RESUMOA contaminação de águas por espécies tóxicas ou recalcitrantes gera grandes impactos ambientais. Nesse contexto, os Processos Oxidativos Avançados (POAs), tecnologias que utilizam principalmente o radical hidroxila (HO • ) para a oxidação dos poluentes, têm se destacado como métodos alternativos promissores no tratamento de águas residuais e efluentes industriais. Os POAs têm sido considerados uma estratégia eficaz do ponto de vista técnico, econômico e ambiental para a degradação de poluentes presentes em águas residuais e efluentes industriais, apesar de possuir limitações como alto custo das fontes de energia, desenvolvimento de novos materiais catalíticos de baixo custo e construção de reatores em escala real. Há uma grande relevância na aplicação desses processos em escala industrial mediante a otimização desses fatores de eficácia. Sendo assim, o objetivo deste trabalho foi realizar um levantamento bibliográfico sobre os POAs e apresentar dados a respeito da eficiência desses processos na degradação de poluentes, comparando os embasamentos teóricos e a sua aplicação industrial. Diante disso, os fundamentos e aplicações dos principais POAs (químicos, fotoquímicos, eletroquímicos, sonoquímicos, sonoeletroquímico e processos baseados em ozônio), bem como suas vantagens e desvantagens foram descritos nesta revisão da literatura.
The aim of the present study was to investigate the electrochemical formation of free chlorine species (HOCl/ClO) and their subsequent use for the degradation of the pesticide atrazine. Initially, the process of electrochemical-free chlorine production was investigated using a bench-scale electrochemical flow-cell. The most significant variables (electrolyte concentration ([NaCl]) and inter-electrode gap) of the process were obtained using a 2 factorial design and the optimum process conditions (1.73 mol L and 0.56 cm) were determined by a central composite design. Following optimization of free chlorine production, three degradation techniques were investigated, individually and in combination, for atrazine degradation: electrochemical, photochemical and sonochemical. The method using the techniques in combination was denominated sono-photo-assisted electrochemical degradation. Constant current assays were performed and the sono-photo-assisted electrochemical process promoted more efficient removal of atrazine, achieving total organic carbon removal of ∼98% and removal of atrazine to levels below the detection limit (>99%) in under 30 min of treatment. Furthermore, the combination of three techniques displayed lower energy consumption, and phytotoxicity tests (Lactuca sativa) showed that there was no increase in toxicity.
The influence of chloride ion concentration during the photo-assisted electrochemical degradation of simulated textile effluent, using a commercial Ti/Ru0.3Ti0.7O2 anode, was evaluated. Initially, the effect of applied current and supporting electrolyte concentration on the conversion of chloride ions to form reactive chlorine species in 90 min of experiment was analyzed in order to determine the maximum production of reactive chlorine species. The optimum conditions encountered (1.5 A and 0.3 mol dm(-3) NaCl) were subsequently employed for the degradation of simulated textile effluent. The efficiency of the process was determined through the analysis of chemical oxygen demand (COD), total organic carbon (TOC), of the presence of organochlorine products and phytotoxicity. Photo-assisted electrochemical degradation was more efficient for COD and TOC removal than the electrochemical technique alone. With simultaneous UV irradiation, a reduced quantity of reactive chlorine was produced, indicating that photolysis of the chlorine species led to the formation of hydroxyl radicals. This fact turns a simple electrochemical process into an advanced oxidation process.
Few studies employ electrochemical technology for urban water disinfection. This paper presents the replacement of a Cl 2 gas system by an on-site chlorine generation system (electrochemical disinfectant solution, EDS) and application at a water treatment plant. The study compares the Cl 2 gas and EDS systems over 36 months, with 18 months for Cl 2 gas and, after the implementation, 18 months for the EDS system (12-month dry season and 6-month wet season). Turbidity, residual Cl 2 , pH, total and faecal coliforms and DBPs were monitored. Turbidity was within legal limits and DBPs below both legal limits and limits of detection. For Cl 2 gas, residual Cl 2 suffered a decrease in wet and dry periods. However, the EDS maintained residual Cl 2 to the network tips without significant variations, with operational costs reduced by $41%.The study demonstrates that on-site Cl 2 generation can be employed for water disinfection for large urban areas with considerable economic and technical advantages. K E Y W O R D S chlorine gas, disinfection, electrochemical disinfectant solution, urban water treatment, water treatment plant 1 | INTRODUCTION An important factor in sanitation policy is the handling of water for human consumption, ranging from collection, treatment and storage to distribution. The most used products for disinfection are chlorine based, such as chlorine dioxide (ClO 2 ), various hypochlorite (ClO À ) forms and chlorine gas (Cl 2 ) itself (Abdullah et al., 2009). Chlorine for disinfection of drinking water has been widely used for more than 100 years, because it is low cost and presents residual disinfection capacity in the distribution systems, whereas other agents, such as ozone (O 3 ) or hydrogen peroxide (H 2 O 2 ), do not present this capacity (Abdullah et al., 2009) and can also form toxic degradation byproducts (Ike, Lee, & Hur, 2019).Researchers have observed that disinfectant stability (concentration) in distribution network can depend on several factors, including line pressure, water quality, mains maintenance and disinfectant type (Blokker, Smeets, & Medema, 2014). In the case of Cl 2 in the distribution network, it has been observed that concentration decreases with distance from the original dosage point (Angulo et al., 2017). Therefore, at the exit point of the water treatment plant (WTP), the concentration is generally higher than at the extremes of the distribution system, as seen in the literature (Angulo, 2017;Fisher, Kastl, & Sathasivan, 2011). It has been reported that maintenance in the distribution system, during pipe opening, removal and substitution, may contribute to drinking water contamination by pathogens by permitting the entrance of contaminated materials (Blokker et al., 2014).
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