Solid-liquid separation of real cellulose- containing wastewaters by extracellular polymeric substances: Mechanism and cost evaluation

Concentration properties of biopolymers via dead-end forward osmosis

Extracellular polymeric substances (EPSs) in excess sludge of wastewater treatment plants are valuable biopolymers that can act as recovery materials. However, effectively concentrating EPSs consumes a significant amount of energy. This study employed novel energy-saving pressure-free dead-end forward osmosis (DEFO) technology to concentrate various biopolymers, including EPSs and model biopolymers [sodium alginate (SA), bovine serum albumin (BSA), and a mixture of both (denoted as BSA-SA)]. The feasibility of the DEFO technology was proven and the largest concentration ratios for these biopolymers were 94.8 % for EPSs, 97.1 % for SA, 97.8 % for BSA, and 98.4 % for BSA-SA solutions. An evaluation model was proposed, incorporating the FO membrane's water permeability coefficient and the concentrated substances' osmotic resistance, to describe biopolymers' concentration properties. Irrespective of biopolymer type, the water permeability coefficient decreased with increasing osmotic pressure, remained constant with increasing feed solution (FS) concentration, increased with increasing crossing velocity in the draw side, and showed little dependence on draw salt type. In the EPS DEFO concentration process, osmotic resistance was minimally impacted by osmotic pressure, FS concentration, and crossing velocity, and monovalent metal salts were proposed as draw solutes. The interaction between reverse diffusion metal cations and EPSs affected the structure of the concentrated substances on the FO membrane, thus changing the osmotic resistance in the DEFO process. These findings offer insights into the efficient concentration of biopolymers using DEFO.

Treatment and utilization of swine wastewater - A review on technologies in full-scale application

The management of swine wastewater has become the focus of attention in the farming industry. The disposal mode of swine wastewater can be classified as field application of treated waste and treatment to meet discharge standards. The status of investigation and application of unit technology in treatment and utilization such as solid-liquid separation, aerobic treatment, anaerobic treatment, digestate utilization, natural treatment, anaerobic-aerobic combined treatment, advanced treatment, are reviewed from the full-scale application perspective. The technologies of anaerobic digestion-land application is most appropriate for small and medium-sized pig farms or large pig farms with enough land around for digestate application. The process of "solid-liquid separation-anaerobic-aerobic-advanced treatment" to meet the discharge standard is most suitable for large and extra-large pig farms without enough land. Poor operation of anaerobic digestion unit in winter, hard to completely utilize liquid digestate and high treatment cost of digested effluent for meeting discharge standard are established as the main difficulties.

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.

A Comparison Study between Wood Flour and Its Derived Biochar for the Enhancement of the Peroxydisulfate Activation Capability of Fe3O4

In this study, both wood flour (WF) and wood flour-derived biochar (WFB) were used as supports for Fe3O4 to activate peroxydisulfate (PDS). The role of different carriers was investigated emphatically from the aspects of catalyst properties, the degradation kinetics of bisphenol A (BPA), the effects of important parameters, and the generation of reactive oxygen species (ROS). Results showed that both WF and WFB could serve as good support for Fe3O4, which could control the release of iron into solution and increase the specific surface areas (SSAs). The WFB/Fe3O4 had stronger PDS activation capability than WF/Fe3O4 mainly due to the larger SSA of WFB/Fe3O4 and the PDS activation ability of WFB. Both radical species (•OH and SO4•−) and non-radical pathways, including 1O2 and high-valent iron-oxo species, contributed to the degradation of BPA in the WFB/Fe3O4–PDS process. Moreover, the WFB/Fe3O4 catalyst also showed stronger ability to control the iron release, better reusability, and higher BPA mineralization efficiency than WF/Fe3O4.

The enhancement on biohydrogen production by the driving forces from extracellular iron oxide respiration

Biohydrogen productions from xylose and glucose under dark condition were enhanced by the presence of natural Fe₃O₄. The electron equivalent of H₂ fractions accounted for 4.55 % and 5.69 % of the total given xylose and glucose in the experiments without Fe₃O₄, and that were correspondingly increased to 5.14 % and 6.50 % in the experiments with 100 mg/L of Fe₃O₄, respectively. Moreover, Fe₃O₄ increased the total intracellular NAD(H) concentrations by 8.84 % and 8.37 %, and boosted the ratios of NADH/NAD⁺ by 8.33 % and 17.72 % in xylose and glucose fermentation, respectively, comparing to the corresponding control experiments. The formation of electron couples of Fe(III)/Fe(II) during the iron oxide respiration and more generation of active extracellular polymeric substances components were determined as the important reasons for the improved biohydrogen production performance. Thus, a promotion mechanism of the internal "driving forces" from extracellular iron oxide respiration on the biohydrogen production was proposed.