Recipient Organization
AUBURN UNIVERSITY
108 M. WHITE SMITH HALL
AUBURN,AL 36849
Performing Department
Biosystems Engineering
Non Technical Summary
Biochar is one of the by-products generated during fast pyrolysis of lignocellulosic biomass residues. Due to the porous structure, large specific surface area, good biological and chemical stability, there is a growing interest in utilizing biochar for environmental applications such as soil amendment and heavy metals remediation. Presence of carbonyl, carboxylic, and hydroxyl functional groups at its surface defines chemical property of biochar. Oxygenated functional groups, for example, at the surface are known to enhance the cation exchange capacity (CEC) and change the surface charge of biochar. In addition, biochar could play an important role in reductive transformation of organic contaminants by facilitating the electron transfer between electron donors and receiving organic compounds. Redox active structures in biochar, namely the quinone-hydroquinone moieties and the conjugated pi-electron system associated with the condensed aromatic structures of the biochar, are known to participate in electron transfer mechanism.It is postulated that biochar can function as a bio-catalyst during anaerobic digestion process by facilitating the electron transfer between the fermentative bacteria and the methanogenic archaea. Preliminary experiments conducted in our laboratory using different organic substrates have shown that biochar considerably reduced the lag time and increased methane (CH4) yield in comparison to no-biochar added (control) cultures. Further, the performance of biochar was found to vary with respect to pyrolysis temperature, and biochar produced at intermediate pyrolysis temperatures (400 °C to 600 °C) showed higher CH4 yields in comparison to biochars produced at high temperatures (> 600 °C). The reason for this has been attributed to the absence of surface functional groups at higher pyrolysis temperatures.Hence, the overall goal of this project is to investigate whether surface modification of biochar could possibly induce certain functional groups such as acidic/oxygenated groups which could then be tailored for a number of environmental applications such as sorption of heavy metals commonly found in environment (such as road run-off and landfill leachate) and herbicides (glyphosate) in agricultural run-off/surface water. The specific objectives of this proposed work include the following: Objective 1- Perform surface modification of woody biochar (loblolly pine) collected at various pyrolysis temperatures (300 °C to 800 °C) using chemical modification and air oxidation methods and characterize the surface properties of biochar; Objective 2- Evaluate the performance of surface modified biochar during anaerobic digestion process; Objective 3- Evaluate the sorption abilities of modified biochars towards model heavy metals such as Pb, As, Zn, Ni, Cd; Objective 4- Evaluate the sorption abilities of modified biochar towards model herbicide such as glyphosate. The proposed work will be performed in the Biosystems Engineering by the PI (Dr. Adhikari) and two of his Post-docs who have distinct but complementary expertise. The data generated from this study will be leveraged to develop competitive research proposals to external agencies.
Animal Health Component
20%
Research Effort Categories
Basic
50%
Applied
20%
Developmental
30%
Goals / Objectives
The overall objective of this study is to perform surface-modification of biochar and evaluate its role as a biocatalyst during anaerobic digestion (AD) and remediation agent during sorption of model heavy metals and herbicides. The specific objectives are as follows: (i) Perform surface modification of loblolly pinewood biochar collected at different pyrolysis temperatures (300 °C to 800 °C) using air oxidation and chemical methods and to characterize the surface properties of biochar; (ii) Evaluate the performance of surface modified biochar during AD of simple (glucose) and complex organic wastes (aqueous phase of bio-oil generated during thermochemical conversion process of biomass such as pyrolysis and hydrothermal liquefaction); (iii) Evaluate the sorption abilities of modified biochars towards heavy metals such as Pb, As, Zn, Ni and Cd; and (iv) Evaluate the sorption abilities of modified biochars towards herbicide such as glyphosate. The objectives of this research are designed to address the following research questions: (i) Does surface-modified biochars show better surface properties such as high cation exchange capacity (CEC), surface functional charges (zeta potential), pH, surface area, pore volume and functional groups compared to no-surface modified biochars