Biodegradation of volatile solids and water mass balance of bio-drying sewage sludge after electro-dewatering pretreatment

Dynamic changes of microbial community and moisture ratio during bio-drying of sludge after electro-dewatering

Using electro-dewatering as the pretreatment process for sludge bio-drying can improve the dewatering performance. It was innovatively investigated including the microbial mechanism and the kinetics of moisture removal by bio-drying with electro-dewatered sludge in this study. Two bio-drying processes using electro-dewatered sludge (EDS) and sludge added cornstalk conditioner (CSS) were compared. Microbial community analysis showed that the abundance of Bacteroidetes increased from 4.21% to 16.67% after electro-dewatering. The dominant phyla were Bacteroidetes (36.79%), Proteobacteria (32.35%), and Actinobacteria (24.58%) at the end of EDS bio-drying. Network analysis revealed that the co-occurrence patterns in EDS included 40 nodes and 97 edges. The prediction results of the Kyoto Encyclopedia of Genes and Genomes demonstrated that the relative abundances of carbohydrate metabolism and metabolism of terpenoids and polyketides in sludge decreased, while the relative abundances of lipid metabolism, xenobiotic biodegradation and metabolism increased after electro-dewatering. Five thin layer drying kinetic models were analyzed to estimate the bio-drying kinetic parameters. The Page's model could be better fitted to the results and the highest R² was 0.9570 in the EDS. The new coefficients k (0.1637) and n (1.2097) were obtained. The results provided mechanism and data support for exploring and applying bio-drying technology after sludge electro-dewatering.

Effect of Electrofiltration on the Dewatering Kinetics of Arthrospira platensis and Biocompound Recovery

Arthrospira platensis (A. platensis) is a microalga with a wide range of commercial uses. One of the main concerns that needs to be addressed in microalgae biorefineries is the costs associated with the harvesting and concentration steps. Filtration has been shown to be an effective technique for concentrating microalgae and recent studies have attempted to enhance membrane filtration by applying an external electric field to the filtration cell. This study consisted of assessing the use of electrically assisted filtration (electrofiltration) at 60 A/m2 and 1 bar for the dewatering of A. platensis, as well as the effect of pretreating the microalgae with ultrasounds (US) on the filtration process. Untreated A. platensis exhibited better filtration kinetics than US-treated A. platensis, and electrofiltration was found to increase the cake dryness. More protein and pigments were present in the US-treated microalgae solution compared to the untreated microalgae, which led to the presence of higher concentrations of protein and pigments in the filtrate streams after pressure filtration at 1 bar without the application of an external electric field. Electrofiltration was found to consume less energy compared to traditional drying techniques used for A. platensis. However, electrofiltration degrades the biocompounds present in the filtrate and cake due to pH changes and other electrophoresis phenomena, which shows the need to optimize the process in future work.

Influences of K+, Ca2+, and Al3+ on electrokinetic process and conductive mechanism of sludge electro-dewatering

In the process of sludge electro-dewatering (EDW), ions migration accompanied has significant influences on the dewatering efficiency. However, the effects of ions on sludge electrochemical properties and the roles in EDW are still not well understood. In this paper, influences of K⁺, Ca²⁺, and Al³⁺ on the mechanical dewatering and EDW process were investigated, and the mechanisms of EDW were analyzed from electrokinetic phenomena and electric conduction model. The results showed that the increase of cationic valence improved sludge mechanical dewatering but deteriorated EDW performance. The spatially distributed voltage used for ionic electromigration indicated that the lagged migration of divalent cation Ca²⁺ consumed more energy and reduced the dewatering rate in the later stage of EDW compared to that of monovalent cation K⁺. And trivalent cation Al³⁺ migrated less and took less water out, while it made the electrochemical reaction of EDW system easier to carry out. The decrease of the absolute zeta potential value of K⁺, Ca²⁺, and Al³⁺ also revealed the degeneration of dewaterability limit. An electric conduction model of partially water-saturated state porous media related to geometric factors was used and clarified the weight variation of continuous phase conductivity and surface conductivity during EDW. The results showed that the conductivity of Al-sludge was more affected by geometric factors and resulted in worse dewatering performance. This study provided a theoretical guidance for understanding the ions behavior affecting the dewatering efficiency and energy consumption of EDW.

Dewaterability and energy consumption model construction by comparison of electro-dewatering for industry sludges and river sediments

Electro-dewatering (EDW) is an emerging technology for improved sludge/sediment dewatering enabling subsequent cost effective treatment for toxicity and pathogenic reduction if required and/or disposal, but the effects of sediment/sludge properties on the efficacy of EDW remain unclear. Here we investigate EDW in the absence of chemical conditioning which can result in secondary pollution. The influence of sediment/sludge volatile solids content (VS), electrical conductivity (EC), pH and zeta potential (ζ), on mechanical and electrical behaviors determining dewaterability and energy consumption (P_E) was investigated. Optimization of EDW parameters increased the final solids content (DS_f) from 40 wt% to more than 55 wt% for river sediment, while the solids content in municipal sludge was only increased from 10 wt% to 15-20 wt%. Multiple linear regression and statistical analysis showed that electro-dewatering performance is primarily affected by VS and P_E is mainly affected by EC. A theoretical basis for engineering design and selection of operational parameters for sludge/sediment electro-dewatering is provided by this study.