Causes And Control Measures Of Biological Foam In Sewage Treatment Plant In Urumqi

In this paper,a sewage treatment plant which adopted oxidation ditch process in Urumqi is tracked and investigated on the spot.Its normal operation and water quality of the effluent were seriously interfered by the biological foam phenomenon in winter.The activated sludge samples which were collected from the oxidation ditch was used to study the biological causes of biological foam by high-throughput sequencing technology.At the same time,the control effect of different control strategies on biological foam in the plant was studied by adding anaerobic biological selection tank,strengthening sludge discharge,increasing aeration and artificial salvage.The main research results are as follows:（1）The results showed that the removal rate of BOD₅、COD、SS and TP of the oxidation ditch process were 91.7%、93.5%、95.7%and 91.7%respectively from January 2016 to July 2018 and the effluent concentration of them had reached the design discharge standard.The removal rate of TN and NH₄⁺-N were 81.7%and 65.2%respectively.During the low water temperature period in winter,the removal rate of NH₄⁺-N decreased,which resulted in the excessive concentration of TN effluent.（2）The biological foam phenomenon occurred from December 2017 to March2018 while the activated sludge expanded.Microscopic examination of sludge and Gram staining showed that the structure of activated sludge tended to disperse and the type of sludge bulking was filamentous bulking.（3）High-throughput sequencing showed that Proteobacteria（28.25%⁴8.96%）and Bacteroidetes（18.00%³8.59%）were important bacterial phylum in activated sludge.Microthrix and Flavobacterium were important bacterial genus.The excessive proliferation of Microthrix（from 1.33%to 8.37¹8.74%）in the winter and spring at low water temperature in 2018 was the main reason for the occurrence of biological foam in the plant.And the high relative abundance of Flavobacterium in the winter of 2017（5.04%¹3.76%）and 2018（6.90%⁸.58%）had an adverse effect on the sedimentation performance and biological foam phenomenon of the sewage treatment plant.（4）Ascomycota（59.81%⁸4.63%）and Basidiomycota（7.84%²1.64%）were important fungi phylum in activated sludge.Norank_Ascomycota and Trichosporon were important fungi genus.And it was speculated that the abnormal proliferation of the Trichosporon was an important cause of biological foam in the plant.（5）Anaerobic selective pool had little effect on bacterial community,and had no significant inhibitory effect on Microthrix and Flavobacterium of foaming microorganisms.The fungal community was significantly affected by anaerobic selection pools,in which norank_Ascomycota were significantly inhibited.The control effect of biological foam phenomenon was not obvious by strengthening mud drainage and increasing aeration.The method of artificially salvaging two mud tanks to reduce the impact of biological foam on operation is obvious.However,the SS of effluent exceeded the standard,which can not fundamentally control the drawbacks of biological foam.