Effect Of Ozone Addition On Sedimentation Performance And Nitrogen And Phosphorus Removal Of Activated Sludge

Activated sludge process has become the main process of municipal wastewater treatment plant because of its advantages of good purification effect,economic reliability and no secondary pollution.However,the problem of sludge bulking during operation has not been completely solved,especially the mass propagation of filamentous bacteria under low temperature conditions,which leads to poor sludge settling performance,difficult separation of mud and water,and affects the effluent quality.The effects of adding ozone on sludge settling performance and nitrogen and phosphorus removal in SBR and A/A/O systems were studied in this paper.The main findings are as follows:Based on two identical SBR reactors,the effects of ozone addition on sludge settling performance and nitrogen and phosphorus removal were studied.The results showed that:?1?The sludge settling performance can be improved by adding different concentrations of ozone?0.085?0.34 g-O₃/g-MLSS?.When the dosage is 0.17g-O₃/g-MLSS,the SVI can be reduced to between 70-90 m L/g,and the sludge settling performance is the best;When the ozone dosage is 0.34 g-O₃/g-MLSS,the SVI instead shows an upward trend.The further study found that there is a positive correlation between the total EPS amount and PS/PN value of activated sludge and the SVI,and the decrease of ozone oxidation and PS/PN value is one of the reasons for improving sludge settling performance.?2?The removal rate of COD and TN was more than 90%after adding ozone.Compared with the SBR system without ozone,the nitrogen removal performance and nitrification rate did not change much.With the increase of ozone dosage,the treatment efficiency and phosphorus removal rate of phosphorus showed a decreasing trend.The phosphorus removal rate gradually decreased from 92%to 60%absorption rate decreased from 7.63 and 5.89 mgP/?gVSS·h?to 4.98 and 3.94 mgP/?gVSS·h?,respectively.?3?After 20 days of ozone,microscopic examination of sludge showed that the mycelium of filamentous bacteria became shorter and the floc became dense.The results of high-throughput sequencing showed that the population diversity decreased,the Nitrispira ratio of nitrogen-removing functional bacteria was stable,and the Tetrasphaera of phosphorus-removing related functional bacteria decreased obviously.The reduction of microbial abundance associated with filamentous bulking,such as Actinobacteria?Microtrichaceae and Candidatusmicrothrix,is another reason to improve sludge settling performance.On this basis,in view of the problem of low temperature sludge bulking in a sewage treatment plant(SV₃₀ is 90%,SVI is about 260 m L/g),the actual sewage and sludge in the sewage treatment plant are taken as the object by trial-manufacturing small scale A/A/O reactor.The effects of ozone addition on sludge bulking control and nitrogen and phosphorus removal were studied.The following results were obtained:?1?The effect of ozone dosage on sludge settling performance was studied by batch test.The results showed that when the dosage was 0.085 and 0.17 g-O₃/g-MLSS,the SVI could be reduced to about 40%.Comprehensive treatment effect and stability,determine the best ozone dosage of 0.17 g-O₃/g-MLSS.?2?Based on the optimum ozone dosage,the variation law of sludge settling performance small scale A/A/O system was studied.The results showed that in the initial 4 days,the SVI value increased slightly to about 300 mL/g;Thereafter,the SVI decreased rapidly,and after 8 days,the SVI fell below 150 mL/g,and the sludge bulking was suppressed.?3?Based on the optimum ozone dosage,the variation law of sludge settling performance small scale A/A/O system was studied.After 30 days of continuous operation,the removal rate of system COD and ammonia nitrogen was stable above90%and 95%,which had little effect on the oxidation rate of ammonia nitrogen.The removal rate of system phosphorus decreased from 92%to 63%,and the rate of phosphorus absorption decreased under aerobic conditions.?4?By microscopic examination and dyeing comprehensive judgment,the type of filamentous bacteria in the sewage plant is Microthrix parvicella type.After adding ozone,the number of sludge filamentous bacteria is reduced,the mycelium is interrupted,and the sludge floc becomes dense,so the settling performance is improved.