Biochar-based solutions for sustainable dye treatment and agricultural waste management

Abdel Azim E., Samy M., Hanafy M., Mahanna H.

The pyrolysis of mint stalks and lemon peels was performed to synthesize mint-stalks (MBC) and lemon-peels (LBC) derived biochars for adsorbing methylene blue (MB). The preparation, characterization, and application of MBC in adsorption have not been reported in the literature. MBC showed higher surface area and carbon content than that of LBC. The removal ratios of MB were 87.5% and 60% within 90 min for MBC and LBC, respectively at pH 7, temperature of 30oC, adsorbent dose of 0.5 g/L, and MB concentration of 5 mg/L. The optimal MBC dose was 1 g/L achieving a removal efficiency of 93.6% at pH 7, temperature of 30oC, contact time of 90 min, and initial dye concentration of 5.0 mg/L. The adsorption efficiency decreased from 98.6% to 31.33% by raising the dye concentration from 3.0 mg/L to 30 mg/L. Further, the increase of adsorbent dose to 10 g/L could achieve 94.2%, 90.3%, 87.6%, and 84.1% removal efficiencies of MB in the case of initial concentrations of 200 mg/L, 300 mg/L, 400 mg/L, and 500 mg/L, respectively. MBC showed high stability in adsorbing MB under five cycles, and the performed analyses after adsorption reaffirmed the stability of MBC. The adsorption mechanism indicated that the adsorption of MB molecules on the biochar's surface was mainly because of the electrostatic interaction, hydrogen bonding, and π-π stacking. Pseudo-second-order and Langmuir models could efficiently describe the adsorption of MB on the prepared biochar. The adsorption process is endothermic and spontaneous based on the adsorption thermodynamics. The proposed adsorption system is promising and can be implemented on a bigger scale. Moreover, the prepared biochar can be implemented in other applications such as photocatalysis, periodate, and persulfate activation-based advanced oxidation processes.

Zhang L., Chen Z., Zhu S., Li S., Wei C.

Many anaerobic activities involve carbon, nitrogen, iron, and sulfur cycles. As a well-developed porous material with abundant functional groups, pyrolytic biochar has been widely researched in efforts to promote microbial activities. However, the lack of consensus on the biochar mechanism has limited its practical application. This review summarizes the effects of different pyrolysis temperatures, particle sizes, and dosages of biochar on microbial activities and community in Fe(III) reduction, anaerobic digestion, nitrogen removal, and sulfate reduction systems. It was found that biochar could promote anaerobic activities by stimulating electron transfer, alleviating toxicity, and providing suitable habitats for microbes. However, it inhibits microbial activities by releasing heavy metal ions or persistent free radicals and adsorbing signaling molecules. Finding a balance between the promotion and inhibition of biochar is therefore essential. This review provides valuable perspectives on how to achieve efficient and stable use of biochar in anaerobic systems.

Wei F., Zhu Y., He T., Zhu S., Wang T., Yao C., Yu C., Huang P., Li Y., Zhao Q., Song W.

Bilal M., Ihsanullah I., Hassan Shah M.U., Bhaskar Reddy A.V., Aminabhavi T.M.

The presence of hazardous dyes in wastewater cause disastrous effects on living organisms and the environment. The conventional technologies for the remediation of dyes from water have several bottlenecks such as high cost and complex operation. This review aims to present a comprehensive outlook of various bio-sorbents that are identified and successfully employed for the removal of dyes from aqueous environments. The effect of physicochemical characteristics of adsorbents such as surface functional groups, pore size distribution and surface areas are critically evaluated. The adsorption potential at different experimental conditions of diverse bio-sorbents has been also explored and the influence of certain key parameters like solution pH, temperature, concentration of dyes, dosage of bio-sorbent and agitation speed is carefully evaluated. The mechanism of dyes adsorption, regeneration potential of the employed bio-sorbents and their comparison with other commercial adsorbents are discussed. The cost comparison of different adsorbents and key technological challenges are highlighted followed by the recommendations for future research.

Mukherjee S., Sarkar B., Aralappanavar V.K., Mukhopadhyay R., Basak B.B., Srivastava P., Marchut-Mikołajczyk O., Bhatnagar A., Semple K.T., Bolan N.

