Investigation on the improvement of activated sludge dewaterability using different iron forms (ZVI vs. Fe(II))/peroxydisulfate combined vertical electro-dewatering processes

Effect of electrolytic zero-valent iron activated sodium hypochlorite on sludge dewatering performance

Using electrolytic zero-valent iron-activated sodium hypochlorite (EZVI-NaClO) to pretreat sludge, the capillary suction time (CST) was utilized to evaluate sludge dewaterability. Ammonia nitrogen (NH4-N), dissolved phosphorus, and total phosphorus in the supernatant were used to analyze sludge disintegration. This approach aimed to evaluate the effectiveness of the pretreatment process and its impact on the sludge composition. The migration and transformation of extracellular polymeric substances (EPS), including dissolved EPS (S-EPS), loosely boundEPS, and tightly bound-EPS (TB-EPS), were analyzed by detecting protein and polysaccharide concentrations and three-dimensional fluorescence excitation-emission spectroscopy (3D-EEM). The sludge particle properties, including sludge viscosity and particle size, were also analyzed. The results suggested that the optimal pH value, NaClO dosage, current, and reaction time were 2, 100 mg/gDS (dry sludge), 0.2A, and 30 min, respectively, with a CST reduction of 43%. Protein and polysaccharide contents in TB-EPS were significantly reduced in the EZVI-NaClO group. Conversely, protein and polysaccharides contents in S-EPS increased, suggesting that EZVI-NaClO treatment could disrupt the EPS. Besides, the viscosity of the treated sludge decreased from 195.4 to 54.9 mPa·S, indicating that sludge fluidity became better. ZEVI-NaClO could enhance sludge dewaterability by destructing protein and polysaccharide structure and improving sludge hydrophobicity.

Sludge biodrying coupled with photocatalysis improves the degradation of extracellular polymeric substances

The efficiency of sludge dewatering is limited by extracellular polymeric substances (EPS) during biodrying. This study investigated the effect of photocatalysis-mediated EPS degradation on sludge dewatering performance during the sludge biodrying process. The photocatalysis of municipal sludge was first carried out to choose a cost-efficient catalyst. Then sludge biodrying tests were performed using TiO2-coated amendment (TCA) and uncoated amendment (TUCA) as the control. Municipal sludge photocatalysis results showed that using TiO2 could efficiently degrade carbohydrates and proteins in the EPS within 60 min. After 20-day biodrying, photocatalysis significantly promoted a reduction in the moisture content and EPS by 17.64% and 6.88%, respectively. The surface-enhanced Raman scattering (SERS) intensities of the C-C-O symmetric stretching vibration peak of D-lactose and the C-S stretching vibration peak of cysteine were significantly decreased by approximately 33.19% and 44.76%, respectively, indicating that photocatalysis indeed promoted the reduction of polysaccharides and cysteine in the EPS, especially after the thermophilic phase. The hydrophilic amino acid content decreased by 23.02%, verifying that photocatalysis could improve EPS hydrophobicity. Consequently, municipal sludge biodrying coupled with photocatalysis promotes sludge EPS degradation and enhances sludge dewaterability, improving the efficiency of sludge biodrying.

Responses of Bacillus sp. under Cu(II) stress in relation to extracellular polymeric substances and functional gene expression level

The production and composition of extracellular polymeric substances (EPS), as well as the EPS-related functional resistance genes and metabolic levels of Bacillus sp. under Cu(II) stress, were investigated. EPS production increased by 2.73 ± 0.29 times compared to the control when the strain was treated with 30 mg L^-1 Cu(II). Specifically, the polysaccharide (PS) content in EPS increased by 2.26 ± 0.28 g CDW^-1 and the PN/PS (protein/polysaccharide) ratio value increased by 3.18 ± 0.33 times under 30 mg L^-1 Cu(II) compared to the control. The increased EPS secretion and higher PN/PS ratio in EPS strengthened the cells' ability to resist the toxic effect of Cu(II). Differential expression of functional genes under Cu(II) stress was revealed by Gene Ontology pathway enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. The enriched genes were most obviously upregulated in the UMP biosynthesis pathway, the pyrimidine metabolism pathway, and the TCS metabolism pathway. This indicates an enhancement of EPS regulation-related metabolic levels and their role as a defense mechanism for cells to adapt to Cu(II) stress. Additionally, seven copper resistance genes were upregulated while three were downregulated. The upregulated genes were related to the heavy metal resistance, while downregulated genes were related to cell differentiation, indicating that the strain had initiated an obvious resistance to Cu(II) despite its severe cell toxicity. These results provided a basis for promoting EPS-regulated associated functional genes and the application of gene-regulated bacteria in heavy metal-containing wastewater treatment.

