Effects Of Powered Activated Carbon On The Formation Of Aerobic Granular Sludge And Variation Of Bacterial Community Structure

Aerobic granular sludge is spherical or ellipsoidal sludge formed by self-flocculation.It consists of aerobic zone,anoxic zone and anaerobic zone.Aerobic granular sludge technology has the characteristics of good settling performance,high microbial concentration,less excess sludge,strong impact resistance capacity and so on.So it has a great potential application on wastewater treatment.Due to its long time of formation and instability,how to speed up the formation of granular sludge and increase the stability of sludge has become a technical bottleneck which restricts the development and application of the technology.Some studies showed that adding activated carbon can shorten the formation time of aerobic granular sludge,but others show controversial results.Therefor,there are no definite conclusions on this issue.Bacterial community structure is the biological basis for the realization of various functions,which has a great effect on the stability of aerobic granular sludge and the removal efficiency of nitrogen and phosphorus.However,the effect of activated carbon on the bacterial community of aerobic granular sludge is not reported yet.In this thesis,we investigated the formation process of granular sludge and the effect of powered activated carbon addition on it through cultivating activated sludge in SBR.Then we analyzed the bacterial communities of activated sludge and granular sludge,and the effect of activated carbon on it.The main results are as follows:?1?The granular sludge was formed at 70 days and 61 days in GS?Aerobic granular sludge?and GSC?Aerobic granular sludge with activated carbon?reactors,suggesting the addition of activated carbon could shorten the sludge granulation time.The mature aerobic granular sludge was spherical and ellipsoidal,and the particle size was about 0.55 mm.After 150 days cultivation,the diameter of granular sludge in GS and GSC reactors increased to 0.76 mm,0.65 mm,respectively.It showed that activated carbon sludge could improve the formation of granular sludge.?2?After cultivation of 150 days,the concentration of MLVSS,SVI,PN/PS varied from 2752 mg/L,188.244 mL/g and 1.31 to 5946 mg/L,16.95 mL/g and 2.01for GS;from 2674 mg/L,196.45 mL/g and 1.27 to 7232 mg/L,16.13 mL/g and 2.64for GSC.After the initial phase of adaptation,the effluent TN,NH₄⁺-N and TP indexes meeted Standard A of the first class,and COD meeted Standard B of the first class in"Discharge standard of pollutants for municipal wastewater treatment plant".Adding activated carbon to the granular sludge could promote the phosphorus removal.?3?During the granulation of sludge,the dominant phyla in sludge changed significantly,from Proteobacteria?70.00%?and Bacteroidetes?15.80%?to Proteobacteria?74.26%?and Nitrospirae?11.83%?for GS.similar results were obtained for GSC,with Proteobacteria?75.45%?and Nitrospirae?11.80%?as the dominant phyla,suggesting that activated carbon did not affect bacterial community at phylum level.?4?The high percent?33.75%?of major genus Dechloromonas in AS?Activated sludge?group decreased to 11.27%?GS?and 10.61%?GSC?after the formation of granular sludge.These bacteria had the capibility of reducing chlorate and/or perchlorate,and some strains of Dechloromonas could use nitrate as an electron acceptor and even produce polyhydroxyalkanoate?PHA?.?5?The percent of Candidatus Accumulibacter?PAO,12.49%?and Zoogloea?denitrifying bacteria,7.17%?turned to 22.47-22.48%and 0.41-0.45%,respectively.Because some strains of Candidatus Accumulibacter had the ability to take up P using nitrate,the increased proportion of these strains compensated for the reduction of Zoogloea,which resulted in the increase of denitrification ability in granular sludge.?6?The percent of Nitrospira?NOB,2.22%?increased greatly to 51.83%?GS?and 51.10%?GSC?.The reason may be that the concentration of ammonia in inflow was high and the operation condition of SBR favored for the formation of nitrous,which promoted the growth and reproduction of Nitrospira.Nitrospira can also excrete extracellular polymers,which may accelerate the formation of granular sludge.