| Textile dyeing sludge?TDS?has the characteristics of high moisture content and poor dewatering performance.The dye,slurry,auxiliaries and heavy metals contained in the TDS make it highly biologically toxic.Once improperly disposed,TDS will cause serious environmental pollution.At present,the transport and disposal of TDS followed a strict restrictions on mositure content,and thus high moisture content has become a key factor restricting the weight/volume reduction of TDS.In addition to the physical,chemical and other traditional methods,enzymatic methods was recently found to be able to using a kind of new,environmentally friendly tools to strengthen the dewatering of sludge.However,the enzyme preparation is expensive and has the risk of easy inactivation,which increases the difficulty of its application and promotion.In view of this,the method of“immobilzed lysozyme lysis and enhance the dewatering of TDS”was carried out,with systematic research to provide theoretical basis and technical support for practical application.The main content of this research includes 4 asoects as below:?1?Preparation of magnetic cellulose microsphere?MCMs?carrier for covalently immobilized lysozyme?LYZ?and investigation of the biological characteristics of immobilized lysozyme?MCMs-LYZ?.?2?To explore the feasibility of improving sludge dewatering performance by MCMs-LYZ treatment;3D-EEM?SEM ansalysis were also performed to clarify the mechanism dewatering.?3?To explore the feasibility of improving TDS dewatering performance by US/MCMs-LYZ co-lysis treatment,and the dewaering machanism,and the drying charateristics of TDS before and after.?4?To investigate the effect of SDBS and o-Anididine on the performance of TDS dewatering by MCMs-LYZ teratment;to clarify the interaction mechanism between the auxiliaries and LYZ by ultraviolet spectrum?UV-vis?,fluorescence spectrum?FS?and circular dichroism?CD?.Results showed that:?1?The MCMs modified with 1,2,3,4-butane tetracarboxylic acid?BTCA?can be used as a covalent bond immobilization carrier for enzymes.The prepared MCMs-LYZ has a wider range of p H and temperature adaptation,stronger thermal stability and storage stability than free LYZ.The residual activity of MCMs-LYZ was 66.57±2.32%after incubation for 180 min at 50?,which was 48.06%higher than free LYZ.The residual activity of MCMs-LYZ was 77.74±3.58%for 20days under 4?,which was 111.08%higher than free LYZ.After 6 cycles of recycling,the relative enzyme activity could be maintained at 51.94±2.09%.Nevertheless,the immobilization process reduced the affinity of MCMs-LYZ to the substrate.the Km value increased by 36.44%,from20.83 mg/m L of free LYZ to 28.42 mg/m L;and the Vmax value decreased by 27.81%,from1.69×105 U/mg to 1.22×105 U/mg.?2?The enzymatic hydrolysis rate of MCMs-LYZ was close to that of natural lysozyme,and the lysis sludge process by MCMs-LYZ fitted well the first-order kinetic model.The optimal parameters of the lysis excess sludge process by MCMs-LYZ were determined as follows:the dosage of MCMs-LYZ was 7%g/g TSS,the reaction temperature was 50?,and the p H of the reaction system was 7.Under this condition,the dewatering performance of excess sludge after treatment was obviously improved,the SRF of sludge was reduced by 49.05%,and SV reduced by37.37%.The content of EPS,protein and polysaccharide in sludge were the main factors affecting the dewatering performance of sludge.The SRF correlated positively to EPS,protein and polysaccharide in the TB layer with the correlation coefficients of R=0.979?p<0.01?,R=0.967?p<0.01?and R=0.981?p<0.01?,respectively.The content of EPS,proteins and polysaccharides in S and TB layers showed a negative correlation with the SRF.3D-EMM and SEM analysis comfirmed that the MCMs-LYZ can effectively destroy the structure of sludge flocs,release intracellular fluorescent protein substances,and improve the sludge dewatering performance.?3?The disintegration degree of TDS floc structure significantly increased under US/?MCMs-LYZ?co-lysis treatment.Larger specific surface area and more developed pore structure were found in the sludge flocs after co-lysis treatment,and the dewatering performance and settling performance of TDS were improved obviously.The optimal parameters of the US/?MCMs-LYZ?co-lysis process were determined as follows:the ultrasonic energy density was2 W/m L,the ultrasonic time was 20 min,and the reaction temperature was 50?.Under the optimal parameters treatment,the SRFof TDS was?3.21±0.12?×1012m/kg,which was 34.73%and 30.52%lower than that of blank and single MCMs-LYZ treatment,respectively.The SV decreased by 34.39%,16.12%and 28.87%,compared with the original sludge,single ultrasonic lysate and single MCMs-LYZ lysate,respectively.The sludge volume ratio decreased by nearly50%.UV-vis and 3D-EEM spectral analysis confirmed that co-lysis treatment can effectively release tryptophan-like proteins and humic substances containing functional groups?COOH,C=C and C=O,etc.?from the TB-EPS.Under co-lysis treatment,the thermal stability of TDS improved obviously.The co-lysis TDS at 30?105?and 105?550?stages has the lowest mass loss rates of 5.75%and 47.80%,respectively,compared with single ultrasound treatment and single MCMs-LYZ.The lowest weight loss rates were found at low temperature combustion stage?250?300??and high temperature combustion stage?400?450??,which were 0.58%/min and0.28%/min.,respectively.?4?The co-lysis treatment can effectively reduce the content of binding water and organic matter,realizing the rapide drying of TDS.The non-isothermal drying process of TDS before and after treatment conforms to the functional models A1,A2,A3 and R3.When the heating rate increased from 5?/min to 10?/min and to 20?/min,the mechanism function model of the non-isothermal drying process of TDS changed from g???=-ln?1-??to g???=[-ln?1-??]1/2.The isothermal drying process of TDS before and after treatment accords with the function model A2,A3,R2 and R3.The optimal model was changed from R2 to R3 after co-lysis treatment,indicating that the drying rate control equation of TDS after co-lysis treatment should be type of phase interface reaction?n=3?.?5?SDBS caused could cause the changes of the secondary structure of lysozyme molecules,which led to the decrease performance of the MCMs-LYZ lysis TDS.The mechanism of interactions were as follows:SDBS form 1:1 complex with LYZ molecules through spontaneous hydrophobic force,reducinge the hydrophobicity around the Trp residue microenvironment in LYZ molecules and,enhancinge polarity,induce partial?-helit structure transformation into?-turn structure,and reduce with lower the activity of immobilized lysozyme.The addition of SDBS could improves the dewatering performance of printing and dyeing sludge.When the SDBS concentration was 1.0×10-4mol/L,the SRF value of treated TDS was 54.51%and 13.18%lower than that of original sludge and single MCMs-LYZ treated original sludge,respectively.?6?o-Anisidine causes should be responsible for the changes of the secondary structure of lysozyme molecules,which leads to the decrease of the efficiency of MCMs-LYZ lysis process and deteriorates the dewatering performance of TDS.The mechanism of the interactions were as follows:o-Anisidine form 1:1 complex with LYZ molecules through spontaneous hydrophobic force,reducinge the hydrophobicity around the Trp residue microenvironment in LYZ molecules and,enhancinge polarity.,induce some Induced transform of?-helit structures in LLYZ molecules to transform into?-sheet structures were also bserved in the LLYZ molecules,respectively,and which further reduce the activity of immobilized lysozyme.To sum up,those results provide theoretical basis and technical support for the practical application of"immobilized lysozyme lys improving sludge dewatering technology". |
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