Improvement Of Nitrogen Removal From Sewage In A~2/O Systems Using Anoxic Biofilm

In recent years,as China continues its rapid development,the environmental problems brought about by further urbanization and industrialization have been difficult to ignore.Water pollution is an important part of many environmental problems which can not be overlooked.The growing eutrophication caused by the drainage of substandard sewage is increasingly serious and it has threaten the health of citizens.As nitrogen and phosphorus is one of the culprits of water eutrophication,the importance of nitrogen and phosphorus removal in urban sewage is becoming stronger and stronger.China's domestic sewage is usually under a low COD/NO3--N?C/N?and thus the lack oforganic carbon source is common phenomenon during the denitrification process.In order to make the effluent up to the standard,many waste water treatment plants?WWTP?are forced to add a large number of additional carbon sources?methanol,ethanol,etc.?,which undoubtedly makes the water treatment costs greatly increased.How to reduce the dependence of the traditional wastewater nitrogen removal technology on the organic carbon source,while maintaining or even improve the efficiency of denitrification,is one of the hot spot in the field of waste treatment.In this paper,a new DEAMOX biofilm strengthen technology for A2/O system which enhanced denitrification capacity was proposed.The biofilm was cultivated by our research group,and it can remove ammonia and nitrate at same time using a small amount of carbon source under anoxic conditions.The DEAMOX biofilm is placed in the anoxic zone of the reactor where the influent organic carbon source and the internal recycle provide a rich substrate for its partial denitrification and Anammox.The autotrophic denitrification capacity provided by the biofilm replenishes the original denitrification capability of the reactor,thus achieving the better effect of denitrification under conditions that contain less organic carbon.The experimental results show that using the anoxic biofilm to strengthen the nitrogen removal capacity of A²/O system is feasible.Under the condition of average C/N = 2.7,the removal rate of total nitrogen?TN?increased from 55% to 67.63% after the system was stable.It can be considered that the implanted biofilm greatly enhances the denitrification ability of the system,especially the ability of the system to reduce NO3--N under low C/N condition.After adjusting the system to a reasonable working condition,the COD,ammonia and TN effluent reach the First Grade A standard,and have certain impact resistance and recovery ability.Batch experiments showed that the Anammox ability was not degraded after the anoxic biofilm was placed in the organic-rich anoxic zone of the A2/O reactor.Before and after acclimation,the removal rate of ammonia was 36.42% and 39.60% and the total nitrogen removal rate increased from 49.26% to 59.79%.Molecular biology experiments also observed that there were still a number of Anammox bacteria in the biofilm.The performance of the anoxic biofilm under different organic carbon sources was investigated by batch experiments.The conclusion was that the sodium acetate was the ideal carbon source.Differences in partial denitrification activity of anoxic biomaterials under sodium acetate,methanol,ethanol and glucose were investigated.When the denitrification was under the sodium nitrate,the nitrite accumulation rate?NAR?was 65%,the maximum accumulation concentration was 4.52mg/L while the NAR of de denitrification with methanol and ethanol was smalle r than that with sodium acetate as the carbon source.The denitrification activity is low when the glucose is carbon source.Differences in DEAMOX activity of anoxic biofilm under different carbon sources were investigated.During the DEAMOX process of the anoxic biofilm that NO₂^--N provided by the partial denitrification,the sodium acetate still achieved the best anaerobic ammonium oxidation effect because of its highest denitrification activity.NH4+-N concentration decreased by 4.22 mg/L.The denitrification activity of methanol and ethanol as carbon source was significantly higher than that of the previous group,suggesting that anammox consumed NO 2--N which in turn promoted the denitrification reaction by promoting the denitrification reaction get on.The differences in N₂O accumulation of the anoxic biofilm under different C/N were investigated by batch experiments.The maximum accumulation of N 2O at the initial C/N = 4 and C/N = 8 was 0.081 mg/L and 0.095 mg/L,respectively.This was due to the activity of nitrous oxide reductase lagging behind the nitrite reductase and NO₂^--N reduced to N2 O after the further reaction,resulting in accumulation.The competition of nitrous oxide reductase?N2OR?and other nitrogen reductase to get electrons supplied by the carbon source is the main reason for the accumulation of N2 O after a large amount of accumulation in the early stage.N2 O accumulation due to endogenous carbon denitrification may occur when the anoxic biofilm is under the low carbon sources condition for a long time.When the carbon source is sufficient,the N2 O accumulation increases with the increase of C/N as the accumulation of NO₂^--N increased with the increase of C/N.