Effect Of Turbulence Intensity And Illumination Time On Wastewater Treatment By Bacteria-Algae System And Its Influencing Mechanism

The bacteria-algae symbiosis system can remove organic matter and nutrient at the same time,without external aeration and adding chemical agents.It has the advantages of small occupation area,low energy consumption and no secondary pollution,so it has a good application prospect.Hydrodynamic condition is the key influence facor in the water treatment.At present,there are few studies on the effects of turbulence intensity on wastewater treatment by bacteria-algae symbiosis system,especially under the coupling effect of turbulence intensity and illumination time.And the mechanism of them is still unclear.Further studies on the effects of turbulence intensity and illumination time are needed.Therefore,Chlorella pyrenoidosa-activated sludge symbiosis system is constructed in a closed reactor in this paper.Turbulence is generated by agitator.The experiments are carried out under different turbulence intensities（formed at three rotational speeds-200,400 and 600r/min）and two kinds of illumination time（22h full illumination and light to dark ratio of 10h:12h）to study the effects of turbulence intensity and illumination time on the treatment capacity,physicochemical properties and bacteria community structure of the bacteria-algae system.The main results are as follows:（1）Effects of turbulence intensity and illumination time on the wastewater treatment by the bacteria-algae system.There is little difference in the total biomass of bacteria-algae under different turbulence intensities.The growth rate of Chlorella and sludge is faster under high turbulence intensity,while the growth rate of Chlorella is gradually lower than that of sludge under low turbulence intensity.Compared with 10h:12h,the total biomass under22h full illumination increased by about 50%.The larger the turbulence intensity is,the better the removal effect of bacteria-algae system on COD and NH₄⁺-N is,and the better the removal effect of PO₄^3--P is when the illumination is limited.The removal rate of COD is always good under 22h full illumination and the removal rates of NH₄⁺-N and PO₄^3--P decrease day by day,while the removal rates of COD,NH₄⁺-N and PO₄^3--P increase day by day under 10h:12h.（2）Effects of turbulence intensity and illumination time on physicochemical properties of bacteria-algae.The larger the turbulence intensity is,the larger the size of the flocs is,the smaller the supernatant MLSS is and the better the flocs settlement is.Under different illumination time,the particle sizes of bacteria-algae flocs and the supernatant MLSS have no obvious rules,but the DSIs of bacteria-algae flocs under 22h full illumination are smaller and the particle size distributions are more concentrated.The larger the turbulence intensity is,the higher the protein content of EPS is,the lower the polysaccharide content is and the higher the proteoglycan ratio is.The contents of polysaccharide and protein in EPS under 10h:12h are higher than those under 22h full illumination.The particle sizes of bacteria-algae flocs are positively correlated with the sedimentation,while the component and content of EPS are not correlated with the sedimentation.（3）Effects of turbulence intensity and illumination time on bacteria community structure.The greater the turbulence intensity is,the greater the diversity,richness and diversity of the bacterial community are.The diversity,richness and difference of bacterial community were greater under 22h illumination time than under 10h:12h.The greater the turbulence intensity is,the greater the abundance of Bacteroidota,Cyanobacteria,Flavobacterium and Acidovorax is,and the smaller the abundance of Proteobacteria,Aeromonas and Enterobacter is.