Critical analysis of pyrolysis process with cellulosic based municipal waste as renewable source in energy and technical perspective

Biohydrogen in a circular bioeconomy: A critical review

Hydrogen produced from biomass feedstocks is considered an effective solution in moving toward a decarbonized economy. Biohydrogen is a clean energy source that has gained global attention for adoption as it promises to mitigate climate change and human environmental damage. Through the circular economy framework, sustainable biohydrogen production with other bioproducts while addressing issues such as waste management is possible. This study presents a comprehensive review of the various biomass feedstocks and processing technologies associated with biohydrogen generation, as well as the possible integration of existing industries into a circular bioeconomy framework. The currently standing challenges and future perspectives are also discussed.

Modalities for conversion of waste to energy - Challenges and perspectives

The United Nation is achieving its sustainable development objectives by focusing on the greener technologies for waste to energy (WTE) conversion. This necessitates the exploration of every conceivable sustainable route in different sectors. Among these, sustainable bio-economy, electricity, and waste management are the most dynamic areas. However, till now sustainability judgments for the generation of electricity from waste-to-energy supply chain (WTE-SC) technologies have been restricted in scale with respect to the three-dimensional sustainability structure (social, environmental, and economic). In most of the cases, the assessments were controlled by various environmental factors/indicators, via overlooking the economic and social indicators. In this review, we have tried to summarize a variety of state-of-the-art WTE technologies including biological and thermal treatment, landfill gas utilization and biorefineries technologies etc. These technologies can be implemented by various policy makers and agencies to deal with the communities fear before spreading and executing the relevant rules and regulations. The implementation of these rules and regulations for WTE-SC were scheduled to decide the barriers and challenges from the perspective of finance, institution, technology, and regulation.

Hydrothermal liquefaction of Scenedesmus abundans biomass spent for sorption of petroleum residues from wastewater and studies on recycling of post hydrothermal liquefaction wastewater

In this study Scenedesmus abundans was used as a biosorbent material for removing hydrocarbons from simulated petroleum wastewater. Batch experiments resulted in the removal of 92.16% of hydrocarbons from simulated wastewater within 60 min. The spent biosorbent was converted to bio-oil through hydrothermal liquefaction process (HTL) at temperature range from 220 to 320 °C with 1 h holding time. Liquid hydrocarbons (bio-oil) yield was 43.4 wt% at 300 °C with 15 g of spent sorbent loading and possessed HHV of 39.10 MJ/Kg. Additionally the HTL wastewater (aqueous phase) was recycled as reaction medium and studied for its effects on bio-oil yield which increased till second cycle (47.91 wt%). HTL bio-char was employed as adsorbent to remove heavy metals from wastewater. It showed greater removal efficiency of 86.5% to Ni(II) ions. From the results it was concluded that the petroleum residues can be effectively recycled back into liquid hydrocarbons with simple waste management pathway.

Enrichment of bio-oil after hydrothermal liquefaction (HTL) of microalgae C. vulgaris grown in wastewater: Bio-char and post HTL wastewater utilization studies

In this study, bio-oil was produced through hydrothermal liquefaction (HTL) of C. vulgaris biomass cultivated in wastewater and was enriched into transportation fuels. Bio-oil yield was 29.37% wt at 300 °C, 60 min, at 15 g/200 mL biomass loading rate with 3% wt nano ZnO catalyst loading. Applying catalyst reduced oxygen and nitrogen content in bio-oil and increased its calorific value (19.6 ± 0.8 MJ/Kg). Bio-oil was enriched through liquid-liquid extraction (LLE) and higher yield was obtained at 30 °C for dichloromethane solvent (18.2% wt). Compounds of enriched oil were within the petro-diesel range (C₈-C₂₁). Bio-char after HTL process was activated and used as adsorbent in wastewater treatment process to remove organic pollutants (COD, NO₃, NH₃ and PO₄). Treated wastewater can be supplied as growth medium for microalgae cultivation in further experiments. Nearly 3-4 times the nanocatalyst can be reused in the HTL process.

Aquatic weeds as the next generation feedstock for sustainable bioenergy production

Increasing oil prices and depletion of existing fossil fuel reserves, combined with the continuous rise in greenhouse gas emissions, have fostered the need to explore and develop new renewable bioenergy feedstocks that do not require arable land and freshwater resources. In this regard, prolific biomass growth of invasive aquatic weeds in wastewater has gained much attention in recent years in utilizing them as a potential feedstock for bioenergy production. Aquatic weeds have an exceptionally higher reproduction rates and are rich in cellulose and hemicellulose with a very low lignin content that makes them an efficient next generation biofuel crop. Considering their potential as an effective phytoremediators, this review presents a model of integrated aquatic biomass production, phytoremediation and bioenergy generation to reduce the land, fresh water and fertilizer usage for sustainable and economical bioenergy.

The comparison of chemical liquid deposition and acid dealumination modified ZSM-5 for catalytic pyrolysis of pinewood using pyrolysis-gas chromatography/mass spectrometry

Catalyst deactivation is the main reason for low petrochemical yield in catalytic fast pyrolysis (CFP) of biomass. ZSM-5 catalysts modified by chemical liquid deposition (CLD) and acid dealumination (AD) were prepared to improve petrochemical yields for CFP of pinewood. The results showed that CLD by SiO₂ led to the coverage of strong acid sites, while AD favored the removal of superficial acid sites. CFP of pinewood showed that the relative area ratio of BTX was boosted by 37.2% and 30.4% over modified ZSM-5 catalysts by CLD and AD, respectively. The yield of indenes and naphthalenes which were important precursors of heavy coke decreased sharply. Considering environmental cost and catalytic performance, CLD seems to be a preferable modification method over ZSM-5 in the catalytic pyrolysis of biomass for petrochemicals.

Pyrolysis of activated sludge: energy analysis and its technical feasibility

A comprehensive study on the potential of pyrolysis of activated sludge to generate substances that can be used to produce energy was evaluated for its technical and environmental viability. The products of the process viz., pyrolysis gas, pyrolysis oil and char can readily be used by the major energy consumers viz., electricity and transportation. Based on the results obtained it is estimated that a 1 ton capacity process for pyrolysis of activated sludge can serve the electrical needs of a maximum of 239, 95 and 47 Indian houses per day, considering lower middle class, middle class and upper middle class, respectively. In addition the process would also produce the daily methane (CNG) requirement of 128 public transport buses. The process was determined to be technically feasible at low and medium temperatures for both, pyrolysis gas and electrical energy. The gas generated could be utilized as fuel directly while the oil generated would require pretreatment before its potential application. The process is potentially sustainable when commercialized and can self-sustain in continuous mode of operation in biorefinery context.