The influence of hydrophobicity on sludge dewatering associated with cationic starch-based flocculants

The performance of quaternary-ammonium chitosan in wastewater treatment: The overlooked role of solubility

Quaternary-ammonium chitosan (CT-CTA) is a popular water treatment agent, and its electropositivity and cation strength are improved compared with chitosan. The use of CT-CTA is widely advocated to remove suspended particles and organic matter from wastewater. However, the solubility of CT-CTA is an important factor affecting the performance of CT-CTA, which is a neglected problem in previous studies. In the study, CT-CTA with different solubilities were prepared by adjusting pH from 2 to 7 in preparation, and their applications were explored in wastewater. When the pH was 2, 2.5, or 3, the obtained CT-CTA was a dissolved state. The turbidity and color removal were 95 % - 98 % and 60 % - 74 %, respectively. When the pH was 4, 5, 6, or 7, the obtained CT-CTA was a solid state. The turbidity and color removal were 30 % - 63 % and 90 % - 97 %, respectively. For domestic-wastewater treatment, CT-CTA in a dissolved state removed 92 % of turbidity and 50 % of chemical oxygen demand (COD). CT-CTA in a solid state removed 86 % of turbidity and 64 % of COD with poly aluminum chloride (PAC). The results illustrated the performance of CT-CTA with different solubilities, which can broaden its application in wastewater treatment.

Physical conditioning methods for sludge deep dewatering: A critical review

Sludge is an inevitable waste product of sewage treatment with a high water content and large volume, it poses a significant threat of secondary pollution to both water and the atmosphere without proper disposal. In this regard, dewatering has emerged as an attractive method in sludge treatment, as it can reduce the sludge volume, enhance its transportability and calorific value, and even decrease the production of landfill leachate. In recent years, physical conditioning methods including non-chemical conditioners or energy input alone, have been extensively researched for their potential to enhance sludge dewatering efficiency, such as thermal treatment, freeze-thaw, microwave, ultrasonic, skeleton builders addition, and electro-dewatering, as well as combined methods. The main objective of this paper is to comprehensively evaluate the dewatering capacity of various physical conditioning methods, and identify key factors affecting sludge dewatering efficiency. In addition, future research anticipated directions and outlooks are proposed. This work is expected to provide valuable insights for developing efficient, eco-friendly, and low-energy consumption techniques for deep sludge dewatering.

Comprehensive hydrothermal pretreatment of municipal sewage sludge: A systematic approach

This study provides a comprehensive analysis of the potential impact of hydrothermal pretreatment (HTP) on municipal thickened waste-activated sludge (TWAS) and its integration with anaerobic digestion (AD). The research demonstrates that HTP conditions (170 °C, 3 bars for 30 min) can increase the solubilization of macromolecular organic compounds by 41%, which enhances biodegradability in semicontinuous bioreactors. This treatment also results in a 50% reduction in chemical oxygen demand (COD) and a 63% increase in the destruction of volatile solids (VS). The combination of HTP with AD significantly boosts methane yields by 51%, reaching 176 ml/g COD, and improves the digestate dewaterability, doubling the solid content in the dewatered cake. However, a higher polymer dose is required compared to conventional AD. Microbial community analysis correlates the observed performance and alterations; it indicates that HTP enhances resilience to stress conditions such as ammonia toxicity. This comprehensive study provides valuable insights into the transition from wastewater treatment plants (WWTPs) to resource recovery facilities (RRF) in line with circular economy principles.

Residue-Free and Recyclable Starch-Based Flocculants for Dye Wastewater Flocculation

Flocculants are crucial agents in wastewater treatment because they can remove oppositely charged impurities effectively and swiftly. However, flocculation also inevitably causes secondary contamination due to the residual properties, nonreusability, and nondegradability of traditional flocculant molecules. Herein, an ecofriendly starch-based flocculant, i.e., 2,4-bis(dimethylamino)-[1,3,5]-triazine-6-starch, was synthesized via a preactivation-etherification strategy. The large molecular weight property of the flocculant produced by this method enhances the intermolecular hydrophobic association, achieving complete phase separation of all flocculant molecules from water and residue-free flocculation for the first time. Importantly, a large molecular weight tertiary amine starch-based flocculant (LMTS) exhibits a remarkable flocculation capacity of over 1800 mg·g-1 for dye wastewater, which is significantly higher than that of traditional polyacrylamide and polyaluminum chloride flocculants. Furthermore, the LMTS flocculant could be recycled by pH adjustment, and its structural stability ensured sustained reusability. This high-performance residue-free biomass-based flocculant offers a green advance for wastewater treatment.

Enhanced dewaterability of sewage sludge by grafted cationic lignin-based flocculants

Lignin-based flocculants are widely used for wastewater purification, but their application in sludge dewatering has not yet been documented. In this study, a novel cationic lignin-based flocculant named LS-g-CPA was prepared by grafting cationic polyacrylamide (CPA) synthesized from methacryloyloxy ethyltrimethyl ammonium chloride (DMC) and acrylamide (AM) onto sodium lignosulfonate (LS), and its roles and underlying mechanisms in sludge conditioning were investigated. The results showed that LS-g-CPA effectively improved the dewaterability of sludge, reducing the filtration resistance and filter cake moisture content of sludge from 0.61 ± 0.05 × 1012 m/kg to 0.14 ± 0.02 × 1012 m/kg and 85.64 ± 0.25 % to 76.84 ± 0.41 %, respectively. The dewatering performance of LS-g-CPA was positively correlated with the DMC/AM ratio. The quaternary ammonium groups brought by DMC disrupted the reticular structure of extracellular polymeric substances, exposing hydrophobic residues and releasing bound water. Nevertheless, the key to LS-g-CPA for improving sludge dewatering lies more in the amphoteric flocculant properties that enhance sludge flocculation and the octopus-type structure that provides good drainage channels. This study reveals that lignin-based flocculants are effective in improving the dewaterability of sludge, which provides direct evidence for their application in sludge dewatering.

Effects of accumulated cyanobacterial bloom biomass contents on the characteristics of surface fluid sediments in a eutrophic shallow lake

In eutrophic shallow lakes, cyanobacterial blooms will occur frequently and then accumulate on sediments, leading to the variation in the surface sediment properties. In this study, the influence of accumulated cyanobacterial blooms biomass (CBB) content on surface sediment properties was determined in microcosm experiments through monitoring surface sediment physicochemical and rheological properties. During one-month incubation, it was found that surface sediment volume increased, and the density decreased from 1.36 g cm^-3 to 1.13 g cm^-3 with increase in accumulated CBB contents. The results of particle size distribution indicated that CBB accumulation in sediments led to sediment flocculation and agglomeration. In the meantime, there were high ratios polysaccharide/protein in extracellular polymeric substances (EPS) with a decrease in bound EPS/colloid EPS under high CBB contents, which enhanced the sediment particle agglomeration and reduced fluid sediment stability. Further, the critical shear stress in rheological test for sediments on day 30 presented an exponential decay (R² = 0.97) with increase in accumulated CBB contents. And a threshold value at 0.15% accumulated CBB content indicated sediments could be resuspended easier when accumulated CBB content was higher than 0.15%. Altogether, this study showed that the accumulated CBB content had a strong influence on surface fluid sediment properties. The results were important in sediment management since CBB affects sediment suspension for eutrophication shallow lakes.