Since an invention of synthetic fibers (textiles), our life quality has been improved. However, the cumulative production and disposal of them have perceived as significant since they are not biodegradable and hard to be upcycled/recycled. From washing textiles, microplastics are released into the environment, which are regarded as emerging contaminants. As a means for source reduction of microplastics, this study proposed a rapid disposal platform for waste textiles (WTs), converting them into value-added products. To this end, catalytic pyrolysis of WT was studied. To offer more environmentally sound process, CO₂ was used as a raw material for WT pyrolysis. Thermal cracking of WT led to the production of syngas and CH₄ under the CO₂ environment. CO₂ resulted in additional CO production via gas phase reaction with volatile compounds evolved from pyrolysis of WT. To expedite the reaction kinetics for syngas formation, catalytic pyrolysis was done over Co-based catalyst. Comparing to non-catalytic pyrolysis, CO₂-assisted catalytic pyrolysis had 3- and 8-times higher production of H₂ and CO, respectively. This process also suppressed catalyst deactivation, converting more than 80 wt% of WT into syngas and CH₄. The more generation of CO from the use of CO₂ as a raw material offers an effective means to minimize the formations of harmful chemical species, such as benzene derivatives and polycyclic aromatic hydrocarbons.

Understanding the migration and conversion of nitrogen in wood-based panels (WBPs) during pyrolysis is fundamentally important for potentially transforming the N-containing species into valuable material-based products. This review firstly summarizes the commonly used methods for examining N evolution during the WBPs pyrolysis before probing into the association between the wood and adhesives.The potential effects of wood-adhesive interaction on the pyrolysis process are subsequently analyzed. Furthermore, the controversial statements from literature on the influence of adhesives on wood pyrolysis behavior are discussed, which is followed by the detailed investigation into the distribution and evolution of N-containing species in gas, liquid and char, respectively, during WBPs pyrolysis in recent studies. The differences in N species due to the heating sources (i.e. electrical heating vs microwave heating) are particularly compared. Finally, based on the characteristics of staged pyrolysis, co-pyrolysis and catalytic pyrolysis, the converting pathways for WBPs are proposed with an emphasis on the production of value-added chemicals and carbon materials, simultaneously mitigating NOₓ emission.

Grape pomace (GP) is a low-value by-product that contains a significant amount of high value-added products. The huge amount of non-edible residues of GP wastes (seeds, skins, leaves and, stems) produced by wine industries causes’ environmental pollution, management issues as well as economic loss. Studies over the past 15–20 years revealed that GP could serve as a potential source for valuable bioactive compounds like antioxidants, bioactive, nutraceuticals, single-cell protein, and volatile organic compounds with an increasing scientific interest in their beneficial effects on human and animal health. However, the selection of appropriate techniques for the extraction of these compounds without compromising the stability of the extracted products is still a challenging task for the researcher. Based on the current scenario, the review mainly summarizes the novel applications of winery wastes in many sectors such as agriculture, pharmaceuticals, cosmetics, livestock fields, and also the bio-energy recovery system. We also summarize the existing information/knowledge on several green technologies for the recovery of value-added by-products. For the promotion of many emerging technologies, the entrepreneur should be aware of the opportunities/techniques for the development of high-quality value-added products. Thus, this review presents systematic information on value-added by-products that are used for societal benefits concerning the potential for human health and a sustainable environment.

Waste residues and acidic effluents (post-processing of E-waste) released into the local surroundings cause perilous environmental threats and potential risks to human health. Only limited research and information are available toward the sustainable management of waste residues generated post resource recovery of E-waste components. In the present study, the manual processing of obsolete computer (keyboard, monitor, CPU, and mouse) and chemical leaching of waste printed circuit boards (WPCBs) (motherboard, hard drive, DVD drive, and power supply) were performed for urban mining. The toxicity characteristics of typical pollutants in the residues of the WPCBs (post chemical leaching) were studied by toxicity characteristics leaching procedure (TCLP) test. Manual dismantling techniques resulted in an efficient urban mining concept with an overall average profit estimation of INR 2513.73/US$ 34.59. The chemical leaching of WPCBs showed a high concentration of metal leaching like Cu (229662 ± 575.3 mg/kg) and Pb (36785.67 ± 13.07 mg/kg) in the motherboard after stripping epoxy coating. The toxicity test revealed that the concentration of Cu (245.746 ± 0.016 mg/l) in the treated waste residue and Cu (430.746 ± 0.0015 mg/l) and Pb (182.09 ± 0.0035 mg/l) in the non-treated waste residue exceeded the threshold limit. The concentrations of other elements As, Cd, Co, Cr, Ag, Mn, Zn, Ni, Fe, Se, and In were within the permissible limit. Hence, the waste residue stands non-hazardous except Cu and Pb. Stripping out the epoxy coating of WPCBs enhances the metal leaching concentrations. The study highlighted that efficient and appropriate E-waste urban mining has immense potential in tracing the waste scrap into secondary resources. This study also emphasized that the final processed waste residue (left unattended or discarded due to lack of appropriate skill and technology) can be taken into consideration and exploited for value-added materials.

