Phosphoric Acid Activation of Municipal Solid Waste-Derived Biochar: How Concentration Changes Proximate Characteristics

Municipal solid waste contains fractions that can be converted into carbonaceous materials, but the effect of chemical activation conditions depends on feedstock and processing parameters. This study examines how nominal phosphoric acid concentrations of 20%, 25%, and 30% affect the proximate characteristics of biochar produced from banana peel, orange peel, and coconut husk. The authors maintain controlled pyrolysis and activation conditions and evaluate moisture, ash, volatile matter, and fixed carbon using measurements and statistical tests. The findings show that acid concentration significantly affects volatile matter and fixed carbon, while moisture and ash differences among activated treatments are not statistically significant.

Bibliographic Information

Item	Information
Article Title	Effect of phosphoric acid activation concentration on the proximate characteristics of municipal solid waste-derived biochar
Authors	Shofwatunnida Septarini; Apip Amrullah; Cindy Aisyah Hakim
Journal	Innovation in Engineering
Volume	3
Issue	2
Publication Year	2026
Pages	169-181
DOI	https://doi.org/10.58712/ie.v3i2.51
Publisher	Researcher and Lecturer Society
License	Creative Commons Attribution 4.0 International License
ISSN	E-ISSN: 3047-5473
Keywords	adsorbent precursor; chemical activation; fixed carbon; pyrolysis; waste valorization
Published	2026-09-26
Official Article Webpage	https://ie.rlsociety.org/index.php/ie/article/view/51

Highlights

Defined mixed-waste precursor: banana peel, orange peel, and coconut husk were combined at a mass ratio of 50:30:20.
Controlled pyrolysis: the feedstock was pyrolyzed at 250 °C for 3 h.
Three activation levels: nominal H₃PO₄ concentrations of 20%, 25%, and 30% were investigated.
Volatile matter response: mean volatile matter decreased progressively as H₃PO₄ concentration increased.
Fixed carbon response: mean fixed carbon increased from 83.74% at 20% H₃PO₄ to 84.68% at 30%.
Statistical distinction: volatile matter showed a significant treatment effect, whereas ash and moisture did not differ significantly among activated treatments.
No optimum established: proximate characteristics alone were insufficient to determine an optimum activation concentration.

Research Background

The article addresses the conversion of the organic fraction of municipal solid waste into carbonaceous materials through pyrolysis and subsequent chemical activation. The authors emphasize that waste-derived biochar can exhibit different physicochemical characteristics depending on feedstock composition and processing conditions. This issue becomes particularly relevant when heterogeneous household organic waste is used instead of a relatively uniform biomass precursor.

The study focuses on phosphoric acid (H₃PO₄) activation because acid concentration can influence dehydration, condensation, cross-linking, structural rearrangement, and pore development. The manuscript also recognizes that increasing activation severity does not necessarily produce proportional improvements in all material properties. Consequently, the authors treat H₃PO₄ concentration as an experimental variable rather than assuming that the highest concentration will provide the most favorable characteristics.

The research gap identified by the authors concerns the concentration-dependent proximate characteristics of biochar produced from a defined mixture of organic household waste. The study therefore examines moisture content, volatile matter, ash content, and fixed carbon under controlled pyrolysis and activation conditions.

Research Objective

To investigate the influence of H₃PO₄ concentration on the proximate characteristics of MSW-derived biochar.
To compare nominal H₃PO₄ concentrations of 20%, 25%, and 30%.
To evaluate moisture content, volatile matter, ash content, and fixed carbon.
To statistically determine whether the activation treatments produce significant differences in the measured characteristics.
To provide a compositional basis for subsequent surface characterization and adsorption studies.

Why This Research Matters

The research provides a controlled experimental examination of how activation concentration affects the basic composition of biochar produced from a defined mixture of household organic waste. This is relevant because the study does not assume that stronger chemical activation automatically produces a better material. Instead, it evaluates the response of individual proximate characteristics and distinguishes numerical changes from statistically significant treatment effects.

