Efficiency of saturated vertical-flow filters planted with Panicum maximum reeds for passive wastewater treatment.

A vertical-flow unit containing four filters filled with shale was used to study the removal of phosphorous, nitrogen and organic matter of an urban residual wastewater during a period of 90 days. The influence of both the shale granulometry and the plant density of Panicum Maximum were studied. The decrease of the shale granulometry led to a significant improvement of all the measured parameters, while the presence of plants did only influence the phosphate retention with a lower extent. By comparing the results to previous studies, we hypothesised that the effect of the root system of Panicum maximum would be different depending on the size and the depth of the reactors. For practical application, adjusting the material granulometry was proposed to be the most important parameter for improving the filtration efficiency. Concomitantly, adjusting the plant density helps to control the clogging percentage of the filters.

Use of laterite as a sustainable catalyst for removal of fluoroquinolone antibiotics from contaminated water.

Although there is a growing interest in Fenton oxidation processes based on natural catalysts, the use of laterite soil to promote sequential adsorption/oxidation treatments of fluoroquinolone antibiotics has been scarcely investigated. In this work, the ability of an african laterite containing goethite and hematite to remove flumequine (FLU), used as a representative compound of fluoroquinolone antibiotics, was evaluated under dark and UVA irradiation. Batch experiments and liquid chromatography analyses showed that the presence of laterite can enhance FLU removal from heavily contaminated water through both sorption and oxidation reactions (up to 94% removal of 77 µmol L-1 of FLU and 72% of mineralization). The heterogeneous reaction rate is dominated by the rate of intrinsic surface chemical reactions including sorption and oxidation of FLU, and light-induced reduction of FeIII sites to produce FeII. Based on the probe and scavenging experiments, OH radicals were mainly involved in the heterogeneous oxidation reaction. The photo-assisted Fenton process showed a high efficiency of FLU removal even in the presence of a second fluoroquinolone antibiotic, norfloxacin (NOR), which can be co-found with FLU in affected environments. Determinations of kinetic rate constants and total organic carbon (TOC) for five sequential adsorption/oxidation cycles showed that laterite exhibited no deactivation of surface sites and an excellent catalytic stability. This cost-effective and environmentally friendly remediation technology may appear as a promising way for the removal of fluoroquinolone antibiotics from multi-contaminated waters.

Activation of persulfate by irradiated laterite for removal of fluoroquinolones in multi-component systems.

Although several emerging contaminants (e.g. fluoro(quinolones) (FQs)) have been simultaneously detected in environmental systems, there is very limited information on their elimination from contaminated waters in multi-component systems. In this study, removal of three FQs including flumequine (FLU), ciprofloxacin (CIP) and norfloxacin (NOR) were investigated in single and mixture systems, using natural laterite soil and persulfate (PS) under UVA irradiation. Both sorption and oxidation reactions contribute to the removal of FQs from aqueous phase, whereas quenching experiments showed that SO4- is mainly responsible for the FQs oxidation. The kinetic rate constants can be ranked as follows: CIP > NOR > FLU, regardless of whether the compound was alone or in mixture. The higher degradation rate constant of CIP relative to those of NOR and FLU could be explained by the high reactivity of SO4- radical with cyclopropane-ring containing compounds. Fall in oxidation performance was observed in synthetic wastewater, probably due to sulfate radical scavenging by wastewater components. However, degradation rate constants of CIP in wastewater remains unchanged in mixture systems as compared to single ones. This environmentally friendly remediation technology may appear as a promising way for the removal of fluoroquinolone antibiotics from multi-contaminated waters.

Fourier transform infra-red (FTIR) spectroscopy investigation, dose effect, kinetics and adsorption capacity of phosphate from aqueous solution onto laterite and sandstone.

Environmental pollution by phosphate in developing countries is growing with extensive and diffuse pollution. Solving these problem with intensive technologies is very expensive. Using natural sorbent such as laterite and sandstone could be a solution. The main objective of the study is to evaluate the P-removal efficiency of these materials under various solution properties. Laterite and sandstone used mainly contain very high levels of finely grained iron and aluminum oxy-hydroxides and diverse dioctahedral clays. Phosphate adsorption tests were carried out using crushed laterite and sandstone. Optimal doses and pH effects on phosphate adsorption were studied with a potassium hydrogeno-phosphate solution of 5 mg/L at 30 °C. The main results were that the optimal dosage is 15 and 20 mg/L respectively for laterite and sandstone. The phosphate adsorptions efficiency of laterite and sandstone are pH-dependent, they increase when the pH grows up to the Point of Zero Charge (PZC) and slowly decrease beyond. The adsorption capacities of the materials also increase proportionally with the initial phosphate concentration. The pseudo-second-order successfully described the kinetics of the phosphate adsorption on the two adsorbents. With this model, the adsorption capacity values are obtained, which give an idea of the maximum phosphate uptake that the laterite and sandstone could achieve. The changes on the FTIR spectra of raw materials and phosphate adsorbed material confirm the mechanism of chemisorptions. Considering the above, laterite and sandstone could be used as efficient and cheap adsorbent for the removal of phosphate in aqueous solution.

A tanks-in-series bioreactor to simulate macromolecule-laden wastewater pretreatment under sewer conditions by Aspergillus niger.

Sewers are typically a means of transporting wastewater to a treatment facility, with little biotransformation of the soluble polymeric organic matter by suspended biomass. In the interest of providing an effective pretreatment of wastewater in a sewer network, it is necessary to design an accurate tool simulating sewer conditions and introduce an appropriate biomass for macromolecular pollutant degradation. Such a model reactor was built using a tanks-in-series design and the degradation of a polysaccharide (starch) by Aspergillus niger MUCL 28817 was studied. Starch degradation and the accumulation of intermediates (hydrolysis fragments) in the individual reactors were quantified under transient conditions, at a mean hydraulic residence time of 17 h. Starch was degraded by 90% in this reactor system and an accumulation of oligosaccharides with molecular weight lower than 1,000 Da was observed. These results may be helpful in the development of wastewater treatment in sewers and in the alleviation of the burden on undersized wastewater treatment systems.