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Interaction between the microwave heating rate and dielectric properties of agricultural wastes is important in identifying suitable microwave operating conditions. This work focuses on the interaction between microwave heating rate (power intensity) and dielectric properties of selected agricultural wastes, namely castor shell, empty fruit bunch and palm kernel shell. Heating rate was recorded every 30 s for 10 min in a 2.45 GHz microwave at power intensities of 100, 300, 450, 600, 700 and 800 W. All materials tested display an increase in heating rate with increasing power intensity. Castor shell and empty fruit bunch at 800 W, and palm kernel shell at 600 W exhibit high heating rates of 0.134, 0.165, 0.247 °C/s, respectively. For dielectric properties, palm kernel shell series shows a high value of loss tangent compared to the other counterparts, indicating its effectiveness to be heated via microwave.

Dye is a major source of water pollution. This mini-review highlights the origin of dye, its removal strategies, and the recent literature of methylene blue and Congo red adsorption by activated carbons. Adsorption is a unique process that relies upon the physicochemical properties of the activated carbon and the inherent characteristics of dye. Also, factors affecting adsorption, such as contact time, temperature, and concentration, were discussed to gain insight into dye removal mechanisms.

Nanofluids contain nanometer-sized particles in suspension to enhance heat transfer by increasing the thermal conductivity. This paper provides an overview of particle size and volume fraction of nanofluids, and their roles in enhancing the heat transfer. Often, the transfer of heat is enhanced by dispersed particles with small diameter and high concentration despite some debate about the governing effects. The design of elliptical cross-section and zigzag tube also sheds insight into augmenting heat transfer for future research directions and applications.

Solid fuel briquette from biomass materials has gained considerable attention as sustainable replacement source of energy. The characteristics of briquette are imperative to ensure its effectiveness as fuel in a long run. This paper is aimed to summarize the key properties of solid briquette made from various natural and waste-based resources, and to highlight the future research directions in the briquette manufacture. The commentary is expected to shed insight towards the greener, cleaner, and efficient briquette materials.

This work was aimed at evaluating the adsorptive characteristics and two-stage adsorber design of banana peel adsorbents for malachite green and methylene blue removal. The adsorbents were characterized for specific surface, functional groups, and morphology. Activated carbon and hydrochar activated carbon exhibit similar textural and surface properties, but different capacities of malachite green and methylene blue. The latter with surface area of 877 m2/g endows a greater malachite green removal at 582 mg/g, while the former with surface area of 897 m2/g displays a higher methylene blue capacity of 503 mg/g. The Langmuir model was employed in a two-stage adsorber design. The second stage of adsorber is necessary to accomplish the adsorption process with high performance and minimum dosage of activated carbon.

This work was aimed at optimizing the adsorbent mass and contact time and evaluating the performance of two-stage batch adsorber of NaOH-activated coconut shell carbon for methylene blue removal. To decrease the dye concentration from 1000 to 89.4 mg/L at any effluent volumes, the two-stage adsorber displays a small mass saving of 0.33% because of the high adsorbent affinity towards methylene blue at 1.80 L/mg. Meanwhile, the contact time can be minimized by 97.6% as opposed to that in one-stage adsorber. The sensitivity analysis of affinity on mass minimization shows a significant saving of 28.5% when the affinity is reduced to 0.01 L/mg. The response surface methodology was used to optimize the two-stage absorber for methylene blue removal, wherein the most significant parameter is the contact time.

The present work was aimed to evaluate the optimum mass of crab shell biochar and adsorption contact time in a two-stage adsorber design for malachite green. The model was developed to predict optimum adsorbent mass and adsorption profiles at specified volumes and concentrations of dye effluent. Results show that the adsorbent mass can only be reduced by 1.91 % because of the adsorbent’s strong affinity towards malachite green. Accordingly, the adsorption contact time to achieve equilibrium has dramatically reduced from 150 min to 31 min. In the performance evaluation, the adsorbent mass in stage-1 is always higher than that in stage-2 to subside the adsorbent load in achieving the target removal at optimum dosage. From the response surface methodology, the most significant parameters in two-stage adsorber design are adsorption time at stage-2 and malachite green concentration. The predicted values of adsorbent mass and time are essential in designing the cost-competitive two-stage adsorption process for industrial wastewater treatment.

