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To improve enzymatic digestibility and sugar concentration, sweet sorghum bagasse was pretreated with alkali and liquid hot water, and then subjected to fed-batch enzymatic hydrolysis. Scanning electron microscopy assay suggested that different pretreatment methods resulted in different composition and structure of residues; these changes had a significant influence on cellulose hydrolysis. Fresh substrate was pretreated and then added at different amounts during the first 48 h to yield a final dry matter content of 30% (w/v). For liquid hot water pretreatment, a maximal glucose concentration of 95.71 g/L, corresponding to 52.85% xylan removal, was obtained with the sweet sorghum bagasse pretreated at 184°C for 18 min. NaOH soaking at ambient conditions removed lignin up to 60%, and the subsequent hydrolysis with cellulase loading of less than 10 FPU/g DM, and substrate supplementation every few hours yield the high glucose and xylose concentrations of 114.89L and 29.93 g/L, respectively after 144 h.

Abstract Influent concentration and effluent standards have strong impacts on technology selection by wastewater treatment plants (WWTPs) and on resource recovery processes. In this paper, resource recovery simulation scenarios incorporated with conventional WWTP models were designed in an imitation of typical existing facilities. We integrated economic analysis and a life cycle assessment to evaluate the impacts of treatment technologies selected for different influent conditions and effluent standards. The results revealed that high concentration influents required the most complicated treatment processes to meet a strict effluent standard. The pattern of total impacts was strongly dependent on the influent conditions. High concentration influent was found to correlate with low energy consumption, low costs, a high nutrient recovery potential but also a high global warming potential when removing 1 kg of pollutants. The incorporation of resource recovery improved the overall performance of WWTPs; however, low concentration influents were not suitable for resource recovery due to their limited benefits. The strict effluent standard limited the resource recovery potential from wastewater, and a loose effluent standard may improve the resource recovery performance, especially for high concentration influents.

Free nitrous acid (FNA i.e. HNO2) was revealed to be effective in enhancing biodegradability of secondary sludge. Also, nitrite-oxidizing bacteria were found to be more susceptible to FNA than ammonium-oxidizing bacteria. Based on these findings, a novel FNA-based sludge treatment technology is proposed to enhance energy recovery from wastewater/sludge. Energy analysis indicated that the FNA-based technology would make wastewater treatment become an energy generating process (yielding energy at 4 kWh/PE/y; kWh/PE/y: kilowatt hours per population equivalent per year), rather than being a large energy consumer that it is today (consuming energy at 24 kWh/PE/y). Importantly, FNA required for the sludge treatment could be produced as a by-product of wastewater treatment. This proposed FNA-based technology is economically and environmentally attractive, and can be easily implemented in any wastewater treatment plants. It only involves the installation of a simple sludge mixing tank. This article presents the concept of the FNA-based technology.