Study On The Criteria Of Limestone In The Re-mineralization Process Of Drinking Water

The water of Pearl River has the qualities of low alkaline and low hardness, which has poor buffering capacity and strong corrosion ability.It is not only the resason to cause the corrosion of pipes,which can cause "yellow water "to harm for people’s lives and the industrial production, but also be bad for human’s health and even cause the cardiovascular and cerebrovascular diseases.In order to improve the chemical stability of water quality, a new treating approach called limestone contactor was invented by some foreign countries.The core process of this approach was that when the water flow through the limestone beds, the limestone was dissoluted into the flowing water,then,the alkaline、hardness and the value of pH in the outleting water could get higher.from this,people can improve the qualities of drinking water.And compared with other technologies, limestone contactor had many advantages,such as easy maintenance, easy management, safe operation and low cost and so on.How to choose the limestone was one of the most important parts of limestone contactor process,because it directly affected the results of treatment. This paper mainly study that limestone contact columns were used to simulate contact tank, and we compared the results of six different kinds of limestone under the same conditions.Then, based on the water quality parameters of each limestone column and the physical and chemical changes of limestone in the process, we can find out the main factors which affected the dissolution of limestone and assess the potential risks of limestone contactor. At last,we can establish the selection criteria of limestone and the analysis methods for limestone.The experiment showed that the content of calcium carbonate was an important factor for limestone’s dissolution rate.When the calcium carbonate’s content was more than98%, the dissolution rate was satisfactory.The content percentage of element in limestone surface had big changes during the test.With the dissolution of calcium carbonate,the content of calcium was decreased,but the percents of magnesium, carbon, oxygen, silicon, aluminum, iron were increased in limestone surface.The L6dolomite insoluble residue layer was mainly formed by magnesium, silicon, aluminum, iron. This insoluble residue layer reduced the rate of mass transfer and the effective contact surface area of calcium carbonate, it was proofed that the dissolution rate of dolomite L6was slower than the others.It was also found that the amount of limestone in column decrease included two parts. One was the consumption of dissolved limestone, which was the main contributions to adjust the chemical stability of water quality; the other part was the loss of small particles volume, which maybe useless or just a limit contribution to the chemical stability,but it had a potential healthy risks. Because a variety of bacteria, viruses were easily to storage on the suspended particles.so the disinfection efficiencies reduced.And if the limestone contactor was used before the carbon filter, activated carbon will be agglomerated by adsorbing these particles, and the carbon filter was easy to be plugged, which was a negative impact for the subsequent process.At the same time, as part of the suspended particles were loss,they had no use for the adjustment of the chemical stability of drinking water.As the efficiency reduced, the consumption of limestone increased, and with the filled cycle became shorter, the economic costs had increased.