collected at various pyrolysis temperatures?; (ii) Does the chemical activation of biochars function as better biocatalyst during AD compared to air oxidation of biochar?; (iii) Does application of surface modified biochar selectively enrich specific type of bacterial and archaeal (methanogenic) populations during AD?; (iv) Does the surface modification of biochar increase the sorption ability of heavy metals compared to un-modified biochar?; (v) Does the sorption of glyphosate (herbicide) enhanced by using surface-modified biochar?. Tailoring biochar towards specific application could improve the overall economics of forest-based bio-refinery. The major outcome of this research will be at the fundamental and applied level that can be used to produce biochar from other types of lignocellulosic biomass wastes for a number of environmental applications. This study will be performed in Biosystems Engineering Department, and Dr. Adhikari, Associate Professor in Biosystems Engineering, has more than nine years of experience working with thermochemical conversion of biomass into bio-oil production, upgrading, and biochar characterization. Dr. Shanmugam, a Post-doctoral fellow and Co-PI in this project, has more than six years of experience in working on biogas production from waste streams. Dr. Hyungseok Nam, a Post-doctoral fellow and Co-PI, has more than five years of experience in thermochemical conversion process such as pyrolysis at both lab- and pilot scales. This research team has right expertise and equipment to work on the proposed project.
Project Methods
Objective 1: Surface modification of loblolly pinewood biochar produced at different fast pyrolysis (FP) temperatures. The working hypothesis of this objective is that surface modified biochar will enhance/modify the surface oxygenated/functional groups in high temperature biochars, which could be then tailored for a variety of applications. Fast pyrolysis of loblolly pinewood at six different temperatureswill be conducted in a fluidized bed reactor as described in the published document. Pinewood chips collected locally will be size-reduced and sieved before FP. Detailed characterization (ultimate and proximate analyses) of pinewood biomass will be performed prior to FP. Biochar collected at end of each experimental run will be stored in air-tight container at 4 °C. Surface modifications of biochar will be performed using both air oxidation and chemical agents. Air oxidation of biochar will be performed as outlined in a published document. Chemical surface modification of biochar using reagents sulfuric acid (H2SO4), phosphoric acid (H3PO4), potassium hydroxide (KOH), nitric acid (HNO3), and ammonium hydroxide (NH4OH) will be performed as outlined in a published document. Treatment with different chemicals result in different types of surface modification. For example, increased level of carboxylic groups were observed in biochar modified using H3PO4 treatment of forestry wood waste. Also, treatment with NH4OH resulted in an increase of phenolic groups compared to unmodified biochar. Similarly, increased levels of oxygenated functional groups were observed with air modification of biochars. Both surface-modified biochars and un-modified (control) biochar will be characterized for the following - elemental analysis (used to calculate atomic H/C, O/C, C/N ratios which are indicative of bonding arrangement and polarity), proximate analysis, gas physisorption analysis (N2 and CO2 adsorption isotherms using BET surface area and porosity analyzer), cation exchange capacity (CEC), pH, electrical conductivity (EC), zeta potential, X-ray photoelectron spectroscopy (XPS) analysis (to quantify the surface functional groups) and Boehm titration (to measure the surface acidic groups) according to the procedure detailed in published document. Additionally, ICP-OES analysis, FT-IR analysis, and scanning electron microscopy (SEM) analysis will be performed for all biochars investigated in this study. Data collected in this study will be helpful in addressing whether the surface modification of biochars result in enhancement of surface functional groups and other properties compared to un-modified biochars. Objective 2: Effect of surface modified biochar as biocatalysts during anaerobic digestion (AD) of organic wastes. The working hypothesis of this objective is that redox active moieties such as quinone and phenolic groups reduce the lag time during AD and enhance biogas (CH4) yields. These surface functional groups are known to participate in redox reactions by serving as electron acceptor/donor and facilitate the electron transfer between the fermentative bacteria and methanogenic archaea. A selected number of surface modified