Effect of alkyl polyglycosides on the performance of thermophilic bacteria pretreatment for saline waste sludge hydrolysis

Effect of rhamnolipid on the performance of compound thermophilic bacteria agent pretreatment system for waste sludge hydrolysis

This study innovatively introduced rhamnolipid (RL) to compound thermophilic bacteria (TB) agent pretreatment system for further accelerating the waste sludge hydrolysis and substrates transformation. The results showed that combined pretreatment was beneficial for the sludge extracellular polymers (EPS) rupture and dissolved organic matters (DOM) release. In the optimal dosage of 40 mg/g SS RL, the activities of protease and α-glucosidase increased by 20.7 % and 33.3 % than that without RL addition, respectively. The addition of RL enhanced efficient contacts between hydrolases and organic substrates, and excitation emission matrix (EEM) spectrum revealed that combined pretreatment with 40 mg/g SS RL could achieve higher soluble microbial by-products occupancy (54 %) and lower fulvic acid-like substances (6 %) occupancy in DOM, promoting the waste sludge biodegradability. High organics availability conducted to more shifts in microbial community structure, compared with TB agent pretreatment, the relative abundance of genus Geobacillus and norank_f__Synergistaceae were enhanced by 29.08 and 0.33 times in combined pretreatment system, respectively, which was conducive to sludge hydrolysis and subsequent anaerobic fermentation process.

Enhancement of methane production from anaerobic digestion of Erigeron canadensis via O2-nanobubble water supplementation

Malignant invasive Erigeron canadensis, as a typical lignocellulosic biomass, is a formidable challenge for sustainable and efficient resource utilization, however nanobubble water (NBW) coupled with anaerobic digestion furnishes a prospective strategy with superior environmental and economic effectiveness. In this study, influence mechanism of various O2-NBW addition times on methanogenic performance of E. canadensis during anaerobic digestion were performed to achieve the optimal pollution-free energy conversion. Results showed that supplementation of O2-NBW in digestion system could significantly enhance the methane production by 10.70-16.17%, while the maximum cumulative methane production reached 343.18 mL g-1 VS in the case of one-time O2-NBW addition on day 0. Furthermore, addition of O2-NBW was conducive to an increase of 2-90% in the activities of dehydrogenase, α-glucosidase and coenzyme F420. Simultaneously, both facultative bacteria and methanogenic archaea were enriched as well, further indicating that O2-NBW might be responsible for facilitating hydrolytic acidification and methanogenesis. Based on Kyoto Encyclopedia of Genes and Genomes (KEGG) cluster analysis, provision of O2-NBW enhanced the metabolism of carbohydrate and amino acid, translation as well as membrane transport of bacteria and archaea. This study might offer the theoretical guidance and novel insights for efficient recovery of energy from lignocellulosic biomass on account of O2-NBW adhibition in anaerobic digestion system, progressing tenor of carbon-neutral vision.

Improved anaerobic sludge fermentation mediated by a tryptophan-degrading consortium: Effectiveness assessment and mechanism deciphering

The hydrolysis of extracellular polymeric substances (EPS) represents a critical bottleneck in the anaerobic fermentation of waste activated sludge (WAS), while tryptophan is identified as an underestimated constituent of EPS. Herein, we harnessed a tryptophan-degrading microbial consortium (TDC) to enhance the hydrolysis efficiency of WAS. At TDC dosages of 5%, 10%, and 20%, a notable increase in SCOD was observed by factors of 1.13, 1.39, and 1.88, respectively. The introduction of TDC improved both the yield and quality of short chain fatty acids (SCFAs), the maximum SCFA yield increased from 590.6 to 1820.2, 1957.9 and 2194.9 mg COD/L, whilst the acetate ratio within SCFAs was raised from 34.1% to 61.2-70.9%. Furthermore, as TDC dosage increased, the relative activity of protease exhibited significant increments, reaching 116.3%, 168.0%, and 266.1%, respectively. This enhancement facilitated WAS solubilization and the release of organic substances from bound EPS into soluble EPS. Microbial analysis identified Tetrasphaera and Soehngenia as key participants in WAS solubilization and the breakdown of protein fraction. Metabolic analysis revealed that TDC triggered the secretion of enzymes associated with amino acid metabolism and fatty acid biosynthesis, thereby fostering the decomposition of proteins and production of SCFAs.

Amelioration of Biogas Production from Waste-Activated Sludge through Surfactant-Coupled Mechanical Disintegration

The current study intended to improve the disintegration potential of paper mill sludge through alkyl polyglycoside-coupled disperser disintegration. The sludge biomass was fed to the disperser disintegration and a maximum solubilization of 6% was attained at the specific energy input of 4729.24 kJ/kg TS. Solubilization was further enhanced by coupling the optimum disperser condition with varying dosage of alkyl polyglycoside. The maximum solubilization of 11% and suspended solid (SS) reduction of 8.42% were achieved at the disperser rpm, time, and surfactant dosage of 12,000, 30 min, and 12 μL. The alkyl polyglycoside-coupled disperser disintegration showed a higher biogas production of 125.1 mL/gCOD, compared to the disperser-alone disintegration (70.1 mL/gCOD) and control (36.1 mL/gCOD).