Numerous harmful chemicals are introduced every year in the environment through anthropogenic and geological activities raising global concerns of their ecotoxicological effects and decontamination strategies. Biochar technology has been recognized as an important pillar for recycling of biomass, contributing to the carbon capture and bioenergy industries, and remediation of contaminated soil, sediments and water. This paper aims to critically review the application potential of biochar with a special focus on the synergistic and antagonistic effects on contaminant-degrading microorganisms in single and mixed-contaminated systems. Owing to the high specific surface area, porous structure, and compatible surface chemistry, biochar can support the proliferation and activity of contaminant-degrading microorganisms. A combination of biochar and microorganisms to remove a variety of contaminants has gained popularity in recent years alongside traditional chemical and physical remediation technologies. The microbial compatibility of biochar can be improved by optimizing the surface parameters so that toxic pollutant release is minimized, biofilm formation is encouraged, and microbial populations are enhanced. Biocompatible biochar thus shows potential in the bioremediation of organic contaminants by harboring microbial populations, releasing contaminant-degrading enzymes, and protecting beneficial microorganisms from immediate toxicity of surrounding contaminants. This review recommends that biochar-microorganism co-deployment holds a great potential for the removal of contaminants thereby reducing the risk of organic contaminants to human and environmental health.

Mittal J., Arora C., Mittal A.

Incessant advancement of industry and agriculture has amplified organic pollutants contents in recent years causing grave threat to environmental well-being. With time, adsorption has established as an effective and financially advantageous process for the elimination of organic contaminants, like dyes, phenolics, pesticides, polynuclear aromatics and antibiotics. Biochar (BC), a carbon-rich material (70% approximate), prepared predominately by pyrolysis of waste materials such as biomass of agriculture and timber origin, is assumed by far the cleanest form of the charcoal. BC can have important physicochemical features like high carbon content as well as elevated surface chemistry heterogeneity, elevated textural features (specific surface area and pores volume), stable structure, cation exchange capacity, and recyclability. These features in combination with BCs low cost since they can be obtained from abundantly naturally available raw material, establish them as prosperous candidates for applications such as energy source (biofuel), as additives for soil amendment, to sequester carbon, pollution remediation and waste management by recycling agricultural by-products. Principal parameters on which BCs’ properties depend are the temperature and atmosphere of pyrolysis, heat transfer rate, feedstock, type and residence time. This article examines in detail the sources, production, characteristics and modification of BC, along with special emphasis on research published in recent 5 years particularly regarding the removal of a benchmark cationic organic dye, Methylene Blue.

Liu Y., Chen Y., Li Y., Chen L., Jiang H., Li H., Luo X., Tang P., Yan H., Zhao M., Yuan Y., Hou S.

The potential risk of various contaminants in water has recently attracted public attention. Biochars and modified biochars have been widely developed for environmental remediation. Metal and heteroatom co-doped biochar composites (MHBCs) quickly caught the interest of researchers with more active sites and higher affinity for contaminants compared to single-doped biochar by metal or heteroatoms. This study provides a comprehensive review of MHBCs in wastewater decontamination. Firstly, the main fabrication methods of MHBCs were external doping and internal doping, with external doping being the most common. Secondly, the applications of MHBCs as adsorbents and catalysts in water treatment were introduced emphatically, which mainly included the removal of metals, antibiotics, dyes, pesticides, phenols, and other organic contaminants. Thirdly, the removal mechanisms of contaminants by MHBCs were deeply discussed in adsorption, oxidation and reduction, and degradation. Furthermore, the influencing factors for the removal of contaminants by MHBCs were also summarized, including the physicochemical properties of MHBCs, and environmental variables of pH and co-existing substance. Finally, futural challenges of MHBCs are proposed in the leaching toxicity of metal from MHBCs, the choice of heteroatoms on the fabrication for MHBCs, and the application in the composite system and soil remediation.

Liu X., Li M., Ma J., Bian J., Peng F.

Methylene blue (MB) in industrial wastewater is a potential threat to human health and environment and the removal of methylene blue attracts wide attention. In this study, corncob lignin was carbonized at 400 °C and cross-linked with chitosan in the presence of epichlorohydrin to prepare a composite (CS-BC), and the adsorption behavior was discussed by using MB as adsorbate. Its removal of methylene blue reached 99.96% with a maximum adsorption capacity of 499.8 mg/g, and the adsorption behavior was in accordance with the Langmuir model. The fitness of pseudo-second-order kinetic model conceded that chemisorption played a major role. Compared with unmodified biochar, the adsorption capacity of CS-BC was increased by ~2 times. CS-BC had good recyclability and was easy to separate from water, which maintained excellent absorption performance after 5 cycles. The excellent adsorption capacity and recycling performance of CS-BC provide a prospect way to eliminate methylene blue from industrial effluents. • Lignin waste released from bioethanol production was used as biochar feedstock. • Chitosan modified lignin-biochar composite was applied to remove methylene blue. • The possible adsorption mechanism of adsorbent composite was proposed. • The maximum adsorption capacity of adsorbent reached 499.8 mg/g.

