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  • 水处理设备反渗透膜胶体污染的预处理
  • 本站编辑:杭州崇高环境科技有限公司发布日期:2019-07-25 12:26 浏览次数:
胶体是非常小的粒子,其尺寸在0.3~1.0μm范围。胶体带电荷并且是悬浮体,它们彼此之间互相排斥。胶体可能来自于下述任何一种来源:①进水穿过或越过黏土质结构就可能带硅酸铝胶体;②碳钢泵、管道、过滤器的腐蚀产物可能存在铁胶体;③用明矾或不适当的澄清剂预处理的水可能含有氢氧化铝胶体。
 
Colloids are very small particles with sizes ranging from 0.3 to 1.0 um. Colloids are charged and suspended, and they repel each other. Colloids may come from any of the following sources: 1) Aluminum silicate colloids may be present when water enters or passes through clayey structures; 2) iron colloids may exist in corrosion products of carbon steel pumps, pipes and filters; 3) Aluminum hydroxide colloids may be present in water pretreated with alum or improper clarifiers.
 
反渗透膜的胶体污堵是由于在反渗透膜设备运行期间的反渗透处理过程中,胶体的凝聚和在反渗透膜上凝聚物质的沉积。
 
Colloidal fouling of reverse osmosis membranes is due to the coagulation of colloids and the deposition of condensates on reverse osmosis membranes during the reverse osmosis treatment process during the operation of reverse osmosis membrane equipment.
 
一.污泥密度指数
 
I. Sludge Density Index
 
胶体的含量(n)是由SDI确定的。SDI是从水在207kPa工作压力下,通过0.45μm微孔过滤器的堵塞速率得出的。虽然SDI的测量时不绝对的,但它是已发现的测量胶体含量的最好方法。人们已经获得在渗透器中SDI与胶体沉积速率二者之间的相互关系。另一种测量胶体含量的方法(浊度和颗粒计算)是不令人满意的。颗粒计算对亚威颗粒范围不能给予的结果。浊度是粒子的尺寸、形状及浓度的函数。因而,浊度与从一位置到另一位置的胶体污堵之间没有相关性存在。
 
The colloid content (n) is determined by SDI. SDI is derived from the clogging rate of water through 0.45 um microporous filter under 207 kPa working pressure. Although SDI measurement is not absolute, it is the best method to measure colloid content that has been found. The relationship between SDI and colloid deposition rate in permeators has been obtained. Another method for measuring colloid content (turbidity and particle calculation) is unsatisfactory. Particle size calculation can not give the results of Yawei particle size range. Turbidity is a function of particle size, shape and concentration. Therefore, there is no correlation between turbidity and colloidal fouling from one location to another.
 
井水SDI通常大约是1.0,并且不需要任何用于去除胶体污堵的预处理。如果井水的SDI超过1.0,可能的原因是:地表水侵入浅井;铁腐蚀产物存在;生物污染的存在;胶体磺化的存在。地表水含有大量的胶体物质,并且SDI值在10~175范围。
 
Well water SDI is usually about 1.0 and does not require any pretreatment for removing colloidal fouling. If the SDI of well water exceeds 1.0, the possible reasons are: surface water intrudes into shallow wells; iron corrosion products exist; biological pollution exists; colloidal sulfonation exists. Surface water contains a large amount of colloidal substances, and SDI values range from 10 to 175.
二.反渗透膜胶体预处理
 
II. Colloid Pretreatment of Reverse Osmosis Membrane
 
SDI与污堵之间的经验关系表示为SDI必须是3.0或再小些,才能使反渗透设备的污堵速率减到最小值,以便使反渗透系统长期稳定运行。必须注意市政水处理工厂处理的地表水通常SDI大于6。因此,这些水如果不进一步处理,将在反渗透膜元件上产生胶体附着。
 
The empirical relationship between SDI and fouling indicates that SDI must be 3.0 or less in order to minimize the fouling rate of reverse osmosis equipment so that the reverse osmosis system can run stably for a long time. It must be noted that surface water treated by municipal water treatment plants usually has SDI greater than 6. Therefore, if the water is not further treated, colloidal adhesion will occur on the reverse osmosis membrane elements.
 
1. 硅藻土(DE)过滤器
 
1. Diatomite (DE) filter
 
如果原始的SDI在4~5内,硅藻土过滤器能够用来减小SDI到2.0;如果胶体的含量非常高,在过滤器中的压降将迅速增加。
 
If the original SDI is within 4-5, diatomite filter can be used to reduce SDI to 2.0; if the colloid content is very high, the pressure drop in the filter will increase rapidly.
 
2. 压力介质过滤器
 
2. Pressure Media Filter
 
通过小型试验可用来测定胶体减少的度数,为给定水质选择一种最佳的滤料或滤料组合。
 
A small scale test can be used to determine the degree of colloid reduction and to select an optimal filter material or combination for a given water quality.
 
3. 凝聚
 
3. Condensation
 
在管道中和凝聚——絮凝——过滤是用来减少胶体含量,使SDI低于3.0的两个基本工艺。为此必须采用适用的混凝剂,调整混凝剂的浓度,以及保证适当的混合和停留所必需的时间。必须进行现场试验来确定最佳工况。监视和控制预处理系统是很重要的,这样能连续生产提供品质好的成品水质。胶体的含量随季节的变化也可能将牵涉到改变混凝剂浓度的问题。
 
In pipeline neutralization, coagulation, flocculation and filtration are two basic processes to reduce colloid content and make SDI less than 3.0. Therefore, it is necessary to use suitable coagulants, adjust the concentration of coagulants, and ensure the proper mixing and retention time. Field tests must be carried out to determine the optimum operating conditions. It is important to monitor and control the pretreatment system so that the quality of finished product water can be continuously produced. The seasonal variation of colloid content may also involve the change of coagulant concentration.
4. 胶体的稳定
 
4. Colloidal stability
速率常数k2与胶体稳定性有直接的关系。如果提高胶体稳定性,胶体污堵速率将降低。在理论上有几种稳定胶体的方法。然而,仅仅发现的实践方法是水软化。也就是原水经过阳离子交换树脂,二价和少量三价铁离子与钠离子交换。软化增加胶体2倍厚度和有效电荷的电量。这两者有效地增加胶体稳定性并延迟凝聚。测量胶体ζ电位能确定交替的稳定性。ζ电位通常在软化水之后增加一倍。为了软化,给的有效的稳定性必须是最近完成尺寸和适当的再生是极其重要的。
 
The rate constant K2 is directly related to the stability of colloids. If the stability of colloid is improved, the fouling rate of colloid will decrease. There are several methods of stabilizing colloids in theory. However, the only practical method found is water softening. That is to say, raw water is exchanged with sodium through cation exchange resin, divalent and a small amount of trivalent iron ions. Softening increases the colloid thickness by two times and the effective charge. Both of them can effectively increase the stability of colloids and delay coagulation. Alternating stability can be determined by measuring colloid_potential. _potential usually doubles after softening water. In order to soften, it is extremely important to give effective stability to the recently completed size and proper regeneration.

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