Study On Ultrasonic Cracking Solution Of Excess Sludge As Denitrifying Carbon Source

In recent years,the content of nitrogen and phosphorus in domestic sewage and industrial wastewater has become higher and higher,which causes the C/N ratio of sewage very low,which results in carbon source insufficient during denitrification.If additional carbon source is added in sewage such as methanol,not only increases operating costs,but may also cause secondary pollution problems.When the sewage treatment plant treats the sewage,it will continuously produce a large amount of excess sludge,and the disposal cost of the excess sludge is very high.If ultrasonic technology is used to pretreat the excess sludge and then use it as a carbon source for biological nitrogen removal,the problem of insufficient biological nitrogen removal carbon source and difficult sludge disposal in the wastewater treatment plant can be solved at the same time.The response surface methodologe was used to investigate the effects of ultrasound energy density,ultrasonic time and pH on BOD₅ and lysis rate.The optimum parameters of ultrasonic treatment for excess sludge were confirmed.The excess sludge was pretreated using the optimum parameters,and the obtained supernatant was used as the denitrifying carbon source.The Up-flow Anaerobic Sludge Bed was used to carry out the continuous denitrification experiment of wastewater,and to investigate the best C/N ratio of the reactor and the denitrification performance parameters under these conditions.The results showed that:With the target value of BOD₅ and lysis rate,the optimal processing parameters were optimized by response surface method:ultrasonic sound energy density was 2.0 W/mL,ultrasonic time was 40 min and pH was 7.0.When the experiment was carried out with this treatment parameter,the corresponding concentration of BOD₅ was 2195±20 mg/L,which was about 24 times higher than that before the pretreatment,and the lysis rate was 33.9%±0.5%.The comparison experiments of three kinds of denitrifying carbon sources showed that the denitrification effect of the Pretreated excess sludge supernatant was the best,and the ultrasonic pretreatment significantly improved the effect of excess sludge as a denitrifying carbon source.The detection of the coliforms including E.coli before and after ultrasonic crack showed that these pathogenic bacteria in sludge could be killed by ultrasonic crack,and it can also reduce the environmental damage of excess sludge.The continuous denitrification experiment of UASB reactor showed that when the hydraulic retention time?HRT?was 6 hours,the effluent quality was best when SCOD/N?the ratio of dissolved COD to nitrate nitrogen?was 6.In this condition,the removal rate of nitrate nitrogen is above 93.5%,the effluent COD is lower than 60 mg/L,NH₄⁺-N is lower than 8.0mg/L,and TN is 19.5±1.0 mg/L.These indicators can meet the first-class b standard for sewage discharge.Most of the protein-like organic substances can be degraded,and the overall effluent water quality is relatively stable.When the influent water quality changes,the effluent water quality can be restored to normal within 1² days,and the reactor has a certain water quality impact load capacity.This study shows that the supernatant of excess sludge after ultrasonic pretreatment can be used as an effective denitrifying carbon source for sewage denitrification system.