Shahib I.I., Ifthikar J., Oyekunle D.T., Elkhlifi Z., Jawad A., Wang J., Lei W., Chen Z.

Unlike agricultural biomass, sludge-derived biochar is rich in nutrients, comprising exchangeable cations and various surface oxygen functional groups with carbonaceous structures. In this study, the influence of different activating reagents such as H 3 PO 4 , H 2 O 2 , K 2 CO 3 , and NaOH on the physicochemical properties of biochar was investigated. It was found that the biochar elemental composition remains nearly the same, while the surface Fe and Si were induced for H 3 PO 4 modification. The pH of the original biochar was varied from acidic to alkali (3.60–10.06) along the chemical treatment process. The surface-active sites of biochar and their nature were dramatically tuned based on their chemical modification. To interpret the relationship between each of the parameters obtained via chemical modification, adsorption of different pollutants, such as Pb(II), Cd(II), Cr(VI), V(V), As(III), and methylene blue (MB) were conducted. Among the biochars, NaOH-modified biochar was revealed as the optimum candidate with maximum uptake capacity for Pb(II) (195.75 mg/g) and MB (160.78 mg/g). Based on the adsorption kinetics and isotherm study, the adsorption process endorsed chemical sorption with multiple interactions along the heterogeneous surface. This study offered a comprehensive approach to manipulating the physicochemical properties of biochar. • Acidic, alkaline and oxidizing chemical agents were used to activate SDBC as an adsorbent. • Both Physical and chemical properties could be broadly altered through cost-effective methods. • Dyes and heavy metals were used to depict the efficiency through a different mechanism. • Four kinetic and isotherm models were used to interpret the sorption mechanism.

Parthasarathy P., Sajjad S., Saleem J., Alherbawi M., Mckay G.

The study provides a review of various applications of biomass-derived biochars, waste-derived biochars, and modified biochars as adsorbent materials for removing dyestuff from process effluents. Processing significant amounts of dye effluent discharges into receiving waters can supply major benefits to countries which are affected by the water crisis and anticipated future stress in many areas in the world. When compared to most conventional adsorbents, biochars can provide an economically attractive solution. In comparison to many other textile effluent treatment processes, adsorption technology provides an economic, easily managed, and highly effective treatment option. Several tabulated data values are provided that summarize the main characteristics of various biochar adsorbents according to their ability to remove dyestuffs from wastewaters.

Osman A.I., Fawzy S., Farghali M., El-Azazy M., Elgarahy A.M., Fahim R.A., Maksoud M.I., Ajlan A.A., Yousry M., Saleem Y., Rooney D.W.

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Gupta R., Pandit C., Pandit S., Gupta P.K., Lahiri D., Agarwal D., Pandey S.

Various paper, oil, leather and textile industries generates a large amount of aromatic recalcitrant organic pollutants and release them into the environment which causes severe health hazards to all living organisms. Residual dyes generated from textile industries are released into the water bodies causes environmental disbalance by getting accumulated in aquatic animals and plants causing death. Many times, this polluted water is used for agriculture purposes and reaches humans through biomagnification and bioaccumulation processes. Synthetic dyes are widely used in the textile industries, when comes in contact with humans via food chain or physical contact causes cancer and genetic mutation. The harmful colour effluent from the textile industries could be managed by various physicochemical and biological methods such as oxidation, phytoremediation, coagulation, or precipitation, using microbial consortium, membrane filtration, chemical, microalgal consortium, enzymatic bioremediation, and adsorbents such as biochar or microbes before releasing into nature. This review focuses on biochar as a viable resource for pollutant removal, climate mitigation, soil and water enhancement and bioethanol production improvement. Its efficiency levels and economic value can also be manipulated by the arrangement of these conditions. We have also discussed different types of dyes used in various industrial and their toxicity. Further, the management of industrial waste effluents containing dyes using agroindustrial waste-derived biochar is discussed in detail. Moreover, other applications of biochar and recent advancements on dye adsorption using biochar are reviewed.