The work is also useful as an initial characterization stage. The authors explicitly position the proximate results as a compositional basis for subsequent investigations rather than as direct evidence of adsorption performance. This distinction is important because fixed carbon calculated by difference does not by itself establish specific surface area, pore volume, surface functionality, or adsorption capacity.

Research Methodology

Feedstock Preparation

The organic MSW was collected from household waste generated in Pancor, East Lombok Regency, Indonesia. Nonbiodegradable materials were removed manually. Banana peel, orange peel, and coconut husk were separated, washed, dried to constant mass, reduced to approximately 2 mm particle size, and homogenized. The three components were mixed at a mass ratio of 50:30:20, and 300 g of the dried mixture was used for each pyrolysis experiment.

Pyrolysis

The prepared feedstock was pyrolyzed in a laboratory-scale reactor at 250 °C for 3 h under oxygen-limited conditions. The pyrolysis conditions were maintained constant across treatments so that H₃PO₄ concentration remained the principal experimental factor.

Chemical Activation

The resulting biochar was activated using nominal H₃PO₄ concentrations of 20%, 25%, and 30% (v/v). The activation solution was prepared from an 85% H₃PO₄ stock solution. The biochar-to-solution impregnation ratio was maintained at 1:2 (w/v), corresponding to 2 mL of activation solution per gram of biochar. Samples were soaked for 24 h at 27 °C, washed with distilled water until the filtrate reached approximately pH 6, and oven-dried at 105 °C for 4 h.

Proximate Characterization

The activated biochars were characterized for moisture content, ash content, volatile matter, and fixed carbon. Moisture and ash were determined using gravimetric procedures, while volatile matter was determined under controlled thermal conditions. Fixed carbon was calculated by difference using the relationship FC (%) = 100 − (MC + AC + VM).

Statistical Analysis

Three replicates were used for each treatment. One-way ANOVA was applied to ash content, volatile matter, and fixed carbon, followed by Tukey's honestly significant difference test when the treatment effect was significant. Moisture content was analyzed using the Kruskal–Wallis test because the normality assumption was not satisfied, followed by Bonferroni-adjusted pairwise comparisons. Statistical significance was evaluated at α = 0.05.

Key Findings

Moisture Content

The mean moisture content of the activated biochars was 8.55% at 20% H₃PO₄, 8.00% at 25%, and 8.35% at 30%, compared with 11.30% for the unactivated biochar. Although the numerical values varied, the activated treatments did not differ significantly according to the Kruskal–Wallis test (p = 0.298). Therefore, the results do not establish a concentration-dependent effect on moisture content within the investigated range.

Ash Content

Ash content decreased substantially after activation compared with the unactivated biochar. The mean values were 3.07%, 3.06%, and 3.04% at 20%, 25%, and 30% H₃PO₄, respectively, compared with 8.67% for the unactivated material. However, the differences among the three activated treatments were not statistically significant (ANOVA, p = 0.559). The results therefore suggest that ash removal approached a relatively stable level within the investigated concentration range.

Volatile Matter

Volatile matter showed the clearest concentration-dependent response. The mean value decreased from 4.64% at 20% H₃PO₄ to 4.43% at 25% and 3.94% at 30%. The overall treatment effect was statistically significant (p < 0.001), and Tukey HSD indicated significant differences among all three activation levels.

Fixed Carbon

Mean fixed carbon increased from 83.74% at 20% H₃PO₄ to 84.51% at 25% and 84.68% at 30%. The overall ANOVA result was significant (p = 0.038). However, Tukey HSD showed that only the 20% and 30% treatments differed significantly, while the difference between 25% and 30% was not statistically significant.

The manuscript reports that the increase in mean fixed carbon from 20% to 30% H₃PO₄ was 0.94 percentage points, corresponding to approximately 1.12%. Because fixed carbon was calculated by difference, the authors appropriately limit its interpretation to relative carbon enrichment rather than treating it as direct evidence of increased surface area or adsorption capacity.

Overall Interpretation

The results demonstrate that H₃PO₄ concentration affected the proximate composition of the investigated biochar, particularly volatile matter and fixed carbon. At the same time, the study does not establish an optimum activation concentration. The absence of significant differences in some characteristics and the lack of direct surface and adsorption measurements prevent the proximate results from being used alone to select an optimal condition.

