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[Display omitted] • Different biochar all improved the anaerobic decolorization efficiency of RR2. • The addition of biochar promoted the secretion of EPS. • Microbial communities with biochar amendment were selectively enriched. • Electrical conductivity and H/C of biochar contribute the most to decolorization. • Possible mechanisms of biochar on enhancement decolorization were investigated. The addition of biochar resulted in a 31.5 % to 44.6 % increase in decolorization efficiency and favorable decolorization stability. Biochar promoted extracellular polymeric substances (EPS) secretion, especially humic-like and fulvic-like substances. Additionally, biochar enhanced the electron transfer capacity of anaerobic sludge and facilitated surface attachment of microbial cells. 16S rRNA gene sequencing analysis indicated that biochar reduced microbial species diversity, enriching fermentative bacteria such as Trichococcus. Finally, a machine learning model was employed to establish a predictive model for biochar characteristics and decolorization efficiency. Biochar electrical conductivity, H/C ratio, and O/C ratio had the most significant impact on RR2 anaerobic decolorization efficiency. According to the results, the possible mechanism of RR2 anaerobic decolorization enhanced by different types of biochar was proposed. [ABSTRACT FROM AUTHOR]

• The optimal SND efficiency of 88.51% was obtained at DO concentration of 0.5 mg/L. • The biofilm played more important roles in N removal than the sludge. • Low DO concentrations promoted unconventional N removal pathways in biofilm. • Some DNB enhanced microbial interactions as keystone genera related to SND. • The synergy of N removal pathways between sludge and biofilm achieving efficient SND. Integrated fixed-film activated sludge (IFAS) is a superior system for achieving simultaneous nitrification and denitrification (SND), however, the impact of dissolved oxygen (DO) has not been fully elucidated. Therefore, this study investigated the effect of DO concentration on performance and mechanism of SND in IFAS system. Results showed that IFAS outperformed control systems and achieved optimal SND performance at a DO concentration of 0.5 mg/L, with an SND efficiency of 88.51% and total nitrogen removal efficiency of 82.78%. Typical cycles analysis demonstrated limited-DO promoted SND performance. Further analysis implied biofilms exhibited high biomass and denitrification activity with decreasing DO. Microbial community analysis revealed low DO concentrations were responsible for abundant functional groups and genes associated with SND and promoted unconventional nitrogen removal pathways. Moreover, co-occurrence network analysis elucidated microbial interactions, responses to DO, and keystone genera. This study helps understanding the roles of DO for enhanced SND in IFAS. [ABSTRACT FROM AUTHOR]

[Display omitted] • A functionalized carrier could improve biofilm tolerance to high loading of RR2. • Biofilms based on functionalized carriers enhanced RR2 decolorization efficiency. • Functionalized carriers shaped and stimulated enrichment of keystone microbes. • Functionalized carriers stimulated growth of biofilms and secretion of EPS. • The concentration of RR2 influenced microbial diversity and richness. Azo dyes are significant organic pollutants known for their adverse effects on humans and aquatic life. In this study, anthraquinone-2-sulfonate (AQS) immobilized on biochar (BC) was employed as a novel carrier in up-flow anaerobic fixed-bed reactors to induce specific biofilm formation and promote the biotransformation efficiency of azo dyes. Novel carrier–packed reactor 1 (R1) and BC-packed reactor 2 (R2) were used to treat red reactive 2 (RR2) under continuous operation for 175 days. The decolorization rates of R1 and R2 were 96–83% and 91–73%, respectively. The physicochemical characteristics and extracellular polymeric substances (EPS) of the biofilm revealed a more stable structure in R1. Furthermore, the microbial community in R1 interacted more closely with each other and contained more keystone genera. Overall, this study provides a feasible method for improving the biotransformation of azo dyes, thus providing support for practical applications in wastewater treatment projects. [ABSTRACT FROM AUTHOR]

