# Evaluation of biochar amendments to retain organic compounds in soil

A Hmaied, A Ben Hassen Trabelsi, Claude Hammecker

► To cite this version:

A Hmaied, A Ben Hassen Trabelsi, Claude Hammecker. Evaluation of biochar amendments to retain organic compounds in soil. International Conference on the Impacts of Soil Amendments on Dryland Agro-Ecosystems (ISADAE-2024), Oct 2024, Reims, France. pp.012005, 10.1088/1755-1315/1455/1/012005 . ird-04965384

HAL Id: ird-04965384

https://ird.hal.science/ird-04965384v1

Submitted on 25 Feb 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

PAPER • OPEN ACCESS

# Evaluation of biochar amendments to retain organic compounds in soil

To cite this article: A Hmaied et al 2025 IOP Conf. Ser.: Earth Environ. Sci. 1455 012005

View the article online for updates and enhancements.

You may also like

- *Effect of organic amendments based on date palm residues on barley crop (Hordeum vulgare L.) in an oasian environment: case of the Oued Righ region, Algeria.*
  A Tirichine, A Abid, L Hafouda et al.

- *Biochar amendment decreases soil microbial biomass and increases bacterial diversity in Moso bamboo (Phyllostachys edulis) plantations under simulated nitrogen deposition*
  Quan Li, Zhaofeng Lei, Xinzhang Song et al.

- *Effect of biochar addition on soil properties and durum wheat production in Northeast of Algeria*
  Z Bounouara, R Negrach, S Larit et al.

UNITED THROUGH SCIENCE & TECHNOLOGY

<figure><img src="image_3.png" /></figure>

The Electrochemical Society
Advancing solid state & electrochemical science & technology

248th
ECS Meeting
Chicago, IL
October 12-16, 2025
Hilton Chicago

<figure><img src="image_4.png" /></figure>

Science +
Technology +
YOU!

SUBMIT
ABSTRACTS by
March 28, 2025

SUBMIT NOW
# Evaluation of biochar amendments to retain organic compounds in soil

A Hmaied<sup>1,2,3</sup>, A Ben Hassen Trabelsi<sup>2</sup> and C Hammecker<sup>1</sup>

<sup>1</sup> LISAH, Univ Montpellier, INRAE, IRD, Institut Agro Montpellier, Montpellier, France

<sup>2</sup> Laboratory of Wind Energy Management and Waste Energy Recovery (LMEEVED), Centre of Energy Research and Technology (CRTEen), B.P. 95, Hammam-Lif 2050, Tunisia

<sup>3</sup> Faculty of Sciences of Tunis, Tunis El Manar University, Campus Universitaire El-Manar, 2092 El Manar, Tunisia

E-mail: asma.hmaied@ird.fr

**Abstract.** The use of biochar is frequently recommended as a low-cost mitigation strategy. Biochar can be easily and inexpensively produced from various agricultural residues. In this study, we produced and evaluated the impact of biochar derived from rosemary, bamboo, St. John's wort, olive tree wood, cypress, and palm trees on the mobility and retention of emerging contaminants. The initial stage of this work involved the evaluation of the potential retention capacity of various biochars produced in a low-cost metallic kiln using local biomass residues. Methylene blue was used as a proxy for organic contaminants to establish adsorption isotherms and quantify the biochars' specific surface area and adsorption capacities. Adsorption isotherms at 20°C were fitted to different models to assess their specific surface areas.

The results showed that biochars derived from rosemary, giant reed, and St. John's wort exhibited significant adsorption capacities. Average adsorption capacities for cypress and olive tree were observed, while traditional olive and palm trees showed low adsorption capacities.

In the second stage, we evaluated the dynamic retention properties of biochar using soil monolith experiments. We analyse methylene blue (MB) elution curves with and without biochar addition. The presence of biochar in the soil monoliths significantly improved the retention of MB, demonstrating its effectiveness as an adsorbent filter. Specifically, biochar-amended soil monoliths exhibited an increase in MB retention compared to unamended controls. The breakthrough curves showed a delay in the elution of MB of 2,33 pore volumes in biochar-amended monolith increase in sorption capacity. Furthermore, the total recovered MB in the effluent was reduced by 66 % in biochar-treated samples. These quantitative findings underscore the robust potential of biochar for improving water quality by mitigating pollutant transport through the soil. The results suggest that the application of biochar could serve as an effective strategy to reduce agricultural runoff contamination in vulnerable watersheds.