Scientific Contribution

Defined mixed organic-waste system: The study investigates a specific heterogeneous precursor composed of banana peel, orange peel, and coconut husk.
Concentration-dependent analysis: The work directly compares three nominal H₃PO₄ concentrations under otherwise controlled processing conditions.
Statistical evaluation: The study distinguishes statistically significant changes from numerical variation through ANOVA, Tukey HSD, Kruskal–Wallis, and Bonferroni-adjusted comparisons.
Clear interpretation of fixed carbon: The manuscript recognizes that fixed carbon calculated by difference should not be interpreted as direct evidence of adsorption-related surface properties.
Foundation for further characterization: The results provide a compositional basis for subsequent investigation of surface properties and adsorption performance.

Industrial Implications

The study has potential relevance to processes that seek to convert selected organic waste fractions into carbonaceous materials. The experimental results indicate that activation conditions can alter the proximate composition of the resulting biochar, particularly volatile matter and fixed carbon.

For process development, the findings suggest that selecting an activation condition should not rely solely on the highest acid concentration or on a single proximate parameter. The manuscript indicates that further surface characterization and adsorption testing are necessary before a treatment can be selected for a specific environmental application.

The study therefore provides an initial materials-characterization framework rather than a complete process optimization or industrial-scale assessment. Economic performance, process scale-up, chemical consumption, and long-term operational considerations are not established by the reported proximate analysis.

Research Limitations

The investigation uses one defined mixture of banana peel, orange peel, and coconut husk; therefore, the findings are specific to the investigated precursor composition.
Only three nominal H₃PO₄ concentrations were evaluated: 20%, 25%, and 30%.
Pyrolysis temperature, pyrolysis time, impregnation ratio, soaking temperature, and activation time were maintained constant rather than systematically optimized.
The characterization focuses on proximate properties and does not directly establish specific surface area, pore volume, surface functional groups, or adsorption capacity.
Fixed carbon was calculated by difference from the other proximate fractions and therefore represents relative carbon enrichment rather than a direct structural or adsorption measurement.
The experimental results do not establish an optimum H₃PO₄ concentration.
The comparison with previously reported materials should be interpreted cautiously because the compared studies used different feedstocks and processing conditions.

Future Research Opportunities

Characterize specific surface area and pore structure to determine how H₃PO₄ concentration affects the physical structure of the biochar.
Investigate surface functional groups to establish chemical changes associated with activation.
Conduct direct adsorption experiments to determine whether changes in proximate composition correspond to changes in pollutant-removal performance.
Examine a wider range of H₃PO₄ concentrations and activation conditions to identify potential response trends.
Evaluate the combined effects of acid concentration, impregnation ratio, activation time, activation temperature, and pyrolysis conditions.
Assess the relationship between proximate composition and the functional suitability of the biochar for wastewater-treatment applications.
Investigate the reproducibility of the results using different batches and compositions of municipal organic waste.

Potential for Public Policy Citation

The article may provide technical evidence for discussions concerning organic-waste valorization and the development of carbonaceous materials from waste streams. Its experimental approach demonstrates how a defined fraction of household organic waste can be transformed through pyrolysis and chemical activation and subsequently characterized according to basic material properties.

For policy-oriented discussion, the study is most appropriately cited as experimental evidence concerning material characterization and waste valorization rather than as evidence of a fully optimized or commercially established treatment process. The authors themselves indicate that additional characterization and adsorption testing are necessary before the activated biochar can be related directly to functional environmental applications.

Who Should Read This Paper?

Environmental engineering researchers studying municipal solid waste valorization.
Researchers working on biochar and chemically activated carbon.
Materials scientists investigating carbonaceous materials derived from waste.
Researchers studying pyrolysis and chemical activation.
Graduate students working on waste-to-resource technologies.
Researchers developing biochar for environmental remediation and adsorption applications.
Engineers interested in experimental characterization of waste-derived materials.

Frequently Asked Questions (FAQ)

What is the main focus of the study?

