Search

Though deemed a prospective method, the bioconversion of organic waste to biohydrogen via dark fermentation (DF) has multiple drawbacks and limitations. Technological difficulties of hydrogen fermentation may, in part, be eliminated by making DF a viable method for biohythane production. Aerobic granular sludge (AGS) is a little-known organic waste spurring a growing interest in the municipal sector; its characteristics indicate the feasibility of its use as a substrate for biohydrogen production. The major goal of the present study was to determine the effect of AGS pretreatment with solidified carbon dioxide (SCO2) on the yield of H2 (biohythane) production during anaerobic digestion (AD). It was found that an increasing dose of SCO2 caused an increase in concentrations of COD, N-NH4+, and P-PO43− in the supernatant at the SCO2/AGS volume ratios from 0 to 0.3. The AGS pretreatment at SCO2/AGS ratios within the range of 0.1–0.3 was shown to enable the production of biogas with over 8% H2 (biohythane) content. The highest yield of biohythane production, reaching 481 ± 23 cm3/gVS, was obtained at the SCO2/AGS ratio of 0.3. This variant produced 79.0 ± 6% CH4 and 8.9 ± 2% H2. The higher SCO2 doses applied caused a significant decrease in the pH value of AGS, modifying the anaerobic bacterial community to the extent that diminished anaerobic digestion performance. [ABSTRACT FROM AUTHOR]

Appropriate management is necessary to mitigate the environmental impacts of wastewater sludge. One lesser-known technology concerns the use of solidified CO2 for dewatering, sanitization, and digestion improvement. Solidified CO2 is a normal byproduct of natural gas treatment processes and can also be produced by dedicated biogas upgrading technologies. The way solidified CO2 is sourced is fully in line with the principles of the circular economy and carbon dioxide mitigation. The aim of this review is to summarize the current state of knowledge on the production and application of solid CO2 in the pretreatment and management of sewage sludge. Using solidified CO2 for sludge conditioning causes effective lysis of microbial cells, which destroys activated sludge flocs, promotes biomass fragmentation, facilitates efficient dispersion of molecular associations, modifies cell morphology, and denatures macromolecules. Solidified CO2 can be used as an attractive tool to sanitize and dewater sludge and as a pretreatment technology to improve methane digestion and fermentative hydrogen production. Furthermore, it can also be incorporated into a closed CO2 cycle of biogas production–biogas upgrading–solidified CO2 production–sludge disintegration–digestion–biogas production. This feature not only bolsters the technology's capacity to improve the performance and cost-effectiveness of digestion processes, but can also help reduce atmospheric CO2 emissions, a crucial advantage in terms of environment protection. This new approach to solidified CO2 generation and application largely counteracts previous limitations, which are mainly related to the low cost-effectiveness of the production process. [ABSTRACT FROM AUTHOR]

The increasing concentration of anthropogenic CO2 in the atmosphere is causing a global environmental crisis, forcing significant reductions in emissions. Among the existing CO2 capture technologies, microalgae-guided sequestration is seen as one of the more promising and sustainable solutions. The present review article compares CO2 emissions in the EU with other global economies, and outlines EU's climate policy together with current and proposed EU climate regulations. Furthermore, it summarizes the current state of knowledge on controlled microalgal cultures, indicates the importance of CO2 phycoremediation methods, and assesses the importance of microalgae-based systems for long-term storage and utilization of CO2. It also outlines how far microalgae technologies within the EU have developed on the quantitative and technological levels, together with prospects for future development. The literature overview has shown that large-scale take-up of technological solutions for the production and use of microalgal biomass is hampered by economic, technological, and legal barriers. Unsuitable climate conditions are an additional impediment, forcing operators to implement technologies that maintain appropriate temperature and lighting conditions in photobioreactors, considerably driving up the associated investment and operational costs. [ABSTRACT FROM AUTHOR]

Microalgae-mediated CO2 sequestration has been a subject of numerous research works and has become one of the most promising strategies to mitigate carbon dioxide emissions. However, feeding flue and exhaust gas into algae-based systems has been shown to destroy chloroplasts, as well as disrupt photosynthesis and other metabolic processes in microalgae, which directly limits CO2 uptake. CO2 biosequestration in existing photobioreactors (PBRs) is also limited by the low biomass concentration in the growth medium. Therefore, there is a real need to seek alternative solutions that would be competitive in terms of performance and cost-effectiveness. The present paper reports the results of experiments aimed to develop an innovative trickle bed reactor that uses immobilized algae to capture CO2 from flue and exhaust gas (IMC-CO2PBR). In the experiment, ambient air enriched with technical-grade CO2 to a CO2 concentration of 25% v/v was used. The microalgae immobilization technology employed in the experiment produced biomass yields approximating 100 g DM/dm3. A relationship was found between CO2 removal rates and gas volume flux: almost 40% of CO2 was removed at a feed of 25 dm3 of gas per hour, whereas in the 200 dm3/h group, the removal efficiency amounted to 5.9%. The work includes a determination of basic process parameters, presentation of a developed functional model and optimized lighting system, proposals for components to be used in the system, and recommendations for an automation and control system for a full-scale implementation. [ABSTRACT FROM AUTHOR]