Keyword: Biochar; pyrolysis; specific surface area; methylene blue; isotherm of adsorption

## 1. Introduction

Environmental pollution, which includes soil, air and water contamination, remains a pressing issue due to the ongoing intensive production systems in agriculture that lead to the excessive use of agricultural contaminants such as pesticides and fertilizers [1, 2], all of which can cause significant environmental harm [3]. Water pollution, in particular, poses serious risks to the environment and the quality of life [4].

<figure><img src="image_5.png" /></figure>

Content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
The management of crop residues presents significant challenges in the agricultural sector. When not used for purposes such as livestock feed, crop residues are often burned or left in fields to decompose naturally. These practices contribute to environmental problems, particularly increased Greenhouse Gas Emissions (GHG)[5, 6, 7, 8]. Burning crop residues releases carbon dioxide, methane, and other pollutants directly into the atmosphere, exacerbating climate change and air quality issues. Alternatively, allowing residues to decompose in fields can result in methane emissions, especially under waterlogged conditions, and can lead to nitrous oxide release during the decomposition process. However, the conversion of agricultural residues into biochar offers a promising and environmentally friendly alternative [9, 10, 11]. This technique not only mitigates the negative impacts associated with traditional residue management, but also provides additional benefits such as improving soil health, enhancing crop productivity, and sequestering carbon, making it a multifaceted solution for sustainable agriculture.

Biochar is a form of charcoal produced through the pyrolysis of organic materials, which involves the thermal decomposition of organic matter, at temperatures ranging from 300 to 700°C in the absence or near absence of oxygen. This product has gained significant interest in recent years due to its potential environmental and agricultural benefits [12, 13, 14].

The physicochemical properties of biochar, including high porosity, large surface area, and abundant functional groups, allow it to act as an effective soil amendment [15]. It has been shown to improve soil structure, water retention, and nutrient availability, thus improving plant growth and resilience [16]. In addition, biochar's ability to absorb contaminants such as pesticides and retain nutrients reduces leaching and runoff, contributing to reducing water pollution [17]. When applied to soil, biochar can stabilise carbon for centuries, thus acting as a long-term carbon sink [18], positioning biochar as a crucial tool in mitigating climate change by reducing atmospheric carbon dioxide levels. In this study, our objective was to evaluate the effectiveness of various types of biomass, readily available in Mediterranean countries like Tunisia, in retaining contaminants in agricultural environments.

## 2. Materials and methods

### 2.1. Biochar production

Biochar was produced from the branches and leaves of six distinct biomass sources: Rosemary (Salvia rosmarinus), Giant Reed (Arundo donax), Cypress (Cupressus), Mexican fan palm tree (Washingtonia Robusta), Olive tree (Olea europea), St John's Wort (Hypericum perforatum). These biomass materials were pyrolyzed in a custom-built metal kiln. The kiln temperature was monitored with type K thermocouple and recorded to range between 700°C and 900°C during the pyrolysis process. In addition to these laboratory-produced biochars, we also tested traditionally produced olive tree charcoal for comparison.

### 2.2. Methylene blue adsorption and specific surface area (SSA)

To evaluate the specific surface area (SSA) of the biochar, the methylene blue adsorption method was employed [19, 20, 21]. A batch experiment was conducted to establish the adsorption isotherm of methylene blue onto the biochar. Adsorption was carried out until the maximum plateau value $Q_m$ was reached, corresponding to the monolayer adsorption of methylene blue that covers the entire surface of the biochar. The resulting data were analysed using both Freundlich and Langmuir isotherm models, and key constants were determined by plotting the data accordingly using (Eq1.) and (Eq2.). Finally, we used the maximum adsorption capacity ($Q_m$) obtained from the Langmuir isotherm to calculate the specific surface area (Eq3.), taking into account the area occupied by a mole blue methylene molecule.

