Bioregeneration of activated carbon and activated rice husk loaded with phenolic compounds: Kinetic modeling

A new function of spent activated carbon in BAC process: Removing heavy metals by ion exchange mechanism

To investigate the potential of the spent activated carbon (AC) on removing heavy metals, the spent ACs used 5 years were collected from a full-scale BAC water treatment plant of southern China. The study found that the spent ACs had very good adsorption capacity for Pb(II) and Cd(II) at low concentrations (about 200 μg/L or less) with the maximum removal rates of more than 95% and 86% respectively (only 10-15% for virgin ACs), which will provide the theoretical basis for the disposal of spent AC (the hazardous waste) in BAC process or the combination reuse of spent AC and the virgin AC. Surface properties analyses showed that compared to virgin AC, the pH and PZC in the spent AC significantly decreased, and the relative abundance of surface carboxyl increased by 81% on average, which are essential for the adsorption of metals. To explore the adsorption mechanism, take Pb(II) for example, the adsorption isotherm and kinetics fittings were carried out, which can be well described by Freundlich model (R² = 0.9356) and the pseudo-second-order kinetic model (R² = 0.9276), respectively. Analyses of influencing factors, FT-IR and XPS before and after Pb(II) adsorption confirmed the ion exchange mechanism of spent AC for the removal of heavy metals.

Kinetic modeling of bioregeneration of chlorophenol-loaded granular activated carbon in simultaneous adsorption and biodegradation processes

A kinetic model incorporating adsorption, desorption and biodegradation processes was developed to describe the bioregeneration of granular activated carbon (GAC) loaded with 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP), respectively, in simultaneous adsorption and biodegradation processes. The model was numerically solved and the results showed that the kinetic model was well-fitted (R(2)>0.83) to the experimental data at different GAC dosages and at various initial 4-CP and 2,4-DCP concentrations. The rate of bioregeneration in simultaneous adsorption and biodegradation processes was influenced by the ratio of initial chlorophenol concentration to GAC dosage. Enhancement in the rate of bioregeneration was achieved by using the lowest ratio under either one of the following experimental conditions: (1) increasing initial chlorophenol concentration at constant GAC dosage and (2) increasing GAC dosage at constant initial chlorophenol concentration. It was found that the rate enhancement was more pronounced under the second experimental condition.

Bioregeneration of granular activated carbon in simultaneous adsorption and biodegradation of chlorophenols

The objectives of this study are to obtain the time courses of the amount of chlorophenol adsorbed onto granular activated carbon (GAC) in the simultaneous adsorption and biodegradation processes involving 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP), respectively, and to quantify the bioregeneration efficiency of GAC loaded with 4-CP and 2,4-DCP by direct measurement of the amount of chlorophenol adsorbed onto GAC. Under abiotic and biotic conditions, the time courses of the amount of chlorophenol adsorbed onto GAC at various GAC dosages for the initial 4-CP and 2,4-DCP concentrations below and above the biomass acclimated concentrations of 300 and 150 mg/L, respectively, were determined. The results show that the highest bioregeneration efficiency was achieved provided that the initial adsorbate concentration was lower than the acclimated concentration. When the initial adsorbate concentration was higher than the acclimated concentration, the highest bioregeneration efficiency was achieved if excess adsorbent was used.

Microbial regeneration of spent activated carbon dispersed with organic contaminants: mechanism, efficiency, and kinetic models

BACKGROUND AND PURPOSE

Regeneration of spent activated carbon assumes paramount importance in view of its economic reuse during adsorptive removal of organic contaminants. Classical thermal, chemical, or electrochemical regeneration methods are constrained with several limitations. Microbial regeneration of spent activated carbon provides a synergic combination of adsorption and biodegradation.

METHODS

Microorganisms regenerate the surface of activated carbon using sorbed organic substrate as a source of food and energy. Aromatic hydrocarbons, particularly phenols, including their chlorinated derivatives and industrial waste water containing synthetic organic compounds and explosives-contaminated ground water are the major removal targets in adsorption-bioregeneration process. Popular mechanisms of bioregeneration include exoenzymatic hypothesis and biodegradation following desorption. Efficiency of bioregeneration can be quantified using direct determination of the substrate content on the adsorbent, the indirect measurement of substrate consumption by measuring the carbon dioxide production and the measurement of oxygen uptake. Modeling of bioregeneration involves the kinetics of adsorption/desorption and microbial growth followed by solute degradation. Some modeling aspects based on various simplifying assumptions for mass transport resistance, microbial kinetics and biofilm thickness, are briefly exposed.

RESULTS

Kinetic parameters from various representative bioregeneration models and their solution procedure are briefly summarized. The models would be useful in predicting the mass transfer driving forces, microbial growth, substrate degradation as well as the extent of bioregeneration.

CONCLUSIONS

Intraparticle mass transfer resistance, incomplete regeneration, and microbial fouling are some of the problems needed to be addressed adequately. A detailed techno-economic evaluation is also required to assess the commercial aspects of bioregeneration.