Effect of acid modified tea-waste biochar on crop productivity of red onion (Allium cepa L.).

Biochar has widely been utilized as an agricultural soil amendment owing to its enhanced surface properties and cost-effectiveness. In the present work, the influence of tea waste biochar (TWBC) upon acid modification on Allium cepa L. (red onion) growth has been studied. Its effect as a soil amendment has also been studied by assessing the nutrient retention, microbial population growth and immobilization of potentially toxic metal ions. A greenhouse experiment was carried out by applying different biochar (BC) ratios (2% and 5% w/w) to soil as the growth media for onion plants. A 2.4 times (2.4 × ) reduction of phosphate from leaching was observed upon BC application at a ratio of 2% than that of 5%. Moreover, red onion plants that grew in the BC-fertilizer amended soil at a 2% ratio showed higher growth compared to that of 5%. A ∼1.3 × and ∼1.2 × increment of total dry weight was observed upon amendment of soil fertilizer system with nitric and sulfuric acid-modified TWBC, respectively. An analysis of the potentially toxic metal ion uptake by the respective plant parts showed that lead uptake by the roots of red onion was ∼8.3 × less in BC amended soil compared to that in contaminated soil. Thus, acid-modified TWBC can be considered a potential soil amendment for an enhanced red onion growth. Employing TWBC as a soil amendment in tropical countries, where tea-waste is in abundance, will boost sustainable agriculture.

Biochar based sorptive remediation of steroidal estrogen contaminated aqueous systems: A critical review.

Remediation of steroidal estrogens from aqueous ecosystems is of prevailing concern due to their potential impact on organisms even at trace concentrations. Biochar (BC) is capable of estrogen removal due to its rich porosity and surface functionality. The presented review emphasizes on the adsorption mechanisms, isotherms, kinetics, ionic strength and the effect of matrix components associated with the removal of steroidal estrogens. The dominant sorption mechanisms reported for estrogen were π-π electron donor-acceptor interactions and hydrogen bonding. Natural organic matter and ionic species were seen to influence the hydrophobicity of the estrogen in multiple ways. Zinc activation and magnetization of the BC increased the surface area and surface functionalities leading to high adsorption capacities. The contribution by persistent free radicals and the arene network of BC have promoted the catalytic degradation of adsorbates via electron transfer mechanisms. The presence of surface functional groups and the redox activity of BC facilitates the bacterial degradation of estrogens. The sorptive removal of estrogens from aqueous systems has been minimally reviewed as a part of a collective evaluation of micropollutants. However, to the best of our knowledge, a critique focusing specifically and comprehensively on BC-based removal of steroidal estrogens does not exist. The presented review is a critical assessment of the existing literature on BC based steroidal estrogen adsorption and attempts to converge the scattered knowledge regarding its mechanistic interpretations. Sorption studies using natural water matrices containing residue level concentrations, and dynamic sorption experiments can be identified as future research directions.

Microwave and open vessel digestion methods for biochar.

Digestion of biomass derived carbonaceous materials such as biochar (BC) can be challenging due to their high chemical recalcitrance and vast variations in composition. Reports on the development of specific sample digestion methods for such materials remain inadequate and thus require considerable attention. Nine different carbonaceous materials; slow-pyrolyzed tea-waste and king coconut BC produced at 300 °C, 500 °C and 700 °C, sludge waste BC produced at 700 °C, wet fast-pyrolyzed Douglas-Fir BC and steam activated coconut shell BC have been tested to evaluate a relatively fast and convenient open-vessel digestion method using seven digestion reagents including nitric acid (NA), fuming nitric acid (FNA), sulfuric acid (SA), NA/SA, FNA/SA, NA/H2O2 and SA/H2O2 mixtures. From the tested digestion reagents, SA/H2O2 mixture dissolved low temperature produced BC (LTBC) within 2 h with occasional shaking and no external heating. Except peroxide mixtures, the other reagents were used to evaluate microwave digestion (MWD) efficiency. Nitric acid mixture was capable of only completely digesting LTBC in the MWD procedure whereas FNA, NA/SA and FNA/SA mixtures resulted in the successful dissolution of all tested carbonaceous materials. Amongst them, FNA provided the least matrix effect in the quantification of the four metals tested using flame atomic absorption spectrophotometry. Tested recoveries for FNA were satisfactory as well. It was concluded that FNA is a preferable reagent for microwave digestion of BC.

The influence of three acid modifications on the physicochemical characteristics of tea-waste biochar pyrolyzed at different temperatures: a comparative study.

Tea-waste is an abundant feedstock for producing biochar (BC) which is considered to be a cost effective carbonaceous adsorbent useful for water remediation and soil amendment purposes. In the present study, tea-waste BC (TWBC) produced at three different temperatures were subjected to nitric, sulfuric and hydrochloric acid modifications (abbreviated as NM, SM and HM respectively). Characteristics of the raw and modified BC such as ultimate and proximate analyses, surface morphology, surface acidity and functionality, point of zero charge, cation exchange capacity (CEC) and thermal stability were compared to evaluate the influence of pyrolysis temperature and of modifications incorporated. The amount of carboxylic and phenolic surface functionalities on TWBC was seen to decrease by 93.44% and 81.06% respectively when the pyrolysis temperature was increased from 300 to 700 °C. Additionally, the yield of BC was seen to decrease by 46% upon the latter temperature increment. The elemental analysis results provided justification for high-temperature BC being more hydrophobic as was observed by the 61% increase in H/C ratio which is an indication of augmented aromatization. The CEC was the highest for the low-temperature BC and was seen to further increase by NM which is attributed to the 81.89% increase in carboxylic functionalities. The surface area was seen to significantly increase for BC700 upon NM (∼27 times). The SM led to pore wall destruction which was observed in scanning electron microscopy images. Findings would enable the rational use of these particular modifications in relevant remediation and soil amendment applications.

Biochar based removal of antibiotic sulfonamides and tetracyclines in aquatic environments: A critical review.

Utilization of biochar (BC) as a low cost adsorbent for water remediation has gained an immense research interest due to their surface functionality and porosity. Although many reports on the BC based sorptive removal of Sulfonamides (SA) and Tetracyclines (TC) are available in literature, a deep insight into sorption mechanisms is yet to be reviewed. Objective of this review is to fill the research gap of a methodological understanding of sorption mechanisms and characteristics which is essential to develop efficient methods for contaminant removal. The most common adsorption mechanism can be considered as electron donor-acceptor interactions of electron withdrawing moieties with surface arene rings. The strongest adsorption of both antibiotics occurs at mildly acidic pH where the dominant species are zwitterionic or cationic. Smaller SAs exhibit micro pore-filling effects while bulky TCs experience size exclusions. Furthermore, the effect of matrix components and modifications are also been taken into account.