| Excessive phosphate and nitrate in rivers or lakes will cause eutrophication of the natural water bodies that results in the deterioration of water ecosystem and, ultimately, harm to human health. In winters, river water is highly dissolved oxygen, and low in temperature and COD content environment. Hence, it’s difficult for anaerobic microorganisms to convert nitrate to nitrogen gas by bio-denitrification after the nitrate is generated in nitrification progress by aerobic microorganisms, which results in the accumulation of nitrate. Meanwhile, a low temperature in winter makes the metabolism of plants slower than that in other seasons. Consequently, the absorption of phosphorus element by plants is also reduced. Not surprisingly, the phosphate in the water body also gets exceeded easily in winters.In this paper, a series of commercialized ion exchange resin were tested to remove the excessive nitrates and phosphates from feed water simulating eutrophic natural water bodies. To meet the requirement, a series of static and dynamic adsorption experiments were conducted to select one kind of ion exchange resin that has better adsorption properties towards phosphate and nitrate. To further enhance the resin’s performance, the synthesis of the resin was optimized to make resins with different crosslinking degrees.The results of these experiments showed that, the adsorption properties of 201×7(717) resin was proven to have the best adsorption performance for both nitrate and phosphate among four kinds of commercialized Styrene-Divinylbenzene exchange resins. According to Langmuir isotherm model, 201×7(717) had a maximum adsorption capacity of 22.22 mgP/g of PO43- and 28.9 mgN/g of NO3-. With a dosage of 2 g/L, the 201×7(717) type of resin could reach adsorption saturation of nitrate and phosphate within 90 min. The dynamic adsorption experimental result showed that the 201 X7(717) type of resin could remove most of the phosphates and nitrates in the slow flow of water.In order to improve the performance this type of resin, the synthetic process of the resin was studied and a series of Styrene-Divinylbenzene type of resin with different cross-linking degree was synthesized. The results showed that when the degree of crosslinking reached 8%, the adsorption properties of the resin towards nitrates and phosphates were the best. The adsorption capacities of this 201x8 were 22.47 mgP/g of PO43- and 37.88 mgN/g of NO3- which increased by 1% and 31% respectively, compared with 201 x 7 (717) resin. But for resins with higher crosslinking degree, the time required to reach its saturation also increased.To make the adsorption rate of the resin towards nitrates and phosphates faster, FeCb was investigated the possibility to replace ZnCl2 as the catalyst in the chloromethylation process. According to the experimental results, the resin produced this way had a maximum adsorption capacity of 28.47 mgP/g of PO43- and 39.06 mgN/g of NO3- which increased by 28% and 3% respectively, compared with using ZnCl2 as the catalyst. With a dosage of 2 g/L, the time required to reach equilibrium adsorption for PO43- had decreased 30 minutes, and that of NO3- had decreased 20 minutes.In the observation with a scanning electron microscope,201×8 (FeCl3) showed a superior specific surface area and a higher Cl- densities that can be used for freely ion exchanging. The following research reveals that the water temperature and the concentration of NH4+ would not affect the adsorption performance of 201x8(FeCb) for phosphate and nitrate, but the concentration of Cl- and SO42- would definitely suppress its adsorption properties of phosphates and nitrates. The phosphates and the nitrates also suppressed each other the adsorption capacity of 201×8(FeCl3) resin. According to the research,3% wt of NaCl solution was considered to be the best economical regeneration liquid in pratical water treatment. |
PDF Full Text Request