The study evaluates how nominal H₃PO₄ concentrations of 20%, 25%, and 30% influence the proximate characteristics of biochar produced from a defined mixture of banana peel, orange peel, and coconut husk.

What feedstock was used?

The feedstock consisted of banana peel, orange peel, and coconut husk mixed at a mass ratio of 50:30:20.

What pyrolysis conditions were used?

The feedstock was pyrolyzed at 250 °C for 3 h under oxygen-limited conditions.

Which property was most clearly affected by H₃PO₄ concentration?

Volatile matter showed a statistically significant concentration-dependent response, decreasing from 4.64% at 20% H₃PO₄ to 3.94% at 30% H₃PO₄.

Did fixed carbon increase with H₃PO₄ concentration?

Yes. Mean fixed carbon increased from 83.74% at 20% H₃PO₄ to 84.68% at 30%. However, the statistically significant pairwise difference was observed only between the 20% and 30% treatments.

Did moisture content significantly differ among the activated treatments?

No. The Kruskal–Wallis test produced p = 0.298, indicating no statistically significant difference among the three activated treatments.

Did ash content significantly differ among the activated treatments?

No. The one-way ANOVA produced p = 0.559, and the reported pairwise comparisons did not identify significant differences among the activation concentrations.

Does the study establish the optimum activation concentration?

No. The authors explicitly conclude that proximate characteristics alone are insufficient to establish an optimum activation condition. Further characterization of surface area, pore structure, surface functional groups, and adsorption performance is required.

Is the study an adsorption-performance study?

No. The principal experimental outcomes are proximate characteristics. The manuscript positions these results as a basis for subsequent surface characterization and adsorption studies rather than as direct evidence of adsorption performance.

Suggested Citations

Teknomekanik Style

Septarini S, Amrullah A, Hakim CA. Effect of phosphoric acid activation concentration on the proximate characteristics of municipal solid waste-derived biochar. Innovation in Engineering. 2026;3(2):169-181. https://doi.org/10.58712/ie.v3i2.51

APA 7th Edition

Septarini, S., Amrullah, A., & Hakim, C. A. (2026). Effect of phosphoric acid activation concentration on the proximate characteristics of municipal solid waste-derived biochar. Innovation in Engineering, 3(2), 169-181. https://doi.org/10.58712/ie.v3i2.51

IEEE Style

S. Septarini, A. Amrullah, and C. A. Hakim, “Effect of phosphoric acid activation concentration on the proximate characteristics of municipal solid waste-derived biochar,” Innovation in Engineering, vol. 3, no. 2, pp. 169-181, 2026, doi: 10.58712/ie.v3i2.51.

Harvard Style

Septarini, S., Amrullah, A. & Hakim, C.A., 2026. Effect of phosphoric acid activation concentration on the proximate characteristics of municipal solid waste-derived biochar. Innovation in Engineering, 3(2), pp.169-181. https://doi.org/10.58712/ie.v3i2.51

Vancouver Style

Chicago Author-Date

Septarini, Shofwatunnida, Apip Amrullah, and Cindy Aisyah Hakim. 2026. “Effect of phosphoric Acid Activation Concentration on the Proximate Characteristics of Municipal Solid Waste-Derived Biochar.” Innovation in Engineering 3 (2): 169-181. https://doi.org/10.58712/ie.v3i2.51.

MLA 9th Edition

Septarini, Shofwatunnida, et al. “Effect of phosphoric Acid Activation Concentration on the Proximate Characteristics of Municipal Solid Waste-Derived Biochar.” Innovation in Engineering, vol. 3, no. 2, 2026, pp. 169-181. https://doi.org/10.58712/ie.v3i2.51.

Editorial Note

This review summarizes the scientific content of the article based on the published study and presents its methodological approach, principal findings, contribution, limitations, and possible directions for further research. Readers who use the findings, numerical results, methodology, or interpretations in their own scholarly work should cite the original article rather than citing this review as the primary scientific source.

The original article is available through the official Innovation in Engineering article webpage and through its official DOI: https://doi.org/10.58712/ie.v3i2.51.

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