Department of Chemical Engineering
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Item Sustainable CO2 bio-mitigation: a life cycle perspective on chemolithotrophic conversion in bubble column bioreactors(RSC, 2025-09) Gupta, Suresh; Raghuvanshi, SmitaThe urgent need for low-carbon energy alternatives has intensified interest in sustainable biofuel production pathways. This study presents a comprehensive Life Cycle Assessment (LCA) of a chemolithotrophic bacterial platform for simultaneous CO2 mitigation and biodiesel production using Bacillus cereus SSLMC2 cultivated in 10 and 20 L bubble column bioreactors. Unlike phototrophic systems, this process leverages light-independent bacterial metabolism, offering year-round operation, high biomass yield, and compatibility with flue gas as a carbon source. Experimental data were integrated with LCA modeling using Umberto NXT Universal software and the ReCiPe 2016 and CML baseline methods to quantify environmental impacts across cultivation, biomass harvesting, lipid extraction, and transesterification stages. The results identify dewatering and homogenization as major environmental hotspots, contributing significantly to climate change, fossil depletion, and human toxicity categories. Endpoint analysis revealed human health and resource availability as the most impacted areas, primarily due to electricity use and chemical inputs. Cumulative energy demand assessments confirmed that scale-up from 10 to 20 L does not proportionally increase energy use, suggesting promising scalability. Recommendations include replacing centrifugation with membrane-based dewatering, solvent recovery systems, integration of renewable energy, and recycling of CO2 and water. This is the first LCA study to evaluate chemolithotrophic CO2 bio-mitigation coupled with biodiesel production at pilot scale using empirical data. The findings provide critical insights for optimizing microbial biorefineries and support the development of scalable, environmentally efficient carbon capture and utilization technologies.Item Bioprocess scale-up through experimental design and process simulation: a case study of succinic acid and 3-hydroxypropionic acid(AIChE, 2025) Raghuvanshi, SmitaThe bioprocess scale-up is at the center when developing an upstream process for mass production [1]. Process understanding at the laboratory scale can guide the scale-up rules [2-4]. These rules are broadly classified into maintaining (1) the same mixing time, (2) constant power supplied per unit volume (P/V), (3) constant overall mass transfer coefficient (kLa), and (4) impeller flow numbers [3,4]. Accordingly, different scale-up correlations have been derived and are functions of impeller Reynolds number (Re), impeller tip speed, power transfer per unit volume, and agitation rate [2-4]. At different scales, this correlation-based scale-up can produce comparable biomass [4 and 5]. Thus, in the process of SA mass-production via fermentation, different studies have attempted to scale up fermentative succinic acid (SA) production via yeast. In one study, from an engineered Yarrowia lipolytica PSA02004 via two-stage pH regulation between 5-6 in fed-batch mode a SA titer value of 42.2 g.L-1 with 0.38 g.g-1 yield and 0.84 g.L-1.h-1 productivity is obtained [6]. In the same study, the shake flask scale is translated to the lab-scale reactor at 6.7 L (Working volume: 3L) [7]. Another study in batch mode resulted in an SA titer of 18.4 g.L-1 with a yield of 0.23 g.g-1 at pH 3.0. However, in fed-batch mode, with seven-time feeding, a higher titer value of 76.8 g.L-1 is achieved. The study utilizes an in situ fibrous bed bioreactor (isFBB) of volume 2.5 L [8]. In other studies, via batch or fed-batch mode with multiple feeding mostly near pH 6, the SA values titer and yield in the range of 53.6 g.L-1-209.7 g.L-1 and 0.92 g.g-1 are reported, respectively [9, 10]. However, almost all these studies are limited either to shake flask or to the bioreactor total volume in the range of 1-10 L [6-10].Item Unraveling the kinetics, mass transfer, and multi-omics for environmentally sustainable CO2 bio-mitigation using Bacillus cereus for bioenergy feedstock production(Elsevier, 2025) Gupta, Suresh; Raghuvanshi, SmitaThis research provides a cost-competitive solution to the conflict between ever-increasing energy demand and hazardous carbon dioxide (CO2) emissions reduction from the industries. The paper outlines the use of chemolithotrophic bacteria (B. cereus SSLMC2) for the bio-mitigation of 10, 15, 20, and 25 % CO2 conducted using a 20 L bubble column bioreactor. For 10, 15, 20, and 25 % CO2 (g), the maximum biomass productivity achieved was 0.042, 0.035, 0.032, and 0.051 g L−1 h−1, respectively. The highest percentages of CO2 (g) removal