RESUMO
This paper reports experimental results on the sequential use of ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) to fractionate alkaline extraction bleaching effluents from kraft cellulose production. The aim was to unveil the way key pollutants are distributed when subjected to sequential UF/NF/RO membrane separation processes. Alkaline bleaching effluents were obtained from a local pinewood-based mill, featuring elementary chlorine free bleaching to produce high-brightness cellulose. The experimental system was based on a laboratory-scale membrane system, DSS LabStak® M20 Alfa Laval, using Alfa Laval UF and NF/RO membranes, operated at a constant transmembrane pressure (6 bar for UF membranes and 32 bar for NF/RO membranes), at 25°C. Results show that 78% chemical oxygen demand (COD) and total phenols, 82% adsorbable organic halogens (AOX) and 98% colour were retained by UF membranes which have molecular weight cut-off (MWCO) above 10â kDa. In all, 16% of original COD, total phenols and AOX, and the remaining 2% colour were retained by UF membranes within the 1 to 10â kDa MWCO range. Chloride ions were significantly present in all UF permeates, and RO was required to obtain a high-quality permeate with a view to water reuse. It is concluded that UF/NF/RO membranes offer a feasible option for water and chemicals recovery from alkaline bleaching effluents in kraft pulp production.
Assuntos
Clareadores/isolamento & purificação , Membranas Artificiais , Eliminação de Resíduos Líquidos/métodos , Poluição da Água/prevenção & controle , Celulose , Poluentes Ambientais/análise , Peso Molecular , Ultrafiltração , MadeiraRESUMO
In this study, the effect of zeolite chemical surface characteristics on the oxidative regeneration of toluene saturated-zeolite samples is investigated. A Chilean natural zeolite (53% clinoptilolite, 40% mordenite and 7% quartz) was chemically modified by acid treatment with hydrochloric acid and by ion-exchange with ammonium sulphate. Thermal pre-treatments at 623 and 823K were applied and six zeolite samples with different chemical surface characteristics were generated. Chemical modification of natural zeolite followed by thermal out-gassing allows distinguishing the role of acidic surface sites on the regeneration of exhausted zeolites. An increase in Brønsted acid sites on zeolite surface is observed as a result of ammonium-exchange treatment followed by thermal treatment at 623K, thus increasing the adsorption capacity toward toluene. High ozone consumption could be associated to a high content of Lewis acid sites, since these could decompose ozone into atomic active oxygen species. Then, surface oxidation reactions could take part among adsorbed toluene at Brønsted acid sites and surface atomic oxygen species, reducing the amount of adsorbed toluene after the regenerative oxidation with ozone. Experimental results show that the presence of adsorbed oxidation by-products has a negative impact on the recovery of zeolite adsorption capacity.
Assuntos
Oxidantes/química , Ozônio/química , Tolueno/química , Zeolitas/química , Oxirredução , Reciclagem , Propriedades de SuperfícieRESUMO
This article presents experimental results on 47 µmol L(-1) sulfathiazole (STZ) degradation by Fenton and photo-Fenton reactions using multivariate analysis. The optimal experimental conditions for reactions were obtained by Response Surface Methodology (RSM). In the case of the Fenton reactions there were 192 µmol L(-1) ferrous ions (Fe(II)) and 1856 µmol L(-1) hydrogen peroxide (H2O2), as compared with 157 µmol L(-1) (Fe(II)) and 1219 µmol L(-1) (H2O2) for photo-Fenton reactions. Under these conditions, around 90% of STZ degradation were achieved after 8 minutes treatment by Fenton and photo-Fenton reactions, respectively. Moreover, a marked difference was observed in the total organic carbon (TOC) removal after 60-min treatment, achieving 30% and 75% for the Fenton and photo-Fenton reactions, respectively. Acetic, maleic, succinic and oxamic acids could be identified as main Fenton oxidation intermediates. A similar pattern was found in the case of photo-Fenton reaction, including the presence of oxalic acid and ammonia at short periods of irradiation with UV-A. The calculated values of Average Oxidation State (AOS) corroborate the formation of oxidized products from the initial steps of the reaction.
