| As the national and local effluent standards become more stricte, the effluent of Tai hu Lake and other key areas should achieve the A in first grade discharge standard of GB18918-2002.Therefore, some urban sewage plants along the Tai hu Lake must have some reform to attain the stability discharge requirements.There are some problems about North Kunshan, such as the inefficient dinitrification, the instability and high total nitrogen of the effluent.This reaserch took a long-time monitroring on several stages about real biological treatment, applied material balance,chemiacal metrology ,microbial growth mechanics and other mathods, found out the reasons and the key factors about nitrogen, and draw the following conclusions:(1)The ammonia removal rates about the first stage and the second stage of aerobic tank are 46.8% and 47.69%,the nitrification rate is higher;the ammonia removal rate about the third stage is 5.51%, and the nitrification rate is very low; the concentration about ammonia at reffluence and outlet is almost equal, the average centration is about 2 mg/l,and have reached the discharge standards.This indicates that the denitrification mainly take place in the first and the second stage,the third stage has little contribution to the nitrification and can be ignored.(2) The total nitrogen removal rate of denitrification tank is 12%, the average total nitrogen removal rate of each tank is 22.6%,the average concentration about nitrate in effluent is 4.2 mg/l, it is higher, the average denitrification rate is 0.0213gNO3--N/gVSSï¹' d-, and it is lower than the normal range 0.03～0.11gNO3--N/gVSSï¹'d- ,indicating that the denitrification efficiency is lower;The average total nitrogen removal rate of anaerobic tank is 21.27%,the average denitrification rate is 0.0656gNO3--N/gVSSï¹'d-,the average concentration about nitrate in effluent is 0.9mg/L which is higher than the theoretical value 0.2mg/L,this indicates that the denitrification in anaerobic tank is incomplete.(3)When the C/N ratio of influent is 3.5 to 5, the total nitrogen removal rate is higher,but not the higher ratio the higher removal rate;when the total nitrogen concentration in influent is increased,the removal rate increased obviously,but the total nitrogen concentration in effluent is also higher; temperature has little effect on the removal of ammonia,but greatly affect the total nitrogen removal rate;when sludge loading is increased, the ammonia removal rate is sharply increased to 95% from 85%,but have little effect on the total nitrogen removal rate;as the ammonia volume loading increased, the ammonia removal rate increased to 99% from 89%, and the total nitrogen removal rate increased to 70% from 50%.(4)The increasement of HRT in anoxic zone has little effect on the denitrification, HRT is not the limitation factors on denitrification;when the reflux ratio increases from 100% to 200%,the total nitrogen in effluent decreased obviously,the average removal rate of total nitrogen increases to 73.7% from 65.2%, but the nitrate concentration in effluent increases at the same time.Therefore,when the increasement of inside reflux ratio can enhance the denitrification ability,but a economical and reasonable reflux ratio still needs evaluation and analysis.(5)The average concentration of dissolved oxygen in inside reflux water is 4mg/L,the dissolved oxygen concentration inverse ratio the denitrification rate.Through the oretical calculation,Carbon consumption of dissolved oxygen in return flow is quite large,averaging 166kg/d.The carbon savings can use for denitrification, carbon savings of 0.773.46mg/L,the Anoxic effluent nitrate nitrogen concentration decreased 0.160.73mg/L.It show that the dissolved oxygen on denitrification carbon source of competition is the effect of anoxic denitrification a major factor. Proposed of non-aerated zone set in return point, reducing the dissolved oxygen back to the anxic,and dissolved oxygen shoud be controlled by implementation. |
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