achieved were 91.68, 86.83, 84.86, and 93.43 %, respectively. The effect of parameters on biomass growth and total carbon (C) assimilation was investigated to determine the correlation between the mitigation of CO2 (g) and the growth of B. cereus SSLMC2. The gas chromatography-mass spectrometry (GC-MS) examination of biomass confirmed the formation of potential products during the bio-mitigation process. The nuclear magnetic resonance (NMR) metabolomics technique identified up to 25 metabolites associated with probable bio-mitigating CO2 (g) pathways. Kinetic models such as Monod, Haldane, Powell, Webb, and Luong provided a mathematical depiction of bacterial growth dynamics. Additionally, the mass and heat transfer characteristics crucial to the bio-mitigation process were determined. By demonstrating high CO2 removal efficiencies and the production of valuable by-products, this research highlights the potential of integrating bio-based technologies into existing industrial processes.Item Sustainable valorization of macroalgae residual biomass, optimization of pyrolysis parameters and life cycle assessment(Elsevier, 2024-04) Sangwan, Kuldip Singh; Raghuvanshi, SmitaThe major challenges for the current climate change issue are an increase in global energy demand, a limited supply of fossil fuels, and increasing carbon footprints from fossil fuels, which have necessitated the exploration of sustainable alternatives to fossil fuels. Biorefineries offer a promising path to sustainable fuel production, converting biomass into biofuels using diverse technologies. Aquatic biomass, such as macroalgae in this context, represents an abundant and renewable biomass resource that can be cultivated from water bodies without competing with traditional agricultural land. Despite this, the potential of macroalgae for biofuel production remains largely untapped, with very limited studies addressing their viability and efficiency. This study investigates the efficient conversion of unexplored macroalgae biomass through a biorefinery process that involves lipid extraction to produce biodiesel, along with the production of biochar and bio-oil from the pyrolysis of residual biomass. To improve the effectiveness and overall performance of the pyrolysis system, Response Surface Methodology (RSM) was utilized through a Box-Behnken design to systematically investigate how alterations in temperature, reaction time, and catalyst concentration influence the production of bio-oil and biochar to maximize their yields. The results showed the highest bio-oil yield achieved to be 36 %, while the highest biochar yield reached 45 %.Item Household biogas technology in cold climate of low-income countries: a review on sustainable technologies for accelerating biogas generation(IOP, 2024-05) Raghuvanshi, SmitaLow-income countries (LICs) have long benefitted from household biogas plants for the extraction of clean energy and fertilizers. Despite their popularity, such ordinary plants do not have heating systems and suffer from low biogas production in cold regions or during winter. This paper presents a comprehensive review of the research and development of household biogas technology in cold climates. This review specifically highlights the influence of temperature on biogas production and technologies, as well as recent advances in psychrophilic biogas production. These measures include the introduction of adapted inocula, maneuvering operational parameters (such as hydraulic retention time and organic loading rate), co-digestion approach and additives, and digester designs. In addition, this review shows that the adoption of low-cost heating arrangements, including the construction of a greenhouse over biodigesters, digester insulation, and integration of solar heating, is crucial for enhancing biogas production. Furthermore, this review identified gaps in the operation of biodigesters under psychrophilic temperature in LICs and recommends operational consistencies in full-scale psychrophilic biogas plants through the development of standards, operational guidelines, and user training.Item Sustainable approach for simultaneously reducing CO2 and NO emissions from synthetic industrial flue gases using bacterial consortium and domestic wastewater in a suspended glass bioreactor(Springer, 2023-02) Raghuvanshi, Smita; Gupta, SureshThe current study showed how a bacterial consortium (Bacillus tropicus SSLMC1 and Bacillus cereus SSLMC2) isolated from the harsh environment of Sambhar Salt Lake could simultaneously remove carbon dioxide (CO2) and nitric oxide (NO) while using domestic wastewater (DWW) as nutrients and an energy source. A 3-L suspended glass bioreactor was used for the lab tests to see how well the bacterial consortium would be able