Publicação

Combined laccase-ultrasound processes for industrial applications

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Resumo:	Bioprocesses including sonochemical systems have been of great importance for various industrial sectors. The improvement of the biological, chemical and physical performances leading to sustainable processes with reduced environmental impact are the main features responsible for the high interest on these technologies at industrial level. In this work, a combined laccase-ultrasound system was introduced in two distinct areas: cotton bleaching and urinary catheters functionalization. Regarding the cotton bleaching, the work was developed in three different phases: 1st phase: characterization of acoustic and hydrodynamic reactors with different geometries, namely two ultrasonic power generators (ultrasonic power generator type K8 with 850 kHz and ultrasonic bath equipment Ultrasonic cleaner USC600TH with 45 kHz) and two homogenizers (EmulsiFlex®-C3 and APV-2000); the optimal operating conditions for cotton bleaching were selected according to the highest hydroxyl radical production and the lowest required energy input; comparing the profile of each reactor, the medium frequency (850 kHz) ultrasonic power generator type K8 was the equipment that promoted highest hydroxyl radical production requiring low energy input, proving to be the best choice for further experiments; 2nd phase: combined laccase–hydrogen peroxide process assisted by ultrasound as an alternative approach to conventional cotton bleaching; two sequential stages were established: (1) laccase pretreatment and (2) hydrogen peroxide bleaching, both assisted by ultrasound; sonication mode (continuous or discontinuous pulse), hydrogen peroxide concentration, reaction temperature and processing time were the experimental parameters optimized; compared with the conventional methods, the combined laccase-hydrogen peroxide bleaching assisted by ultrasound (continuous pulse mode) allowed increase whiteness levels and reduce the amount of hydrogen peroxide in 50%; the energy consumption in terms of temperature (reduction of 40 ºC) and operating time (reduction of 90 minutes) was also reduced; 3rd phase: scale up of the combined laccase-hydrogen peroxide/ultrasound system aiming to develop a novel ultrasonic pilot scale reactor for cotton bleaching; an existing dyeing machine was transformed and adapted by including piezoelectric ultrasonic devices; standard half (4 g/L H2O2 at 90 ºC for 60 minutes) and optical (8 g/L H2O2 at 103 ºC for 40 minutes) cotton bleaching processes were used as references; laboratory experiments demonstrated that both low frequency, high power (22 kHz, 2100 W) and high frequency, low power ultrasounds (850 kHz, 400 W) were required to achieve satisfactory results; the laccase pretreatment assisted by high frequency ultrasound followed by the bleaching treatment using high power ultrasound promoted the highest whitening values; the developed ultrasonic pilot scale reactor allowed improving the cotton whitening efficiency using the combined laccase-hydrogen peroxide bleaching assisted by ultrasound and subsequently, less energy (temperature) and chemicals (hydrogen peroxide) were needed resulting in operational costs reduction. Overall, this technology allowed the laccase and hydrogen peroxide treatment combination in a continuous process. The developed pilot-scale reactor offers an enhancement of the cotton bleaching process with lower environmental impact as well as conducts to a better performance of further finishing operations. Concerning the urinary catheter functionalization, it was studied the polyurethane (PU) and silicone (SI) catheters coating with poly(catechin) to reduce the bacterial adhesion onto the devices surface. Laccase was used as a biocatalyst to oxidize the catechin monomer and produce the corresponding polymer. The catheter surface functionalization was optimized following two different approaches: with and without previous alkali pretreatment. The results indicated higher polymer attachment levels for the alkali-treated catheters (+18% for PU and +33% for SI catheters). The reduction of biofilm formation onto the catheter surface was quantitatively evaluated under static adhesion conditions against Escherichia coli (96% reduction on PU) and Staphylococcus epidermidis (81% reduction on SI). Though the catheter material type greatly influenced the bacterial adhesion, the alkali treatment was consistently beneficial for the poly(catechin) attachment and consequent biofilm reduction. Thus, the produced polymer was efficiently attached onto the catheters surface hindering the bacterial adhesion and the antibiofilm activity was dependent on the material-microorganism set. Functionalized PU catheter had strong effect on E. coli adhesion while functionalized SI catheter had activity against S. epidermidis. The oxidized flavonoid revealed to be a promising approach to prevent bacterial adhesion thus prolonging the life-span of catheters inside the human body. Nevertheless, aiming improving the antibiofilm activity of poly(catechin) coated catheters, it was explored the enzymatic synthesis of poly(catechin)-antibiotic conjugates as an alternative antimicrobial coating. Catechin was conjugated with two antibiotics, namely trimethoprim (TMP) and sulfamethoxazole (SMZ) via activation with N,N’-disuccinimidyl carbonate(DSC) and subsequent coupling to molecules containing α-amine terminals. SI and PU catheters were in-situ functionalized through laccase oxidation of catechin-antibiotic conjugates. Four antimicrobial coatings were produced, namely with poly(catechin), poly(catechin)-TMP, poly(catechin)-SMZ and poly(catechin)-TMP-SMZ. The bacterial adhesion reduction was tested on the functionalized devices using gram-negative and gram-positive strains. The most significant reduction in adhesion was observed with poly(catechin)-TMP (gram-negative: - 85% and gram-positive: - 87%) and with poly(catechin)-TMP-SMZ (gram-negative: - 85% and gram-positive: - 91%). The cytotoxicity to mammalian cells was assessed by indirect contact for 5 days and revealed that all the tested coatings supported more than 90% of viable cells. Concluding, in this work, a novel promising approach for increasing the indwelling catheters life-span was developed aiming to reduce catheter-associated chronic infections. Combined laccase-ultrasound processes revealed a great potential for industrial fields with distinct application topics allowing the overall costs processing reduction, a minor environmental impact and the production of novel products with improved or new properties contributing therefore to the enhancement of human life quality.
Autores principais:	Gonçalves, Idalina
Assunto:	Engenharia e Tecnologia::Outras Engenharias e Tecnologias
Ano:	2014
País:	Portugal
Tipo de documento:	tese de doutoramento
Tipo de acesso:	acesso aberto
Instituição associada:	Universidade do Minho
Idioma:	inglês
Origem:	RepositóriUM - Universidade do Minho