$$Q_e = K_f \times C_e^n \qquad (1)$$
where $Q_e$ is the amount adsorbed per unit mass of adsorbent, $C_e$ is the equilibrium concentration of adsorbate, $K_f$ and n are Freundlich constants.

$$Q_e = \frac{K_l \cdot C_e \cdot Q_m}{1 + K_l \cdot C_e} \qquad (2)$$

where $Q_e$ is the amount adsorbed per unit mass of adsorbent, $K_l$ is Langmuir constant, $Q_m$ is the maximum adsorption capacity

$$SSA = \frac{Q_m}{M_{MB} \cdot m_b} \cdot A_{MB} = \frac{Q_m}{m_b} \times 2447.64 \qquad (3)$$

where $M_{MB}$ is the molar weight of methylene blue (319.85 g/mol), $m_b$ the weight of biochar and $A_{MB}$ the molar surface area for methylene blue (782878 m²/mol).

## 2.3. Soil column experiment

To develop a conceptual model explaining the effects of biochar on the hydrodynamic properties of the soil, we performed a series of well-constrained laboratory experiments using a sandy soil monolith matrix to test the impact of biochar on the retention of methylene blue [22, 23]. The experiments were carried out using soil monoliths with dimensions of 20 cm in height and 10 cm in diameter. The water flow was maintained at a constant rate of 0.72 cm/min with a peristaltic pump and the outflow was collected in a vessel placed directly on a balance. An aliquot for analysis was sampled every 10 minutes. We evaluated breakthrough curves for methylene blue under two conditions: (i) a control monolith containing only soil and (ii) a composite monolith with 1% of biochar showing the highest SSA, distributed homogeneously within the soil column. This setup allowed us to compare the retention and transport of methylene blue in soil with and without the influence of biochar.

# 3. Results

## 3.1. Specific Surface Area

The results indicate that the highest adsorption capacity was observed for rosemary biochar, followed by Giant Reed and St. John's Wort biochar. In the lower end, palm biochar and traditional olive tree charcoal exhibited significantly lower adsorption capacities. The Freundlich isotherm provided a better fit to the experimental data compared to the Langmuir isotherm.

The specific surface area (SSA), calculated from the maximum methylene blue adsorption using equation 3, revealed that Rosemary biochar had the highest SSA at 62.14 m²/g, while palm tree biochar had the lowest at 6.85 m²/g (Table 1). Based on these findings, rosemary biochar, with the highest SSA, was selected for use in the dynamic soil monolith experiment.

## 3.2. Breakthrough curves

In the soil column treated with Rosemary biochar, which had a higher specific surface area, there was a marked increase in the retention of MB molecules, as evidenced by a reduced concentration in the effluent compared to the control. Rosemary biochar adsorbed 81% of the initial amount of MB used in the column, while soil only retained 45% (Figure 1). The biochar-amended column also exhibited slower breakthrough times for the solute, indicating enhanced adsorption and delayed release into the effluent.

