Transformation and immobilization of hexavalent chromium in the co-presence of biochar and organic acids:effects of biochar dose and reaction time

A batch experiment was conducted to examine the effects of biochar dose and reaction duration on the transformation and immobilization of Cr(VI)in the combined biochar and low-molecular-weight organic acid systems.The results showed that increase in the dosage level of biochar caused increase in the solution pH,particularly for the Biochar300 treatments but did not enhance the reduction of Cr(VI)after 1-day reaction.Over 35%of the converted Cr(III)was immobilized by sorption to the biochar due to increased negatively charged sites on the biochar surfaces driven by pH rise.The elevated pH due to biochar dose increase tended to slow down the reduction of Cr(VI)to Cr(III),resulting in more Cr(VI)being adsorbed at a higher biochar dose.For the higher-temperature biochars,the increase in biochar dose did not markedly change the transformation and immobilization of the added Cr.Increase in the reaction duration markedly increased the pH for Biochar300.This resulted in the disappearance of all Cr(VI)in the solution after the 7-day reaction,possibly through sorption of cationic Cr(III)to the biochar surfaces.Increase in reaction time for the higher-temperature biochars resulted in re-oxidation of Cr(III)to Cr(VI)due to the increased exposure of solution Cr(III)to atmospheric oxygen.The research findings obtained from this study have implications for optimizing treatment procedure for wastewater that contains elevated level of toxic Cr(VI).Simulation experiments are required to determine appropriate biochar dose and reaction time to achieve cost-effective treatment goals.

Length-based separation of Bacillus subtilis bacterial populations by viscoelastic microfluidics

In this study,we demonstrated the label-free continuous separation and enrichment of Bacillus subtilis populations based on length using viscoelastic microfluidics.B.subtilis,a gram-positive,rod-shaped bacterium,has been widely used as a model organism and an industrial workhorse.B.subtilis can be arranged in different morphological forms,such as single rods,chains,and clumps,which reflect differences in cell types,phases of growth,genetic variation,and changing environmental factors.The ability to prepare B.subtilis populations with a uniform length is important for basic biological studies and efficient industrial applications.Here,we systematically investigated how flow rate ratio,poly(ethylene oxide)(PEO)concentration,and channel length affected the length-based separation of B.subtilis cells.The lateral positions of B.subtilis cells with varying morphologies in a straight rectangular microchannel were found to be dependent on cell length under the co-flow of viscoelastic and Newtonian fluids.Finally,we evaluated the ability of the viscoelastic microfluidic device to separate the two groups of B.subtilis cells by length(i.e.,1-5μm and>5μm)in terms of extraction purity(EP),extraction yield(EY),and enrichment factor(EF)and confirmed that the device could separate heterogeneous populations of bacteria using elasto-inertial effects.