Enhanced anaerobic degradation of azo dyes by biofilms supported by novel functionalized carriers

Boosting the Performance of a Zero-gap Flow Microbial Fuel Cell by Immobilized Redox Mediators

Although microbial fuel cells (MFC) could be a promising energy source, their implementation is largely limited by low performance. There are several approaches to overcome this issue. For example, MFC performance can be enhanced using redox mediators (RM) capable of transferring electrons between microorganisms and MFC electrodes. The other, quite novel approach is to use zero-gap electrochemical cells, which minimize the distance between MFC electrodes and, therefore, its internal resistance. This work aims to investigate the compatibility of these approaches. First, a template electropolymerization of polypyrrole (PPy) on carbon felt was carried out in the presence of 2,7-anthraquinone disulfonate (AQDS) acting as an RM. These materials were then used as the anode of a zero-gap double chamber MFC inoculated with sediment from a natural water body and continuously fed with artificial wastewater. On the scales of 45 and 64 days, such cells exhibited power density of up to 900 mW m-2, while unmodified cells demonstrated values tens of times lower, indicating that RM appears to extensively incorporate weak electricigens from the inoculant in the MFC operation. PPy/AQDS electrodes retain electroactive properties during long-term tests, resulting in a theoretical turnover rate of AQDS molecules up to 590.

Synthetic biofilm community for efficient phosphorus removal from high-salinity wastewater

Substantial amounts of phosphorus are discharged into water bodies, leading to an urgent need to develop methods for phosphorus removal. Here, 12 novel polyphosphate-accumulating organisms were identified from marine biofilms through genomic screening and incorporated into a stable community for phosphorus removal from high-salinity water. The synthetic biofilm community achieved an 82% removal efficiency in a marine broth medium. Electron microscopy showed storage of polyphosphate particles in the bacterial cells. Metatranscriptomic analysis indicated expression changes of genes for phosphate transport, as well as relevant metabolic pathways. In particular, pst genes encoding transporters with high phosphate affinity were downregulated at high-phosphorus concentration, whereas pit genes encoding transporters with low phosphate affinity were constitutively expressed. Furthermore, the synthetic biofilm community exhibited remarkable efficiency in removing over 92% of phosphorus from fish farming facility wastewater. Taken together, synthetic community using marine biofilm bacteria is a new strategy of phosphorus removal.

Deciphering the roles of attached and suspended sludges in simultaneous nitrogen and phosphorus removal in an IFAS system based on metagenomic analysis

Integrated fixed-film activated sludge (IFAS) system, an improvement of the activated sludge process, combines the advantages of both attached sludge (AS) and suspended sludge (SS). This study aimed to fully decipher the roles of AS and SS in simultaneous N and P removal in an IFAS system through metagenomic analysis. It was found that AS contributed about 84.04%, 97%, and 95.12% to exogenous NO3--N reduction, endogenous NO3--N reduction, and endogenous NO2--N reduction, respectively. Compared with AS, SS exhibited a greater contribution to anaerobic P release (69.06%) and aerobic P uptake (73.48%). Nitrate and nitrite reductase enzymes showed higher activities in AS, while the activities of exopolyphosphatase and alkaline phosphatase D were more active in SS. P content further indicated that in AS, only a small amount of P was stored in EPS, with most presented intracellularly. In SS, the amount of P stored in EPS was found to be higher. Metagenomic analysis revealed genes related to the synthesis and degradation of endogenous carbon were higher in AS, whereas the TCA cycle exhibited higher activity in SS. P removal-related genes (such as ppk2, ppx, and adk) was significantly higher in SS than in AS. The alteration of genes associated with nitrogen metabolism suggested that the microbes in AS had a higher capacity for nitrification and denitrification. In summary, the discrepancy in the roles of AS and SS in N and P removal in IFAS can be attributed to variations in enzyme activity, P storage in EPS, microbial community composition, and functional gene abundance.

Ciprofloxacin affects nutrient removal in manganese ore-based constructed wetlands: Adaptive responses of macrophytes and microbes

Ciprofloxacin (CIP) has received considerable attention in recent decades due to its high ecological risk. However, little is known about the potential response of macrophytes and microbes to varying levels of CIP exposure in constructed wetlands. Therefore, lab-scale manganese ore-based tidal flow constructed wetlands (MO-TFCWs) were operated to evaluate the responses of macrophytes and microbes to CIP over the long term. The results indicated that total nitrogen removal improved from 79.93% to 87.06% as CIP rose from 0 to 4 mg L-1. The chlorophyll content and antioxidant enzyme activities in macrophytes were enhanced under CIP exposure, but plant growth was not inhibited. Importantly, CIP exposure caused a marked evolution of the substrate microbial community, with increased microbial diversity, expanded niche breadth and enhanced cooperation among the top 50 genera, compared to the control (no CIP). Co-occurrence network also indicated that microorganisms may be more inclined to co-operate than compete. The abundance of the keystone bacterium (involved in nitrogen transformation) norank_f__A0839 increased from 0.746% to 3.405%. The null model revealed drift processes (83.33%) dominated the community assembly with no CIP and 4 mg L-1 CIP. Functional predictions indicated that microbial carbon metabolism, electron transfer and ATP metabolism activities were enhanced under prolonged CIP exposure, which may contribute to nitrogen removal. This study provides valuable insights that will help achieve stable nitrogen removal from wastewater containing antibiotic in MO-TFCWs.

