Waste wood biomass as precursor for manufacturing activated carbon (AC) can provide a solution to ever increasing global water quality concerns. In our current work, Melia azedarach derived phosphoric acid-treated AC (MA-AC400) was manufactured at a laboratory scale. This novel MA-AC400 was tested for RO16 dye removal performance as a function of contact time, adsorbent dosage, pH, temperature and initial dye concentration in a batch scale arrangement. MA-AC400 was characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering (DLS) and fluorescence spectroscopy. MA-AC400 is characterized as mesoporous with BET surface area of 293.13 m² g⁻¹ and average pore width of 20.33 Å. pH_PZC and Boehm titration confirm the acidic surface charges with dominance of phenolic functional groups. The average DLS particle size of MA-AC400 was found in the narrow range of 0.12 to 0.30 µm and this polydispersity was confirmed with multiple excitation fluorescence wavelengths. MA-AC400 showed equilibrium adsorption efficiency of 97.8% for RO16 dye at its initial concentration of 30 mg L⁻¹ and adsorbent dose of 1 g L⁻¹. Thermodynamic study endorsed the spontaneous, favorable, irreversible and exothermic process for RO16 adsorption onto MA-AC400. Equilibrium adsorption data was better explained by Langmuir with high goodness of fit (R², 0.9964) and this fitness was endorsed with lower error functions. The kinetics data was found well fitted to pseudo-second order (PSO), and intra-particle diffusion kinetic models. Increasing diffusion constant values confirm the intraparticle diffusion at higher RO16 initial concentration and reverse was true for PSO chemisorption kinetics. MA-AC400 exhibited low desorption with studied eluents and its cost was calculated to be $8.36/kg.

Chromium (Cr(VI)) is often released from various industries in excess in developing countries, which constitutes non-compliance with environmental regulations. This metal is hazardous for the aquatic ecosystem and is responsible for toxicity, carcinogenicity, and mutagenicity in humans. Adsorption is an effective and relatively inexpensive approach for treating the excess Cr(VI) compared to conventional methods. Commercially available adsorbents cannot be considered economical yet for industrial applications, which has alternatively resulted in the use of natural adsorbents. The current study focuses on Cr(VI) removal using low-cost natural adsorbents and discusses the different conditions used for such treatments. Previous studies have shown the following order of average Cr(VI) removal using different adsorbents: leaves > bark > agriculture > dry shell > tea = fungi > yeast > algae > sawdust > bacteria. Moreover, acid modification has been reported to offer the best results. The adsorption data are best fitted to both the Langmuir and Freundlich isotherms. Hence, the abovementioned low-cost natural biomasses hold promising potential for Cr(VI) removal from wastewater, whose removal efficiency can be improved by adopting economical and effective pretreatment techniques. Literature also shows that leaves are more efficient and economical for Cr(VI) removal without pretreatment from among the various available bulk biomasses. The present review is expected to provide guidance for low-cost treatment of Cr(VI) at the industrial scale.

Eucalyptus wood is made up of lignocellulosic material; this lignocellulosic material contains two types of biopolymers, i.e., carbohydrate and aromatic polymers. In this study, this lignocellulosic material was used to prepare biochar. Three biochar, i.e., laboratory-based (B1), barrel-based (B2), and brick kiln-biochar (B3), were used for fluoride and arsenic removal from aqueous solution. Barrel-based biochar was prepared by using the two-barrel method’s alteration. The highest fluoride removal (99%) was attained at pH 2 in the presence of B1, while in the presence of B2 and B3, maximum fluoride removal was 90% and 45.7%, respectively. At pH 10, the maximum arsenic removal in the presence of B1, B2, and B3 was 96%, 94%, and 93%, respectively. The surface characteristics obtained by Fourier-transform infrared spectroscopy (FTIR) showed the presence of carbonyl group (C-O), and alkene (C=C) functional groups on all the three studied biochars. Isotherm studies showed that the adsorption was monolayered (all the adsorbed molecules were in contact with the surface layer of the adsorbent) as the Langmuir isotherm model best fits the obtained data. Adsorption kinetics was also performed. The R² value supports the pseudo-second-order kinetics, which means that chemisorption was involved in adsorbing fluoride and arsenic. It is concluded that B1 gives maximum removal for both fluoride (99%) and arsenic (96%). The study shows that lignocellulose-based biochar can be used for arsenic and fluoride removal from water.

Tobacco stalk biomass (TSB) is explored for reactive black 5 (RB5) dye treatment in batch reactor. TSB displayed RB5 adsorption efficiency of 93.5% at 120 min. The RB5 data were fitted to linear and non-linear isotherms and kinetic models. Error functions were determined to have a holistic view on optimum parameters and to validate prediction of models. Harkin-Jura exhibited better fit than that of Freundlich and Langmuir isotherms suggesting multilayer adsorption of RB5 onto TSB on the basis of R2 and chi-square (χ2) error values. Adsorption kinetics was best explained by intraparticle diffusion model (IPD) at increasing initial concentration of RB5. Among the error functions evaluated, the χ2 values for the IPD model were found to be smaller than those for PSO. This suggests that kinetics of RB5 dye is better controlled by IPD phenomenon. Fourier transform infrared spectroscopy confirms the physical adherence of dye to the adsorbent. Values of Gibbs free energy were found to be -19.55 -21.41, -23.40 and -25.33 kJ/mol which shows spontaneous adsorption. Moreover, it is found that TSB adsorbent could be utilized as the effective and economically viable adsorbent for RB5 dye from aqueous solution.

Energy crisis and wastewater treatment are critical global issues. In this study, a novel separator was made by boiling cotton rope with solutions of various salts and their concentrations. It was then employed in a dual‐chamber microbial fuel cell (MFC) to treat municipal wastewater collected from 25 Area Wah Cantt, Punjab, Pakistan. Batch scale experiments were carried out to evaluate the effect of various variables, that is, different salts (NaCl, KCl, and MgCl ₂ ) and their concentrations (0.2, 0.5, and 1 M) used in separator, wastewater volume (50, 500, and 1000 mL), and aluminum mesh thickness (0.6, 0.8, and 1 mm) on MFC performance in terms of current generation and wastewater treatment for 7 days. Analysis of collected wastewater showed that among the six studied physicochemical parameters, only two, that is, biological oxygen demand (BOD) and chemical oxygen demand (COD) were above the permissible limits of National Environmental Quality Standards (NEQS). Results after MFC experiments showed that separator containing 0.5 M NaCl produced a significantly ( p < 0.05) high current of 68.16 µA as compared to the other studied salts and their concentrations, whereas COD and BOD were reduced up to 124.15 and 62.12 mg L ⁻¹ , respectively. A wastewater volume of 1000 mL generated a significantly ( p < 0.05) high current of 83.41 µA compared to the other studied volumes, where COD and BOD residual values were 123.25 and 59.56 mg L ⁻¹ , respectively. An aluminum mesh thickness of 1 mm produced a significantly ( p < 0.05) high current of 103 µA, while 120.89 and 68.93 mg L ⁻¹ were achieved COD and BOD values, respectively. It was concluded that MFC performance was enhanced with an increase in wastewater volume and mesh thickness. Therefore, it is recommended that further pilot‐scale continuous studies be carried out to implement this research on a larger scale.