Multicriteria Decision Model and Thermal Pretreatment of Hotel Food Waste for Robust Output to Biogas: Case Study from City of Jaipur, India

Decision-making in biogas production projects: Paradigms and prospection

The decision to implement a biogas production project involves the evaluation of multiple variables, such as the problem to be solved, the biodigester, business model, investment, and final products. An integrative literature review was conducted, in which 58 papers were obtained and relevant criteria for decision-making in biogas production projects from organic waste were identified. Three stages were considered in the analysis of the biogas production cycle: initial, plant, and final, as well as the economic, environmental, and social aspects that influence the decision. In general, the publications are dispersed over 30 different journals. The methodology used in most studies is empirical, quantitative, and descriptive, with data collected mainly from secondary sources. From the studies, 499 original criteria were identified, which were classified into one of four categories: economic, environmental, social, and technical, which cover a total of 39 sub-criteria. Economic and technical criteria were the most frequent in publications, while environmental and social criteria were less common and less prioritized. This suggests that there is a tendency to prioritize economic and technical dimensions over environmental and social dimensions in the analysis of the papers found. Finally, a preliminary decision-making model based on the findings is proposed.Implications: The integrative review of the literature on biogas and decision-making presented in this study holds significant implications for policy and practice in the field of sustainable energy production, organic waste management and decision making for public managers. By analyzing 159 papers and developing a comprehensive classification system, we have identified key sub-criteria for decision-making in various stages of the biogas production cycle. The predominance of technical and economic sub-criteria demonstrates the priorities of the current state of biogas projects and, at the same time, the need to promote balance between the technical, economic, social and environmental spheres in decision-making in order to achieve truly sustainable biogas projects. Policymakers can utilize these findings to promote the adoption of more holistic decision-making approaches that consider diverse factors, fostering the development of environmentally-friendly and socially equitable biogas ventures. This research provides valuable insights into aligning biogas production with broader sustainability goals and guides policymakers in formulating evidence-based strategies for the advancement of renewable energy technologies.

Influence of microwave temperature and power on the biomethanation of food waste under mesophilic anaerobic conditions

Food waste is an attractive feedstock for Anaerobic Digestion due to its high biodegradability and moisture content. Nevertheless, due to its complex structure and composition, methane yield is typically compromised with 50-60% of the theoretical maximum obtained. The well-known limitation of the hydrolysis step can be circumvented by adopting feedstock pre-treatments, such as microwave irradiation. It improves solubilization of various FW components making them more readily available for the microorganisms and reducing AD process duration. In this work different heating rates (7.8, 3.9 and 1.9 °C/min) and temperatures (85, 115, 145, 175 °C) were applied when pre-treating food waste as a substrate for AD. Increase in the solubilization of organic matter in the form of Soluble Chemical Oxygen Demand was the most significative change in FW characteristics after pre-treatment, with final temperature of 175 °C and heating rate of 3.9 °C showing a 73.19% increment. Nevertheless, process performance of AD of MW FW was optimum at 85 °C 7.8 ramp, showing no intermediate products accumulation, up to 77% more methane produced in the first week of digestion compared to the other conditions tested and reduction of 96.36% on the lag phase duration, compared to the control. On the other hand, samples treated at 175 °C, regardless of heating rate, consistently showed poor process performance, with low methane yield, possibly due to the formation of hard-to-digest compounds. This work underlines the importance of adjusting microwave temperature and power when pre-treating FW for biomethane production so the process is optimized.

Low-Temperature Pretreatment of Biomass for Enhancing Biogas Production: A Review

Low-temperature pretreatment (LTPT, Temp. < 100 °C or 140 °C) has the advantages of low input, simplicity, and energy saving, which makes engineering easy to use for improving biogas production. However, compared with high-temperature pretreatment (>150 °C) that can destroy recalcitrant polymerized matter in biomass, the action mechanism of heat treatment of biomass is unclear. Improving LTPT on biogas yield is often influenced by feedstock type, treatment temperature, exposure time, and fermentation conditions. Such as, even when belonging to the same algal biomass, the response to LTPT varies between species. Therefore, forming a unified method for LTPT to be applied in practice is difficult. This review focuses on the LTPT used in different biomass materials to improve anaerobic digestion performance, including food waste, sludge, animal manure, algae, straw, etc. It also discusses the challenge and cost issues faced during LTPT application according to the energy balance and proposes some proposals for economically promoting the implementation of LTPT.

