The process and energy intensifications for the synthesis of glycerol carbonate (GC) from glycerol and dimethyl carbonate (DMC) using an eggshell-derived CaO heterogeneous catalyst were investigated. The transesterification reaction between glycerol and DMC was typically limited by mass transfer because of the immiscible nature of the reactants. By varying the stirring speed, it was observed that the mass transfer limitation could be neglected at 800 rpm. The presence of the CaO solid catalyst made the mass transport-limited reaction process more prominent. Mass transfer intensification using a simple kitchen countertop blender as an alternative to overcome the external mass transfer limitation of a typical magnetic stirrer was demonstrated. A lower amount of the catalyst and a shorter reaction time were required to achieve 93% glycerol conversion or 91% GC yield, and the turnover frequency (TOF) increased almost 5 times from 1.5 to 7.2 min−1 when using a conventional magnetic stirrer and countertop blender, respectively. In addition, using a simple kitchen countertop blender with 7200 rpm, the reaction temperature of 60 °C could be reached within approximately 3 min without the need of a heating unit. This was the result of the self-frictional heat generated by the high-shear blender. This was considered to be heat transfer intensification, as heat was generated locally (in situ), offering a higher homogeneity distribution. Meanwhile, the trend toward energy intensification was promising as the yield efficiency increased from 0.064 to 2.391 g/kJ. A comparison among other process intensification techniques, e.g., microwave reactor, ultrasonic reactor, and reactive distillation was also rationalized.
Anaerobic treatment processes are widely recognized as a sustainable wastewater management system for their encouraging results in treating highly concentrated wastewater (bCOD > 4000 mg/L) with low energy requirement, which is more economical than aerobic processes. High rate anaerobic reactors, particularly up-flow anaerobic sludge blanket (UASB) reactors, have been extensively employed worldwide due to their high volumetric organic capacity and less sludge yield. However, some limiting factors need to be resolved for large-scale applications. This review aims to emphasize the organic removal of municipal and industrial wastewater using UASB technology and its application in the anammox process in treating ammonia-rich wastewater.Keywords: Anaerobic, anammox, granulation, Up-flow Anaerobic Sludge Blanket (UASB)
Abstract A common challenge for the anaerobic digestion (AD) of food waste (FW) is the contamination by disposable plastic materials and utensils. The objective of this batch study was to investigate the effects of disposable plastic materials – polystyrene (PS), polypropylene (PP), high density polyethylene (HDPE) and wooden chopsticks (WC) on the AD of FW. Results showed that methane production from the AD of FW was inhibited to different extents when different materials were present in FW. PS and PP were found to reduce methane production from food waste more than HDPE and WC. The reduction in methane production was hypothesized to be due to the production of toxic plastic by-products or due to reduced contact between microbes and FW. Pyrosequencing and Field Emission Scanning Electron Microscope (FESEM) results indicated that the reduction in methane production was more likely due to the interference of good contact necessary between microbes and FW for biodegradation, and that the biological processes of AD were not affected by the contamination of plastics. Greater reductions in methane yields were also observed when the surface areas of the disposable materials were increased. Studying the effects of disposable materials on the AD of FW would provide plant operators with more information that could optimise the process of resource recovery from food waste.
Stabilized landfill leachate is well known to contain high concentration of nitrogen particularly in the ammonium nitrogen (-N) form. Also considering of high toxicity of non-biodegradable and low proportion of biodegradable compounds in stabilized landfill leachate, the conventional biological treatment of nitrogen is usually inefficient. As such, the quest of this study was to revise the operational strategies of bioreactor, i.e. moving bed sequencing batch reactor (MBSBR), for the enhancement of nitrogen removal from stabilized landfill leachate. The performance of MBSBRs packed with 8% (v/v) of polyurethane (PU) cubes and polyethylene (PE) rings, respectively, in removing nitrogen from a combined stabilized landfill leachate and domestic wastewater in increasing leachate volumetric ratio under various operational strategies was investigated. On increasing the leachate volumetric ratio to 14%, the performance of both MBSBRs in -N removal was comparable under the continuous aeration strategy. When the aeration strategy was changed to intermittent aeration (IA), the MBSBR with PU media achieved a higher -N removal rate, while the MBSBR with PE media failed to remove -N completely. For the MBSBR with PU media, the adoption of IA coupled with step feeding strategy had yielded a removal efficiency of 80% for total nitrogen in comparison to 64% if only IA strategy was adopted at the leachate volumetric ratio of 14%. Nevertheless, further increase in leachate volumetric ratio to 20% had led to the accumulation of -N in the effluent of MBSBR under IA-SF strategy. At this stage, the MBSBR operated with IA strategy could still remove -N completely. Thus, the IA-MBSBR with PU media is the preferred operational strategy for nitrogen removal at higher leachate volumetric ratio.
The surge of toxic contaminants and harmful microorganisms in aquatic environment have posed irreparable and deplorable impacts to human health and progressively disturbance to ecosystem and environment. Herein, we have successfully devised a novel visible light S-scheme Fe2WO6/SrTiO3 composite using a two-step hydrothermal technique and tested by myriad material characterization methods. An intimate contact and a heterojunction constructed between Fe2WO6 nanoparticles and cube-like SrTiO3 has been verified by microscopic images. The as-synthesized composite exhibited enhanced light absorption and lower charge carrier recombination rate as demonstrated by UV–vis absorption spectra and photoelectrochemical data. Under visible light exposure, 20 wt% Fe2WO6/SrTiO3 displayed the best photodegradation of Rhodamine B and the apparent rate constant of which was 1.9 and 2.7 times higher than those of pristine Fe2WO6 and pristine SrTiO3, respectively. The boosted photoactivity of the composite can be attributed to the superior charge carrier segregation efficiency and high redox capabilities resulted from S-scheme heterojunction. A stable photocatalytic performance of Fe2WO6/SrTiO3 was also found after fifth cyclic runs. Moreover, the mineralization efficiency of real printed ink wastewater treatment over Fe2WO6/SrTiO3 was scrutinized by chemical oxygen demand analysis. Excellent antibacterial property of Fe2WO6/SrTiO3 has been confirmed from its destructive action against Escherichia coli and Bacillus cereus. Furthermore, the comprehensive photodegradation mechanism was elucidated in detail.
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