In this study, the co-pyrolysis of food waste with lignocellulosic biomass (wood bark) in a continuous-flow pyrolysis reactor was considered as an effective strategy for the clean disposal and value-added utilization of the biowaste. To achieve this aim, the effects of major co-pyrolysis parameters such as pyrolysis temperature, the flow rate of the pyrolysis medium (nitrogen (N₂) gas), and the blending ratio of food waste/wood bark on the yields, compositions, and properties of three-phase pyrolytic products (i.e., non-condensable gases, condensable compounds, and char) were investigated. The temperature and the food waste/wood bark ratio were found to affect the pyrolytic product yields, while the N₂ flow rate did not. More non-condensable gases and less char were produced at higher temperatures. For example, as the temperature was increased from 300 °C to 700 °C, the yield of non-condensable gases increased from 6.3 to 17.5 wt%, while the yield of char decreased from 63.6 to 30.6 wt% for the co-pyrolysis of food waste and wood bark at a weight ratio of 1:1. Both the highest yield of hydrogen (H₂) gas and the most significant suppression of the formation of phenolic and polycyclic aromatic hydrocarbon (PAH) compounds were achieved with a combination of food waste and wood bark at a weight ratio of 1:1 at 700 °C. The results suggest that the synergetic effect of food waste and lignocellulosic biomass during co-pyrolysis can be exploited to increase the H₂ yield while limiting the formation of phenolic compounds and PAH derivatives. This study has also proven the effectiveness of co-pyrolysis as a process for the valorization of biowaste that is produced by agriculture, forestry, and the food industry, while reducing the formation of harmful chemicals.

This study aims to investigate the adsorption behavior of cationic and anionic dyes of methylene blue (MB) and Congo red (CR) onto wet-torrefied Chlorella sp. microalgal biochar respectively, as an approach to generate a waste-derived and low-cost adsorbent. The wet-torrefied microalgal biochar possessed microporous properties with pore diameter less than 2 nm. The optimum adsorbent dosage of wet-torrefied microalgal biochar for MB and CR dyes removal were determined at 1 g/L and 2 g/L, respectively, with their natural pHs as the optimum adsorption pHs. The determined equilibrium contact times for MB and CR were 120 h and 4 h, respectively. Based on the equilibrium modeling, the results revealed that Langmuir isotherm showed the best model fit, based on the highest R² coefficient, for both the adsorption processes of MB and CR using the wet-torrefied microalgal biochar, indicating that the monolayer adsorption was the dominant process. From the modeling, the maximum adsorption capacities for MB and CR were 113.00 mg/g and 164.35 mg/g, respectively. The kinetic modeling indicated the adsorption rate and mechanism of the dyes adsorption processes, which could be crucial for future modeling and application of wet-torrefied microalgal biochar. From the results, it suggests that the valorization of microalgae by utilizing wet-torrefied microalgal biochar as the effective adsorbent for the removal of toxic dyes with an approach of microalgal biorefinery and value-added application to the environment is feasible.

Converting biowaste into value-added products has raised the researchers’ interests. In this study, bioconversion was applied to produce chain acids from food waste by anaerobic fermentation. To improve the caproic acid production, different pretreatments (i.e., ultrasonic, hydrothermal, and alkaline-thermal) were used for investigating their effects on the acidogenic production and microbial communities. The results showed that ultrasonic and hydrothermal pretreatments (207.8 and 210.1 mg COD/g VS, respectively) were very efficient for enhancing the caproic acid production, compared to the alkaline-thermal pretreated samples and control samples (72.6 and 97.5 mg COD/g VS, respectively). The ultrasonic pretreatment was beneficial for reducing volatile fatty acids (VFAs) during the caproic acid production, resulting in converting more lactic acid to caproic acid by adding the hydrothermal pretreatment. The microbial community analysis showed that the acidogenic bacteria Caproiciproducens dominated the fermentation in this bioconversion process of food waste into chain acids. The Caproiciproducens mainly degraded the proteins and carbohydrates from the saccharified residues of food waste to produce caproic acids through chain elongation procedure. The investigation and optimized method may help develop the bioconversion technology for producing VFAs products from food wastes.