In contrast, soil columns without biochar amendment displayed faster solute transport and a lower degree of adsorption, suggesting that the addition of biochar played a crucial role in altering the movement and availability of the solutes within the soil matrix. These observations were consistent across multiple experimental runs, further underscoring the impact of biochar
<table><caption>**Table 1.** Freundlich and Langmuir adsorption parameters with corresponding correlation coefficients (r²) and specific surface area (SSA) of the different biochars. K_L is expressed in l/kg and Q_m in mg/g.</caption><thead><tr><th rowspan="2">Biochar</th><th colspan="3">FREUNDLICH</th><th colspan="3">LANGMUIR</th><th>SSA</th></tr><tr><th>K<sub>f</sub></th><th>n</th><th>r<sup>2</sup></th><th>K<sub>l</sub></th><th>Q<sub>m</sub></th><th>r<sup>2</sup></th><th>m<sup>2</sup>/g</th></tr></thead><tbody><tr><td>Rosemary</td><td>6.15</td><td>4.51</td><td>0.97</td><td>0.01</td><td>27.93</td><td>0.85</td><td>62.14</td></tr><tr><td>Palm tree</td><td>1.48</td><td>3.12</td><td>0.98</td><td>0.82</td><td>3.05</td><td>0.95</td><td>6.85</td></tr><tr><td>Olive tree</td><td>2.67</td><td>4.99</td><td>0.87</td><td>0.77</td><td>1.98</td><td>0.85</td><td>12.83</td></tr><tr><td>Giant Reed</td><td>2.76</td><td>2.12</td><td>0.81</td><td>0.2</td><td>12.32</td><td>0.83</td><td>47.97</td></tr><tr><td>Cypress</td><td>2.68</td><td>5.00</td><td>0.84</td><td>1.66</td><td>1.94</td><td>0.43</td><td>10.91</td></tr><tr><td>St.John Wort</td><td>3.63</td><td>3.18</td><td>0.82</td><td>1.38</td><td>17.09</td><td>0.93</td><td>45.20</td></tr><tr><td>Trad Olive tree</td><td>7.74</td><td>2.13</td><td>0.797</td><td>0.25</td><td>3.43</td><td>0.75</td><td>7.28</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>**Figure 1.** Breakthrough curves for monolith with soil representing the Methylene Blue concentration (C) versus the number of pore volumes (V_p = constant flow × time/porosity).</figcaption></figure>

on soil-solution interactions. The presence of biochar appears to influence the interaction of the solution with the column [24] promoting biochar's role in improving water retention and reducing contaminant mobility [25], thereby modifying its behaviour and distribution within the environment.

## 4. Conclusion

Among the various types of biochar evaluated, in addition to the pyrolysis conditions, supposed to be equivalent for all the types of biochar, the feedstock source proved critical. Biochar derived from non-wooden biomass consistently exhibited the highest specific surface area (SSA) and adsorption capacities. In particular, rosemary biochar, which showed the highest SSA, significantly increased the retention of methylene blue (MB) in soil monoliths and notably altered
solution-soil interactions in column experiments. By enhancing solute retention and adsorption, biochar demonstrated its potential as a soil amendment to improve contaminant capture, reduce nutrient leaching, and increase soil water retention.

These findings underscore the importance of further research into how different types of biochar and soil conditions can optimize these benefits, especially for environmental remediation and sustainable agriculture applications.

## Acknowledgments

The authors gratefully acknowledge the financial support provided by LMI-NAILA project and a special thanks to IRD Tunis for their technical support.

## References

[1] Biao, S., Guangmin, Z., Jilai, G., Jie, L., Piao, X., Zhifeng, L., Yi, Z., Chen, Z., Min, C., Yang, L., Shujing, Y., Huan, Y., Xiaoya, R. (2017). Evaluation methods for assessing effectiveness of in situ remediation of soil and sediment contaminated with organic pollutants and heavy metals. Environment International, Volume 105, 43-55, 0160-4120.

[2] Hanyan, Z., Xingzhong, Y., Ting, X., Hou, W., Longbo, J. (2020). Bioremediation of co-contaminated soil with heavy metals and pesticides: Influence factors, mechanisms and evaluation methods. Chemical Engineering Journal, Volume 398, 125657, ISSN 1385-8947.

[3] Jeong, H., Choi, J. Y., Lee, J., Lim, J., and Ra, K. (2020). Heavy metal pollution by road-deposited sediments and its contribution to total suspended solids in rainfall runoff from intensive industrial areas. Environmental Pollution, 265, 115028.

[4] Li, X., et al. (2021). Rapid monitoring of heavy metal pollution in lake water using nitrogen and phosphorus nutrients and physicochemical indicators by support vector machine. Chemosphere, 280, 130599.

[5] Lal, R. (2005). World crop residues production and implications of its use as a biofuel. Environment International, 31(4), 575-584.

[6] Verma, S. K., and Dhaliwal, H. S. (2016). Crop Residue Burning: Consequences and Challenges for Sustainable Environment. Journal of Soil and Water Conservation, 15(4), 302-309.

