Effect of sodium dichloroisocyanurate treatment on enhancing the biodegradability of waste-activated sludge anaerobic fermentation

Disinfectant sodium dichloroisocyanurate synergistically strengthened sludge acidogenic process and pathogens inactivation: Targeted upregulation of functional microorganisms and metabolic traits via self-adaptation

Harmless and resourceful treatment of waste activated sludge (WAS) have been the crucial goal for building environmental-friendly and sustainable society, while the synergistic realization approach is currently limited. This work skillfully utilized the disinfectant sodium dichloroisocyanurate (NaDCC) to simultaneously achieve the pathogenic potential inactivation (decreased by 60.1 %) and efficient volatile fatty acids (VFAs) recovery (increased by 221.9 %) during WAS anaerobic fermentation in rather cost-effective way (Chemicals costs:0.4 USD/kg VFAs versus products benefits: 2.68 USD/kg chemical). Mechanistic analysis revealed that the C=O and NCl bonds in NaDCC could spontaneously absorb sludge (binding energy -4.9 kJ/mol), and then caused the sludge disintegration and organic substrates release for microbial utilization due to the oxidizability of NaDCC. The disruption of sludge structure along with the increase of bioavailable fermentation substrates contributed to the selectively regulation of microbial community via enriching VFAs-forming microorganisms (e.g., Pseudomonas and Streptomyces) and reducing VFAs-consuming microorganisms, especially aceticlastic methanogens (e.g., Methanothrix and Methanospirillum). Correspondingly, the metabolic functions of membrane transport, substrate metabolism, pyruvate metabolism, and fatty acid biosynthesis locating in the central pathway of VFAs production were all upregulated while the methanogenic step was inhibited (especially acetate-type methanogenic pathway). Further exploration unveiled that for those enriched functional anaerobes were capable to activate the self-adaptive systems of DNA replication, SOS response, oxidative stress defense, efflux pump, and energy metabolism to counteract the unfavorable NaDCC stress and maintain high microbial activities for efficient VFAs yields. This study would provide a novel strategy for synergistic realization of harmless and resourceful treatment of WAS, and identify the interrelations between microbial metabolic regulations and adaptive responses.

Bactericidal Activity of Superabsorbent Polymer Granules for Their Applications in Respiratory Fluid Solidification Systems

Disposal of respiratory secretions from patients having contagious diseases (e.g., COVID-19 and tuberculosis) poses a high risk of infection for healthcare workers. AcryloSorb canister liner bags are highly efficient for the safe handling of contagious respiratory secretions via solidification and disinfection processes. The canister liner bags are lined with disinfectant-impregnated superabsorbent polymer (DSAP) granules. The liner structure in the bag has a patented design that has upward progressive absorbent availability (Indian Patent application # 202041019872). AcryloSorb canister liner bags can decontaminate the fluid secretions absorbed in the bag and solidify within 10 min. The present study focused on the bactericidal effect of DSAP using Gram-negative bacteria, Klebsiella pneumoniae, and Gram-positive bacteria, methicillin-resistantStaphylococcus aureus (MRSA). Disinfectants such as peracetic acid (ethaneperoxic acid), sodium dichloroisocyanurate (sodium 3,5-dichloro-2,4,6-trioxo-1,3,5-triazinan-1-ide), rose bengal (disodium; 2,3,4,5-tetrachloro-6-(2,4,5,7-tetraiodo-3-oxido-6-oxoxanthen-9-yl) benzoate), and N,N-dimethyl-N-[3-(triethoxysilyl)propyl]octadecan-1-aminium chloride at different weight ratios were impregnated in superabsorbent polymer (SAP) granules. The bactericidal activities of DSAP were studied along with its solidification capacity. Disinfectants showed different bactericidal activities when impregnated with SAP granules. For example, peracetic acid-impregnated SAP granules (DSAP-P) showed 100% bactericidal activity for both Klebsiella pneumoniae and MRSA at 0.5 wt % peracetic acid. Sodium dichloroisocyanurate-impregnated SAP granules showed 100% bactericidal activity only at 5 wt % sodium dichloroisocyanurate (DSAP-S5). Even though peracetic acid was highly effective, SAP granules collapsed when impregnated with peracetic acid. The ease of handling, disinfection efficacy, and preserving the morphology of SAP granules make DSAP-S5, a suitable candidate for AcryloSorb canister liner bags.

Bacterial antioxidant mechanism in calcium peroxide aided sludge anaerobic fermentation

Although calcium peroxide (CaO₂) can enhance the short-chain fatty acids (SCFAs) production in sludge anaerobic fermentation, the microbiological mechanisms underlying this process remain unclear. In this study, it is aimed to elucidate the bacterial protective mechanisms in response to the oxidative stress induced by CaO₂. Results show that extracellular polymeric substance (EPS) and anti-oxidant enzymes play vital roles in protecting bacterial cells from CaO₂. The addition of CaO₂ resulted in increased relative abundances of genes exoP and SRP54, which are associated with EPS secretion and transportation. Superoxide dismutase (SOD) played a crucial in alleviating oxidative stress. The dosage of CaO₂ significantly influences the succession of the bacterial community in the anaerobic fermentation system. With 0.3 g CaO₂/g VSS, the net income was approximately 4 USD/ton of sludge treated. The CaO₂-assisted anaerobic fermentation process has the potential to recover more resources from sludge and thus, benefit the environment.