Assuntos
Peróxido de Hidrogênio/química , Ferro/química , Sulfatiazóis/química , Amônia/análise , Carbono/análise , Cinética , Modelos Químicos , Análise Multivariada , Ácido Oxálico/análise , Oxirredução , Fotoquímica/métodos , SulfatiazolRESUMO
Photocatalytic degradation of phenylmercury was studied using TiO2 in aqueous suspension assisted by UV-A irradiation. Reaction conditions, such as pH and amount of TiO2 were set using a factorial design of experiments resulting in a greater influence of pH on phenylmercury degradation. Hg (II) reduction and simultaneous oxidation of aromatic group was observed. Optimum reaction conditions were obtained under nitrogen atmosphere at pH 10 and 0.35 g/L(-1) TiO2. Under these conditions almost 100% reduction of mercury was reached after 30 min UV irradiation. Total mercury reduction was achieved after 40 min reaction under saturated oxygen. Furthermore, phenol and diphenylmercury were identified as intermediate products of oxidation. It was observed that a major fraction of the reduced mercury was removed as metallic vapor by gas stripping, whereas a minor fraction was adsorbed on the catalyst surface, probably as Hg(OH)2. Under optimal conditions obtained by multivariable analysis, total mineralization of organic matter was achieved after about 60-min irradiation.
Assuntos
Compostos de Fenilmercúrio/química , Compostos de Fenilmercúrio/efeitos da radiação , Titânio/química , Raios Ultravioleta , Poluentes Químicos da Água/química , Poluentes Químicos da Água/efeitos da radiação , Fungicidas Industriais/química , Fungicidas Industriais/efeitos da radiação , Cromatografia Gasosa-Espectrometria de Massas , Microscopia Eletrônica de Varredura , Modelos Teóricos , Fotólise , Espectrometria por Raios XRESUMO
Among indoor pollutants, ozone is recognised to pose a threat to human health. Recently, low cost natural zeolites have been applied as alternative materials for ozone abatement. In this work, the effect of compensating cation content of natural zeolite on ozone removal is studied. A Chilean natural zeolite is used here as starting material. The amount of compensating cations in the zeolite framework was modified by ion exchange using an ammonium sulphate solution (0.1 mol L(-1)). Characterisation of natural and modified zeolites were performed by X-ray powder diffraction (XRD), nitrogen adsorption at 77K, elemental analysis, X-ray fluorescence (XRF), thermogravimetric analysis coupled with mass spectroscopy (TGA-MS), and temperature-programmed desorption of ammonia (NH(3)-TPD). Ozone adsorption and/or decomposition on natural and modified zeolites were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Results show that the zeolite compensating cation content affects ozone interaction with zeolite active sites. Ammonium ion-exchange treatments followed by thermal out-gassing at 823 K, reduces ozone diffusion resistance inside the zeolite framework, increasing ozone abatement on zeolite surface active sites. Weak and strong Lewis acid sites of zeolite surface are identified here as the main active sites responsible of ozone removal.
Assuntos
Poluentes Atmosféricos/química , Ozônio/química , Compostos de Amônio Quaternário/química , Zeolitas/química , Poluição do Ar em Ambientes Fechados/prevenção & controle , Amônia/química , Troca Iônica , Difração de Raios XRESUMO
Chemical oxidation using ozone in the presence of appropriate catalysts offers an attractive option for removing poorly biodegradable pollutants. However, the effect of such catalysts on ozone aqueous decomposition is not well documented. This study compares experimental results on ozone aqueous decomposition promoted by zeolite and volcanic sand. These are two low costs natural materials identified as suitable catalysts for heterogeneous ozonation. The effects of pH (2-8) and free radical scavengers (acetic acid) on the dissolved ozone decay rate are evaluated at laboratory scale. Results show that the ozone decay rate increases in the presence of natural materials tested here. Under alkaline conditions, the effect of free radical scavengers on ozone self-decomposition is significantly reduced when such materials were present, particularly in the case of volcanic sand. Results suggest that ozone aqueous decomposition in the presence of zeolite and volcanic sand take place mainly on the natural material surface. The presence of metal oxides in zeolite and volcanic sand might catalyse ozone decomposition into more active radicals, thus enhancing the oxidation of organic pollutant.
