Electroreduction of hexavalent chromium using a porous titanium flow-through electrode and intelligent prediction based on a back propagation neural network

Flow-through electrodes have been demonstrated to be effective for electroreduction of Cr(VI),but shortcomings are tedious preparation and short lifetimes.Herein,porous titanium available in the market was studied as a flow-through electrode for Cr(VI)electroreduction.In addition,the intelligent prediction of electrolytic performance based on a back propagation neural network(BPNN)was developed.Voltametric studies revealed that Cr(VI)electroreduction was a diffusion-controlled process.Use of the flow-through mode achieved a high limiting diffusion current as a result of enhanced mass transfer and favorable kinetics.Electroreduction of Cr(VI)in the flow-through system was 1.95 times higher than in a parallel-plate electrode system.When the influent(initial pH 2.0 and 106 mg/L Cr(VI))was treated at 5.0 V and a flux of 51 L/(h·m2),a reduction efficiency of~99.9%was obtained without cyclic electrolysis process.Sulfate served as the supporting electrolyte and pH regulator,as reactive CrSO72−species were formed as a result of feeding HSO4−.Cr(III)was confirmed as the final product due to the sequential three-electron transport or disproportionation of the intermediate.The developed BPNN model achieved good prediction accuracy with respect to Cr(VI)electroreduction with a high correlation coefficient(R2=0.943).Additionally,the electroreduction efficiencies for various operating inputs were predicted based on the BPNN model,which demonstrates the evolutionary role of intelligent systems in future electrochemical technologies.

Abatement of sulfide generation in sewage by glutaraldehyde supplementation and the impact on the activated sludge accordingly

Hydrogen sulfide emission in sewer systems is associated with toxicity, corrosion, odour nuisance and high costs treatment. In this study, a novel method to inhibit sulfide generation from sewage by means of glutaraldehyde supplementation has been suggested and evaluated under anaerobic conditions. Different concentra- tions of glutaraldehyde at 10, 15, 20, 30 and 40mg.L1 have been investigated. Besides, the possible impacts of glutaraldehyde supplementation on an activated sludge system and an appraisal of the economic aspects are presented as well. As observed from the experimental results, a dosage of 20 mg. L-1 glutaraldehyde resulted in a significant decrease of the sulfide production by 70%-80% in the simulated sewage. Moreover, the impacts of additional glutaraldehyde at 20mg·L^-1 on activated sludge, in terms of chemical oxygen demand removal and oxygen uptake rates, were negligible. From an economical point of view, the cost of the commercial glutaraldehyde products required in the operation, which was calculated on the basis of activated sulfide removal avoidance, was around ε3.7-4.6 S·kg^-1. Therefore it is suggested that glutaraldehyde supplementation is a feasible technique to abate the sulfide problems in sewer systems. Yet further research is required to elucidate the optimum ＂booster＂ dosage and the dosing frequency in situ accordingly.