Mathematical modeling of trichloroethylene (TCE) degradation in membrane-attached biofilms

A mathematical model for the counter-diffusional membrane-attached methanotrophic biofilm reactor was developed. The model included competitive inhibition between trichloroethylene (TCE) and methane, production of inactive cells by TCE byproduct toxicity, and biomass detachment as a function of inactive cell concentration. Simulation results indicated that the optimum oxygen to methane ratio was dependent on the biofilm and the membrane thickness. Furthermore, the model confirmed experimental observations that the efficiency of the process is not limited by competitive inhibition or substrates mass transfer, but by the back-diffusion of TCE through the membrane and the consequent TCE accumulation in the gas phase.</jats:p

Comparing biofilm models for a single species biofilm system

A benchmark problem was defined to evaluate the performance of different mathematical biofilm models. The biofilm consisted of heterotrophic bacteria degrading organic substrate and oxygen. Mathematical models tested ranged from simple analytical to multidimensional numerical models. For simple and more or less flat biofilms it was shown that analytical biofilm models provide very similar results compared to more complex numerical solutions. When considering a heterogeneous biofilm morphology it was shown that the effect of an increased external mass transfer resistance was much more significant compared to the effect of an increased surface area inside the biofilm.</jats:p

QUALIDADE FISICO-QUÍMICA DA ÁGUA PARA IRRIGAÇÃO EM DIFERENTES AQUÍFEROS NA ÁREA SEDIMENTAR DO ESTADO DO RIO GRANDE DO NORTE

RESUMO Mais de 600 amostras de água de diferentes mananciais do semi-árido nordestino foram analisadas e estudadas a partir do banco de dados do Laboratório de Análises de Águas e Fertilidade do Solo, no Departamento de Solos e Geologia da Escola superior de Agricultura de Mossoró. As análises fisico-químicas permitiram avaliar a qualidade da água para irrigação, empregando-se índices clássicos da literatura, como Índice de Saturação de Langelier, CE, RAS, RASaj e RAScor. Na maioria das amostras estudadas observou-se que mais de 30% apresentam problemas devido ao risco de sodicidade (RAS elevada). A maior incidência de água com problemas de salinidade (elevada CE) e sódio ocorreu naquela proveniente de poços tubulares, que captam água de calcário ou aquíferos abastecidos diretamente pelo lençol freático. Dependendo do modo como se calculou a RAS, algumas amostras de água mudaram de classe, quando se empregou o ábaco desenvolvido pelo Laboratório de Salinidade dos Estados Unidos (USSL)

The VP3 gene of human group C rotavirus

The complete nucleotide sequence of genome segment 4 from the human group C rotavirus (Bristol strain) was determined. Comparison of the nucleotide sequences of the genome termini with the consensus 5' and 3' terminal non-coding sequences of the human group C rotavirus genome revealed characteristic 5' and 3' sequence motifs. Human group C rotavirus genome segment 4 is 2,166bp long and encodes a single open reading frame of 2,082 nucleotides (693 amino acids) starting at nucleotide 55 and terminating at nucleotide 2,136 giving a 3' untranslated region of 30 nucleotides. Alignment with the porcine group C VP3 equivalent gene showed the human gene is one amino acid longer, and that the proteins have 84.1% amino acid sequence identity. A conserved potential nucleotide binding motif shared with the porcine VP3 sequence was identified. Analogy with the group A rotaviruses suggested that the genome segment 4 encodes the group C rotavirus guanylyltransferase

Sediment diffusive fluxes of Fe, Mn, and P in a eutrophic lake: Contribution from lateral vs bottom sediments

Water column data and porewater profiles are used to study the chemical evolution with time and with depth of a eutrophic lake. By using different approaches, diffusion fluxes for dissolved iron, manganese and phosphate are calculated and used to describe the processes occurring at the sediment-water interface as well as in the hypolimnion of the lake. These data are used in the elaboration of a qualitative model to describe the chemical behaviour of the sedimentary interface of an anoxic lake with emphasis on the Fe/P/S system. Acorona model is proposed to explain the evolution with time of the diffusion process by estimating the relative contribution of bottom and lateral sediment surfaces to the total fluxes of dissolved elements diffusing from the sediment to the overlying water. As the hypolimnion becomes more anoxic, it has been observed that lateral sediment surfaces (16 to 10 meters in depth) represents a larger supplier of diffusing dissolved components than the bottom sediment portion (bottom to 18 meters)

Molecular mechanisms and biological role of Campylobacter jejuni attachment to host cells.

Adhesion to host cells is an important step in pathogenesis of Campylobacter jejuni, which is the most prevalent bacterial cause of human gastroenteritis worldwide. In contrast to other bacteria such as E. coli and Salmonella, adherence of C. jejuni is not mediated by fimbria or pili. A number of C. jejuni adhesion-related factors have been described. However, the results obtained by different researchers in different laboratories are often contradictory and inconclusive, with only some of the factors described being confirmed as true adhesins. In this review, we present the current state of studies on the mechanisms of attachment of C. jejuni to host cells