The exclusive properties of β-cyclodextrin (β-CD) combined with its harmless characters making it as an interesting and potential carbon adsorbent for water pollutants removal via adsorption. This work was aimed at evaluating the kinetics and isotherm parameters of methylene blue dye adsorption onto β-CD polymers. The carbon polymers were prepared by citric acid cross-linking, followed by post-treatment with sodium p-toluenesulfinate. The adsorbents were characterized using TGA, BET and FTIR. The adsorption of methylene blue was studied at varying concentrations (5–300 mg/L) and contact times (10–2880 min), and the kinetics and isotherm models were employed to describe the adsorption data. The post-treated carbon polymer exhibits a greater specific surface of 16.6 m2/g. The maximum adsorption of methylene blue by cross-linked and post-treated β-CD adsorbents are 263 and 227 mg/g, respectively. The kinetics data fitted well into pseudo-first order model, indicating physical adsorption. The Boyd’s model showed that film diffusion may be the controlling mechanism. The equilibrium data of methylene blue adsorption for the two β-CD polymers obeyed Langmuir model. To conclude, β-CD is a promising adsorbent candidate for the treatment of dye wastewater.

The excessive amount of phosphate in domestic wastewater treatment plant effluent must be removed to protect the natural environment of healthy aquatic ecosystem. Though a number of adsorption techniques with various low-cost adsorbent have been proposed, it is still ambiguous how the iron-coated waste mussel shell properties affect the adsorption kinetics of phosphate removal from an effluent. The analysis of experimental data was carried out using the bed depth service time, Thomas, and modified mass transfer factor models to study the adsorption kinetics of phosphate deposited on the surface of iron-coated waste mussel shell observed from hybrid plug flow column reactor. The overall adsorption kinetics of phosphate investigated using the Ka and No values referred to the bed depth service time models and the KT and qo values referred to the Thomas models are still acceptable. Detailed analysis of the mechanisms of film mass transfer and porous diffusion using the modified mass transfer factor models is able to determine the kinetic rate of phosphate adsorption. Mass transfer resistance for the adsorption of phosphate onto iron-coated waste mussel shell from domestic wastewater treatment plant effluent is dependent on porous diffusion ultimately contributing to develop advanced iron-coated waste mussel shell adsorbent for enhancing the performance of hybrid plug flow column reactor in future.

Chitosan is a low-cost natural adsorbent. Its derivatives from chemical and physical modification processes possess superior properties for wide applications to meet the growing demands. The chemical modification includes replacement reactions, chain elongation and depolymerization, while the physical modification is to obtain polymeric forms such as powders, nanoparticles and gels. This paper is aimed to highlight the present trends in chitosan preparation and modification, the enhancement in adsorptive properties and the remarks into future directions. The mechanisms involved in adsorption by chitosan derivatives and how the spent adsorbent can be regenerated were also discussed. Meanwhile, for the adsorption of heavy metals from wastewater, chitosan modified with activated carbon showed a better adsorption capacity of 90.90 mg g−1 for Cr(VI) and 50.50 mg g−1 for Cd(II), and for dye adsorption, chitosan modified with activated neem leave showed better adsorption capacity of 90.8 mg g−1 for methylene blue, and for phenol removal, chitosan modified with salicylaldehyde and β-cyclodextrin polymer showed better adsorption capacity of 179.73 mg g−1.

The objective of the present work was to evaluate the performance of two-stage adsorber of activated carbon from oil palm empty fruit bunch for methylene blue removal. The model was developed to predict optimum adsorbent mass and time at a specified volumes and concentrations of dye solution. Results show that the adsorbent mass can be reduced by 6.67%. Operating time taken to attain the equilibrium in a two-stage adsorber has dramatically decreased from 22 h to 0.52 h. In the performance evaluation, the adsorbent mass in stage-1 is higher than in stage-2, which lessen the workload to achieve equilibrium. A two-stage adsorber aids to optimize the mass and contact time for different percentage of dye removal that economically feasible for industrial applications.

The discharge of excessive amounts of phosphorus (P) from domestic wastewater treatment plant effluent is of interest in this study because the abnormally high levels of P as one of the nutrient elements can lead to eutrophication for the receiving waters. Although many methods have been proposed for the removal of P matter from industrial and municipal wastewater, such as Phoredox, A2OTM and UCT-type, the use of alternating aerobic-anoxic (AAA) system must be verified. This study proposes the use of Discontinuous Aerobic-Anoxic Reactor to remove P from domestic wastewater treatment plant effluent using the nitrification and denitrification type of activated sludge. The objectives of this study are: (1) to evaluate the efficiency of P removal from domestic wastewater treatment plant effluent by a single reactor under aerobic digestion (AD) condition, and (2) to assess the performance of AAA process of using the different cycles of nitrification-denitrification to remove P from domestic wastewater treatment plant effluent. The average efficiency of AD to remove P from domestic wastewater treatment plant effluent was 48%. The efficiencies of AAA system to remove P from domestic wastewater treatment plant effluent, were verified as follows: (1) at 6 h AD and 6 h anoxic time (AT), (2) at 5 h AD and 5 h AT, (3) at 4 h AD and 4 h AT, (4) at 3 h AD and 3 h AT, and (5) at 2 h AD and 2 h AT, resulting to the average removal efficiencies of 0, 48, 82, 91, and 88%, respectively. The AAA system has exhibited a better performance compared to AD. The best condition of AAA system had a period of 3 h AD and 3 h AT and reached 91% efficiency with an average treated effluent concentration of less than 1.0 mg L–1 P. High performance of the AAA process has been proven, giving new insights into environmental engineering practices.

