Experimental Research On Excess Sludge Treatment By Homogenization-alkaline-ultrasonic Disintegration And Anaerobic Digestion

With the continuous improvement of sewage treatment rate gradually increases and the number of new sewage treatment plants increases in China,the amount of excess sludge generated by sewage treatment plant increases rapidly.The sludge contains a large number of harmful and toxic substances,such as parasite eggs,bacteria,pathogenic microorganisms,synthetic organic matter and heavy metal ions,which will adversely affect the surrounding environment if it is not properly disposed.Sludge treatment and disposal has become one of the environmental problems to be solved in China.Anaerobic digestion is the most widely used method for disposal of excess sludge,but the traditional sludge anaerobic digestion process has the disadvantages of catalyzed degradation of extracellular polymer,difficult cell wall breaking,slow reaction,long sludge residence time,low methane production and poor sludge degradation,which severely limits sludge anaerobic digestion technology.Many studies have proved that pretreatment can promote the degradation of extracellular polymers,improve the hydrolysis of macromolecular organic matter in sludge,break the cell wall of sludge cells,effectively improve the anaerobic digestion performance of sludge and shorten the hydraulic retention time.This study intends to study the effect of homogenization combined with alkaline hydrolysis and ultrasonic pretreatment to solve the waste actived sludge.Firstly,the single factor experiment and orthogonal test are carried out on the homogenized cracked sludge respectively,and the influence of homogenization time,homogenization speed and sludge concentration.and the optimal operating parameters are obtained.Secondly,under the optimal operating parameters of the homogenization experiment,combined with alkaline hydrolysis and ultrasonic pretreatment of the excess sludge,the optimal pretreatment combination and operating parameters of the cracked sludge were obtained.Lastly the optimal operation combination of cracked sludge was selected to connect the subsequent anaerobic digestion experiments,and compared with the untreated sludge anaerobic digestion experiment.The single factor experiment of homogenizing cracked excess sludge was carried out using a laboratory high shear dispersing emulsifier homogenizer equipped with two dispersing heads of 25S6 and 25G.The single factor experiment of homogenizing cracked excess sludge showed that the cracking effect of 25G dispersing head was better than 25S6;With the increase of time,the cracking efficiency is significant at 0-20 min,and then the cracking efficiency is relatively low;With the increase of the rotational speed,the sludge cracking effect is increased.At 19000 rpm,the cracking rate has basically reached the optimal state;With the increase of sludge concentration,the crack rate first increased and then decreased.When the sludge concentration was 10100 mg/L,the cracking effect was the best.The results of orthogonal experiment showed that with DDCOD as the response value,when the homogenization time was 35 min,the homogenate rotation speed was 19000 rpm,and the sludge concentration was 8000 mg/L,the maximum crack rate was reached.The primary and secondary order of the three factors was the homogenization time>homogenization speed>sludge concentration.The alkaline hydrolysis combined with homogenization experiments showed that the cracking rate reached the optimal value when the concentration of NaOH was 0.055 mol/L.The homogenate combined with ultrasonic experiments showed that the COD dissolution was almost optimal at 10 min after ultrasonication,the removal rate of MLSS and VSS was maximized,and the ultrasonic treatment could further reduce the particle size.Investigate the effect of homogenate,homogenate+ultrasonic,alkaline hydrolysis,alkaline hydrolysis+homogenization,alkaline hydrolysis+homogenization+ultrasonic pretreatment methods on the cracking of sludge.The results show that the pretreatment method of homogenization+ultrasound is the best for the dissolution of organic matter in sludge,and the pretreatment method with alkaline hydrolysis performs better in MLSS and VSS reduction rate.Finally,homogenate+ultrasound is selected for subsequent anaerobic digestion experiments.Anaerobic experiments showed that the daily production of biogas by homogenization+sonication was higher than that of untreated raw sludge in the first 2 days of reactor operation.On the first day,the daily output of biogas is the highest level during the whole reactor operation.The methane content on the first day after homogenization+sonication and untreated sludge was 1.71%and 0.21%,respectively,which proved that the sludge pretreated by homogenization+ultrasonication contains a large amount of organic matter that can be rapidly biodegraded.After 10 days of anaerobic digestion,the pre-treated cracked sludge MLSS and VSS removal rates were 18.48%and 19.25%,respectively,which were 7.33%and 3.79%higher than the untreated sludge degradation removal rate.