Operation Management Optimization Technologies And Carbon Source Dosing Technology Based On Total Nitrogen Improvement In Wastewater Treatment Plant

In recent years,the upgrading of the first-class B standard to the first-class A standard has become the operational management target of urban wastewater treatment plants.According to the removal mechanism of the main pollution indicators TP,TN and SS,TP and SS can be removed by biological or chemical or physical multi-technical methods,while NO3-N nitrificated from NH₃-N can only be removed with biological method in water solution.Despite the emergence of new types of biological nitrogen removal technologies,the technology for biological nitrogen removal in urban wastewater is still a heterotrophic denitrification technology that consumes carbon sources.Carbon sources have become an important factor limiting the efficiency of biological nitrogen removal.The addition of external carbon sources such as methanol,glucose or fermented materials has become an important safeguard for the TN upgrade and improvement in wastewater treatment plants,especially low-carbon source wastewater treatment plants.At present,in order to achieve TN stability or standardization,most of the wastewater treatment plants adopt a complete nitrification mode.The dissolved oxygen?DO?in aeration tank is much higher than 2 mg/L.The carbon source organic matter can be completely oxidized,while activated sludge autotrophy attenuation coefficient is also in a high state.Obviously,this operating state exacerbates the lack of carbon sources in the low carbon source wastewater treatment process and affects the denitrification efficiency of the external carbon source.Based on this,this study takes a low-carbon source wastewater treatment plant in Chongqing as the research object,optimizes the operating parameters of dissolved oxygen and internal reflux ratio on the existing basis,and improves the biological nitrogen removal of the low-carbon source wastewater treatment system as much as possible.And then based on the optimization of operating parameters,the external carbon source dosing technology based on TN standard is further studied.The results show that:?1?Properly reducing the dissolved oxygen in the aerobic section contributed to the improvement of the biological nitrogen removal effect.The test results showed that when the influent COD average was 220 mg/L and the TN average was 57.3 mg/L,and the dissolved oxygen at the end of the aerobic section was reduced from the initial 2.5 mg/L to 1.5 mg/L,the removal rate of biological nitrogen removal was the highest,from 62%to more than 70%.The effluent TN can reach the first-class B standard stably,and the minimum was 17.9 mg/L,which was mainly due to the improvement of the SND capacity in the aerobic section and that improved the the efficiency of biological nitrogen removal.?2?When the DO at the end of the aerobic section was controlled at 1.5 mg/L,the average influent COD was 261 mg/L,the TN was 52.1 mg/L,and the internal reflux ratio was increased from 180%to 250%and 300%,respectively,the TN removal rate increased from 60.8%before optimization to 62.7%and 66.5%,and the effluent TN decreased from an average of 20.5 mg/L before optimization to 18.7 mg/L,and the minimum of which was 17.1 mg/L.?3?The external carbon source was added to the anoxic section of the biochemical pool of the wastewater treatment plant when the DO at the end of aerobic section was 1.5mg/L,the internal reflux ratio was 300%,and the SRT was 25d.When the influent COD was averaged at 229 mg/L and the TN was averaged at 49 mg/L,added 1.3 times of the calculated sodium acetate,the effluent TN can reach 3.29 mg/L and the TN removal rate was as high as 91.4%.When adding the same amount of glucose,the effluent TN reached a minimum of 8.19 mg/L,the removal rate was about 80%,and the effect of dosing was not as good as that of dosing sodium acetate.According to the test results of sodium acetate,if the wastewater treatment plant with a daily treatment capacity of 90,000 m³ is to be cut by 10 mg/L of TN per day,the daily cost of sodium acetate is about 29,234.25yuan.?4?After continuously adding carbon sources for a period of time,reducing the dosage of the external carbon source,the reactor can still maintain high-efficiency nitrogen removal for about one week.The results showed that when the influent COD was about 190 mg/L and the TN was about 40 mg/L,the reactor can still maintain high-efficiency of nitrogen removal when stopping adding external carbon sources after continuously addition of 14 days in summer.Compared with the average effluent TN of17.14 mg/L and the removal rate of 57.8%when the carbon source was not added,the TN of the effluent after the carbon source was stopped was 3.17 mg/L,and the removal rate reached 91.5%.However,after the continuous addition of external carbon sources in winter,the TN will quickly rise back to 11.2 mg/L and losing the effect of high efficient nitrogen removal.When adding external carbon sources,it showed more NO₃-N reduction than the accounting amount.Therefore,it can reduce the external carbon source dosage and save the operating cost while ensuring the biological nitrogen removal efficiency.?5?The results showed that when the influent COD was about 190 mg/L,the TN was about 40 mg/L,and the sludge load was increased from 0.12kg COD/?kg MLSS·d?to 0.18kg COD/?kg MLSS·d?,the effluent TN could still reach 2.20 mg/L and the removal rate was as high as 94.4%when stopped dosing the external carbon sources after continuously adding 14 days.According to the high-efficiency nitrogen removal calculation for 8 days,it can save about 233,000 yuan for the cost of carbon sources of a90,000 m³ wastewater treatment plant.