Effectiveness of biological drying for citric acid dewatered sludge: Evaluating the impact of energy-efficient ventilation strategies.

The effectiveness of dehydration and utilization processes for citric acid dewatered sludge is hampered by its high concentrations of polysaccharides, proteins, and water-binding properties of microbial extracellular polymers (EPS). This research explores the efficacy and mechanisms involved in extracting water from this type of sludge using biological drying technology, with varying rates of ventilation. Especially pertinent was the use of low ventilation rates as control variables. Our results suggest that a scheduled intermittent ventilation at lower rates allows for the most efficient removal of water, achieving a rate of 41.71 % within eight days, according to the zero-order kinetic model. Remarkably, the peak temperature registered was 60 °C, reaching this threshold in just 0.1 days and maintaining high temperatures for approximately 5.9 days. Component analysis of organic matter illustrated a preferential degradation process for lipids under these ventilation conditions which is pivotal for releasing and transforming bound water for efficient extraction, as well as facilitating the breakdown of easily hydrolysable materials. Further, polysaccharide/protein (EPS) decomposition contributed to water removal, though less significantly. The periodic ventilation strategy allowed for the maximum cumulative temperature to be sustained, demonstrating superior efficiency in harnessing bio-generated heat (82.77 % for water evaporation), resulting in dry sludge suitable for self-sustained combustion at relatively low cost ($26.61/t). Highlighted by this study is the considerable potential of energy-efficient ventilation methods in the biological drying treatment of citric acid fermented sludge and similar industrial waste materials.

New insight into the catalytic mechanism of ester hydrogenation over the Cu/ZnO catalyst: the contribution of hydrogen spillover.

The dimethyl maleate hydrogenation activity of Cu, ZnO-X and physically mixed Cu+ZnO-X samples was systematically investigated to probe the essential role of ZnO in ester hydrogenation processes. Cu samples exhibited high CC bond hydrogenation ability with dimethyl succinate as the main product. Comparatively, ZnO was inactive in hydrogenation due to its weak ability to dissociate hydrogen while the CO group could be activated and adsorbed on the ZnO surface. Interestingly, physical mixing with ZnO significantly improved the CO hydrogenation activity of Cu samples. The H2-TPD results reveal the origin of "Cu-ZnO synergy": hydrogen atoms formed on the copper surface can spill over to the ZnO surface and react with the adsorbed CO group.