Cultivation And Salt Tolerance Of The Aerobic Nitrifying Granules

Aerobic granules have good settleability,high biomass retention,high microbial activity, good ability to withstand high organic loading rate and toxic substances,and simple separation process for effluent.Meanwhile,the reactor with aerobic granules performs compact structure and without the secondary sendimentation tank and refluxing equipment, which make the technology of aerobic granules for wastewater present many advantages,such as simple process,flexible operation,small occupation area and low cost of investment and operation,thus,it has wined more and more attentions in the filed of wastewater treatment. Many processes generate high-salinity wastewaters,which is one of the most difficult to treat. Many researchers have treated saline wastewater by biotreatment,but generally fell in the problem of instability.This study is based upon aerobic granular sludge to treat the saline (NaCl)wastewater.In this paper,aerobic nitrifying granules were successfully cultivated under stepwise increased substrate NH₄⁺-N concentrations.Aerobic nitrifying granules which were dominated by both heterotrophs and nitrifying bacteria had excellent stability and were able to simultaneous organic oxidation,nitrification,and partial denitrification.Futhermore,the physical characteristics and the ability to remove substrates were investigated during the period of granulation.Then,the aerobic nitrifying granules treatment processes was acclimated in the saline environment bygradually increasing salinity.The physical characteristics,stability of aerobic granules and the ability to nitrification and denitrification were also investigated under different salinity.Finally,this study also investigated and confirmed the feasibility of aerobic nitrifying granules in synthetic high ammonia-nitrogen catalytic wastewater treatment.The main experimental results were listed as follows:(1) The aerobic nitrifying granules with excellent performance were successfully cultivated.The value of sludge volume index(SVI) is below 20mL/g,and the mean granules size was about 0.92mm.The removal efficiency of COD was about 70%to 90%and ammonium removal efficiency is over 98%.(2) After acclimation the microorganism could maintain a relatively high bioactivity under the salinity of 30g/L.The studies showed that the acclimated nitrifiers could rapidly oxidize ammonia to nitrite and nitrate.The reactor performs excellent ability to remove COD with removal efficiency of over 80%and ammonium removal efficiency is over 98%.The acclimated denitrifiers could remove nitrate and nitrite effectively with the denitrification.TN removal efficiency is below 20%because of high dissolved oxygen(DO).High salinity resulted in high settling velocityand big density,the value of sludge volume index(SVI) is below 20mL/g.(3) This study investigated and confirmed the feasibility of aerobic nitrifying granules in synthetic high ammonia-nitrogen catalytic wastewater treatment in SBAR.At cycle time of 6 h and NH₄⁺-N concentration of 600mg/L,the NH₄⁺-N removal efficiency exceeded 98%.The system had a high capacity in resistance to shock loading.The removal efficiency of COD was about 70%to 90%when the COD concentration was fluctuated between 100mg/L and 400mg/L.When the NH₄⁺-N concentration was fluctuated between 300mg/L and 600mg/L, NH₄⁺-N removal efficiency was basically above 98%.The effluent reached the first class integrated wastewater discharge standard(GB 8978-1996).