Membrane technology is important in industrial wastewater and water treatment. Recently, the polymeric membrane technology is widely chosen in these applications. However, they are lowtemperature ranges, low corrosion resistance, and low lifespan. Thus, researchers are actively trying to develop a better membrane technology such as natural clay ceramic membrane due to their excellent in chemical, mechanical and thermal resistance, high-pressure application and long lifespan. This detailed review compiles through the literature of current scientific research over the last ten years. Its highlights the key findings of factors in the fabrication of natural clay ceramic membrane that contributed to its properties. This review article presented an outline of the advantages, disadvantages, and how to overcome the disadvantages, structure, and preparation of ceramic membrane, including method, raw materials, drying and sintering temperature. The review confirmed that the sintering temperature, the composition of raw materials and pore-forming agent are significantly enhanced the mechanical strength and porosity of the natural clay ceramic membrane. However, further development and modification of the natural clay ceramic membrane technology and their applications to treat different environmental pollutants is still necessary.

Fiber-based activated carbons were prepared from phenolic and rayon fibers through physical activation methods. The raw materials were activated using steam and CO2, and the resultant activated carbons were characterized for pore distribution, textural properties and heavy metals removal. Two commercial activated carbon fibers, namely Fe400 and A10 were also employed for comparison. Activated carbon fiber with a higher specific surface area of 2938 m2/g was prepared from phenolic fiber by steam activation at 900 °C for 1 h. The material is microporous with pores concentrated at supermicropore region. The activated carbon fiber also demonstrates a greater removal of copper(II) and lead(II) at 50% and 75%, respectively, tied-up with its textural properties.

The present work was aimed to evaluate the performance of low-cost activated carbon from coffee residue for Bisphenol A removal. Coffee residue was activated using phosphoric acid and iron (III) chloride. The resultant activated carbons were characterized for textural properties, surface chemistry and surface morphology. The results show that AC-CoR I (H3PO4-activated coffee residue carbon) exhibits high surface area of 1030 m2/g and mesopore size of 2.13 nm, favourable for Bisphenol A removal at 105 mg/g. The adsorption data fitted well with the pseudo-second-order and Langmuir models. In conclusion, coffee residue is a promising precursor of activated carbon for wastewater treatment.

The fundamental understanding about dielectric properties is not completely understood even though it is crucial in microwave-assisted heating. The present work was aimed at evaluating the dielectric properties of reagent mixtures and solids of potassium hydroxide-treated castor residue carbons at varying frequencies and temperatures. Chemical treatment at solid mass ratios (KOH pellet:castor residue) of 0.0 to 2.0 in 50 mL water was carried out using a microwave oven at 70% intensity. The dielectric properties were determined using an open-ended co-axial probe. Results show that the dielectric properties of materials changed with frequency, temperature, water content and ionic strength. Also, the presence of potassium hydroxide solution aids in improving the propensity of castor residue to be heated via microwave. The potassium hydroxide-treated carbons exhibit a 90% removal efficiency of methylene blue at Co = 189 mg/L.

This work was aimed at evaluating the adsorptive properties of beta-cyclodextrin (β-CD) adsorbent towards methylene blue and congo red dyes removal. The adsorbent was characterized for specific surface area and surface chemistry. The results show that the surface area of β-CD adsorbent is small at 0.1 m2/g and the surface chemistry is rich in acidic oxygen groups. The dyes adsorption onto β-CD is favourable. Congo red adsorption exhibits a greater rate constant of 0.103 min−1 and a relatively shorter time to reach equilibrium at 40 min as opposed to 1500 min for methylene blue. On a molar basis, both dyes display a comparable maximum capacity of 1.80 × 10−2 mmol/g, with β-CD shows a greater affinity for congo red. The congo red adsorption is governed by hydrophobic host-guest complex interactions, while that for methylene blue is thru weak electrostatic interactions at the hydrophilic exterior of β-CD. To conclude, β-CD could be a promising adsorbent candidate for the treatment of dyes wastewater, where future works will be centred in improving the versatility and performance of the material.