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.

Sorptive removal of toluene and m-xylene by municipal solid waste biochar: Simultaneous municipal solid waste management and remediation of volatile organic compounds.

The remediation of volatile organic compounds (VOCs) from aqueous solution using Municipal solid waste biochar (MSW-BC) has been evaluated. Municipal solid waste was pyrolyzed in an onsite pyrolyzer around 450 °C with a holding time of 30 min for the production of biochar (BC). Physiochemical properties of BC were assessed based on X-Ray Fluorescence (XRF) and Fourier transform infra-red (FTIR) analysis. Adsorption capacities for the VOCs (m-xylene and toluene) were examined by batch sorption experiments. Analysis indicated high loading of m-xylene and toluene in landfill leachates from different dump sites. The FTIR analysis corroborates with the Boehm titration data whereas XRF data demonstrated negligible amounts of trace metals in MSW-BC to be a potential sorbent. Adsorption isotherm exhibited properties of both Langmuir and Freundlich which is indicative of a non-ideal monolayer adsorption process taking place. Langmuir adsorption capacities were high as 850 and 550 µg/g for toluene and m-xylene respectively. The conversion of MSW to a value added product provided a feasible means of solid waste management. The produced MSW-BC was an economical adsorbent which demonstrated a strong ability for removing VOCs. Hence, MSW-BC can be used as a landfill cover or a permeable reactive barrier material to treat MSW leachate. Thus, the conversion of MSW to BC becomes an environmentally friendly and economical means of solid waste remediation.

Removal of Arsenic(III) from water using magnetite precipitated onto Douglas fir biochar.

Magnetic Fe3O4/Douglas fir biochar composites (MBC) were prepared with a 29.2% wt. Fe3O4 loading and used to treat As(III)-contaminated water. Toxicity of As(III) (inorganic) is significantly greater than As(V) and more difficult to remove from water. Removal efficiency was optimized verses pH, contact time and initial concentration. Column sorption and regeneration were also studied. Adsorption kinetics data best fitted the pseudo second order model (R2 > 0.99). Adsorption was analyzed with three isotherm models at 20, 25 and 40 °C. The Sips isotherm showed the best fit at 25 °C with a 5.49 mg/g adsorption capacity, which is comparable with other adsorbents. MBC gave faster kinetics (~1-1.5 h) at pH 7 and ambient temperature than previous adsorbents. The Gibbs free energy (ΔG) of this spontaneous As(III) adsorption was -35 kJ/mol and ΔH = 70 kJ/mol was endothermic. Experiments were performed on industrial and laboratory wastewater samples in the presence of other co-existing contaminants (pharmaceutical residues, heavy metals ions and oxi-anions). The composite reduced the arsenic concentrations below the WHO's safe limit of 0.2 mg/L for waste water discharge. X-ray photoelectron spectroscopy (XPS) studies found As(III) and less toxic As(V) on Fe3O4 surfaces indicating adsorbed (or adsorbing) As(III) oxidation occurred upon contact with O2 and possibly dissolved Fe(III) or upon drying under oxic conditions. Under anoxic conditions magnetite to maghemite transformation drives the oxidation. A pH-dependent surface chemisorption mechanism was proposed governing adsorption aided by XPS studies vs pH.

Analysis of trace dicyandiamide in stream water using solid phase extraction and liquid chromatography UV spectrometry.

An improved method for trace level quantification of dicyandiamide in stream water has been developed. This method includes sample pretreatment using solid phase extraction. The extraction procedure (including loading, washing, and eluting) used a flow rate of 1.0mL/min, and dicyandiamide was eluted with 20mL of a methanol/acetonitrile mixture (V/V=2:3), followed by pre-concentration using nitrogen evaporation and analysis with high performance liquid chromatography-ultraviolet spectroscopy (HPLC-UV). Sample extraction was carried out using a Waters Sep-Pak AC-2 Cartridge (with activated carbon). Separation was achieved on a ZIC(®)-Hydrophilic Interaction Liquid Chromatography (ZIC-HILIC) (50mm×2.1mm, 3.5µm) chromatography column and quantification was accomplished based on UV absorbance. A reliable linear relationship was obtained for the calibration curve using standard solutions (R(2)>0.999). Recoveries for dicyandiamide ranged from 84.6% to 96.8%, and the relative standard deviations (RSDs, n=3) were below 6.1% with a detection limit of 5.0ng/mL for stream water samples.

