Continuous Sorption of Chromium Ions from Simulated Effluents using Citric Acid Modified Sweet Potato Peels

Adsorptive removal of chromium ion in aqueous medium using activated sweet potato peel (SPP) was studied in a laboratory-scale fixed bed column. Specifically, the effect of process parameters such as bed depth, flowrate and chromium ion concentration in aqueous solution, on the adsorption efficiency of the acid modified sweet potato peel was examined. Column adsorption analysis showed that at the flow rate of 0.5 cm3/min, bed height of 6 cm and column influent concentration of 30 mg/dm3, the optimum chromium (VI) ion removal of 87.5% was attained with the equilibrium adsorption capacity of 2.4548 mg/g. Continuous adsorption models such as Yoon-Nelson, Adam-Bohart and the Bed-Depth Service Time (BDST) model, were used to analyse the experimental data and based on correlation coefficient, BDST model best aligned with the obtained experimental data with correlation coefficient, R2, value of 96.43%. The bed capacity, No, and the rate constant, Ka, were calculated as 4.259 mg/dm3 and 0.01045 L/mgmin respectively at optimum column conditions. Results confirmed that acid modified SPP can be used to remove or reduce concentrations of Cr (VI) ions to allowable limits before disposal into water bodies. Keywords: Continuous sorption, chromium ions, sweet potato peel, kinetic isotherms, breakthrough curves

Batch and fixed-bed column study for p-nitrophenol, methylene blue, and U(VI) removal by polyvinyl alcohol–graphene oxide macroporous hydrogel bead

There is an increasing need to explore effective and clean approaches for hazardous contamination removal from wastewaters. In this work, a novel bead adsorbent, polyvinyl alcohol–graphene oxide (PVA-GO) macroporous hydrogel bead was prepared as filter media for p-nitrophenol (PNP), dye methylene blue (MB), and heavy metal U(VI) removal from aqueous solution. Batch and fixed-bed column experiments were carried out to evaluate the adsorption capacities of PNP, MB, and U(VI) on this bead. From batch experiments, the maximum adsorption capacities of PNP, MB, and U(VI) reached 347.87, 422.90, and 327.55 mg/g. From the fixed-bed column experiments, the adsorption capacities of PNP, MB, and U(VI) decreased with initial concentration increasing from 100 to 400 mg/L. The adsorption capacities of PNP, MB, and U(VI) decreased with increasing flow rate. Also, the maximum adsorption capacity of PNP decreased as pH increased from 3 to 9, while MB and U(VI) presented opposite tendencies. Furthermore, the bed depth service Time (BDST) model showed good linear relationships for the three ions' adsorption processes in this fixed-bed column, which indicated that the BDST model effectively evaluated and optimized the adsorption process of PVA-GO macroporous hydrogel bead in fixed-bed columns for hazardous contaminant removal from wastewaters.

Uptake of Pb and Zn from a binary solution onto different fixed bed depths of natural zeolite – the BDST model approach

The removal of lead and zinc from a binary solution by fixed bed depths (40, 80 and 120 mm) of a natural zeolite was examined at a flow rate of 1 mL/min. The results obtained were fitted to the Bed Depth Service Time (BDST) model and the parameters of the model (q and k) were used to design a column system for flow rates of 2 and 3 mL/min at a bed depth of 80 mm. The experimental results were in excellent agreement with those predicted and experimental breakthrough curves for the binary systems were obtained. This approach facilitates the design of effective binary column processes without additional experimentation. Two major design parameters, the Empty Bed Contact Time (EBCT) and the zeolite usage rate, were calculated. The highest EBCT value of 13.56 min represents the optimal conditions for the binary (Pb+Zn) solution.

Investigating simplified fixed bed design models for the adsorption of fluoride onto crushed burnt clay pot

The breakthrough curves of fluoride adsorption onto crushed burnt clay pot in mini column fixed bed depths of 15, 20, and 25 cm at a continuous flow rate of 2.5, 5, 10 and 15 ml/min were used to investigate the simplified fixed bed design models (BDST and EBRT). The influent fluoride concentration was 5 mg/L and the breakthrough point was taken at 30% of the influent concentration. Results indicate that the BDST curve had the form of straight line explaining more than 99.6% of the data and thus confirmed to obey the BDST model. For the same operating parameters of 50 cm bed depth and 36 cm/h flow rate, 350 L water could have been defluoridated using BDST model, however, in the case of the pilot experiment, 324 L were defluoridated from 5 to 1.5 mg/L fluoride. This was 8% higher only and hence was not significant. Similarly, when the bed depth data were analyzed, results indicate that at higher EBRT values, the adsorbent exhaustion rate were similar to the batch adsorption and thus the EBRT model could be used to optimize for the design of defluoridation unit. Therefore, the simplified fixed bed design models (BDST and EBRT) could be successfully applied to analyze the column performance and design a fluoride adsorption system based on crushed burnt clay pot as a sorbent media. Keywords: Breakthrough Curve, BDST, EBRT, Crushed Burnt Clay Pot, Fluoride Adsorption.

Packed bed column studies for the removal of dyes using novel sorbent

A continuous fixed bed study was carried out by using tamarind seed as a sorbent for the removal of malachite green (MG) and acid blue 9(AB9) from aqueous solution. The effect of factors, such as flow rate and bed depth was studied. Data confirmed that the breakthrough curves were dependent on flow rate and bed depth. Thomas, Adams-Bohart, and Yoon-Nelson models were applied to experimental data to predict the breakthrough curves using non-linear regression and to determine the characteristic parameters of the packed bed column. Bed depth/service time analysis (BDST) model was used to express the effect of bed depth on breakthrough curves. The results showed that Thomas model was found suitable for the normal description of breakthrough curve at the experimental condition, while Adams-Bohart and Yoon-Nelson model were able to explain only the initial part of dynamic behaviour of the tamarind seed column. The data were in good agreement with BDST model. It was concluded that the tamarind seed can be effectively used as a sorbent for the removal of dyes.