Study On Vacuum Drainage Of Sludge Considering Clogging Effect

With the rapid development of China's economy,the sewage production is also growing rapidly.Sludge production increased sharply.How to deal with sludge reasonably and effectively becomes particularly important.As a new method of sludge drainage,sludge vacuum drainage technology has the advantages of low cost and simple equipment compared with mechanical drainage method in existing sewage treatment plants.In the process of sludge vacuum drainage,the effect of vacuum degree and silting makes most sludge drainage results still fall short of expected results..In this paper,the vacuum drainage effect of sludge is studied.The air permeable vacuum sludge drainage test and bottom vacuum sludge drainage test are carried out by using self-made test equipment.The different permeable geotextiles,rice and wheat straw drainage bodies were studied.The drainage effect of different test methods and sludge drainage from different drainage bodies is analyzed.The mechanism is studied.The numerical simulation is carried out with Midas GTS finite element software.The main research contents and results are as follows:(1)Using self-made air permeable vacuum sludge drainage test device,five different kinds of permeable geotextiles were tested for air permeable vacuum sludge drainage.The results show that the drainage process of air permeable vacuum sludge can be divided into four stages: sludge granule sedimentation and flocculation stage,sludge granule flocculation and remolding stage,sludge granule flocculation concentration and breakdown stage,and permeable vacuum formation stage.Among them,the effective pore size of 0.071 mm permeable construction cloth had the largest total drainage and the shortest use time.After the test,the water content of sludge is still as high as 94%.And the time consumed is still the Longer.Although the volume reduction rate is relatively high(about50%),the final water content of sludge has not reached the expected effect.(2)Using a self-made bottom vacuum sludge drainage test device,the experiments of rice and wheat straw drainage bodies with thickness of 5 cm,10 cm and 15 cm were carried out respectively.The results showed that the bottom vacuum sludge drainage experienced the stage of sludge granule sedimentation and flocculation and the stage of upper atmospheric pressure compaction.Under the same conditions,the drainage effect of rice drainage sludge was far less than that of wheat drainage sludge.The drainage effect of wheat drainage sludge with 15 cm thickness was the best.After the experiment,the final water content of sludge was reduced to 75.81%.The volume was reduced by about 90%.The effect was remarkable.(3)Using the calculation method of average permeability coefficient of drainage body and combining with the test results,the change of silting degree of different drainage bodies in the test is analyzed.It shows that the bottom vacuum sludge drainage technology is superior to the air permeable vacuum sludge drainage technology.The plant straw drainage body can greatly improve the silting of sludge.(4)The results of experiment and numerical analysis show that the bottom vacuum sludge has Mandel effect at the initial stage of drainage.The pore water pressure does not decrease at the initial stage.With the increase of vacuum time,the drainage boundary extends from the bottom to the top.The negative pressure transfers to the top,which promotes sludge drainage.