New management strategy for the exploitation of activated carbon used in water treatment systems for medical care services

Abstract

In water treatment system for the production of water for dialysis and clinical analysis, granular activated carbon (GAC) is used to remove residual free chlorine. The formation of complexes (Ca-carboxylates) on the GAC surface together with the degradation of the carbonaceous matrix due to oxidation initiates the GAC depletion process, thus reducing its adsorption capacity and thus affecting the reliability of the water treatment system and the hemodialysis therapy itself. Currently, the management strategy used in water treatment system for the production of dialysis water is not effective as it does not include a characterization, regeneration or reuse of GAC which once depleted is usually dumped and replaced by fresh GAC thus creating an economic and environmental problem. This doctoral dissertation proposes a new strategy for the management of GAC in the medical care services. The scientific novelty and uniqueness of this research, seen in general, is the proposed GAC management strategy together with a new analytical technique for GAC characterization based on X-ray absorption analysis (XRA) using advanced digital image processing techniques. The gray scale levels (GSI) and photonic absorption profiles produced by exposing the GAC to ionizing radiation (X-rays) are, after a suitable digital image processing, correlated with the textural properties of the GAC by means of mathematical models supported by software applications such as MATLAB®. In addition, deep learning algorithms are implemented and used for the first time for the quantification of the degree of GAC depletion in order to extend the field of application of the XRA method. The proposed architectures provided very good results in estimating the degree of GAC depletion at different layers. Finally, a new economic cost-benefit model for the reuse of hemodialyzers has been developed using statistical analyses based on information obtained from patients undergoing maintenance hemodialysis for approximately 4 years. The proposed model indicates that the practice of reuse/disinfection will always be economically viable compared to a policy of no reuse/disinfection. The results of the XRA method were successfully correlated and validated with conventional X-ray fluorescence (XRF), thermogravimetry (TGA), elemental analysis (EA), electron microscopy (SEM), thermal desorption coupled to gas chromatography/mass spectrometry (TD-GC/MS), ATR-FTIR: Attenuated Total ReflectanceFourier Transform Infrared Spectroscopy, X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) relaxometry analyses. The XRA method proved to be a suitable, fast, robust and reliable analytical tool to provide information on the textural characteristics of GAC. Chemical regeneration of spent GAC from a hemodialysis water treatment system was successfully performed using hydrochloric acid (20 % v/v). The results obtained represent an effective tool that can allow the optimization of the regeneration management strategy according to the maximum exploitation yield of the GAC and its reuse cycle in water treatment systems in medical care services.