A comparative assessment and economic implications of physical, chemical, and enzymatic treatments of lignocellulosic waste

Abstract

A significant portion of the organic waste generated globally comprises garden and agricultural waste, which are primarily lignocellulosic and recalcitrant, making them unsuitable substrates for biorefineries. This investigation focuses on the effect of eight different treatments on grass clippings, providing a comprehensive comparison of mechanical combined with physical, chemical, and biological treatment methods. Additionally, it examines the economic implications of stirring during treatment. The effects of these treatments on grass clippings were assessed using Van Soest Fiber Analysis, Scanning Electron Microscopy (SEM), X-Ray Diffractometry (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The influence of stirring was explored by repeating the top four treatments, which achieved maximum lignin reduction, with and without stirring. Alkaline treatment with 0.9% NaOH at 37 °C achieved a 58% reduction in lignin content while preserving cellulose and hemicellulose. Subsequent effective treatment methods included ultrasound, hydrothermal, and ammonia treatments. Although acid thermal hydrolysis did not reduce lignin, it significantly removed hemicellulose. Stirring’s impact on lignin removal efficiency was found to be minimal with insignificant p-values from Welsch’s t-test. Overall, alkaline treatment at 37 °C emerges as a cost-effective and scalable approach for converting lignocellulosic waste into valuable products. This study uniquely contributes to the optimisation of lignocellulosic waste management by providing a comparative analysis of various treatments of lignin-rich grass clippings and evaluating the role of stirring in enhancing treatment efficiency and reducing costs, thereby paving the way towards sustainable waste valorisation.

Keywords

Lignin reduction / Cost-effectiveness / Anaerobic digestion / Ultrasonication / Enzymatic treatment / Sustainable biorefinery

References

[1] Antonopoulou, G., Vayenas, D., & Lyberatos, G. (2020). Biogas production from physicochemically pretreated grass lawn waste: Comparison of different process schemes. Molecules, 25(2), Article 296. https://doi.org/10.3390/molecules25020296

[2] Arce C, Kratky L. Mechanical pretreatment of lignocellulosic biomass toward enzymatic/fermentative valorization. iScience, 2022, 25(7): 104610.

[3] Chakraborty D, Palani SG, Ghangrekar MM, Anand N, Pathak P. Dual role of grass clippings as buffering agent and biomass during anaerobic co-digestion with food waste. Clean Technol Environ Policy, 2022, 24(9): 2787-2799.

[4] Chang M, Li D, Wang W, Chen D, Zhang Y, Hu H, Ye X. Comparison of sodium hydroxide and calcium hydroxide pretreatments on the enzymatic hydrolysis and lignin recovery of sugarcane Bagasse. Bioresour Technol, 2017, 244: 1055-1058.

[5] Devi KB, Malakar R, Kumar A, Sarma N, Jha DK (2023) Chapter 17 - Ecofriendly utilization of lignocellulosic wastes: mushroom cultivation and value addition. In: Kuddus M, Ramteke P (Eds), Value-addition in agri-food industry waste through enzyme technology. Academic Press, pp 237–254. https://doi.org/10.1016/B978-0-323-89928-4.00016-X

[6] Feng, L., Kristensen, E. F., Moset, V., Ward, A. J., & Møller, H. B. (2018). Ensiling of tall fescue for biogas production: Effect of storage time, additives and mechanical pretreatment. Energy for Sustainable Development, 47, 143-148. https://doi.org/10.1016/j.esd.2018.10.001

[7] Frydendal-Nielsen, S., Jørgensen, U., Hjorth, M., Felby, C., & Gislum, R. (2017). Comparing methods for measuring the digestibility of miscanthus in bioethanol or biogas processing. GCB Bioenergy, 9(1), 168-175. https://doi.org/10.1111/gcbb.12377

[8] Gao Z, Alshehri K, Li Y, Qian H, Sapsford D, Cleall P, Harbottle M. Advances in biological techniques for sustainable lignocellulosic waste utilization in biogas production. Renew Sustain Energy Rev, 2022, 170: 112995.

[9] Giacobbe S, Pezzella C, Lettera V, Sannia G, Piscitelli A (2018) Laccase pretreatment for agrofood wastes valorization. Bioresour Technol 265:59–65. https://doi.org/10.1016/j.biortech.2018.05.108

[10] Guan M, Che P, Wu M, Liu X, Qian S, Xiao F. Performance and economical evaluation of rotary peeling veneer from logs fermented by lactic acid bacteria: a low-cost, green log pretreatment method. Ind Crops Prod, 2025, 227: 120841.

