Industrial processes for the valorization of medical waste fractions
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Keywords
Medical waste ; Medical cotton waste ; Medical paper waste ; Torrefaction ; Acid hydrolysis ; Enzymatic hydrolysis ; Severity factor ; Response surface methodologyAbstract
The present dissertation innovates as regards the research for the valorization of cellulosic and lignocellulosic fractions of medical wastes (MW), aiming to production of energy, fuels, and materials, within the framework of zero waste circular economy. Initially, an extensive literature review was conducted to collect data on MW production, collection and segregation methods, and technologies used for their utilization or final disposal. The design of the experimental study was based on the collected data with a view to highlighting the capabilities of medical cotton and paper waste in energy production by increasing its higher heating value, as well as their use as adsorbents for the decontamination of wastewater. The enzymatic digestion capacity of medical cotton waste and medical paper waste were also studied.
More specifically, the adsorption and the higher heating value of medical cot-ton waste have been studied with torrefaction. Pretreatment was performed on a specific temperature range with a maximum at 340oC. Different reaction times have been used in each experiment in order to elucidate the parameters that affect process efficiency. 14 experiments were performed in a blast furnace. A Parr 1341 Plain Jacket Bomb calorimeter was used to measure the calorific value of the samples, whereas ad-sorption was tested for all samples. The simulated wastewater used herein was Methylene Blue solution (C16H18ClN3S.xH2O), whereas the samples were analyzed with a HACH DR6000 UV-VIS spectrophotometer (λ = 664 nm).
Kinetic modeling was used, along with the Combined Severity Factor (R0), which unifies in one variable the effect of reaction time and temperature.
Box-Behnken's Design of Experiments (DoE) was carried out through the Design Expert program using the Surface Response methodology (RSM) to study the effect of acid hydrolysis on the medical cotton and paper waste fractions to correlate with R0 in terms of experimental results. In this case R0, apart from reaction time and temperature, incorporate the acid concentration used herein. DoE consists of 15 experiments The products obtained from the treatment were studied for their adsorption capacity and their higher heating value (HHV). The experiments were performed in a 3.75 L Parr 4553 batch reactor (autoclave). All the above experiments were conducted at the Industrial Processes Simulation Laboratory, Industrial Management and Technology department, University of Piraeus.
The Agilent 1260 Infinity II LC System high performance liquid chromatography (HPLC) system was used to analyze the solid phase samples composition after quantitative saccharification. 30 measurements were made for each material. An Aminex HPX-87H column at 50oC was used. The same procedure was performed in the liquid phase to check for degradation products as well as to determine the kind and the amount of the total sugars. 30 measurements were conducted for the liquid phase and 30 for the solid phase of each material.
These solid samples were then used to produce fermentable glucose by enzymatic hydrolysis. Novozymes A / S Cellic® CTec2 enzyme mixture was used to hydrolyze the samples at 50°C. Liquid samples were taken at 24 and 48 hours and then measured using the DNS (Dinitrosalicylic acid) method and Glucotest spectrophotometric method (30 measurements were made for each method and each material at 24 and 48 hours). Τhese experiments were made at the Biotechnology Laboratory, Chemical Engineer Department of National Technology University of Athens.
According to the results, the medical cotton waste treated by acid hydrolysis had a better performance as a heat source than paper, Similarly, the hydrolyzed samples proved better adsorbents than the torrefied ones. It also presented a higher conversion efficiency to fermentable glucose than medical paper waste, rendering it more appropriate for bioethanol production. In conclusion, medical cotton waste (MCW) has been proven a suitable and promising source of energy and materials in the context of the zero-waste circular economy.