Investigation of kinetics and adsorption isotherm for fluoride removal from aqueous solutions using mesoporous cerium-aluminum binary oxide nanomaterials.

Herein, we report the synthesis of Ce-Al (1 : 1, 1 : 3, 1 : 6, and 1 : 9) binary oxide nanoparticles by a simple co-precipitation method at room temperature to be applied for defluoridation of an aqueous solution. The characterization of the synthesized nanomaterial was performed by XRD (X-ray diffraction), FTIR (Fourier transform infrared) spectroscopy, TGA/DTA (thermogravimetric analysis/differential thermal analysis), BET (Brunauer-Emmett-Teller) surface analysis, and SEM (scanning electron microscopy). Ce-Al binary oxides in 1 : 6 molar concentration were found to have the highest surface area of 110.32 m2 g-1 with an average crystallite size of 4.7 nm, which showed excellent defluoridation capacity. The adsorptive capacity of the prepared material towards fluoride removal was investigated under a range of experimental conditions such as dosage of adsorbents, pH, and initial fluoride concentration along with adsorption isotherms and adsorption kinetics. The results indicated that fluoride adsorption on cerium-aluminum binary metal oxide nanoparticles occurred within one hour, with maximum adsorption occurring at pH 2.4. The experimental data obtained were studied using Langmuir, Freundlich, and Temkin adsorption isotherm models. The nanomaterial showed an exceptionally high adsorbent capacity of 384.6 mg g-1. Time-dependent kinetic studies were carried out to establish the mechanism of the adsorption process by pseudo-first-order kinetics, pseudo-second-order kinetics, and Weber-Morris intraparticle diffusion kinetic models. The results indicated that adsorption processes followed pseudo-second-order kinetics. This study suggests that cerium-aluminum binary oxide nanoparticles have good potential for fluoride removal from highly contaminated aqueous solutions.

Application of Fe-Cu binary oxide nanoparticles for the removal of hexavalent chromium from aqueous solution.

The adsorption process has been used as an effective technique for the removal of metal ions from aqueous solutions. Groundwater remediation by nanoparticles has received interest in recent years. In the present study, a binary metal oxide of Fe-Cu was prepared and used for the removal of hexavalent chromium from aqueous solution. Batch experiments were performed to investigate the effects of initial Cr (VI) concentration, dose of adsorbent, and pH of solution on the removal efficiency of Cr (VI). The prepared nanostructured Fe-Cu binary oxides were able to reduce the concentration of Cr (VI) in aqueous solution. Binary metal oxides nanoparticle exhibited an outstanding ability to remove Cr (VI) due to high surface area, low particle size, and high inherent activity. The percentage removal efficiency of Cr (VI) increased with nanoparticles doses (0.1 g L(-1)-2.5 g L(-1)), whereas it decreased with initial Cr (VI) concentration (1 mg L(-1)-25 mg L(-1)) and with pH (3-9). The Freundlich model was found to be the better fit for adsorption isotherm. The prepared nanomaterial was characterized using powder X-ray diffraction, scanning electron microscopy (SEM), and ultraviolet (UV)-visible spectroscopy. It showed that the Fe-Cu binary oxides were formed in single phase. SEM micrograph showed aggregates with many nano-sized particles. UV-visible spectroscopy showed quantum confinement effect.

Biodegradation of m-cresol by aerobic granules in a sequencing batch reactor.

The present study was aimed at the development of aerobic granules in a sequencing batch reactor for the biodegradation of m-cresol. The reactor was started with 100 mg L(-1)of m-cresol. Aerobic granules first appeared within 1 month of the start-up of the reactor. The granules were large and strong and had a compact structure. The diameter of stable granules on day 200 was in the range of 1.5 - 5 mm. The integrity coefficient and density of the granules was found to be 98% and 1046 kg m(-3), respectively. The settling velocity of the granules was found to be in the range of 2-6 x 10(-2) m s(-1). The aerobic granules were able to degrade m-cresol up to 800 mg L(-1) at a removal efficiency of 87%. UV and GC/MS studies confirmed that the biodegradation ofm-cresol occurred via catechol via the ortho-cleavage pathway. The specific m-cresol degradation rate in aerobic granules followed the Haldane model for substrate inhibition. A high specific m-cresol degradation rate of up to 0.718 g m-cresol g(-1)VSS(-1)d(-1) was sustained up to an m-cresol concentration of 400 mgL(-1). The higher removal efficiency and good settling characteristics of aerobic granules make the sequencing batch reactor method suitable for enhancing the microorganism potential for biodegradation of inhibitory compounds.

Biodegradation of o-nitrophenol by aerobic granules with glucose as co-substrate.

Aerobic granules to treat wastewater containing o-nitrophenol were successfully developed in a sequencing batch reactor (SBR) using activated sludge as inoculum. Stable aerobic granules were obtained with a clearly defined shape and diameters ranging from 2 to 6 mm after 122 days of operation. The integrity coefficient (IC) and granules density was found to be 98% and 1,054 kg m(-3) respectively. After development of aerobic granules, o-nitrophenols were successfully degraded to an efficiency of 78% at a concentration of 70 mg L(-1). GC-MS study revealed that the biodegradation of o-nitrophenol occurred via catechol via nitrobenzene pathway. Specific o-nitrophenol biodegradation rates followed the Haldane model and the associated kinetic parameters were found as follows: V(max) = 3.96 g o-nitrophenol g(-1)VSS(-1)d(-1), K(s) = 198.12 mg L(-1), and K(i) = 31.16 mg L(-1). The aerobic granules proved to be a feasible and effective way to degrade o-nitrophenol containing wastewater.

Biodegradation of p-cresol by aerobic granules in sequencing batch reactor.

The cultivation of aerobic granules in sequencing batch reactor for the biodegradation of p-cresol was studied. The reactor was started with 100 mg/L of p-cresol. Aerobic granules first appeared within one month of start up. The granules were large and strong and had a compact structure. The diameter of stable granules was in the range of 1-5 mm. The integrity coefficient and granules density was found to be 96% and 1046 kg/m3, respectively. The settling velocity of granules was found to be in the range of 2x10(-2)-6x10(-2) m/sec. The aerobic granules were able to degrade p-cresol upto 800 mg/L at a removal efficiency of 88%. Specific p-cresol degradation rate in aerobic granules followed Haldane model for substrate inhibition. High specific p-cresol degradation rate up to 0.96 g p-cresol/(g VSS x day) were sustained upto p-cresol concentration of 400 mg/L. Higher removal efficiency, good settling characteristics of aerobic granules, makes sequencing batch reactor suitable for enhancing the microorganism potential for biodegradation of inhibitory compounds.

Sewage treatment by anaerobic hybrid reactor.

Attempts were made to utilize anaerobic hybrid reactor for sewage treatment. The reactor was seeded with digested sewage sludge and a HRT of 24 hrs. was kept in the start up. The HRT was subsequently decreased to 20, 16, 12, 8 and 4 hrs. A maximum COD removal efficiency of 74% was achieved at minimum HRT. The pH, alkalinity, solids and VFA of the effluent were within the permissible limits.