水系统中微生物与碳酸钙混合垢形成过程的研究

Formation Process of Mixed Fouling of Microbe and CaCO3 in Water Systems

目的:由微生物和钙镁沉积所共同形成的污垢是实际水系统中混合垢的主要成份。对这种混合垢的形成过程进行研究不仅更接近实际情况,而且可以深入认识微生物与钙镁离子之间的相互作用、成垢顺序等结垢的机理问题,并为开发适宜有效的控制混合垢形成的新技术奠定理论基础。方法:将发酵罐中培养的荧光假单胞菌以及Na2CO3与CaCl2溶液各自按设定流量加入到三级过滤水中以形成模拟工业循环冷却水。将10种由不同固体材料制成的实验件嵌入平行平板流道的底面上,并在不同碳酸钙饱和程度及主体流速下,用称量法测定不同材料表面上形成的混合垢重量,从而获得各种条件下混合垢随时间的生长曲线。荧光假单胞菌和碳酸钙在固体表面上附着过程与沉积的顺序以及混合垢的结构则采用显微摄像技术进行实时观测与记录。结果:聚合物材料上形成的混合垢量明显多于金属材料上的,但在CaCO3饱和程度很高时,这些差异变小。在无壁面加热的条件下,各种材料表面上形成的平均混合垢量随水体中CaCO3饱和程度及流速的增加而减少。研究结果还表明,混合垢的结垢诱导期随流速的增加而缩短。当饱和程度小于1而大于0时,结垢诱导期长于纯生物垢的诱导期。当CaCO3饱和程度大于等于1之后,混合垢的诱导期随CaCO3饱和程度的增加而减小。此外。

Purpose: The mixed fouling consisting of microbes and calcium or magnesium salts is the major part of the fouling in practical water systems. It will more accord with practical processes to investigate the mixed fouling formed with these substances. Also the investigation is essential to understand the interaction between bacteria and minerals, the mechanism and the sequence of the mixed fouling, and to develop novel techniques for effective controlling of the mixed fouling. Methods: Pseudomonas fluorescens cultured in fermenter, Na2CO3 and CaCl2 solutions were respectively added into 3-stage micro filtered water in designed flow rates to make simulated industrial cooling water. 10 coupons made of different solid materials were inlayed onto the bottom surface in the flow chamber of parallel plates. And the weight of mixed fouling formed on these coupons was measured with an analytical balance with 0.1mg accuracy under the conditions of different CaCO3 saturation levels and bulk velocities. Therefore the growth curves of mixed fouling can be obtained. On the other hand, the sequence of adhesion and deposit of the bacteria and CaCO3 on glass surface was measured and recorded with micro video technology. Results: The mixed fouling mass developed on polymer materials is much more than that on metal surfaces. With the increase of saturation level of CaCO3 however, this difference becomes decreased. The results also indicate that the mixed fouling mass decreases with the increase of CaCO3 saturation degree and flow velocity when the temperature of solid surface is equal to that of the fluid. And the induction period of mixed fouling declines with the rising of flow velocity. Moreover, the induction period of mixed fouling is longer than that of pure bacterial biofouling when the saturation level of CaCO3 is less than 1 and greater than 0. And the induction period decreases with CaCO3saturation degree when the level is more than or equal to 1. In addition, the sequence of the mixed fouling with bacteria and CaCO3 on glass surface is that CaCO3 first deposits on the solid surface, while the bacteria need longer time to adhere on the surface. Conclusions: The mixed fouling behavior on various material surfaces mainly depends on the anfinity of bacteria to the material. The physical and chemical properties of material surfaces, flow velocity and CaCO3 saturation degree are important factors influencing the formation of the mixed fouling.