Conventional and Microwave Pyrolysis for Preparation of Sewage Sludge- Activated Carbons for Pharmaceuticals Removal: A Mini-Review

Abstract:

Sewage sludge shows excellent potential as pyrolysis feedstock in generating valuable products such as Activated Carbons (ACs). In this mini-review the preparation of sewage sludge- ACs by two kinds of pyrolysis conventional and microwave heating is presented and discussed. The main difference between conventional pyrolysis and the microwave-assisted method is the way the heat is generated, and both can provide ACs with different textural and chemical properties. Based on what was demonstrated in this work, it is possible to say that both kinds of pyrolysis (microwave and conventional methods) can produce high specific surface area and efficiently activated carbons from sewage sludge. It was also demonstrated that sludge-ACs produced by both pyrolysis methods could reach very high uptakes of pharmaceuticals from aqueous solutions. The van der Waals interactions, hydrogen bonding and π-π interactions of the aromatic ring of the adsorbent with the aromatic rings of the pharmaceuticals have been mentioned to be some of the main mechanisms governing the pharmaceuticals adsorption by ACs.

Removal of pharmaceutical compounds from aqueous solution by novel activated carbon synthesized from lovegrass (Poaceae)

In this work, lovegrass (Cpa), an abundant grass of the Poaceae family, was employed as feedstock for the production of activated carbon in a conventional furnace using ZnCl₂ as a chemical activator. The prepared material (Cpa-AC) was characterized by pH of the point of zero charges (pH_pzc), Boehm's titration method, CHN/O elemental analysis, ATR-FTIR, N₂ adsorption/desorption curves, and SEM. This carbon material was used for adsorption of acetylsalicylic acid (ASA) and sodium diclofenac (DFC). FTIR analysis identified the presence of O-H, N-H, O-C=O), C-O, and aromatic ring bulk and surface of (Cpa-AC) adsorbent. The quantification of the surface functional groups showed the presence of a large amount of acidic functional groups on the surface of the carbon material. The isotherms of adsorption and desorption of N₂ confirm that the Cpa-AC adsorbent is mesopore material with a large surface area of 1040 m² g^-1. SEM results showed that the surface of Cpa-AC is rugous. The kinetic study indicates that the system followed the pseudo-second-order model (pH 4.0). The equilibrium time was achieved at 45 (ASA) and 60 min (DCF). The Liu isotherm model best fitted the experimental data. The maxima sorption capacities (Q_max) for ASA and DFC at 25 °C were 221.7 mg g^-1 and 312.4 mg g^-1, respectively. The primary mechanism of ASA and DFC adsorption was justified considering electrostatic interactions and π-π interactions between the Cpa-AC and the adsorbate from the solution.

Removal of amoxicillin from simulated hospital effluents by adsorption using activated carbons prepared from capsules of cashew of Para

High-surface-area activated carbons were prepared from an agroindustrial residue, Bertholletia excelsa capsules known as capsules of Para cashew (CCP), that were utilized for removing amoxicillin from aqueous effluents. The activated carbons were prepared with the proportion of CCP:ZnCl₂ 1:1, and this mixture was pyrolyzed at 600 (CCP-600) and 700 °C (CCP700). The CCP.600 and CCP.700 were characterized by CHN/O elemental analysis, the hydrophobic/hydrophilic ratio, FTIR, TGA, Boehm titration, total pore volume, and surface area. These analyses show that the adsorbents have different polar groups, which confers a hydrophilic surface. The adsorbents presented surface area and total pore volume of 1457 m² g^-1 and 0.275 cm³ g^-1 (CCP.600) and 1419 m² g^-1 and 0.285 cm³ g^-1 (CCP.700). The chemical and physical properties of the adsorbents were very close, indicating that the pyrolysis temperature of 600 and 700 °C does not bring relevant differences in the physical and chemical properties of these adsorbents. The adsorption data of kinetics and equilibrium were successfully adjusted to Avrami fractional-order and Liu isotherm model. The use of the adsorbents for treatment of simulated hospital effluents, containing different organic and inorganic compounds, showed excellent removals (up to 98.04% for CCP.600 and 98.60% CCP.700). Graphical abstract.