Biodegradation of sorbed 2,4-dinitrotoluene in a clay-rich, aggregated porous medium

The availability of clay-sorbed 2,4-dinitrotoluene (2,4-DNT) for degradation by Burkholderia sp. strain DNT was investigated in column experiments. Artificial aggregates of montmorillonite glued to glass spheres served as the sorbent. Sorption isotherms and bacterial kinetic parameters were determined in batches. Sorption of 2,4-DNT to clay aggregates gave reasonable fit to the Langmuir equation. The degradative activity of Burkholderia sp. strain DNT followed Michaelis−Menten kinetics. This allowed inferring bioavailable concentrations in the presence of clay from degradation rates. It appeared that montmorillonite-sorbed 2,4-DNT was readily available to Burkholderia sp. strain DNT. However, despite the accumulation of biomass in the columns due to filtration, absolute degradation rates remained constant, and specific rates continuously decreased toward the end of the experiments. Removal of suspended cells by miscible displacement led to a drastically reduced degradation rate that was not due to decreasing desorption, as 2,4-DNT concentrations in column effluents increased simultaneously. Decreasing degradation could be explained fairly well assuming that the specific activity of suspended cells remained at the initial value of 0.93 nmol mg dw-1 min-1, whereas the specific activity of adhered bacteria steadily dropped to 0.12 nmol mg dw-1 min-1. A likely explanation is the prolonged exposure (up to 6 h) to 2,4-DNT and nitrite for adhered cells, compared with a maximum exposure for suspended cells of 19.5 min, i.e., their residence time in the column. According to the Michaelis−Menten equation, the initial activity corresponded to a bioavailable concentration that exceeded the aqueous equilibrium concentration in the absence of bacteria by a factor of roughly two. The most probable explanation is a shift of the sorption equilibrium in the presence of cells, as direct accessibility of sorbed 2,4-DNT for suspended cells can be excluded.Peer Reviewe

Índice de uniformidade de distribuição do amônio, nitrato, potássio e fósforo, em Latossolos sob condições de fertigação Uniformity distribution index of ammonium, nitrate, potassium and phosphorus in fertigated Oxisols

Se realizada de forma inadequada, a fertigação pode levar à salinização do solo ou lixiviação dos nutrientes, com a consequente contaminação do lençol freático. Neste sentido, se propõe, no presente estudo, um índice para determinar a uniformidade de distribuição de amônio, nitrato, potássio e fósforo, ao longo de colunas de Latossolos fertigadas, com o objetivo de nortear o manejo adequado da fertigação. Este índice foi calculado a partir de dados coletados em um ensaio de laboratório, seguindo-se um fatorial 4 x (1 + 6), ou seja, quatro Latossolos de Minas Gerais (dois Latossolos Vermelho-Amarelos distróficos, um Latossolo Vermelho distroférrico e um Latossolo Vermelho distrófico), uma testemunha (aplicação de água deionizada) e seis formas de aplicação de 1 mmol c de N-NH4+, 1 mmol c de N-NO3-, 2 mmol c de K e 2 mmol c dm-3 de P. Calcularam-se os coeficientes de variação para o teor de cada nutriente, ao longo das colunas e a relação entre o teor médio e o maior teor do nutriente (índice de uniformidade de distribuição de nutrientes) considerando-se o solo e o tratamento. Concluiu-se, portanto, que a relação maior teor, teor médio é um índice de uniformidade de distribuição de nutrientes adequado para avaliar a movimentação de íons com maior mobilidade no solo, como nitrato, amônio e potássio. O coeficiente de variação é menos adequado para mostrar a uniformidade de distribuição dos nutrientes.<br>Fertigation if conducted inadequately may cause soil salinization and consequently leaching of nutrients can pollute ground water. An index is proposed to determine the uniformity of distribution of ammonium, nitrate, potassium and phosphorus in columns of fertigated Oxisols, which relates the highest content of the nutrient in a column segment with the mean nutrient content in the experimental unit. The higher the index value, the more irregular is the nutrient distribution. This index was calculated based on laboratory data evaluated in a 4 x (1 + 6) factorial design including four Oxisols of Minas Gerais (two distrophic Red-Yellow, one dystroferric Red and one dystrophic Red oxisol), one control (application of deionized water) and six application modes of application of 1 mmol c of N-NH4+, 1 mmol c N-NO3-, 2 mmol c K and 2 mmol c dm-3 P. The coefficient of variation was calculated for the content of each nutrient along the columns. The ratio between the mean and the highest nutrient content was computed as well, considering the soil and the treatment. It was inferred that the ratio mean/highest content is an adequate index of uniformity of nutrient distribution to evaluate the movement of major mobile ions such as nitrate, ammonium and potassium in the soil. The coefficient of variation is less appropriate to show the uniformity of nutrient distribution