Photocatalytic membrane filtration and its advantages over conventional approaches in the treatment of oily wastewater: A review

Clean water supply has become one of the biggest challenges of the 21st century; therefore, water source protection is of increasing importance. Beyond environmental protection reasons, economic concerns-derived from increasing costs of processing water and wastewater discharge-also prompt industries to use advanced wastewater treatment methods, which ensure higher purification efficiency or even the recycling of water. Therefore, highly effective treatment of oily wastewaters has become an urgent necessity because they are produced in high quantities and have harmful effects on both the environment and human population. However, high purification efficiency can be difficult to achieve, because some compounds are hard to eliminate. Conventional methods are effective for the removal of floating and dispersed oil, but for finely dispersed, emulsified and dissolved oil advanced methods must be used, such as membrane filtration which exhibits several advantages. The application of this technology is restricted by fouling-the major limiting factor-which jeopardizes the membrane performance. In order to reduce fouling, in-depth research is being conducted to make the treatment of oil-contaminated water technically and economically feasible. The present work aims to review the conventional oil separation methods with their limitations and to focus on membrane filtration, which ensures significantly higher purification efficiencies, including the main problem: the flux reduction caused by fouling. This paper also discusses promising solutions, such as membrane modification methods, mostly with hydrophilic and/or photocatalytic nanoparticles and nanocomposites, overviewing the efforts that are being made to develop feasible technologies to treat oil-contaminated waters

Investigation of the applicability of TiO2, BiVO4, and WO3 nanomaterials for advanced photocatalytic membranes used for oil-in-water emulsion separation

In the present study, a commercial TiO2, several BiVO(4)photocatalysts, a WO(3)nanomaterial, and their composites were used to prepare photocatalytic polyvinylidene fluoride (PVDF) ultrafilter membranes. Their photocatalytic activities and the effects of coatings on the filtration of oil-in-water emulsion (crude oil; c(oil)= 100 mg L-1) were investigated. Fluxes, filtration resistances, purification efficiencies, and fouling resistance abilities-like flux decay ratios (FDRs) and flux recovery ratios (FRRs)-were compared. The solar light-induced photocatalytic decomposition of the foulants was also investigated. WO(3)was used as a composite component to suppress the electron-hole recombination with the goal of achieving higher photocatalytic activity, but the presence of WO(3)was not beneficial concerning the filtration properties. However, the application of TiO2, one of the investigated BiVO(4)photocatalysts, and their composites was also beneficial. In the case of the neat membrane, only 87 L m(-2)h(-1)flux was measured, whereas with the most beneficial BiVO(4)coating, 464 L m(-2)h(-1)flux was achieved. Pure BiVO(4)coating was more beneficial in terms of filtration properties, whereas pure TiO(2)coating proved to be more beneficial concerning the photocatalytic regeneration of the membrane. The TiO2(80%)/BiVO4(20%) composite was estimated to be the most beneficial combination taking into account both the aspects of photocatalytic activity and filtration properties

Effects of treated effluent recirculation on the bleaching plant of a Kraft pulp mill

O branqueamento é o estágio da produção de polpa celulósica kraft que gera maior carga hídrica poluente e muitas fábricas têm buscado minimizar ou até mesmo eliminar a quantidade de efluente gerado. O fechamento de circuitos d ́água vislumbra-se como uma opção atrativa para a redução do consumo de água e da geração de efluentes. O objetivo do presente trabalho foi avaliar a viabilidade técnica de utilizar efluentes tratados como água de lavagem nos estágios do branqueamento. A sequência D ht (EP)DP de branqueamento foi simulada em laboratório utilizando quatro tipos de água de lavagem: a) água deionizada, b) água branca (AB) da máquina de secagem, c) efluente de baixa carga orgânica (EBC) proveniente da planta química e do pátio de madeira da fábrica, tratado por decantação; e d) efluente de alta carga orgânica (EAC) tratado biologicamente por um processo de lodos ativados. Para alcançar alvura da polpa de 90% ISO, o consumo de ClO 2 da sequência completa de branqueamento foi de 8,1, 8,0, 16,3 e 13,8 kgClO 2 tas -1 ao utilizar água deionizada, AB, EBC e EAC, respectivamente. A viscosidade, n° kappa e o teor de ácido hexenurônico da polpa branqueada com os efluentes diminuíram em relação à polpa branqueada com água deionizada. Os testes físicos e ópticos dos papéis confeccionados não demonstraram alterações estatísticas significativas com a mudança do tipo de água utilizada para lavagem. Os filtrados dos estágios D ht e EP apresentaram valores de condutividade elétrica, cor, turbidez, DQO, SDT e teor de Ca, Fe, K, Na e Cu maiores para os branqueamentos realizados com os efluentes em relação às referências (água deionizada e AB). Não obstante, sua qualidade não compromete a eficiência da Estação de Tratamento de Efluentes (ETE). Conclui-se que foi possível utilizar efluente na lavagem dos estágios de branqueamento, uma vez que as qualidades dos filtrados gerados, da polpa branqueada e dos papéis confeccionados foram satisfatórias, havendo, contudo, um incremento no consumo de reagentes ao longo da sequência e, consequentemente, um aumento do custo de produção de polpa celulósicaThe bleaching plant is the kraft pulp mill sector that generates the highest volume of effluents and many mills have sought to minimize or even eliminate this pollution source. The recycling of water can be seen as an attractive option to reduce water consumption and effluent generation. The objective of the present research was to evaluate the technical feasibility of using treated effluent as wash water in the bleaching stages. The bleaching sequence D ht (EP)DP was simulated in laboratory using four types of wash water: a) deionized water, b) whitewater (WW) from drying machine, c) low effluent organic load (LEL) from the chemical plant and wood yard of the mill and treated by sedimentation; and d) high organic load effluent (HEL) treated biologically by an activated sludge process. To achieve pulp brightness of 90% ISO, the consumptions of ClO 2 in the bleaching sequence were 8.1, 8.0, 13.8 and 16.3 kgClO 2 odt -1 when using deionized water, WW, LEL and HEL, respectively. The viscosity, kappa number and hexenuronic acid of the bleached pulp, when effluents were applied as wash water, decreased in comparison to the bleached pulp when deionized water was used. Physical and optical tests of the papers did not show any statistically significant difference whatever wash water used. The filtrates of D ht and EP stages presented values of electrical conductivity, color, turbidity, COD and Ca, Fe, K, Na and Cu content higher when effluent was used in relation to the references (deionized water and WW). Nevertheless, the filtrates quality would not jeopardize the Wastewater Treatment Plant (WTP) efficiency. It was possible to use effluent as wash water in the bleaching stages, since the filtrates and the paper produced with the bleached pulp complied with the quality standards. However, there was an increase in the consumption of chemicals in the bleaching sequence when effluents were used, and, consequently, an increase on the pulp production costsConselho Nacional de Desenvolvimento Científico e Tecnológic

Purification of oily wastewaters with membrane filtration: opportunities, problems and possible solutions

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