Revealing the mechanisms of rhamnolipid enhanced hydrogen production from dark fermentation of waste activated sludge

Isolation and characterization of novel bacterial strain from sewage sludge and exploring its potential for hydrogen production

Hydrogen (H2) energy has garnered significant attention due to its numerous advantages. Nonetheless, for future commercialization, it is imperative to screen and identify strains with enhanced H2-producing capacities. In order to attain a high and consistent production performance, the conversion of biomass sources into H2 requires careful selection of the most appropriate H2-producing bacteria. This study aimed to isolate and identify a highly effective H2 producing bacteria from local sewage sludge and assess its fermentability for H2 production. The isolate was first identified by means of morphological, phenotypic, biological, and 16 S rRNA investigations. A facultative anaerobe that produces H2 and is gram-negative was identified as Alcaligenes ammonioxydans strain SRAM. For the purpose of determining whether the isolate could produce H2 using glucose as the substrate, its fermentability was evaluated in 500 mL serum bottles. This strain demonstrated the ability to produce H2 from glucose under anaerobic environment, achieving a maximum H2 yield of 2.9 mol H₂/mol of glucose. The highest rate of H2 production, 9.261 mmol H₂/ g dry cell weight per hr, was attained at 37 °C and an initial pH of 6.8. This work effectively illustrated the use of a novel locally isolated strain in the biotechnological conversion of glucose to H2. This strategy offers an effective remedy for the world's energy instability in addition to addressing environmental issues related to industrial operations.

Novel Insights into Alkyl Polyglucoside Biosurfactant Promoting Anaerobic Dark Fermentation for Hydrogen Production in Sludge

Anaerobic fermentation of excess sludge (ES) for hydrogen production is a crucial strategy for resource utilization and environmentally friendly treatment. However, the low hydrolysis efficiency of ES and the depletion of produced hydrogen have become the limiting factors for low hydrogen yield. This study innovatively applied the bio-based surfactant alkyl polyglucoside (APG) to enhance the efficiency of dark fermentation for hydrogen production from ES. When the APG content was 100 mg/g (calculated based on total suspended solids), the maximum hydrogen production reached 17.8 mL/g VSS, approximately 3.7 times that in the control group. Mechanistic analysis revealed that APG promoted the release of organic matter from ES. APG also facilitated the release of soluble protein and soluble polysaccharide, increasing the organic matter reduction rate to 34.8%, significantly higher than other groups. APG enhanced the accumulation of volatile fatty acids and promoted the proportion of small molecular carboxylic acids. Enzyme activity analysis revealed that APG promoted the activity of hydrolytic enzymes but inhibited the activity of hydrogen-consuming enzymes. The research results provide a green and environmentally friendly strategy for the efficient resource utilization of ES.

Alkyl polyglycosides enhanced the dark fermentation of excess sludge and plant waste to produce hydrogen: performance and mechanism

Alkyl polyglycosides (APG), a biodegradable biosurfactant, have been widely used in environmental pollution control. However, the application of APG to enhance anaerobic dark fermentation of excess sludge (ES) and plant waste (PW) to improve hydrogen production has not been reported so far. In order to fill this gap, the effect of APG on hydrogen production from ES and PW was studied in mesophilic (30 °C) environment. The results showed that APG increased the yield of hydrogen, and the recommended dose was 0.15 g/g (calculated as volatile suspended solids), accompanied by 18.7 mL/g. The contribution of APG self-degradation to hydrogen can be ignored. Mechanism investigation revealed that APG promoted the dissolution, hydrolysis, and acidification of complex organic matter, and when the content of APG was 0.15 g/g, the concentration of dissolved chemical oxygen demand (COD) was as high as 3151 mg/L; however, the dissolved concentration of COD in the blank group was only 1548 mg/L. In addition, APG improved the output of volatile fatty acids (VFA). APG promoted the proportion of acetate and butyrate in VFA, which was conducive to hydrogen production. As for the process of methanogenesis, APG reduced the consumption of hydrogen and accumulates hydrogen. This work provides an alternative strategy for the recycling of organic waste and the enhanced generation of hydrogen.

Comparative Analysis of Support Vector Machine Regression and Gaussian Process Regression in Modeling Hydrogen Production from Waste Effluent

Organic-rich substrates from organic waste effluents are ideal sources for hydrogen production based on the circular economy concept. In this study, a data-driven approach was employed in modeling hydrogen production from palm oil mill effluents and activated sludge waste. Seven models built on support vector machine (SVM) and Gaussian process regression (GPR) were employed for the modeling of the hydrogen production from the waste sources. The SVM was incorporated with linear kernel function (LSVM), quadratic kernel function (QSVM), cubic kernel function (CSVM), and Gaussian fine kernel function (GFSVM). While the GPR was incorporated with the rotational quadratic kernel function (RQGPR), squared exponential kernel function (SEGPR), and exponential kernel function (EGPR). The model performance revealed that the SVM-based models did not show impressive performance in modeling the hydrogen production from the palm oil mill effluent, as indicated by the R2 of −0.01, 0.150, and 0.143 for LSVM, QSVM, and CSVM, respectively. Similarly, the SVM-based models did not perform well in modeling the hydrogen production from activated sludge, as evidenced by R2 values of 0.040, 0.190, and 0.340 for LSVM, QSVM, and CSVM, respectively. On the contrary, the SEGPR, RQGPR, SEGPR, and EGPR models displayed outstanding performance in modeling the prediction of hydrogen production from both oil palm mill effluent and activated sludge, with over 90% of the datasets explaining the variation in the model output. With the R2 > 0.9, the predicted hydrogen production was consistent with the SEGPR, RQGPR, SEGPR, and EGPR with minimized prediction errors. The level of importance analysis revealed that all the input parameters are relevant in the production of hydrogen. However, the influent chemical oxygen demand (COD) concentration and the medium temperature significantly influenced the hydrogen production from palm oil mill effluent, whereas the pH of the medium and the temperature significantly influenced the hydrogen production from the activated sludge.

Freezing-low temperature treatment facilitates short-chain fatty acids production from waste activated sludge with short-term fermentation

This study proposed a novel and high-efficiency strategy, i.e., freezing followed by low-temperature thermal treatment, to significantly promote short-chain fatty acids (SCFAs) production from waste activated sludge compared to traditional freezing/thawing treatment. The maximal production of SCFAs was 212 mg COD/g VSS with a shortened retention time of five days, and the potentially recovered carbon source, including SCFAs, soluble polysaccharides and proteins, reached 321 mg COD/g VSS, increased by 92.1 and 28.3% compared to sole freezing and thermal treatment. Both the solubilization and hydrolysis steps of WAS were accelerated, and the acid-producing microorganisms, such as Macellibacteroides, Romboutsia and Paraclostridium, were greatly enriched, with a total abundance of 13.9%, which was only 0.54% in control. Interestingly, the methane production was inhibited at a shortened retention time, resulting in SCFAs accumulation, whereas it was increased by 32.0% at a longer sludge retention time, providing a potential solution for energy recovery from WAS.