Drivers of food waste generation and best practice towards sustainable food waste management in the hotel sector: a systematic review

The growing volumes of food globally are lost or wasted along the entire food chain. However, a high effort in investigating why food waste (FW) occurs remains scattered for each subsector in detail, particularly in the hotel sector. Therefore, this systematic review focuses on FW issues in the hotel sector to identify FW generation drivers and good business practices towards mitigating FW. The review compiled literature from 25 related studies and adopted the PRISMA statement, utilising two leading journal databases: Scopus and Web of Science. This review shows that hoteliers initially feel guilty about wasting food, primarily based on financial loss rather than concerns about the social and environmental footprint. Based on the review, hotel staff from various internal departments faced conflicts between good intentions with reducing FW and the guests' unsustainable food consumption patterns. Within the scope of this review, we suggest that further research is necessary with a focus on procedures and regulations (hotel policy) to encourage guests to minimise plate waste and redistribute unsold hotel food to charities or food banks. Overall, this review offers some interesting guidelines and actionable inferences to reduce FW generation in the hotel sector.

A comprehensive review of the recent development and challenges of a solar-assisted biodigester system

The extensive use of fossil fuels and the environmental effect of their combustion products have attracted researchers to look into renewable energy sources. In addition, global mass production of waste has motivated communities to recycle and reuse the waste in a sustainable way to lower landfill waste and associated problems. The development of waste to energy (WtE) technology including the production of bioenergy, e.g. biogas produced from various waste through Anaerobic Digestion (AD), is considered one of the potential measures to achieve the sustainable development goals of the United Nations (UN). Therefore, this study reviews the most recent studies from relevant academic literature on WtE technology (particularly AD technology) for biogas production and the application of a solar-assisted biodigester (SAB) system aimed at improving performance. In addition, socio-economic factors, challenges, and perspectives have been reported. From the analysis of different technologies, further work on effective low-cost technologies is recommended, especially using SAB system upgrading and leveraging the opportunities of this system. The study found that the performance of the AD system is affected by a variety of factors and that different approaches can be applied to improve performance. It has also been found that solar energy systems efficiently raise the biogas digester temperature and through this, they maximize the biogas yield under optimum conditions. The study revealed that the solar-assisted AD system produces less pollution and improves performance compared to the conventional AD system.

Significance of Pretreatment in Enhancing the Performance of Dry Anaerobic Digestion of Food Waste: An Insight on Full Scale Implementation Strategy with Theoretical Analogy

The aim of this study was to treat food waste containing 25% total solids (TS) through dry anaerobic digestion (dry AD) process at various pressures (0.5 to 2.5 kg/cm2) and different time duration (20 to 100 min) to understand the impact of pretreatment in enhancing the methane generation potential along with insights on scale up. The findings revealed that vs. reduction and methane yield of 60% and 0.25 L CH4/(g VSadded) can be achieved with pretreated food waste at two kilograms per square centimeter, while pretreatment of food waste at 2 kg/cm2 for 100 min enhanced the vs. reduction from 60% to 85% and methane yield from 0.25 to 0.368 L CH4/(g VSadded). However, the net energy indicated that 40 min of pre -treatment at two kilograms per square centimeter can be a suitable option as methane yield and vs. reduction of 0.272 L CH4/(g VSadded) and 70%, respectively was achieved. The vs. reduction and the methane yield of 45% and 0.14 L CH4/(g VSadded), respectively was obtained from untreated food waste which illustrated that pretreatment had significantly impacted on the enhancement of methane generation and organic matter removal which can make the dry AD process more attractive and feasible at commercial scale.

Prioritization of solid concentration and temperature for solid state anaerobic digestion of pearl millet straw employing multi-criteria assessment tool

India produces huge quantities of agricultural residues and stubbles and mainly disposed by burning on site causing air pollution. The organic matter present in the residues and stubble may be utilized by anaerobic digestion as a source of renewable energy subsequently reducing emission of greenhouse gases caused by burning. In the present study, solid state anaerobic digestion (SSAD) of pearl millet straw was investigated at mesophilic and thermophilic temperature with four different total solid (TS) content (15, 20, 25 and 30%). Results showed that 20 and 25% TS generated maximum methane (124.1 ± 7 and 162.4 ± 9L/kg VS) at mesophilic and thermophilic temperature respectively. However, increasing TS content beyond 25% did not show significant increment on methane yield. Analytical analysis showed correlation between the reduction of volatile solids and methane yield as well as VFA (volatile fatty acid) accumulation at high TS content. Also, VlseKriterijuska Optimizacija Komoromisno Resenje (VIKOR) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) methods as MultiCriteria Decision Making modelling (MCDM) applied to select best possible alternative for SSAD of pearl millet. MCDM analysis showed that VIKOR method endorsed the experimental results.