[11] Hamalainen V, Gronroos T, Suonpaa A, Heikkila MW, Romein B, Ihalainen P, Malandra S, Birikh KR. Enzymatic processes to unlock the lignin value. Front Bioeng Biotechnol, 2018, 6: 20.

[12] Heller, R., Brandhorst, C., Hülsemann, B., Lemmer, A., & Oechsner, H. (2023). Comparison of Different Mechanical Pretreatment Methods for the Anaerobic Digestion of Landscape Management Grass. Energies, 16(24), Article 8091. https://doi.org/10.3390/en16248091

[13] Jiang D, Ge X, Zhang Q, Zhou X, Chen Z, Keener H, Li Y (2017) Comparison of sodium hydroxide and calcium hydroxide pretreatments of giant reed for enhanced enzymatic digestibility and methane production. Bioresour Technol 244:1150–1157. https://doi.org/10.1016/j.biortech.2017.08.067

[14] Jin S, Zhang G, Zhang P, Jin L, Fan S, Li F (2015) Comparative study of high-pressure homogenization and alkaline-heat pretreatments for enhancing enzymatic hydrolysis and biogas production of grass clipping. Int Biodeterior Biodegradation 104:477–481. https://doi.org/10.1016/j.ibiod.2015.08.005

[15] Jomnonkhaow U, Sittijunda S, Reungsang A. Assessment of organosolv, hydrothermal, and combined organosolv and hydrothermal with enzymatic pretreatment to increase the production of biogas from Napier grass and Napier silage. Renew Energy, 2022, 181: 1237-1249.

[16] Karki R, Chuenchart W, Surendra KC, Sung S, Raskin L, Khanal SK. Anaerobic co-digestion of various organic wastes: kinetic modeling and synergistic impact evaluation. Bioresour Technol, 2022, 343: 126063.

[17] Kang X, Sun Y, Li L, Kong X, Yuan ZImproving methane production from anaerobic digestion of Pennisetum Hybrid by alkaline pretreatment [Article]2018

[18] Khor WC, Vervaeren H, Rabaey K (2018) Combined extrusion and alkali pretreatment improves grass storage towards fermentation and anaerobic digestion. Biomass Bioenergy 119:121–127. https://doi.org/10.1016/j.biombioe.2018.09.003

[19] Kullavanijaya P, Chavalparit O. The effect of ensiling and alkaline pretreatment on anaerobic acidification of Napier grass in the leached bed process. Environ Eng Res, 2020, 25(5): 668-676.

[20] Liczbiński P, Borowski S, Cieciura-Włoch W (2022) Anaerobic co-digestion of kitchen waste with hyperthermophilically pretreated grass for biohydrogen and biomethane production. Bioresour Technol 364:128053. https://doi.org/10.1016/j.biortech.2022.128053

[21] Lizasoain J, Rincón M, Theuretzbacher F, Enguídanos R, Nielsen PJ, Potthast A, Zweckmair T, Gronauer A, Bauer A (2016) Biogas production from reed biomass: effect of pretreatment using different steam explosion conditions. Biomass Bioenergy 95:84–91. https://doi.org/10.1016/j.biombioe.2016.09.021

[22] Marta K, Paulina R, Magda D, Anna N, Aleksandra K, Marcin D, Kazimierowicz J, Marcin Z. Evaluation of ultrasound pretreatment for enhanced anaerobic digestion of Sida hermaphrodita. Bioenergy Res, 2020, 13(3): 824-832.

[23] Masran R, Bahrin EK, Ibrahim MF, Phang L-Y, Abd-Aziz S (2020) Simultaneous pretreatment and saccharification of oil palm empty fruit bunch using laccase-cellulase cocktail. Biocatal Agric Biotechnol 29. https://doi.org/10.1016/j.bcab.2020.101824

[24] Narinthorn R, Choorit W, Chisti Y (2019) Alkaline and fungal pretreatments for improving methane potential of Napier grass. Biomass Bioenergy 127:105262. https://doi.org/10.1016/j.biombioe.2019.105262

