Strontium-Containing Wastewater Treatment By A Mechanical Mixing Prilling-Microfiltration Combination Process

A prilling method was investigated through mechanical stirring in order to solve the problems that the settled sludge was difficult to be concentrated and the membrane fouling was serious in precipitation–microfiltration combination process for strontium removal. The strontium element was removed by forming compacted crystal particles when Na₂CO₃ and CaCO₃ were used as precipitating agent and crystal seed, respectively. The sedimentation performance of the particles formed by prilling was improved; the effluent turbidity was reduced so that the load of following microfiltration process was alleviated.The concentration of strontium in the raw water was about 5.0 mg/L in the mechanical stirring test. When the water temperature was 20℃and 25℃, the mean removal rate of strontium and hardness were 97% and 55%, pH values were about 10.5, the turbidity were 0.45 - 2.0 NTU in the precipitated effluent. The mean strontium concentration were decreased to 0.050 mg/L and 0.071 mg/L after filtered through a 0.22μm membrane, and the mean decontamination factors ( DF ) were 92 and 73, respectively. The minimum size of crystal particles that obtained after 700 prilling cycles was 45.71μm at 25℃, the corresponding settling velocity was 2.5 mm/s. The stacking volume of sedimental particles was only 49 mL, the total treated volume was 504 L. Further more, sludge concentration factor ( CF ) was more than 1.0×10⁴, which demonstrated the potential for practical application.On the basis of above tests, a submerged membrane microfiltration module was added after prilling method to investigate the strontium-containing wastewater treatment effect by the mechanical mixing prilling-microfiltration combination process. In this test, Na₂CO₃ was still used as precipitating agent. In order to improve the settling effect and reduce membrane fouling, flocculant FeCl₃ was auxiliary dosed in the membrane separator with concentration of 10 mg/L. The results showed that the settling velocity of the minimum size particles in the stirrer was improved and increased of 100⁴00 times more than that of the crystal seeds after treating of 3 m³ strontium-containing wastewater. When the strontium concentration of influent were 5.0 mg/L and 9.2 mg/L, the mean effluent strontium DF were 279 and 296, and the mean CF were 3.17×10³ and 3.01×10³, respectively.For the future, the strontium DF can be improved furture with the increased initial strontium concentration.