Is it possible to remove polymeric nanoparticles from aqueous paints during the activated sludge treatment?

The market for emulsion polymers (latexes) is large and growing at the expense of other manufacturing processes that emit higher amounts of volatile organic solvents. The paint industry is not an exception and solvent-borne paints have been gradually substituted by aqueous paints. In their life-cycle, much of the aqueous paint used for architectural or decorative purposes will eventually be discharged into wastewater treatment facilities, where its polymeric nanoparticles (mainly acrylic and styrene-acrylic) can work as xenobiotics to the microbial communities present in activated sludge. It is well established that these materials are biocompatible at macroscopic scale. But is their behaviour the same at nanoscale? What happens to the polymeric nanoparticles during the activated sludge process? Do nanoparticles agregate and are discharged together with the sludge or remain in emulsion? How do microorganisms interact with these nanoparticles? Are nanoparticles degradated by them? Are they adsorbed? Are these nanoparticles toxic to the microbial community? To study the influence of these xenobiotics in the activated sludge process, an emulsion of cross-linked poly(butyl methacrylate) nanoparticles of ca. 50 nm diameter was produced and used as model compound. Activated sludge from a wastewater treatment plant was tested by the OCDE’s respiration inhibition test using several concentrations of PBMA nanoparticles. Particle aggregation was followed by Dynamic Light Scattering and microorganism surfaces were observed by Atomic Force Microscopy. Using sequential batch reactors (SBRs) and continuous reactors, both inoculated with activated sludge, the consumption of carbon, ammonia, nitrite and nitrate was monitored and compared, in the presence and absence of nanoparticles. No particles were detected in all treated waters by Dynamic Light Scattering. This can either mean that microorganisms can efficiently remove all polymer nanoparticles or that nanoparticles tend to aggregate and be naturally removed by precipitation. Nevertheless respiration inhibition tests demonstrated that microorganisms consume more oxygen in the presence of nanoparticles, which suggests a stress situation. It was also observed a slight decrease in the efficiency of nitrification in the presence of nanoparticles. AFM images showed that while the morphology of some organisms remained the same both in the presence and absence of nanoparticles, others assumed a rough surface with hilly like shapes of ca. 50 nm when exposed to nanoparticles. Nanoparticles are thus likely to be either incorporated or adsorbed at the surface of some organisms, increasing the overall respiration rate and decreasing nitrification efficiency. Thus, despite its biocompatibility at macroscopic scale, PBMA is likely to be no longer innocuous at nanoscale.

Simulação numérica aplicada ao tratamento de efluentes

A existência de estações de tratamentos de águas residuais (ETAR) é, nos dias de hoje, fundamental na medida em que permite, reduzir a poluição ambiental associada às águas e, também, a reutilização da água tratada para diversos fins. A constante necessidade de cumprir os limites de descargas nos meios recetores conduziu a um melhoramento nas técnicas e processos de tratamento de efluentes, nomeadamente, nos processos biológicos. O processo por lamas ativadas é um processo amplamente utilizado para a remoção de poluentes orgânicos presentes nas águas residuais, pelo que um estudo mais intensivo sobre estes tratamentos resultou na publicação de uma série de conceitos e pressupostos, através de modelos numéricos. A modelação numérica de processos de tratamento de águas residuais e a utilização de ferramentas de simulação numérica têm sido largamente utilizadas, a nível mundial, por exemplo em investigação, desenvolvimento de processos, atividade de consultoria e igualmente por entidades reguladoras, na medida em que os auxiliam no planeamento, dimensionamento e análise do comportamento de infraestruturas de tratamento. No presente trabalho, recorreu-se ao software de simulação GPS-X (versão 6.0) para implementar o esquema de tratamento da ETAR de Beirolas. O objetivo deste trabalho é verificar a aplicabilidade de modelos numéricos na simulação de unidades de tratamento de efluentes e avaliar a resposta dos diferentes modelos, assim como a influência na alteração de características das águas afluentes no comportamento dos modelos. Os resultados obtidos permitiram concluir que os modelos numéricos podem ser utilizados para prever a resposta dos sistemas biológicos e as suas perturbações. Conclui-se ainda que o comportamento, dos modelos estudados (ASM1, ASM2d, ASM3 e mantis), é semelhante, contudo deve-se referir que devido à complexidade do modelo e a falta de informação experimental sobre as características do efluente, não permitiram efetuar uma completa caracterização e calibração do caso de estudo, e toda a informação disponível sobre as características físico-químicas da água foram baseadas em estimativas de concentrações de carências de oxigénio e sólidos suspensos.

Light-activated amplification in SiC Tandem devices: A capacitive active filter model

Characteristics of tunable wavelength pi'n/pin filters based on a-SiC:H multilayered stacked cells are studied both experimentally and theoretically. Results show that the device combines the demultiplexing operation with the simultaneous photodetection and self amplification of the signal. An algorithm to decode the multiplex signal is established. A capacitive active band-pass filter model is presented and supported by an electrical simulation of the state variable filter circuit. Experimental and simulated results show that the device acts as a state variable filter. It combines the properties of active high-pass and low-pass filter sections into a capacitive active band-pass filter using a changing capacitance to control the power delivered to the load.