of sulfide to element sulfur and high removals of contaminants. The sulfate and ammonium in the influent could decrease the removals of sulfide and nitrate. The competive power of nitrite to electron donors was higher than nitrate. The mixotrophic desulfurization-denitrification bioreactor was adjusted by the proportion of each substrate in the effluents from pretreatment bioreactors. The removal efficiencies of sulfide, organic carbon, nitrite and nitrate could reach 95.9%, 81.9%, 99.9% and 99.9%, respectively.The sulfide and organic carbon could be oxidized respectively to element sulfur and carbon dioxide, when their electrons were transfered to nitrate and nitrite. Meanwhile, the nitrate could be reduced to nitrite and the nitrite could be reduced to nitrogen gas. The rate of element sulfur convertion to sulfate was lower than the rate of sulfide conversion to element sulfur. Therefore, the element sulfur would be accumulated in the bioreactor. The degradation of sulfide and nitrite to element sulfur and nitrogen gas decreased the inhibition on the microorganisms, which made it easy for the microorganisms to carry out the mixotrophic desulfurization-denitrification. The quantities and species of the microorganisms attached on the media at lower layer were more than the upper layer. And the quantities and species of the microorganisms attached on the media at outer layer were more than the inner layer. On the outer layer of the media at the lower layer, the filamentous bacteria, coccus and brevibacterium predominated. On the inner layer of the media at lower layer, the bacillus was the dominant bacteria. The coccus predominated on the outer layer of the media at upper layer, while the the long bacilli was the dominant bacteria on the inner layer of the media at upper layer. The more species and higher quantities of the microorganisms attached on the media were advantageous for the denitrification-desulfurization process to treat wastewater with complicated characteristics and obtain high removals of contaminants.According to the aerobic nitrification/anaerobic sulfate reduction -anaerobic desulfurization-denitrification process, each single bioreactor was connected. The removal efficiencies of ammonium-nitrogen, sulfate and organic carbon were around 99.8%, 91.5% and 97.5%, respectively. The mass balance calculation of nitrogen, sulfur and carbon in the process was carried out. The measurement occation error and microorganisms anabolism led to the nitrogen, sulfur and carbon disappearance of 3.3%, 5.4% and 3.8%, respectively.