Effects Of Organic Loading On The EPS Secretion And Particle Formation Characteristics Of Aerobic Sludge

Aerobic granular sludge has dense structure,strong impact load resistance,high biomass,good settling property,and the ability to remove nitrogen and phosphorus synchronously.Therefore,more and more attention has been paid to the formation mechanism of aerobic granular sludge and the degradation of pollutants.Organic loading plays a key role in the formation of aerobic granular sludge.At present,a large number of studies have shown that organic loading can be successfully cultured between 1.2¹5 kg COD m^-3·d^-1,but the low organic loading will seriously inhibit the formation of aerobic granular sludge,which leads to the obvious limitation when treating low organic wastewater with aerobic granular sludge technology.In the process of aerobic sludge granulation,EPS?Extracellular polymeric substances?plays an important role in the process of aerobic sludge granulation.There is no clear conclusion about the relationship between organic loading and EPS,so it is necessary to explore the secretory characteristics of EPS under different organic loading conditions,and then reveal the influence mechanism of different organic loadings on the process of aerobic sludge granulation.The results show that:?1?Under the condition of high organic loading(4.8kg COD m^-3·d^-1),the aerobic granular sludge size is bigger,and the mature stage can reach about 2.5 mm.Under low organic loading(1.2 kg COD m^-3·d^-1),the particle size of mature granular sludge is about 1.2 mm,but aerobic granular sludge cultivated by low organic loading is more regular.High organic loading is beneficial to shorten the formation cycle of aerobic granular sludge.Compared with the high organic loading,there were less filamentous bacteria in the low organic loading reactor during the formation of aerobic granular sludge.Compared with the target loading start-up method,the aerobic granular sludge cultivated by increasing loading start-up mode has better stability.?2?High organic loading is helpful for promoting the secretion of extracellular polymeric substances?EPS?,the initial sludge EPS content was 54.82 mg·g^-11 MLSS,and at the granules formation stage,the EPS content in high organic loading reactor increased to 220.5 mg·g^-11 MLSS,and the EPS content in low organic loading reactor increased to 182.57 mg·g^-11 MLSS;In addition,high organic loading was also more helpful to increase the content of protein?PN?and polysaccharide?PS?,and the change of protein content was more obvious than that of polysaccharides.At the granules formation stage,the PN/PS value in high organic loading reactor increased from the initial 4.2 to 12.4,and the PN/PS value in low organic loading reactor increased from the initial 4.2 to 12.19.?3?In combination with three-dimensional fluorescence spectrum and Fourier infrared spectrum analysis,in the process of sludge granulation,only the three peaks of peak A,peak B and peak D were detected in the whole sludge granulation process,indicating that organic loading had no significant effect on the composition of EPS.The location of the fluorescence peak had a certain movement,indicating that organic loading could change the structure of EPS,thus affecting the formation and characteristics of granular sludge.In aerobic granular sludge formation,the functional groups of EPS in the two reactors were basically the same,indicating that the organic loading did not affect the functional groups of EPS.?4?With the process of sludge granulation,the content of hydrophobic acid?HOA?increased a lot.The second is hydrophobic neutral substance?HON?,the content of hydrophobic alkaline substance?HOB?increased less,and the content of hydrophilic substance?HI?changed little.It can be seen that hydrophobic substances,especially HOA,play a major role in the process of sludge granulation.The growth rate of components in high organic loading was significantly higher than that of low organic loading,indicating that high organic load was more beneficial to promote the secretion of EPS components.?5?The fluorescence peaks of HOB,HOA,HI and HON were the same in the two reactors,indicating that the organic loading had no significant influence on each component.Comparing the fluorescence peaks of each component in low organic loading,the fluorescence intensity of fluorescence peak in high organic loading is stronger,indicating that high organic loading is more conducive to the secretion of protein and soluble microbial metabolites.