Assuntos
Poluentes Ambientais/química , Ozônio/química , Dióxido de Silício/química , Zeolitas/química , Ácido Acético , Catálise , Recuperação e Remediação Ambiental/métodos , Sequestradores de Radicais Livres , Concentração de Íons de Hidrogênio , Cinética , Oxirredução , SoluçõesRESUMO
This paper presents experimental results on the imidacloprid removal from wastewater using homogeneous photo-Fenton reactions illuminated with black light lamps. Multivariate experimental design was used to identify the effect of initial Fe(II) and H(2)O(2) concentrations on process performance. The initial iron concentration played a key role in the process kinetics, whereas hydrogen peroxide concentration directly affected the extent of the oxidation process. Imidacloprid degradation proceeded via two distinctive kinetics regimes, an initial stage of rapid imidacloprid reduction, followed by a slower oxidation process until complete removal. Under optimal conditions, more than 50% imidacloprid degradation was observed after less than 1 min treatment, and TOC and COD removal up to 65% and 80%, respectively, were measured after all hydrogen peroxide was consumed. Raw imidacloprid samples presented significant acute toxicity to Daphnia magna and genotoxic effects on Bacillus subtilis sp. Such toxic effects remained detectable even after significant pesticide removal had been achieved, due to the presence of toxic by-products. Both acute toxicity and genotoxicity disappeared after considerable mineralization resulting in final low molecular weight by-products. Results obtained here confirm that design and operation of photo-Fenton processes should focus on toxicity removal rather than on specific target pollutants.
Assuntos
Imidazóis/química , Imidazóis/efeitos da radiação , Inseticidas/química , Inseticidas/efeitos da radiação , Nitrocompostos/química , Nitrocompostos/efeitos da radiação , Raios Ultravioleta , Poluentes Químicos da Água/química , Poluentes Químicos da Água/efeitos da radiação , Purificação da Água/métodos , Animais , Bacillus subtilis/efeitos dos fármacos , Bacillus subtilis/genética , Dano ao DNA , Daphnia/efeitos dos fármacos , Peróxido de Hidrogênio/química , Imidazóis/toxicidade , Inseticidas/toxicidade , Ferro/química , Dose Letal Mediana , Neonicotinoides , Nitrocompostos/toxicidade , Oxirredução , Fotoquímica , Poluentes Químicos da Água/toxicidadeRESUMO
Ozone oxidation combined with activated carbon adsorption (O(3)/AC) has recently started to be developed as a single process for water and wastewater treatment. While a number of aspects of aqueous ozone decomposition are well understood, the importance and relationship between aqueous ozone decomposition and organic contaminant degradation in the presence of activated carbon is still not clear. This study focuses on determining the contribution of homogeneous and heterogeneous reactions to organic contaminants removal in O(3)/AC system. Benzothiazole (BT) was selected as a target organic pollutant due to its environmental concern. A reactor system based on a differential circular flow reactor composed by a 19 cm(3) activated carbon fixed bed column and 1 dm(3) storage tank was used. Ozone was produced from pure and dry oxygen using an Ozocav ozone generator rated at 5 g O(3)h(-1). Experimental results show that BT removal rate was proportional to activated carbon dosage. Activated carbon surface contribution to BT oxidation reactions with ozone, increased with pH in absence of radical scavengers. The radical reaction contribution within the pH range 2-11 accounted for 67-83% for BT removal in O(3)/AC simultaneous treatment. Results suggest that at pH higher than the pH of the point of zero charge of the activated carbon dissociated acid groups such as carboxylic acid anhydrides and carboxylic acids present on activated carbon surface could be responsible for the observed increase in the ozone decomposition reaction rate. A simplified mechanism and a kinetic scheme representing the contribution of homogeneous and heterogeneous reactions on BT ozonation in the presence of activated carbon is proposed.
