Elsevier

Bioresource Technology

Volume 360, September 2022, 127446
Bioresource Technology

Critical factors influence on acidogenesis towards volatile fatty acid, biohydrogen and methane production from the molasses-spent wash

https://doi.org/10.1016/j.biortech.2022.127446Get rights and content

Highlights

  • Design of experiment aided in assessing optimized acidogenic fermentation.

  • Inoculum pretreated aided in VFA and bio-H2 production.

  • Higher OL aided in higher VFA production while lower in higher degree of acidification.

  • Factors like pH, inoculums,buffering agents,C:N, and temperature were considered in the study.

Abstract

The study explored the spent wash valorisation into value added biobased products viz. volatile fatty acids (VFAs), biohydrogen (bio-H2), methane (CH4) and biohythane (bio-H-CNG) based on eight selected parameters employing design of experiment (DOE) approach. Selectively enriched biocatalyst showed marked influence on the production of acidogenic products (bio-H2 and VFA) while untreated inoculum resulted in higher CH4 and bio-H-CNG generation. CaCO3 showed potential for butyric acid (HBu) production while Na2CO3 specifically yielded higher acetic acid (HAc) when supplemented as buffering agents. Higher degree of acidification (DOA; 49.8%) was observed at lower organic load (OL; 30 g/L). Biogas production and profile was influenced by OL, enrichment of biocatalyst and supplemented buffering agent. Higher OL related to higher bioproduct production, while yields of the respective products were higher at lower OL.

Introduction

The sugarcane industry is one of the most important agro-based industries in around 130 countries (Fito et al., 2019). Sugar production from sugarcane generates a variety of byproducts, including bagasse, press mud, fly ash, molasses, and wastewater, all of which can be valorized to produce alcohol, energy, and compost (Katakojwala and Mohan, 2020). Furthermore, molasses-based distilleries generates spent wash 12 to 15 times greater than the alcohol produced during the distillation process (Shinde et al., 2020). Spent wash is high in organic load, acidity, and dissolved inorganic salts (Fito et al., 2019). Valorization of spent wash is an important and sustainable option in the context of emerging environmental issues and fossil depletion (Dahiya et al., 2022). Spent wash is more prominently used for methane production by anaerobic digestion (Shinde et al., 2020). Alternatively, acidogenesis process can produce biohydrogen (bio-H2) and volatile fatty acids (VFAs) (Santhosh et al., 2021, Mikucka and Zielińska, 2020, Dahiya et al., 2018) and thus can be considered as a focal feedstock for biorefinery (Sarkar et al., 2016, Venkata Mohan et al., 2016). The H2 based economy is characterized as a developing trend of future society with zero carbon emissions (Sarkar et al., 2021), as it is clean and sustainable compared with the present fossil fuel-based economy. Biohythane (bio-H-CNG) production favored by simultaneous synthesis of methane (CH4) and H2 accounts for renewability with benefits over CNG in terms of fuel economy and pollution reduction (Liu et al., 2012, Santhosh et al., 2021).

Production of specific products in acidogenesis is a challenge. The major end products of regulated/distributed acidogenesis are energy and precursor molecules (Venkata Mohan et al., 2007, Mohanakrishna et al., 2011). The operating microenvironment is crucial for achieving products of interest (Venkata Mohan, 2008). Selective enrichment of biocatalyst aids in the elimination of non-spore-forming microorganisms under high thermophilic and acidic conditions by modifying the germination receptors (Goud and Venkata Mohan, 2012). Substrate concentration directly impacts the productivity (Magdalena et al., 2019), and the appropriate C:N ratio triggers the shift in the pathway by promoting cell development (Tunçay et al., 2017). pH plays a significant role in VFAs formation during the acidogenic process, which have a direct impact on the productivity and profile of metabolites (Dahiya and Venkata Mohan, 2019, Pasupuleti and Venkata Mohan, 2015). Na2CO3 and CaCO3 were employed as buffering agents as they are cheaper, easy-to-handle alkaline/hydrolysis agents with a high buffering capability (Dahiya and Venkata Mohan, 2019). Fe is essential for hydrogenase activity and is also a component of the ferredoxin protein, which serves as an electron carrier for hydrogenase while Mo allows effective catalysis for increased VFAs/bio-H2 production (Shanmugam et al., 2020). The experiment was designed to study the selected operational parameters influence on utilizing spent wash as substrate for the production of various bioproducts (VFAs, bio-H2, CH4 and bio-H-CNG) employing a Taguchi based design of experiment methodology.

Section snippets

Spent wash

Spent wash collected from M/s Gayatri Sugars Ltd., Kama Reddy (pH, 4.45 ± 0.8; COD, 12,2000 ± 50000 mg/L; VFA, 16,000 ± 4000 mg/L; BOD, 50,000 ± 3700 mg/L, TDS, 17,647 ± 3000 mg/L, Nitrates, 10,000 mg/L, Phosphates, 210 mg/L, Sulphates, 674 mg/L, TKN, 2.5%±0.5%, Potassium, 14300 mg/L) was used as feed.

Experimental design and operation

Experiments were designed with Taguchi’s design of experimental (DOE) methodology to determine the effect of eight selected factors (independent variables) viz., nature of biocatalyst,

Volatile fatty acids

The VFA produced from the spent wash majorly dependent on the operating conditions. Nature of biocatalyst, its enrichment and OL influenced the fatty acid production positively except in the case of R3, R10, and R11 systems which were operated with untreated biocatalyst. Other systems operated with untreated biocatalyst showed marginal production of VFA during the last hours of the cycle operation. Reactors operated with higher organic load showed comparatively higher VFA production except in

Conclusion

The functional role of eight parameters using Taguchi DOE methodology provided an insight into the spent wash valorisation towards the production of VFAs, bio-H2, CH4 and bio-H-CNG. Higher OL along with enriched biocatalyst and CaCO3 as buffering agent led to the higher VFAs and bio-H2 production while untreated inoculum along with lower OL and alkaline pH led to higher CH4 and bio-H-CNG production. Each bioproduct has its own set of optimum parameters that had to be chosen depending on the

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors would like to acknowledge Department of Biotechnology (DBT), Government of India, for supporting the project grant (BIOREVIEW; BT/Indo-UK/SVM/09/2018-19). The authors would like to thank the Director of CSIR-IICT for his encouragement and assistance (IICT/Pubs./2021/28).

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