[25] Overend, R. P., Chornet, E., & Gascoigne, J. A. (1987). Fractionation of lignocellulosics by steam-aqueous pretreatments [and discussion]. Philosophical Transactions of the Royal Society of London. Series A: Mathematical and Physical Sciences, 321, 523–536. https://doi.org/10.1098/rsta.1987.0029

[26] Pedersen, M., & Meyer, A. S. (2010). Lignocellulose pretreatment severity – relating pH to biomatrix opening. New Biotechnology, 27(6), 739-750. https://doi.org/10.1016/j.nbt.2010.05.003

[27] Phuttaro C, Sawatdeenarunat C, Surendra KC, Boonsawang P, Chaiprapat S, Khanal SK. Anaerobic digestion of hydrothermally-pretreated lignocellulosic biomass: influence of pretreatment temperatures, inhibitors and soluble organics on methane yield. Bioresour Technol, 2019, 284: 128-138.

[28] Pinpatthanapong K, Boonnorat J, Glanpracha N, Rangseesuriyachai T (2022) Biogas production by co-digestion of sodium hydroxide pretreated Napier grass and food waste for community sustainability. Energy Sources Part A Recov Util Environ Eff 44(1):1678–1692. https://doi.org/10.1080/15567036.2022.2055232

[29] Reddy K, Sharon H (2018) Energy and environmental analysis. the role of exergy in energy and the environment. 339

[30] Saidkhilli H, Dhanya MS. Enhanced anaerobic co-digestion of rice straw by alkaline thermal pre-treatment. Res J Biotechnol, 2025, 20(6): 37-41.

[31] Saini S, Kuhad RC, Sharma KK. Valorization of rice straw biomass for co-production of bioethanol, biopesticide and biofertilizer following an eco-friendly biorefinery process. Process Saf Environ Prot, 2023, 173: 823-836.

[32] Saritpongteeraka K, Kaewsung J, Charnnok B, Chaiprapat S. Comparing low-temperature hydrothermal pretreatments through convective heating versus microwave heating for Napier grass digestion. Processes, 2020, 8(10): 1-16. Article 1221

[33] Semeraro B, Summa D, Costa S, Zappaterra F, Tamburini E (2021) Bio-delignification of green waste (Gw) in co‐digestion with the organic fraction of municipal solid waste (OFMSW) to enhance biogas production. Appl Sci (Switzerland) 11(13):6061. https://doi.org/10.3390/app11136061

[34] Tsapekos P, Kougias PG, Egelund H, Larsen U, Pedersen J, Trénel P, Angelidaki I. Mechanical pretreatment at harvesting increases the bioenergy output from marginal land grasses. Renew Energy, 2017, 111: 914-921.

[35] Vakalis S, Georgiou A, Moustakas K, Fountoulakis M (2022) Assessing the effect of hydrothermal treatment on the volatile solids content and the biomethane potential of common Reed (phragmites australis). Bioresource Technol Rep 17:100923. https://doi.org/10.1016/j.biteb.2021.100923

[36] Van Soest, P. J., Robertson, J. B., & Lewis, B. A. (1991). Methods for Dietary Fiber, Neutral Detergent Fiber, and Nonstarch Polysaccharides in Relation to Animal Nutrition [Article]. Journal of Dairy Science, 74(10), 3583-3597. https://doi.org/10.3168/jds.S0022-0302(91)78551-2

[37] Wells JM, Crow SE, Khanal SK, Turn S, Hashimoto A, Kiniry J, Meki N (2021) Anaerobic digestion and hot water pretreatment of tropically grown c4 energy grasses: mass, carbon, and energy conversions from field biomass to fuels. Agronomy 11(5):838. https://doi.org/10.3390/agronomy11050838

[38] Wen B, Yuan X, Li QX, Liu J, Ren J, Wang X, Cui Z. Comparison and evaluation of concurrent saccharification and anaerobic digestion of Napier grass after pretreatment by three microbial consortia. Bioresour Technol, 2015, 175: 102-111.

[39] Xie X, Peng C, Song X, Peng N, Gai C. Pyrolysis kinetics of the hydrothermal carbons derived from microwave-assisted hydrothermal carbonization of food waste digestate. Energy, 2022, 245: 123269.

[40] Zhou X, Li Q, Zhang Y, Gu Y. Effect of hydrothermal pretreatment on miscanthus anaerobic digestion. Bioresour Technol, 2017, 224: 721-726.

Funding

BITS RMIT Higher Education Academy(BITSRMIT100067)

RIGHTS & PERMISSIONS

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