Analysis of estrogens in wastewater using solid-phase extraction, QuEChERS cleanup, and liquid chromatography/ tandem mass spectrometry.

We present an improved method for trace level quantification of five estrogens including estriol, estrone, 17alpha-estradiol, 17beta-estradiol, and 17alpha-ethinylestradiol in wastewaters. Our method includes sample preparation using SPE followed by a Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) cleanup step, a derivatization, and LC/MS/MS determination. Sample extraction was carried out using Oasis HLB cartridges and a dispersive solid-phase cleanup pack containing MgSO4 and primary-secondary amine and C18 sorbents. The resulting extract was derivatized with dansyl chloride. Separation was achieved on an Agilent Zorbax Extend C18, Narrow Bore RR 2.1 x 100 mm, 3.5 pm column; quantification was accomplished in the positive ion mode using multiple reaction monitoring. The cleanup method is quick, efficient, inexpensive, and requires only 200 mL of water. Reliable linearities were obtained for all calibration curves (r2 > 0.995). Matrix effects calculated were less than 12% for all analytes, and, hence, matrix matched calibration curves were not needed. The recoveries for the estrogens ranged from 81-103%, with a high repeatability (n = 3, RSD < or = 9%) and low LOQs (0.6-0.9 ng/L). The method was used to analyze effluent and influent wastewaters in Mississippi wastewater treatment plants, but it is broadly applicable for the determination of trace estrogens in any municipal wastewater samples.

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.

Batch and fixed bed sorption of low to moderate concentrations of aqueous per- and poly-fluoroalkyl substances (PFAS) on Douglas fir biochar and its Fe3O4 hybrids.

Per- and poly-fluoroalkyl substances (PFAS) can cause deleterious effects at low concentrations (70 ng/L). Their remediation is challenging. Aqueous µg/L levels of PFOS, PFOS, PFOSA, PFBS, GenX, PFHxS, PFPeA, PFHxA, and PFHpA (abbreviations defined in Table 1) multi-component adsorption (pH dependence, kinetics, isotherms, fixed-bed adsorption, regeneration, complex matrix) was studied on commercial Douglas fir biochar (BC) and its Fe3O4-containing BC. BC is a waste product when syn-gas is produced in a large scale from wet Douglas fir wood fed to gasification at 900-1000 °C and held for 1-20 s. This generates a relatively high surface area (∼700 m2/g) and large pore volume (∼0.25 cm3/g) biochar. Treatment of BC with FeCl3/FeSO4 and NaOH to chemically precipitate Fe3O4 onto BC. BC and its magnetic Fe3O4/BC analogue rapidly adsorbed (20-45 min equilibrium time) significant amounts of PFOS (∼14.6 mg/g) and PFOA (∼652 mg/g) at natural waters' pH range (6-8). Adsorption from µg/L concentrations has produced remediated aqueous PFAS concentrations of ∼50 ng/L or below the detection limits, which is closing in on EPA advisory limits. Column capacities of PFOS were 215.3 mg/g on BC and 51.9 mg/g Fe3O4/BC vs 53.0 mg/g and 21.8 mg/g, respectively, for PFOA. Hydrophobic and electrostatic interactions are thought to drive this sorption. Successful stripping regeneration by methanol was achieved. Thus, hydrophobic Douglas fir biochar produced by fast high temperature pyrolysis and its Fe3O4/BC analogue are adsorbent candidates for PFAS remediation from the dilute PFAS concentrations often found in polluted environments. Small Fe3O4/BC particles can be magnetically removed from batch treatments avoiding filtration.

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.