Promotion of short-chain fatty acids production and fermented sludge properties via persulfate treatments with different activators: Performance and mechanisms

Persulfates ((peroxymonosulfate (PMS) and peroxydisulfate (PDS)) can disintegrate waste activated sludge (WAS), but their influence on volatile fatty acid (VFA) production during anaerobic fermentation is largely unclear. Particularly, it is unknown whether persulfates can improve fermentation without any preactivation. This study investigated how the direct addition of PMS and PDS into the fermenter influences VFA production from WAS, and uncovered possible mechanisms of improved VFA production. At the PMS dosage of 1.0 mM/gVS, maximum VFA yield (1025 ± 55 mg COD/L) was observed in 5 days of fermentation, which was 24% higher than that with an equimolar addition of PDS and 132% higher than that without persulfate addition. However, the cost-effectiveness of PMS in enhancing VFA production is lower than that of PDS. The in situ generated hydroxyl and sulfate radicals from persulfates in the fermenter enhanced not only WAS disintegration and solubilization but also the formation of biodegradable substances for acidification. Moreover, the direct addition of persulfates into the fermenter shifted the microbial community toward hydrolysisacidification such as Clostridium_sensu_stricto_10 and Fonticella. Results of this study also suggest that preactivation is not necessary when persulfates are applied to improve WAS fermentation.

Section: Resultsmentioning

confidence: 95%

Enhancing Volatile Fatty Acid Production during Anaerobic Fermentation of Waste Activated Sludge with Persulfates: Peroxymonosulfate versus Peroxydisulfate

Fang

Zhang

Spanjers

et al. 2021

“…Anaerobic fermentation has been considered as an appropriate method for the treatment of sludge due to its ability to recover resources in sludge and effectively control sludge . Generally, the biodegradable substances contained in WAS could be easily degraded and utilized during the anaerobic fermentation. , However, apart from the biodegradable substances, toxic and hazardous substances were concentrated in large quantities in sludge, which has been demonstrated to be hard to biodegrade in conventional anaerobic fermentation. , These persistent toxic and harmful substances would inevitably enter the environment with the final disposal of WAS, bringing potential risks to the ecological environment and even human health. , Therefore, it was necessary to adopt pertinent pretreatment for sludge during the anaerobic fermentation.…”

Section: Resultsmentioning

confidence: 99%

“…Anaerobic fermentation or digestion is currently the conventional method used for WAS treatment, during which sludge reduction, recovery of resources and energy (e.g., organic acids, H 2 , and CH 4 ), and environmental risk relief (e.g., inactivation of pathogenic microbes) can be simultaneously achieved. − However, in view of the protective effect of cell wall/membrane and EPS on sludge cells, organic substances contained in sludge are difficult to release from sludge, causing poor sludge solubilization, which is intensively recognized as the rate-determining step of anaerobic treatment of sludge . Moreover, concentrated toxic and hazardous substances in sludge are difficult to effectively biodegrade during numerous sludge treatments such as anaerobic digestion or fermentation. − For example, Golet et al found that only about 10% of norfloxacin was degraded during sludge anaerobic digestion.…”

Section: Introductionmentioning

confidence: 99%

“…7−9 However, in view of the protective effect of cell wall/membrane and EPS on sludge cells, organic substances contained in sludge are difficult to release from sludge, causing poor sludge solubilization, which is intensively recognized as the rate-determining step of anaerobic treatment of sludge. 10 digestion or fermentation. 11−13 For example, Golet et al 11 found that only about 10% of norfloxacin was degraded during sludge anaerobic digestion.…”

Section: ■ Introductionmentioning

confidence: 99%

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Performance and Mechanism of Potassium Ferrate(VI) Enhancing Dark Fermentative Hydrogen Accumulation from Waste Activated Sludge

Kuang

Zhang

et al. 2020

Potassium ferrate (K2FeO4, PF), as a multifunctional green oxidant, has been used for oxidative degradation of pollutants and recovery of resources in sludge. However, its impact on the generation of hydrogen in anaerobic fermentation of waste activated sludge (WAS) is still unclear. The purpose of this work is to study the influence of PF on the dark fermentative hydrogen production. Experimental result suggested that as PF increased from 0 to 0.09 g/g of TSS (total suspended solids), the maximal hydrogen production increased from 1.47 to 8.35 mL/g VSS (volatile suspended solids). A further increase to 0.12 g/g of TSS resulted in a decrease in hydrogen yield. Mechanism studies revealed that that the addition of PF not only facilitated the disruption of sludge cell and extracellular polymeric substances (EPS) but also increased the proportion of biodegradable organics, providing more bioavailable organics for subsequent reactions involved in hydrogen accumulation. Although the activities of microorganisms relevant to dark fermentation were suppressed to a certain extent in the presence of PF, the induced suppression to hydrogen consumers was more severe. Microbial studies indicated that the relative abundances of hydrogen producers (such as Petrimonas and Proteiniborus) were augmented while hydrogen consumers (such as Methanosaeta and Methylocaldum) decreased in the presence of PF.

“…On the one hand, the fermentation can achieve the reduction and harmlessness of excess sludge. On the other hand, the produced VFAs can also serve as a kind of high-quality carbon source for biological phosphorus and nitrogen removal, which has been regarded as a promising strategy. , However, the excess sludge produces less VFAs under conventional fermentation conditions, which limits the wide application of excess sludge anaerobic fermentation. Exogenous pollutants existing in excess sludge, such as heavy metals and nanoparticles, could also influence the anaerobic fermentation process .…”

Section: Introductionmentioning

confidence: 99%

Humic Acid Promotes Volatile Fatty Acids Production from Excess Sludge in Anaerobic Fermentation

Zou

Zheng

et al. 2021

Excess sludge was used to produce volatile fatty acids (VFAs) by fermentation, which has recently attracted much attention because the sludge-derived VFAs were able to function as a kind of ideal carbon source for wastewater biological treatment. This study specifically targeted the mechanism behind the effects of humic acid (HA) on promoting production of VFAs from excess sludge during acidogenic fermentation. The HA was characterized using Fourier-transform infrared (FTIR) spectrum, 13C nuclear magnetic resonance (13C NMR), and 3D excitation–emission matrix (3D-EEM). When HA was present at 1.20 g/g of total chemical oxygen demand, the content of VFAs produced was maximal (1752 mg COD/L) and was about 2.15 times that of the control without HA (815 mg/L). Mechanism exploration revealed that the dominant population of microbial community in the sample with added HA had shifted to Firmicutes, which was related to the acid production. More importantly, the electron transfer between nicotinamide adenine dinucleotide hydrogen (NADH) and nicotinamide adenine dinucleotide (NAD+) was enhanced by HA, contributing to improve the VFAs’ accumulation. In contrast, the activities of the key enzymes, including acetic kinase (AK) and phosphotransferase (PTA), in the acidogenic stage had little change with HA addition, which meant that HA could not stimulate acidification by the way of changing enzymatic activities.