• Energy Research

Contamination of soil with heavy metals is a worldwide problem, which causes heavy metals to release into the environment. Remediation of such contaminated soil is essential to protect the environment. The aims of this study are: first, to compare the effect of biochar and the joint application of biochar with fertilizer for the phytoremediation of heavy metals-contaminated soil using Acacia auriculiformis; second, to study the effect of the application rate of biochar in improving the physicochemical properties of the soil. The soil samples were collected from an active coal mine dump and assessed for their physicochemical properties and heavy metals toxicity. Initial results indicated that the soil has poor physicochemical properties and was contaminated with the presence of heavy metals such as Zn, Ni, Cu, Cr, and Co. Later, the heavy metals-contaminated soil was mixed with the 400 and 600 °C biochar, as well as the respective biochar–fertilizer combination in varying mixing ratios from 0.5 to 5% (w/w) and subjected to a pot-culture study. The results showed that the application of both varieties of biochar in combination with fertilizer substantially improved the physicochemical properties and reduced the heavy metals toxicity in the soil. The biochar and fertilizer joint application also substantially improved the soil physiochemical properties by increasing the application rate of both varieties of biochar from 0.5 to 5%. The soil fertility index (SFI) of the biochar and biochar–fertilizer amended soil increased by 49.46 and 52.22%, respectively. The plant’s physiological analysis results indicated a substantial increase in the plant’s shoot and root biomass through the application of biochar and biochar–fertilizer compared to the control. On the other hand, it significantly reduced the heavy metals accumulation and, hence, the secretion of proline and glutathione hormones in the plant cells. Therefore, it can be concluded that the joint application of biochar with the application rate varying between 2.5 to 5% (w/w) with the fertilizer significantly improved the physicochemical properties of the soil and reduced the heavy metals toxicity compared to the controlled study.

Abstract Co-pyrolysis of Eucalyptus wood (EW) and Single-use plastic (SUP) can be a sustainable and green technological option ensuring optimum resource recovery and plastic waste management in a circular economy. This study aims to optimize the variables of pyrolysis [temperature (300, 400, 500, 600 °C), residence time (90, 120, 150 min), and proportion of plastic (w/w - 0.25, 0.33)] for application of SUP - EW char composite in soil. Statistical analysis showed that all three process variables had significant influence on properties of the char. With temperature and residence time, the char became dense, carbonaceous, ash-rich, aromatic, and alkaline for both the proportions of SUP in the feed. Further characterization also revealed that the highest plant extractable concentrations of major nutrients, cation exchange capacity, and electrical conductivity of char composite were recorded with temperatures of 400–500 °C, residence time of 120 min, and 33% (w/w) of SUP. The surface morphology analysis revealed the char to have a porous structure with a coating of plastic at lower temperatures of 300 °C and an increase in microporosity at higher temperatures of 500, 600 °C. Significant positive correlations between radicle root growth and prominent plant growth parameters observed through seed germination test indicate the char’s potential applicability in soil. The optimized process parameters of char obtained through regression modeling for application in soil were 415.2 °C, 125.2 min, and 0.325 (w/w) proportion of SUP. The highest mean seed length of ≈17.5 cm observed at 400 °C, 120 min, and 0.33 (w/w) proportion of SUP was consistent with these optimized parameters. Soil incubation test further showed that amendment with optimized char composite significantly improved its properties with a 3.7-fold increase in soil fertility index at 5% rate of application. So, the application of optimized SUP - EW char composite could significantly improve the properties of soil while promoting greener sustainable development through ideal utilization of the so far mismanaged waste resources.

Abstract The study reports an investigation into the effects of temperature and duration of the pyrolysis on the yield and properties of the rice straw biochar and their optimization for application in soil based on the results of seed germination test. As a continuation, the effects of rice straw biochar on the growth of mung beans germinated using extracts of biochar, which were maintained at different pHs was studied. Biochar solvent extraction was done by mixing a predetermined dose of rice straw biochar to solutions initially maintained at five different pH conditions (4, 6, 7, 8, and 10). The biochar extracts were also characterized for their pH, electrical conductivity, and nutrient values and correlated with the germinated seed lengths. Further, this study based on the results of seed germination optimized the rice straw biochar production conditions with such properties to promote maximum seedling growth. Results showed that the yield of biochar decreased from 45.04% to 33.45% as temperature raised from 400 °C to 700 °C. The properties of biochar are primarily affected by the temperature as compared to the heating duration of the pyrolysis. The crystallinity index in the rice straw biochar decreased by 15.25% with the increase in the temperature from 400 °C to 700 °C. Correlation test among seed lengths and biochar extracts properties showed that the seed growth was directly correlated with the increase in the nutrient values at all pH conditions. Based on the germination test, the optimized conditions for the maximum seedling growth observed as for high nutrients, carbon (35–40%) and moderate nitrogen (3–4%), ash (32–35%), yield (35–40%) and cation exchange capacity (40–45 cmol/kg), carbon-nitrogen ratio (22–25:1), low oxygen-carbon ratio (0.7–0.8), ideal pH (8–9), and low volatiles (44–48%). The optimized pyrolytic temperature and duration to produce rice straw biochar with above-listed properties modelled as 500–600 °C and 80–100 min respectively.

