Characteristics Of Aerobic Granular Sludge And Its Microorganism Under Different Salinity

Aerobic granular sludge is the self-immobilized consortia and a special three-dimensional case of biofilm.As a new wastewater treatment technology,aerobic microbial granules have good settleability,high biomass retention,high microbial activity,and good ability to withstand high organic loading rate and toxic substances, which has wined more and more attentions in the filed of wastewater treatment.Saline wastewater is widely produced in many industries.Nowadays,saline wastewater is mainly from food,chemical,petroleum,pesticide industry,and so on. High salinity can change the osmotic pressure and can cause plasmolysis and/or loss of activity of cells,so saline wastewater is one of the most difficult to treat wastewater. Many researcher have treated saline wastewater by biotreatment,but generally fell in the problem of instability.This study is based upon the novel aerobic granular sludge to treat the saline(NaCl) wastewater.Three identical Sequencing Batch Reactors(SBRs)were used,the active sludge was inoculated,by adjusting aeration rate and settling time,the aerobic granules were successfully cultivated.Then the salinity of the reactors was changed gradually, the salinity of R1,R2 and R3 was finally set at 1%,2.5%and 5%.The aerobic granules and their microorganism under different salinity were studied.The main experiment results were as follows:The aerobic granulation was appeared on about 20 days.The mature aerobic granules were almost in the rang of 0.4-0.8mm.The higher salinity benefited the settleability,density,and compaction of aerobic granules.The hollow structure was easily formed inside the granules under low salinity(1%);There were no voids found in the granules under medium salinity(2.5%),but some granules broke up happened in this case;In the high salinity,the granules were the most compact.Extracellular polymeric substances(EPS),as well as its protein and polysaccharide amount increased with the salinity raised,i.e.R1＞R2＞R3.In addition,the protein and polysaccharide amount were both higher in the mature period than the old period.In high salinity(5%),the surface of the granules was rather coarse;whereas in low(1%) and medium(2.5%)salinity,the surface of the granules was relatively smooth.After acclimation the microorganism could maintain a relatively high bioactivity under the salinity of 2.5%.but when the salinity increased to 5%,there was filamentous bacteria appeared in R3,the whole reactor was in a unstable state,Then the prolification of filamentous bacteria happened in R3,the foregoing bacteria granules gradually changed into filamentous granules.Here,the filamentous granules were still had good settleability and compaction,but then the filamentous granules became larger and looser, which led to the broke up of the granules and the failure of the experiment;The bioactivity increased gradually after acclimation,and the granules were also stable under the lower salinity(R1,R2).In addition,the experiment shows that the SS,NH₃-N and pH value increased with the salinity raise.High salinity resulted in high settling velocity,low porosity,and big density,i.e. compact granules.Although compact granules could be formed under the high salinity, they may be outcompeted by the filamentous granules.Therefore,to control the proliferation of filamentous microorganism should be of great concern on the application of aerobic granules for the wastewater treatment with high salinities.