Ali L., Palamanit A., Techato K., Ullah A., Chowdhury M.S., Phoungthong K.

This study investigated the characteristics of biochars derived from the pyrolysis of rubberwood sawdust (RWS) and sewage sludge (SS) and their co-pyrolysis at mixing ratios of 50:50 and 75:25. Biochars were produced at 550 °C through slow pyrolysis in a moving bed reactor and then characterized. Results showed that the rubberwood sawdust biochar (RWSB) had high carbon content (86.70 wt%) and low oxygen content (7.89 wt%). By contrast, the sewage sludge biochar (SSB) had high ash content (65.61 wt%) and low carbon content (24.27 wt%). The blending of RWS with SS at the mentioned ratios helped enhance the gross and element contents of the biochar samples. The elemental analysis of the biochars was also reported in the form of atomic ratios (H/C and O/C). The functional groups of biochars were observed by Fourier-transform infrared spectroscopy (FTIR). X-ray fluorescence spectroscopy (XRF) revealed that the biochar from SS contained a high content of inorganic elements, such as Si, Ca, Fe, K, Mg, P, and Zn. The pH of the biochars ranged from 8.41 to 10.02. Brunauer, Emmett, and Teller (BET) and scanning electron microscopy (SEM) showed that RWSB had a lower surface area and larger pore diameter than the other biochars. The water holding capacity (WHC) and water releasing ability (WRA) of the biochars were in the range of 1.01–3.08 mL/g and 1.19–52.42 wt%, respectively. These results will be the guideline for further application and study of biochar from RWS, SS, and blended samples.

Karić N., Maia A.S., Teodorović A., Atanasova N., Langergraber G., Crini G., Ribeiro A.R., Đolić M.

• Bio-waste recovery tackles pollution issues related to water, solid waste and air. • Studies using bio-waste to treat real wastewater samples were reviewed. • Bio-sorbents were reported to tackle in/organic pollutants (including emerging ones). • Realistic studies on the removal of residues in complex matrices are needed. • Thermally activated bio-waste is proven to efficiently remove metals/organics/dyes. The conventional waste management practices dispose or incinerate agricultural and forestry waste, contributing to the environmental pollution while misusing biomass, a valuable resource with a great potential of reuse. In fact, cultivation of agricultural crops and harvesting generate an abundant amount of waste (e.g., stones, shells, straw) that can be used for wastewater treatment. Waste biomass may be used as: (i) an adsorbent in its original, raw form, following ambient drying and grinding; (ii) modified bio-based sorbents; or (iii) a source material for the synthesis of activated carbon adsorbents through carbonization. Despite the numerous publications in this field examining the removal of a wide range of target pollutants (metals, metalloids, dyes, pesticides, as well as emerging contaminants) by several materials, more realistic studies are still required to evaluate the potential to remove residual compounds in complex matrices, by testing natural matrices, i.e., environmental samples without spiking the target compounds. This perspective paper highlights how an integrated-engineering approach may help solving environmental-pollution issues related to water, solid waste, and air pollution. Chiefly, the application of locally produced bio-waste as an adsorbent for wastewater treatment tackles water contamination, decreases the overall amount of agricultural waste, and reduces the potential gas emissions caused by waste transportation, treatment and/or disposal.

Amalina F., Razak A.S., Krishnan S., Zularisam A.W., Nasrullah M.

• Biochar production in various techniques is elucidated. • Biomass feedstock pyrolysis conditions are the key influencing biochar production is reviewed. • Biochar shows excellent promise for the pollutants removal from water and wastewater are overviewed. • Biochar as an innovative adsorbent to remove aqueous contaminants is discussed. • The biochar produced utilized for various applications technology are summarized. There is a rise of interest in various aspects of biochar derived from waste biomass to address the most pressing ecosystem challenges. This study contributes to understanding biochar's usage in the remediation of hazardous pollutants. The synthesis of biochar using a variety of different techniques has been explored. Numerous analysts have considered biochar as a strategy for enhancing their ability to remediate pollutants. Process factors are primarily responsible for determining biochar yield. Biochar-derived biomass is an exceptionally rich wellspring of carbon produced from biomass utilizing thermal combustion. Activating biochar is another field where biochar is increasingly used to remove specific contaminants. Closed-loop methods to produce biochar expand options. Distributed biochar manufacturing processes are an efficient method to develop businesses, manage waste, and increase resource proficiency in environmental applications. Additionally, this research discusses knowledge gaps and future directions in toxic pollutant remediation through biochar.