Abstract The co-pyrolysis of Single-use low density polyethylene (LDPE) and Eucalyptus biomass (EuBm) can be considered as a sustainable waste management technique to produce viable byproducts. This study elucidates the effects of variable temperatures (300–600 °C), residence times (90–150 minutes), and proportions of LDPE (0.25, 0.33 (w/w)) on physicochemical characteristics of LDPE - EuBm char composites. The interference of liquified polymer coating on the surface with degradation of biomass could be the reason for low nutrient extractability of chars synthesized at 300 and 400 °C. These chars were rich in volatile matter (> 68 %) and their pores were filled with partially pyrolyzed products. Interestingly however, substantial changes in properties were observed at 500 °C due to the likely synergetic effect between the feeds. The highest plant-extractable concentrations of major nutrients (Na, K, Ca, Mg, NO3−, PO43-), electrical conductivity (4.73 mS/cm), and cation exchange capacity (50.5 Cmolc/kg) of char were observed at this temperature. The optimization through regression modeling identified 524 °C, 118 min, and 31 % (w/w) of LDPE as optimal process parameters to obtain char suitable for application in soil. Soil incubation test fortified the benefits of char to soil with 3.5 times improvement in soil fertility index at 5 % (w/w) rate of application.

Abstract The prospects of chars derived from the co-pyrolysis of waste polystyrene (WPS) and eucalyptus biomass at variable temperatures (300–550 °C), residence times (90–150 min) and proportions of WPS (w/w) (33% and 25%) for their potential use as a solid fuel were assessed. The production of char suggested an improved fuel quality compared to the raw feedstock because of reduced volatile and oxygen contents, along with an increase in the carbon and fixed carbon contents. While the properties of the char such as energy density (1.12–1.30), high heat value (28.03–32.5 MJ/kg) had their maximum values observed with 33% WPS content at 300 °C, fixed carbon (4.5–34.19%), fuel ratio (0.05–0.64) were maximum with 25% WPS content at 550 °C. Moreover, the energy yield of the char was higher than the mass yield. The chars produced at 300, 350 °C were observed to have O/C and H/C ratios similar to that of sub-bituminous and bituminous coal. Principal component analysis presented the variable effects of WPS on the properties of the char through physical inhibition and synergistic interactions below and above the complete volatilization temperature of WPS.

Abstract The co-pyrolytic behaviour of single-use plastics (Polystyrene, Low-density polyethylene) and Eucalyptus biomass was investigated at variable temperatures (300, 400, 500, and 600 °C) and the effects of their interactions on the characteristics of solid chars were also studied. The variation in thermal profiles of ‘Δ Mass loss%’ showed the inhibitory and synergistic effects of plastics on the biomass degradation, resulting in higher and lower yields of char composite, respectively. The blend containing polystyrene exhibited the highest synergistic (Δ M ≈ 15.1) and inhibitory (Δ M ≈ - 4) effects. The thermal kinetics of blends also indicated the presence of both the effects through relatively higher and lower apparent activation energies compared to the calculated, before and during the degradation of plastics. Despite low fixed carbon contents and high volatile matter, polymer-coated char composites had higher fuel value indices (36–136%), energy yields (1–26%) and calorific values (15–21%), relative to biochar. After the complete degradation of plastics, char composites exhibited higher values of electrical conductivity (2–40%), surface area (15–64%), and cation exchange capacity (5–19%). These properties advocate the flexibility of char composites' applicability as solid fuel or soil amender depending on the optimized conditions of co-pyrolysis.

Land degradation and the release of contaminants such as heavy metals into the environment due to mining activities is a concerning issue worldwide. The bioaccumulation of heavy metals in the environmental matrix can severely damage flora and fauna and negatively impact human health. The poor physicochemical properties of mine spoil generated through mining operations make restoration of such contaminated and degraded lands challenging. In recent years, an exponential growth in the development and applications of biochar and its composites for the remediation of heavy metal-polluted environmental matrices such as soil and water has been observed. The literature review found that 95 review papers were published in the last five years reviewing the utility of biochar for heavy metals removal from the aqueous environment. However, no paper was published focusing on the application of biochar and its composites for the remediation of heavy metal-contaminated coal mine soil. The objective of the present review is to critically review the impact of mining activities on the environment and the role of biochar and its composites in the remediation of heavy metal-contaminated mine soil. This review presented a detailed discussion and sufficient data on the impact of mining practices in India on the environment. In addition, it critically discussed the methods of the production of biochar from various wastes and methods of modifying the pristine biochar to develop functionalized biochar composites. The detailed mechanism through which biochar and its composites remove and immobilize the heavy metals in the soil was discussed. The efficacy of biochar for the remediation of contaminated mine soil was also critically evaluated using various case studies and data from previously published articles. Thus, the major conclusion drawn from the review is that the application of various functionalized biochar composites could effectively manage and remediate heavy metal-contaminated mine soil.