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نقش یک بیوفیلم میکروبی بر خوردگی و مس و رهاسازی در سیستم های لوله کشی
The Role of a Microbial Biofilm on Corrosion and Copper and Release in Plumbing Systems
Drinking water distribution systems (DWDS) are extreme environments, considering the oligotrophic conditions in them. Simultaneously, these systems are designed to maintain a low microbial burden since the drinking water has disinfectant residual and uses a biocidal material as copper to build them. Despite this, microorganisms can survive in them, mainly due to biofilm development.
Biofilms are one of the most widely distributed modes of life on Earth, in which a high cell density is composed of many species, and cells are frequently embedded in a self-produced matrix of extracellular polymeric substances (EPS). EPS is one of the essential components of biofilms because it helps create a barrier that controls the diffusional processes and chemical reactions.
The safety of drinking water can be affected by the microbial settlement over the copper pipe's inner wall. The processes that the microorganisms modify are diverse, as an example: i) biocorrosion process or microbiologically influenced corrosion, which increase the copper release up to levels hazardous for the people; ii) enhancing the growth of other microorganisms into copper pipes since the biofilm acts as nutrient storage, and iii) storing of metals on the biofilm surface, due to sorption capacities on it.
Despite the severe impact on public health than those situations can create, this topic has not been appropriately studied. This thesis proposes to study the characteristics and changes that the biofilm makes on the copper release and its influence on water quality. The experiments included field and laboratory approaches for a) determining the impact of microbial biofilm in the copper release and other water quality parameters, b) showing new evidence of how the biofilm development modifies the biocorrosion, and c) knowing the potential of the native bacterial isolate as storage of metals potentially hazardous.
The strategy to establish the biofilm role in the corrosion and copper released on drinking water systems included field and laboratory approaches. The analysis of copper pipes extracted from field sampling did not directly relate to the exposure time, corrosion rate, and amount of copper released in the water. Moreover, the outcomes revealed that biocorrosion is a dynamic biologic process that can be characterized neither a unique aging time nor extrapolation of a short time experiment, especially when the system study is a plumbing system.
On the other hand, the studies done under laboratory conditions emphasize the need to put the environment where the bacteria are involved. Our results indicate that the first isolate, identified as Variovorax sp, showed a striking loss of biofilm formation capacity when interacting with the second isolate, identified as Ralstonia pickettii.
Similarly, the characterization functional of EPS groups involved in the copper accumulation from bacterial isolate showed how the amine group modifications (by methylation) on the surface of bacteria isolated, increasing up to 30 % the copper sorption concerning the same bacterial isolate without modification. These results suggest the need to understand the environmental context to predict how each microorganism can act.
Finally, this thesis provides evidence that supports the idea of potential hazardous microbial contamination on the drinking water due to biofilm detachment and the accumulation of the metal by the microbial sorb capacity and later release. This knowledge will be the beginning to create a protocol on biofilm monitoring to reduce the water quality deterioration by the copper contamination and microorganisms, avoiding the negative effect on public health.
کلاهک های GAC به عنوان یک مانع بالقوه برای درمان سیانوتوکسین های آب آشامیدنی
GAC Caps as a Potential Treatment Barrier for Drinking Water Cyanotoxins
Incorporation of GAC in media filtration is a useful means for improving treatment outcomes via adsorption and subsequent enhanced biological treatment. Although beneficial, complete GAC replacement often results in higher operational costs. A seven-month pilot study examined the benefits of replacing the top few centimeters of anthracite media with GAC “caps” to enhance control of a cyanotoxin as well as organics. Removal of the cyanotoxin cylindrospermopsin by GAC adsorption was assessed utilizing a surrogate dye. A GAC capped filter demonstrated higher reduction when compared to a control throughout the study period. However, increased operational time resulted in lower reduction. While installation of a GAC cap increased biomass density (ATP), it did not improve DOC or DBP FP removal. Chlorine demand was significantly reduced, representing a potential side-benefit. This study presents evidence that incorporation of GAC caps can provide a low-capacity barrier for cylindrospermopsin exposure over multiple months of continuous operation.