Abstract: Investigating how a bioreactor functions is a necessary precursor for successful reactor design and operation. Traditional methods used to investigate flow-field cannot meet this challenge accurately and economically. Hydrodynamics model can solve this problem, but to understand a bioreactor in sufficient depth, it is often insufficient. In this paper, a coupled hydrodynamics-reaction kinetics model was formulated from computational fluid dynamics (CFD) code to simulate a gas–liquid–solid three-phase biotreatment system for the first time. The hydrodynamics model is used to formulate prediction of the flow field and the reaction kinetics model then portrays the reaction conversion process. The coupled model is verified and used to simulate the behavior of an expanded granular sludge bed (EGSB) reactor for biohydrogen production. The flow patterns were visualized and analyzed. The coupled model also demonstrates a qualitative relationship between hydrodynamics and biohydrogen production. The advantages and limitations of applying this coupled model are discussed. [ABSTRACT FROM AUTHOR]

Abstract: There has been little work on the optimal configuration of biohydrogen production reactors. This paper describes three-dimensional computational fluid dynamics (CFD) simulations of gas–liquid flow in a laboratory-scale continuous stirred-tank reactor used for biohydrogen production. To evaluate the role of hydrodynamics in reactor design and optimize the reactor configuration, an optimized impeller design has been constructed and validated with CFD simulations of the normal and optimized impeller over a range of speeds and the numerical results were also validated by examination of residence time distribution. By integrating the CFD simulation with an ethanol-type fermentation process experiment, it was shown that impellers with different type and speed generated different flow patterns, and hence offered different efficiencies for biohydrogen production. The hydrodynamic behavior of the optimized impeller at speeds between 50 and 70rev/min is most suited for economical biohydrogen production. [Copyright &y& Elsevier]

[Display omitted] • Cost-benefit optimization of combined systems of WWTP and CW was developed. • Integrate ASM2d, random forest, and genetic algorithm-II aided decision-making. • Trade-offs between energy, cost, and effluent quality are revealed. • WWTP cuts energy consumption by 27 % and CW cost by 44 % while effluent compliant. • Design optimization can be performed in minutes on a laptop. This study proposed an efficient framework for optimizing the design and operation of combined systems of wastewater treatment plants (WWTP) and constructed wetlands (CW). The framework coupled a WWTP model with a CW model and used a multi-objective evolutionary algorithm to identify trade-offs between energy consumption, effluent quality, and construction cost. Compared to traditional design and management approaches, the framework achieved a 27 % reduction in WWTP energy consumption or a 44 % reduction in CW cost while meeting strict effluent discharge limits for Chinese WWTP. The framework also identified feasible decision variable ranges and demonstrated the impact of different optimization strategies on system performance. Furthermore, the contributions of WWTP and CW in pollutant degradation were analyzed. Overall, the proposed framework offers a highly efficient and cost-effective solution for optimizing the design and operation of a combined WWTP and CW system. [ABSTRACT FROM AUTHOR]

The effect of different gases, CO2 concentration, and separation of CO2 from reaction system on photo-fermentation H2 production was investigated by batch culture in this study. Experimental results showed that different gases (Ar,N2,CO2, and air) as gas phase have obviously affected on photo-H2 production and a high concentration of CO2 can inhibit the growth and H2 evolution of Rhodopseudomonas faecalis RLD-53. When CO2 concentration at 5%, cell increased most rapidly the specific growth rate of 0.489g/l/h and the specific growth rate fell to be 0.265g/l/h when CO2 concentration at 40%. However, the growth of RLD-53 at CO2 concentration of 60–100% was almost completely inhibited. At CO2 concentrations of 5% and 10%, the maximum H2 yield was 2.54 and 2.59mol-H2/mol acetate, respectively, and it was similar with the control (2.61mol-H2/mol acetate). H2 not produced when CO2 concentration at 60–100%. In conclusion, separation of CO2 from reaction system can stimulate H2 production in the entire photo-H2 production process and H2 yield increased about 12.8–18.85% than the control. [Copyright &y& Elsevier]

The Rhodopseudomonas faecalis strain RLD-53 was isolated from freshwater pond sludge and was demonstrated it could produce hydrogen. This study to investigate their ability of hydrogen production under some conditions in batch culture experiments. At pH 7.0, temperature 35°C and light intensity of 4000lux, the H2 yield was 2.64mol-H2/mol-acetate, 2.34mol-H2/mol-propionate, 1.75mol-H2/mol-lactate and 3.55mol-H2/mol-malate, respectively. The maximal H2 production rate of 32.62ml-H2/l/h and H2 yield of 2.84mol-H2/mol-acetate were achieved when beef extract was used as nitrogen source. Light intensity is the most important factor for H2 production, H2 production yield and rate decreased with increasing light intensity and reached highest under light intensity of 3000–5000lux. Result indicated the strain RLD-53 was a high efficient bacteria for hydrogen production. [Copyright &y& Elsevier]

