以水熱法進行污泥資源化的研究

Using sewage sludge (SS) as renewable resource is an appropriate way to manage the continuously increasing generation of this waste and protect the environment. Hydrothermal treatment (HT), a thermal-chemical process to treat SS under elevated pressure and temperature, is an effective method and attracts attentions in recent years. HT is not only applied independently to treat sludge (hydrothermal liquefaction (HTL), hydrothermal carbonization (HTC), hydrothermal gasification (HTG), acid-catalyzed hydrolysis (ACH), etc.) but also combined with anaerobic digestion (AD) to pretreat sludge and increase the yield of biogas (hydrothermal pretreatment (HTP)). HTP is an advantageous technology due to its efficacy, simplicity and sanitation effects and can effectively break down the crystalline complexes of lignocellulose, protein and lipid in waste and thus become more accessible to the bacteria. HTP of sewage sludge (SS) has been shown to improve the subsequent biogas production by anaerobic digestion (AD), but the effect of catalysts on HTP performance was less explored. This study intended to investigate the SS pretreatment by wet air oxidation (WAO) with the addition of K2CO3 as a catalyst on the performance of methane production by AD. WAO was found to improve the solubilization of SS, the soluble chemical oxygen demand, dissolved organic carbon, and total dissolved nitrogen. The methane yield from WAO increased from 202 mL/gVSin with no catalyst added to 277 mL/gVSin with 10 wt% of K2CO3 added at 180°C with 30 min of residence time. Under this pretreatment condition, the highest methane production rate could achieve 15.8 mL/gVSin day, and the percentage of methane reached 73%. The structure of the microbial community involved in the AD was affected by the residence time, working gas, and catalyst of the HTP process. The results showed that Bacteroidetes, Bacteroidia, and SC103 were the dominant phylum, class, and genus of bacteria, respectively, of almost all of the samples. In addition, the most abundant archaeal order was Methanosarcinales, while Methanosaeta was the dominant archaeal genus of most of the samples. However, Methanosarcina largely increased the relative abundance, corresponding to the amount of K2CO3 catalyst used. The findings in this study demonstrated the potential use of K2CO3 during WAO of SS and implied the link between shift of methanogen community and the enhanced methane yield in AD. Although AD has many benefits such as lower cost, lower energy consumption, and stable operation in comparison with other techniques, it still has long start-up time and recovery time. Besides, ACH, applied to the production of biofuel and chemicals from biomass has been extensively investigated in the past few decades, stabilizes SS in short time. SS is an organic biomass from wastewater treatment plants, but the use of SS to produce bio-based chemicals under ACH processes is not well investigated. In this study, ACH processes were performed at 120, 150, and 180°C using sulfuric acid (H2SO4) with concentrations of 0–0.5M within a reaction time of 90–180 min to produce bio-based chemicals from SS. The results showed that the reaction temperature, reaction time, and concentrations of H2SO4 affected the yields of sugars, levulinic acid (LA), and 5-hydroxymethylfurfural (HMF). The highest xylose and glucose yields were 7.69 mol% and 5.22 mol% at 120°C with 0.5M H2SO4 during the 180 min of reaction time, respectively. Besides, under the ACH process at 180°C and 180 min, the yield of LA reached a maximum value of 0.48 mol% at 0.5M H2SO4, and the highest yield of HMF was 1.66 mol% at 0.1M H2SO4. The obtained data also indicated that the ACH process led to an increase in soluble chemical oxygen demand, dissolved organic carbon, and total dissolved nitrogen. Fluorescence excitation-emission matrix of dissolved organic matter and thermogravimetric analysis of the treated SS further supported the enhanced solubilization of SS after ACH process, especially under higher reaction temperature and concentrations of H2SO4. Although the lower yields of bio-based chemicals might restrict the downstream recovery of the target products, the largely improved SS solubilization by ACH suggests that acid-catalyzed hydrothermal hydrolysis process has potential as an alternative pretreatment method of SS. In this study, the obtained results revealed that added K2CO3 during WAO of SS improved the biogas yield in AD process, and ACH process could be applied for the recovery of green material and fuel additives from SS.

並列關鍵字

Sewage sludge ； hydrothermal pretreatment ； anaerobic digestion ； acid-catalyzed hydrolysis ； sugars ； levulinic acid ； 5-hydroxymethylfurfural

參考文獻

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以水熱法進行污泥資源化的研究

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