Research On The Removal Of Hardness From Groundwater

With the development of Yucheng High-Tech Industrial Development Zone and the expansion of urban area, the construction of urban water supply facilities were far behind the objective water demand. Now, because the limited daily supply capacity of the water supply plant had made the contradiction of inadequate water supplies become an emerging problem, it is very necessary to project a new water plant. According to the groundwater in Yucheng city, parameters were determined by experiment for the transformation of water treatment plant.Groundwater quality in Yucheng city was that pH was7.27-7.61, turbidity was7.6-21.7NTU and total hardness494-582mg/L. The comparative tests used PAC, PFC and PAFC, the best coagulant was presented:the best dosage of PAC, PFC and PAFC are8mg/L、6mg/L and3.6mg/L respectively, the removal rate of turbidity, hardness and iron are respectively85.2%、19.7%、99.7%,84.1%、19.7%、99.6%,86.4%、20.5%、99.1%. The hardness of treated water could not reach the limiting value of 《Standards for drinking water quality》(GB5749-2006).The experiment of lime softening showed that:The total hardness and the turbidity were found to be more efficiently removed with a lime dosage of140mg/L, under the condition of which the total hardness reached a concentration of402mg/L and the turbidity was2.35NTU, which reached the requirements of the filter influent water turbidity. The experiment of lime and sodium carbonate softening were found to be no efficiently removed with sodium carbonate dosage less than40mg/L compared with single dosing lime. As the dosage of sodium carbonate was more than40mg/L, the removal rat of hardness was increased.The results of pH effects on the coagulation experiment showed that:The condition of a lime dosage of140mg/L, the pH value was less than7, total hardness in water was not only not removed, but rising up. As the pH value was more than7, total hardness and turbidity were reduced accordingly, the pH value effect on the coagulation was very significant. The results of optimal lime and PAC dosage determined by with different pH experiment showed that: With the rising of pH, the optimum dosage of milk of lime milk reduced accordingly. The total hardness and the turbidity were found to be more efficiently removed without adding milk of lime or coagulant, when the value of pH exceeded11.The results of pH experiment showed that:Under the condition of a lime dosage of140mg/L and the PAC dosage of10mg/L, as for adjustment the effluent pH,0.18mol/L concentrated sulfuric acid was significantly better than0.12mol/L hydrochloric acid under the condition of the same dosage. As the value of pH was about7.5, dosage of concentrated sulfuric acid was5ml, and dosage of hydrochloric acid was16ml. However, it is suggested that hydrochloric acid should be used to adjust the pH value, considerring the high content of sulfate in the raw water.The water plant was designed with water supply of3.0×104m3/d, with the actual running of the water plant, the indexes of treated water quality can reach the limiting value of 《Standards for drinking water quality》(GB5749-2006) by Aeration+Lime Softening+Coagulation+Sediment+Filter+Disinfection water treatment process.