DOI: 10.57755/9c6w-3868
title: Influence of Biochar Particle Size on Biomethane Production from Glucose

description: <p>The particle size of biochar affects the degradation of biomass during anaerobic digestion. This study investigated the influence of particle sizes (&gt;2.0, 2.0-1.0, 1.0-0.5, 0.5-0.25, 0.25-0.15, 0.15-0.063, and &lt;0.063 mm) of wheat straw biochar (BC), synthesized at 900°C for 1 hour on the biomethane potential (BMP) of glucose under mesophilic condition (37 °C). The results show that course biochars enhanced the biomethane potential of glucose compared to fine-sized ones. The significant breakthrough found was that the reactors doped with a particle size of 1.0-0.5 mm (BC0.5) had the highest cumulative BMP of 247.64 mL·[g-volatile solid (VS)]-1 followed by &gt;2.0 and 2.0-1.0 mm (231.45 and 222.40 mL·(g·VS)-1, respectively). Adding biochar particles smaller than 0.5 mm resulted in significantly (p&lt;0.05) lower BMP values. The particle size also influenced the biomethane production constant rate (k), with BC1.0 having the highest k (0.0083 day-1) compared to BC&lt;0.063 (0.0044 day-1). The biochars BC&gt;0.5 had higher volatile solids (8.18%) than smaller ones. SEM-EDX analysis revealed that BC0.5 exhibits trace elements (Co, Mn, Ni, and Fe) of equal proportions distributed on the surface. The concentrations of heavy metals (Cr, Zn, Pb, Cu, and Cd) are relatively the same among the biochars. Therefore, their inhibitory effect on biomethane production could be neglected. However, BC0.5 also had the highest DFT-specific surface area of 496 m2/g, which could result in the improvement of the kinetics of biomethane production.</p>
description: <h2 style="margin:8pt 0in 4pt;text-align:justify;line-height:1.2;font-family:&#39;calibri light&#39; , sans-serif;color:rgb( 47 , 84 , 150 );font-size:16pt">Materials and Methods</h2>
<h3 style="margin:8pt 0in 4pt;text-align:justify;line-height:1.2;font-family:&#39;arial&#39; , sans-serif;color:rgb( 47 , 84 , 150 );font-size:14pt">Materials</h3>
<p class="MsoNormal" style="margin:0px 0px 11px;line-height:107%;font-size:15px;font-family:&#39;calibri&#39; , sans-serif">In this work, three materials were used, namely wheat straw
    biochar, inoculum from a biogas plant, and glucose. A single carbon-source
    substrate (glucose) was chosen to isolate and examine the specific
    influence of biochar particle size on anaerobic digestion, minimizing variables
    that could obscure the effects of particle size. Wheat straw biochar was
    synthesized at 900 °C for 60 min. The obtained BC was screened using
    sieves available at the laboratory (&gt;2.0, 2.0–1.0, 1.0–0.5, 0.5 –0.25,
    0.25–0.15, 0.15–0.063, and &lt;0.063 mm) and were named BC2.0, BC1.0, BC0.5,
    BC0.25, BC0.15, BC0.063, and BC&lt;0.063, respectively. For the inoculum,
    a quantity of digestate was collected from an existing commercial
    agricultural biogas plant treating food waste and agricultural residues in
    Świdnica, Poland. The digestate underwent filtration to remove solid materials
    and the suspended liquid was set aside in a climatic chamber (Pollab,
    model 140/40, Wilkowice, Poland) at 4 °C for subsequent use as inoculum in the
    anaerobic digestion. Glucose (Geyer, Warsaw, Poland) was used as a substrate in
    the AD experiment. The inoculum has a TS, VS and AC of 92.61, 63.40, and