Synergic role of ferrate and nitrite for triggering waste activated sludge solubilisation and acidogenic fermentation: Effectiveness evaluation and mechanism elucidation

Enhancing anaerobic treatment efficiency of waste activated sludge (WAS) toward preferable resource recovery would be an important requirement for achieving carbon-emission reduction, biosolids minimization, stabilization and security concurrently. This study demonstrated the synergic effect of potassium ferrate (PF) and nitrite on prompting WAS solubilisation and acidogenic fermentation toward harvesting volatile fatty acids (VFAs). The results indicated the PF+NaNO₂ co-pretreatment boosted 7.44 times and 1.32 times higher WAS solubilisation [peak soluble chemical oxygen demand (SCOD) of 2680 ± 52 mg/L] than that by the single nitrite- and PF-pretreatment, respectively, while about 2.77 times and 2.11 times higher VFAs production were achieved (maximum VFAs accumulation of 3536.25 ± 115.24 mg COD/L) as compared with the single pretreatment (nitrite and PF)-fermentations. Afterwards the WAS dewaterability was improved simultaneously after acidogenic fermentation. Moreover, a schematic diagram was established for illustrating mechanisms of the co-pretreatment of PF and nitrite for enhancing the VFAs generation via increasing key hydrolytic enzymes, metabolic functional genes expression, shifting microbial biotransformation pathways and elevating abundances of key microbes in acidogenic fermentation. Furthermore, the mechanistic investigations suggested that the PF addition was conducive to form a relatively conductive fermentation environment for enhancing electron transfer (ET) efficiency, which contributed to the VFAs biotransformation positively. This study provided an effective strategy for enhancing the biodegradation/bioconversion efficiency of WAS organic matters with potential profitable economic returns.

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.

Revealing the intrinsic drawbacks of waste activated sludge for efficient anaerobic digestion and the potential mitigation strategies

Anaerobic digestion (AD) is an effective approach for waste activated sludge (WAS) disposal with substantial recovery of valuable substrates. Previous studies have extensively explored the correlations of common operational parameters with AD efficiency, but the impacts of intrinsic characteristics of WAS on the AD processes are generally underestimated. This study focused on disclosing the association of intrinsic drawbacks in WAS with AD performance, and found that the cemented WAS structure, low fraction of biomass and various high levels of inhibitory pollutants (e.g., organic pollutants and heavy metals), as the integral parts of WAS all greatly restricted the AD performance. The main potential strategies and underlying mechanisms to mitigate the restrictions for efficient WAS digestion, including the practical pretreatment methods, bioaugmentation and aided substances addition, were critically analyzed. Also, future directions for the improvement of WAS digestion were proposed from the perspectives of technical, management and economic aspects.

Polysorbate-80 pretreatment contributing to volatile fatty acids production associated microbial interactions via acidogenic fermentation of waste activated sludge

Polyoxyethylene dehydration sorbitol monooleate (polysorbate-80) pretreatment enhanced volatile fatty acids (VFAs) production of waste activated sludge (WAS) in acidogenic fermentation. The results showed that polysorbate-80 ameliorated WAS solubilization obviously with a soluble chemical oxygen demand (SCOD) increasing to 1536 mg/L within 4 h. Within 2 days of acidogenic fermentation, the maximal VFAs arrived to 2958.35 mg COD/L via polysorbate-80-pretreatment. The polysorbate-80 pretreatment boosted microbial diversity and richness in fermentation process. The Clostridium, Macellibacteroides and Acidocella strengthened microbial cooperation for the metabolic functions enhancement (e.g. amino acid metabolism and carbohydrate metabolism) for VFAs generation from WAS organics. Overall, the polysorbate-80 could play positive roles on the transformation of organic matter from sludge solid matters to VFAs, which was turned out to become an effective enhancing strategy for future WAS treatment / bioresource recovery with relatively low cost.

Thermophilic bacteria combined with alkyl polyglucose pretreated mariculture solid wastes using as denitrification carbon source for marine recirculating aquaculture wastewater treatment

In marine recirculating aquaculture systems (RAS), efficient nitrogen removal is challenging due to the high NO₃^--N concentration, low organic matters content, and high salinity. In this study, mariculture solid wastes (MSW) acidogenic liquid pretreated by thermophilic bacteria (TB) combined with alkyl polyglucose (APG) was first used as carbon source for denitrification to remove NO₃^--N. TB + APG pretreatment could accelerate the hydrolysis of MSW, and the highest volatile fatty acids (VFAs) yield (40.3%) was obtained with TB + 0.2 g/g VSS APG pretreatment. MSW acidogenic liquid pretreated by TB + 0.2 g/g VSS APG was a reliable carbon source for denitrification, and the optimum COD/NO₃^--N ratio (C/N) was 8 with no residue of NO_x^--N. VFAs were more effectively utilized by denitrifiers than carbohydrate and protein. The high denitrification potential (P_DN) and denitrification rate (V_DN) indicated the higher denitrification ability at C/N of 8 using MSW acidogenic liquid as carbon source. The outcomes of this work could provide useful information for promoting technological innovation in marine RAS wastewater treatment.