Recovering and potentially applying of alginate like extracellular polymers from anaerobic digested sludge

Evaluating the contact angle as an indicator of sludge dewatering performance: Limitations and methodological insights

This study evaluates the utility of contact angle (CA) as an indicator of sludge dewatering performance, addressing inconsistencies in previous findings and the lack of a clear standard. We systematically compared four pretreatment methods-agar coating, in-situ filtration, lyophilization, and hot air drying-to assess contact angle efficacy. Measurement reliability was determined using standard deviation and coefficient of variation (CV), revealing that hot air drying (74.85° ± 4.24°, CV 5.67 %) and lyophilization (71.48° ± 4.74°, CV 6.6 %) exhibited significantly lower variability than agar coating (42.54° ± 12.24°, CV 28.7 %) and in-situ filtration (53.35° ± 9.66°, CV 18.1 %). Correlation matrix and Variable Importance in Projection (VIP) analyses indicated that contact angle only partially correlates with dewatering performance indicators, including water content, capillary suction time (CST), and specific resistance to filtration (SRF). Importantly, the predictive power of CA measurements varies across different pretreatment methods, underscoring its limitations as a standalone metric. Over-reliance on CA measurements may lead to biased conclusions. This study offers key perspectives on refining CA measurement methods and highlights the importance of comprehensive evaluation of sludge dewatering performance, guiding the development of more efficient treatment technologies.

Efficacy and application potential of purified hydrocolloid coatings sprayed onto maize seeds subjected to anti-aging

The use of purified hydrocolloids extracted from waste-activated sludge has significant potential for preventing seed deterioration caused by aging. In this study, we compared the advantages and disadvantages of 3 types of purified hydrocolloid seed coatings from different waste sludges and one commercial seed coating at different spraying times (2, 4, 6, and 8). Compared with coated maize seeds, uncoated maize seeds underwent significant functional changes during the aging process according to the infrared spectroscopy results. Subsequent pot experiments were conducted at 4 days after aging. The average germination rate of the coated maize seeds was greater than that of the uncoated seeds at all spraying times. In terms of antioxidant enzyme activities, seeds treated with different coatings presented an increasing trend with increasing spraying time, indicating a difference between different spraying times. Principal component analysis revealed that the optimum number of sprays to achieve the results of carboxymethyl cellulose seed coating was 8 for the Xiaohongmen Wastewater Treatment Plant, 6 for the Dongba Wastewater Treatment Plant, and 4 for the Nanyang Wastewater Treatment Plant. The number of sprays applied in practice is an important determining factor during seed storage.

Effects of Extraction Methods on the Thermal Stability of Extracellular Polymeric Substances-Based Biomaterials from Wastewater Sludge

Various methods for recovering extracellular polymeric substances (EPS)-based biomaterials from wastewater sludge exist. However, the relationships between extraction methods and properties of biomaterials have not been fully explored. In this study, the thermal properties, including activation energy (AE) and thermal decomposition mechanism, of EPS-based biomaterials extracted by different methods have been determined by thermogravimetric analysis integrated with the deconvolution method. Simultaneously, the chemical properties of these biomaterials, such as the extraction yield, chemical composition, and functional groups, have been monitored to clarify the influences of extraction methods. Notably, proteins and humic-like substances have been found as the major components to determine thermal stability and AE. Moreover, the physicochemical method shows significant effects on enhancing extraction yield and AE, with the NaOH and heat methods proving to be outstanding by delivering the highest AE of 300 kJ/mol and a substantial char formation of 24%. The results have demonstrated the significant impact of extraction methods on the thermal stability of EPS-based biomaterials. Moreover, this finding provides insights into the linkages between the properties of EPS-based biomaterials and extraction methods to guide the selection of appropriate extraction methods tailored to specific applications, including flame-resistant materials.

Occurrence and mechanism of sulfamethoxazole in alginate-like extracellular polymers from excess sludge

The recovery of biopolymers, particularly alginate-like extracellular polymers, from municipal sludge represents a promising step toward sustainable sludge treatment practices. Originating from wastewater plants in complexly polluted environments, alginate-like extracellular polymers carry potential environmental risks concerning their reuse. This study employs ultrahigh-performance liquid chromatography-tandem mass spectrometry to investigate the distribution coefficients and occurrence of alginate-like extracellular polymers and sulfamethoxazole. Results demonstrate a negative distribution coefficient, suggesting an inhibitory effect on sulfamethoxazole dissolution. The ethanol-extracted alginate-like extracellular polymers exhibits higher sulfamethoxazole levels (approximately 52%) than those obtained via dialysis extraction. Three-dimensional excitation-emission matrix analysis and adsorption studies indicate the absence of tyrosine-like substances in the alginate-like extracellular polymers, unlike in other extracellular polymeric substances. This absence diminishes hydrophobic interactions, highlighting that electrostatic interactions play a more important role. These insights are crucial for understanding the adsorption behavior of alginate-like extracellular polymers and optimizing their large-scale extraction processes.

The feasibility and applicability of sequential extraction of high value-added biogenic materials from sewage sludge

The sequential extraction routes of biogenic materials from sewage sludge (SS) were investigated. Physical methods (ultrasound, heating) and chemical methods (sodium hydroxide, sodium carbonate) were used to extract extracellular polymeric substances (EPS) and alginate-like extracellular polymers (ALEs) from SS. The residues after extraction were further subjected to physical methods (heating) and chemical methods (sulfuric acid, sodium hydroxide) for protein extraction. A comparison was made between sequential extraction routes and direct extraction of biomaterials from sludge in terms of extraction quantity, material properties, and applicability. The results showed that sequential extraction of biomaterials is feasible. The highest extraction quantities were obtained when using sodium carbonate for EPS and ALE extraction and sodium hydroxide for protein, reaching 449.80 mg/gVSS, 109.78 mg/gVSS, and 5447.08 mg/L, respectively. Sequential extraction procedures facilitate the extraction of biomaterials. Finally, suitable extraction methods for different application scenarios were analyzed.