| Anaerobic digestion liquid of vegetable wastes is a high-concentration organic wastewater that contains a large amount of nutrients required for plant growth,as well as high levels of ammonia nitrogen,COD,and substances such as phosphates and humic acid.If this type of wastewater is discharged directly into natural water bodies without subsequent treatment,it will not only cause secondary pollution to the environment but also waste valuable substances in the wastewater.Therefore,it is necessary to treat the anaerobic digestion liquid from vegetable residues,which can not only solve the problem of biogas slurry pollution but also recover and utilize valuable substances,with important economic value and scientific significance.Membrane treatment technology has the advantages of high selectivity,no phase change,and simple operation,and is widely used in the field of valuable substance recovery from wastewater.A vegetable residue treatment plant in Yunnan was greatly affected by the high content of suspended solids（SS）in the anaerobic digestion liquid,which hindered the efficiency of subsequent biochemical treatment and affected the actual production operation of the plant.Therefore,this article mainly focuses on the experimental study of ultrafiltration membrane treatment of this anaerobic digestion liquid,using ultrafiltration membrane technology to intercept SS in the anaerobic digestion liquid and explore measures to improve membrane fouling.This experimental study mainly includes three parts:the first part is a small-scale experimental study of ultrafiltration membrane treatment of anaerobic digestion liquid from vegetable residues,exploring the feasibility of using submerged ultrafiltration membrane technology to remove pollutants in the digestion liquid.The focus is on exploring the effect of removing SS in the experimental biogas slurry and further analyzing the effect of this technology on improving the biochemical properties of the wastewater.The second part is a single ultrafiltration membrane treatment of anaerobic digestion liquid from vegetable residues,optimizing operating conditions and conducting single-factor experiments.The constant suction pressure,operating mode,aeration pressure,and operating cycle in the operating conditions were studied to investigate the effect on the ultrafiltration water production,and the response surface optimization method was used to establish a response surface model to explore the interaction between response variables.Under the optimal operating conditions,the performance of the ultrafiltration membrane was observed.The third part is a study of the treatment of anaerobic digestion liquid from vegetable residues using a disc filter and ultrafiltration.In order to alleviate the fouling rate of the ultrafiltration membrane and improve the stability of the ultrafiltration device,the disc filter effect of different filter materials was compared,and the filter cloth was selected as the disc filter layer to observe the continuous operation performance of the disc filter and ultrafiltration device.The study shows that:（1）Using ultrafiltration membrane technology to pretreat anaerobic digested slurry,the removal rate of suspended solids（SS）almost reaches100%,with SS removal to 3-5mg/L;the removal rate of chemical oxygen demand（COD）reaches 40%-55%,with COD removal to 12000-14000mg/L;the removal rate of total nitrogen（TN）is 30%-40%,with TN removal to 1000-1300mg/L.Compared with the on-site IC anaerobic treatment process,the removal rate of pollutants in the digestate is improved,which can effectively improve the water quality of the biochemical influent and reduce the biochemical treatment load.（2）Through small-scale testing of the ultrafiltration membrane performance,it was found that the initial membrane flux of the ultrafiltration membrane should not be too high and should be set at 9.27L/（m2·h）.During a single operating cycle,the continuous suction time of the ultrafiltration membrane in a constant 1-minute pause mode will affect the performance of the ultrafiltration membrane in producing water.（3）Using response surface methodology to optimize the operating conditions,with the suction pressure（X1）,suction time（X2）,and operating cycle（X3）of the ultrafiltration membrane as response variables and the water production rate as the response value（Y）,it was determined that the significance of the response value influencing factors was in the order of operating cycle X3>suction time X2>pressure X1.The response surface model fitting equation was obtained as=64.40-1.501+1.882-4.133-3.2512-1.7513-3.5023-6.2012-14.9522-7.4532。The fitting degree of the equation R2was 0.9893,and the optimal operating conditions were found to be a suction pressure of 14.45k Pa,a suction time of9.54min,and an operating cycle of 13.55,corresponding to a water production rate of65.18L/h,which was close to the actual operating flow rate,indicating a high credibility of the model.（4）After optimizing the operating conditions,observe the continuous operation performance of a single ultrafiltration pilot plant.That is,the ultrafiltration pilot plant maintains a constant suction pressure of 15k Pa,operates in a"9+1"mode（continuous suction for 9 minutes,rest for 1 minute）,and the aeration pressure is 13k Pa.Every three cycles,a water production backwash process is introduced,with a backwash time of 30 seconds.After 15 cycles,the membrane flux decays to 8L/（m2·h）during the clean water oscillation and washing for 10 minutes.At this point,a 5%citric acid chemical cleaning for 10 minutes is used,and it is found that the membrane flux can be restored,and the ultrafiltration water production flow rate changes periodically.（5）Using a combination of rotary filtration and ultrafiltration processes to treat anaerobic digestion effluent from vegetable waste,when the ultrafiltration pilot plant is operated under the previously optimized conditions,the membrane flux of the ultrafiltration unit is improved.Under the same 24-hour continuous operation,the ultrafiltration water production is stable,reducing the need for chemical cleaning and extending the life of the membrane.In addition,in terms of economic costs,adding a rotary filtration pretreatment device can save the amount of ultrafiltration membrane used and replace it with a lower-cost filter cloth.Considering the cost of the membrane（without considering other supporting equipment）,the combined process can save about 20%of the membrane cost compared to direct ultrafiltration treatment. |
PDF Full Text Request