Study On Membrane Coagulation Reactor (MCR) For Drinking Water Production And Removal Of Fluoride

With the conflict of water source pollution and stringent Sanitary Standards forDrinking Water, it is necessary to develop new technology and devices formicro-polluted water treatment. Membrane separation, an important technique to getsafe drinking water, has been increasingly concerned in the field of water andwastewater treatment while the price of the material is reduced and the performanceof the membrane is improved. Under such circumstances, microfiltration is widelyused in water production because of the steady quality of finished water and easyautomation with low operating pressure. In this experiment, two devices (MCR-500and MCR-15) based on combining microfiltration-coagulation with different scaleswere respectively tested for production of drinking water from micro-polluted surfacewater and removal of fluoride from groundwater. MCR-500 is a movable compact device with self-contained generator whosehydraulic residence time (HRT) is less than an hour and is suitable to be used for fieldand emergency water supply. In order to remove microorganisms and organicpollutants, ultraviolet disinfector could be used and powdered activated carbon (PAC)could be added into the reactor. During the test there were good removals of turbidity,bacteria and organic pollutants when proper dosage of ferric chloride and PAC wereadded. Turbidity and total amount of bacteria in finished water were respectively lessthan 0.3 NTU and 100 CFU/mL. When raw water belonged in class Ⅴ defined byEnvironmental Quality Standards for Surface Water (GB3838-2002), the finishedwater quality met the requirement of Sanitary Standards for Drinking Water (2001)and when raw water was poor than class Ⅴ, the finished water quality was very closeto the Standard. At low temperature (even below 5℃), good removals of organics wasachieved when enhanced coagulation was adopted and ferric was used as thecoagulant. After purifying 172.2 m3 water, the membrane was cleaned with physicaland chemical methods and the specific flux (SF) recovered to 99.7 percent of the newmembrane. Decline of SF was caused by membrane fouling and sludge cake. Thereversible fouling was composed of inorganic compounds. MCR-15 is another device for removal of fluoride from groundwater andaluminum sulphate was used as the major chemical. After operating for four months,7.9 m3 water was treated. In the jar test, the optimum pH value ranged from 6.0 to 6.7.In the lab-scale test, when proper dosage of aluminum sulphate and sodium hydroxidewere added into the reactor, the concentration of fluoride was reduced from 4.0 mg/Lin raw water to less than 1.0 mg/L in finished water, and the concentration ofaluminum in finished water was no more than 0.05 mg/L. The sizes of the dominantparticles of aluminum hydroxide in the mixed liquor are larger than 1 μm. The smallparticles whose sizes range from 0.2 μm to 0.4 μm are less, but they play an importantrole in the membrane fouling. The ratio of the volume of treated water to dischargedsludge was between 60 and 350 and it increased to 744 after the sludge wasconcentrated and dried in normal temperature for 41 days.