to fix CO2 and NO from three different gaseous mixtures (only CO2, only NO and a mixture of CO2 and NO). The simultaneous removal of CO2 and NO was shown to have the highest values of biokinetic parameters such as biomass productivity, specific growth rate, fixation efficiency, fixation rate, utilization efficiency and nutrient utilization efficiency. The starting and final amounts of nutrients and pollutants present in DWW were examined for checking the simultaneous removal of CO2 and NO. The presence of fatty acids, fatty alcohols and long-chain hydrocarbons found in cell lysate and cell-free supernatant was analysed using Fourier-transform infrared spectroscopy (FT-IR) and gas chromatography-mass spectroscopy (GC–MS). The potential mechanism for the bio fixation of CO2 and NO was presented based on the findings of the experimental work and the product analysis. The resulting biokinetic characteristics were compared to those from earlier studies and showed that using DWW as a nutrient and energy source would allow bacterial consortia to simultaneously biofix CO2 and NO.Item Evaluating the influence of calcined eggshells and ultrasonication in the Co-digestion of avoidable and unavoidable Food Waste and OLS regression analysis of the reactor system(Elsevier, 2024-08) Raghuvanshi, SmitaThe technological advancements in the bio-conversion of food waste (FW) into biogas signify substantial advancements in the field of waste management. However, persistent operational challenges like rapid acidification and difficulties in maintaining the C/N ratio in mono-digestion remain, despite extensive research efforts. The present study aims to evaluate the reactor performance in co-digestion, specifically using a 1:1 ratio of unavoidable food waste (UAFW) and avoidable food waste (AFW), with the addition of calcined eggshells as an additive. Further, the study employs Ordinary Least Square (OLS) regression modeling to predict the biogas production from the co-digestion process. The experimental process involves ultrasonication pretreatment, focusing on calcined eggshells for their ability to preserve carbohydrates via Ca(OH)2, an alkaline material. The semi-continuous operation of the reactor spanned for 120 days and was divided into three phases with varying Organic Loading Rates (OLR) from 0.6 to 2.2 gVS/l/d. Characterization studies such as SEM, FTIR and TGA-DTA were performed to validate the pretreatment method and addition of egg-shells. Results indicated increased OLR led to higher Volatile Solids (VS) reduction. This was attributed to the calcined eggshells' role in adsorbing NH4+ and NO3− ions while maintaining pH levels, resulting in significantly higher biogas production. The multiple regression models used in the study yielded promising results, surpassing simple linear regression, with an adjusted R-squared value > 0.9 and p-value <0.05. The model effectively anticipated the specific methane yield, demonstrating the capability to improve energy production by co-digesting AFW and UAFW. The study presents an opportunity to divert organic waste from landfills, reduce greenhouse gas emissions, and promote sustainable waste management by using bio-waste additives, reducing reliance upon synthetic chemicals.Item Optimization of bacterial biorefineries for sustainable biodiesel production and flue gas reduction: a holistic approach to climate change mitigation and circular economy(RSC, 2025) Raghuvanshi, Smita; Gupta, SureshThe primary obstacles to addressing the current climate change problem include a rise in worldwide energy consumption, a restricted availability of fossil fuels, and the escalating carbon emissions associated with fossil fuels. Consequently, there is a pressing need to investigate sustainable alternatives to fossil fuels. Biorefineries present a potentially viable avenue for the sustainable production of fuel, as they employ a range of technologies to convert biomass into biofuels. This research aims to examine the cultivation of bacterial biomass and biodiesel production using a biorefinery approach. This process achieves a removal efficiency of 96, 93, and 98% for CO2, SO2, and NO, respectively, and a bacterial biomass of 274 g cultivated in a 20 L integrated bioreactor. The biomass entails extracting lipids (58% w/w) to generate biodiesel (91% w/w). The metabolic pathway followed by bacteria to reduce flue gas and produce lipids was analyzed to improve the production of lipids and biodiesel. A life cycle assessment was performed to assess the environmental impacts during the process. Implementing alternative and safe chemicals can potentially mitigate the adverse effects of processes and GWP100. The techno-economic analysis aimed to systematically examine the capital investment required to set