| Low temperature(4-15?)is one of the major limiting factors of microbial activaty of activated sludge.As temperature plays a decisive role on the growth of individual microorganisms,reproduction,metabolism,community distribution and community size,low temperature becomes the key problem of process running in sewage treatment plant.Existing studies are needed to search for effective strengthening technology to ensure the normal characteristics of activated sludge microorganisms(ASM)at low temperatures.Magnetic field(MF)has biological magnetic effects,with good value in biological wastewater treatment processes.The purpose of this paper is to study the effect of MF strengthening on cold adaptability of microorganisms in activated sludge.Microorganisms adapted to low-temperature environment by regulating the phosphorylation and dephosphorylation of lipopolysaccharide,lipid composition,protein synthesis,and cold-shock protein.Phospholipid fatty acid(PLFA)as the major component of cell membrane lipids can fully reflect the variation status of microbial cell membrane at low temperature.The species and composition variation of PLFA were analyzed in ASM at low temperature.Enhanced by different MF strengthening methods and intensities at low temperature,the enhancement effect of cold adaptability,organics removal performance and resistance to cold shock were analyzed.The community analysis of ASM was applied to get the effect of MF strengthening on community structure variation.Low temperature led to gradually increase of unsaturated fatty acids(UFAs)in cell membranes of ASM.Compared to 25 C,the content of UFAs of reactors with glucose and sodium acetate carbon source were 13.66%and 24.96%higher,respectively.More Gram-negative bacteria were enriched in ASM at low temperature.At 5 C,the PLFA diversity of reactor with glucose carbon source was lower than that of at 25?,but the sodium acetate reactor was reverse.The strengthening effect of heteropolar MF can effectively improve the TTC-DHA of ASM at low temperature.The contents of UFAs of R2(heteropolar MF)and R1(homopolar MF)were 1.03%and 4.90%higher than that of R0(without MF),respectively.Fatty acids C16:1 ?7c,C18:1?7c and C18:1?9c were the essential UFAs of ASM at low temperature,but the MF enriched the species and promoted the synthesis of other UFAs.R2 had higher PLFA diversity index than that of R1.The strengthening effect of heteropolar MF was better than that of homopolar MF.At 5?,TTC-DHA reached the maximum activity 8.12 mgTF/gSS at 40 mT.More UFAs were promoted to produce at 20-40 mT,while improving TTC-DHA to adjust to low-temperature environment.Gram-negative bacteria with better cold adaptability were enriched at 30 mT.The PLFA diversity of R2(heteropolar MF)was higher than that of R1(without MF)at 20-40 mT.The injury to ASM and effect on enzyme activity resulted by low temperature was a continuous accumulation process.SOD activity was severely inhibited exposed to drastic temperature variation with increasing microbial damage.MDA showed that MF had certain strengthening effect on ASM cells against low temperature injury,and the effect of fast cooling phase was better than that of slow cooling.The enhancement effect on CAT activity was better under slow cooling and rewarming.MF had strengthening effect on TTC-DHA under slow cooling,and fast cooling inhibited the TTC-DHA severely.It is the focus to enhance the activity of ASM under low temperature and lower the cost of sewage treatment.It is the key question to search for different MF strengthening methods and improve the processes.It is the important issue to analyze the function of certain PLFA,low-temperature enzyme enhancement and regulation of cold adaptability gene expression for future research. |
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