The Responses Of Aerobic Granular Sludge To Toxicity Inhibition

Aerobic granule technology,as a new biological treatment technology,shows a promising prospect of the application in wastewater treatment.Due to its unique structural characteristics,aerobic granular sludge possesses special superiority in the treatment of toxic substances.Thiamethoxam?TMX?is a typical pesticide of low toxicity which has been widely used for decades in agriculture while benzenediol is a kind of highly toxic substance existing in phenolic wastewater.Thus,the investigation of the toxic effects of TMX and benzenediol on aerobic granular sludge will provide useful information for treating toxic wastewater by using aerobic granular sludge.Main contents and results of this disseration are as follows:?1?Aerobic granular sludge was cultivated in a sequencing batch reactor?SBR?with sucrose.After 105-day-operation,the flocculent sludge gradually took the shape of mature faint yellow granules,which consisted of large quantities of rod-like bacteria and a small number of coccus-like bacteria.At the same time,the sluge volume index?SVI?retained at around 40 m L/g.In the SBR,the removal rate of chemical oxygen demand?COD?could reach to the level of more than 90 %,nevertheless the removal rates of NH₄⁺-N and PO₄^3--P were remained at the low level of 67 % and 55 %,respectively.Live bacteria mainly distributed on the surface of aerobic granules,while dead bacteria were noted to distribute throughout the whole granule.According to the fluorescent staining results of extracellular polymeric substances?EPS?,the ?-D-glucopyranose polysaccharide accumulated in the outer layer of granules,while protein and ?-D-glucopyranose polysaccharide were not only concentrated in the outer layer but spread throughout the granule interior.?2?The toxic effects of TMX and benzenediol on aerobic granules and flocs were investigated.The toxicity of TMX and benzenediol caused inhibition to specific oxygen uptake rate?SOUR?,and the formation of EPS contents,as well as the removal efficiency of COD,NH₄⁺-N and PO₄^3--P.In addition,the inhibitory effect of benzenediol on aerobic granules was weaker than that of flocs.The comparision of the results of the inhibitory effect on aerobic granules showed that the toxicity of TMX was much weaker than that of benzenediol.?3?The toxic effect of benzenediol on aerobic granules was investigated in a SBR.In the SBR,aerobic granules gradually disintegrated under the instantaneous shock of the addition of benzenediol.At the same time,SOUR,the activity of live bacteria and the formation of EPS,as well as the removal of COD,NH₄⁺-N,and PO₄^3--P were inhibited.The removal rate of COD maintained at around 60 %,but the removal efficiency of NH₄⁺-N and PO₄^3--P could only keep at the lower level of 10 % and 20 %,respectively.In addition,the contents of ntracellular protein and ?-D-glucopyranose polysaccharide were less than before shock.After a period of acclimation,significant changes had taken place in bacteria on the surface of the granules.Firstly,the granules mainly comprised bacterial populations with coccus-like morphologies after 26 days-domestication.Secondly,SOUR and the removal efficiency of COD,NH₄⁺-N,as well as PO₄^3--P gradually recovered.The COD removal rate was even risen to around 90 %.However,the removal efficiency of NH₄⁺-N,and PO₄^3--P couldn't back to the original level but sustained at the level of 40 %.Finally,the total cells slowly spread outward from aerobic granules,in the meantime ?-D-glucopyranose polysaccharides had a tendency to spread inward.