Removal of two waterborne pathogenic bacterial strains by activated carbon particles prior to and after charge modification

Waterborne diseases constitute a threat to public health despite costly treatment measures aimed at removing pathogenic microorganisms from potable water supplies. This paper compared the removal of Raoultella terrigena ATCC 33257 and Escherichia coli ATCC 25922 by negatively and positively charged types of activated carbon particles. Both strains display bimodal negative zeta-potential distributions in stabilized water. Carbon particles were suspended to an equivalent external geometric surface area of 700 cm(2) in 250 mL of a bacterial suspension, with shaking. Samples were taken after different durations for plate counting. Initial removal rates were less elevated for the positively charged carbon particle than expected, yielding the conclusion that bacterial adhesion under shaking is mass-transport limited. After 360 min, however, the log-reduction of the more negatively charged R. terrigena in suspension was largest for the positively charged carbon particles as compared with the negatively charged ones, although conditioning in ultrapure or tap water of positively charged carbon particles for 21 days eliminated the favorable effect of the positive charge due to counterion adsorption from the water. Removal of the less negatively charged E. coli was less affected by aging of the (positively charged) carbon particles, confirming the role of electrostatic interactions in bacterial removal by activated carbon particles. The microporous, negatively charged coconut carbon performed less than the mesoporous, positively charged carbon particle prior to conditioning but did not suffer from loss of effect after conditioning in ultrapure or tap water

Perylene toxicity in the estuarine environment of Ria de Aveiro (Portugal)

Perylene, a 5-ring polycyclic aromatic hydrocarbon is common in estuarine sediments and its toxicity in the benthic and planktonic compartments is not yet clarified. The objectives of this work were: (1) to follow the toxicity of high concentrations of perylene (110 mg l−1) on benthic bacteria and macrofauna (amphipod Corophium multisetosum); (2) to determine the effects of a low load of perylene (2 μg l−1) on the metabolism of suspended bacteriobenthos after 9-day exposure, mimicking the effects of tidal erosion; (3) to contrast the effects of this low perylene load on the particle-free bacterioplankton and on the suspended and particle-adhered bacteriobenthos. No impact was detected in bacterial abundance exposed to 110 mg perylene l−1 for 9 days. This concentration of perylene evoked no acute effects in C. multisetosum but, chronic toxicity assays revealed statistically significant negative effects on survival, growth and number of pregnant females. The bacterioplankton and the suspended bacteriobenthos, exposed to 2 μg perylene l−1 during 2 weeks, responded with altered profiles of activity when compared to the control suspension. These values ranged, respectively, for bacterial biomass production from 134 to 210 and from 24 to 184 μg C l−1 h−1, for aminopeptidase from 1824 to 11,127 and from 1464 to 15,488 nmol l−1 h−1, and for β-glucosidase from 87 to 400 and from 57 to 1278 nmol l−1 h−1. The rate of oxygen consumption in the perylene-exposed suspension (0.04–2.85 mmol O2 kg−1 dw sed h−1) exhibited a clearly distinct profile in relation to the control (0.57–1.60 mmol O2 kg−1 dw sed h−1). The overall reactivity of the bacteriobenthos to perylene was interpreted as the result of toxic pressure followed by evolution of a diverse bacterial community