    36.40%, respectively.<br /><br /></p>

<h3 style="margin:8pt 0in 4pt;text-align:justify;line-height:1.2;font-family:&#39;arial&#39; , sans-serif;color:rgb( 47 , 84 , 150 );font-size:14pt">SEM imaging and elemental analysis (SEM-EDX)</h3>
<p class="MsoNormal" style="margin:0px 0px 11px;line-height:107%;font-size:15px;font-family:&#39;calibri&#39; , sans-serif">The external topography of biochar surfaces was imaged using
    a Zeiss Evo LS15 Scanning Electron Microscope. These analyses were conducted at
    the Electron Microscope Laboratory of the Wrocław University of Environmental
    and Life Sciences. A semi-quantitative elemental analysis of various biochar
    samples was carried out via energy-dispersive X-ray spectrometry (EDX),
    utilizing a Quantax 200 XFlash detector (Bruker, Berlin, Germany), operating at
    20 kV. EDX uses X-rays to excite chemical elements within a material, enabling
    the identification of the elements based on their unique atomic structures,
    which emit characteristic electromagnetic peaks upon excitation. Precautions
    were taken to ensure that the biochar samples were free from contamination by
    pollutants or dust, avoiding any interference from external environmental
    factors. The biochar was affixed to the sample holder using double-sided carbon
    tape, and random regions of each sample were examined. The detected surface
    elements were presented as weight percentages (wt.%). Additionally, elemental
    maps (C, O, Mg, K, Pb, Si, P, Ca, Fe) were generated to characterize the
    spatial distribution of elements on the biochar surface.</p>

<h3 style="margin:8pt 0in 4pt;text-align:justify;line-height:1.2;font-family:&#39;arial&#39; , sans-serif;color:rgb( 47 , 84 , 150 );font-size:14pt">Characterization of the Biochar</h3>
<p class="MsoNormal" style="margin:0px 0px 11px;line-height:107%;font-size:15px;font-family:&#39;calibri&#39; , sans-serif">The major elements C, H, N, and S were measured in
    triplicate using a CHNS analyzer (PerkinElmer, 2400 CHNS/O Series II, Waltham,
    MA, USA). Proximate analysis was done using a thermogravimetric analyzer
    (Mettler Toledo). Volatile matter (VM) was determined by pyrolysis at
    950 °C for 7 min. The ash content (AC) was determined using a muffle
    furnace (Snol 8.1/1100, Utena, Lithuania). The fixed carbon was obtained by
    subtracting the percentage of volatile matter and ash content from 100 <span class="citationintextchar"><span style="color:rgb( 0 , 112 , 192 )">[22]</span></span>. The pH
    values of all samples were measured at a ratio of 1:20 (w/v) in water after
    being shaken for 24 hours at 130 RPM.</p><p class="MsoNormal" style="margin:0px 0px 11px;line-height:107%;font-size:15px;font-family:&#39;calibri&#39; , sans-serif"><br /></p>
<h3 style="margin:8pt 0in 4pt;text-align:justify;line-height:1.2;font-family:&#39;arial&#39; , sans-serif;color:rgb( 47 , 84 , 150 );font-size:14pt">Fourier transform infrared analyses</h3>
<p class="MsoNormal" style="margin:0px 0px 11px;line-height:107%;font-size:15px;font-family:&#39;calibri&#39; , sans-serif">The samples were transported to the Chemical Laboratory of
    Wrocław University of Environmental and Life Sciences, where Attenuated total
    reflection-Fourier transform infrared (ATR-FTIR) analyses were performed using
    the Thermo Scientific Nicolet iZ10 FT-IR spectrometer (a module of Thermo
