Nitrogen removal efficiency of a continuous flow biofilm reaction system under different sequence arrangement

• Main Authors: Hsin-Yu Chou, 周欣諭
• Other Authors: Chun-Hsiung Hung
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107NCHU5087019%22.&searchmode=basic

碩士 === 國立中興大學 === 環境工程學系所 === 107 === This study is based on the wastewater recycling and recycling policy that the government is actively promoting. Cooperating with a wastewater treatment plant in Taichung, taking its effluent and capturing the principle of the biological treatment system in the sewage treatment plant to build a small model plant. The aerobic biological treatment (nitrification tank) was connected to the anaerobic biological treatment (denitrification tank) to form a continuous flow biological reaction system, and in order to prevent the microorganisms from flowing out with the water, BioNET was placed in both of the tanks. It will make the microorganisms grown on top of BioNET. The above design of experiment attempts to reduce NH3-N and NO3--N of effluent to a lower standard and examine the feasibility of its reuse as reclaimed water in the future. Before starting the system experiment, we conducted a one-month water quality monitoring of the effluent from the wastewater treatment plant. According to the results, NH3-N and NO3--N of the effluent was 8.77 mg NH3-N/L and 10.59 mg NO3--N/L, respectively. Its COD was 13.18 mg/L, pH 7.16 and dissolved oxygen concentration was 5.86 mg/L. The above values were in line with the current effluent standards by Taiwan regulations. However, if it is to be used as a source of reclaimed water, it is necessary to reduce NO3--N, NH3-N and organic matters in the effluent to a lower standard, in order to prevent the surface of the equipment at the demand side from sticky, oxidizing or producing odor, so that the machine cannot be used normally.Therefore, this study carried out a system simulation experiment in the laboratory. For the stability of the system, the highest concentration of NH3-N and NO3--N were monitored as the standard value, and the average concentration of NH3-N and NO3--N in the effluent were set to 10 mg/L and 15 mg/L, respectively. If NH3-N and NO3--N concentrations of the effluent are not as good as the set value on the day, NH3-N and NO3--N are additionally added to make the concentration reach the set value. In order to maintain the operation of nitrification and denitrification reaction, it was a big cost to add alkalinity and carbon source in the traditional nitrogen removal process. Therefore, in phase I, the denitrification tank is used to treat the effluent before nitrification tank and hoped that the alkalinity generated by denitrification reaction can be used for nitrification reaction to reduce the operating cost of the system. According to the results, when COD/NO3--N of 4, and both tanks had a HRT of 50 minutes, the concentration of NO3--N in the denitrification tank effluent and NH3-N in the nitrification tank effluent was 2.58 mg NO3--N/L and 1.63 mg NH3-N/L, respectively. Because of COD in the denitrification tank effluent was high, and was suspected that the carbon source utilization rate may be low, phase II reduced carbon/nitrogen ratio. After changing COD/NO3--N of 3, and maintain HRT of 50 minutes, the concentration of NO3--N in the denitrification tank effluent and NH3-N in the nitrification tank effluent was 3.70 mg NH3-N/L and 2.75 mg NO3--N/L, respectively. Since the system of phase I and phase II was to perform oxygen-free denitrification reaction first, it was necessary to pay attention to the dissolved oxygen concentration of the influent from time to time, and the average dissolved oxygen concentration of the effluent in the wastewater treatment plant was 5.86 mg/L, which is unfavorable. Then, replaced the order of the nitrification tank and the denitrification tank, maintained COD/NO3--N to 3 and HRT of both of the tanks were 50 minutes. After adjustment, the concentration of NH3-N in the nitrification tank effluent and NO3--N in the denitrification tank effluent was 0.30 mg NH3-N/L and 6.53 mg NO3--N/L, respectively. At this time, the effect to remove NH3-N can reach 97%, and the dissolved oxygen in the denitrification tank can also be maintained in a low concentration. Only COD of the denitrification tank effluent was still high, so it was suspected that the possibility of reducing carbon/nitrogen ratio. Final, in phase IV, changed COD/NO3--N to 2. Because of the excellent nitrogen removal effect in phase III, considered the feasibility of shortening its HRT to 30 minutes in the nitrification tank. In phase IV, the concentration of NH3-N in the nitrification tank effluent and NO3--N in the denitrification tank effluent was 0.75 mg NH3-N/L and 10.38 mg NO3--N/L, respectively. The effect to remove NH3-N was still up to 93%. Based on the above results, this study found that the carbon source utilization rate of the system in all four phases were only 50%, and there was no change in HRT of the denitrification tank. It was speculated that insufficient HRT may be the cause of poor efficiency of denitrification reaction. In addition, the system in this study can also be speculated that in the environment of low nitrogen concentration, sewage regeneration can be carried out simply by aerobic nitrification reaction, and this setting will be the most economical. This study expects to recycle the effluent from the wastewater treatment plant in a simplest, low-cost and low-energy way, which will save the wastewater treatment plant from being shut down due to upgraded equipment. In addition, the simulation system of this study can also provide reference and application for the reuse of reclaimed water by future generations.