Gavin Walker

Kinetics of a reactive dye adsorption onto dolomitic sorbents.

A novel wastewater treatment technique has been investigated, for reactive dye removal, in batch kinetic systems. These experimental studies have indicated that charred dolomite has the potential to act as an adsorbent for the removal of Brilliant Red reactive dye from aqueous solution. The effect of initial dye concentration, adsorbent mass:liquid volume ratio, and agitation speed on dye removal have been determined with the experimental data mathematically described using empirical external mass transfer and intra-particle diffusion models. The experimental data show conformity with an adsorption process, with the removal rate heavily dependent on both external mass transfer and intra-particle diffusion.

Adsorption of acid dyes on to granular activated carbon in fixed beds

This work involved the treatment of industrial wastewater from a nylon-carpet printing plant in Northern Ireland which currently receives no treatment and is discharged straight to sea. As nylon is particularly difficult to dye, acid dyes are required for successful colouration, but they cause major problems with the plants effluent disposal. Granular activated carbon Filtrasorb 400 was used to treat this effluent in a fixed-bed column system. Breakthrough curves from the fixed-bed column were shallow, even at low flow rates, which indicated a large mass transfer zone and inefficient use of adsorbent. Decrease in adsorbent particle size and decrease in linear flow rate produced a better bed performance. The bed depth service time (BDST) model proved effective for comparison of column variables, with calculated BDST constants providing a useful indication of bed performance. The BDST model also gave good approximation in predicting a bed performance using the relationships postulated by Hutchins (1973).

Adsorption of dyes from aqueous solution — the effect of adsorbent pore size distribution and dye aggregation

The removal of acid dyes, Tectilon Blue 4R, Tectilon Red 2B and Tectilon Orange 3G, from single component solution by adsorption on activated carbon and bone char has been investigated in isotherm experiments. Results from these experiments were successfully modelled using Langmuir and Freundlich isotherm analyses. Nitrogen adsorption analysis was also undertaken and indicated that the activated carbon had a much higher specific surface than the bone char. Calculations involving the pore size distribution data indicate that only 14% of the total specific surface of the activated carbon is available for adsorption due to the high molecular area and aggregation of the dye. The equilibrium data indicate that dye aggregation takes place in the solid phase of both adsorbents with higher solid phase aggregation numbers found using the bone char, which is indicative of multilayer adsorption.

Adsorption mechanisms of removing heavy metals and dyes from aqueous solution using date pits solid adsorbent

A potential usefulness of raw date pits as an inexpensive solid adsorbent for methylene blue (MB), copper ion (Cu(2+)), and cadmium ion (Cd(2+)) has been demonstrated in this work. This work was conducted to provide fundamental information from the study of equilibrium adsorption isotherms and to investigate the adsorption mechanisms in the adsorption of MB, Cu(2+), and Cd(2+) onto raw date pits. The fit of two models, namely Langmuir and Freundlich models, to experimental data obtained from the adsorption isotherms was checked. The adsorption capacities of the raw date pits towards MB and both Cu(2+) and Cd(2+) ions obtained from Langmuir and Freundlich models were found to be 277.8, 35.9, and 39.5 mg g(-1), respectively. Surface functional groups on the raw date pits surface substantially influence the adsorption characteristics of MB, Cu(2+), and Cd(2+) onto the raw date pits. The Fourier transform infrared spectroscopy (FTIR) studies show clear differences in both absorbances and shapes of the bands and in their locations before and after solute adsorption. Two mechanisms were observed for MB adsorption, hydrogen bonding and electrostatic attraction, while other mechanisms were observed for Cu(2+) and Cd(2+). For Cu(2+), binding two cellulose/lignin units together is the predominant mechanism. For Cd(2+), the predominant mechanism is by binding itself using two hydroxyl groups in the cellulose/lignin unit.

Kinetics of acid dye adsorption on GAC

Abstract This work involves the treatment of simulated industrial waste water containing acid dyestuffs with granular activated carbon adsorption selected as the treatment method. Predicting the rate at which adsorption takes place for a given system is probably the single most important factor for adsorber design, with adsorbate residence time and ultimately the reactor dimensions controlled by the system’s kinetics. A fixed volume stirred tank reactor was used to study the kinetics of adsorption in a single component system. Process parameters including the rate of agitation, dye concentration and phase ratio were studied with results being modelled using a dual resistance external mass transfer and solid diffusivity model. A single value of solid diffusivity described the adsorption decay curves in most instances and also indicated that chemisorption is the likely process of acid dye adsorption onto activated carbon.