[Display omitted] • First study to reveal the role of microalgae on SND for nitrogen removal in MB-SBR. • Microalgae improved the SND efficiency by 16.36% in MB-SBR compared to C-SBR. • Microalgae enhanced transfer, conversion, and storage of inorganic nitrogen in EPS. • Microalgae were closely related to bacteria as the keystone connector in MB-SBR. • Microalgae promoted the synergy of nitrogen removal pathways to efficient SND. This study explored the influence and mechanism of microalgae on simultaneous nitrification and denitrification (SND) in microalgal-bacterial sequencing batch reactors (MB-SBR). It particularly focused on nitrogen transformation in extracellular polymeric substances (EPS) and functional groups associated with nitrogen removal. The results showed that MB-SBR achieved more optimal performance than control, with an SND efficiency of 68.01% and total nitrogen removal efficiency of 66.74%. Further analyses revealed that microalgae changed compositions and properties of EPS by increasing EPS contents and improving transfer, conversion, and storage capacity of nitrogen in EPS. Microbial community analysis demonstrated that microalgae promoted the enrichment of functional groups and genes related to SND and introduced diverse nitrogen removal pathways. Moreover, co-occurrence network analysis elucidated the interactions between communities of bacteria and microalgae and the promotion of SND by microalgae as keystone connectors in the MB-SBR. This study provides insights into the roles of microalgae for enhanced SND. [ABSTRACT FROM AUTHOR]

Biofilm membrane bioreactor (BF-MBR) is considered as an important wastewater treatment technology that incorporates advantages of both biofilm and MBR process, as well as can alleviate membrane fouling, with respect to the conventional activated sludge MBR. But, to be efficient, it necessitates the establishment of proper methods for the assessment of membrane fouling. Four Hermia membrane blocking models were adopted to quantify and evaluate the membrane fouling of BF-MBR. The experiments were conducted with various operational conditions, including membrane types, agitation speeds and transmembrane pressure (TMP). Good agreement between cake formation model and experimental data was found, confirming the validity of the Hermia models for assessing the membrane fouling of BF-MBR and that cake layer deposits on membrane. Moreover, the influences of membrane types, agitation speeds and transmembrane pressure on the Hermia pore blocking coefficient of cake layer were investigated. In addition, the permeability recovery after membrane cleaning at various operational conditions was studied. This work confirms that, unlike conventional activated sludge MBR, BF-MBR possesses a low degree of membrane fouling and a higher membrane permeability recovery after cleaning. [ABSTRACT FROM AUTHOR]

A self-sustained hybrid bioelectrochemical system consisting of microbial fuel cell (MFC) and microbial electrolysis cell (MEC) was developed to reduce multiple metals simultaneously by utilizing different reaction potentials. Three heavy metals representing spontaneous reaction (chromium, Cr) and unspontaneous reaction (lead, Pb and nickel, Ni) were selected in this batch-mode study. The maximum power density of the MFC achieved 189.4 mW m −2 , and the energy recovery relative to the energy storage circuit (ESC) was ∼450%. At the initial concentration of 100 mg L −1 , the average reduction rate of Cr(VI) was 30.0 mg L −1 d −1 , Pb(II) 32.7 mg L −1 d −1 , and Ni(II) 8.9 mg L −1 d −1 . An electrochemical model was developed to predict the change of metal concentration over time. The power output of the MFC was sufficient to meet the requirement of the ESC and MEC, and the “self-sustained metal reduction” was achieved in this hybrid system. [ABSTRACT FROM AUTHOR]

