| Developing seawater desalination technology is an important approach to solve the problem of water shortage. Reverse osmosis (RO) seawater desalination technology has an instant development in recent 10 years and will become the primary desalination technology in the future because it has many advantages, such as less equipment investment, lower energy consumption and shorter construction period than other desalination method. However, at present membrane scaling is a serious problem which affects the operator of seawater RO plants and shortens the life of membrane, so it must be solved in the RO desalination process. Membrane scaling is caused by the deposition of unsoluble salts as feedwater is converted to brine. In this process the ion concentration of calcium, magnesium and so on increases greatly which will lead to that the ion product of sparingly soluble salts exceeds its solubility product, and the unsoluble salts deposite on the surface of RO membrane to form membrane scaling.In our research the component of membrane scaling and feedwater in Dalian RO desalination plant is analysed first. Based on the characteristic of Dalian seawater, a new environmental friendly and biodegradable antiscalant named PAP-1 is prepared in the laboratory. The performance of PAP-1 to inhibit calcium and magnesium-containing scale is studied in the laboratory with static method. It is found that PAP-1 is effective in inhibiting scale formation. The experimental results in the lab indicate that the proper dose is 3-5mg/L when the concentration of calcium is l000mg/L and magnesium is 2800mg/L. When pH is 3.00, the efficiency to inhibit scale formation reaches 100% with 3mg/L PAP-1. While pH is 9.00, calcium scale inhibition percentage of PAP-1 is 97.24% and magnesium scale inhibition percentage is 98.63% with 9mg/L PAP-1. At the same time, the algae growth inhibition test shows that the addition of PAP-1 doesn't affect the normal growth of algae, which is an indication that PAP-1 has no toxicity. The experiment of biodegradability shows that percentage biodegradability of PAP-1 reaches 38.25% at day 8 and 58.3% at day 20. PAP-1 is eazily biodegraded at the test conditions.Based on the results of static experiment, the pilot plant test is performed in Dalian RO desalination plant. A direct comparison between PAP-1 and PermaTreat 191 in inhibiting calcium and magnesium scale has been carried out. The random samples of feed, reject and product are analysed, simultaneously scale formation rates of calcium and magnesium are calculated at a fixed recovery. The test confirms the scale inhibition ability to calcium andmagnesium scale of PAP-1 compared with scale inhibitor PermaTreat 191. The average scale formation rates in each membrane unit of calcium and magnesium are 2.822g/h and 5.562g/h separately with the addition of PAP-1, while they are 3.585g/h and 5.849g/h for PermaTreat 191. PAP-1 is more effective compared to PermaTreat 191. And PAP-1 is cheaper, so it will be of advantage in market.Moreover the CaCC>3 crystal structure and morphology are determined with X-ray diffraction and scanning electronic microscopy. It has been found that the crystal type of precipitated CaCO3 has been changed from stable calcite to less stable vaterite and morphology is altered due to the presence of antiscalant PAP-1.In the last part of this paper, the softwares to calculate the dose of antiscalant and scale-formation rate are developed based on the VB flat according to the performance of antiscalant, RO system parameters and water analysis data. The dose-calculation software can supply useful help for the application of antiscalant PAP-1. Because it can calculate the dose required in the RO desalination accurately, the dose-calculation software is favorable for reducing the waste of antiscalant and promotes the rational utilization of it. The software to calculate the scale-formation rate is a useful tool for evaluating the performance of antiscalant and selecting the time and frequency of membrane cleaning. Through the systemic research on the above content, a whole system about the antiscalant in RO membrane desalination is developed.
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