Removal of insecticides/pesticides from wastewater using heterogeneous photocatalysis

Porast svjetske populacije i potreba za proizvodnjom sve većih količina hrane uzrokuju prekomjernu i neodgovornu primjenu herbicida, koji putem ispiranja tla dospijevaju u površinske i podzemne vode. Herbicidi su postojani spojevi koji se teško razgrađuju u okolišu, što dovodi do nepoželjne bioakumulacije koja štetno djeluje na sve žive organizme, uključujući i čovjeka. Strogim zakonskim regulativama i propisima nastoje se smanjiti koncentracije ovakvih štetnih spojeva u okolišu, a novija znanstvena istraživanja usmjerena su na pronalaženje optimalnih metoda i tehnologija za uklanjanje herbicida iz otpadnih vodotokova. Jedna od metoda koja se intenzivno proučava u svrhu razgradnje i uklanjanja postojanih organskih onečišćivala iz otpadnih voda je heterogena fotokaliza, koja se ubraja u napredne oksidacijske procese (eng. advanced oxidation processes, AOPs). Cilj ovog rada je istražiti utjecaj različitih reakcijskih uvjeta, kao što su volumen reakcijske smjese, masa suspendiranog fotokatalizatora, brzina miješanja te protok recirkulacije na fotokatalitičku razgradnju modelne komponente herbicida. Kao modelna komponenta korišten je terbutilazin kao predstavnik s-triazinskih herbicida. Fotokatalitička razgradnja provedena je primjenom UV-C zračenja u anularnom fotokatalitičkom reaktoru sa suspendiranim slojem TiO2 katalizatora. Na temelju dobivenih rezultata predloženi su kinetički model i model fotoreaktora, procijenjeni su parametri modela te je provedena ocjena prihvatljivosti predloženog modela. Nađeno je da povećanje protoka recirkulacije reakcijske smjese kroz sustav te povećanje brzine miješanja poboljšavaju učinkovitost fotokatalitičke razgradnje terbutilazina, što je objašnjeno smanjenjem debljine difuzijskog graničnog sloja odnosno smanjenjem otpora prijenosu tvari međufaznom difuzijom. Kinetika reakcije opisana je primjenom pojednostavljenog Langmuir-Hinshelwoodovog mehanističkog kinetičkog modela koji je uvršten u model fotoreaktora. Usporedbom slaganja predloženih modela procesa s eksperimentalnim rezultatima doneseni su zaključci o prihvatljivosti modela za opis sustava korištenog u sklopu ovog rada.The overgrowing world population and the increasing need to produce large amounts of food often cause excessive and irresponsible use of herbicides, which, through soil washing, reach surface water and groundwater. Herbicides are persistent and difficult to decompose in the environment which causes their unwanted bioaccumulation that can be harmful to all living things, including humans. Strict laws and regulations seek to reduce concentrations of such harmful compounds in the environment. Therefore, more recent studies are focused on finding the optimal methods and technologies for eliminating these compounds from waste water streams. One of the methods intensively studied for the decomposition and removal of persistent organic pollutants from wastewater is heterogeneous photocatalysis, which belongs to the group of advanced oxidation processes (AOPs). The objective of this study is to examine the effect of operating conditions, such as volume of the reaction mixture, mass of suspended nanoparticles of photocatalyst, mixing rate and recirculation flow on the process of photocatalytic degradation of the model component which was herbicide. Terbuthylazine was used as a model component to represent s-triazine herbicides. Photocatalytic degradation was performed using a UV-C radiation source in an annular photocatalytic reactor with TiO2 photocatalyst nanoparticles suspended in solution. Based on the results of the conducted experiments, kinetic model and a photoreactor model were proposed, parameters of the model were evaluated and the acceptability of the proposed model was examined. Based on the experimental results obtained in this study, it is found that the increase of the recirculation flow of the reaction mixture through the system and the increase of the mixing rate improve the efficiency of photocatalytic degradation of terbuthylazine. This is explained by a decrease in the thickness of the diffusion boundary layer and a decrease in the mass transfer resistance by interphase diffusion. The reaction kinetics was described by using a simplified Langmuir-Hinshelwood mechanistic kinetic model which was incorporated into the photoreactor model. By comparing the proposed models of the process with the experimental results, conclusions were made on the acceptability of the models for the description of the system used in this study