Study On Dewatering And Drying Of Excess Sludge From Biological Treatment Of Printing And Dyeing Wastewater

With the rapid development of China’s printing and dyeing industry,printing and dyeing sludge is increasing,which has become a serious problem in environmental protection.Dewatering,drying and recycling are important ways of reducing printing and dyeing sludge.At present,these methods have attracted extensive attention,but the efficiency,cost and resource utilization effect still need to be improved.In order to find an efficient,convenient and low-cost method for reducing printing and dyeing sludge,this study first analyzed the differences between physicochemical and biochemical sludge collected after sewage treatment process in a printing and dyeing plant in Shuyang County,Jiangsu Province,and then determined the printing and dyeing biochemical sludge as the research object of dehydration,drying and recycling afterwards.Then sodium-based bentonite(BTN)was modified with chitosan quaternary ammonium salt(CQAS)by traditional wet method and improved wet method respectively,and the modified bentonite MBTN(Ⅰ)and(Ⅱ)were prepared.The optimum modification conditions for the preparation of MBTN(Ⅱ)-5 were determined by single factor influence test and orthogonal test;Then,the optimal dosage of MBTN(Ⅱ)-5 was determined by the dehydration test of printing and dyeing biochemical sludge with MBTN(Ⅱ)5;The dewatering effect of MBTN(Ⅱ)-5 and traditional dewatering flocculant on printing and dyeing biochemical sludge was compared,and the influence of the dosage of MBTN(Ⅱ)-5 on the dewatering effect of printing and dyeing biochemical sludge was determined;The adsorption mechanism of MBTN(Ⅱ)was deduced through the analysis of adsorption isotherm and adsorption kinetics of CQAS on BTN;The adsorption and removal capacities of MBTN(Ⅱ)-5 to pollutants in sludge were determined by the changes of organic matter and heavy metal ion concentration in the filtrate after dehydration of printing and dyeing biochemical sludge;Through the characterization of MBTN(Ⅱ)-5,the mechanism of MBTN(Ⅱ)-5 improving dehydration effect was analyzed.Finally,through the influence of ultrasonic pretreatment on the vacuum drying of printing and dyeing biochemical sludge dehydrated by different flocculants,the drying mode was determined;Then the dried sludge was slowly pyrolyzed to prepare sludge-based biochar(SBC),and then the SBC was modified by KOH to prepare modified sludge-based biochar(MBC).SBC,MBC and MBTN(Ⅱ)-5 were used in the dewatering test of printing and dyeing biochemical sludge to investigate their influence on the dewatering effect of printing and dyeing biochemical sludge;Through characterization,the surface groups,pore structure and components of SBC and MBC were analyzed to reveal the influence mechanism of SBC and MBC on the dehydration of printing and dyeing biochemical sludge.The main experimental results of this study are as follows:(1)Biochemical sludge had low dewatering efficiency,high organic matter content,high carbon content and low heavy metal content,and there would be a large sludge specific resistance in the dehydration process.The contents of COD,TN and NH3-N in the filtrate after dehydration were much higher than those of physicochemical sludge;The vacuum drying dehydration efficiency of biochemical sludge was much lower than that of physicochemical sludge;Compared with physicochemical sludge,the research on the dehydration,drying and resources of biochemical sludge had more practical value.(2)MBTN(I)and(Ⅱ)were affected by the dosage of modifier,reaction temperature,reaction time and pH in the preparation process.The single factor experiment was designed and compared with orthogonal test to determine the best modification conditions for the preparation of MBTN(Ⅱ)-5,and the mass fraction of CQAS in MBTN(Ⅱ)-5 reached 5.41%.Compared with PAM and CQAS,MBTN(Ⅱ)-5 could significantly improve the dehydration rate of printing and dyeing biochemical sludge after conditioning,and further reduced the water content(Wc)of printing and dyeing biochemical sludge by more than 11.70%,and it proved that MBTN was economic;At the same time,MBTN(Ⅱ)-5 could effectively adsorb and fix heavy metal ions and organic pollutants in printing and dyeing biochemical sludge,and the adsorption and removal rates of Cu and Ni could reach 84.76%and 74.47%respectively.It could also reduce the COD in the filtrate from 1333 mg/L to 495.1 mg/L.(3)By analyzing the adsorption isotherm and adsorption kinetics of MBTN(Ⅱ),the results showed that the adsorption isotherm of MBTN(Ⅱ)conformed to the Langmuir isotherm and the adsorption kinetics conformed to the pseudo-first-order adsorption kinetics.The maximum adsorption capacity of CQAS in MBTN(Ⅱ)could be roughly estimated through the adsorption isotherm and kinetics.(4)The FTIR characterization results of MBTN(Ⅱ)-5 showed that the modification of BTN by CQAS was successful.Compared with BTN,MBTN(Ⅱ)-5 had obvious changes in characteristic peaks.The characteristic peaked at 1490 and 2890 cm-1 could confirm the adsorption modification of CQAS,and the shift of Si-O-Si peak at 1080 cm-1 indicated that the crystalline structure of MBTN had been changed.The SEM and BET characterization of MBTN(Ⅱ)-5 and BTN confirmed that MBTN(Ⅱ)-5 had better adsorption capacity than BTN.The pore size of modified MBTN(Ⅱ)-5 increased,which verified the FTIR test results.(5)The effect of ultrasonic pretreatment on the drying of printing and dyeing biochemical sludge dehydrated by different flocculants was analyzed,and the drying mode was determined;Then the dried sludge was pyrolyzed at high temperature to prepare different SBC and MBC.Then the dehydration test of printing and dyeing biochemical sludge was carried out with SBC and MBC.The test results showed that SBC and MBC could significantly reduce the specific resistance SRF of sludge.In the experiment of MBTN(Ⅱ)-5 combined with SBC and MBC conditioning printing and dyeing biochemical sludge,when MBTN(Ⅱ)-5 combined with MBC,the minimum moisture content of sludge reached 62.51%,which could be further reduced by 2.4%compared with 64.91%of MBTN(Ⅱ)-5 alone;MBTN(Ⅱ)-5 combined with SBC and MBC to regulate printing and dyeing biochemical sludge could greatly improve SRF;MBC had a good adsorption effect on heavy metal ions,while SBC had a certain adsorption and fixation effect on organic matter in printing and dyeing biochemical sludge.(6)SEM and bet characterization of SBC/MBC showed that MBC had richer pore structure,larger specific surface area and higher ability to adsorb heavy metal ions than SBC,while SBC had larger pore size and pore volume and was easier to adsorb macromolecular organic pollutants than MBC.