up a bacterial biorefinery as compared to conventional fuel refineries. The findings indicated that the bacterial biorefinery had a net present value of $193 per litre of biodiesel produced. A bacterial biorefinery holds promise in fostering a circular economy characterized by sustainable practices and systems that aim to minimize waste, optimize resource utilization, and encourage the reuse and recycling of materials.Item Industrial scale-up of flue gas bio-mitigation with chemolithotrophs in packed bed reactors: Exploring metabolite synthesis, mass transfer, and techno-economic analysis(Elsevier, 2025-03) Raghuvanshi, Smita; Gupta, SureshElevated emissions of flue gases deteriorate the quality of air, impacting both terrestrial and aquatic ecosystems through their contribution to acid rain and eutrophication. This study examines the bio-mitigation process in a packed bed reactor and its capacity to concurrently decrease the environmental consequences of industrial flue gases (CO2, NO, and SO2) and wastewater by employing mixed bacterial consortia. The highest biomass productivity achieved during the growth phase was 0.002 g L−1 h−1 in the aqueous medium and 0.006 g L−1 h−1 in the PU foam. The highest level of CO2 removal efficiency was 86.60%, while for NO and SO2, it was 77.03% and 82%, respectively. The comprehensive nutrient balance analysis revealed that the flue gas was primarily utilized for biomass assimilation. The FT-IR and GC-MS analysis detected metabolites, including carboxylic acids, esters, and fatty alcohols, that were produced during the process. The NMR study examined alterations in the concentration of metabolites within the cell, indicating metabolic pathways such as the TCA cycle, alanine, pyruvate, butanoate metabolism, and glycolysis. The mass transfer coefficient estimated for the gas-liquid-solid phase was ∼2.0 m s−1 for the flue gases. The scale-up of the reactor based on the mass transfer coefficient up to 20,000 L gives a net present value of $2,66,116.13 with a benefit-to-cost ratio of 1.47. Therefore, this study suggests that employing bacteria is a viable and energy-efficient approach to mitigate the adverse effects of flue gas on air quality. Additionally, it aids industries in minimizing waste and repurposing it for advantageous purposes, thereby diminishing their environmental footprint.Item Climate - adaptive anaerobic digestion of food waste in household digesters: insights from extreme temperature conditions(Elsevier, 2025-06) Raghuvanshi, SmitaAnaerobic digestion (AD) is a widely used method for organic waste treatment, but the energy requirement for temperature control poses challenges, especially for household digesters. This study focuses on the semi-continuous AD process of FW in household digesters at an ambient temperature in Pilani, adjusting organic loading rates (OLR) based on daily temperature fluctuations. Additionally, it assesses ammonium removal efficiency during the degradation of FW using a low-cost magnesite-derived stabilizing agent. The findings highlight the feasibility of generating inoculum from cow dung in anaerobic conditions within a few weeks. The average specific biogas production was 0.591 ± 0.20 m3/kgVS, with a 58 ± 3 % methane concentration. The addition of the stabilizing agent resulted in a 30.3 % increase in biogas production by precipitating struvite, which led to a 22.6 % reduction in total ammonia nitrogen, thereby preventing the inhibition of methanogenic bacteria. Characterization studies, including FTIR, XRF, XRD, and SEM analyses, validate the stabilizing agent's formation and struvite precipitation. However, during a sudden and significant drop in winter temperatures, biogas production decreased to 0.210 ± 0.052 m3/kg VS, with methane content falling to 49 %, highlighting the need for microbial acclimatization. The study indicates that anaerobic digesters can operate effectively at low temperatures with a reduced OLR when the microbial community is adequately acclimatized. Furthermore, the effluent characteristics post-digestion exhibits favorable nitrogen and potassium values, and phosphate recovery through struvite precipitation is evident. Economically, the study demonstrated that replacing non-subsidized LPG with biogas yielded a pay-back period of 6 years and an internal rate of return of 15.6 %. Additionally, the challenges of household biogas production and corresponding potential recommendations are thoroughly addressed. The study highlights the potential of the investigated AD system at ambient conditions, incorporating cost-effective innovations to enhance the efficiency of the process. It provides valuable insights for decision-makers and waste management planners, extending its relevance beyond Pilani to similar settings.