Study On Performance Of Autotrophic Nitrogen Removal System With Granular Sludge Under Low Ammonia Nitrogen Concentration At Room Temperature

Single-stage autotrophic nitrogen removel based on partial nitritation-anammox?PN/A?process is an economical and environmentally friendly technology for nitrogen removel.In contrast with traditional nitrification/denitrification process,PN/A process has advantages such as low energy consumption,low infrastructure cost and high energy recovery.Introduction of autotrophic nitrogen removal technology to municipal sewage treatment appears as aprerequisite to make wastewater treatment plants?WWTPs?energetically selfsufficient.At present,this technology has been successfully applied to the treatment of high temperature and high ammonia nitrogen wastewater,because of the high environmental demanding of functional bacteria,the process in mainstream conditions is still under investigation.The granular sludge with high density,good settling property,excellent biological retention ability and strong impact load capacity,has been more and more used in fully autotrophic denitrification process.Hence,this thesisis dedicated to study autotrophic nitrogen removal for low strength wastewater treatment at room temperatures with granular sludge.The main research contents and results of this paper include the following 3 aspects:1.The PN/A granular sludge for long-term storage was inoculated into an air-lift bioreactor to investigate the nitrogen removal performance during the start-up of single-stage partial nitritation and ANAMMOX process under the following conditions:temperature at?23±2??,pH at 7.7-8.0.Synthetic wastewater with ammonia nitrogen concentration of 70 mg·L^-1 was used as influent.By stepwise shortening hydraulic retention time?1.1?0.5 h?and increasing ammonia nitrogen loading rate[1.53?3.36 kg·?m³·d?^-1],the bioactivity as the synergy between the ammonia oxidizing bacteria?AOB?and anaerobic oxidizing bacteria?AMX?were gradually restored.After 95 d operation and regulation,the process was successfully established and the removal rate of NH₄⁺-N and TN were 85%and 69%,respectively.According to the performance of sludge at each stage,the nitrite oxidizing bacteria?NOB?were selectively inhibited by controlling dissolved oxygen strictly.The average particle size gradually increased and finally was reached to 1.30mm after the sludge was adapted to the environment.The profile of the mature autotrophic granular sludge was smooth and clear,SEM showed that the center of granular sludge formed a cavity with porous structure on the surface,the sludge morphology consisted mainly of cocci,with a small amount of bacilli and short bacilli.The major component of EPS in granular sludge was protein?81.48%?indicating that it had a good settling performance.2.The reactor was operated under the natural environment?summer-autumn-winter-spring-summer season?without controling the temperature over 1 a.The temperature ranges from 7°C to 29°C,by indirectly regulating ammonia nitrogen loading rate and increasing ammonia nitrogen loading rate control the operation.During stable process operations at summer temperatures?27°C?the total nitrogen removal rate was 2.70kg·?m³·d?^-1 while at winter temperatures?7°C?total nitrogen removal rate was maintained at 0.60 kg·?m³·d?^-1.The activity of AOB and AMX in the single-stage autotrophic denitrification system was consistent with the temperature response,and both were positively correlated with temperature changes while NOB was negatively correlated with temperature changes.Initially,q?NH₄⁺-N?and q?TN?were 0.30g·?gVSS·d?^-1 and 0.24 g·?gVSS·d?^-1,respectively.With the decrease of temperature,q?NH₄⁺-N?and q?TN?showed a downward trend and q?NO₃^--N?showed a upward trend.In the low temperature range,q?NH₄⁺-N?and q?TN?fluctuated slightly,but both did not continue to decrease and remained at 0.14 g·?gVSS·d?^-11 and 0.11 g·?gVSS·d?^-1.In the low temperature environment,it can be found that the fluctuation range of AMX activity is higher than AOB in the same temperature range,and the effect of low temperature on AMX is more serious than AOB.When the reactor was stably operated for a long time in the low temperature stage,the activity of some bacteria was affected,and it may be in a dormant state.Once the environmental conditions were improved,the activity of the sludge can be gradually restored.During the temperature fall,the particle size of the granular sludge released from 1.30 mm to 0.91mm,the color of the granular sludge in the reactor gradually changed from brownish red to brownish brown when temperature was below 20?,and then brownish yellow when temperature was below 15?.A considerable amount of floc sludge appeared and loose floc sludge with granular sludge coexisted in the reactor.As the temperature rising,the particle size of the granular sludge increased constantly.While temperature was higher than 20?,the color of the granular sludge became brownish red,the granular sludge formed in the reactor gradually and became dense and smooth,and the floc sludge gradually reduced then disappeared.3.Under the DO/RAN controlling strategy,change the ammonia nitrogen loading rate and aeration according to the ammonia nitrogen removal rate of the reactor during operation under the room temperature.The result showed that there was a direct and rapid response relationship between DO/RAN and NOB inhibition.Under stable operation conditions,the DO/RAN level was positively correlated with temperature.Temperature changed from 29°C to 10°C,the value of DO/RAN during the steady-state reduced from 0.15 to 0.03.At the same time,when the temperature was above 20°C,the control range of DO/RAN was wide,and below 20°C,the DO/RAN regulation was narrow.Compared with the NO₃^--N production rate in the control and recovery phases of each stage,in situ q?NO₃^--N?decreased in the recovery period compared with the interference period,it showed that DO/RAN was successfully used to inhibit NOB activity.However,during the two periods,ectopic q?NO₃^--N?was basically flat,indicating that NOB was still present in the granular sludge.When appropriate conditions were met?such as NH₄⁺-N depleted or supplied with oxygen?,oxidation of NO₂^--N can be resumed.By fitting the particle size to the ratio of DO to residual ammonia nitrogen concentration,it was found that there was a positive correlation between them,and R²was 0.757.This means that changes in particle size can be an important reference for applying DO/RAN regulation.