Enhancing anaerobic fermentation of waste activated sludge by investigating multiple electrochemical pretreatment conditions: Performance, modeling and microbial dynamics

Electrochemical pretreatment (EPT) is an efficient technology to improve volatile fatty acids (VFAs) production during anaerobic fermentation of waste activated sludge (WAS). This study investigated the co-effects of different current intensities, electrolyte NaCl dosage and pretreatment time for promoting VFAs production. The results showed that it was considerably enhanced by 51.6 % when EPT was performed at 1.0 A, 1.0 g/L and 60 min, and response surface methodology strategy adjusted the optimal EPT conditions to 1.0 A, 1.2 g/L and 66 min. The potential mechanisms were proposed that EPT at optimal conditions greatly enhanced solubilization and hydrolysis of WAS and selectively inactivated methanogens, causing the enrichment of acidogenic bacteria (i.e., Lactobacillus, Saccharimonadales, Tetrasphaera and Prevotella) due to generated reactive chlorine species. Finally, the economic analysis indicated the promising application potential with the profit of EPT at optimal conditions increasing by 36.0 %.

Quantitative and Qualitative Changes in the Genetic Diversity of Bacterial Communities in Anaerobic Bioreactors with the Diatomaceous Earth/Peat Cell Carrier

This paper analyses the impact of the diatomaceous earth/peat (DEP; 3:1) microbial carrier on changes in the bacterial microbiome and the development of biofilm in the anaerobic digestion (AD) of confectionery waste, combined with digested sewage sludge as inoculum. The physicochemical properties of the carrier material are presented, with particular focus on its morphological and dispersion characteristics, as well as adsorption and thermal properties. In this respect, the DEP system was found to be a suitable carrier for both mesophilic and thermophilic AD. The evaluation of quantitative and qualitative changes in the genetic diversity of bacterial communities, carried out using next-generation sequencing (NGS), showed that the material has a modifying effect on the bacterial microbiome. While Actinobacteria was the most abundant cluster in the WF-control sample (WF—waste wafers), Firmicutes was the dominant cluster in the digested samples without the carrier (WF-dig.; dig.—digested) and with the carrier (WF + DEP). The same was true for the count of Proteobacteria, which decreased twofold during biodegradation in favor of Synergistetes. The Syntrophomonas cluster was identified as the most abundant genus in the two samples, particularly in WF + DEP. This information was supplemented by observations of morphological features of microorganisms carried out using fluorescence microscopy. The biodegradation process itself had a significant impact on changes in the microbiome of samples taken from anaerobic bioreactors, reducing its biodiversity. As demonstrated by the results of this innovative method, namely the BioFlux microfluidic flow system, the decrease in the number of taxa in the digested samples and the addition of DEP contributed to the microbial adhesion in the microfluidic system and the formation of a stable biofilm.

Mechanism of dielectric barrier discharge plasma technology to improve the quantity of short-chain fatty acids in anaerobic fermentation of waste active sludge

The mechanism of improving the anaerobic fermentation performance of waste active sludge by using dielectric barrier discharge (DBD) plasma pretreatment technology was investigated. The maximum accumulation of short-chain fatty acids (SCFAs) was observed on the 7th day of anaerobic fermentation when the DBD power was 76.50 W, which was 1726.70 mg COD/L, 1.50 times of the control group. The ratio of acetic acid in DBD group was 9.30% higher than that in the control. Further mechanism research indicated that DBD pretreatment can destroy the structure of extracellular polymer substances and release organic substances such as protein and polysaccharide. The dissolved organic matter analysis indicated that the DBD technique could increase the release of biodegradable organics (eg., tyrosine proteins, soluble microbial by-products), thus accelerate the biotransformation of organic substance. Bacterial community structure analysis showed that the increase in the abundance of Firmicutes and Bacteroidetes and the decrease in the abundance of Proteobacteria in DBD group were beneficial to the accumulation of SCFAs. Besides, further archaeal analysis indicated that the decrease of Methanosaeta sp. and Methanosarcina sp. abundance in the DBD group facilitate acetic acid accumulation. This study demonstrated that the DBD technique can be used as an effective and potential pretreatment method to improve sludge anaerobic fermentation performance.

A collaborative strategy for enhanced anaerobic co-digestion of food waste and waste activated sludge by using zero valent iron and ferrous sulfide

The application of sulfidated zero-valent iron as an alternative used in coupled anaerobic systems to improve methane production is usually restricted by its high production costs and toxic gasses and wastewater generation. In this study, a collaborative strategy for coupling zero-valent iron (ZVI) and ferrous sulfide (FeS) together into anaerobic systems was used to evaluate the enhancement of methanogenesis during the co-digestion of food waste and waste activated sludge, with the microbial evolution and metabolic pathway revealed. Results showed that the enhanced hydrolysis and acidogenesis process of co-digestion in this coupled anaerobic system could be attributed to synergistic interactions among ZVI, FeS, and microorganisms. Furthermore, both acetoclastic and hydrogenotrophic pathways could be promoted by coupling ZVI and FeS. This study demonstrated that coupling ZVI and FeS together into anaerobic systems would be a promising method for improving the methanogenic performance for municipal solid waste treatment.