    Scientific Nicolet iN10 MX microscope equipped with Smart iTX accessory with a
    diamond plate). Each spectrum was the average of 32 scans in the 400<span lang="EN-US">–</span>4000 cm<sup>-1</sup> wavenumber
    range at the 4 cm<sup>-1</sup> spectral resolution.</p><p class="MsoNormal" style="margin:0px 0px 11px;line-height:107%;font-size:15px;font-family:&#39;calibri&#39; , sans-serif"><br /></p>
<h3 style="margin:8pt 0in 4pt;text-align:justify;line-height:1.2;font-family:&#39;arial&#39; , sans-serif;color:rgb( 47 , 84 , 150 );font-size:14pt">Batch Experiment</h3>
<p class="MsoNormal" style="margin:0px 0px 11px;line-height:107%;font-size:15px;font-family:&#39;calibri&#39; , sans-serif"><span lang="EN-US">The AD
        experiment was performed in a</span>n automatic methane potential test system
    (AMPTS) bioprocess control (BPC) (BPC Instruments AB, AMPTS® II, Lund,
    Sweden) <span lang="EN-US">with a working
        volume set to 400 mL. The reactors were incubated and maintained at 37 °C. The
        AD mixture comprised 250 mL digestate, 3.0 g glucose, and 150 mL nutrient
        solution. The inoculum-to-substrate ratio (ISR) by volatile solids
        was  2.0. Experimental reactors received BC at 8.0 g</span>·L<sup>-1</sup>. <span lang="EN-US">The control reactor did not receive
        biochar and glucose and was labeled as C. The 150 mL nutrient solution
        contained (per liter) 0.2 g MgCl<sub>2</sub>·6H<sub>2</sub>O, 1.0 g NH<sub>4</sub>Cl,
        0.1 g CaCl<sub>2</sub>, 0.2 g Na<sub>2</sub>S·9H<sub>2</sub>O, 2.77 g K<sub>2</sub>HPO<sub>4</sub>,
        2.8 g KH<sub>2</sub>PO<sub>4</sub>, 0.1 g yeast extract, 5 mL trace element
        solution, and 2.0 mL vitamin solution. The composition of trace element
        solution (per liter) was 1000 mg Na2-EDTA·2H<sub>2</sub>O, 300 mg CoCl<sub>4</sub>,
        200 mg MnCl<sub>2</sub>·4H<sub>2</sub>O, 200 mg FeSO<sub>4</sub>·7H<sub>2</sub>O,
        200 mg ZnCl<sub>2</sub>, 80 mg AlCl<sub>3</sub>·6H<sub>2</sub>O, 60 mg NaWo<sub>4</sub>·2H<sub>2</sub>O,
        40 mg CuCl<sub>2</sub>·2H<sub>2</sub>O, 40 mg NiSO<sub>4</sub>·6H<sub>2</sub>O,
        20 mg H<sub>2</sub>SeO<sub>4</sub>, 200 mg HBO<sub>3</sub> and 200 mg
        NaMoO<sub>4</sub>·2H<sub>2</sub>O. Vitamin solution consisted of (per liter) 10
        mg biotin, 50 mg Pyridoxin HCl, 25 mg Thiamine HCl, 25 mg D-Calcium
        pantothenate, 10 mg Folic acid, 25 mg Riboflavin, 25 mg Nicotinic acid, 25 mg
        P-aminobenzoic acid and 0.5 mg vitamin B1. In addition to biogas production,
        the total volatile fatty acids (TVFA), FOS/TAC ratio (FOS is the volatile
        organic acids content and TAC is the buffer capacity), and pH were measured.
        The measurements took place on days 1, 3, 5, 7, 14 and 20.<br /><br /></span></p>
<h3 style="margin:8pt 0in 4pt;text-align:justify;line-height:1.2;font-family:&#39;arial&#39; , sans-serif;color:rgb( 47 , 84 , 150 );font-size:14pt">Low-temperature N<sub>2</sub> Adsorption</h3>
<p class="MsoNormal" style="margin:0px 0px 11px;line-height:107%;font-size:15px">The BET surface area was determined via Low-Temperature
    Nitrogen Adsorption Isotherms. The isotherms were measured at 77.5 K using
    the Autosorp iQ gas adsorption apparatus (Quantachrome, USA). Before each
    measurement, the carbon samples were desorbed in a vacuum (below 10<sup>–3</sup> Pa)
    at 393 K for 12 h.</p>