The Combination Of Paper Filtration And Hollow Fiber Ultrafiltration For The Pretreatment Of The Digestate From Swine Manure

Both nutrient concentrated liquid and clean water could be obtained from the pig farm digestate by membrane concentration process.However,the large number of suspended solids and dissolved organic matters in the digestate might cause membrane fouling and blocking,which might prevent the safe operation of membrane concentration,thus,the effective pretreatments have become the key to membrane concentration of the digestate.To explore the effective pretreatment for membrane concentration of the digestate,in this study,the new combination of paper filtration?PF?and hollow fiber ultrafiltration?UF?was designed as the pretreatment for the membrane concentration process of nanofiltration combined with reverse osmosis?NF+RO?.The operating parameters of PF and UF process were optimizated by the experiments.Then,a comparation experiment of ceramic microfiltration membrane?MF?and UF as different pretreatments was performed.Finnaly,the combinated process of PF+UF pretreatment and NF+RO menmbrane concentration was conducted at multi-batch operation.The objective was to provide scientific basis for PF+UF as practical pretreatment of the digestate from swine manure.The results showed:?1?The experiments of the optimization of operating parameters of PF and UF process showed,the optimized paper filtration precision?15,30,50?m?was 50?m,the preferred operating pressure?0.06,0.10,0.14,0.18,0.22,0.26 MPa?of UF was 0.10 MPa,the preferred backwash frequency?10,20,30,40min?was 20 min.In the combined process of PF and UF at the optimized operating parameters,the volumetric transmittance was 86.67±0.62%.In the UF permeate,the removal rates of turbidity,TSS,TS,VS and COD was 89.60±5.35%,90.84±7.08%,49.75±1.82%,28.82±5.29%,respectively,most of the suspended solids were removed.While the removal rates of EC,TN,NH₃-N and TP was 5.49±0.76%?7.65±1.57%,6.23±1.81%,21.38±3.83%,respectively,most of the ions and nitrogen nutrients were retained.?2?In the comparion of PF+MF and PF+UF pretreatment processes of the digestate,the membrane flux of MF?180 L/?m²·h?¹00 L/?m²·h??was about 5 times that of UF?35 L/?m²·h?¹7L/?m²·h??.In the MF permeate,the removal rate of turbidity,TSS were about 99%,while in the UF permeate,they were about 90%.There was no significant difference in the removal rate of COD,TS,EC,TN,and NH₃-N between the MF and UF permeates.The removal rates of COD were about 30%,and the removal rates of EC,TN,and NH₃-N were all below 20%.In the comparation of the combined processes of PF+MF+NF+RO and PF+UF+NF+RO,there were no significant difference in the membrane flux of NF and RO under PF+MF and PF+UF.At a processing volume of 500 L,the single batch power consumption of MF was 5.4 kW·h,accounting for 29.65%of the power consumption of the combined process,which was 10 times that of UF with 0.54 kW·h,accounting for 3.66%of the power consumption of the combined process.There was no significant difference in the RO permeate under the MF and UF pretreatments.The removal rates of TS,COD,TP,chloride,EC,TN and NH₃-N all reached 91%,the content of TSS,COD and chloride reached the national farmland irrigation water quality standard,and the content of NH₃-N and TP reached the national livestock and poultry breeding waste discharge standard.In the RO permeate under MF and UF pretreatment,the removal rates of sulfonamides,safranin antibiotics and doxycycline reached 99%,while the removal rates of oxytetracycline were about 80%,60%,respectively.In the NF and RO concentrates,there was no significant difference in the content of TN,TK and COD under MF and UF pretreatment,the concentration factor was 1.6-2.3.However,antibiotics was concentrated in NF concentrate by about 2times,and chlorides were concentrated in RO cconcentrate by about 3 times,which required further attention.?3?In the processing of 9 batches of the digestate by the combined process of PF+UF+NF+RO,the volumetric transmittance and water quality of the final RO permeate were basically stable.The membrane flux of UF,NF,RO process showed a downward trend,however,after the chemical cleaning,the initial membrane flux recovered by the recovery rates of 92.80%,90.98%,and 94.70%,respectively.The average processing cost of the combined process was 24.08 yuan per m³,among which the cost of PF+UF pretreatment was 4.24 yuan per m³,accounting for 17.61%.