Microalgae have become imperative for biological wastewater treatment. Its capability in biological purification of wastewaters from different origins while utilizing wastewater as the substrate for growth has manifest great potentials as a sustainable and economical wastewater treatment method. The wastewater grown microalgae have also been remarked in research to be a significant source of value-added bioproducts and biomaterial. This paper highlights the multifaceted roles of microalgae in wastewater treatment from the extent of microalgal bioremediation function to environmental amelioration with the involvement of microalgal biomass productivity and carbon dioxide fixation. Besides, the uptake mechanism of microalgae in wastewater treatment was discussed in detail with illustrations for a comprehensive understanding of the removal process of undesirable substances. The performance of different microalgae species in the uptake of various substances was studied and summarized in this review. The correlation of microalgal treatment efficacy with various algal strain types and the bioreactors harnessed for cultivation systems was also discussed. Studies on the alternatives to conventional wastewater treatment processes and the integration of microalgae with accordant wastewater treatment methods are presented. Current research on the biological and technical approaches for the modification of algae-based wastewater system and the maximization of biomass production is also reviewed and discussed. The last portion of the review is dedicated to the assertion of challenges and future perspectives on the development of microalgae-based wastewater treatment technology. This review serves as a useful and informative reference for readers regarding the multifaceted roles of microalgae in the application of wastewater biotreatment with detailed discussion on the uptake mechanism.

In this study, wasted mask is chosen as a pyrolysis feedstock whose generation has incredibly increased these days due to COVID-19. We suggest a way to produce value-added chemicals (e.g., aromatic compounds) from the mask with high amounts through catalytic fast pyrolysis (CFP). To this end, the effects of zeolite catalyst properties on the upgradation efficiency of pyrolytic products produced from pyrolysis of wasted mask were investigated. The compositions and yields of pyrolytic gases and oils were characterized as functions of pyrolysis temperature and the type of zeolite catalyst (HBeta, HY, and HZSM-5), including the mesoporous catalyst of Al-MCM-41. The mask was pyrolyzed in a fixed bed reactor, and the pyrolysis gases evolved in the reactor was routed to a secondary reactor inside which the zeolite catalyst was loaded. It was chosen 550 °C as the CFP temperature to compare the catalyst performance for the production of benzene, toluene, ethylbenzene, and xylene (BTEX) because this temperature gave the highest oil yield (80.7 wt%) during the non-catalytic pyrolysis process. The large pore zeolite group of HBeta and HY led to 134% and 67% higher BTEX concentrations than HZSM-5, respectively, likely because they had larger pores, higher surface areas, and higher acid site density than the HZSM-5. This is the first report of the effect of zeolite characteristics on BTEX production via CFP.

In China, more than 10,000 tons of bean-worm, which is rich in protein (68.5%) and essential amino acids (52.8%), is consumed annually. Thus, a large amount of bean-worm skin waste is generated, and is often indiscriminately disposed of, potentially causing environment problems. In this study, bean-worm skin (BWS) waste was pyrolyzed at 500 °C to produce biochar (BWS-BC), and the surface properties of BWS and BWS-BC were characterized using various spectroscopic techniques. Pb(II) adsorption properties of BWS and the corresponding biochar as a function of solution pH, contact time, and equilibrium concentration of Pb(II) were examined using adsorption isotherm, kinetics and thermodynamics studies. The maximum Pb(II) adsorption capacities based on the Langmuir isotherm model were calculated as 45 and 62 mg g⁻¹ for BWS and BWS-BC, respectively, which were comparable to the values obtained for biochars derived from other agro-wastes. The adsorption feasibility, favorability and spontaneity of Pb(II), as derived from the thermodynamic parameters, indicated that chemisorption and precipitation (e.g., hydroxypyromorphite) were the main adsorption mechanism in case of BWS and BWS-BC, respectively. Thus, conversion of BWS to biochar for Pb(II) adsorption can be considered as a feasible, promising and high value-added approach for BWS recycling.