Encapsulation of zero valent iron nanoparticles in biodegradable amphiphilic janus particles for groundwater remediation

Reactive Zero Valent Iron (ZVI) nanoparticles have been widely explored for in situ ground water remediation to degrade both non-aqueous phase liquid (NAPL) and water-soluble contaminants. However, they usually suffer from rapid oxidation and severe agglomerations restricting their delivery at NAPL/water interface. Aim of this study was to encapsulate the ZVI nanoparticles (50 nm) in amphiphilic bicompartmental Janus particles (711 ± 11 nm) fabricated by EHDC (electrohydrodynamic co-jetting). The dual compartments were composed of PLA (polylactic acid) and a blend of PLA, PE (poly (hexamethylene 2,3-O-isopropylidenetartarate) and PAG (photo acid generator). Upon UV irradiation, PAG releases acid to unmask hydroxyl groups present in PE to make only PE compartment hydrophilic. The entrapped ZVI nanoparticles (20 w/w%; ∼99 % encapsulation efficiency) were observed to degrade both hydrophilic (methyl orange dye) and hydrophobic (trichloro ethylene) contaminants. UV treated Janus particles provided stable dispersion (dispersed up to 3 weeks in water), prolonged reactivity (∼24 days in contaminated water), and recyclability (recyclable up to 9 times) as compared to non-treated ones. In addition, the amphiphilic Janus particles demonstrated high transportability (>95%) through porous media (sand column) with very low attachment efficiency (0.07), making them a promising candidate to target contaminants at NAPL/water interface prevailed in groundwater.

Enhanced dewaterability of lake dredged sediments by electrochemical oxidation of peroxydisulfate on BDD anode

Dredged sediments, as a product of mitigating endogenous pollution of rivers and lakes, cause severe environmental pollution without suitable disposal. To reduce dredged sediments, the electrochemical oxidation (EO) of peroxydisulfate (PS) on a boron-doped diamond (BDD) anode (EO/BDD-PS) was utilized to enhance the dewaterability of the dredged sediments. The soluble chemical oxygen demand increased in the EO/BDD-PS system, and more than 70.0% of the specific resistance to filtration was reduced by EO/BDD-PS within 20 min. The optimal conditions were determined to be as follows: current density, 30 mA cm^-2; PS dosage 4 g L^-1; and initial pH, 6.96. After treatment with EO/BDD-PS, the electronegativity of the sludge flocs was alleviated and the particle size increased from 7.61 to 10.64 μm. Furthermore, proteins and polysaccharides were degraded, and tightly bound extracellular polymeric substances (TB-EPS) and loosely bound EPS (LB-EPS) were effectively transported to soluble EPS (S-EPS). Furthermore, humification of organic matter occurred in S-EPS and LB-EPS when the dredged sediment was treated with EO/BDD-PS. Dominant hydroxyl radicals (•OH) and sulfate radicals (SO₄•^-) were generated in the EO/BDD-PS system. Moreover, the efficiency of the filtrate as an electrolyte decreased slightly after recycling five times. Therefore, this method may be economical for enhancing the dewaterability of dredged sediments.

Application of Advanced Oxidation Technology in Sludge Conditioning and Dewatering: A Critical Review

Sludge dewatering is an important link in sludge treatment. In practical engineering, the dewatering effect of unconditioned sludge is very poor. The use of advanced oxidation technology can improve sludge dewatering performance, reduce sludge capacity, and remove micro-pollutants, which is beneficial for sludge post-treatment and disposal. Based on the current status of sludge conditioning and dehydration, the characteristics of the advanced oxidation method for sludge dehydration were systematically explained using various free radical reaction mechanisms and dehydration conditions. The effects of various advanced oxidation technologies on sludge conditioning and dewatering has been extensively discussed. Finally, the application prospects of the advanced oxidation technology in sludge conditioning and dewatering are presented.