Abstract: In this study, some key factors, for example, diluted ratio of effluents, the ratio of dark-photo bacteria, light intensity and light/dark cycle influencing hydrogen production by combining Clostridium butyricum and immobilized Rhodopseudomonas faecalis RLD-53 in batch culture, were investigated. Experimental results showed the photo-hydrogen yield decreased when increasing diluted ratio from 1:0.5 to 1:3, and it reached the maximum value of 4368ml-H2/l-effluents at the ratio of 1:0.5. When the ratio of dark-photo bacteria was at 1:2, the hydrogen yield reached highest value of 4.946mol-H2/mol-glucose and cumulative hydrogen volume was 5357ml-H2/l-culture during the combination process. When the light intensity was at 10.25W/m2, the hydrogen volume of photo-fermentation and the combination process reached maximum value of 4260ml-H2/l-effluents and 5892ml-H2/l-culture, respectively. During the combination process, maximum total hydrogen yield was 5.374mol-H2/mol-glucose. Meanwhile, hydrogen production under light/dark cycle was evaluated. [Copyright &y& Elsevier]

Abstract: In order to increase the hydrogen yield from glucose, hydrogen production by immobilized Rhodopseudomonas faecalis RLD-53 using soluble metabolites from ethanol fermentation bacteria Ethanoligenens harbinense B49 was investigated. The soluble metabolites from dark-fermentation mainly were ethanol and acetate, which could be further utilized for photo-hydrogen production. Hydrogen production by B49 was noticeably affected by the glucose and phosphate buffer concentration. The maximum hydrogen yield (1.83mol H2/mol glucose) was obtained at 9g/l glucose. In addition, we found that the ratio of acetate/ethanol (A/E) increased with increasing phosphate buffer concentration, which is favorable to further photo-hydrogen production. The total hydrogen yield during dark- and photo-fermentation reached its maximum value (6.32mol H2/mol glucose) using 9g/l glucose, 30mmol/l phosphate buffers and immobilized R. faecalis RLD-53. Results demonstrated that the combination of dark- and photo- fermentation was an effective and efficient process to improve hydrogen yield from a single substrate. [Copyright &y& Elsevier]

The design of an optimum and cost-efficient medium for high-level production of hydrogen by Ethanoligenens harbinense B49 was attempted by using response surface methodology (RSM). Based on the Plackett–Burman design, Fe2+ and Mg2+ were selected as the most critical nutrient salts. Subsequently, the optimum combination of the selected factors and the sole carbon source glucose were investigated by the Box–Behnken design. Results showed that the maximum hydrogen yield of 2.21mol/molglucose was predicted when the concentrations of glucose, Fe2+ and Mg2+ were 14.57g/L, 177.28mg/L and 691.98mg/L, respectively. The results were further verified by triplicate experiments. The batch reactors were operated under an optimized condition of the respective glucose, Fe2+ and Mg2+ concentration of 14.5g/L, 180mg/L and 690mg/L, the initial pH of 6.0 and experimental temperature of 35±1 oC. Without further pH adjustment, the maximum hydrogen yield of 2.20mol/molglucose was obtained based on the optimized medium with further verified the practicability of this optimum strategy. [Copyright &y& Elsevier]

• H 2 production by biofilms and granules in a moving bed biofilm reactor (MBBR). • Development of a sequential immobilization and deoxygenization (SIDO) approach. • Inoculation with aerobic P. aeruginosa shortened the start-up period of an MBBR. • Highly-abundant hydrogen-producing bacteria were enriched in SIDO-MBBRs. • Predominant populations in SIDO-MBBR were Clostridium and Enterobacter. To reduce start-up time and enhance hydrogen production efficiency, a sequential immobilization and deoxygenization (SIDO) strategy for hydrogen production was investigated in continuous-flow moving bed biofilm reactors (MBBRs). The pre-immobilization process accelerated the initial enrichment of hydrogen-producing bacteria (HPB) and promoted the biofilm formation, which contribute to higher hydrogen production efficiency in SIDO-MBBRs compared to a non-immobilized reactor. A similar deoxygenization effect was achieved by inoculation with Pseudomonas aeruginosa compared with N 2 sparging, and the P. aeruginosa pre-immobilized MBBR (Pse-MBBR) showed a higher H 2 yield in the initial stage of operation. Microbial community analysis found a higher abundance of putative HPB in the range of 82.82–96.56%, with the predominant populations in the SIDO-MBBR assigned to genera Clostridium and Enterobacter. The results suggest that the SIDO-MBBR is an effective approach for rapid recruitment of HPB and start-up of fermentative hydrogen production. [ABSTRACT FROM AUTHOR]