Biological activated carbon treatment of industrial wastewater in stirred tank reactors

The industrial effluent under investigation was the simulated aqueous discharge from a carpet printing plant in Northern Ireland, comprising of a ternary solution of acid dyes. This effluent was investigated using the biological activated carbon (BAC) process for colour removal in an aerobic stirred tank reactor configuration. The following systems were experimentally investigated: bacteria immobilised on granular activated carbon (GAC); bacteria immobilised on sand particles; GAC (with no biological activity) and free bacterial cells. The bacterium used in this study was Pseudomonas putida (NCIMB 9776) and the activated carbon was Filtrasorb 400. Ternary dye concentrations were determined by spectrophotometry. Results indicated that BAC system outperformed the combination conventional GAC and biological water treatment processes. For biodegradable anthraquinone dyes, this enhanced colour removal was due to higher dye utilisation rates caused by the increase in substrate concentration at the granule surface found in BAC systems. For non-biodegradable azo dyes, increased biosorption was found in BAC systems compared to conventional immobilised systems.

Fixed bed adsorption of acid dyes onto activated carbon

The context of the study here is the adsorption of acid dyes from wastewater arising from a nylon carpet printing plant which currently receives no treatment. Since nylon is a particularly difficult fibre to dye, acid dyes are required for successful coloration. However, their presence, in high concentrations, in aqueous effluent arising from the plant can create major problems with respect to disposal. A treatment method based on adsorption onto granular activated carbon (GAC F400) in a fixed column configuration is described and breakthrough data of the dyes determined. The breakthrough data were correlated using a model based on liquid and pore diffusion with a good fit of experimental results obtained. Trends in the effective diffusivity used in the model correlated with other authors. A slight decrease in effective diffusivity was found with decrease in particle size and was attributed to interactions between the relatively large molecular sized dye and the microspore structure found in granular activated carbon.

Biodegradation and biosorption of acid anthraquinone dye

The acid anthraquinone dye Tectilon Blue (TB4R) is a major coloured component from the aqueous effluent of a carpet printing plant in Northern Ireland. The aerobic biodegradation of TB4R has been investigated experimentally in batch systems, using three strains of bacteria, namely, Bacillus gordonae (NCIMB 12553), Bacillus benzeovorans (NCIMB 12555) and Pseudomonas putida (NCIMB 9776). All three strains successfully decolourised the dye, and results were correlated using Michaelis-Menten kinetic theory. A recalculation of the reaction rate constants, to account for biosorption, gave an accurate simulation of the colour removal over a 24-h period. Up to 19% of the decolorisation was found to be caused by biosorption of the dye onto the biomass, with the majority of the decolorisation caused by utilisation of the dye by the bacteria. The reaction rate was found to be intermediate between zero and first order at dye concentrations of 200-1000 mg/l.

Textile Wastewater Treatment Using Granular Activated Carbon Adsorption in Fixed Beds

This work involved the treatment of industrial wastewater from a nylon carpet printing plant which currently receives no treatment and is discharged to sea. As nylon is particularly difficult to dye, acid dyes are required for successful coloration and cause major problems with the plants effluent disposal in terms of color removal. Granular activated carbon Filtrasorb 400 was used to treat a ternary solution of acid dyes and the process plant effluent containing the dyes in a fixed-bed column system. Experimental data were correlated using the bed depth service time (BDST) model to previously published work by the authors for single dye adsorption. The results were expressed in terms of the BDST adsorption capacity, in milligrams of adsorbate per gram of adsorbent, and indicated that there was a 12-25% decrease in adsorption capacity in the ternary system compared to the single component system. This reduction has been attributed to competitive adsorption occurring in the ternary component system. Dye adsorption from the process plant effluent showed an approximate 65% decrease in adsorption capacity compared to the ternary solution system. This has been attributed to interference caused by the other colorless textile effluent pollutants found in the process wastewater. A chemical oxygen demand analysis on these components indicated that the dyes accounted for only 14% of the total oxygen demand.

Influence of solution chemistry on Cr(VI) reduction and complexation onto date-pits/tea-waste biomaterials.

Tea waste (TW) and Date pits (DP) were investigated for their potential to remove toxic Cr(VI) ions from aqueous solution. Investigations showed that the majority of the bound Cr(VI) ions were reduced to Cr(III) after biosorption at acidic conditions. The electrons for the reduction of Cr(VI) may have been donated from the TW and DP biomasses. The experimental data obtained for Cr(VI)-TW and Cr(VI)-DP at different solution temperatures indicate a multilayer type biosorption, which explains why the Sips isotherm accurately represents the experimental data obtained in this study. The Sips maximum biosorption capacities of Cr(VI) onto TW and DP were 5.768 and 3.199 mmol/g at 333 K, respectively, which is comparatively superior to most other low-cost biomaterials. Fourier transform infrared spectroscopic analysis of the metal loaded biosorbents confirmed the participation of -COOH, -NH(2) and O-CH(3) groups in the reduction and complexation of chromium. Thermodynamic parameters demonstrated that the biosorption of Cr(VI) onto TW and DP biomass was endothermic, spontaneous and feasible at 303-333 K. The results evidently indicated that tea waste and date pits would be suitable biosorbents for Cr(VI) in wastewater under specific conditions.