Design And Performance Research Of Filtration Media For The Contact Precipitation Defluoridation Process

Fluoride removal from drinking water by contact precipitation is a low-cost and easy-to-manage water treatment technology.It is made more convenient by the fact that the filtration media can be used for long periods of time without replacement.The performance of the filtration media determines the efficiency and stability of the fluoride removal process.Filtration media currently used for contact precipitation defluoridation cannot be used long term due to compaction problems.This study designed a new filtration media for use in contact precipitation that is able to overcome these problems and is suitable for practical application.A study of the literature related to defluoridation via contact precipitation shows that fluorapatite is able to speed up the precipitation of fluorine from water.This thesis discusses the process of creating and testing filtration media that contains fluorapatite.It explains why fluorapatite should be chosen as the functional ingredient of the filtration media,summarizes relevant technical requirements for the filter,discusses the appropriate manufacturing techniques and,finally,puts forward a program for filter design.The manufactured filtration media has the form of a spherical particle,with particle size of 0.9~1.3 mm and true density of 1.32~1.36 g/cm3.The main components are fluorine apatite and resin.Using electron microscopy,it can be seen that the filtration media has a good porous structure,with pore size between 0.5~2 ?m.The outer surface of the particle is not a dense skin,meaning water can easily pass into the particle.Defluoride tests showed the filtration media is effective in contact precipitation defluoridation,and can be used to treat three different types of raw water.Under conditions where filter bed height is 25 cm,dosage Ca:P:F is 5:3:1 and empty bed contact time is 60 min,the effluent fluoride concentration is less than 1 mg/L.This study shows that the filtration media can treat 2600 bed volumes of raw water without a decline in defluoridation performance.Using a backwash intensity of 16 L/(s·m2)and backwash time of 5 min,the defluoridation performance of the filtration media is fully restored.This test indicates that the filtration media is highly resistant to compaction.The optimum backwash cycle was 24 h.The results of performance and material testing show that the filtration media developed and tested in this study meets the specified technical requirements.The new media improves on other materials available for contact precipitation defluoridation,and enables the practical application of this technology in the field of drinking water...