[7] Yadav, M. P., and Pandey, K. P. (2019). Impact of crop residue burning on climate change: a review. International Journal of Chemical Studies, 7(1), 131-137.

[8] Sharma, S., Jain, S., Khare, M., and Sharma, P. (2019). Seasonal variability of air pollutants and their source apportionment using PMF: A four-year study in Delhi, India. Environmental Pollution, 248, 704-715.

[9] Qambrani, N. A., Rahman, M. M., Won, S., Shim, S., and Ra, C. S. (2017). Biochar properties and eco-friendly applications for climate change mitigation, waste management, and wastewater treatment: A review. Renewable and Sustainable Energy Reviews, 79, 255-273.

[10] Kumar, A., Singh, E., and Kumar, S. (2020). Biochar: A sustainable solution for crop residue management and climate change mitigation. In Biochar: Applications in Agriculture and Environment (pp. 41-62).

[11] Zhang, J., Zhang, L., Zhang, Q., Zhu, Z., Liu, J., and Tan, W. (2022). Biochar enhances soil quality and microbial activity in tea plantations with an effective reduction in carbon emissions. Journal of Cleaner Production, 367, 133029.

[12] Jones, S., Lu, Y., Pantaleo, A., and Wang, Z. (2023). Biochar for carbon sequestration and climate mitigation: A global perspective. Renewable and Sustainable Energy Reviews, 171, 113022.

[13] Liu, Z., and Sohi, S. (2022). Long-term effects of biochar amendments on carbon and nitrogen cycles in soil. Science of the Total Environment, 846, 157248.

[14] Gamage, K. A. A., Zhang, L., and Soomro, A. (2023). Biochar in soil-water-carbon nexus: A critical review of recent advances and opportunities. Environmental Science and Technology, 57(8), 3412-3427.

[15] Xu, X., He, Y., and Xing, B. (2023). Influence of biochar on soil carbon stabilization and environmental pollutant adsorption: A review of mechanisms. Journal of Environmental Management, 339, 117922.

[16] Chen, W., Li, Z., and Zhao, C. (2022). Enhancing water retention and nutrient availability in arid soils using biochar amendments. Agricultural Water Management, 272, 107851.

[17] Lehmann, J., Joseph, S., and Amonette, J. E. (2023). The role of biochar in mitigating climate change: Soil carbon stabilization and reduction in water pollution. Nature Sustainability, 6(2), 134-145.

[18] Hale, S. E., and Arp, H. P. H. (2022). Mechanisms of nutrient and contaminant retention in biochar-amended soils: Implications for soil health and water quality. Science of the Total Environment, 841, 156707.

[19] Deng, Y., Li, X., and Liu, X. (2022). Characterization of clay minerals using the methylene blue adsorption method: Insights into surface properties and applications. Applied Clay Science, 227, 106537.
[20] Zhang, H., Liu, X., and Wang, Y. (2022). Comparative study on the adsorption of methylene blue by biochars from different feedstocks: Role of surface functional groups and pore structure. Bioresource Technology, 344, 126200.

[21] Tang, L., Yu, J., and Pang, Y. (2023). "Methylene blue adsorption on biochar derived from agricultural waste: A comprehensive study of adsorption mechanisms and environmental applications. Journal of Environmental Chemical Engineering, 11(2), 109012.

[22] Sun, L., Liu, C., and Chen, Z. (2022). Effects of biochar on contaminant transport and solution-soil interactions in column studies: A review. Journal of Soils and Sediments, 22(4), 1291-1304.

[23] Wang, J., and Zheng, M. (2023). Biochar-enhanced retention of heavy metals and nutrient leaching in soil column experiments. Environmental Science and Technology, 57(3), 2082-2090.

[24] Li, Y., Jin, Y., and Wei, Y. (2022). The impact of biochar on the interaction of water and solutes within soil columns: A mechanistic study. Environmental Pollution, 306, 119433.

[25] Trazzi, P. A., Bonetti, J. A., and Santos, A. (2023). Column leaching studies on biochar-amended soils: Implications for nutrient retention and contaminant migration. Chemosphere, 318, 137783.