Effect Of Influent Phosphate On The Granulation Process Of Aerobic Sludge

In recent years,the water pollution is becoming more and more serious and eutrophic water can be seen everywhere,owing to the rapid development of China’s industrial and agricultural economy.The aerobic granular sludge（AGS）with good settling characteristics,shock load capability,robust rules of dense structure of microbes,microbial flora rich,et al.,it has a good development prospects in the sewage treatment.Phosphorus is a necessary nutrient element in biological activities,such as microbial growth,metabolism,etc.The deficiency of phosphorus can cause the metabolic disorder of microbes and the degree of microbial aggregation.There was little information about phosphorus on the formation of granular sludge under aerobic conditions,and the researches mainly focused on the influence of phosphorus on the formation and stable operation of AGS that the state of phosphorus deficiency or under aerobic anaerobic condition.In this study,the AGS was cultivated by changing the influent phosphorus concentration.The morphology and characteristics of sludge and the changes of phosphorus in sludge during the process of floc sludge granulation were studied.The removal effect of pollutants and the characteristics of extracellular polymeric substances（EPS）were analyzed.And the fluorescence characteristics of EPS in the process of floc sludge granulation were investigated by three-dimensional fluorescence spectroscopy and synchronous fluorescence spectroscopy.In order to provide a theoretical basis for the formation and stable operation of aerobic granular sludge.The color of sludge changed from light black to light yellow,the surface relative hydrophobicity and flocculability of sludge were low and the activity of sludge was general after the acclimatization of 15 d.The removal rates of chemical oxygen demand（COD）and ammonium（NH₄⁺-N）were 88.7%and 99%respectively,and the effluent was mainly nitrate（NO₃^--N）.Three-dimensional fluorescence showed that the various types of EPS mainly contained aromatic protein-like substances and metabolites of soluble microorganism.The high influent phosphorus was beneficial to the granulation of sludge of AGS.The acclimated sludge was cultured in R1（the concentration of influent phosphorus was 4.48-8.16mg/L）and R2（the concentration of influent phosphorus was 25.05-31.01 mg/L）sequence batch reactor（SBR）formed the spherical or ellipsoidal,tightly structured and yellow brown aerobic granular sludge,and the average particle size of granular sludge were 900μm and 1150μm,respectively.The sludge activity of aerobic granular sludge were 6.09 mg/（g*MLSS·h）and 6.99mg/（g*MLSS·h）,the surface hydrophobicity were 48.07%and 65.80%respectively,and the flocculation were 29.68%and 46.79%respectively,in R1 and R2 reactors.High influent phosphorus concentration is also promotes the absorption of phosphorus in the sludge.The content of TP in R1 and R2 sludge increased to 24.85 mg/g and 27.20 mg/g,respectively,and the increase of TP content mainly depended on the increase of IP,while OP and AP were relatively stable during the process of sludge granulation.There was a good removal of pollutants in the process of aerobic granular sludge culture,and high influent phosphorus was contributed to improve the purification efficiency of pollutants.The average removal rate of R1 and R2 to COD were 83.33%and 94.66%,respectively.When the ammonium concentration in influent increased to about 200 mg/L,in addition to the low MLSS,the removal rate of ammonium was around 99%in other periods.And the effluent of the reactors were mainly nitrite（NO₂^--N）.Three-dimensional fluorescence showed that the EPS mainly contained two kinds of characteristic peaks of aromatic protein-like substances and metabolites of soluble microorganism,and the fluorescence intensity and peak position of the characteristic peaks from the growth period to the mature period were all changed.Phosphorus had a dynamic quenching on EPS at phosphorus concentration between 0 mg/L and 17.5 mg/L,and it is the indirect production of phosphorus by cations.During the formation of granular sludge,polysaccharide（PS）and protein（PN）are mainly present in close-layer extracellular polymer substances（TB-EPS）and the content of PS and PN in TB-EPS were close to that of T-EPS.The PN content of EPS in R2 was higher than that of R1,and the content of PS in R2 was lower than that of R1.And in loose-layer extracellular polymer substances（LB-EPS）,PS>PN,it is just the opposite in TB-EPS and T-EPS.