Assuntos
Benzotiazóis/química , Carbono/química , Ozônio/química , Poluentes Químicos da Água/química , Catálise , Cinética , Purificação da ÁguaRESUMO
Daily particle samples were collected in Chillán, Chile, at six urban locations from September 1, 2001, through September 30, 2003. Aerosol samples were collected using monitors equipped with a Sierra Andersen 246-b cyclone inlet on Teflon filters. Average concentrations of coarse particulate matter (PM10) for the 2001-2003 period ranged from 43.4 microg/m3 to 81.8 microg/m3 across the six sites. Annual PM10 concentration levels exceeded the European Union concentration limits. Mean PM10 levels during the cold season (April through September) were more than twice as high as those observed in the warm season (October through March). Average contributions to PM10 from organic matter, soil dust, nitrate (NO3-), elemental carbon, ammonium (NH4+), and sulfate (SO4(2-)) were 31%, 27%, 11%, 8%, 7%, and 5%, respectively. The chemical analyses indicated that carbonaceous substances were the most abundant components of PM10 in cold months, whereas crustal material was the most abundant component of PM10 during warm months. Higher concentration levels were observed in the downtown area suggesting a clear anthropogenic origin, whereas in the rural sites the source was mainly natural, such as resuspended soil dust associated with traffic on unpaved roads and agricultural activities.
Assuntos
Poluentes Atmosféricos/análise , Poeira/análise , Aerossóis , Chile , Cidades , Elementos Químicos , Monitoramento Ambiental , Nitratos/análise , Tamanho da Partícula , Compostos de Amônio Quaternário/análise , Estações do Ano , Sulfatos/análiseRESUMO
Inhalable particulate matter (PM10) concentrations were measured over 24-h intervals at six different urban sites in the city of Chillán from September 2001 to April 2003. Sampling locations were selected to represent central city, commercial, residential, and industrial portions of the city. Chemical composition of PM10 was performed to samples of 47 mm diameter Teflon membranes within the city of Chillán. The spatial and temporal variability of the chemical composition of PM10 was evaluated taking into account additional data from meteorology and further air pollutants. The majority of PM mass was comprised of carbon, nitrate, sulfate, ammonium, and crustal components but in different proportion on different days and at different sites. The chemical analyses showed that carbonaceous substances and crustal material were the most abundant component of PM10 during the winter and summer, respectively. The concentrations of PM10 were higher during the cold season than during the warm season. The PM10 concentrations were higher in the downtown area of the city of Chillán, where also the chemical composition was more variable due to urban traffic and other anthropogenic sources.
Assuntos
Poluentes Atmosféricos/análise , Poluentes Atmosféricos/química , Aerossóis/análise , Atmosfera , Chile , Elementos Químicos , Monitoramento Ambiental , Incineração , Microscopia Eletrônica , Tamanho da Partícula , Estações do Ano , Poluentes do Solo/análise , Fatores de Tempo , População Urbana , Tempo (Meteorologia) , MadeiraRESUMO
Effluents from small and medium sized chemical plants may contain significant amounts of poorly biodegradable aromatic compounds, which could negatively affect water quality and public health. This is a key environmental issue, particularly in areas where effluents are discharged into drinking water sources. Unfortunately, conventional biological treatment may not be able to meet discharge standards, and combined systems should be implemented. In this context, this paper presents experimental results on the application of a combined sequential ozonation-activated carbon-biological system to treat effluents containing chlorinated aromatic contaminants from chlorine based pulp bleaching. The experimental system consisted of an ozone bubble column reactor (0.3 dm3), an activated carbon fixed bed reactor (0.2 dm3), and an aerobic bioreactor (20 dm3). Ozone was produced from pure O2 using a generator rated at 2 mmol O3 h(-1). The bleaching effluent was pretreated and fed into the aerated sequencing batch bioreactor containing preconditioned biological sludge (3-4 g VSS dm(-3)), and cultured for 24 h. Samples of raw and treated effluents were assayed for biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total organic carbon (TOC), total phenols, and adsorbable organic halogens (AOX), using standard techniques. The presence of potential genotoxic activity in untreated and treated samples was assessed using the Ames tests. Results show that biological treatment of raw samples could not remove mutagenic activity on its own. On the other hand, ozonation followed by activated carbon treatment and biological treatment successfully removed genotoxicity in all cases. Reductions in BOD, COD, TOC, AOX, and phenols by biological treatment increased when samples were pretreated with ozone/activated carbon.