Lanthanum-based Adsorbent For Highly Efficient Removal Of Phosphate And Its Effect On The Biological Stability Of Water

How to guarantee the biological safety of drinking water has been a research hotspot in water treatment.Disinfection process cans not inactivate all microorganisms.And disinfection byproducts?DBPs?produced during disinfection process can cause a greater threat to human health.The method of reducing nutrient source is relatively green and safe.Thereinto,assimilable organic carbon?AOC?has been widely used as an evaluation index for the biological stability of water.However,the AOC removal effect of conventional process is difficult to achieve the biological stability of drinking water.In addition to carbon,phosphorus is also an important element for microbial growth.Compared with AOC,phosphorus is easier to remove and the pollution source is relatively controllable.Therefore,the decrease of phosphorus content in water may be a more effective way to achieve the biological stability of water.In addition to AOC and phosphorus,humic acid residues in water would also cause the re-growth of microorganisms in the pipe network.Humic acid?HA?can be decomposed into small molecule organic matter by oxidants to increase AOC content.And HA can be directly used as a nutrient source promoting microbial growth,which has been verified by this paper.Moreover,HA can be a breeding ground for nourishing microorganisms by complexing with other nutrients,affecting microbial growth control effect of phosphorus.Therefore,the HA residue should be reduced as much as possible while removing phosphorus from water.Firstly,this work clarified the ability of AOC and phosphate to promote bacterial growth and reproduction and gave the suggested values of AOC content,phosphorus content and water age to achieve biological stability of water through investigating the relationship between the concentration of AOC and phosphate and the total bacterial count.The results showed that phosphate was easier to promote the growth and reproduction of bacteria than AOC,and phosphorus removal was more effective than AOC to achieve the biological stability of water.To achieve the biological stability,the phosphorus concentration must be under at least 3?g P/L.In order to meet the requirement of total bacteria<100 CFU/mL in drinking water,phosphorus in water should be completely removed.At this time,if water age?4 d,the requirement of AOC content could be relaxed to 300 g C/L.If the treated water can be delivered to the clients within 1 d,the limit of AOC could broaden to 500 g C/L,which greatly reduced the AOC removal requirements.In addition,this work preliminary discussed the effect of HA on the bacteria growth.The results showed that HA can be directly used by bacteria as a nutrient source for growth and reproduction and the coexisting phosphate and HA could greatly promote bacterial growth and reproduction.To effectively realize biological stability of water through“Phosphate Nutrient-Starvation Antibacteria”,it was not only necessary to effectively remove phosphorus from water,but also to reduce the residual HA in water as much as possible.Previously prepared La?OH?₃/polyacrylonitrile fibers?LPNFs?could control microbial growth by removing phosphate from water.In order to effectively achieve the biological stability of water through“Phosphate Nutrient-Starvation Antibacteria”,the phosphate adsorption capacity needs to be further improved so that the phosphate in water can be removed until it is undetectable,and at the same time,the HA content in water needs to be reduced.Therefore,LPNFs was carbonized to prepare carbon nanofibers embedded with La-based compounds?LCNFs?.The phosphate adsorption capacity of LCNFs was 20.21mg P/g,which was more than that of LPNFs.And LCNFs could remove HA under the combined action of carbon physical adsorption and lanthanum complex.When HA and phosphate coexisted,LCNFs was still able to remove 100?g P/L of phosphate to below the detection limit of ICP-MS?0.6?g/L?and remove 56.7⁷4.4%of HA simultaneously.The biological stability of the water sample after treated by LCNFs was significantly improved compared with the untreated water sample.However,the coexistence of phosphate and HA would interfere with each other's removal rate.And the phosphate adsorption capacity of LCNFs was still low and could not be used for a long time,and the removal time of phosphate and HA was too long to meet the production requirements of water plants.In order to further improve the phosphate adsorption capacity,the inorganic treatment of La-MOF was carried out to prepare the inorganic La-based compound adsorbent?LMC?with micro/nano dual structure.The micro/nano dual structure could provide abundant adsorption sites and pore structures so that LMC could obtain the phosphate adsorption capacity of 118.7 mg P/g,and the interference of phosphate and HA on each other's removal rate could be reduced.LMC could remove 100?g P/L of phosphate to below the detection limit of ICP-MS in 50 min,and remove 43.5⁶5.4%of HA in 60 min.Thus,the removal time was shortened compared with LCNFs.In order to save costs and meet the requirements of water treatment engineering,the removal time should be further shortened based on high adsorption removal rates.Hence,this paper took La-MOF as the lanthanum source and adopted the glucose hydrothermal method to obtain the carbon-coated lanthanum nanorods?C-LM?with rich C-La micro-interfaces and easy to be separated from water.C-La micro-interfaces could provide abundant adsorption sites so that C-LM had a phosphate adsorption capacity of 54.4 mg P/g,the interference of phosphate and HA on each other's removal rate was greatly reduced.In addition,the C-La micro-interfaces could also produce capillarity,so that phosphate and HA quickly reached the adsorption sites,shortening the removal time.When HA and phosphate coexisted,C-LM could remove the phosphate to below the detection limit of ICP-MS and obtain the HA removal balance with 70%of HA removal rate in 10 minutes,which were better than LMC and LCNFs.LCNFs,LMC and C-LM these three La-based adsorbents could remove the low concentration of phosphate to below the detection limit of ICP-MS and simultaneously reduce HA residue,thereby improving the biological stability of water.LMC has the highest phosphate adsorption capacity and could be used for a long time to reduce the regeneration and replacement frequency of adsorbents.The removal time of C-LM was the shortest,which could reduce the hydraulic retention time.