| According to the statistics of“China’s ecological environment buttetin in 2019”issued by the Ministry of ecology and environment,the processing capacity of urban sewage treatment plants in our country was 177 million m~3 per day.Generally,the sludge production(80%moisture content)accounts for 0.5-1‰of the total wastewater treatment.The sludge production is 32.3-64.6 million tons in 2019,and is likely to have exceeded 60 million tons in 2020.In response to“the Notice of the State Council on Printing and Distributing the action plan for prevention and control of water pollution”,the department of housing construction,the ministry of ecology and environment and the national development and reform commission jointly issued the"Notice on the three-year action plan for improving the quality and efficiency of urban sewage treatment"in May 2019.With the expansion of the scale of sewage collection and the improvement of sewage collection and treatment facilities as the main means of action,the output of sludge will definitely increase substantially.The treatment and disposal of sludge has always been an important issue in the field of sewage and wastewater treatment in our country.If it is not effectively treated,it will seriously affect the water ecological environment.Therefore,In order to achieve sludge reduction and resource utilization,to improve the performance of sludge dewatering,and to promote the degradation of organic matter in the anaerobic digestion process of sludge,based on the different mechanisms of ultrasonic(US)and persulfate(SPS)on sludge cracking,this study uses separate and combined pretreatment of sludge to explore the effects of sludge dewatering and anaerobic digestion.The main conclusions of this study are as follows:(1)The results showed that the optimal dosage of SPS in the range of 0.3-2.7mmol/g VSS was 1.8 mmol/g VSS,and the SCOD was 1254 mg/L,which was 5.6times of the original sludge.In the meantime,CST,SRF and WC were 32.3s,353×1010m/kg and 75.8%,which decreased by 70.5%,69.3%and 8.5%compared with raw sludge.However,with the continuous increase of dosage,they increased to a certain extent,indicating that SPS alone had better effect on sludge dewatering,while excessive dosage was not conducive to sludge dewatering.(2)The results showed that ultrasonic pretreatment alone had a good effect on sludge cracking.When the treatment time was up to 160min,the sludge could be completely cracked.At this time,the SCOD was 1625mg/L,which was 7.3 times of the original sludge.With the increase of ultrasonic treatment time,the values of CST and SRF were 14.2 times and 13.3 times higher than those of raw sludge in 40 min of ultrasonic treatment,respectively,and WC was 85.6%in 60 min of ultrasonic treatment,which was 1.3%higher than that of raw sludge,indicating that ultrasonic treatment alone would lead to the deterioration of sludge dewatering.(3)The results showed that the SCOD of US/SPS pretreated sludge had a significant jump within 10-90 min of ultrasonic treatment,and reached the peak value of 1501 mg/L at 40 min,which indicated that ultrasonic treatment could significantly promote the activation of SPS,but too long ultrasonic treatment would gradually make SPS lose its activation state.Therefore,it is very important to choose the appropriate ultrasonic treatment time according to the actual situation.At the same time,the indexes of CST,SRF and WC have increased to a certain extent,but compared with the sludge pretreated by ultrasonic alone,the dewatering performance of sludge has been improved.(4)The SCOD of US/SPS reached the peak value of 2612mg/L on the 11th day,which was 4.4 times of that of the original sludge.The soluble protein and polysaccharide of US/SPS were 434mg/L and 186mg/L,respectively,which were 5.8and 5.3 times of that of the original sludge.The results showed that US/SPS could promote the hydrolysis process of sludge during anaerobic digestion,but the peak value of US/SPS would shift backward.(5)The VFAs content of US/SPS reached the peak of 1586mg/L on the 11th day of anaerobic digestion,which was 5.0 times of that of raw sludge.The VFAs content at the end of the experiment was 1305mg/L,which was significantly higher than that of897mg/L only treated by SPS.In VFAs composition,the acetic acid content of US/SPS group was the highest,reaching 63%,which was 2.9 times higher than that of raw sludge,indicating that the system could significantly contribute to the acid production process of sludge and promote the conversion of fatty acids to acetic acid.(6)The methane production of US/SPS reached a peak of 52m L on the 13th day of anaerobic digestion.The cumulative methane production of US/SPS in the first 12days was lower than that of SPS alone.The cumulative methane production of US/SPS in the 21st day was 658 m L,which was 4.4 times of that of raw sludge.The results showed that the system promoted the methanogenic process of anaerobic digestion of sludge and increased the methane production,but the methanogenic rate was low in the early stage. |
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