Bioaugmented biological contact oxidation reactor for treating simulated textile dyeing wastewater

In this study, modified polyamide fibers were used as biocarriers to enrich dense biofilms in a multi-stage biological contact oxidation reactor (MBCOR) in which partitioned wastewater treatment zone (WTZ) and bioaugmentation zone (BAZ) were established to enhance the removal of methyl orange (MO) and its metabolites while minimizing sludge yields. WTZ exhibited high biomass loading capacity (5.75 ± 0.31 g/g filler), achieving MO removal rate ranging from 68 % to 86 % under different aeration condition within 8 h in which the most dominant genus Chlorobium played an important role. In the BAZ, Pseudoxanthomonas was the dominant genus while carbon starvation stimulated the enrichment of chemoheterotrophy and aerobic_chemoheterotrophy genes thereby enhanced the microbial utilization of cell-released substrates, MO as well as its metabolic intermediates. These results revealed the mechanism bioaugmentation on MBCOR in effectively eliminating both MO and its metabolites.

Advances from conventional to biochar enhanced biotreatment of dyeing wastewater: A critical review

DW (Dyeing wastewater) contains a large amount of dye organic compounds. A considerable proportion of dye itself or its intermediate products generated during wastewater treatment process exhibits CMR (Carcinogenic/Mutagenic/Toxic to Reproduction) toxicity. Compared with physicochemical methods, biological treatment is advantageous in terms of operating costs and greenhouse gas emissions, and has become the indispensable mainstream technology for DW treatment. This article reviews the adsorption and degradation mechanisms of dye organic compounds in wastewater and analyzed different biological processes, ranging from traditional methods to processes enhanced by biochar (BC). For traditional biological processes, microbial characteristics and communities were discussed, as well as the removal efficiency of different bioreactors. BC has adsorption and redox electron mediated effects, and coupling with biological treatment can further enhance the process of biosorption and degradation. Although BC coupled biological treatment shows promising dye removal, further research is still needed to optimize the treatment process, especially in terms of technical and economic competitiveness.

Physicochemical fabrication of chitosan and algae with crosslinking glyoxal for cationic dye removal: Insight into optimization, kinetics, isotherms, and adsorption mechanism

Herein, a highly efficient and sustainable adsorbent of cross-linked chitosan-glyoxal/algae biocomposite (CHT-GLX/ALG) adsorbent was developed through an innovative hydrothermal cross-linking method. The CHT-GLX/ALG biocomposite was characterized using several complementary analytical methods that include CHN-O, XRD, FTIR, SEM-EDX, and pHpzc. This new adsorbent, named CHT-GLX/ALG, was utilized for the adsorption of a cationic dye (methyl violet 2B; MV 2B), from synthetic wastewater. The optimization of the dye adsorption process involved key parameters is listed: CHT-GLX/ALG dosage (from 0.02 to 0.1 g/100 mL), pH (from 4 to 10), and contact time (from 20 to 180 min) that was conducted using the Box-Behnken design (BBD). The optimal adsorption conditions for the highest decolorization efficiency of MV 2B (97.02 %) were estimated using the statistical model of the Box-Behnken design. These conditions include a fixed adsorbent dosage of 0.099 g/100 mL, pH 9.9, and a 179.9 min contact time. The empirical data of MV 2B adsorption by CHT-GLX/ALG exhibited favorable agreement with the Freundlich isotherm model. The kinetic adsorption profile of MV 2B by CHT-GLX/ALG revealed a good fit with the pseudo-second-order model. The maximum adsorption capacity (qmax) for MV 2B by CHT-GLX/ALG was estimated at 110.8 mg/g. The adsorption of MV 2B onto the adsorbent can be attributed to several factors, including electrostatic interactions between the negatively charged surface of CHT-GLX/ALG and the MV 2B cation, as well as n-π and H-bonding. These interactions play a crucial role in facilitating the effective adsorption of MV 2B onto the biocomposite adsorbent. Generally, this study highlights the potential of CHT-GLX/ALG as an efficient and sustainable adsorbent for the effective removal of organic dyes.

Regulating mechanism of denitrifier Comamonas sp. YSF15 in response to carbon deficiency: Based on carbon/nitrogen functions and bioaggregation

There is an urgent demand to investigate mechanisms for the improvement of denitrification in carbon-deficient environment, which will effectively reduce the eutrophication in water bodies polluted by nitrate. In this study, denitrifying bacterium Comamonas sp. YSF15 was used to explore the differences in different carbon source concentrations, with the complete genome, metabolomics, and other detecting methods. Results showed that strain YSF15 was able to achieve efficient denitrification, with complete pathways for denitrification and central carbon metabolism. The carbon deficiency prompted the bacteria to use extracellular amino acid-like metabolites initially, to alleviate inhibition and maintain bioactivity, which also facilitated glycogen storage. The biogenic inhibitors (tautomycin, navitoclax, and glufosinate) at extremely low level potentially favored the competitiveness and intraspecific utilization of extracellular polysaccharides (PS). Optimal solutions for bioaggregation in carbon-deficient condition are achieved by regulating the hydrophobicity, and hydrogen bond in extracellular metabolites. The strategy contributes to the maintenance of bioactivity and adaptation to carbon deficiency. Overall, this study provides a new perspective on understanding the denitrification strategies in carbon-deficient environment, and helps to improve the nitrate removal in low-carbon wastewater treatment.