Adsorption of acid and basic dyes by sludge-based activated carbon:Isotherm and kinetic studies

A batch experiment was conducted to investigate the adsorption of an acid dye(Acid Orange 51) and a basic dye(Safranine) from aqueous solutions by the sludge-based activated carbon(SBAC). The results show that the adsorption of Acid Orange 51 decreases at high p H values, whereas the uptake of Safranine is higher in neutral and alkaline solutions than that in acidic conditions. The adsorption time needed for Safranine to reach equilibrium is shorter than that for Acid Orange 51. The uptakes of the dyes both increase with temperature increasing, indicating that the adsorption process of the dyes onto SBAC is endothermic. The equilibrium data of the dyes are both best represented by the Redlich-Peterson model. At 25 °C, the maximum adsorption capacities of SBAC for Acid Orange 51 and Safranine are 248.70 mg/g and 525.84 mg/g, respectively. The Elovich model is found to best describe the adsorption process of both dyes, indicating that the rate-limiting step involves the chemisorption. It can be concluded that SBAC is a promising material for the removal of Acid Orange 51 and Safranine from aqueous solutions.

Sludge-based biochar adsorbent:pore tuning mechanisms,challenges,and role in carbon sequestration

Sludge biochar,a carbonized product of raw sludge,contains porous architectures that can act as epicenters for adsorbing external molecules through physical or chemical bonding.Sludge biochar also immobilizes innate micropollutants,which is advantageous over conventional sludge disposal methods.To date,numerous strategies have been discovered to improve sludge biochar morphology,but the influential factors,pore tuning mechanisms,and process feasibility remain imprecise.This knowledge gap limits our ability to design a robust sludge-based biochar.Herein,we present state-of-the-art sludge biochar synthesis methods with insight into structural and chemical transformation mechanisms.Roadblocks and novel concepts for improving sludge biochar porous architecture are highlighted.For the first time,sludge biochar properties,adsorption performances,and techno-economic perspectives were compared with commercial activated carbon(AC)to reveal the precise challenges in sludge biochar application.More importantly,sludge biochar role in carbon sequestration is detailed to demonstrate the environmental significance of this technology.Eventually,the review concludes with an overview of prospects and an outlook for developing sludge biochar-based research.

Effects of chemical modification on physicochemical properties and adsorption behavior of sludge-based activated carbon

This study aimed to explore the adsorption performance of sludge-based activated carbon(SBC)towards dissolved organic matters(DOMs)removal from sewage,and investigated the modification effect of different types of chemicals on the structure of synthesized SBC.Waste activated sludge(WAS)was used as a carbon source,and HCl,HNO 3,and Na OH were used as different types of chemicals to modify the SBC.With the aid of chemical activation,the modified SBC showed higher adsorption performances on DOMs removal with maximum adsorption of 29.05 mg/g and second-order constant(k)of 0.1367(L/mol/sec)due to the surface elution of ash and minerals by chemicals.The surface elemental composition of MSBC suggested that the content of C-C and C-O functional groups on the surface of modified sludge-based activated carbon(MSBC)played an important role on the adsorption capacities of MSBC towards DOMs removal in sewage.Additionally,the residual molecular weight of DOMs in sewage was investigated using a 3-dimension fluorescence excitationemission matrix(3 D-EEM)and high-performance size exclusion chromatography(HP-SEC).Results showed that the chemical modification significantly improved the adsorption capacity of MSBC on humic acids(HA)and aromatic proteins(APN),and both of Na OH-MSBC and HCl-MSBC were effective for a wide range of different AMW DOMs removal from sewage,while the HNO 3-MSBC exhibited poorly on AMW organics of 2,617 Da and 409 Da due to the reducing content of macropore.In brief,this study provides reference values for the impact of the chemicals of the activation stage before the SBCs application.

Removal of lead(II) from aqueous solutions by activated carbon developed from surplus sludge

Activated carbon(AC) was prepared from surplus sludge using chemical activation method with the assistance of ZnCl2. The influences of process parameters on the AC's specific surface area and adsorption capacity for Pb2+ were examined to optimize these parameters. The optimal conditions for the preparation of AC were determined to be activation temperature of 500 °C, activation time of 1 h, impregnation ratio of 1:1(solid-to-liquid volume) with the 30% ZnCl2 solution(mass fraction), giving the BET surface area of 393.85 m2/g and yield of 30.14% with 33.45% ash. Also, the pyrolysis temperature was found to be the most important parameter in chemical activation. FTIR spectra provided the evidence of some surface structures such as C=C and C—O—C. In the adsorption studies, a rise in solution pH led to a significant increase in adsorption capacity when the pH value varied from 3.0 to 7.0, and the optimal pH for removal of Pb2+ was 7.0. It was observed that the pseudo-second-order equation provided better correlation for the adsorption rate than the pseudo-first-order and the Langmuir model fitted better than the Freundlich model for adsorption isotherm. The adsorption capacity of AC to Pb2+ was 11.75 mg/L at solution pH 7.0, the equilibrium time 480 min and 25 °C. Moreover, the adsorption process is endothermic according to the value of enthalpy change.