A / O Process Experimental Study On Properties Of High-salinity Wastewater Denitrification

A/O reactor was used for the treatment of simulated high salinity wastewater in this paper.An experiment was conducted to study the domestication and training of salt-resistant activated sludge,the effect of different seawater salinity on ammonia removal efficiency,microorganism nitrification rate,as well as the configuration and performance of activated sludge at normal temperature.The factors which influence the denitrifying efficiency were investigated and the feasibility and stability of shortcut nitrification-denitrification in the high salinity condition was explored.All of these researches were promotive for the biological treatment of high salinity wastewater.The experimental results indicated that the ammonia removal efficiency of A/O system decreased gradually when the seawater proportion was increased from 10%to 70%and the decreasing extent was different.The experimental parameters were influent COD concentration:800～900mg/L,NH₃-N concentration:80～90mg/L,pH:7.0～8.0,DO: 2.0～3.0mg/L,MLSS:3000mg/L,internal recirculation flow rate:2～3 and sludge recirculation flow rate:0.8～1.When seawater proportion was below 30%,the ammonia removal efficiency was more than 90%and the salinity had little effect on the removal efficiency.When seawater proportion was 50%,the ammonia removal efficiency was slightly reduced but also could be achieved about 86%after sludge domestication. Whereas the ammonia removal efficiency drop to 76%sharply when seawater proportion was increased to 70%.The average nitrification rate was reduced along with the increase of seawater proportion from 1.51 mgN/(gMLSS·h) to 1.02 mgN/(gMLSS·h) as seawater proportion was increased from 10%to 70%.The nitrite oxidizer bacteria were easily influenced by salinity than ammonia oxidizer bacteria.The system could achieve shortcut nitrification-denitrification by controlling seawater proportion above 30%.The nitrite growth rate was 2.65 mg/(L·h),and the nitrosation rate could stay at 97%when seawater proportion was 50%.The high salinity had advantages to the settling performance of activated sludge,and SVI drop from 80 to 40 along with the seawater proportion increased from 10%to 70%.The filamentous bacteria decreased gradually and sludge flocculation changed to closed and compact from open and loose along with the increase of seawater salinity.The experiment also studied the effect of several parameters on the nitrogen removal in the condition of 50%seawater salinity at normal temperature,such as the influent pH, ammonia load,HRT,sludge recirculation flow rate(R) and internal recirculation flow rate(r).The results showed that the higher influent pH(8.0～8.5) was advantageous in enhancing the activity of ammonia oxidizer bacteria and the ammonia removal efficiency. A longer HRT was needed to ensure the better ammonia removal efficiency in the condition of high salinity,and the ammonia removal efficiency could reached at 87.8%as for the influent pH at 8.0 and HRT at 15h.The ammonia removal efficiency and the effluent nitrite concentration drop and increased respectively along with the increase of influent ammonia concentration.The ammonia removal efficiency began to be under 80% when the influent ammonia concentration was above 100mg/L.Increasing the sludge recirculation flow rate(R) was advantageous in enhancing ammonia removal efficiency. The ammonia removal efficiency could be reached at 88.67%by controlling R at 1.0 in the condition of high salinity.The nitrite concentration in the end of the anoxic area could be under 0.2mg/L,and the complete denitrification could be realized by controlling internal recirculation flow rate(r) at 3.5～4 in the system.The high salinity and low temperature had important influence on the denitrifying efficiency.The ammonia removal efficiency was reduced along with the temperature drop (20℃～4℃).The ammonia efficiency at 18～20℃,15℃and 4℃was above 85%,80% and 56.4%respectively for 50%seawater proportion.Being affected adversely by low temperature and high salinity,the effluent nitrate concentration was always in a low level. Although the nitrite concentration was reduced continually along with the temperature drop,the system was at the shortcut nitrification-denitrification stage throughout.In the view of biology,not only the effective quantity and activity of microorganism was drop but also the community configuration of microorganism was changed,affected by the low temperature.As the wastewater temperature was below 10℃,the cold-adapted bacteria were the main microorganism to decompose ammonia in wastewater and the settling performance of activated sludge became worse.