Study On The Effect Of Compatible Solutes On The Treatment Of Hypersaline Wastewater From Anaerobic Granular Sludge

Because of the high salinity,the biological treatment of hypersaline wastewater is difficult.When the osmotic pressure of microbial environment is too high,such phenomena as cell dehydration,plastic-wall separation and cell death will occur,which will greatly reduce the treatment effect of bioreactor.Therefore,for the biological treatment of high-salt wastewater,how to enable microorganisms to survive in hypersaline environment and play its effectiveness is the key.Compatible solutes can accumulate in large quantities in cells,and the intracellular enzyme activity was not affected,other intracellular biomolecules do not need to adapt to the new environment with high concentration of compatible solutes any more.Just like perfect fusion with cells,they balance the osmotic pressure inside and outside the cell,enabling microorganisms to grow and metabolize normally in a hypersaline environment.In this paper,the effect of compatible solutes on the treatment of hypersaline wastewater by anaerobic granular sludge was studied on the premise of referring to domestic and foreign literatures and long-term cultivation and domestication of granular sludge.High throughput sequencing was used to analyze the microbial diversity in anaerobic biological systems in order to study the effect of compatible solutes on anaerobic biological systems.The results of the study are as following:（1）For the granular sludge without salinity acclimation in the treatment of no salt wastewater,when the organic load rate was 3898mg/（L·d）,the COD removal rate was all above 70%at the temperature of 25℃and 35℃,the highest were 83.5%and 87%,respectively,eflluent VFA and p H value were 7-8mg/L and 7-7.5,respectively,the effect of temperature on granular sludge is weak.When the organic load rate was 7796 mg/（L·d）,the COD removal rate was around 70%at the temperature of 25℃and 35℃,the highest were82.3%and 82.6%,respectively,eflluent VFA and p H value were 10-11mg/L and 6.5-7.3,respectively.Removal rate decreases with the increases of organic load rate,the effluent VFA value increases with the increases of the organic load rate,the effluent p H value increases with the increases of the organic load rate.For the granular sludge with 20g/L salinity acclimation in the treatment of 20g/L hypersaline wastewater,when the organic load rate was 3898mg/（L·d）,the COD removal rate was 50%and 40%at the temperature of 35℃and 25℃,eflluent VFA and p H value were11-12mg/L and 5.7-6.3,respectively.When the organic load rate was 7796mg/（L·d）,the COD removal rate was 40%and 30%at the temperature of 35℃and 25℃,eflluent VFA and p H value were 17-18mg/L and 5.3-5.7,respectively.The variation of the three indexes with OLR and temperature is the same as described above.While the COD removal rate decreases strikingly with the increases of the salinity,the effluent VFA value increases with the increases of the salinity,the effluent p H decreases with the increases of the salinity.（2）By comparing the promotion effect of three compatible solutes of betaine trehalose and glutamate on the anaerobic reaction system,it was found that within a salinity of 20,the strength relation of the three solutes was betaine>trehalose>glutamate,and all of them could effectively alleviate the inhibition effect of microorganisms under high-salt environment.（3）The best mixture ratio was explored by combining compatible solutes,The treatment system works best when the mass ratio of betaine trehalose glutamate proline to KCl is80-120:10-30:50:50:1,The COD removal rate reached 93.4%,83.7%and 83.3%at the salinity of 0,10 and 20g/L,respectively,11.1%,27.6%and 38.8 higher than the control group.The alkalinity of the effluent increased with the increase of OLR.In the experimental group A#2,the alkalinity of water with salinity of 10g/L and 20g/L was the highest,reaching1376mg/L and 1341mg/L respectively.However,the alkalinity of effluent from non-saline waste water was not significantly different among the three experimental groups.With the increasing of organic load and salinity,the specific methanogenic activity（Y_g value）decreases gradually,The experimental group A#2 showed the most significant improvement in Yg,reaching a maximum of 14.38,11.88 and 10.63ml CH₄/(g COD_removal·d),respectively,under the three salinities,which is consistent with the conclusion of COD removal rate and alkalinity of effluent.Compared with the control group,the activity of methane production increased by 43.5%,138%and 240%,respectively.（4）The results of multi-factor orthogonal experiment show that the optimum technological conditions for the treatment of 20g/L hypersaline wastewater by anaerobic reaction bottle are:OLR 4500mg/（L·d）,the mixing ratio of compatible solutes 110:20:50:50:1,p H8,35℃,the significance order of the influence of each factor on COD removal rate was OLR>mixing ratio>temperature>inlet p H.The optimum technological conditions for the treatment of 10g/L hypersaline wastewater by anaerobic reaction bottle are:OLR5000mg/（L·d）,the mixing ratio of compatible solutes 90:20:50:50:1,p H7,30℃,the significance order of the influence of each factor on COD removal rate was mixing ratio>temperature>OLR>inlet p H.The optimum technological conditions for the treatment of no salt wastewater by anaerobic reaction bottle are:OLR 4500mg/（L·d）,the mixing ratio of compatible solutes 90:20:50:50:1,p H8,35℃,the significance order of the influence of each factor on COD removal rate was OLR>inlet p H>temperature>mixing ratio.（5）The analysis of community genus level composition shows that the composition of the community A2 and A3 changed significantly compared with A1.The proportion of dominant bacteria of the sample A1 is Clostridium＿sensu＿stricto＿12（30.63%）,Prevotella＿7（21.58%）,Caproiciproducens（5.14%）and Acetobacter（5.04%）.The proportion of dominant bacteria of the sample A2 is Fonticella（42.14%）,Oscillibacter（20.57%）and Caproiciproducens（8.33%）.The proportion of dominant bacteria of the sample A3 is Fonticella（31.07%）,Oscillibacter（27.69%）and Caproiciproducens（6.82%）.The analysis of community phylum level composition shows that the composition of three sample community are basically the same,but the content varies greatly.The proportion of dominant bacteria of the sample A1 is Firmicutes（71.86%）,Bacteroidetes（21.58%）and Proteobacteria（5.11%）.The proportion of dominant bacteria of the sample A2 is Firmicutes（89.28%）,Bacteroidetes（2.67%）and Actinobact（6.41%）.The proportion of dominant bacteria of the sample A3 is Firmicutes（83.27%）,Actinobact（5.81%）and Proteobacteria（5.36%）.Firmicutes,as the dominant phylum,can produce spores to resist the external environment under the adverse environment of high salt,and play an important role in the production of methane precursors represented by acetic acid during anaerobic digestion.Clostridium and bacteroides are responsible for the hydrolysis and fermentation of organic compounds.