Experimental Research Of Pretreatment Technology Of Reverse Osmosis Used In Removing Fluorine

Endemic fluorosis, a chronic fluorosis caused by a long-term diet of local high fluoridewater or food, is an endemic disease severely endangering people’s health. Reducing fluorideof the raw water is an effective solution to prevent endemic fluorosis caused by drinking water,and in most cases people get clean drinking water in this process. Among the drinking waterfluoride removal methods, the process of reverse osmosis, a new fluoride removal technologyfeaturing high efficiency, low cost, easy operation, safety and drinking water of good quality,is the best alternative to traditional fluoride removal methods. Reverse osmosis equipmenthave a strict request on water quality, which is very important to keep the entire systemrunning properly. Depending on the pretreatment demand, the fluoride removal method byreverse osmosis membrane can be used to remove suspended solids, organic matter, colloidalsubstances, microorganisms, oxides, and certain hazardous substances （such as iron,manganese, calcium, etc.）. Therefore, the pretreatment of raw water, as the main way toinhibit membrane from contaminating, is the critical step to ensure the normal functioning ofthe entire system and maintain the rate of fluoride removal.This paper analyses application defects of traditional fluoride removal methods throughthe experiment, with reverse osmosis technology of fluoride removal for the foothold,optimizing the pretreatment process of fluoride removal technology by reverse osmosis thepurpose, technology foothold, pretreatment equipment the core. In the research, fieldexperiments were carried out, to promote the application of fluoride removal technology byreverse osmosis in the rural drinking water projects. Main conclusions of the research are asfollows.（1） Fluoride concentration of shallow groundwater is higher than that of deepgroundwater, water fluoride in well as deep as20m could reach up to3.56mg/L. Fluoride inthe surface soils influence crop growing, and then increase the intake of fluoride in humanbody through the food chain. In terms of solution of local high fluoride water, both the localofficial water department and the local people being concerned about investment issues, a low-investment, fast-effective solution dealing with high fluoride program is urgent needed.（2） For the rich plain water with fluoride concentration of1.68mg/L, to reduce fluorideconcentration to the national standards for drinking water, as much basic aluminum chlorideas500times the amount of chlorine ion is needed to consume, which is a high ratio. In theexperiment of fluoride removal effects by concrete sedimentation, the fluoride removalefficiency decreased gradually, as the coagulant dosage increased, and other anions in watersamples saw decreases of varying degrees in content when the reaction was over. Coagulantdosage had an impact on the efficiency of fluoride removal. In the fluoride removalexperiment by aluminum chloride, in terms of the influence effect to remove the fluoride,from big to small, anions rank as follows: OH^-,SO₄²⁺, Cl^-.（3） For the Qinghe water, fluoride absorption performance of pretreated activatedalumina was much better than that of unprocessed, of which the adsorption capacity had asignificant gap. However, when the water dosage BV=57, in other words, volume of waterdosage was less than7L, the fluoride concentration exceeds1.0mg/L, so the adsorptioncapacity is relatively limited. In some degree, activated alumina had impacts on sulfate ions,OH, total alkalinity, and TDS in water samples. As the experiment goes, their contentchanges according to certain disciplines, while chloride ion was almost not affected. Waterquality ingredients of drinking water from different sources varying, influenced activatedalumina in different degrees, then determined fluorine abortion capacity. That limited itspractical application in different drinking water sources.（4）1μmPP cotton filter adopted in the first level of pretreatment could reduce SDI to alower value well. Number of particles larger than2μm was less than3per ml, measured by aparticle number counter. PP cotton still worked well after40tons of water passed. Under thecondition of stable incoming water pressure, the passing water flow fluctuated in a smallscope, with a little reduction in the pressure after water passed. The second level adoptedcompressed activated carbon to remove most of the organic, free residual chlorine in the water.Drinking water of the experiment point was disinfected not by chlorine ion, so there were nosoluble residual chlorine. Granular activated carbon were mainly used to adsorb water-solubleorganic matter, and showed excellent defluoridation. It reduced fluoride from3.7mg/L in Qinghe raw water to0.1mg/L, producing3.7tons clean water. Both water production withbackflow and without could be in good running under the condition that fluoride removalefficiency were ensured.