biochars from Objective 1 will be used for AD of simple (glucose) and complex (aqueous phase of bio-oil (BOAP) generated during thermochemical conversion process) organic wastes. AD of organics will be performed using mixed anaerobic microbial cultures as discussed elsewhere. The biogas (CH4, CO2) produced will be analyzed using a SRI-GC equipped with a TCD. Initial and final COD of organic wastes will be performed to understand its degradability following different types of biochar addition. Microbial community analysis will be performed on samples, which result in good biogas production. DNA extraction will be conducted using the MoBio PowerSoil DNA extraction kit (MoBio Laboratories, Solana Beach, CA, USA) according to the protocol provided by the supplier. The extracted DNA was then immediately stored at -20 °C until further used. DNA samples will be shipped for community characterization to molecular research (MR DNA) laboratory (Shallowater, TX, USA). This task will help to address the following research questions: Does surface modification using chemical agents show better biogas yields in comparison to air oxidized and un-modified biochar? Does the bacterial and archaeal (methanogenic populations) compositions vary with different type of surface modifications?Objective 3: Evaluation of surface-modified biochar on sorption of heavy metals. The working hypothesis of this objective is that cation exchange capacity (CEC) and surface area of biochar are highly correlated with the amount of heavy metals that can be absorbed. A selected number surface-modified biochars based on CEC and surface area from Objective 1 will be used to sorb heavy metals such as Zn, Pb, As, Ni and Cd, which are common in landfill leachate and road run-off. Previous study in literature has shown that air oxidation of biochars increased the CEC of woody biochars. Heavy metals (> 97.0 - 99.0 % purity) will be obtained from Sigma Aldrich. Background metal composition of biochar used in this study will be analyzed using inductively coupled plasma (ICP-OES) analysis following nitric acid digestion. Stock solutions of heavy metals (Zn, Pb, As, Ni and Cd) will be prepared in de-ionized water and the concentrations of stock solutions will be confirmed using ICP analysis before performing the sorption experiments. The effect of various process parameters such as pH (3.0 - 7.0), contact time (0 - 480 min), initial concentration of adsorbate (heavy metals) (25-300 mg/L), adsorbent dosage (surface-modified and un-modified biochar concentration) (100 mg per 25 mL metal solution) and temperature (25 °C) will be investigated in this study. pH at the start of this experiment will be adjusted using dilute HCl or NaOH. Experimental vials will be placed in a temperature controlled orbital shaker rotating at 200 rpm. Adsorbent dosage was determined from previously published study in literature using activated carbon. Batch sorption experiments will be conducted in a 40 mL glass vials in triplicates. Statistical comparison will be made on the removal efficiencies using Tukey's pair wise comparison procedure at 95 % confidence interval. Sorption isotherm models such as Freundlich and, Langmuir isotherm model fits will be used to describe the sorption of heavy metals by surface-modified biochar. This task will help identifying suitable biochar for specific heavy metal removal.Objective 4: Evaluation of surface-modified biochars on sorption of model herbicide. The working hypothesis of this objective is that surface-modification of biochar will result in enhancement/introduction of surface functional charges, which could then be used to sorb herbicide such as glyphosate which is amphoteric in nature. Surface-modified biochar from Objective 1 will be selected to sorb glyphosate (model herbicide). Analytical grade of herbicide glyphosate (N-(phosphonomethyl) glycine) will be purchased from Sigma Aldrich (96 % purity). Batch sorption tests will be conducted in 160 mL serum bottles capped with a rubber septa and an aluminum cap in triplicates. Varying levels of glyphosate ranging between 5 to 100 mg/L will be added to 200 mg of surface modified and un-modified biochar. The resulting mix is shaken using an orbital shaker, set at 200 rpm at 25 °C. The effect of solution pH (between 2.0 to 8.0) will be investigated in this study. Dilute HCl and NaOH solutions will be used for pH adjustment in this study. Measurement of residual solution of glyphosate will be performed according to the methods mentioned in literature. pH at point of zero charge (pHpzc) will be measured for the adsorbents according to the methods outlined in literature. This task will help in the development of suitable biochar for biocide sorption applications.