Study On Formation Mechanism And Control Measures Of Foaming Sludge In Municipal Wastewater Treatment Plants

Sludge foaming and bulking are the main problems affecting the stable operation of activated sludge process.In this study,5 WWTPs in Fuzhou city of Fujian province were chosen and a continuous observation conducted,including the characteristics of foaming sludge,the dominant bacterial community and the operation factors influencing on microorganisms,etc.Finally,specific preventing and contorl proposals were put forward.Firstly,the results of sludge component tests indicated that foams contained inorganic substances with hydrophobicity,sludge lack of metal ions and microbial community with high secretions of EPS were floating to the surface of aeration tank.The results of SOUR performance tests showed that foams also remain active.Floating rate of foams indicated that there were different content of hydrophobic and low-density stable substances existing in the foams,moreover,showed a significantly positive correlation with the EPS content.Secondly,high-throughput sequencing(HTS)by MiSeq platform was used to obtain16S rRNA-sequences of the foams,foaming activated sludge and non-foaming activated sludge from 5 WWTPs.The results showed that Bacteroidetes phylum and Actinobacteria phylum were enriched in the foams from Yangli(phase ?),Jinshan,Xiangban,and Houguan,and Actinobacteria phylum was enriched in Yangli(phase ?)and yangli(phase ?).The result of LEfSe analysis showed that Mycobacterium,Mycobacteriaceae,Nocardiaceae,A ctinomycetales,Chryseobacterium,Flavobacterium,Ormithobacterium,Flavobacteriaceae and Portibacter were playing important roles in the foaming sludge groups.Among them,Mycolata(including Mycobacterium and Nocardiaceae)was a kind of mycolic acid producing bacterium,which existed and enriched in all of these investegated wastewater treatment plants suffering from foaming in different levels.Then,microbial community morphology was identified and distinguished out of Type 1863,Type 0092,H.hydrossis,Nocardiaforms and Nostocoida limicola ?,etc.Finally,parameters of influent wastewater quality,system design and actual operations of 5 WWTPs were investigated and analyzed.The RDA(Redundancy analysis)showed that the excessive growth of filamentous bacterias in Houguan directly led to bulking with high SVI,and was positively correlated with SRT and negatively correlated with dissolved oxygen,which means long SRT and low DO may lead to the bulking of Houguan,then lead to foaming.In addition,the dominant bacterial community showed significant positive correlations with SS and MLSS in the foam from Yangli(phase ?)?Jinshan and Xiangban,while positive correlations with temperature and DO in the the foam from Yangli(phase ?)and Yangli(phase ?).Based on the different causes of foaming,including the dominant bacterial comunity and actual operations,corresponding control measures were put forward.From the microcosmic point of view.,basic characteristics of foaming sludge and microbial community structures were studied;and from the macroscopical point of view.,the influencing factors including parameters of influent wastewater quality,system design and actual operation were investigated and analyzed.Then the formation mechanism of foam was explored.And based on that,specific contorl measures were proposed.This study will provide theoretical foundation to practical engineering from foaming prevention and control.