Advanced Treatment Of Zn-containing Livestock Wastewater By Modified Reverse Osmosis Membrane For Lettuce Hydroponics

With the rapid development of society in recent years,water scarcity and water security issues have become one of the main constraints on economic development.In response to water pollution problems caused by Farm water and intensive farming in water-scarce areas,in this study,silver sulfide nanoparticles（Ag₂S）and 1-vinylimidazole（VI）were grafted onto the modified reverse osmosis membrane by low temperature plasma（PLA）,the modified membrane was used to treat the simulated Zn-containing livestock wastewater,and the pure nutrient solution（BK）was used as blank control,the effects of livestock wastewater（WW）,ultrafiltration membrane（UF）and modified reverse osmosis membrane（RO）on the quality of hydroponic lettuce were studied,in order to evaluate the safety and feasibility of advanced treatment of Zn-containing livestock and poultry wastewater with modified membrane for agricultural production,the results showed that:（1）The hydrophilic properties,pure water flux and anti-fouling properties of the modified membrane have been improved to some extent,among which the modification effect of Ag₂S/VI/PLA membrane is the most significant.The water contact Angle is reduced by 38.68%compared with the original membrane,the pure water flux is 67.01±2.44 L/m²h after 8 hours of compaction,and the salt interception rate is 98.32±0.24%.Compared with the original membrane,the recovery flux increased by 31.53%to 42.22%.The survival rate of the modified membrane was 15.15%of that of the original membrane,while the total amount of contaminants on the surface was only 4.08%of that observed by confocal microscope.（2）The removal rates of COD,NH₄⁺-N,NO₃^--N and Zn²⁺from Zn-containing livestock wastewater by Ag₂S/VI/PLA membrane were 96.77±0.85%,93.4±2.00%,91.56±0.67%and 99.11±0.26%,respectively,especially for the heavy metal Zn in wastewater,it has excellent river closure ability,and the P content is not detected in the effluent,and all indexes meet the water quality standard for irrigation.（3）The fresh weight,dry weight and leaf area of lettuce in RO group were higher than those in BK group at the late growth stage.The use of modified reverse osmosis membrane to further treat livestock and poultry wastewater for hydroponics could promote the growth of lettuce to a certain extent.The photosynthetic activity of lettuce in RO group at late growth stage was the highest,which was 67.60%,57.91%and 20.39%higher than that in WW,UF and BK groups,respectively.The contents of total chlorophyll and soluble protein in RO group were 6.43%and 21.33%higher than that in BK group,respectively,and the content of nitrate was 31.05%lower than that in BK group.（4）The Zn target hazard coefficient（THQ）of adults and children was much lower than that of UF and WW groups.The contents of Na,K,Ca and MG in lettuce showed a trend of K>Mg>Ca>Na,but the contents of MG in WW and UF groups were much higher than those in the other two groups,on the one hand,the concentrations of ions in WW and UF were higher,and on the other hand,Zn stress promoted the absorption of ions in lettuce to some extent.MG tends to migrate from the underground to the aboveground parts of lettuce,while Zn tends to accumulate in the roots.In a word,the performance of the modified ro membrane has been improved to some extent,among which Ag₂S/VI/PLA membrane has the best modification effect,with better hydrophilicity,filtration performance,antibacterial and anti-pollution performance,it is helpful to prolong the service life of membrane and improve economic benefit.The advanced treatment of Zn-containing livestock and poultry wastewater with the modified membrane can remove the heavy metal Zn in the wastewater to a great extent,it can increase fresh weight,dry weight,leaf area,chlorophyll and soluble protein content of lettuce to a certain extent,and is harmless to human health,the application of reverse osmosis membrane in agriculture has great potential.