Developing a More Fundamental Understanding of Drinking Water Biofiltration

在过去的十年里，人们对使用生物工艺作为饮用水处理的一部分的兴趣大幅增加。这是因为它们能够生物降解水中部分天然有机物(NOM)，这可能会干扰良好的处理。与NOM相关的一个经典问题是潜在有害消毒副产物的形成。 尤其令人感兴趣的是快速生物过滤，这是在通常用于去除颗粒和病原体的过滤器中进行的。在没有消毒剂残留的情况下，过滤器中非常大的表面积允许形成能够进行生物降解的生物膜。在过去的几年里，研究表明，这种生物过滤器还可以有效地降低生物聚合物的浓度，即NOM的高分子量部分。生物聚合物已被证明是污染低压膜的关键，如超滤，这些膜正越来越多地被用于饮用水处理中的病原体和颗粒去除。这为生物过滤定义了一个潜在的新应用，即作为一种“绿色”膜前处理。在过去的几年里，申请人的很大一部分研究都是针对这一点的。 在进行这项研究的过程中，出现了几个重要的问题，需要进行更加根本性的调查。这些研究问题构成了这一应用的基础，对于理解和成功应用生物过滤非常重要，无论其治疗目标如何。 第一个问题是，关于生物滤池适宜的大量营养素比例，文献中出现了相互矛盾的信息，这样氮或磷就不会受到限制。这具有重要的实际意义，因为例如，如果要补充磷，可能需要在下游污水处理厂将其去除。此外，胞外聚合物(EPS)在生物过滤中的作用还没有得到适当的解决。此外，通常用于量化生物量的参数，如三磷酸腺苷(ATP)，已被证明与生物过滤器的性能没有唯一的关系。 第二个研究问题是，就作为膜预处理的生物过滤而言，生物聚合物部分的生物降解性对于不同的水似乎是不同的。生物过滤前的臭氧氧化有助于减少膜污染，但似乎对生物过滤去除生物聚合物有负面影响。 -- 由于生物过滤还可以去除反渗透(RO)膜中容易生物降解的NOM，这些NOM对用于海水淡化的反渗透(RO)膜造成生物污染，第三个需要是探索生物过滤在反渗透应用中的潜力，在反渗透应用中，它可以减少用于膜清洗的化学物质的使用。

In the last decade, the interest in using biological processes as part of drinking water treatment has increased substantially. This is driven by their ability to biodegrade portions of the natural organic matter (NOM) in water that can interfere with good treatment. A classical issue associated with NOM is the formation of potentially harmful disinfection byproducts. Of particular interest is rapid biofiltration, which takes place in filters normally used for particle and pathogen removal. In the absence of a disinfectant residual, the very high surface area in the filters allows for the development of biofilm that can undertake biodegradation. In the last several years, research has shown that such biofilters can also effectively reduce the concentrations of biopolymers, the high molecular weight fraction of the NOM. Biopolymers have been shown to be critical in fouling low-pressure membranes such as ultrafiltration that are increasingly being used for pathogen and particle removal in drinking water treatment. This defines a potential new application for biofiltration, i.e. as a “green” membrane pretreatment. In the last several years, a significant portion of the applicant’s research has been directed towards this. In the conduct of this research several important issues have arisen that require more fundamentally-oriented investigation. These research questions form the basis of this application and are important for the understanding and successful application of biofiltration, regardless of its treatment objective. The first issue is that conflicting information has appeared in the literature regarding the appropriate macronutrient ratio for biofilters so that nitrogen or phosphorus are not limiting. This is of important practical significance, because if, for example, phosphorus were to be supplemented, it could potentially need to be removed at the downstream wastewater treatment plants. Additionally, the role of extracellular polymeric substances (EPS) in biofiltration has not been properly addressed. Further, commonly used parameters to quantify biomass such as adenosine triphosphate (ATP) have been shown not to have a unique relationship with biofilter performance. A second research question is that in terms of biofiltration as a membrane pretreatment, the biodegradability of the biopolymer fraction appears to be different for different waters. Ozonation prior to biofiltration assists in reducing membrane fouling, but appears to negatively impact the removal of biopolymers by biofiltration.   Because biofiltration can also remove the easily biodegradable NOM that contributes to biofouling in reverse osmosis (RO) membranes used for desalination, a third need is to explore biofiltration's potential in RO applications, where it could reduce chemical usage for membrane cleaning.